Subduction metamorphism in the Himalayan ultrahigh-pressure Tso Morari massif: An integrated geodynamic and petrological modelling approach

NASA Astrophysics Data System (ADS)

Palin, Richard M.; Reuber, Georg S.; White, Richard W.; Kaus, Boris J. P.; Weller, Owen M.

2017-06-01

The Tso Morari massif is one of only two regions where ultrahigh-pressure (UHP) metamorphism of subducted crust has been documented in the Himalayan Range. The tectonic evolution of the massif is enigmatic, as reported pressure estimates for peak metamorphism vary from ∼2.4 GPa to ∼4.8 GPa. This uncertainty is problematic for constructing large-scale numerical models of the early stages of India-Asia collision. To address this, we provide new constraints on the tectonothermal evolution of the massif via a combined geodynamic and petrological forward-modelling approach. A prograde-to-peak pressure-temperature-time (P-T-t) path has been derived from thermomechanical simulations tailored for Eocene subduction in the northwestern Himalaya. Phase equilibrium modelling performed along this P-T path has described the petrological evolution of felsic and mafic components of the massif crust, and shows that differences in their fluid contents would have controlled the degree of metamorphic phase transformation in each during subduction. Our model predicts that peak P-T conditions of ∼2.6-2.8 GPa and ∼600-620 ∘C, representative of 90-100 km depth (assuming lithostatic pressure), could have been reached just ∼3 Myr after the onset of subduction of continental crust. This P-T path and subduction duration correlate well with constraints reported for similar UHP eclogite in the Kaghan Valley, Pakistan Himalaya, suggesting that the northwest Himalaya contains dismembered remnants of what may have been a ∼400-km-long UHP terrane comparable in size to the Western Gneiss Region, Norway, and the Dabie-Sulu belt, China. A maximum overpressure of ∼0.5 GPa was calculated in our simulations for a homogeneous crust, although small-scale mechanical heterogeneities may produce overpressures that are larger in magnitude. Nonetheless, the extremely high pressures for peak metamorphism reported by some workers (up to 4.8 GPa) are unreliable owing to conventional thermobarometry having been performed on minerals that were likely not in equilibrium. Furthermore, diagnostic high-P mineral assemblages predicted to form in Tso Morari orthogneiss at peak metamorphism are absent from natural samples, which may reflect the widespread metastable preservation of lower-pressure assemblages in the felsic component of the crust during subduction. If common in such subducted continental terranes, this metastability calls into question the reliability of geodynamic simulations of orogenesis that are predicated on equilibrium metamorphism operating continuously throughout tectonic cycles.

U-Pb SHRIMP geochronology and trace-element geochemistry of coesite-bearing zircons, North-East Greenland Caledonides

USGS Publications Warehouse

McClelland, W.C.; Power, S.E.; Gilotti, J.A.; Mazdab, F.K.; Wopenka, B.

2006-01-01

Obtaining reliable estimates for the timing of eclogite-facies metamorphism is critical to establishing models for the formation and exhumation of high-pressure and ultrahigh-pressure (UHP) metamorphic terranes in collisional orogens. The presence of pressure-dependent phases, such as coesite, included in metamorphic zircon is generally regarded as evidence that zircon growth occurred at UHP conditions and, ifdated, should provide the necessary timing information. We report U-Pb sensitive high-resolution ion microprobe (SHRIMP) ages and trace-element SHRIMP data from coesite-bearing zircon suites formed during UHP metamorphism in the North- East Greenland Caledonides. Kyanite eclogite and quartzofeldspathic host gneiss samples from an island in J??kelbugt (78??00'N, 18??04'W) contained subspherical zircons with well-defined domains in cathodoluminescence (CL) images. The presence of coesite is confirmed by Raman spectroscopy in six zircons from four samples. Additional components of the eclogite-facies inclusion suite include kyanite, omphacite, garnet, and rutile. The trace-element signatures in core domains reflect modification of igneous protolith zircon. Rim signatures show flat heavy rare earth element (HREE) patterns that are characteristic of eclogite-facies zircon. The kyanite eclogites generally lack a Eu anomaly, whereas a negative Eu anomaly persists in all domains of the host gneiss. The 207Pb- corrected 206Pb/238U ages range from 330 to 390 Ma for the host gneiss and 330-370 Ma for the kyanite eclogite. Weighted mean 206Pb/238U ages for coesite-bearing domains vary from 364 ?? 8 Ma for the host gneiss to 350 ?? 4 Ma for kyanite eclogite. The combined U-Pb and REE data interpreted in conjunction with observed CL domains and inclusion suites suggest that (1) Caledonian metamorphic zircon formed by both new zircon growth and recrystallization, (2) UHP metamorphism occurred near the end of the Caledonian collision, and (3) the 30-50m.y. span of ages records long residence times at eclogite-facies conditions for the UHProcks of North-East Greenland. This spread in observed ages is interpreted to be characteristic of metamorphic rocks that have experienced relatively long (longer than 10 m.y.) residence times at UHP conditions. ?? 2006 Geological Society of America.

Devonian to Carboniferous collision in the Greenland Caledonides: U-Pb zircon and Sm-Nd ages of high-pressure and ultrahigh-pressure metamorphism

NASA Astrophysics Data System (ADS)

Gilotti, Jane A.; Nutman, Allen P.; Brueckner, Hannes K.

2004-10-01

A variety of eclogites from an east-west transect across the North-East Greenland eclogite province have been studied to establish the timing of high pressure (HP) and ultrahigh-pressure (UHP) metamorphism in this northern segment of the Laurentian margin. Garnet + omphacite ± amphibole + whole rock Sm-Nd isochrons from a quartz eclogite, a garnet + omphacite + rutile eclogite and a partially melted zoisite eclogite in the western HP belt are 401±2, 402±9 and 414±18 Ma, respectively. Corresponding sensitive high-resolution ion microprobe (SHRIMP) 206Pb/238U ages of metamorphic zircon in the same samples are 401±7, 414±13, and 393 ±10 Ma. Metamorphic zircon domains were identified using morphology, cathodoluminescence (CL) imaging, U, Th, Th/U and trace element contents. Zircon from the quartz eclogite and the garnet + omphacite + rutile eclogite are typical of eclogite facies zircon with rounded to subhedral shapes, patchy to homogenous CL domains, low U, and very low Th and Th/U. The partially melted eclogite contains euhedral zircons with dark, sector-zoned, higher U, Th and Th/U inherited cores. Three cores give a Paleoproterozoic 207Pb/206Pb age of 1,962±27 Ma, interpreted as the age of the leucogabbroic protolith. CL images of the bright overgrowths show faint oscillatory zoning next to homogenous areas that indicate zircon growth in the presence of a HP melt and later recrystallization. Additional evidence that zircon grew during eclogite facies conditions is the lack of a Eu anomaly in the trace element data for all the samples. These results, combined with additional less precise Sm-Nd ages and our earlier work, point to a Devonian age of HP metamorphism in the western and central portions of the eclogite province. An UHP kyanite eclogite from the eastern part of the transect contains equant metamorphic zircon with homogeneous to patchy zoning in CL and HP inclusions of garnet, omphacite and kyanite. These zircons have slightly higher U, Th and Th/U values than the HP ones, no Eu anomaly, and are thus comparable to UHP zircons in the literature. The 206Pb/238U age of these zircons is 360±5 Ma, much younger than the HP eclogites. The same sample gives a Sm-Nd age of 342±6 Ma. Unlike the HP eclogites, the Sm-Nd age of the UHP rock is ca. 20 Ma younger than the U-Pb zircon age and most likely records slow cooling through the closure temperature, since peak temperatures were in excess of 900°C. Widespread HP metamorphism of both the Laurentian and Baltica continental margins marks the culmination of this continent continent collision in the Devonian. Carboniferous UHP conditions, though localized in the east, suggest a prolonged collisional history rather than a short-lived Scandian orogeny. The traditional Silurian Scandian orogeny should thus be extended through the Devonian.

The timing of eclogite facies metamorphism and migmatization in the Orlica–Śnieżnik complex, Bohemian Massif: Constraints from a multimethod geochronological study

USGS Publications Warehouse

Brocker, M.; Klemd, R.; Cosca, M.; Brock, W.; Larionov, A.N.; Rodionov, N.

2009-01-01

The Orlica–Śnieżnik complex (OSC) is a key geological element of the eastern Variscides and mainly consists of amphibolite facies orthogneisses and metasedimentary rocks. Sporadic occurrences of eclogites and granulites record high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic conditions. A multimethod geochronological approach (40Ar–39Ar, Rb–Sr, Sm–Nd, U–Pb) has been used to gain further insights into the polymetamorphic evolution of eclogites and associated country rocks. Special attention was given to the unresolved significance of a 370- to 360 Ma age group that was repeatedly described in previous studies. Efforts to verify the accuracy of c.370 Ma K–Ar phengite and biotite dates reported for an eclogite and associated country-rock gneiss from the location Nowa Wieś suggest that these dates are meaningless, due to contamination with extraneous Ar. Extraneous Ar is also considered to be responsible for a significantly older 40Ar–39Ar phengite date of c. 455 Ma for an eclogite from the location Wojtowka. Attempts to further substantiate the importance of 370–360 Ma zircon dates as an indicator for a melt-forming high-temperature (HT) episode did not provide evidence in support of anatectic processes at this time. Instead, SHRIMP U–Pb zircon dating of leucosomes and leucocratic veins within both orthogneisses and (U)HP granulites revealed two age populations (490–450 and 345–330 Ma respectively) that correspond to protolith ages of the magmatic precursors and late Variscan anatexis. The results of this study further underline the importance of Late Carboniferous metamorphic processes for the evolution of the OSC that comprise the waning stages of HP metamorphism and lower pressure HT overprinting with partial melting. Eclogites and their country rocks provided no chronometric evidence for an UHP and ultrahigh-temperature episode at 387–360 Ma, as recently suggested for granulites from the OSC, based on Lu–Hf garnet ages (Anczkiewicz et al., 2007).

Origin of retrograde fluid in ultrahigh-pressure metamorphic rocks: Constraints from mineral hydrogen isotope and water content changes in eclogite gneiss transitions in the Sulu orogen

NASA Astrophysics Data System (ADS)

Chen, Ren-Xu; Zheng, Yong-Fei; Gong, Bing; Zhao, Zi-Fu; Gao, Tian-Shan; Chen, Bin; Wu, Yuan-Bao

2007-05-01

By taking advantage of having depth profiles between contrasting lithologies from core samples of the Chinese Continental Scientific Drilling (CCSD) project, a combined study was carried out to examine changes in mineral H isotope, total water and hydroxyl contents in garnet and omphacite across the contacts between ultrahigh-pressure (UHP) eclogite and gneiss in the Sulu orogen, east-central China. The samples of interest were from two continuous core segments from the CCSD main hole at depths of 734.21-737.16 and 929.67-932.86 m, respectively. The results show δD values of -116‰ to - 64‰ for garnet and -104‰ to -82‰ for omphacite, consistent with incorporation of meteoric water into protoliths of UHP metamorphic rocks by high-T alteration. Both equilibrium and disequilibrium H isotope fractionations were observed between garnet and omphacite, suggesting fluid-assisted H isotope exchange at local scales during amphibolite-facies retrogression. While bulk water analysis gave total H 2O concentrations of 522-1584 ppm for garnet and 1170-20745 ppm for omphacite, structural hydroxyl analysis yielded H 2O contents of 80-413 ppm for garnet and 228-412 ppm for omphacite. It appears that significant amounts of molecular H 2O are present in the minerals, pointing to enhanced capacity of water storage in the UHP eclogite minerals. Hydrogen isotope variations in the transition between eclogite and gneiss show correlations with variations in their water contents. Petrographically, the degree of retrograde metamorphism generally increases with decreasing distance from the eclogite-gneiss boundary. Thus, retrograde metamorphism results in mineral reactions and H isotope variation. Because hydroxyl solubility in nominally anhydrous minerals decreases with dropping pressure, significant amounts of water are expected to be released from the minerals during decompression exhumation. Decompression exsolution of structural hydroxyl from 1 m 3 volume of eclogite composed of only garnet and omphacite results in release of a quantitative estimate of 3.07-3.44 kg water that can form 140-156 kg amphibole during exhumation. Therefore, it is concluded that fluid for retrogression of the eclogites away from the eclogite-gneiss boundary was derived from the decompression exsolution of structural hydroxyl and molecular H 2O in nominally anhydrous minerals. For the eclogites adjacent to gneiss, in contrast, the retrograde metamorphism was principally caused by aqueous fluid from the gneiss which is relatively rich in water. Consequently, both the origin and availability of metamorphic fluid during exhumation of deeply subducted continental crust are deciphered by this combined study focusing on the transitions and the retrograde processes between the felsic and mafic UHP rocks.

Stable isotope geochemistry of ultrahigh pressure metamorphic rocks from the Dabie-Sulu orogen in China: implications for geodynamics and fluid regime

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Fu, Bin; Gong, Bing; Li, Long

2003-07-01

Discovery of coesite, diamond, and extreme 18O-depletion in eclogites from the Dabie-Sulu orogen in central-east China has contributed much to our understanding of subduction of continental crust to mantle depths and its subsequent exhumation. Hydrogen, oxygen, and carbon isotope distributions were systematically investigated in the past 8 years for ultrahigh pressure (UHP) eclogites, gneisses, granulites, marbles, and peridotites from this exciting region. The available data show the following characteristic features: (1) variable δ18O values of -11‰ to +10‰ for the eclogites and gneisses, with both equilibrium and disequilibrium fractionations of oxygen isotopes among minerals; (2) disequilibrium fractionation of hydrogen isotopes between mica and epidote from both eclogites and gneisses, with low δD values up to -127‰ to -100‰ for phengite; (3) negative δ13C values of -28‰ to -21‰ for apatite as well as host-eclogites and gneisses; (4) positive δ13C values of +1‰ to +6‰ for coesite-bearing marble associated with eclogites; (5) zircons from metamorphic rocks of different grades show a large variation in δ18O from -11‰ to +9‰, with U-Pb ages of 700 to 800 Ma for the timing of low- δ18O magma crystallization. It appears that the UHP metamorphic rocks exhibit ranges of δ18O values that are typical of potential precursor protolith rocks. Preservation of the oxygen isotope equilibrium fractionations among the minerals of the UHP eclogites and gneisses suggests that these rocks acquired the low δ18O values by meteoric-hydrothermal alteration before the UHP metamorphism. Thus, the UHP metamorphic rocks largely reflect the δ18O values of their premetamorphic igneous or sedimentary precursors. The stable isotope data demonstrate that basaltic, granitic, and sedimentary protoliths of the eclogites, orthogneiss, and paragneiss in the orogen were at or near the earth's surface, and subjected to varying degrees of water-rock interaction at some time before plate subduction. The low- δ18O rocks were isolated from water-rock interactions during their descent to and return from mantle depths. It appears that the oxygen, hydrogen, and carbon on the earth's surface were recycled into the mantle at depths of >200 km by the continental subduction. A fried ice cream model is advanced as an analogy to the rapid processes of both plate subduction and exhumation, with a short residence time of the UHP slab at mantle depths. The entire cycle of subduction, UHP metamorphism, and exhumation is estimated to take place in about 10 to 20 Ma. The 18O-depleted zircons and other minerals acquired their oxygen isotope compositions from low- δ18O magmas that incorporated the isotopic signatures of meteoric water in rifting tectonic zones prior to solidification. The U-Pb discordia dating for the 18O-depleted zircons revealed that the meteoric water-rock interaction occurred at Neoproterozoic, a time being much earlier than the UHP metamorphism at Triassic, but correlated with the Rodinian breakup, positive carbon isotope anomaly in carbonates, and the snowball earth event. The unusually low δ18O values can be acquired from either the meteoric water of cold paleoclimates or the melt water of glacial ice or snow. Neoproterozoic rift magmatism along the northern margin of the Yangtze craton may have provided sufficient heat source to trigger the meteoric-hydrothermal circulation. It is possible that the unusual 18O-depletion in the meta-igneous rocks occurs at some time prior to the snowball earth event, when there is a transition from a very cold earth with continental glaciers to a widely glaciated earth where bulk of the earth is covered by sea ice as defined for the snowball earth. The heterogeneity of oxygen isotope compositions at outcrop scales demonstrates the absence of pervasive fluid infiltration during prograde, peak UHP, and retrograde metamorphism; most rocks appear to have recrystallized under virtually closed system conditions characterized by widespread lack of an aqueous fluid phase. Volatiles may not escape from the rock series during the rapid subduction of the continental crust, resulting in a general lack of syn-collisional arc-magmatism in this orogen. Big differences in pressure and time from the peak UHP stage to the retrograde HP eclogite-facies stage cause significant release of aqueous fluid by dehydration from decompressing slabs during exhumation. As a result, fluid flow occurred in a channellized way on small scales subsequent to the UHP metamorphism, with very limited mobility of fluid at peak UHP conditions. The fluid for retrograde reactions was internally buffered in stable isotope compositions. While some fluids were locally derived from the surrounding gneisses, more fluid was probably derived from internal dehydration of the rock units in question. In addition to the breakdown of hydroxyl-bearing minerals, exsolution of structural hydroxyl dissolved in nominally anhydrous minerals due to abrupt decrease in pressure may have been an important source for the retrograde fluid.

Petrology, geochemistry and isotopic ages of eclogites from the Dulan UHPM Terrane, the North Qaidam, NW China

NASA Astrophysics Data System (ADS)

Song, Shuguang; Yang, Jingsui; Liou, J. G.; Wu, Cailai; Shi, Rendeng; Xu, Zhiqin

2003-10-01

The Dulan eclogite-gneiss region is located in the eastern part of the North Qaidam eclogite belt, NW China. Widespread evidence demonstrates that this region is a typical ultrahigh-pressure (UHP) metamorphic terrane. Eclogites occur as lenses or layers in both granitic and pelitic gneisses. Two distinguished sub-belts can be recognized and differ in mineralogy, petrology and geochemistry. The North Dulan Belt (NDB) has tholeiitic protoliths with high TiO 2 and lower Al 2O 3 and MgO contents. REE patterns and trace element contents resemble those of N-type and E-type MORB. In contrast, eclogites in the South Dulan Belt (SDB) are of island arc protoliths with low TiO 2, high Al 2O 3 and show LREE-enriched and HFSE-depleted patterns. Sm-Nd isotope analyses give isochron ages of 458-497 Ma for eclogite-facies metamorphism for the two sub-belts. The ages are similar to those of Yuka and Altun eclogites in the western extension of the North Qaidam-Altun eclogite belt. The Dulan UHP metamorphic terrane, together with several other recently recognized eclogite-bearing terrenes within the North Qaidam-Altun HP-UHP belt, constitute the key to the understanding of the tectonic evolution of the northern Tibetan Plateau. The entire UHP belt extends for more than 1000 km from the Dulan UHP terrane in the southeast to the Altun eclogite-gneiss terrane in the west. This super-belt marks an early Paleozoic continental collision zone between the Qaidam Massif and the Qilian Massif.

>2500-km-Long Contemporaneous Deep Continental Subduction in the West Gondwana Orogen

NASA Astrophysics Data System (ADS)

Rubatto, D.; Ganade de Araujo, C. E.; Hermann, J.; Cordani, U. G.; Caby, R.; Basei, M. A. S.

2014-12-01

The 5000-km-long, deeply eroded West Gondwana Orogen (WGO) is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks (i.e. eclogites) along its strike. The position of these eclogites marks the suture zone between colliding cratons and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. We investigated the metamorphic conditions and age of high-pressure (HP) and ultrahigh-pressure (UHP) eclogites from Mali, Togo and NE-Brazil . P-T estimates confirm UHP to HP conditions for all these localities. The U-Pb age and trace element composition of metamorphic zircon domains demonstrate that continental subduction in the WGO occurred within 20 m.y. over at least 2500 km during the Ediacaran period (620-610 Ma). We consider this to be the first record of modern, large-scale deep-continental subduction and the consequent appearance of Himalayan-scale mountains in the geological record. The rise of such mountains in the Late Ediacaran is perfectly timed to deliver by erosion the sediments (nutrients) that have been deemed necessary for life sustainability in the following Earth evolution.

Terrane-Scale Metastability in Subducted Himalayan Continental Crust as Revealed by Integrated Petrological and Geodynamic Modeling

NASA Astrophysics Data System (ADS)

Palin, R. M.; Reuber, G. S.; White, R. W.; Kaus, B. J. P.; Weller, O. M.

2017-12-01

The Tso Morari massif, northwest India, is one of only two regions in the Himalayan Range that exposes subduction-related ultrahigh-pressure (UHP) metamorphic rocks. The tectonic evolution of the massif is strongly debated, however, as reported pressure estimates for peak metamorphism range between 2.4 GPa and 4.8 GPa. Such ambiguity hinders effective lithospheric-scale modeling of the early stages of the orogen's evolution. We present the results of integrated petrological and geodynamic modeling (Palin et al., 2017, EPSL) that provide new quantitative constraints on the prograde-to-peak pressure-temperature-time (P-T-t) path, and predict the parageneses that felsic and mafic components of the massif crust should have formed under equilibrium conditions. Our model shows that peak P-T conditions of 2.6-2.8 GPa and 600-620 °C, representative of subduction to 90-100 km depth (assuming lithostatic pressure), were reached just 3 Myr after the onset of collision. These P-T-t constraints correlate well with those reported for similar UHP eclogite in the along-strike Kaghan Valley, Pakistan, suggesting that the northwest Himalaya contains dismembered remnants of a 400-km long UHP terrane comparable in size to the Western Gneiss Region, Norway, and the Dabie-Sulu belt, China. The extremely high pressures (up to 4.8 GPa) for peak metamorphism reported by some workers are likely to be unreliable due to thermobarometry having been performed on minerals that did not represent equilibrium assemblages. Furthermore, key high-P minerals predicted to form in subducted Tso Morari continental crust (e.g. jadeite, Mg-rich garnet) are absent from natural samples in the region, reflecting the widespread metastable preservation of lower-pressure protolith assemblages during subduction and exhumation. This result questions the reliability of geodynamic simulations of orogenesis that are commonly predicated on equilibrium metamorphism operating continuously throughout tectonic cycles.

On the preservation mechanism of intragranular coesite in the Yangkou, Sulu UHP eclogite

NASA Astrophysics Data System (ADS)

Wang, L.; Zhang, J.; Wang, S.; Shi, F.; Cen, Y.

2012-12-01

Yangkou Bay, in the Sulu ultrahigh-pressure (UHP) belt of eastern China is the only known locality in the world in which UHP eclogite contains intragranular coesite. The question remains then, how is the extremely rare occurrence of intragranular coesite preserved in the Sulu belt, and if we can identify the reasons for its preservation, might it be found in other UHP belts? Preservation of coesite inclusions or intragranular coesite has been interpreted to result from multiple reasons, but lack of fluid availability is a critical factor, and the survival is not only because of their incorporation in a strong host phase but because of the ability of the host to prevent fluid infiltration until fracturing occurs at low temperatures. High-precision field structural geology mapping in the Yangkou area has revealed the complex deformation history including multi-stage folding events. The earliest folding event occurred before the eclogite reached peak metamorphism, and is preserved as rootless F1 isoclines that preserve the earliest evidence for UHP metamorphism, including intragranular coesite. We report the structural and petrological phenomenon that the intragranular coesite is uniquely preserved within the hinge zones of F1 rootless eclogite folds that have a mineral assemblage of Grt+Omp+Rt+Cs. However, the limbs of F1 folds or overprinted F1+F2 folds have a mineral assemblage of Grt+Omp+Rt+Qtz+Phg, and experienced different degrees of retrogression. The peak metamorphic P-T condition for coesite-bearing eclogite is P=4.0-4.5GPa, 745-909°C. however, the peak metamorphic P-T condition for phengite-quartz bearing eclogite is 3.8-4.1GPa, 733-840°C. The hydrogen concentration was investigated by FTIR (Fourier Transform Infrared Spectroscopy) in these two samples. In the intragranular coesite eclogite, coesite is basically free of water (<10 ppm), very low in garnet (8-50 ppm) and average hydrogen concentration of omphacite is 106-200 ppm; however, with the appearance of phengite and coesite's transformation into quartz, the water content within phengite bearing eclogite is raised. The average hydrogen concentration of garnet is 26-157 ppm , that of omphacite is 270-405 ppm. This indicates that with the appearance of phengite and retrogression, the water content of eclogite is raised up gradually, but at this stage, the eclogite is still within a localized "dry" environment compared to most water-rich (1000-2000ppm) eclogite in the Dabie-Sulu orogen. Through the structural and petrological analysis, we find that the intragranular coesite is more likely preserved within the F1 rootless isoclinal folds which formed prior to the peak metamorphism. This suggests that F1 rootless folds act as rigid and impervious shells under ultrahigh-pressure conditions, and shelter the eclogite from the surrounding fluid, which is helpful to maintain a relatively dry environment during rapid exhumation of UHP rocks, allowing the intergranular coesite to be preserved. This mechanism may have important implications for understanding the prograde path of continental-continental collision, and understanding the structural setting of the preserved intergranular coesite, which has important implications for the search for the early fabrics and metamorphic assemblages in other UHP-terrains around the world.

Zircon U-Pb dating of eclogite from the Qiangtang terrane, north-central Tibet: a case of metamorphic zircon with magmatic geochemical features

NASA Astrophysics Data System (ADS)

Zhai, Qing-guo; Jahn, Bor-ming; Li, Xian-hua; Zhang, Ru-yuan; Li, Qiu-li; Yang, Ya-nan; Wang, Jun; Liu, Tong; Hu, Pei-yuan; Tang, Suo-han

2017-06-01

Zircon is probably the most important mineral used in the dating formation of high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks. The origin of zircon, i.e., magmatic or metamorphic, is commonly assessed by its external morphology, internal structure, mineral inclusions, Th/U ratios and trace element composition. In this study, we present an unusual case of metamorphic zircon from the Qiangtang eclogite, north-central Tibet. The zircon grains contain numerous eclogite-facies mineral inclusions, including omphacite, phengite, garnet and rutile; hence, they are clearly of metamorphic origin. However, they display features similar to common magmatic zircon, including euhedral crystal habit, high Th/U ratios and enriched heavy rare earth elements pattern. We suggest that these zircon grains formed from a different reservoir from that for garnet where no trace elements was present and trace element equilibrium between zircon and garnet was achieved. U-Pb dating of zircon gave an age of 232-237 Ma for the eclogite, and that of rutile yielded a slightly younger age of ca. 217 Ma. These ages are consistent with the reported Lu-Hf mineral isochron and phengite Ar-Ar ages. The zircon U-Pb and mineral Lu-Hf isochron ages are interpreted as the time of the peak eclogite-facies metamorphism, whereas the rutile U-Pb and phengite Ar-Ar ages represent the time of exhumation to the middle crust. Thus, the distinction between metamorphic and magmatic zircons cannot be made using only Th/U ratios and heavy REE compositions for HP-UHP metamorphic rocks of oceanic derivation.

Raman imaging of fluid inclusions in garnet from UHPM rocks (Kokchetav massif, Northern Kazakhstan).

PubMed

Korsakov, Andrey V; Dieing, Thomas; Golovin, Aleksandr V; Toporski, Jan

2011-10-01

Confocal Raman imaging of fluid inclusions in garnet porphyroblasts from diamond-grade metamorphic calc-silicate rocks from the Kumdy-Kol microdiamond deposit (Kokchetav Massif, Northern Kazakhstan) reveals that these fluid inclusions consist of almost pure water with different step-daughter phases (e.g., calcite, mica and rare quartz). These fluid inclusions are characterized by negative crystal shape of the host-garnet and they exclusively occur within the core of garnet porphyroblasts. These observations are consistent with their primary origin, most likely at ultrahigh-pressure (UHP) metamorphic conditions. The euhedral newly formed garnet, different in color and composition, was found to be associated with these fluid inclusions. It is proposed that newly formed garnet and water fluid inclusions appear by reaction between the hydrous fluid and the garnet-host. These fluid inclusions provide an unequivocal record of almost pure H(2)O fluids, indicating water-saturated conditions within subducted continental crust during prograde stage and/or ultrahigh-P metamorphism. Copyright © 2011 Elsevier B.V. All rights reserved.

Tectonic exhumation and boundary structure of the Kokchetav HP - UHP metamorphic belt (Northern Kazakhstan): constraints from 40Ar/39Ar geochronology

NASA Astrophysics Data System (ADS)

Zhimulev, Fedor; de Grave, Johan; Travin, Aleksey; Buslov, Mikhail

2010-05-01

The Kokchetav metamorphic belt (KMB) is part of the Early Paleozoic orogenic belt of Northern Kazakhstan and constitutes one of the most famous, classical ultra-high pressure (UHP) metamorphic terranes. The KMB mainly consists of gneisses, mica schists and eclogites. These were formed by Cambrian continental subduction and associated metamorphism of the Precambrian Kokchetav microcontinent and subsequent exhumation of fragments of this metamorphosed continental crust. Several subterranes can be distinguished in the KMB: Barchi, Kumdi-Kol, Sulu-Tube, Enbek-Berlyk, Kulet and Borovoe. These subterranes differ not only in rock composition or in genetic pT conditions, but also in the age of the individual metamorphic events, including the timing of peak, and regressive stages. Most geochronological data indicate a Cambrian age of UHP and HP metamorphism and subsequent exhumation of the KMB. However, there is no field evidence of Cambrian geodynamic processes in the region: Cambrian sediments, volcanic rocks, or large magmatic bodies are completely absent in the KMB setting. The youngest geochronological information in the KMB was obtained on the garnet-mica schists from the Enbek-Berlyk subterrane. The 40Ar/39Ar ages of the muscovite from these schists lies in the range of 490 to 475 Ma (mainly 480-485 Ma). All 40Ar/39Ar stepwise heating experiments yield well-defined plateau and isochron ages. This age is considered to represent the time of emplacement of various heterogeneous nappes, including nappes that consist of HP - UHP metamorphic rocks, to upper crustal levels. To the north, the Kokchetav HP - UHP metamorphic belt is bounded by the Northern Kokchetav tectonic zone (NKTZ). This zone includes thin nappes of (1) Palaeo-Mesoproterozoic gneiss of the metamorphic basement of the Kokchetav microcontinent and Neoproterozoic meta-sandstones and dolomites of its deformed sedimentary cover, (2) pre-Ordovician volcanic rocks of island-arc affinity, (3) Early Ordovician turbidities with olistostrome lenses, and (4) gneiss with eclogite boudins. These nappes are tectonically juxtaposed distinctly against unmetamorphosed rocks. The fault zones between the different tectonic units are formed by quartz-muscovite schists. The 40Ar/39Ar ages of the muscovite from these schists cluster between 492-476 Ma (mainly about 490 Ma). The NKTZ was formed by the Early Ordovician collision between the Kokchetav microcontinent, including the Kokchetav metamorphic belt, and the Stepnyak island-arc. Late Ordovician and Silurian granites cross-cut the internal structural architecture of both the KMB and NKTZ, providing a relative upper age limit. As a consequence, only the youngest stage of the formation of the metamorphic belt is directly related to a collision event. Comparison of the structural-metamorphic history of the KMB with the regional geological context, indicates that tectonic exhumation of the Kokchetav HP - UHP rocks must be precollisional. In this model, the individual nappes, detached from the underthrusting slab during progressive continental subduction, were exhumated before subduction cessation. The observed imbricated-nappe structure in the field, where UHP and HP rocks are juxtaposed against unmetamorphosed Ordovician sediments and volcanic deposits was formed during subsequent Ordovician collisional deformation events.

The role of serpentinite melanges in the unroofing of UHPM rocks: An example from the Western Alps of Italy: Chapter 6

USGS Publications Warehouse

Blake, M. Clark; Moore, D.E.; Jayko, A.S.; Coleman, Robert G.

1995-01-01

The ultrahigh pressure metamorphic rocks (UHPM) of the Dora-Maira continental massif are overlain by a stack of oceanic nappes. Metamorphic grade appears to increase downward but with marked discontinuities between each of the nappes, suggesting that section has been removed along the bounding faults. This apparent omission of section is greatest in the lowest oceanic unit where a serpentinite melange containing blocks and slabs of eclogite, metamorphosed at 12–19 kbar, lies on the UHPM rocks. We suggest that this serpentinite melange represents a highly attenuated upper mantle section that structurally overlay the UHP rocks during subduction. Similar serpentinite melanges are known from other high-pressure (HP) and UHPM areas and may have a similar origin.

Trace-element record in zircons during exhumation from UHP conditions, North-East Greenland Caledonides

USGS Publications Warehouse

McClelland, W.C.; Gilotti, J.A.; Mazdab, F.K.; Wooden, J.L.

2009-01-01

Coesite-bearing zircon formed at ultrahigh-pressure (UHP) conditions share general characteristics of eclogite-facies zircon with trace-element signatures characterized by depleted heavy rare earth elements (HREE), lack of an Eu anomaly, and low Th/ U ratios. Trace-element signatures of zircons from the Caledonian UHP terrane in North-East Greenland were used to examine the possible changes in signature with age during exhumation. Collection and interpretation of age and trace-element analyses of zircon from three samples of quartzofeldspathic gneiss and two leucocratic intrusions were guided by core vs. rim zoning patterns as imaged by cathodoluminesence. Change from igneous to eclogite-facies metamorphic trace-element signature in protolith zircon is characterized by gradual depletion of HREE, whereas newly formed metamorphic rims have flat HREE patterns and REE concentrations that are distinct from the recrystallized inherited cores. The signature associated with eclogite-facies metamorphic zircon is observed in coesite-bearing zircon formed at 358 ?? 4 Ma, metamorphic rims formed at 348 ?? 5 Ma during the initial stages of exhumation, and metamorphic rims formed at 337 ?? 5 Ma. Zircons from a garnet-bearing granite emplaced in the neck of an eclogite boudin and a leucocratic dike that cross-cuts amphibolite-facies structural fabrics have steeply sloping HREE patterns, variably developed negative Eu anomalies, and low Th/U ratios. The granite records initial decompression melting and exhumation at 347 ?? 2 Ma and later zircon rim growth at 329 ?? 5. The leucocratic dike was likely emplaced at amphibolite-facies conditions at 330 ?? 2 Ma, but records additional growth of compositionally similar zircon at 321 ??2 Ma. The difference between the trace-element signature of metamorphic zircon in the gneisses and in part coeval leucocratic intrusions indicates that the zircon signature varies as a function of lithology and context, thus enhancing its ability to aid in the interpretation of U-Pb data and track the exhumation history of UHP terranes. The differences may reflect variation in elemental availability through breakdown reactions in quartzofeldpathic gneiss vs. availability during melt production and/or crystallization. UHP rocks in North-East Greenland began exhumation by 347 ?? 2 Ma, were still at HP eclogite-facies conditions at 337 ?? 5 Ma and were at amphibolite-facies conditions by 330 ?? 2 Ma. ?? 2009 E. Schweizerbart'sche Verlagsbuchhandlung.

Metamorphism of eclogites from the UHP Maksyutov Complex, south Ural Mountains, Russia

NASA Astrophysics Data System (ADS)

Burlick, T. D.; Leech, M. L.

2013-12-01

The Maksyutov Complex is a mid- to late Paleozoic ultrahigh-pressure (UHP) subduction terrane in the south Ural Mountains of Russia. Radial fractures around quartz inclusions in garnet, omphacite, and glaucophane interpreted as pre-existing coesite; and microdiamond aggregates in garnet identified by Raman spectroscopy demonstrate Maksyutov rocks were subducted to UHP conditions (>2.8 GPa for coesite and >3.0 GPa for diamond at 600°C). Peak UHP eclogite-facies metamorphism (Grt+Omp+Ph+Coe+Rt ×Ttn) took place at c. 385 M and Maksyutov rocks were exhumed through retrograde blueschist-facies metamorphism (Grt+Gln+Ph+Qz×Chl×Ep) by 360 Ma. Pseudosections were constructed to constrain the P-T conditions recorded by the equilibrium mineral assemblanges in eclogites and their retrograded equivalents using bulk rock XRF analysis in the system Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 and the suite of free energy minimization programs, Perple_X 6.6.8 [Connolly 2009] with the internally consistent end-member thermodynamic database from Holland and Powell [1998] (mod 2004); solution models for omphacite (Holland and Powell, 1996), clinoamphibole (Dale et al. 2005), white mica (Coggon & Holland 2002, Auzanneau et al 2010), chlorite and garnet (Holland and Powell 1998; Powell and Holland 1999), and feldspar (Thompson and Hovis 1979; Newton et al. 1980) were used with H2O as a saturated component. Both conventional thermometry, using microprobe analyses and Grt-Cpx cation exchange as well as pseudosection modeling result in higher peak equilibrium temperatures than has been previously been reported in the Maksyutov. Pseudosection modeling gives minimum P-T conditions of 625°-675°C and 2.8-3.1 GPa for peak assemblages from the least retrogressed eclogites, while Fe-Mg exchange thermometry yields temperatures of 775°C × 25°C for pressures ranging from 2.5 to 3.5 GPa.

White mica K-Ar geochronology of HP-UHP units in the Lago di Cignana area, western Alps, Italy: Tectonic implications for exhumation

NASA Astrophysics Data System (ADS)

Gouzu, Chitaro; Yagi, Koshi; Thanh, Ngo Xuan; Itaya, Tetsumaru; Compagnoni, Roberto

2016-04-01

High-pressure and ultra-high pressure (HP-UHP) blueschist- and eclogite-facies metabasaltic and metasedimentary rocks occur in four different tectonic units near Lago di Cignana, western Alps. We have determined K-Ar ages for white micas (matrix phengite and paragonite) from the Lago di Cignana UHP unit (LCU; 39-41 Ma); the lower and upper units of the Zermatt-Saas meta-ophiolite (LU and UU; 37-38 Ma and 38-41 Ma respectively), and the Combin unit (CU; 36-40 Ma). These K-Ar ages overlap with single-grain Ar-Ar plateau ages (36-42 Ma) previously determined for phengites from LCU metasediments. Matrix white micas have been severely deformed during exhumation, and their chemistries differ from those of micas included in garnet. Although individual mica grains in the matrix could have experienced different degrees of deformation which have reset their K-Ar systems, "bulk" white mica separates provide the average age of all the individual grains in the separate. The similarity of ages determined for white micas from the LCU, LU, UU and CU units, regardless of rock type and mineral species, suggests that these four units were metamorphosed together as part of a single metamorphic sequence in the Piemonte-Liguria paleosubduction zone and were subsequently exhumed together. However, present-day structural relationship among those units and the limited occurrence of UHP minerals in LCU suggests that the exhumation of LCU was more rapid than that for LU, UU and CU. The age gaps between the youngest value of white mica K-Ar ages in each unit and the inferred timing of the metamorphic peak (U-Pb age: 44 Ma) is 5, 7, 6 and 8 Myr for LCU, LU, UU and CU, respectively. These intervals are considerably shorter than that determined for the Sanbagawa HP metamorphic belt of Southwest Japan (> 31 Myr). The short interval observed for the Lago di Cignana units that we have studied is consistent with the model of rapid exhumation of the UHP-bearing metamorphic domain, suggesting the exhumation rate is higher than 18 mm/y in the early stage of exhumation from the deepest level (ca. 120 km) to the lower crust (ca. 30 km).

Geochronology and tectonic significance of Middle Proterozoic granitic orthogneiss, North Qaidam HP/UHP terrane, Western China

USGS Publications Warehouse

Mattinson, C.G.; Wooden, J.L.; Liou, J.G.; Bird, D.K.; Wu, C.L.

2006-01-01

Amphibolite-facies para- and orthogneisses near Dulan, in the southeast part of the North Qaidam terrane, enclose minor ultra-high pressure (UHP) eclogite and peridotite. Field relations and coesite inclusions in zircons from paragneiss suggest that felsic, mafic, and ultramafic rocks all experienced UHP metamorphism and a common amphibolite-facies retrogression. Ion microprobe U-Pb and REE analyses of zircons from two granitic orthogneisses indicate magmatic crystallization at 927 ?? Ma and 921 ?? 7 Ma. Zircon rims in one of these samples yield younger ages (397-618 Ma) compatible with partial zircon recrystallization during in-situ Ordovician-Silurian eclogite-facies metamorphism previously determined from eclogite and paragneiss in this area. The similarity between a 2496 ?? 18 Ma xenocrystic core and 2.4-2.5 Ga zircon cores in the surrounding paragneiss suggests that the granites intruded the sediments or that the granite is a melt of the older basement which supplied detritus to the sediments. The magmatic ages of the granitic orthogneisses are similar to 920-930 Ma ages of (meta)granitoids described further northwest in the North Qaidam terrane and its correlative west of the Altyn Tagh fault, suggesting that these areas formed a coherent block prior to widespread Mid Proterozoic granitic magmatism. ?? Springer-Verlag 2006.

Geochemistry of continental subduction-zone fluids

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Hermann, Joerg

2014-12-01

The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure (UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks and multiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophile elements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion of high field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating their crystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts with the mantle wedge peridotite leads to modal metasomatism with the generation of new mineral phases as well as cryptic metasomatism that is only manifested by the enrichment of fluid-mobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and their adjacent active continental margins. The study of such metasomatic processes and products is of great importance to understanding of the mass transfer at the slab-mantle interface in subduction channels. Therefore, the property and behavior of subduction-zone fluids are a key for understanding of the crust-mantle interaction at convergent plate margins.

SHRIMP U-Pb zircon dating from eclogite lenses in marble, Dabie-Sulu UHP terrane: restriction on the prograde, UHP and retrograde metamorphic ages

NASA Astrophysics Data System (ADS)

Liu, F.; Gerdes, A.; Xue, H.; Liang, F.

2006-12-01

Eclogite as lenses in impure marbles from Dabie-Sulu UHP terrane, represent parts of deeply subducted meta- sedimentary rocks. To constrain the age of metamorphism during subduction and exhumation, zircons from 2 eclogite samples in Dabie-Sulu impure marbles have been investigated. Beside Inherited (detrital) grains, 3 different metamorphic zircon domains have been identified based on distribution of mineral inclusion, trace elements and cathodoluminescence (CL) imaging: 1. Dark-luminescent rounded cores with quartz eclogite- facies mineral inclusions suggest formation at high-pressure (HP) metamorphic conditions. 2. White- luminescent zircon, either surrounding domain 1 or as rounded to spindly cores with index coesite eclogite- facies mineral inclusions indicates formation at UHP conditions. 3. Grey-luminescent rims around domain 2 with low-pressure mineral inclusions suggest formation during late regional amphibolite-facies retrogression. The three distinct zircon domains were dated by SHRIMP and yielded three discrete and meaningful age groups: 245±4 Ma for prograde HP metamorphism, 235±3 Ma for UHP metamorphism and 215±6 Ma for late amphibolite-facies retrogression from Dabie-Sulu eclogite. This data suggests that subduction and exhumation took place in about 10-11 Myr and 19-20 Myr, respectively. Continental materials was subducted from surface to the deep mantle depth at rates of 10 km/Myr, and subsequently exhumed from the mantle to the base of the crust at rates of 7 km/Myr. Ultrafast exhumation of the Dabie-Sulu UHP terrane from depth of 160 to 30 km was probably driven by buoyancy forces after UHP slab break-off at deep mantle depths.

Magnetic susceptibility of ultrahigh pressure eclogite: The role of retrogression

NASA Astrophysics Data System (ADS)

Xu, Haijun; Jin, Zhenmin; Mason, Roger; Ou, Xingong

2009-09-01

Retrograde metamorphism played the dominant role in changing the low-field rock magnetic properties and density of 198 specimens of variably retrograded eclogites from the main borehole of the Chinese Continental Scientific Drilling Project (CCSD) and from surface outcrops in the Donghai area in the southern part of the Sulu UHP belt, China. Bulk magnetic susceptibility ( κ) of unretrogressed UHP eclogite is controlled by whole-rock chemical composition and ranges from 397 to 2312 μSI with principal magnetic susceptibility carrying minerals paramagnetic garnet, omphacite, rutile and phengite. Partially retrograded eclogites show large variations in magnetic susceptibility between 804 and 24,277 μSI, with high mean magnetic susceptibility values of 4372 ± 4149 μSI caused by appreciable amounts of Fe-Ti oxide minerals such as magnetite, ilmenite and/or titanohematite produced by retrograde metamorphic reactions. Completely retrograded eclogites have lower susceptibilities of 1094 ± 600 μSI and amphibolite facies mineral assemblages lacking high magnetic susceptibility minerals. Jelínek's corrected anisotropy ( Pj) of eclogites ranges from 1.001 to 1.540, and shows a positive correlation with low-field magnetic susceptibility ( κ). Arithmetic mean bulk density ( ρ) shows a steady decrease from 3.54 ± 0.11 g/cm 3 (fresh eclogite) to 2.98 ± 0.06 g/cm 3 (completely retrograded eclogite). Retrograde metamorphic changes in mineral composition during exhumation appear to be the major factor causing variations in low field magnetic susceptibility and anisotropy. Retrograde processes must be taken into account when interpreting magnetic surveys and geophysical well logs in UHP metamorphic terranes, and petrophysical properties such as density and low-field magnetic susceptibility could provide a means for semi-quantifying the degree of retrogression of eclogite during exhumation.

Multi-stage barites in partially melted UHP eclogite: implications for fluid/melt activities during deep continental subduction in the Sulu orogenic belt

NASA Astrophysics Data System (ADS)

Wang, Songjie; Wang, Lu

2015-04-01

Barite (BaSO4) is well-known from deep-sea sedimentary environments but has received less attention to its presence in high-grade metamorphic rocks. Recently, barite in ultrahigh pressure (UHP) eclogite has drawn increasing attention from geologists, especially in the Dabie-Sulu orogen, since it is an important indicator for high-salinity fluid events, thus aiding in further understanding HP-UHP fluid / melt evolution. However, its formation time and mechanism in UHP eclogite are still controversial, with three representative viewpoints: (1) Liu et al. (2000) found barite-anhydrite-coesite inclusions in zircon and interpreted them to have formed by UHP metamorphic fluids; (2) Zeng et al. (2007) recognized isolated barite within K-feldspar (Kfs) and Quartz (Qz) surrounded by radial cracks in omphacite, and interpreted Kfs+Qz to be reaction products of potassium-rich fluid/melt and coesite, with the barite formed by prograde metamorphic fluids; (3) Gao et al. (2012) and Chen et al. (2014) found barite-bearing Multiphase Solid (MS) inclusions within garnet and omphacite and assumed that the barite formed by phengite breakdown possibly caused by eclogite partial melting during exhumation, though no direct evidence were proposed. The controversy above is mainly due to the lack of direct formation evidence and absence of a clear link with the metamorphic evolution of UHP eclogite along the subduction-exhumation path. We report detailed petrological and micro-structural analyses revealing four types of barites clearly linked with (1) the prograde, (2) earlier stage of partial melting and (3) later stage of crystallization differentiation, as well as (4) high-grade amphibolite-facies retrogression of a deeply subducted and partially melted intergranular coesite-bearing eclogite from Yangkou Bay, Sulu Orogen. Round barite inclusions (type-I) within UHP-stage garnet and omphacite are formed by internally buffered fluids from mineral dehydration during prograde metamorphism. Zr-in-rutile thermometry shows their formation temperature to be 586-664 oC at 1.5-2.5 GPa. Barite-bearing MS inclusions with Ba-bearing K-feldspar (type-II) connected by Kfs+Pl+Bt veinlets of in-situ phengite breakdown and thin barite veinlets along grain boundaries (type-III) are products of phengite breakdown and induced fluid flow during exhumation. These barites have witnessed the gradational separation process of melt/ fluid from miscibility on/above the second critical endpoint during UHP metamorphism, to immiscibility along the exhumation path of the subducted slab. Associated reactions from pyrite to hematite and goethite with the type-III barite ring surrounding the pyrite provide evidence for a local high oxygen fugacity environment during eclogite partial melting and subsequent melt/fluid crystallization processes. Moreover, large grain barite aggregations (type-IV) modified by amphibole+albite symplectite are most likely formed by release of molecular and hydroxyl water from anhydrous minerals of eclogite during high-grade amphibolite-facies retrogression. The growth of multi-stage barites in UHP eclogite further advances our understanding of fluid/melt transfer, crystallization processes along the subduction-exhumation path of the partially melted eclogite, broadening our knowledge of melt/fluid evolution within subduction-collision zones worldwide. REFERENCES Chen Y.X., et al., 2014, Lithos, 200, 1-21. Liu J.B., et al., 2000, Acta Petrologica Sinica 16(4), 482-484. Zeng L.S., et al., 2007, Chinese Science Bulletin, 52(21), 2995-3001. Gao X.Y., et al., 2012, Journal of Metamorphic Geology, 30(2), 193-212.

Ultrahigh Pressure Processing Produces Alterations in the Metabolite Profiles of Panax ginseng.

PubMed

Lee, Mee Youn; Singh, Digar; Kim, Sung Han; Lee, Sang Jun; Lee, Choong Hwan

2016-06-22

Ultrahigh pressure (UHP) treatments are non-thermal processing methods that have customarily been employed to enhance the quality and productivity of plant consumables. We aimed to evaluate the effects of UHP treatments on ginseng samples (white ginseng: WG; UHP-treated WG: UWG; red ginseng: RG; UHP-treated RG: URG; ginseng berries: GB; and UHP-treated GB: UGB) using metabolite profiling based on ultrahigh performance liquid chromatography-linear trap quadrupole-ion trap-tandem mass spectrometry (UHPLC-LTQ-IT-MS/MS) and gas chromatography time-of-flight mass spectrometry (GC-TOF-MS). Multivariate data analyses revealed a clear demarcation among the GB and UGB samples, and the phenotypic evaluations correlated the highest antioxidant activities and the total phenolic and flavonoid compositions with the UGB samples. Overall, eight amino acids, seven organic acids, seven sugars and sugar derivatives, two fatty acids, three notoginsenosides, three malonylginsenosides, and three ginsenosides, were identified as significantly discriminant metabolites between the GB and UGB samples, with relatively higher proportions in the latter. Ideally, these metabolites can be used as quality biomarkers for the assessment of ginseng products and our results indicate that UHP treatment likely led to an elevation in the proportions of total extractable metabolites in ginseng samples.

On protolith-, metamorphic overprint, microstructure and rheology of mineral assemblages in orogenic peridotites of the central Scandinavian Caledonides

NASA Astrophysics Data System (ADS)

Gilio, Mattia; Clos, Frediano; Van Roermund, Herman L. M.

2013-04-01

The Scandinavian Caledonides (SC) are a deeply eroded Alpine-type orogenic belt formed by closure of the Iapetus ocean and collision between Baltica and Laurentia (500-380 Ma). The SC consists of a stack of Nappe Complexes (from bottom to top called Lower, Middle, Upper and Uppermost Allochthons) thrusted to the east over the Baltic Shield (Brueckner and Van Roermund, 2004; Gee et al., 2008). Fossil lithospheric mantle fragments, called orogenic peridotites, have been found within the (upper part of) middle, upper and uppermost Allochthons, as well as in the reworked basement gneisses (a.o Western Gneiss Complex (WGC)) along the Norwegian west coast. They occur as isolated lenses that contain diverse mineral parageneses and/or bulk rock compositions. Crustal incorporation of orogenic peridotite is classically interpreted to be the result of plate collisional processes related to orogeny (Brueckner and Medaris, 2000). The WGC and parts of the upper part of the Middle Allochthon (a.o. Seve Nappe Complex (SNC) in N Jämtland/S Västerbotten, central Sweden), are well known for the occurrence of high (HP) and ultrahigh pressure (UHP) metamorphic terranes (of Caledonian age). The (U)HPM evidence clearly demonstrates the deep metamorphic origin of these rocks interpreted to be caused by continental subduction and/or collision. Other metamorphic rocks (of Caledonian age) exposed in allochthonous nappes are solely characterised by greenschist-, amphibolite- and/or MP granulite "facies" mineral assemblages that can be interpreted, in the absence of retrogression, to have formed in less deeply subducted (and/or metamorphic) environments. This duality in metamorphic "facies" allows for a discrimination (at least theoretically) between "deep" versus "shallow" rooted nappes (in central parts of the Scandinavian Caledonides). Conform this reasoning, this duality should also be present within the Caledonian mineral assemblages (= metamorphic overprint) of orogenic peridotites (in central parts of the orogen), which, at least in the allochtonous nappes, have been interpreted to be "isofacial" with their host country rocks (Bucher, 1991). The latter strongly contrast to the interpretation of their "primary" (="protolith"- related) mineral assemblage(s) which clearly suggest a bimodal origin: here called thick (>80 km) versus thin (< 70 km) rooted lithospheric mantle protoliths. Distinction can be made on the basis of the presence of the stable (minimal Proterozoic) garnet-olivine assemblages in the protolith (i.e. much older than the Scandian collision event (Brueckner et al., 2010). For this reason orogenic garnet peridotite was first called "relict" garnet peridotite (Brueckner and Medaris, 2000), later rephrased into mantle wedge garnet peridotite (MWgp) by Van Roermund (2009). MWgp occurs in the WGC and in the SNC of the Upper Allochthon in central Sweden (Zhang et al., 2009). Most (All?) other protolith assemblages of orogenic peridotite in the CSC belong to the thin-rooted protolith subtype. No examples are known to us in which thin rooted prototypes became overprinted (during the Caledonian orogeny) by (U)HP metamorphic minerals, except for the subduction zone garnet peridotites (SZgp) in the WGC (Van Roermund, 2009). The latter can thus savely be interpreted as being enclosed within normal "MP" (or lower pressure) nappe sequences. As such it will be clear that this duality in protolith (and/or metamorphic) mineral assemblages of orogenic peridotite can be used to identify former, but now strongly retrogressed, (U)HP metamorphic terranes in other parts of the CSC (Gee et al, 2012). For this reason a comparative study has been made concerning field, (micro-)structural, mineral-chemical and/or geochemical aspects of two major orogenic peridotites from the SNC, central Sweden; here called the Friningen Garnet Peridotite (FGP) and the Kittelfjäll Spinel Peridotite (KSP), both exposed within the central belt of the SNC in central Sweden. The ultimate aim was to investigate whether the MWgp sub-type can be extended towards (Al-poor) spinel-bearing protolith assemblages or not. Results, including some hitherto unexpected mechanical effects, will be presented. References: Brueckner, H.K., Carswell, D.A., Griffin, W.L., Medaris, L.G., Van Roermund, H.L.M., Cuthbert, S.J. (2010). The mantle and crustal evolution of two garnet peridotite suites from the Western Gneiss Region, Norwegian Caledonides: An isotopic investigation. Lithos, 117, 1-19. doi:10.1016/j. Lithos.2010.01.011 Brueckner, H.K.and Medaris, L.G. (2000). A general model for the intrusion and evolution of "mantle" garnet peridotites in high-pressure and ultra-high-pressure metamorphic terranes. J. Metamorphic Geol., 18, 123-133. Brueckner H.K. and Van Roermund,H.L.M. (2004). Dunk tectonics: A multiple subduction//eduction model for the evolution of the Scandinavian Caledonides. Tectonics, 23, TC2004, doi:10.1029/2003tc001502. Bucher, K. (1991). Mantle fragments in the Scandinavian Caledonides. Tectonophysics, 190, 173-192. Gee, D.G., Fossen, H., Henriksen, N., Higgins, K. (2008). From the Early Paleozoic Platforms of Baltica and Laurentia to the Caledonide Orogen of Scandinavia and Greenland. Episodes, 31, 44-51. Gee, D.G., Janak, M., Majka, J., Robinson, P., Van Roermund, H.L.M (2012). UHP metamorphism along the Baltoscandian outer margin: evidence from the Seve Nappe Complex of the Swedish Caledonides. Lithosphere, in press. Janak, M., Van Roermund, H., Majka, J., Gee, D. (2012). UHP metamorphism recorded by kyanite-bearing eclogite in the Seve Nappe Complex of northern Jämtland, Swedish Caledonides. Gondwana Research, in press. Van Roermund, H.L.M. (2009). Mantle-wedge garnet peridotites from the northernmost ultra-high pressure domain of the Western Gneiss Region, SW Norway. Eur. J. Mineralogy, 21, 1085-1096. Zhang, C., Van Roermund, H.L.M., Zhang, L.F (2011). 16 - Orogenic Garnet Peridotites: Tools to Reconstruct Paleo-Geodynamic Settings of Fossil Continental Collision Zones. In: Ultrahigh Pressure Metamorphism, 25 Years After The Discovery Of Coesite And Diamond. London. Doi:10.1016/B978-0-12-385144-4.00015-1

Crustal structure and continental dynamics of Central China: A receiver function study and implications for ultrahigh-pressure metamorphism

NASA Astrophysics Data System (ADS)

He, Chuansong; Dong, Shuwen; Chen, Xuanhua; Santosh, M.; Li, Qiusheng

2014-01-01

The Qinling-Tongbai-Hong'an-Dabie-Sulu orogenic belt records the tectonic history of Paleozoic convergence between the South China and North China Blocks. In this study, the distribution of crustal thickness and P- and S-wave velocity ratio (Vp/Vs) is obtained by using the H-k stacking technique from the Dabie-Sulu belt in central China. Our results show marked differences in the crustal structure between the Dabie and Sulu segments of the ultrahigh-pressure (UHP) orogen. The lower crust in the Dabie orogenic belt is dominantly of felsic-intermediate composition, whereas the crust beneath the Sulu segment is largely intermediate-mafic. The crust of the Dabie orogenic belt is thicker by ca. 3-5 km as compared to that of the surrounding region with the presence of an ‘orogenic root’. The crustal thickness is nearly uniform in the Dabie orogenic belt with a generally smooth crust-mantle boundary. A symmetrically thickened crust in the absence of any deep-structural features similar to that of the Yangtze block suggests no supportive evidence for the proposed northward subduction of the Yangtze continental block beneath the North China Block. We propose that the collision between the Yangtze and North China Blocks and extrusion caused crustal shortening and thickening, as well as delamination of the lower crust, resulting in asthenospheric upwelling and lower crustal UHP metamorphism along the Dabie Orogen. Our results also reveal the presence of a SE to NW dipping Moho in the North China Block (beneath the Tran-North China Orogen and Eastern Block), suggesting the fossil architecture of the northwestward subduction of the Kula plate.

Crustal structure of the Dabie orogenic belt (eastern China) inferred from gravity and magnetic data

NASA Astrophysics Data System (ADS)

Yang, Yu-shan; Li, Yuan-yuan

2018-01-01

In order to better characterize the crustal structure of the Dabie orogen and its tectonic history, we present a crustal structure along a 500 km long profile across the Dabie orogenic belt using various data processing and interpretation of the gravity and magnetic data. Source depth estimations from the spectral analysis by continuous wavelet transform (CWT) provide better constraints for constructing the initial density model. The calculated gravity effects from the initial model show great discrepancy with the observed data, especially at the center of the profile. More practical factors are then incorporated into the gravity modeling. First, we add a high density body right beneath the high pressure metamorphic (HPM) and ultrahigh pressure metamorphic (UHPM) belt considering the exposed HPM and UHPM rocks in the mid of our profile. Then, the anomalous bodies A, B, and C inferred from the CWT-based spectral analysis results are fixed in the model geometry. In the final crustal density structure, two anomalous bodies B and C with high density and low magnetization could possibly be attributed to metasomatised mantle materials by SiO2-rich melt derived from the foundering subducted mafic lower crust. Under the extensional environment in the early Cretaceous, the upwelling metasomatised mantle was partially melted to produce the parental magma of the post-collisional mafic-ultramafic intrusive rocks. As for the low density body A with strong magnetization located in the lower crust right beneath the HP and UHP metamorphic belt, it is more likely to be composed of serpentinized mantle peridotite (SMP). This serpentinized mantle peridotite body (SMPB) represents the emplacement of mantle-derived peridotites in the crust, accompanying the exhumation of the UHP metamorphic rocks.

SHRIMP U-Pb dating, trace elements and the Lu-Hf isotope system of coesite-bearing zircon from amphibolite in the SW Sulu UHP terrane, eastern China

NASA Astrophysics Data System (ADS)

Liu, Fulai; Gerdes, Axel; Zeng, Lingsen; Xue, Huaimin

2008-06-01

In this study, we link mineral inclusion data, trace element analyses, U-Pb age and Hf isotope composition obtained from distinct zircon domains of complex zircon to unravel the origin and multi-stage metamorphic evolution of amphibolites from the Sulu ultrahigh-pressure (UHP) terrane, eastern China. Zircon grains separated from amphibolites from the CCSD-MH drill hole (G12) and Niushan outcrop (G13) were subdivided into two main types based on cathodoluminescence (CL) and Laser Raman spectroscopy: big dusty zircons with inherited cores and UHP metamorphic rims and small clear zircons. Weakly zoned, grey-white luminescent inherited cores preserve mineral inclusions of Cpx + Pl + Ap ± Qtz indicative of a mafic igneous protolith. Dark grey luminescent overgrowth rims contain the coesite eclogite-facies mineral inclusion assemblage Coe + Grt + Omp + Phe + Ap, and formed at T = 732-839 °C and P = 3.0-4.0 GPa. In contrast, white luminescent small clear zircons preserve mineral inclusions formed during retrograde HP quartz eclogite to LP amphibolite-facies metamorphism (T = 612-698 °C and P = 0.70-1.05 GPa). Inherited zircons from both samples yield SHRIMP 206Pb/238U ages of 695-520 Ma with an upper intercept age of 800 ± 31 Ma. The UHP rims yield consistent Triassic ages around 236-225 and 239-225 Ma for G12 and G13 with weighted means of 229 ± 3 and 231 ± 3 Ma, respectively. Small clear zircons from both samples give 206Pb/238U ages around 219-210 Ma with a weighted mean of 214 ± 3 Ma, interpreted as the age of retrograde quartz eclogite-facies metamorphism. Matrix amphibole from both samples indicate Ar-Ar ages of 209 ± 0.7 and 207 ± 0.7 Ma, respectively, probably dating late amphibolite-facies retrogression. The data suggest subduction of Neoproterozoic mafic igneous rocks to UHP conditions in Middle Triassic (∼230 Ma) times and subsequent exhumation to an early HP (∼214 Ma) and a late LP stage (∼208 Ma) over a period of ∼16 and 6 Myr, respectively. Thus, early exhumation from a mantle depth of 120-100 km to about 60 km occurred at an average rate of 0.3 cm/y, while subsequent exhumation to a middle crustal level took place at approximately 0.54 cm/y. These exhumation rates are considerably slower than those obtained for UHP rocks in the Dora Maira and Kokchetav massifs (2-3 cm/y). Based on similar P-T estimates and trace element and Hf isotope compositions, Sulu amphibolites can be identified as retrograde UHP eclogites. The εHf(800) of +8 implies a significant input from the depleted mantle to the Sulu-Dabie terrane during the middle Neoproterozoic. Overgrown rims are characterized by a distinct trace element composition with low Lu/Hf and Th/U and significantly higher 176Hf/177Hf ratios than inherited cores, consistent with formation during/after garnet (re-)crystallization and fractionation of the Lu-Hf system during UHP metamorphism. The combined dataset suggests homogenization of the 176Hf/177Hf ratio within the metamorphic mineral assemblage and during protolith formation. Observed variations are explained by mixing of material from both domains during laser ablation, e.g., due to partial recrystallization of inherited cores.

Recent progress in recognition of UHP metamorphism in allochthons of the Scandinavian Caledonides (Seve Nappe Complex and Tromsø Nappe)

NASA Astrophysics Data System (ADS)

Janák, Marian; Ravna, Erling; Majka, Jarosław; Klonowska, Iwona; Kullerud, Kåre; Gee, David; Froitzheim, Nikolaus

2017-04-01

During the last ten years, UHP rocks have been discovered within far-travelled allochthons of the Scandinavian Caledonides including the Seve Nappe Complex (SNC) of the Middle Allochthon and Tromsø Nappe within the Uppermost Allochthon. The first evidence for UHP conditions in the SNC was documented in a kyanite-bearing eclogite dike within the Friningen garnet peridotite. Subsequently, UHP conditions were determined for phengite eclogite and garnet pyroxenite from Stor Jougdan and pelitic gneisses from Åreskutan. Finally, diamond was found in metasedimentary rocks of the SNC at three localities (Snasahögarna, Åreskutan and most recently near Saxnäs), c. 250 km apart, confirming regional UHP conditions within this allochthon. In the Tromsø Nappe (northern Norway), evidence for UHP metamorphism comes from phengite- and kyanite-bearing eclogites from Tønsvika and Tromsdalstind, and diamond-bearing gneisses from Tønsvika. Microdiamond occurs in-situ as single and composite (mostly with Mg-Fe carbonate) inclusions within garnet and zircon. The calculated P-T conditions for the diamond-bearing samples are 4.1-4.2 GPa/830-840°C (Åreskutan), and 3.5-4.0 GPa/ 750-800°C (Tønsvika), in the diamond stability field. The UHP metamorphism in the SNC and Tromsø Nappe is probably Late Ordovician (c. 460-450 Ma), i.e. c. 40-50 Ma older than that in the Western Gneiss Region of southwestern Norway. Whereas the latter occurred during the collision between Laurentia and Baltica in the Late Silurian to Early Devonian, the processes leading to Ordovician UHP metamorphism occurred during closure of the Iapetus Ocean and are less well understood. The occurrence of two UHP metamorphic events in the Scandinavian Caledonides implies subduction, exhumation, and re-subduction of continental crust. This is an observation that could be of importance for the understanding of orogeny at convergent plate boundaries in general. The following questions remain to be answered: (1) Was UHP metamorphism in the SNC related to continent-continent or arc-continent collision? (2) Which processes lead to the emplacement of peridotite bodies with subcontinental mantle affinity into Baltican continental crust? (3) Was the Tromsø Nappe of Laurentian origin, or a part of the Baltoscandian margin emplaced by out-of-sequence thrusting, or a terrane of unknown affinity? Therefore, it is important to constrain the areal extent, pressure-temperature conditions, timing, and kinematics of UHP metamorphism in these allochthonous units.

Unraveling the Switch from Subduction to Exhumation within a Collisional Orogen: Split-stream U-Pb and Trace-element Results from the Western Gneiss Region, Norway (Invited)

NASA Astrophysics Data System (ADS)

Gordon, S. M.; Whitney, D. L.; Teyssier, C. P.; Fossen, H.; Desormeau, J. W.; Jessen, B.

2013-12-01

During continental collision, crustal material may be subducted to great depths and subsequently exhumed. Ultrahigh-pressure (UHP) terranes preserve a record of the subduction of crustal material during suturing of colliding continents and the exhumation of this material during extension and, in some cases, collapse of the orogen. The UHP rocks of the Western Gneiss Region (WGR), Norway, resulted from the collision of Baltica with Laurentia during the final stages of the Caledonian orogeny. The WGR represents one of the two largest UHP terranes on Earth and consists of a UHP eclogite-bearing domain south of the Møre-Trøndelag strike-slip fault and a HP mafic granulite-bearing domain north of the fault. At least some of the HP granulite is overprinted eclogite. To evaluate the metamorphic and structural relationship of mafic rocks and associated migmatite in both regions, we obtained LA-ICP-MS U-Pb dates and trace-element analyses for zircon from a variety of textural types of leucosome associated with mafic layers and lenses. Five leucosomes within highly deformed migmatite in the HP granulite complex on the Roan Peninsula reveal U-Pb lower-intercept ages from ca. 405 to 409 Ma and upper-intercept Proterozoic dates. These zircons have distinct trace-elements patterns: all of the zircons that yield Proterozoic dates have overall much higher REE concentrations, a more significant negative Eu anomaly (-0.3 to -0.7) and steeper HREE patterns (Lu/Dy = 5-12). In comparison, the Caledonian zircons reveal flatter Eu anomalies (-0.3 to 0.2) and less steep HREE patterns (Lu/Dy = 2-7), although the individual patterns do not seem to correlate with age. The Caledonian zircon patterns suggest crystallization at high-pressures and are distinct from the inherited Proterozoic grains. Similar results were obtained from zircon rims extracted from layer-parallel to crosscutting leucosomes from the UHP domain. Trace elements in zircon in these samples record the transition from high-pressure (garnet-present, plagioclase-absent) crystallization to lower-pressure (plagioclase-present) crystallization with garnet-present × plagioclase-absent REE patterns. Moreover, dates from the layer-parallel leucosomes are as old as 410-406 Ma. The new U-Pb dates suggest a similar melt crystallization history that was coeval with previously determined ages of (U)HP metamorphism of WGR eclogite. The More-Trondelag fault acted as a transform fault and accommodated coeval extension that exhumed both the (U)HP and granulite domains. Results are consistent with the presence of partially molten crust in a large part of the WGR at HP or UHP conditions during the latest stages of the Caledonian orogeny. The decreased viscosity and increased buoyancy and strain weakening induced by partial melting may have triggered or at least contributed to the switch from subduction to exhumation in the WGR, marking the end of collisional orogeny.

Petrology, geochemistry and isotope data on a ultrahigh-pressure jadeite quartzite from Shuanghe, Dabie Mountains, East-central China

NASA Astrophysics Data System (ADS)

Liou, J. G.; Zhang, R. Y.; Jahn, Bor-ming

1997-08-01

In the Dabie ultrahigh-pressure terrane of east-central China, coesite-bearing jadeite quartzites occur locally as intercalated layers with marble and mafic eclogite. This rock assemblage is, in turn, enclosed within quartzofeldspathic gneisses. Metamorphic parageneses and kelyphitic textures reveal a multistage metamorphic evolution and complex exhumation history. The primary peak metamorphic assemblage consists of jadeite + garnet + coesite + rutile ± apatite. Minor coesite and coesite pseudomorphs occur as inclusions in jadeite and garnet. Three stages of retrograde assemblages are observed in the jadeite quartzites. Stage A is represented by the polymorphic transformation of coesite to quartz aggregates. Stage B is characterized by formation of coronas around jadeite porphyroblasts consisting of an inner layer of oligoclase + amphibole and an outer layer of albite ± aegirine—augite. The last stage (stage C) involved total replacement of jadeite and most garnets by taramitic amphibole + albite + aegirine-augite. Peak metamorphic P-T conditions were > 26 kbar at 660°C and are consistent with the estimates from the adjacent coesite-bearing eclogites. The jadeite quartzites display clockwise P-T path that matches those of the adjacent eclogites. Major and trace element data suggest that the protolith of the jadeite quartzite could have been an albitized siltstone enriched in Na and depleted in K and Ca. The highly negative present-day ɛNd value (-24.7) indicates a very old age for the protolith. Its late Archean model age (TDM) of 2.58 Ga is among the oldest so far identified for rocks from the Dabie UHPM terrane. Concordant field relations and petrogenetic considerations suggest that all mafic, politic, carbonate and gneissic rocks have experienced in-situ UHP metamorphism during Triassic continental collision between the Sino-Korean and Yangtze cratons.

Provenance of Jurassic sediments in the Hefei Basin, east-central China and the contribution of high-pressure and ultrahigh-pressure metamorphic rocks from the Dabie Shan

NASA Astrophysics Data System (ADS)

Li, Renwei; Wan, Yusheng; Cheng, Zhenyu; Zhou, Jianxiong; Li, Shuangying; Jin, Fuquan; Meng, Qingren; Li, Zhong; Jiang, Maosheng

2005-03-01

The provenance of the Jurassic sediments in the Hefei Basin is constrained by compositions of the detrital K-white micas and garnets, and SHRIMP dating of the detrital zircons, which can help to understand the evolution and to reconstruct the paleogeographic distribution of HP-UHP rocks in the Jurassic Dabie Shan. (1) For the oldest Mesozoic sediments at the bottom of the Fanghushan Formation ( J1), the predominance of the early Paleozoic and Luliang (1700-1900 Ma) zircons indicates a major source from the North China Block. However, Neoproterozoic zircons as the major component in other Jurassic sediments indicate that the source rocks were mainly derived from the exhumed Yangtze Block in the Dabie Shan. (2) The co-occurrence of high-Si phengites and Triassic zircons provides stratigraphic evidence that the first exposure of the UHP rocks at the Earth's surface in the Dabie Shan occurred in the Early Jurassic during deposition of the Fanghushan Formation. (3) From the east to the west of the Hefei Basin, there is a spatial variation in the compositions for detrital micas and garnets, and in the U-Pb ages of detrital zircons. Evidently, HP-UHP rocks were widely distributed at outcrop in the eastern Dabie Shan. In contrast, they were less important in the western Dabie Shan during the Jurassic.

Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence

NASA Astrophysics Data System (ADS)

Wang, Lu; Kusky, Timothy; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

2015-04-01

Partially Melted UHP Eclogite in the Sulu Orogenic Belt, China and its rheological significance to deep continental subduction: Micro- to Macro-scale Evidence Numerous studies have described partial melting processes in low-high pressure meta-sedimentary rocks, some of which may generate melts that coalesce to form plutons. However, migmatized ultrahigh pressure (UHP) eclogite has never been clearly described from the microscale to macroscale, though experimental studies prove dehydration partial melting of eclogite at high pressure condition1 and low degrees of partially melted eclogite have been reported from the Qaidam UHP orogenic belt in NW China2,3 or inferred from multiphase solid (MS) inclusions within eclogite4 in the Sulu UHP belt. We present field-based documentation of decompression partial melting of UHP eclogite from Yangkou and General's Hill, Sulu Orogen. Migmatized eclogite shows successive stages of anatexis, initially starting from intragranular and grain boundary melt droplets, which grow into a 3D interconnected intergranular network, then segregate and accumulate in pressure shadow areas, and finally merge to form melt channels and dikes that transport melts to upper lithospheric levels. In-situ phengite breakdown-induced partial melting is directly identified by MS inclusions of Kfs+ barium-bearing Kfs + Pl in garnet, connected by 4-10 μm wide veinlets consisting of Bt + Kfs + Pl next to the phengite. Intergranular veinlets of plagioclase + K-feldspar first form isolated beads of melt along grain boundaries and triple junctions of quartz, and with higher degrees of melting, eventually form interconnected 3D networks along grain boundaries in the leucosome, allowing melt to escape from the intergranular realm and collect in low-stress areas. U-Pb (zircon) dating and petrological analyses on residue and leucocratic rocks shows that partial melting occurred at 228-219 Ma, shortly after peak UHP metamorphism (~230 Ma), and at depths of 30-90 km. Whole-rock trace element analyses show that the leucocratic rocks, residue and peak metamorphic stage eclogite (no decompression partial melting) show well matched mass balance relationships. Melts derived from eclogite partial melting lubricated the subducted eclogite slices and facilitated their buoyant rise from mantle depths to crustal levels. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behavior of subducted lithosphere and its rapid exhumation, controlling flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. Deeply subducted, partially melted eclogite from General's Hill show that eclogites can develop regularly spaced melt channels, a meter or two thick, that would act as significant seismic anomalies5. This may provide direct evidence for the nature of enigmatic 'bright zones' presented in some deep-crustal seismic reflection profiles which have been interpreted to represent areas of melt, high fluid content or unusual rock compositions6. Hermann, J. & Green, D. H. (2001). Earth Planet. Sci. Lett. 188, 149-168. Song, S.G., et al. (2014). Geochim. Cosmochim. Acta 130 42-62. Zhang, G.B., et al. (2014). Lithos, doi: 10.1016/j.lithos.2014.12.009 Gao, X. Y., et al. (2012). J. Metamorph. Geol. 30, 193-212. Wang, L., et al. (2014). Nature Communications. 5:5604 doi: 10.1038/ncomms6604. Brown, L. et al. (1996). Science 274, 1688-1690.

Geochronology of Zircon in Eclogite Reveals Imbrication of the Ultrahigh-Pressure Western Gneiss Region of Norway.

NASA Astrophysics Data System (ADS)

Young, D. J.; Kylander-Clark, A. R.; Root, D. B.

2014-12-01

Eclogite provides the only record of kinematic events at the deepest levels of orogens. Integrating the U-Pb geochronology and trace element chemistry of zircon in eclogite reveals the most complete view of the PTt history, yet low concentrations of uranium and zirconium and drier compositions that hinder zircon growth at peak conditions render it a challenging rocktype for this approach. The iconic Western Gneiss Region (WGR) in Norway is one of the largest terranes of deeply subducted continental rocks in the world, and contains many indicators of ultrahigh-pressure metamorphic conditions (P>2.8 GPa) that developed during the Siluro-Devonian Caledonian Orogeny. A metamorphic transition from amphibolite-facies to ultrahigh-pressure eclogite facies broadly coincides with a km-scale shear zone that underlies the majority of the WGR. A critical unknown is the timing of movement on this feature, which emplaced allochthonous units above the Baltica basement, but might also have accommodated late-orogenic exhumation of the WGR from mantle depths. We carried out laser ablation split-stream ICPMS (LASS) and selected multigrain TIMS analyses of zircons from eleven eclogites across the southern WGR, of which eight are located within or above the shear zone. LASS spots on polished grains mostly yield weakly discordant Proterozoic intrusive ages, and often minimal indication of a Caledonian (U)HP metamorphic overprint. Direct ablation into unpolished zircon reveals thin rims of Caledonian age in some cases. Overall, the dataset shows that all samples began zircon growth at approximately the same time (ca. 430-420 Ma). Eclogite from lower levels of the shear zone does not contain any dates younger than ca. 410 Ma, however, while eclogite from higher levels continued growth until ca. 400 Ma. We interpret this to result from thrusting of the WGR above cooler basement after 410 Ma, terminating new zircon crystallization within the shear zone but allowing limited further growth in rocks above.

Pressure - temperature estimates of a phengite eclogite from the Grapesvåre Nappe, Norrbotten, Swedish Caledonides

NASA Astrophysics Data System (ADS)

Bukała, Michał; Majka, Jarosław; Walczak, Katarzyna; Barnes, Christopher; Klonowska, Iwona

2017-04-01

The Seve Nappe Complex (SNC) of the Scandinavian Caledonides has well documented history of high pressure (HP) and ultra-high pressure (UHP) metamorphism (e.g. Klonowska et al. 2014). Eclogites of the SNC occur in two areas in Sweden, namely Jämtland and Norrbotten. The Jämtland eclogites and associated rocks are well studied and provide evidence for the Late Ordovician UHP metamorphism, whereas the Norrbotten eclogites, formed during the Late Cambrian/Early Ordovician, have not been studied in detail, especially in terms of pressure-temperature (P-T) conditions of their formation. Within the SNC in Norrbotten, eclogites are limited to two tectonic lenses - Vaimok and Tsäkkok (e.g. Albrecht, 2000). Within the Vaimok Lens three nappes have been distinguished: (1) the eclogite-free Lower Seve Nappe, (2) the Grapesvåre Nappe and (3) the Maddåive Nappe. The two latter nappes are eclogite-bearing. For this study eclogites were collected from the lowermost part of the Grapesvåre Nappe (from the highly heterogeneous Daunasvagge unit dominated by garnet-bearing mica schists, quartzites and marbles). Eclogite boudins (former dolerite dikes and sills) are usually highly altered due to retrogressive recrystallization. Rare fresh eclogites occur within large boudins (>5m in diameter) and display only minor alteration limited to the scarce veinlets composed of amphibole + feldspar + garnet + zoisite + biotite + rutile + titanite. Metamorphic peak conditions mineral assemblage consists of garnet + omphacite + phengite + quartz + rutile. For P-T estimates the geothermobarometric method of Ravna & Terry (2004) has been used. The garnet-clinopyroxene Fe2+-Mg exchange thermometer and the net-transfer reaction barometer based on the garnet-phengite-omphacite equilibrium yielded a maximum pressure of 26.7 kbar and temperature of 677°C. The obtained temperature might be underestimated due to uncertainties in Fe2+/Fe3+ ratio in pyroxene. Therefore Zr-in-rutile geothermometer by Tomkins et al. (2007) has also been used and calculcated temperatures are in a 715-762°C range. The obtained results are somewhat similar to scarce former P-T estimates of eclogites from Norrbotten provided by Santallier (1988) (i.e. T=690-730°C and Pmin=18.5-19.5 kbar) and Albrecht (2000) (i.e. T=650-720°C and P=18.9-27.5 kbar). However, as Albrecht (2000) claimed, pressure values might have been largely underestimated due to limitation of the used methods. Thus our study provides for the first time an evidence for near UHP metamorphism recorded by eclogites of the Grapesvåre Nappe, hence shedding a new light on evolution of the SNC in Norrbotten. We speculate that maximum pressures of metamorphism might have been higher (even approaching coesite stability field), but further studies are required to pinpoint the maximum PT conditions. This work is financially supported by the NCN "CALSUB" research project no. 2014/14/E/ST10/00321. References: Albrecht L.G. (2000) PhD thesis, Lund University. Klonowska I., Majka J., Janák M., Gee D.G., Ladenberger A. (2014) New Perspectives on the Caledonides of Scandinavia and Related Areas. Geological Society, London, Special Publications, 390: 321-336. Ravna E.J., Terry M.P. (2004) Journal of Metamorphic Geology 22: 579-592. Santallier D.S. (1988) Geologiska Föreningen i Stockholm Förhandlingar 110: 89-98. Tomkins H.S., Powell R., Ellis J.D. (2007) Journal of Metamorphic Geology 25: 703-713.

Mantle Lithosphere Rheology, Vertical Tectonics, and the Exhumation of (U)HP Rocks

NASA Astrophysics Data System (ADS)

Bodur, Ömer F.; Göǧüş, Oǧuz H.; Pysklywec, Russell N.; Okay, Aral I.

2018-02-01

Numerical modeling results indicate that mantle lithosphere rheology can influence the pressure-temperature-time (P-T-t) trajectories of continental crust subducted and exhumed during the onset of continental collision. Exhumation of ultrahigh-pressure ( 35 kbar)/high-temperature ( 750°C) metamorphic rocks is more prevalent in models with stronger continental mantle lithosphere (e.g., dry), whereas high-pressure ( 9-22 kbar)/low-temperature (350°C-630°C) metamorphic rocks occur in models with weaker rheology (e.g., hydrated) for the same layer. In the latter case, the buried crustal rocks can remain encased in ablatively subducting mantle lithosphere, reach only moderate temperatures, and exhume by dripping/detachment of the lithospheric root. In this transition from subduction to a dripping style of "vertical tectonics," burial and exhumation of crustal rocks are driven without imposed far-field plate convergence. The model results are compared against thermobarometric P-T estimates from major (ultra)high-pressure metamorphic terranes. We propose that the exhumation of high-pressure/low-temperature metamorphic rocks in Tavşanlı and Afyon zones in western Anatolia may be caused by viscous dripping of mantle lithosphere suggesting a weaker continental mantle lithosphere, whereas (ultra)high-pressure exhumation (e.g., Dabie Shan-eastern China and Dora Maira-western Alps) may be associated with plate-like subduction. In the latter case, the slab is much stronger and deformation is localized to the subduction interface along which rocks are buried to >100 km depth before they are exhumed to the near surface.

The relationship between continental collision process and metamorphic pattern in the Himalayan collision belts

NASA Astrophysics Data System (ADS)

Oh, Chang-Whan

2015-04-01

Both UHP and HP eclogites are reported from the Kaghan Valley and Tso Morari Massif in the western part of the Himalayan collision belt (Ghazanfar and Chaudhry, 1987; Thakur, 1983). UHP eclogites in the Kaghan record peak metamorphic conditions of 770 °C and 30 kbar (O'Brien et al., 2001) and was retrograded into the epidote-amphibolite or blueschist (580-610 °C, 10-13 kbar; Lombardo and Rolfo, 2000). Sensitive high-resolution ion microprobe dating of zircon reveals that the UHP eclogite formed at ca. 46 Ma (Kaneko et al., 2003; Parrish et al., 2006). The Tso Morari UHP eclogite had formed at 750 °C, > 39 kbar (Mukheerjee et al., 2003; Bundy, 1980) and underwent amphibolite facies retro-grade metamorphism (580 °C, 11 kbar) during uplift (Guillot et al., 2008). Peak metamorphism of the Tso Morari Massif was dated at ca. 53-55 Ma (Leech et al., 2005). Only HP eclogites have been reported from the mid-eastern part of the Himalayan collision belt (Lombardo and Rolfo, 2000; Corrie et al., 2010). The HP eclogite in the mid-eastern part may have formed at ca. > 780 °C and 20 kbar and was overprinted by high-pressure granulite facies metamorphism (780-750°C, 12-10 kbar) at ca. 30 Ma (Groppo et al. 2007; Corrie et al., 2010). HP granulite (890 °C, 17-18 kbar) is reported from the NBS, at the eastern terminus of the Himalayan collision belt; the granulite was subjected to retrograde metamorphism to produce lower-pressure granulite (875-850°C, 10-5 kbar), representing near-isothermal decompression (Liu and Zhong, 1997). The HP granulite metamorphism may have occurred at ca. 22-25 Ma. Along the Himalayan collision belt, peak metamorphism changes eastward from UHP eclogite facies through HP eclogite facies to high-pressure granulite facies, indicating a progressive eastwards decrease in the depth of subduction of continental crust and an eastwards increase in the geothermal gradient. The peak metamorphic ages also decrease from 53-46 Ma in the west to 22-25 Ma in the east indicating propagation of collision towards east. The following collision model of the Himalayan collision belt is proposed based on data published in previous studies. Collision between the Indian and Asian blocks started in the west before ca. 55 Ma. In the western part, the amount of oceanic slab subducted prior to continent collision was enough to pull the continental crust down to the depths of UHP metamorphism, as a wide ocean existed between the Asian and Indian blocks prior to collision. Following UHP metamorphism, oceanic slab break-off started at ca. 55~46 Ma in the west due to the very strong buoyancy of the deeply subducted continental block. In contrast, the subduction of continental crust continued at this time in the middle and eastern parts of the belt. The zone of break-off migrated eastward, initiating a change from steep- to low-angle subduction. Final break-off may have occurred in the easternmost part of the belt at ca. 22-25 Ma. The depth of slab break-off decreased toward the east due to the westward decrease of the amount of subducted oceanic crust along the Himalayan collision belt, resulting eastwards decrease of an uplifting rate due to a decrease in buoyancy of the continental slab. The slower uplift resulted in a longer period of thermal relaxation and a higher geothermal gradient. In the west, the high rate of uplift resulted the epidote amphibolite facies (580-610°C) retrograde metamorphic overprint on the UHP eclogites, whereas the relatively slow uplift in the mid-eastern part caused high-grade granulites (850°C) retrograde metamorphic overprint on the HP eclogites. The study indicates that the metamorphic pattern along the collision belt is strongly related to the amount of subducted oceanic crust between continents before collision and the depth of slab break-off. Therefore metamorphic pattern can be used to interpret both the disappeared and ongoing tectonic process during continental collision.

Ca. 400 Ma Recrystallization of Norwegian Ultrahigh-pressure Eclogites: an ion Microprobe and Chemical Abrasion Study

NASA Astrophysics Data System (ADS)

Root, D. B.; Mattinson, J. M.; Hacker, B. R.; Wooden, J. L.

2002-12-01

Understanding the formation and exhumation of the ultrahigh-pressure (UHP) rocks of western Norway hinges on precise determination of the time of eclogite recrystallization. Our study consists of SHRIMP analysis, in conjunction with CL imagery, of zircon from four UHP and high-pressure (HP) eclogites; and detailed TIMS analysis of zircon from two samples subjected to combined thermal annealing and multi-step chemical abrasion (CA). SHRIMP analyses of the Otnheim and Langenes eclogites yield Caledonian spot ages of ca. 400 Ma from zircon rims. CL imagery and Th/U ratios from the Langenes eclogite indicate formation of rims by recrystallization of inherited zircon. SHRIMP analysis of the UHP Flatraket eclogite yielded a broad range of apparently concordant Caledonian ages. CA analyses of two fractions yielded moderate Pb loss from the first (lowest T) steps; possible minor Pb loss or minor growth at 400 Ma from the second steps; and a 407-404 Ma cluster of slightly discordant 206Pb/238U ages, most likely free from Pb loss, from the remaining steps. We interpret the latter to reflect recrystallization of inherited zircon, with possible new growth, at ca. 400-395 Ma. Alternatively, the high-temperature CA steps could represent growth at 407-404 Ma, with apparent discordance due to intermediate daughter product effects. HP/UHP zircon recrystallization in the Flatraket eclogite is inferred from three lines of evidence: i) zircon occurs as inclusions in garnet, omphacite, breunnerite, dolomite, and quartz, as well as in symplectites after phengite and omphacite; ii) association of zircon with rutile implies zircon formation during HP breakdown of Zr-ilmenite; and iii) chondrite-normalized ICP-MS analyses of the CA steps reveal small Eu anomalies and shallow HREE profiles, indicating zircon recrystallization in the presence of garnet. CA analysis of the Verpeneset eclogite yielded distinctly discordant step ages from two steps comprising <90% of the sample, with 206Pb/238U ages of 408 and 414 Ma. CL imagery indicates incomplete recrystallization of inherited igneous zircon, in keeping with steep HREE profiles determined from chondrite-normalized ICP-MS analyses. Our zircon age of ca. 400-395 Ma for the Flatraket eclogite is significantly younger than the 425 Ma age often cited for western Norway eclogite recrystallization, implying, in conjunction with 390-385 Ma 40Ar/39Ar white mica cooling ages, faster rates of exhumation (ca. 15 km/m.y.), and weakening the link between UHP metamorphism and ophiolite emplacement at 430-425 Ma.

Partial melting of UHP calc-gneiss from the Dabie Mountains

NASA Astrophysics Data System (ADS)

Liu, Penglei; Wu, Yao; Liu, Qiang; Zhang, Junfeng; Zhang, Li; Jin, Zhenmin

2014-04-01

Exhumation melting has been proposed for the ultra-high pressure (UHP) metamorphic rocks in the Dabie Mountains based on melting experiments. We document here the first petrological and mineralogical evidence demonstrating that the UHP calc-gneisses from the Ganjialing area in the Dabie Mountains experienced partial melting during early exhumation. The assemblage of garnet, phengite (Si = 3.65 pfu), coesite, rutile and carbonate preserved in the calc-gneisses indicates a peak metamorphic condition of 692-757 °C and 4.0-4.8 GPa. Partial melting is indicated by several lines of evidence: the melting textures of phengite, the feldspar-dominated films, bands, branches, blebs and veins, the euhedral K-feldspars, the intergrowth film of plagioclase and K-feldspar, the plagioclase + biotite intergrowth after garnet and the epidote poikiloblasts. Polyphase inclusions in garnet are characterized with wedge-like offshoots and serrate outlines whereas those in epidote display negative crystal shapes, which can be best interpreted by entrapment of former melts. We propose a wet melting reaction of Phn + Q ± Na-Cpx + H2O = Bt + Pl + Grt + felsic melts, which likely took place at ca.650-800 °C and ca.1.0-2.0 GPa, to interpret the melting event in the calc-gneisses. Chemical exchanges between garnet and melts produced new garnet domains with higher almandine, spessartine, MREE, HREE and Y but lower grossular, pyrope, P, Sc, Ti, V and Zr contents. Zr-in-rutile thermometer reveals a low temperature of 620-643 °C at 5 GPa, indicating a later reset for Zr in rutile. Healed fractures are suggested to be responsible for the formation of some polyphase inclusions in garnet.

Thermobaric structure of the Himalayan Metamorphic Belt in Kaghan Valley, Pakistan

NASA Astrophysics Data System (ADS)

Rehman, Hafiz Ur; Yamamoto, Hiroshi; Kaneko, Yoshiyuki; Kausar, Allah Bakhsh; Murata, Mamoru; Ozawa, Hiroaki

2007-02-01

The thermobaric structure of the Himalayan Metamorphic Belt (HMB) has been constructed along the Kaghan Valley transect, Pakistan. The HMB in this valley represents mainly the Lesser Himalayan Sequence (LHS) and Higher Himalayan Crystallines (HHC). Mineral parageneses of 474 samples, from an approximately, 80-km traverse from southwest to northeast, were examined. Microprobe analyses were carried out to quantify the mineral composition. To determine the pressure-temperature (P-T) conditions, 65 thin sections (7 pelites from LHS and 25 pelites, 9 mafic rocks/amphibolites and 19 eclogites from HHC) were selected. Based on field observations and mineral paragenesis, low-grade to high-grade metapelites, show Barrovian-type progressive metamorphic sequence, with chlorite, biotite, garnet and staurolite zones in LHS and staurolite, kyanite and sillimanite zones in HHC. By using well-calibrated geothermobarometers, P-T conditions for pelitic and mafic rocks are estimated. P-T estimates for pelitic rocks from the garnet zone indicate a condition of 534 ± 17 °C at 7.6 ± 1.2 kbar. P-T estimates for rocks from the staurolite and kyanite zones indicate average conditions of 526 ± 17 °C at 9.4 ± 1.2 kbar and 657 ± 54 °C at 10 ± 1.6 kbar, respectively. P-T conditions for mafic rocks (amphibolites) and eclogites from HHC are estimated as 645 ± 54 °C at 10.3 ± 2 kbar and 746 ± 59 °C at 15.5 ± 2.1 kbar, respectively. The coesite-bearing ultrahigh-pressure (UHP) eclogites record a peak P-T condition of 757-786 °C at 28.6 ± 0.4 kbar and retrograde P-T conditions of 825 ± 59 °C at 18.1 ± 1.7 kbar. These results suggest that HMB show a gradual increase in metamorphic grade from southwest to northeast. The P-T conditions from Pelitic and adjacent mafic rocks having identical peak conditions in the same metamorphic zone, while the structural middle in HHC reached the highest P-T condition upto the UHP grade.

A crustal model of the ultrahigh-pressure Dabie Shan orogenic belt, China, derived from deep seismic refraction profiling

USGS Publications Warehouse

Wang, Chun-Yong; Zeng, Rong-Sheng; Mooney, W.D.; Hacker, B.R.

2000-01-01

We present a new crustal cross section through the east-west trending ultrahigh-pressure (UHP) Dabie Shan orogenic belt, east central China, based on a 400-km-long seismic refraction profile. Data from our profile reveal that the cratonal blocks north and south of the orogen are composed of 35-km-thick crust consisting of three layers (upper, middle, and lower crust) with average seismic velocities of 6.0±0.2 km/s, 6.5±0.1 km/s, and 6.8±0.1 km/s. The crust reaches a maximum thickness of 41.5 km beneath the northern margin of the orogen, and thus the present-day root beneath the orogen is only 6.5 km thick. The upper mantle velocity is 8.0±0.1 km/s. Modeling of shear wave data indicate that Poisson's ratio increases from 0.24±0.02 in the upper crust to 0.27±0.03 in the lower crust. This result is consistent with a dominantly felsic upper crustal composition and a mafic lower crustal composition within the amphibolite or granulite metamorphic facies. Our seismic model indicates that eclogite, which is abundant in surface exposures within the orogen, is not a volumetrically significant component in the middle or lower crust. Much of the Triassic structure associated with the formation of the UHP rocks of the Dabie Shan has been obscured by post-Triassic igneous activity, extension and large-offset strike-slip faulting. Nevertheless, we can identify a high-velocity (6.3 km/s) zone in the upper (<5 km depth) crustal core of the orogen which we interpret as a zone of ultrahigh-pressure rocks, a north dipping suture, and an apparent Moho offset that marks a likely active strike-slip fault.

Blueschist- and Eclogite facies Pseudotachylytes: Products of Earthquakes in Collision- and Subduction zones

NASA Astrophysics Data System (ADS)

Andersen, T. B.; Austrheim, H.; John, T.; Medvedev, S.; Mair, K.

2009-04-01

Pseudotachylytes are the products of violent geological processes such as metorite impacts and seismic faulting. The fault-rock weakening processes leading to release of earthquakes are commonly related to phenomena such as grain size reduction and gouge formation, pressurization of pore-fluids and in some cases to melting by frictional heating. Explaining the frequently observed intermediate and deep earthquakes by brittle failure is, however, inherently difficult to reconcile because of extremely high normal stresses occuring at depth. In recent years several mechanisms for seismic events on deep faults have been suggested. These include: a) The most commonly accepted mechanism, dehydration embrittlement coupled to prograde metamorphic dehydration of wet rocks, such as serpentinites, at depth. b) Grain-size dependent flow-laws coupled with shear heating instability has been suggested as an alternative to explain repeated seismic faulting in Wadati-Benioff zones. c) Self-localized-thermal-runaway (SLTR) has been forwarded as a mechanism for ultimate failure of visco-elastic materials and as mechanism to explain the co-existence of shear zones and pseudotachylyte fault veins formed at eclogite facies conditions. All these mechanism point to the importance of metamorphism and/or metasomatism in understanding the mechanism(s) of intermediate- and deep earthquakes. Exhumed high to ultra-high pressure [(U)HP] metamorphic rocks are recognized in many orogenic belts. These complexes provide avenues to study a number of important products of geological processes including earthquakes with hypocentres at great depths. (U)HP co-seismic fault rocks are difficult to find in the field; nevertheless, a number of occurrences of co-seismic fault rocks from such complexes have been described after the initial discovery of such rocks in Norway (see: Austrheim and Boundy, Science 1994). In this talk we review some observations and interpretations based on these hitherto rarely observed but important co-seismic fault rocks from deep-crust and mantle complexes.

UHP metamorphism in Greece: Petrologic data from the Rhodope Mountains

NASA Astrophysics Data System (ADS)

Baziotis, I. P.; Mposkos, E.; Krohe, A.; Wawrzenitz, N. H.; Liu, Y.; Taylor, L. A.

2012-12-01

Metamorphic rocks contain invaluable information for understanding the orogenic mechanisms of a tectonic regime. It is now well recorded and recognized that subduction of oceanic lithosphere and collision of continental blocks can result in sinking of subducted rocks to deeper levels than normal (>100 km). Further, the discovery of coesite and diamond in apparently regionally metamorphosed rocks provoked issues, for returning these rocks to the surface relatively fast, thereby preserving the UHP conditions. These UHPM terrains have been identified in more than twenty provinces worldwide. In Greece, UHPM rocks occur in the Rhodope area, one of the major tectono-metamorphic units located in NE Greece. This region consists of different metamorphic complexes involved in the Alpine collisional history between the Eurasian and African plates (e.g., Krohe & Mposkos, 2002-Geol Soc London Spec Pub, 204, 151). In Rhodope, a Jurassic UHP metamorphism is confirmed in the uppermost Kimi and the underlying Sidironero complexes (Mposkos & Kostopoulos, 2001- EPSL, 192, 497; Perraki et al., 2004-5th ISEMG, T2-35, 2006- EPSL, 241, 672; Liati, 2005- Con Min Pet, 150, 608; Bauer et al., 2007- Lithos, 99, 207). UHP metamorphism is evidenced by the presence of octahedral microdiamond inclusions (3 to 10 μm) in protective garnets, within the metapelitic gneisses. Microdiamonds probably formed from a supercritical fluid under extreme P-T conditions. The latter is strengthened by the presence of composite inclusions consisting of CO2, calcite, and microdiamonds. Other UHP indicators include: 1) quartz rods and rutile needle exsolutions in metapelitic garnet, suggesting a former titaniferous super-silicic (majoritic) garnet formed at P >4GPa; 2) oriented quartz lamellae in eclogitic clinopyroxene having been exsolved from a former super-silicic UHP precursor; and 3) coesite pseudomorphs in garnet, where radial cracks around multi-crystalline-quartz aggregates are indicative of the former coesite existence (e.g., Mposkos & Krohe, 2006- Can J Earth Sci, 43, 1755). Jurassic UHP rocks are overprinted by late Jurassic/early Cretaceous HP granulite facies metamorphism (P >1.5GPa; T~900 oC). In the Eastern and Western Rhodope, exhumation of these rocks occurred along different P-T paths. In the eastern Rhodope (Kimi Complex), UHP rocks re-equilibrated under relatively static annealing conditions and emerged at the surface in the Eocene. In the western Rhodope (Sidironero Complex), these rocks have been subjected to an overprinting Eocene MP to HP metamorphism, followed by exhumation along a major shear zone at about 40 Ma. In either case, a long-lasting post-UHP metamorphic history retrograded and almost completely destroyed the UHP minerals, thereby limiting the UHP record mainly to textural evidences and scarce UHP polymorphs. Consequently, some of the micro-diamonds have been partially or fully graphitized during this extensive exhumation period.

Water dynamics and retrogradation of ultrahigh pressurized wheat starch.

PubMed

Doona, Christopher J; Feeherry, Florence E; Baik, Moo-Yeol

2006-09-06

The water dynamics and retrogradation kinetics behavior of gelatinized wheat starch by either ultrahigh pressure (UHP) processing or heat are investigated. Wheat starch completely gelatinized in the condition of 90, 000 psi at 25 degrees C for 30 min (pressurized gel) or 100 degrees C for 30 min (heated gel). The physical properties of the wheat starches were characterized in terms of proton relaxation times (T2 times) measured using time-domain nuclear magnetic resonance spectroscopy and evaluated using commercially available continuous distribution modeling software. Different T2 distributions in both micro- and millisecond ranges between pressurized and heated wheat starch gels suggest distinctively different water dynamics between pressurized and heated wheat starch gels. Smaller water self-diffusion coefficients were observed for pressurized wheat starch gels and are indicative of more restricted translational proton mobility than is observed with heated wheat starch gels. The physical characteristics associated with changes taking place during retrogradation were evaluated using melting curves obtained with differential scanning calorimetry. Less retrogradation was observed in pressurized wheat starch, and it may be related to a smaller quantity of freezable water in pressurized wheat starch. Starches comprise a major constituent of many foods proposed for commercial potential using UHP, and the present results furnish insight into the effect of UHP on starch gelatinization and the mechanism of retrogradation during storage.

Evidence for a Mid-Crustal Continental Suture and Implications for Multistage (U)HP exhumation, Liverpool Land, East Greenland

NASA Astrophysics Data System (ADS)

Johnston, S.; Brueckner, H.; Gehrels, G.; Manthei, C.; Hacker, B.; Kylander-Clark, A.; Hartz, E. H.

2008-12-01

The East Greenland Caledonides consists of a series of west-directed sheets that formed from 460-360 Ma as Baltica subducted westward beneath Laurentia, and offer an opportunity to study high- and ultrahigh- pressure exhumation in orogenic hangingwalls. The Liverpool Land (LL) gneiss complex, 100 km east of the nearest Caledonian gneisses, provides a window into the deepest levels of the Greenland Caledonides. From the bottom up, the LL tectonostratigraphy is comprised of the eclogite-bearing Tvaerdal orthogneiss and the granulite-facies Jaettedal paragneiss structurally below the top-N Hurry Inlet Detachment. We present new thermobarometry and U/Pb zircon and titanite geochronology from the LL gneisses to define the tectonostratigraphy, continental affinity, and exhumation histories of the LL gneiss complex. The Tvaerdal orthogneiss consists of felsic orthogneisses that host rare ultramafic bodies (Fo92) and mafic boudins that yield peak pressures of >25 kbar at 800°C. Host gneiss zircons dated using LA-MC- ICPMS yield 1676 ± 17 Ma (2s) cores with 403 ± 6 Ma (2s) rims that suggest Mesoproterozoic emplacement of the original intrusive body followed by late-Caledonian deformation. The Tvaerdal orthogneiss also includes voluminous decompression melts; one yielded a TIMS U/Pb titanite age of 387.5 ± 2.2 Ma (2s). The structurally higher Jaettedal paragneiss consists of pelitic gneisses interlayered with granodioritic-dioritic orthogneisses. The Jaettedal-Tvaerdal contact is petrologically abrupt and concordant to regional foliation and lacks sub-amphibolite-facies displacement. Aluminum silicate-bearing pelitic assemblages within the Jaettedal paragneiss yield peak metamorphic conditions of 10-11 kbar at 750- 800°C. U/Pb age maps made using LA-MC-ICPMS from three paragneisses reveal Mesoproterozoic- Archean detrital cores with Caledonian rim overgrowths that cluster between 439-434 Ma. An amphibolite restite from the Jaettedal paragneiss yielded a TIMS U/Pb titanite age of 413 ± 1 Ma (2s). This new data defines two distinct LL gneiss complexes beneath the Hurry Inlet Detachment and suggests the presence of a previously unidentified continental suture between the Tvaerdal and Jaettedal gneisses. Similar timing, metamorphic conditions, and detrital zircon signatures to units farther inland, as well as the presence of Archean detrital zircons indicate a Laurentian continental affinity for Jaettedal paragneiss. In contrast, ~400 Ma (U)HP metamorphism and Mesoproterozoic basement ages, which have not been identified in Laurentia, suggests correlation of the Tvaerdal gneiss with the Baltican-derived Western Gneiss Region. Furthermore, the suture between the Tvaerdal and Jaettedal gneisses, with kinematics that remain undefined, represents a structure responsible for the juxtaposition of the younger (U)HP Tvaerdal orthogneiss against the older mid-crustal Jaettedal paragneiss, and the initial stages of (U)HP exhumation from mantle depths to lower-middle crustal levels. This initial exhumation may have triggered subsequent displacement along the Hurry Inlet Detachment responsible for the final stages of (U)HP exhumation in the upper crust.

Large-Scale, Long-Lived Subduction of Ultrahigh-Pressure Terranes: Western Gneiss Region, Norway

NASA Astrophysics Data System (ADS)

Kylander-Clark, A. R.; Hacker, B. R.; Johnson, C. M.; Beard, B. L.; Corfu, F.; Mahlen, N. J.

2007-12-01

Recent Lu-Hf and Sm-Nd ages of garnets and a U-Pb age of zircon of eclogites from the Western Gneiss Region (WGR) ultrahigh-pressure (UHP) terrane, Norway, demonstrate that eclogite-facies metamorphism occurred over a large area (60,000 km2) for an unexpectedly long time. This observation stands in stark contrast to the general belief that continental subduction, and attendant (U)HP metamorphism, occurs over short timescales. Four HP eclogites (~700-800°C, ~2.0-2.5 GPa) from the central WGR yielded equivalent Lu-Hf ages of ~416 Ma; three of these samples gave Sm-Nd ages of ~400 Ma. Given the distribution coefficients for Lu and Sm, the older Lu-Hf ages reflect prograde growth, but are younger than the initiation of garnet crystallization. The younger Sm-Nd ages represent either eclogite-facies cooling through the blocking temperature of the Sm-Nd system or an 'average' age of garnet growth. Both cases imply >16 m.y. of eclogite- facies conditions. Two UHP eclogites (~750-850°C, ~3 GPa) from the same region yielded significantly younger, but equivalent Lu-Hf and Sm-Nd ages of ~380 Ma, which likely indicate passage through the blocking temperature of both systems up to 20 m.y. after the HP eclogites had passed through the blocking temperature. Because these eclogites are unretrogressed, their ages are the youngest known for eclogite stability in the WGR. An eclogite from the northern WGR yielded a Sm-Nd age of 413.9 ± 3.7 Ma. This could represent a different HP history than that of the central WGR: U/Pb ages in the north are also ~15 m.y. older. Two HP (~650°C, ~2 GPa) eclogites from the southern WGR yielded Lu-Hf ages of 410.2 ± 3.1 and 427.5 ± 7.7 Ma, indicating a similar garnet growth history to the central WGR eclogites. A retrogressed eclogite from the undated eastern portion of the WGR gave a 206Pb/238U age of 408.0 ± 1.7 Ma. Thermal models mirror results from similar studies (Roselle et al., 2002), and confirm that slow subduction likely produced the P-T-t record observed in the WGR. For subduction of a continent into a formerly Andean-style subduction zone, Calculated temperatures of ~700-800°C are reached at 100 km depth only at burial rates slower than 4 mm/yr. These same temperatures are achieved with slow burial (4-7 mm/yr) during intracontinental subduction.

Cathodoluminescence of diamond as an indicator of its metamorphic history

NASA Astrophysics Data System (ADS)

Kopylova, Maya; Bruce, Loryn; Longo, Micaela; Ryder, John; Dobrzhinetskaya, Larissa

2010-05-01

Diamond displays a supreme resistance to chemical and mechanical weathering, ensuring its survival through complex and prolonged crustal processes, including metamorphism and exhumation. For these reasons, volcanic sources and secondary and tertiary collectors for detrital placer diamonds, like Ural or Bingara diamonds, may be difficult to determine. If metamorphic processes leave their marks on diamond, they can be used to reconstruct crustal geologic processes and ages of primary diamondiferous volcanics. Four diamond suites extracted from metamorphic rocks have been characterized using optical CL, infrared and CL spectroscopy, and photoluminescence at the liquid nitrogen temperature. The studied diamonds are from the ~2.7 Ga sedimentary conglomerate and lamprophyric breccia metamorphosed in the greenschist facies (Wawa, Northern Ontario, Canada) during the 2.67 Ga Kenoran orogeny, and from the ultra-high pressure (UHP) terranes of Kokchetav (Kazakhstan) and Erzgebirge (Germany) exhumated in the Paleozoic. Wawa diamonds (Type IaAB and Type II) displayed green, yellow, orange, and red CL colours controlled by the CL emittance at 520, 576 nm, and between 586 and 664 nm. The UHP terranes diamonds show much weaker CL; few luminescent stones display CL peaks at 395, 498, 528 nm and a broad band at 580-668 nm. In contrast, most common diamonds found in unmetamorphosed rocks, i.e. octahedrally grown Type IaAB stones, luminescence blue emitting light at ~415-440 nm and 480-490 nm. There is a noticeable difference between cathodoluminescence of these diamonds and diamonds in metamorphic rocks. The studied diamonds that experienced metamorphism show a shift of CL emission to longer wavelengths (above 520 nm) and to green, yellow and red CL colours. Photoluminescence has the high resolution necessary to assign luminescence to specific optical centers of diamond. Diamonds in metamorphic rocks contain H3 (pairs of substitutional nitrogen atoms separated by a vacancy) and NVo optical centers (neutrally charged complexes of a vacancy and a single nitrogen). We ascribe the effect of metamorphism on the diamond CL to low-T, low-P deformation that creates lattice dislocations and vacancies. These combine with substitutional N to make and enhance optical centers. The metamorphism-induced CL anneals when diamonds are stored at high-T mantle conditions, as the mobility of dislocations at T>750oC quenches the luminescence. Indeed, all studied diamonds that displayed unusual green, yellow and red CL were found in low and medium grade metamorphic rocks, i.e. Wawa greenschists (T<350oC and P< 3 kb) and Kokchetav and Erzgebirge UHP terranes retrograded in the amphibolite facies (T<750oC, P<14 kb) Our study suggest that a low abundance of octahedrally grown Type IaAB diamonds with blue CL colours among detrital diamonds may indicate that the stones may have once been a part of a low- or medium-grade metamorphic terrane. The CL characteristics superimposed by metamorphism could survive through billions of years of the geological history if not annealed by a high -T process. The discovered record of metamorphism in the diamond crystal lattice provides an opportunity for a better reconstruction of the crustal history and provenance studies of diamond.

Petrological and zircon evidence for the Early Cretaceous granulite-facies metamorphism in the Dabie orogen, China

NASA Astrophysics Data System (ADS)

Gao, Xiao-Ying; Zhang, Qiang-Qiang; Zheng, Yong-Fei; Chen, Yi-Xiang

2017-07-01

An integrated study of petrology, mineralogy, geochemistry, and geochronology was carried out for contemporaneous mafic granulite and diorite from the Dabie orogen. The results provide evidence for granulite-facies reworking of the ultrahigh-pressure (UHP) metamorphic rock in the collisional orogen. Most zircons from the granulite are new growth, and their U-Pb ages are clearly categorized into two groups at 122-127 Ma and 188 ± 2 Ma. Although these two groups of zircons show similarly steep HREE patterns and variably negative Eu anomalies, the younger group has much higher U, Th and REE contents and Th/U ratios, much lower εHf(t) values than the older group. This suggests their growth is associated with different types of dehydration reactions. The older zircon domains contain mineral inclusions of garnet + clinopyroxene ± quartz, indicating their growth through metamorphic reactions at high pressures. In contrast, the young zircon domains only contain a few quartz inclusions and the garnet-clinopyroxene-plagioclase-quartz barometry yields pressures of 4.9 to 12.5 kb. In addition, the clinopyroxene-garnet Fe-Mg exchange thermometry gives temperatures of 738-951 °C. Therefore, the young zircon domains would have grown through peritectic reaction at low to medium pressures. The younger granulite-facies metamorphic age is in agreement not only with the adjacent diorite at 125 ± 1 Ma in this study but also the voluminous emplacement of coeval mafic and felsic magmas in the Dabie orogen. Mineral separates from both mafic granulite and its adjacent diorite show uniformly lower δ18O values than normal mantle, similar to those for UHP eclogite-facies metaigneous rocks in the Dabie orogen. In combination with major-trace elements and zircon Lu-Hf isotope compositions, it is inferred that the protolith of mafic granulites shares with the source rock of diorites, both being a kind of mafic metasomatites at the slab-mantle interface in the continental subduction channel. The spatial and temporal distribution of Early Cretaceous granulite-facies metamorphic rocks in this region is associated with the bimodal magmatism within a short period of 120-130 Ma in the postcollisional stage. This provides a direct link in petrogenesis between the granulitic, migmatic and magmatic rocks in the collisional orogen to active continental rifting, whereby high heat flow was transferred from the asthenospheric mantle into the thinned orogenic lithosphere for partial melting.

Constraining Metamorphic Timing and Processes by Dating Garnet, Zircon, Titanite and Monazite in UHP and HP Rocks from Weihai, Sulu UHP Terrane, Eastern China

NASA Astrophysics Data System (ADS)

Wang, D.; Vervoort, J. D.; Fisher, C. M.; Cao, H.

2016-12-01

The Sulu UHP terrane is the extension of the Dabie orogenic belt to the east, offset 500 km to the northeast by the Tanlu fault [1]. The focus of this study, the Weihai area, is located at the northernmost part of the Sulu UHP terrane, and consists mainly of gneisses overprinted by amphibolite-facies assemblages, in addition to minor eclogite, granulite, and some ultramafic rocks [1]. Time constrains are critical to our understanding of the processes of UHP metamorphism, as well as the tectonic evolution of the region. In the last decade, U-Pb dating of metamorphic domains of zircons has been widely applied to determine the history of the UHP metamorphism (240 - 220 Ma) [1]. Recent garnet Lu-Hf dating from the Dabie terrane (240 - 220Ma) suggests the initiation of prograde metamorphism to be prior to ca. 240 Ma [2]. In-situ U-Pb dating of accessary minerals using LA-ICPMS (i.e. monazite, titanite, rutile, etc.), can provide important information to augment and complement the zircon U-Pb metamorphic dates. In this study, we collected samples throughout the Weihai area. Protolith ages of these samples range from Paleoproterozoic to Neoproterozoic ( 1850 - 700 Ma) as indicated by U-Pb dating of zircon cores. Zircon metamorphic rims yield U-Pb ages of 240 - 220 Ma, likely indicating the UHP stage of the Sulu terrane [3]. Four eclogites yield Lu-Hf garnet isochrons with dates between 239 and 224 Ma, consistent with garnet Lu-Hf dates from Dabie UHP terrane [2]. Sm-Nd isochrons indicate systematic younger dates (220 - 210 Ma) interpreted as cooling ages. Titanites extracted from four samples give U-Pb ages ranging from 220 to 200 Ma, in agreement with the titanite dates from the southern Sulu terrane [4]. Monazites from three samples give precise dates between 214 and 211 Ma. Collectively, monazite and titanite U-Pb ages are broadly consistent with the garnet Sm-Nd isochrons, and thus we interpret these as cooling ages. Based on the dates of different systems/minerals presented above, we suggest the prograde metamorphism of Weihai UHP terrane likely took place prior to 240 Ma, and the peak of the UHP stage is likely between 240 and 220 Ma. [1] Zhang et al., Gondwana Res., 16 (2009) 1-26 [2] Cheng et al., J. Metamorphic Geol., 26 (2008), 741-758 [3] Liou et al., J. Asian Earth Sci., 35 (2009), 199-231 [4] Chen and Zheng, GCA, 150(2015), 53-73

The exhumation of the (U)HP rocks of the Central and Western Penninic Alps: comparison study between thermo-mechanical models and field data

NASA Astrophysics Data System (ADS)

Schenker, Filippo Luca; Schmalholz, Stefan M.; Baumgartner, Lukas P.; Pleuger, Jan

2015-04-01

The Central and Western Penninic (CWP) Alps form an orogenic wedge of imbricate tectonic nappes. Orogenic wedges form typically at depths < 60 km. Nevertheless, a few nappes and massifs (i.e. Adula/Cima Lunga, Dora-Maira, Monte Rosa, Gran Paradiso, Zermatt-Saas) exhibit High- and Ultra-High-Pressure (U)HP metamorphic rocks suggesting that they were buried by subduction to depths >60 km and subsequently exhumed into the accretionary wedge. Mechanically, the exhumation of the (U)HP rocks from mantle depths can be explained by two contrasting buoyancy-driven models: (1) overall return flow of rocks in a subduction channel and (2) upward flow of individual, lighter rock units within a heavier material (Stokes flow). In this study we compare published numerical exhumation models of (1) and (2) with structural and metamorphic data of the CWP Alps. Model (1) predicts the exhumation of large volumes of (U)HP rocks within a viscous channel (1100-500 km2 in a 2D cross-section through the subduction zone). The moderate volume (e.g. ~7 km2 in a geological cross-section of the UHP unit of the Dora-Maira) and the coherent architecture of the (U)HP nappes suggests that the exhumation through (1) is unlikely for (U)HP nappes of the CWP Alps. Model (2) predicts the exhumation of appropriate volumes of (U)HP rocks, but generally the (U)HP rocks exhume vertically in the overriding plate and are not incorporated into the orogenic wedge. Nevertheless, the exhumation through (2) is feasible either with a vertical or with an extremely viscous and dense subduction channel. Whether these characteristics are applicable to the CWP UHP nappes will be discussed in light of field observations.

A petro-structural review of the Zermatt-Saas Fee zone

NASA Astrophysics Data System (ADS)

Schenker, Filippo Luca; Markus Schmalholz, Stefan; Baumgartner, Lukas

2014-05-01

The Zermatt-Saas Fee zone (ZSZ) is an imbricate of fragments of blueschist- to eclogite-facies metabasalts and metagabbros, serpentinites and mélange zones containing blocks of the above mentioned rocks. The ZSZ is usually interpreted as a fragment of oceanic crust belonging to the Piemont-Ligurian (Tethyan) Ocean that was accreted into the Alpine nappe pile. In the last decades the discovery of several Ultra-High Pressure (UHP, >2.7 GPa at 550-600 °C from coesite bearing eclogites and diamond-bearing fluid inclusions in garnet) localities lead to the interpretation of deep subduction (> 100 km) of the ZSZ in the Eocene, and subsequent uplift from mantle depth with high exhumation rates (e.g. Amato et al., 1999). However, these high pressures are in apparent contrast to the regional metamorphic conditions that reflect pressures peaking at < 2 GPa for 550-600°C (blueschist and eclogite mineral assemblages in mafic rocks). These latter metamorphic conditions do not need anomalous high burial histories and exhumation velocities higher than the plate velocities. The magnitude and distribution of pressure in the tectonic units of the ZSZ are important for constraining dynamic models for the evolution of the ZSZ and the Western Alps. Before entering into dynamic models, we propose a petro-structural overview where the published petrological data on pressure and temperature are critically reviewed, and positioned on a geological map and cross section in order to integrate them into the proper structural and tectonic framework. The questions we seek to answer are: How is the pressure distributed within the main tectonic units and within the entire ZSZ? Do we observe sharp or gradual pressure gradients within the ZSZ? Can the UHP conditions be averaged/extended to the entire ZSZ? If not, do they correspond to conditions of observable subunits, or do they reflect anomalies in the pressure field? Answering these questions is fundamental to better understand the thermobarometric evolution patterns of the ZSZ, to properly evaluate the geodynamic mechanism of accretion of oceanic crust into orogens, and to better understand the formation of tectonic nappes in general.

Influence of mid-crustal rheology on the deformation behavior of continental crust in the continental subduction zone

NASA Astrophysics Data System (ADS)

Li, Fucheng; Sun, Zhen; Zhang, Jiangyang

2018-06-01

Although the presence of low-viscosity middle crustal layer in the continental crust has been detected by both geophysical and geochemical studies, its influence on the deformation behavior of continental crust during subduction remains poorly investigated. To illustrate the crustal deformation associated with layered crust during continental subduction, we conducted a suite of 2-D thermo-mechanical numerical studies with visco-brittle/plastic rheology based on finite-differences and marker-in-cell techniques. In the experiments, we established a three-layer crustal model with a quartz-rich middle crustal layer embedded between the upper and lower continental crust. Results show that the middle crustal layer determines the amount of the accreted upper crust, maximum subduction depth, and exhumation path of the subducted upper crust. By varying the initial effective viscosity and thickness of the middle crustal layer, the further effects can be summarized as: (1) a rheologically weaker and/or thicker middle crustal layer results in a larger percentage of the upper crust detaching from the underlying slab and accreting at the trench zone, thereby leading to more serious crustal deformation. The rest of the upper crust only subducts into the depths of high pressure (HP) conditions, causing the absence of ultra-high pressure (UHP) metamorphic rocks; (2) a rheologically stronger and/or thinner middle crustal layer favors the stable subduction of the continental crust, dragging the upper crust to a maximum depth of ∼100 km and forming UHP rocks; (3) the middle crustal layer flows in a ductile way and acts as an exhumation channel for the HP-UHP rocks in both situations. In addition, the higher convergence velocity decreases the amount of subducted upper crust. A detailed comparison of our modeling results with the Himalayan collisional belt are conducted. Our work suggests that the presence of low-viscosity middle crustal layer may be another possible mechanism for absence of UHP rocks in the southern Tibet.

Lithology and mineralogy recognition from geochemical logging tool data using multivariate statistical analysis.

PubMed

Konaté, Ahmed Amara; Ma, Huolin; Pan, Heping; Qin, Zhen; Ahmed, Hafizullah Abba; Dembele, N'dji Dit Jacques

2017-10-01

The availability of a deep well that penetrates deep into the Ultra High Pressure (UHP) metamorphic rocks is unusual and consequently offers a unique chance to study the metamorphic rocks. One such borehole is located in the southern part of Donghai County in the Sulu UHP metamorphic belt of Eastern China, from the Chinese Continental Scientific Drilling Main hole. This study reports the results obtained from the analysis of oxide log data. A geochemical logging tool provides in situ, gamma ray spectroscopy measurements of major and trace elements in the borehole. Dry weight percent oxide concentration logs obtained for this study were SiO 2 , K 2 O, TiO 2 , H 2 O, CO 2 , Na 2 O, Fe 2 O 3 , FeO, CaO, MnO, MgO, P 2 O 5 and Al 2 O 3 . Cross plot and Principal Component Analysis methods were applied for lithology characterization and mineralogy description respectively. Cross plot analysis allows lithological variations to be characterized. Principal Component Analysis shows that the oxide logs can be summarized by two components related to the feldspar and hydrous minerals. This study has shown that geochemical logging tool data is accurate and adequate to be tremendously useful in UHP metamorphic rocks analysis. Copyright © 2017 Elsevier Ltd. All rights reserved.

Divergent plate motion drives rapid exhumation of (ultra)high pressure rocks

NASA Astrophysics Data System (ADS)

Liao, Jie; Malusà, Marco G.; Zhao, Liang; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Gerya, Taras

2018-06-01

Exhumation of (ultra)high pressure [(U)HP] rocks by upper-plate divergent motion above an unbroken slab, first proposed in the Western Alps, has never been tested by numerical methods. We present 2D thermo-mechanical models incorporating subduction of a thinned continental margin beneath either a continental or oceanic upper plate, followed by upper-plate divergent motion away from the lower plate. Results demonstrate how divergent plate motion may trigger rapid exhumation of large volumes of (U)HP rocks directly to the Earth's surface, without the need for significant overburden removal by erosion. Model exhumation paths are fully consistent with natural examples for a wide range of upper-plate divergence rates. Exhumation rates are systematically higher than the divergent rate imposed to the upper plate, and the modeled size of exhumed (U)HP domes is invariant for different rates of upper-plate divergence. Major variations are instead predicted at depth for differing model scenarios, as larger amounts of divergent motion may allow mantle-wedge exhumation to shallow depth under the exhuming domes. The transient temperature increase, due to ascent of mantle-wedge material in the subduction channel, has a limited effect on exhumed continental (U)HP rocks already at the surface. We test two examples, the Cenozoic (U)HP terranes of the Western Alps (continental upper plate) and eastern Papua New Guinea (oceanic upper plate). The good fit between model predictions and the geologic record in these terranes encourages the application of these models globally to pre-Cenozoic (U)HP terranes where the geologic record of exhumation is only partly preserved.

Age of UHP metamorphism in the Western Mediterranean: Insight from rutile and minute zircon inclusions in a diamond-bearing garnet megacryst (Edough Massif, NE Algeria)

NASA Astrophysics Data System (ADS)

Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Vitale-Brovarone, Alberto; Fernandez, Laure; Hammor, Dalila; Laouar, Rabah; Ouabadi, Aziouz; Abdallah, Nachida; Mechati, Mehdi

2017-09-01

Diamond-bearing UHP metamorphic rocks witness for subduction of lithospheric slabs into the mantle and their return to shallow levels. In this study we present U-Pb and trace elements analyses of zircon and rutile inclusions from a diamond-bearing garnet megacryst collected in a mélange unit exposed on the northern margin of Africa (Edough Massif, NE Algeria). Large rutile crystals (up to 300 μm in size) analyzed in situ provide a U-Pb age of 32.4 ± 3.3 Ma interpreted as dating the prograde to peak subduction stage of the mafic protolith. Trace element analyses of minute zircons (≤30 μm) indicate that they formed in equilibrium with the garnet megacryst at a temperature of 740-810 °C, most likely during HP retrograde metamorphism. U-Pb analyses provide a significantly younger age of 20.7 ± 2.3 Ma attributed to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean Orogen to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. Exhumation of these UHP units is coeval with the counterclockwise rotation of the Corsica-Sardinia block and most likely resulted from subduction rollback that was driven by slab pull.

Insights into a fossil plate interface of an erosional subduction zone: a tectono-metamorphic study of the Tianshan metamorphic belt.

NASA Astrophysics Data System (ADS)

Bayet, Lea; Moritz, Lowen; Li, Jilei; Zhou, Tan; Agard, Philippe; John, Timm; Gao, Jun

2016-04-01

Subduction zone seismicity and volcanism are triggered by processes occurring at the slab-wedge interface as a consequence of metamorphic reactions, mass-transfer and deformation. Although the shallow parts of subduction zones (<30-40 km) can be partly accessed by geophysical methods, the resolution of these techniques is insufficient to characterize and image the plate interface at greater depths (>60km). In order to better understand the plate interface dynamics at these greater depths, one has to rely on the rock record from fossil subduction zones. The Chinese Tianshan metamorphic belt (TMB) represents an ideal candidate for such studies, because structures are well exposed with exceptionally fresh high-pressure rocks. Since previous studies from this area focused on fluid-related processes and its metamorphic evolution was assessed on single outcrops, the geodynamic setting of this metamorphic belt is unfortunately heavily debated. Here, we present a new geodynamic concept for the TMB based on detailed structural and petrological investigations on a more regional scale. A ~11km x 13km area was extensively covered, together with E-W and N-S transects, in order to produce a detailed map of the TMB. Overall, the belt is composed of two greenschist-facies units that constitute the northern and southern border of a large high-pressure (HP) to ultra high-pressure (UHP) unit in the center. This HP-UHP unit is mainly composed of metasediments and volcanoclastic rocks, with blueschist, eclogite and carbonate lenses. Only the southern part of the HP-UHP unit is composed of the uppermost part of an oceanic crust (e.g., pillow basalts and deep-sea carbonates). From south to north, the relative abundance and size of blueschist massive boudins and layers (as well as eclogite boudins) decreases and the sequence is increasingly interlayered with metasedimentary and carbonate-rich horizons. This indicates that the subducted material was dominated by trench filling made of sediments and volcanoclastic rocks, with only subordinate pieces of oceanic crust/lithosphere. The whole sequence is cut by km-scale major shear planes orientated WNW-ESE showing consistent top-to-the north shear senses. Lineations marked by glaucophane indicate that most of the deformation occurred during exhumation-related blueschist-facies conditions. Peak pressure and temperatures (P-T) were estimated by Raman spectroscopy, using the degree of organisation of carbonaceous material in metapelites for T and Raman peak shifts of quartz inclusions in garnets for P. In the whole HP-UHP region, consistent and homogeneous peak P-T conditions of 530±30°C and 2.3±3 GPa point to depths around 70 km and HP to UHP conditions, which is further supported by the local presence of coesite. The continuity of the lithological sequence and the lack of significant P/T offsets across the major shear planes indicate that, during exhumation, the HP-UHP unit primarily behaved as a single stack of essentially metasedimentary slices, and was only poorly dismembered on its way to the surface. Our study thus advocates for deep accretion/underplating and stacking of these tectonic slices (dominated by trench infill material) at depths of ~70 km, which has so far rarely been documented.

Timing of metamorphism and exhumation in the Nordøyane ultra-high-pressure domain, Western Gneiss Region, Norway: New constraints from complementary CA-ID-TIMS and LA-MC-ICP-MS geochronology

NASA Astrophysics Data System (ADS)

Butler, J. P.; Jamieson, R. A.; Dunning, G. R.; Pecha, M. E.; Robinson, P.; Steenkamp, H. M.

2018-06-01

We present the results of a combined CA-ID-TIMS and LA-MC-ICP-MS U-Pb geochronology study of zircon and associated rutile and titanite from the Nordøyane ultra-high-pressure (UHP) domain in the Western Gneiss Region (WGR) of Norway. The dated samples include 4 eclogite bodies, 2 host-rock migmatites, and 2 cross-cutting pegmatites and leucosomes, all from the island of Harøya. Zircon from a coesite eclogite yielded an age of ca. 413 Ma, interpreted as the time of UHP metamorphism in this sample. Zircon data from the other eclogite bodies yielded metamorphic ages of ca. 413 Ma, 407 Ma, and 406 Ma; zircon trace-element data associated with 413 Ma and 407 Ma ages are consistent with eclogite-facies crystallization. In all of the eclogites, U-Pb dates from zircon cores, interpreted as the times of protolith crystallization, range from ca. 1680-1586 Ma, consistent with Gothian ages from orthogneisses in Nordøyane and elsewhere in the WGR. A zircon core age of ca. 943 Ma from one sample agrees with Sveconorwegian ages of felsic gneisses and pegmatites in the western part of the area. Migmatites hosting the eclogite bodies yielded zircon core ages of ca. 1657-1591 Ma and rim ages of ca. 395-392 Ma, interpreted as the times of Gothian protolith formation and Scandian partial melt crystallization, respectively. Pegmatite in an eclogite boudin neck yielded a crystallization age of ca. 388 Ma, interpreted as the time of melt crystallization. Rutile and titanite from 3 samples (an eclogite and two migmatites) yielded concordant ID-TIMS ages of 378-376 Ma. The results are similar to existing U-Pb data from other Nordøyane eclogites (415-405 Ma). In combination with previous pressure-temperature data from the coesite eclogite, these ages indicate that peak metamorphic conditions of 3 GPa/760 °C were reached ca. 413 Ma, followed by decompression to 1 GPa/810 °C by ca. 397 Ma and cooling below ca. 600 °C by ca. 375 Ma. The results are compatible with protracted UHP metamorphism followed by relatively slow exhumation. The question of whether partial melting began at UHP conditions is not resolved by this study.

Enhanced inactivation of foodborne pathogenic and spoilage bacteria by FD&C Red no. 3 and other xanthene derivatives during ultrahigh pressure processing.

PubMed

Waite, Joy G; Yousef, Ahmed E

2008-09-01

Variability among microorganisms in barotolerance has been demonstrated at genus, species, and strain levels. Identification of conditions and additives that enhance the efficacy of ultrahigh pressure (UHP) against important foodborne microorganisms is crucial for maximizing product safety and stability. Preliminary work indicated that FD&C Red No. 3 (Red 3), a xanthene derivative, was bactericidal and acted synergistically with UHP against Lactobacillus spp. The objective of this study was to determine the antimicrobial efficacy of Red 3 and other xanthene derivatives, alone and combined with UHP, against spoilage and pathogenic bacteria in citrate-phosphate buffer (pH 7.0). Xanthene derivatives tested were fluorescein, Eosin Y, Erythrosin B, Phloxine B, Red 3, and Rose Bengal. Halogenated xanthene derivatives (10 ppm) were effective at reducing Listeria monocytogenes survivors but ineffective against Escherichia coli O157:H7. When combined with UHP (400 MPa, 3 min), the presence of derivatives enhanced inactivation. Because Red 3 was the only xanthene derivative to produce synergistic inactivation of both pathogens, further studies using this colorant were warranted. Efficacy of Red 3 against gram-positive bacteria (Lactobacillus plantarum and L. monocytogenes) was concentration dependent (1 to 10 ppm). E. coi O157: H7 strains were resistant to Red 3 concentrations up to 300 ppm. When Red 3 was combined with UHP, the lethality against gram-positive and gram-negative bacteria was dose dependent, with synergy being significant for most strains at > or = 3 ppm. Additional gram-positive and gram-negative bacteria showed lethalities similar to those observed for L. plantarum or L. monocytogenes, and E. coli O157:H7, respectively. Red 3 is a potentially useful additive to enhance the safety and stability of UHP-treated food products.

Structure and Activity Changes of Phytohemagglutinin from Red Kidney Bean (Phaseolus vulgaris) Affected by Ultrahigh-Pressure Treatments.

PubMed

Lu, Yunjun; Liu, Cencen; Zhao, Mouming; Cui, Chun; Ren, Jiaoyan

2015-11-04

Phytohemagglutin (PHA), purified from red kidney beans (Phaseolus vulgaris) by Affi-Gel blue affinity chromatography, was subjected to ultrahigh-pressure (UHP) treatment (150, 250, 350, and 450 MPa). The purified PHA lost its hemagglutination activity after 450 MPa treatment and showed less pressure tolerance than crude PHA. However, the saccharide specificity and α-glucosidase inhibition activity of the purified PHA did not change much after UHP treatment. Electrophoresis staining by periodic acid-Schiff (PAS) manifested that the glycone structure of purified PHA remained stable even after 450 MPa pressure treatment. However, electrophoresis staining by Coomassie Blue as well as circular dichroism (CD) and differential scanning calorimetry (DSC) assay proved that the protein unit structure of purified PHA unfolded when treated at 0-250 MPa but reaggregates at 250-450 MPa. Therefore, the hemagglutination activity tends to be affected by the protein unit structure, while the stability of the glycone structure contributed to the remaining α-glucosidase inhibition activity.

U-Pb zircon geochronology and Zr-in-rutile thermometry of eclogites from the Dulan area, North Qaidam ultra-high pressure (UHP) terrane, western China

NASA Astrophysics Data System (ADS)

Hernández Uribe, D.; Stubbs, K.; Lehman, M. R.; Gilmore, V.; Kylander-Clark, A. R.; Mattinson, C. G.

2016-12-01

The Dulan area, in the North Qaidam terrane, exposes UHP eclogites and gneisses that experienced a 20 Myr UHP event at P-T conditions of 30 kbar and 700 °C. Two eclogites were analyzed using Zr-in-rutile thermometry and zircon U-Pb + trace element analysis to constrain the metamorphic evolution of the area. A kyanite-phengite eclogite presents a mineral assemblage of grt + omp + ph + ky + rt + zo + qz. Rutile analyses show a Zr concentration of 173-250 ppm with a mean of 207 ± 19 ppm. The calculated temperatures yielded 685-716 °C with an average of 700 ± 7°C. Zircon U-Pb analyses gave an upper intercept age of 880 ± 89 Ma. These analyses from cathodoluminiscence (CL)-dark core zircons show a negative Eu anomaly and a steep HREE slope suggesting a magmatic origin for the protolith. Analyses from CL-bright rims gave a weighted mean age of 427 ± 2 Ma. These zircons show an eclogite facies trace elements pattern suggesting that the age represent the HP-UHP event. Titanium concentration in zircons gave a weighted mean of 4.41 ± 0.25 ppm. This Ti concentration yielded a calculated temperature of 674 °C A phengite eclogite shows a mineral assemblage of grt + omp + ph + rt + zo + qz. Rutile in matrix analyses show a Zr concentration of 123-161 ppm with a mean of 139 ± 9 ppm. Calculated temperatures for these rutiles ranges from 659-680 °C with a mean temperature of 668 ± 5 °C. U-Pb analyses from CL-dark zircon cores gave a weighted mean age of 844 ± 7 Ma. These zircons show a negative Eu anomaly and a steep HREE slope suggesting a magmatic origin for the protolith. Analyses from CL-grey rims gave a weighted mean age of 433 ± 4 Ma. These zircons show an eclogite facies trace elements pattern, representing the timing of the HP-UHP event. Titanium concentration in zircons gave a weighted mean of 3.13 ± 0.34 ppm. This concentration yielded calculated temperature 647 °C. The obtained ages are in the same range as the ones obtained for the northern and southern Dulan area suggesting that all the area belongs to the same tectonic unit and experienced the same continental collision metamorphism.

Mantle Recycling of Crustal Materials through Study of Ultrahigh-Pressure Minerals in Collisional Orogens, Ophiolites, and Xenoliths

NASA Astrophysics Data System (ADS)

Liou, J. G.; Tsujimori, T.; Yang, J.; Zhang, R. Y.; Ernst, W. G.

2014-12-01

Newly recognized ultrahigh-pressure (UHP) mineral occurrences including diamonds in ultrahigh-temperature (UHT) felsic granulites of orogenic belts, in chromitites associated with ophiolitic complexes, and in mafic/ultramafic xenoliths suggest the recycling of crustal materials through profound subduction, mantle upwelling, and return to the Earth's surface. Recycling is supported by unambiguously crust-derived mineral inclusions in deep-seated zircons, chromites, and diamonds from collision-type orogens, from eclogitic xenoliths, and from ultramafic bodies of several Alpine-Himalayan and Polar Ural ophiolites; some such phases contain low-atomic number elements typified by crustal isotopic signatures. Ophiolite-type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone. In addition to ringwoodite and stishovite, a wide variety of nanometric minerals have been identified as inclusions employing state-of-the-art analysis. Reconstitution of now-exsolved precursor UHP phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier UHP conditions. Some podiform chromitites and associated peridotites contain rare minerals of undoubted crustal origin, including Zrn, corundum, Fls, Grt, Ky, Sil, Qtz, and Rtl; the zircons possess much older U-Pb ages than the formation age of the host ophiolites. These UHP mineral-bearing chromitites had a deep-seated evolution prior to extensional mantle upwelling and its partial melting at shallow depths to form the overlying ophiolite complexes. These new findings plus stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere, recycling of biogenic carbon into the lower mantle, and ascent to the Earth's surface through deep mantle ascent.

Evolution of supercritical fluid in deeply subducted continental crust: a case study of composite granite-quartz veins in the Sulu belt, China

NASA Astrophysics Data System (ADS)

Wang, S.; Wang, L.; Brown, M.

2016-12-01

Although fluid plays a key role in element transport and rock strength during subduction to and exhumation from ultrahigh pressure (UHP) metamorphic conditions, the source of supercritical fluid at P above the second critical endpoints (SCE) and the subsequent evolution are not well constrained. To provide insight into the evolution of supercritical fluid in continental subduction zones, we undertook an integrated study of composite granite-quartz veins in retrogressed and migmatitic UHP eclogite at General's Hill, N of Qingdao, in the central Sulu belt. The composite veins are irregularly distributed in the eclogite, which occurs as blocks within gneiss. The granite component is enriched in large ion lithophile elements and light rare earth elements but depleted in high field strength elements and heavy rare earth elements, indicating crystallization from a melt phase of crustal origin. Additionally, the granite contains high modal phengite (22-30 vol%) and clinozoisite/epidote (3-10 vol%), implying precipitation from a H2O-rich silicate melt. By contrast, the quartz component is dominated by SiO2 (99.10 wt%), and contains low total rare earth elements (ΣREE = 0.46 ppm), indicating precipitation from an aqueous fluid. The crystallization age of the composite veins is 221 ± 2 Ma, which is younger than the UHP metamorphism in the Sulu belt at ca 230 Ma, consistent with formation during exhumation. Initial 176Hf/177Hf ratios and δ18O values of metamorphic zircons from the composite veins, and Sr-Nd isotope compositions of the granites all lie between values for eclogite and gneiss, indicating a mixed source. Accordingly, we propose that a supercritical fluid generated from the gneiss and the included blocks of eclogite at P-T conditions above the SCE for both compositions became trapped in the eclogite during exhumation. At P below the SCE for the hydrous granite system, the mixed supercritical fluid separated into immiscible aqueous melt and aqueous fluid and crystallized as the composite veins. Thus, these vein systems provide information critical to understanding the evolution of supercritical fluid during exhumation and the partitioning of elements between hydrous granite and aqueous fluid. These data inform our understanding of crust-mantle interactions in continental subduction zones.

Ultrahigh pressure fast size exclusion chromatography for top-down proteomics.

PubMed

Chen, Xin; Ge, Ying

2013-09-01

Top-down MS-based proteomics has gained a solid growth over the past few years but still faces significant challenges in the LC separation of intact proteins. In top-down proteomics, it is essential to separate the high mass proteins from the low mass species due to the exponential decay in S/N as a function of increasing molecular mass. SEC is a favored LC method for size-based separation of proteins but suffers from notoriously low resolution and detrimental dilution. Herein, we reported the use of ultrahigh pressure (UHP) SEC for rapid and high-resolution separation of intact proteins for top-down proteomics. Fast separation of intact proteins (6-669 kDa) was achieved in < 7 min with high resolution and high efficiency. More importantly, we have shown that this UHP-SEC provides high-resolution separation of intact proteins using a MS-friendly volatile solvent system, allowing the direct top-down MS analysis of SEC-eluted proteins without an additional desalting step. Taken together, we have demonstrated that UHP-SEC is an attractive LC strategy for the size separation of proteins with great potential for top-down proteomics. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stable Isotopes, Multidisciplinary Studies, and the Leadership of J.G. Liou in UHP Metamorphism

NASA Astrophysics Data System (ADS)

Rumble, D.

2005-12-01

J.G. Liou has played a crucial role in improving knowledge of UHP metamorphism by leading multi-disciplinary, multi-institutional teams of researchers and by encouraging new investigators and providing them access to samples. Stable isotope geochemistry has made important contributions to understanding UHP metamorphism including: (1) The discovery of O- and H-isotope signatures of meteoric water in UHP rocks from China and Kazakhstan demonstrates that their protoliths originated at or near Earth's surface in a cold climate(a); (2) The mapping of contiguous tracts of outcrops extending over distances of 100 km where both eclogites and their wall rocks retain unusually low d18O and dD is consistent with the subduction and exhumation of UHP slabs as coherent structural units(b); (3) Analysis of samples from the Chinese Continental Scientific Drilling project reveals not only that UHP metamorphic rocks have not exchanged O-isotopes with mantle rocks while they were buried in the upper mantle but also that garnet peridotite slabs from the mantle have not exchanged with crustal wall rocks(c). Recent advances have resulted from multidisciplinary geochemical investigations. The analysis of zircons for both d18O and U-Pb established the age of cold climate, meteoric water alteration of protoliths to be Neoproterozoic for UHP rocks from Dabie and Sulu, China(d). Thus, O-isotopes plus age dating raises the possibility that evidence of snowball Earth conditions has been preserved in an unlikely host: UHP metamorphic rocks. A comparison of U-Pb, Sm-Nd, and Rb-Sr isotope data with analyses for d18O in coexisting minerals shows that discordant age dates correlate with mineral pairs that are not in O-isotope exchange equilibrium(e). It may be seen that multidisciplinary geochemical investigations provide mutually reinforcing data that greatly strengthens interpretations. New discoveries of de novo microdiamonds accompanied by multiphase mineral inclusions in UHP metamorphosed crustal rocks raise exciting possibilities for future stable isotope research on their origin(f). Micron-scale analytical techniques including ion microprobe, "Nano-SIMS", and UV-laser ablation, should be applied to the mineral assemblages to determine whether parent fluids were super-critical C-O-H fluids or carbonate-rich melts. (a) Geochim.Cosmochim.Acta (GCA) 59, 2859; Euro.J.Mineral 8, 317; GCA 61, 1658.(b) GCA 62, 3307.(c) Amer.Mineral. 90, 857.(d) GCA 66, 2299; GCA 68, 4145.(e) GCA 66, 625.(f) J.Metamorph.Geol. 21, 425.

Constraining cooling rates of UHP metamorphic rocks with closure temperature geospeedometry: a case study from the Dabie orogen

NASA Astrophysics Data System (ADS)

Lloyd, M. K.; Shimizu, N.; Wang, Z.; Zheng, Y.

2011-12-01

UHP metamorphic rocks can reach peak temperatures and pressures >800°C and >3GPa, and provide unique opportunities for studying geochemical processes in subduction zones. How and how fast they were exhumed are, however, still outstanding questions. Here we report SIMS-based Zr concentrations in rutiles from an eclogite sample from Huangzhen in the South Dabie low-T/UHP zone, east-central China, and present a closure temperature-based approach to constrain the cooling/exhumation rate of UHP rocks. Li et al. (2004) put peak metamorphism at a time prior to 236.1 ± 4.2 Ma., but estimates for peak temperatures and pressures in South Dabie vary wildly depending on the rock suite. The fine-grained eclogites in the Dabie orogen were estimated to have reached conditions of 641-839 °C and 2.00-3.54 GPa (Shi and Wang, 2006) based on Fe-Mg partition thermometry and metamorphic phase equilibria. These samples were reported to contain quartz, zircon, and rutile phases that reached thermodynamic equilibrium with each other. In this study, Zr concentrations of rutiles were obtained using the Cameca IMS 1280 ion microprobe at Northeast National Ion Microprobe Facility, by converting secondary ion intensity ratios, 90Zr/46Ti, to concentrations using rutile standards described by Luvizotto et al. (2009), with analytical uncertainties of 5.1%. Temperatures were then calculated using the method of Ferry and Watson (2007). It was found that Zr concentrations range from 38.6(2.4) to 134.6(4.5) ppm, resulting in a temperature range of 504(24) to 583(27)°C for 72 grains with size spanning from 62 to 440 microns cross in long axis. Minor rim-ward decrease of Zr content was observed with no appreciable temperature decrease. Assuming that the rutiles grew at one stage during the peak metamorphism and that their Zr concentrations were independent of pressure, a cooling rate can be estimated for the target sample. By applying the Dodson (1973) formula for closure temperature in conjunction with the Cherniak et al. (2007) diffusion rates for Zr in rutile to the core of each grain, we derived a maximum possible cooling rate to allow for complete peak temperature memory loss: i.e., since the largest grain requires most diffusion to reset, we are able to limit the maximum possible cooling rate for all grains in the sample to 5.4 ± 15.6 °C/my. This value is comparable to estimates for the Central Dabie mid-T/UHP eclogite (e.g., Li et al., 2000). Li XP et al. (2004) CMP, 148, 443-470. Shi & Wang (2006) J. Met. Geol., 24, 803-822. Luvizotto et al. (2009) Chem. Geol., 3-4, 346-369. Ferry & Watson (2007) CMP, 154, 429-437. Dodson (1973) CMP, 40, 259-274. Cherniak et al. (2007) EPSL, 261, 267-279. Li SG et al. (2000) GCA, 64, 1077-1093.

Generating Melt During Exhumation of Continental Crust from Ultrahigh Pressure (UHP) Conditions

NASA Astrophysics Data System (ADS)

Brown, M.; Wang, S.; Wang, L.; Piccoli, P. M.; Johnson, T. E.

2017-12-01

Hydrate breakdown rather than fluid-present melting is commonly cited during exhumation of UHP continental crust, but may have been overemphasized in relation to petrographic evidence. In this study from the central Sulu belt, China, we posit that dm- to m-scale dikes of leucosome in stromatic migmatite, formerly UHP eclogite, crystallized from hydrous melt derived by evolution of supercritical fluid as it drained through exhuming crust and increased in solute content. Leucosomes comprise Qz + Ph + Ab + Aln/Ep + Grt. Overgrowths of Zrn on inherited cores and new grains crystallized at ca. 223-219 Ma, within the age range of HP eclogite facies recrystallization in the belt. Si-in-Ph/Ti-in-Zrn thermobarometry yields crystallization conditions of 3.0-2.5 GPa at 830-770 °C. Compositions are granitic with normalized TE patterns enriched in LREE relative to HREE and enriched in LILE relative to HFSE, features consistent with crystallization from crustally derived hydrous melt. The leucosomes have Sr-Nd isotope compositions intermediate between host eclogites and surrounding gneisses. At the metamorphic peak, the source rocks were likely fluid deficient or fluid absent. During exhumation from UHP conditions, structural water stored in nominally anhydrous minerals during the prograde evolution was exsolved to form a grain boundary supercritical fluid in eclogite and gneiss. By migrating from grain boundaries into channels and draining from the volumetrically dominant gneiss through eclogite, the fluid acquired a blended Sr-Nd isotope composition intermediate between end-members. Concomitantly, the ascending fluid evolved to a denser, more viscous and more polymerized hydrous melt by dissolution of the silicate matrix. Trapped around the transition from UHP to HP eclogite facies conditions, the melt crystallized by diffusive loss of water to the host eclogite. Aggregates of Pl + Bt around Ph and thin films and cuspate veinlets/patches of Kfs along grain boundaries in leucosomes are consistent with subsequent low degrees of melting by Ph breakdown. Phase equilibria modeling indicates melting occurred during the transition from HP eclogite to amphibolite facies, with final subsolidus equilibration at 1.04-0.87 GPa and T <640 °C. However, Ph-breakdown melting was not the mechanism by which the leucosomes formed.

Garnet from diamondiferous metamorphic rocks of Kokchetav massif, Kazakhstan as a peak pressure recorder

NASA Astrophysics Data System (ADS)

Sobolev, N. V.; Palyanov, Y. N.; Shatsky, V. S.; Sokol, A. G.; Tomilenko, A. A.

2003-12-01

Garnet is a key mineral coexisting with diamond both in kimberlite (as xenocrysts, in diamondiferous garnet peridotites and eclogites, as inclusions in diamond) and in UHP metamorphic rocks of Kokchetav massif (diamondiferous gneisses, garnet-pyroxene rocks, dolomitic marbles and diamond facies eclogites). In UHPM rocks garnets are of particular importance as inclusions in zircons protected from retrograde metamorphism. Diamond formation conditions in eclogitic (E-type) upper mantle environment are estimated based upon Grt-Cpx thermometry and coesite barometry (e.g. Sobolev et al., PNAS, 2000, 97:11875) at P=5.5-6.0 GPa and T=1000-1300° C. These data are supported by diamond synthesis in carbonate-silicate fluid (e.g. Palyanov et al., Nature, 1999, 400: 417). E-type garnet may dissolve up to 0.3 wt.% Na2O (Sobolev, Lavrentyev, Contr. Min. Petr., 1971, 31:1) depending on pressure and Na2O contents in coexisting pyroxene and melts (fluids). Majorite component (pyroxene solid solution) was reported in rare garnets from diamonds (e.g. Moore, Gurney, Nature, 1985, 318:553) and UHP conditions were experimentally confirmed for such garnets (Irifune, Phys. Eart. Pl. Int., 1987, 45:324; Gasparik, Phys. Chem. Min., 2002, 29:170; Luth, Am. Miner., 1997, 82:1198). Garnets from Kokchetav diamondiferous metamorphic rocks demonstrate considerably lower Na2O solubility (up to 0.2 wt.% in rare samples) and absence of majorite component. However, coexisting pyroxenes may contain up to 50 mol.% jadeite. Several UHP experiments performed with Kokchetav eclogites and dolomitic marbles using a split-sphere apparatus resulted in detection of up to 0.3-0.4 wt.% Na2O in newly formed eclogitic garnets at P=5.7 and 7.0 GPa, T=1400 and 1700° C respectively. Majorite component was also determined in newly formed garnets reaching about 5% with Si (pfu)=3.05-3.06. Similar garnets without Na2O were also obtained in UHP experiments with diamondiferous dolomitic marbles (e.g. Palyanov et al., Dokl. Earth. Sci., 2001, 380:671). Based on the difference in Na2O and majorite contents in natural Kokchetav garnets, and those coexisting with diamonds in kimberlite and obtained in UHP experiments, we conclude that the peak of metamorphism at Kokchetav massif occurred at P about 4.5-5.0 GPa and T=900-1000° C (Sobolev, Shatsky, Nature, 1990, 343:742; Shatsky et al., Contr. Min. Petr., 1999, 137:185; Sobolev et al., Dokl. Earth. Sci., 2001, 380:237) but not exceeding 6.0 GPa (e.g. Ogasawara et al., Island Arc, 2000, 9:400).

Mantle wedge exhumation beneath the Dora-Maira (U)HP dome unravelled by local earthquake tomography (Western Alps)

NASA Astrophysics Data System (ADS)

Solarino, Stefano; Malusà, Marco G.; Eva, Elena; Guillot, Stéphane; Paul, Anne; Schwartz, Stéphane; Zhao, Liang; Aubert, Coralie; Dumont, Thierry; Pondrelli, Silvia; Salimbeni, Simone; Wang, Qingchen; Xu, Xiaobing; Zheng, Tianyu; Zhu, Rixiang

2018-01-01

In continental subduction zones, the behaviour of the mantle wedge during exhumation of (ultra)high-pressure [(U)HP] rocks provides a key to distinguish among competing exhumation mechanisms. However, in spite of the relevant implications for understanding orogenic evolution, a high-resolution image of the mantle wedge beneath the Western Alps is still lacking. In order to fill this gap, we perform a detailed analysis of the velocity structure of the Alpine belt beneath the Dora-Maira (U)HP dome, based on local earthquake tomography independently validated by receiver function analysis. Our results point to a composite structure of the mantle wedge above the subducted European lithosphere. We found that the Dora-Maira (U)HP dome lays directly above partly serpentinized peridotites (Vp 7.5 km/s; Vp/Vs = 1.70-1.72), documented from 10 km depth down to the top of the eclogitized lower crust of the European plate. These serpentinized peridotites, possibly formed by fluid release from the subducting European slab to the Alpine mantle wedge, are juxtaposed against dry mantle peridotites of the Adriatic upper plate along an active fault rooted in the lithospheric mantle. We propose that serpentinized mantle-wedge peridotites were exhumed at shallow crustal levels during late Eocene transtensional tectonics, also triggering the rapid exhumation of (U)HP rocks, and were subsequently indented under the Alpine metamorphic wedge in the early Oligocene. Our findings suggest that mantle-wedge exhumation may represent a major feature of the deep structure of exhumed continental subduction zones. The deep orogenic levels here imaged by seismic tomography may be exposed today in older (U)HP belts, where mantle-wedge serpentinites are commonly associated with coesite-bearing continental metamorphic rocks.

Recycling of crustal materials through study of ultrahigh-pressure minerals in collisional orogens, ophiolites, and mantle xenoliths: A review

NASA Astrophysics Data System (ADS)

Liou, Juhn G.; Tsujimori, Tatsuki; Yang, Jingsui; Zhang, R. Y.; Ernst, W. G.

2014-12-01

Newly recognized occurrences of ultrahigh-pressure (UHP) minerals including diamonds in ultrahigh-temperature (UHT) felsic granulites of orogenic belts, in chromitites associated with ophiolitic complexes, and in mantle xenoliths suggest the recycling of crustal materials through deep subduction, mantle upwelling, and return to the Earth's surface. This circulation process is supported by crust-derived mineral inclusions in deep-seated zircons, chromites, and diamonds from collision-type orogens, from eclogitic xenoliths in kimberlites, and from chromitities of several Alpine-Himalayan and Polar Ural ophiolites; some of these minerals contain low-atomic number elements typified by crustal isotopic signatures. Ophiolite-type diamonds in placer deposits and as inclusions in chromitites together with numerous highly reduced minerals and alloys appear to have formed near the mantle transition zone. In addition to ringwoodite and inferred stishovite, a number of nanometric minerals have been identified as inclusions employing state-of-the-art analytical tools. Reconstitution of now-exsolved precursor UHP phases and recognition of subtle decompression microstructures produced during exhumation reflect earlier UHP conditions. For example, Tibetan chromites containing exsolution lamellae of coesite + diopside suggest that the original chromitites formed at P > 9-10 GPa at depths of >250-300 km. The precursor phase most likely had a Ca-ferrite or a Ca-titanite structure; both are polymorphs of chromite and (at 2000 °C) would have formed at minimum pressures of P > 12.5 or 20 GPa respectively. Some podiform chromitites and host peridotites contain rare minerals of undoubted crustal origin, including zircon, feldspars, garnet, kyanite, andalusite, quartz, and rutile; the zircons possess much older U-Pb ages than the time of ophiolite formation. These UHP mineral-bearing chromitite hosts evidently had a deep-seated evolution prior to extensional mantle upwelling and partial melting at shallow depths to form the overlying ophiolite complexes. These new findings together with stable isotopic and inclusion characteristics of diamonds provide compelling evidence for profound underflow of both oceanic and continental lithosphere, recycling of surface 'organic' carbon into the lower mantle, and ascent to the Earth's surface through mantle upwelling. Intensified study of UHP granulite-facies lower crustal basement and ophiolitic chromitites should allow a better understanding of the geodynamics of subduction and crustal cycling.

Seismic probing of continental subduction zones

NASA Astrophysics Data System (ADS)

Zhao, Liang; Xu, Xiaobing; Malusà, Marco G.

2017-09-01

High-resolution images of Earth's interior provide pivotal information for the understanding of a range of geodynamic processes, including continental subduction and exhumation of ultrahigh-pressure (UHP) metamorphic rocks. Here we present a synthesis of available global seismic observations on continental subduction zones, and selected examples of seismic probing from the European Alps, the Himalaya-Tibet and the Qinling-Dabie orogenic belts. Our synthesis and examples show that slabs recognized beneath exhumed continental UHP terranes generally have shallow dip angles (<45°) at depths <100 km, to become much steeper at depths >100 km. Slabs underlined by a clear high velocity anomaly from Earth's surface to the mantle are generally Cenozoic in age. Some of these slabs are continuous, whereas other continental subduction zones are located above discontinuous high velocity anomalies possibly suggesting slab breakoff. The density of seismic stations and the quality of recordings are of primary importance to get high-resolution images of the upper mantle to be used as a starting point to provide reliable geodynamic interpretations. In some cases, areas previously indicated as possible site of slab breakoff, such as the European Alps, have been later proven to be located above a continuous slab by using higher quality travel time data from denser seismic arrays. Discriminating between oceanic and continental slabs can be challenging, but valuable information can be provided by combining teleseismic tomography and receiver function analysis. The upper mantle beneath most continental UHP terranes generally shows complex seismic anisotropy patterns that are potentially preserved even in pre-Cenozoic subduction zones. These patterns can be used to provide information on continental slabs that are no longer highlighted by a clear high-velocity anomaly.

Dolomitic marbles from the ultrahigh-pressure metamorphic Kimi complex in Rhodope, N.E. Greece

NASA Astrophysics Data System (ADS)

Mposkos, E.; Baziotis, I.; Proyer, A.; Hoinkes, G.

2006-09-01

Dolomitic marbles from the Organi and Pandrosos areas of the ultrahigh-pressure (UHP) metamorphic Kimi complex in East Rhodope, N.E. Greece have the mineral assemblage: Cal + Dol + Ol + Phl ± Di ± Hbl ± Spl ± Ti Chu + retrograde Srp and Chl. Several generations of calcite and dolomite with variable composition and texture represent different stages of the P T evolution: The first stage is represented by matrix dolomite (X_MgCO_3 = 0.48) and relic domains of homogenous composition in matrix calcite (X_MgCO_3 = 0.11 0.13); the second stage is evident from precipitation of lath-shaped and vermicular dolomite in matrix calcite. The third stage is represented by veinlets of almost pure CaCO3 and domainal replacement of prior calcite by nearly pure CaCO3 + Ca-rich dolomite (X_MgCO_3 = 0.34 0.43). Matrix dolomite adjacent to CaCO3 veinlets also becomes Ca-rich (X_MgCO_3 = 0.42). In fact, Ca-rich dolomites with X_MgCO_3 in the range of 0.40 0.34 are reported for the first time from metamorphic marbles. Coexisting Ca-rich dolomite and Mg-poor calcite cannot be explained by the calcite-dolomite miscibility gap. This assemblage rather suggests that Mg-poor calcite was aragonite originally, which formed together with Ca-rich dolomite according to the reaction Mg Cal → Arg + Dol (1) at ultrahigh pressures and temperatures above at least 850 °C, when dolomite becomes disordered and incorporates more Ca than coexisting aragonite does in terms of Mg. The simplest explanation of these observations probably is to suggest two metamorphic events: The first one represented by relic matrix carbonates at relatively low to moderate pressures and temperatures of ca. 750 °C, and the second one limited by the minimum temperatures for dolomite disorder (ca. 850 °C) and in the aragonite + dolomite stability field, i.e. at a minimum pressure of 3 GPa and, if the presence of diamond-bearing metapelites nearby is considered, at conditions of at least 850 °C and 4.3 GPa in the diamond stability field. As there is hardly any back-reaction of Ca-rich dolomite + Mg-poor calcite to Mg-rich calcite, peak temperatures remained below the reaction (1) and the exhumation path probably crossed the aragonite-calcite transition at much lower than peak temperature. Cooling and decompression must have both occurred extremely fast in order for the µm-sized Ca-rich dolomite textures to be preserved. An alternative explanation of the formation of “UHP”-textures and compositions is by a fluid influx that not only caused serpentinisation and chloritisation of silicates but also Mg-leaching from carbonates, particularly from Mg-rich calcite and its fine grained dolomite-precipitates, thus transforming them into Mg-poor calcite + Ca-rich dolomite.

Dual sources of water overprinting on the low zircon δ18O metamorphic country rocks: Disequilibrium constrained through inverse modelling of partial reequilibration

PubMed Central

Wei, Chun-Sheng; Zhao, Zi-Fu

2017-01-01

Since water is only composed of oxygen and hydrogen, δ18O and δ2H values are thus utilized to trace the origin of water(s) and quantify the water-rock interactions. While Triassic high pressure (HP) and ultrahigh pressure (UHP) metamorphic rocks across the Dabie-Sulu orogen in central-eastern China have been well documented, postcollisional magmatism driven hydrothermal systems are little known. Here we show that two sources of externally derived water interactions were revealed by oxygen isotopes for the gneissic country rocks intruded by the early Cretaceous postcollisional granitoids. Inverse modellings indicate that the degree of disequilibrium (doD) of meteoric water interactions was more evident than that of magmatic one (−65 ± 1o vs. −20 ± 2°); the partial reequilibration between quartz and alkali feldspar oxygen isotopes with magmatic water was achieved at 340 °C with a water/rock (W/R) ratio of about 1.2 for an open-hydrothermal system; two-stage meteoric water interactions were unraveled with reequilibration temperatures less than 300 °C and W/R ratios around 0.4. The lifetime of fossil magmatic hydrothermal system overprinted on the low zircon δ18O orthogneissic country rocks was estimated to maintain up to 50 thousand years (Kyr) through oxygen exchange modellings. Four-stage isotopic evolutions were proposed for the magmatic water interacted gneiss. PMID:28091552

Effect of crustal heterogeneities and effective rock strength on the formation of HP and UHP rocks.

NASA Astrophysics Data System (ADS)

Reuber, Georg; Kaus, Boris; Schmalholz, Stefan; White, Richard

2015-04-01

The formation of high pressure and ultra-high pressure rocks has been controversially discussed in recent years. Most existing petrological interpretations assume that pressure in the Earth is lithostatic and therefore HP and UHP rocks have to come from great depth, which usually involves going down a subduction channel and being exhumed again. Yet, an alternative explanation points out that pressure in the lithosphere is often non-lithostatic and can be either smaller or larger than lithostatic as a function of location and time. Whether this effect is tectonically significant or not depends on the magnitude of non-lithostatic pressure, and as a result a number of researchers have recently performed numerical simulations to address this. Somewhat disturbingly, they obtained widely differing results with some claiming that overpressures as large as a GPa can occur (Schmalholz et al. 2014), whereas others show that overpressures of exhumed rocks are generally less than 20% and thus insignificant (Li et al. 2010; Burov et al. 2014). In order to understand where these discrepancies come from, we reproduce the simulations of Li et al (2010) of a typical subduction and collision scenario, using an independently developed numerical code (MVEP2). For the same model setup and parameters, we confirm the earlier results of Li et al. (2010) and obtain no more than ~20% overpressure in exhumed rocks of the subduction channel. Yet, a critical assumption in their models is that the subducted crust is laterally homogeneous and that it has a low effective friction angle that is less than 7o. The friction angle of (dry) rocks is experimentally well-constrained to be around 30o, and low effective friction angles require, for example, high-fluid pressures. Whereas high fluid pressures might exist in the sediment-rich upper crust, they are likely to be much lower or absent in the lower crust from which melt has been extracted or in rocks that underwent a previous orogenic cycle. In a next step, we performed several hundred numerical simulations to understand the effects of km-scale heterogeneities and material parameters on pressure magnitudes, using a model setup that is otherwise very similar to the one of Li et al. (2010). Results show that significant non-lithostatic pressures occur if (lower) crustal rocks are dry or if km-scale (nappe-sized) heterogeneities with dryer rocks are present within the crust. Overpressure magnitudes can be up to 1 GPa or 100% and in some cases rock assemblages are temporarily in the coesite stability field at a depth of only 40 km, followed by rapid exhumation to the surface. Tectonic overpressures can vary strongly in magnitude versus time, but peak pressures are present sufficiently long for metamorphic reactions to occur. The presence of heterogeneities can affect the crustal-scaled deformation pattern, and the effective friction angle of crustal-scale rocks (or the dryness of these rocks) is a key parameter that determines the magnitude of non-lithostatic pressures. Our results thus reconcile previous findings and highlight the importance of having an accurate knowledge of the fluid-pressure, initial crustal structure and rock composition during continental collision. If rocks are dry by the time they enter a subduction zone, or are stronger/dryer than surrounding rocks, they are likely to develop significantly higher pressures than nearby rocks. This might explain the puzzling observation that some nappes have very high peak pressures, while juxtaposed nappes have much lower values, without clear structural evidence for deep burial and exhumation along a subduction channel of the high-pressure nappe. Our models might also give a partial explanation of why the reported timescales for high and ultra-high pressure stages of peak metamorphism are often very short. References: Burov, E., Francois, T., Agard, P., Le Pourhiet, L., Meyer, B., Tirel, C., Lebedev, S., Yamato, P., Brun, J.-P., 2014. Tectonophysics. Tectonophysics 631, 212-250. doi:10.1016/j.tecto.2014.04.033 Li, Z.H., Gerya, T.V., Burg, J.-P., 2010. Influence of tectonic overpressure on P-T paths of HP-UHP rocks in continental collision zones: thermomechanical modelling. J Metamorph Geol 28, 227-247. doi:10.1111/j.1525-1314.2009.00864.x Schmalholz, S.M., Duretz, T., Schenker, F.L., Podladchikov, Y.Y., 2014. Tectonophysics. Tectonophysics 631, 160-175. doi:10.1016/j.tecto.2014.05.018

Nature and geodynamic setting of the protoliths of the UHP metamorphic Complex and migmatites in Bixiling area, the Dabie Orogen, China

NASA Astrophysics Data System (ADS)

Li, H.; Jahn, B.; Wang, D.; Yu, H.; Liu, Z.; Hou, G.

2013-12-01

As the largest coesite-bearing mafic-ultramafic body in the Dabie-Sulu orogen, the Bixiling Complex is composed of meta-ultramafic rocks, MgAl-rich eclogites and FeTi-rich eclogites. The FeTi-rich eclogites are further divided into low-Si-high-Fe type (Type I) and high-Si-low-Fe type (Type II) according to their mineral assemblages and bulk chemical composition. Field, petrographic, petrological and geochemical characteristics of these rocks, although suffered an ultra-high pressure metamorphism, still show a magmatic differentiation process among the protoliths of the meta-ultramafic rocks, MgAl-rich eclogites and Type I FeTi-rich eclogites. A small degree of lower crustal contamination occurred during their magma chamber process. Amphibolite is widespread in the periphery of the complex. Non-foliation and fine-grained texture are their obvious characteristics. Geochemical and isotopic affinities suggest that the amphibolites represent a product of complete retrogression from type II FeTi-rich eclogites. The UHP complex is enclosed in granitic gneisses, which variably include two-mica plagioclase gneiss, epidote two-mica plagioclase gneiss, or white-mica plagioclase gneiss. They all show TTG, especially trondjhemitic composition. A migmatite outcrop was found near the northeastern end of the complex. The migmatites consist of dark colored, non-foliated amphibolites and light-colored, fine-grained trondhjemitic gneisses. Field occurrences, microstructures observed under optical microscope and SEM, Sr-Nd isotopic data suggest an origin of partial melting. Chemical composition of two stages of amphiboles occurred in both the amphibolites and the trondhjemitic gneisses also imply a partial melting process occurred. Trace element, Sr-Nd isotope and SHRIMP zircon U-Pb dating of MgAl-rich eclogite, amphibolites and trondhjemite suggest that the migmatites represent a partial melting of crustal materials at about 780Ma, possibly accompanied by the coeval emplacement of a differentiated mafic intrusive body. These rocks were deeply subducted into a mantle depth during the Triassic continental collision between the Yangtze Craton and North China Craton, and thereafter were exhumed to the surface. Their residual geochemical characteristics and spatial / temporal relationship could impose constraints on the tectonic evolution of the Dabieshan UHP terrane.

Geology of ultra-high-pressure rocks from the Dabie Shan, Eastern China

NASA Astrophysics Data System (ADS)

Schmid, Robert

2001-02-01

A multidisciplinary study has been carried out to contribute to the understanding of the geologic evolution of the largest known occurrence of ultra-high-pressure (UHP) rocks on Earth, the Dabie Shan of eastern China. Geophysical data, collected along a ca. 20 km E-W trending seismic line in the eastern Dabie Shan, indicate that the crust comprises three layers. The upper crust has a homogeneously low reflectivity and exhibits roughly subhorizontal reflectors down to ca. 15 km. It is therefore interpreted to portray a crustal UHP slab thrust over non-UHP crust. An aprubt change in intensity and geometry of observed reflectors marks the boundary of a mid- to lower crustal zone which is present down to ca. 33 km. This crustal zone likely represents cratonal Yangtze crust that was unaffected by the Triassic UHP event and which has acted as the footwall during exhumation of the crustal wedge. Strong and continuous reflectors occurring at ca. 33-40 km depth most likely trace the Moho at the base of the crust. Any trace of a crustal root, that may have formed in response to collision tectonics, is therefore not preserved. A shollow tomographic velocity modell based on inversion of the first arrivals is constructed additionally. This model clearly images the distinct lithologies on both sides of the Tan Lu fault. Sediments to the east exhibit velocities of about 3.4 - 5.0 km* s^-1, whereas the gneisses have 5.2 - 6.0 km*s^-1. Geometry of velocity isolines may trace the structures present in the rocks. Thus the sediments dip shallowly towards the fault, whereas isoclinal folds are imaged to occur in the gneisses. Field data from the UHP unit of the Dabie Shan enables definition of basement-cover sequences that represent sections of the former passive margin of the Yangtze craton. One of the cover sequences, the Changpu unit, still displays a stratigraphic contact with basement gneisses, while the other, the Ganghe unit, includes no relative basement exposure. The latter unit is in tectonic contact with the basement of the former unit via a greenschist-facies blastomylonite. The Changpu unit is chiefly constituted by calc-arenitic metasediments intercalated with meta-basalts, whereas the Ganghe unit contains arenitic-volcanoclastic metasediments that are likewise associated with meta-basalts. The basement comprises a variety of felsic gneisses, ranging from preserved eclogitic- to greenschist-facies paragenesis, and locally contains mafic-ultramafic meta-plutons in addition to minor basaltic rocks. Metabasites of all lithologies are eclogite-facies or are retrogressed equivalents, which, with the exception of those from the Ganghe unit, bear coesite and thus testify to an UHP metamorphic overprint. Mineral chemistry of the analysed samples reveal large compositional variations among the main minerals, i.e. garnet and omphacite, indicating either distinct protoliths or different degrees of interaction with their host-rocks. Contents of ferric iron in low Fetot omphacites are determined by wet chemical titration and found to be rather high, i.e. 30-40 %. However, a even more conservative estimate of 50% is applied in the corresponding calculations, in order to be comparable with previous studies. Textural constraints and compositional zonation pattern are compatible with equilibrium conditions during peak metamorphism followed by a retrogressive overprint. P-T data are calculated with special focus on the application of the garnet-omphacite-phengite barometer, combined with Fe-Mg exchange thermometers. Maximum pressures range from 42-48 kbar (for the Changpu unit) to ~37 kbar (for the Ganghe unit and basement rocks). Temperatures during the eclogite metamorphism reached ca. 750 °C. Although the sample suite reveals variable peak-pressures, temperatures are in reasonable agreement. Pressure differences are interpreted to be due to strongly Ca-dominated garnet (up to 50 mol % grossular in the Changpu unit) and modification of peak-compositions during retrogressive metamorphism. The integrated geological data presented in this thesis allow it to be concluded that, i) basement and cover rocks are present in the Dabie Shan and both experienced UHP conditions ii) the Dabie Shan is the metamorphic equivalent of the former passive margin of the Yangtze craton iii) felsic gneisses undergoing UHP metamorphism are affected by volume changes due to phase transitions (qtz coe), which directly influence the tectono-metamorphic processes iv) initial differences in temperature may account for the general lack of lower crustal rocks in UHP-facies Um das Verständnis der geologischen Entwicklung des größten bekannten Vorkommens von ultra-hochdruck (UHP) Gesteinen auf der Erde, des Dabie Shan im östlichen China, zu erhöhen, wurde eine multidisziplinäre Studie durchgeführt. Geophysikalische Daten wurden entlang einer ca. 20 km langen seismischen Linie im östlichen Dabie Shan gesammelt. Diese reflektionsseismischen Daten zeigen, dass die Kruste aus drei Lagen besteht. Die Oberkruste besitzt eine durchgehend niedrige Reflektivität und meist subhorizontale Reflektoren bis in eine Tiefe von ca. 15 km. Aufgrund dieser Charakteristika wird diese Zone als UHP-bezogener krustaler Keil interpretiert, der auf nicht UHP Kruste überschoben wurde. Ein abrupter Wechsel in der Geometrie aber auch Intensität der Reflektoren markiert die Grenze zu einer mittel- bis unterkrustalen Zone, die sich bis ca. 33 km Tiefe erstreckt. Diese Zone repräsentiert wahrscheinlich kratonale Yangtze Kruste, die von der triassischen UHP-Orogenese nicht erfasst wurde, aber während der Exhumierung das Liegende relativ zum UHP Keil war. Starke und kontinuierliche Reflektoren im Tiefenintervall von 33-40 km bilden höchstwahrscheinlich die Moho an der Basis der Kruste ab. Relikte einer Krustenwurzel, die sich wahrscheinlich während der Kollisionstektonik gebildet hatte, sind nicht sichtbar. Ein flaches tomographisches Geschwindigkeitsmodell, das auf der Inversion der Ersteinsätze gründet, konnte zusätzlich erstellt werden. Dieses Modell bildet deutlich die unterschiedlichen Lithologien auf beiden Seiten der Tan Lu Störung ab. Sedimente östlich der Störung zeigen Geschwindigkeiten von 3.4 - 5.0 km* s^-1, wohingegen die Gneise im Westen 5.2 - 6.0 km*s^-1 aufweisen. Die Geometrie der Geschwindigkeits-Isolinien kann als Ausdruck der Strukturen der Gesteine angenommen werden. Somit zeigen die Sedimente ein nordwestliches Einfallen zur Störung hin, wohingegen isoklinale Falten in den Gneisen abgebildet werden. Geländedaten aus der UHP Einheit des Dabie Shan ermöglichen die Definition von Grundgebirgs- und Deckeinheiten, die Teile des ehemaligen passiven Kontinentalrandes des Yangtze Kratons repräsentieren. Eine der Deckeinheiten, die Changpu Einheit, besitzt nach wie vor einen stratigraphischen Kontakt zu den Grundgebirgs-Gneisen. Der anderen Einheit hingegen, der Ganghe Einheit, fehlt ein entsprechendes Grundgebirge. Diese Einheit steht vielmehr über einen Blasto-Mylonit in tektonischem Kontakt zum Grundgebirge der vorherigen. Die Changpu Einheit baut sich aus kalk-arenitischen Metasedimenten auf, die mit Metabasalten assoziiert sind. Die Ganghe Einheit wird von arenitisch-vulkanoklastischen Metasedimenten, die ebenfalls mit metabasaltischen Gesteinen vergesellschaftet sind, dominiert. Das Grundgebirge baut sich aus diversen felsischen Gneisen auf, die von reliktisch eklogitfaziell bis grünschieferfaziell ausgeprägt sind, und in denen, zusätzlich zu Metabasalten, sporadisch mafisch-ultramafische Meta-Plutone auftreten. Mit Ausnahme der Ganghe Einheit, führen die Metabasite Coesit und belegen somit das UHP Ereignis. Die Mineralchemie der analysierten Proben dokumentiert deutliche Variationen in der Zusammensetzung der Hauptminerale, Granat und Omphazit, was entweder unterschiedliche Protolithe oder unterschiedliche Grade von Stoffaustausch mit den Wirtsgesteinen reflektiert. Gehalte von dreiwertigem Eisen in Omphaziten mit geringen Gesamteisengehalten, wurden mittels Titration bestimmt, wobei sich Werte von 30-40 % ergaben. Dennoch wurde ein noch konservativerer Wert von 50% dreiwertigem Eisen in den entsprechenden Berechnungen angenommen, hauptsächlich, um mit anderen Arbeiten vergleichbar zu sein. Texturen und chemische Zonierungen in den Mineralen sind kompatibel mit Gleichgewichtsbedingungen während dem Höhepunkt der Metamorphose, der retrograd überprägt wird. P-T Daten wurden mit deutlicher Betonung auf das Granat-Omphazit-Phengit Barometer, das mit Fe-Mg Austausch-Thermometern kombiniert wurde, berechnet. Höchstdrucke reichen von 42-48 kbar (für die Changpu Einheit) bis ca. 37 kbar (für das Grundgebirge und die Ganghe Einheit). Während der eklogitfaziellen Metamorphose wurden Temperaturen von ca. 750 °C erreicht. Obwohl die maximalen Drucke deutlich schwanken, sind die Temperaturbestimmungen in guter Übereinstimmung. Die Druckschwankungen können zum einen durch deutlich Ca-dominierte Granate (bis zu 50 mol% Grossular in der Changpu Einheit) und/oder zum anderen durch Modifikationen der Mineralzusammensetzungen während der retrograden Metamorphose erklärt werden. Die präsentierten integrativen geologischen Daten ermöglichen die folgenden Schlussfolgerungen i) Grundgebirgs- und Deckeinheiten treten im Dabie Shan auf und wurden beide UHP metamorph überprägt ii) Der Dabie Shan ist das metamorphe Äquivalent des früheren passiven Kontinentalrandes des Yangtze Kratons iii) felsische Gneise, die eine UHP Metamorphose durchlaufen, sind von Volumenver-änderungen betroffen, die durch großräumige Phasenumwandlungen (Quarz Coesit) hervorgerufen werden, was direkt die tektono-metamorphen Prozesse beeinflusst iv) Initiale Unterschiede in der Temperatur sind möglicherweise dafür verantwortlich, dass generell Unterkrustengesteine in UHP Fazies fehlen

Protracted or multiple subduction of metapelites (Rhodope UHP domain, Greece)?

NASA Astrophysics Data System (ADS)

Krohe, A.; Wawrzenitz, N. H.; Mposkos, E.; Romer, R. L.

2012-12-01

The Rhodope domain formed along the suture between the European and the Apulian/Adriatic plate, which collided in the early Tertiary (closure of the Vardar/Axios ocean). Its metamorphic history includes UHP metamorphism documented by diamond inclusions in garnet (Mposkos & Kostopoulos 2001, Perraki et al. 2006, Schmidt et al. 2010), presumably of Jurassic age, and Eocene stages of MP and HP metamorphism. The age of UHPM is still a matter of debate: U-Pb SHRIMP ages extend from 184-172 Ma (monazite in metapelites) to ca. 42 Ma with clusters at 170-160, 150-140, 80-60, 50, 42 Ma, (U-Pb SHRIMP dating of zircon from amphibolitized eclogites and metapelites). These ages are interpreted to date subsequent stages of (U)HP metamorphism and decompression (Liati et al., 2005, Hoinkes et al. 2008, Bauer et al. 2006, Krenn et al 2010). However, these ages are obviously difficult to link with the metamorphic reactions. The metamorphic history has been interpreted in different ways, reflecting: (i) successive accretion of small terranes with rapid subduction and uplift histories (e.g. Liati et al. 2005); (ii) a composite of different tectonic units varying in earlier P-T histories, assembled by shear zones that reflect tectonic erosion and differential exhumation along the plate interface and that are now erased and overprinted (Krohe and Mposkos, 2002, Mposkos et al., 2010). These interpretations imply a different kinematics of the tectonic movements at depths, mechanical processes and process rates. Additionally, a protracted polymetamorphic history of larger volumes of the Rhodope UHP domain may be considered; e.g. the Kimi complex stayed in the lower crust for ca. 50-60 Ma after exhumation of the UHP rocks to this lower crustal level (Mposkos and Krohe, 2006). To constrain a precise age of the HP granulite facies and a minimum age of UHP metamorphism, we conduct an integrated structural, petrologic and geochronological study in a metapelite from the Sidronero Complex. The mineral assemblages Grt-Ky-Bt-Pl-Kfs-Qtz-Rt and Grt-Ky-Bt-Ms-Pl-Qtz-Rt, record a HP granulite facies metamorphism followed by upper amphibolite facies. The rock is particularly well suited for studying the granulite facies metamorphism, as it contains domains that are only weakly overprinted by later metamorphic episodes. ID-TIMS U-Pb ages of single monazite grains and fractions of few grains, that are only locally patchy-zoned and associated with garnet and kyanite, plot along the concordia between 64 to 60 Ma. One date of 55 Ma might represent Pb-loss during later fluid-induced dissolution-reprecipitation, probably related to biotite growth during the amphibolite facies overprint. On the base of these data, a model is discussed, in which rocks from the upper plate and HP-rocks that have been already exhumed, were dragged again into the subduction channel by subduction erosion Bauer et al. 2006, Lithos, 29, 207-228; Hoinkes et al. 2008, 3rd IGC Oslo, UHP-4; Krenn et al 2010, Tectonics, 29, TC4001; Krohe & Mposkos, 2002, Geol. Soc. Sp. Pub. 204, 151-178; Liati, A., 2005, Contrib. Mineral. Petrol., 150, 608-630; Mposkos, & Kostopoulos, 2001, EPSL, 192, 497-506; Mposkos & Krohe, 2006. Can. J. Earth Sci., 43, 1755-1776; Mposkos et al., 2010 Proc. XIX CBGA Congress, 100, 173-178; Perraki et al., 2006, EPSL, 241, 672-685; Schmidt et al., 2010, EJM, 22, 189-198.

The duration of prograde garnet crystallization in the UHP eclogites at Lago di Cignana, Italy

NASA Astrophysics Data System (ADS)

Skora, Susanne; Lapen, Thomas J.; Baumgartner, Lukas P.; Johnson, Clark M.; Hellebrand, Eric; Mahlen, Nancy J.

2009-10-01

The distinct core-to-rim zonation of different REEs in garnet in metamorphic rocks, specifically Sm relative to Lu, suggests that Sm-Nd and Lu-Hf isochron ages will record different times along a prograde garnet growth history. Therefore, REE zonations in garnet must be measured in order to correctly interpret the isochron ages in terms of the garnet growth interval, which could span several m.y. New REE profiles, garnet crystal size distributions, and garnet growth modeling, combined with previously published Sm-Nd and Lu-Hf geochronology on a UHP eclogite of the Zermatt-Saas Fee (ZSF) ophiolite, Lago di Cignana (Italy), demonstrate that prograde garnet growth of this sample occurred over a ~ 30 to 40 m.y. interval. Relative to peak metamorphism at 38 to 40 Ma, garnet growth is estimated to have begun at ~ 11 to 14 kbar pressure at ~ 70 to 80 Ma. Although such a protracted garnet growth interval is surprising, this is supported by plate tectonic reconstructions which suggest that subduction of the Liguro-Piemont ocean occurred through slow and oblique convergence. These results demonstrate that REE zonations in garnet, coupled to crystal size distributions, provide a powerful means for understanding prograde metamorphic paths when combined with Sm-Nd and Lu-Hf geochronology.

Unraveling P-T-t-D Evolution of Zermatt-Saas Ophiolites from Valtournanche: from Ocean Opening to Mountain Building

NASA Astrophysics Data System (ADS)

Rebay, G.; Tiepolo, M.; Zanoni, D.; Langone, A.; Spalla, M. I.

2015-12-01

The Zermatt-Saas (ZS) Zone, formerly part of Tethyan oceanic crust and variously affected by oceanic metamorphism, is now part of the orogenic suture that developed in the Western European Alps during the Alpine subduction and collision. The ZS rocks preserve a dominant HP to UHP metamorphic imprint overprinted by greenschist facies metamorphism. The age of the oceanic protoliths is considered to be middle to upper Jurassic whereas the HP metamorphism is mostly considered to be Eocene. In upper Valtournanche ZS ophiolites, the dominant regional S2 foliation is mapped with spatial continuity in serpentinite, metarodingite and eclogite and is defined by HP/UHP parageneses in all lithotypes. It developed at 2.5 ± 0.3 GPa and 600 ± 20°C during Alpine subduction. S2 foliation of serpentinites wraps rare clinopyroxene and zircon relics. Trace element composition of clinopyroxene suggests that they crystallised from a melt in equilibrium with plagioclase: they most likely represent relicts of gabbroic assemblages. The clinopyroxene porphyroclasts have rims indented within S2 and compositions similar to fine-grained clinopyroxeneII defining S2, suggesting that they recrystallised during Alpine subduction. Zircon cores show, under CL, sector zoning typical of magmatic growth. U-Pb dates suggest their crystallisation during Middle Jurassic. Magmatic cores have thin fringe overgrowths parallel to the S2 foliation. U-Pb concordant analyses on these domains reveal an Upper Cretaceous-Paleocene crystallization most likely representing the HP to UHP Alpine re-equilibration. This suggests that some sections of the ZS have experienced HP to UHP metamorphism earlier than previously thought, opening new interpretative geodynamic scenarios. Remarkably, these new dates are similar to those recorded for the HP re-equilibration in the continental crust of the adjacent Austroalpine units (upper plate of the Alpine subduction system) and to those recorded for prograde metamorphism in other parts of the ZS ophiolites.

Zircon geochronology and ca. 400 Ma exhumation of Norwegian ultrahigh-pressure rocks: An ion microprobe and chemical abrasion study

USGS Publications Warehouse

Root, D.B.; Hacker, B.R.; Mattinson, J.M.; Wooden, J.L.

2004-01-01

Understanding the formation and exhumation of the remarkable ultrahigh-pressure (UHP) rocks of the Western Gneiss Region, Norway, hinges on precise determination of the time of eclogite recrystallization. We conducted detailed thermal ionization mass spectrometry, chemical abrasion analysis and sensitive high-resolution ion-microprobe analysis of zircons from four ultrahigh- and high-pressure (HP) rocks. Ion-microprobe analyses from the Flatraket eclogite yielded a broad range of apparently concordant Caledonian ages, suggesting long-term growth. In contrast, higher precision thermal ionization mass spectrometry analysis of zircon subject to combined thermal annealing and multi-step chemical abrasion yielded moderate Pb loss from the first (lowest temperature) abrasion step, possible minor Pb loss or minor growth at 400 Ma from the second step and a 407-404 Ma cluster of slightly discordant 206Pb/238U ages, most likely free from Pb loss, from the remaining abrasion steps. We interpret the latter to reflect zircon crystallization at ???405-400 Ma with minor discordance from inherited cores. Zircon crystallization occurred at eclogite-facies, possibly post-peak conditions, based on compositions of garnet inclusions in zircon as well as nearly flat HREE profiles and lack of Eu anomalies in zircon fractions subjected to chemical abrasion. These ages are significantly younger than the 425 Ma age often cited for western Norway eclogite recrystallization, implying faster rates of exhumation (>2.5-8.5 km/Myr), and coeval formation of eclogites across the UHP portion of the Western Gneiss Region. ?? 2004 Published by Elsevier B.V.

UHP metamorphism in the Western Mediterranean : A tale of a Tethys fragment (Edough Massif, NE Algeria) and its geodynamic consequences

NASA Astrophysics Data System (ADS)

Bruguier, Olivier; Bosch, Delphine; Caby, Renaud; Fernandez, Laure; Abdallah, Nachida; Arnaud, Nicolas; Hammor, Dalila; Laouar, Rabah; Mechati, Medhi; Monié, Patrick; Ouabadi, Aziouz; Toubal, Abder

2016-04-01

The Edough Massif of NE Algeria is part of the Maghrebides, a peri-Mediterranean Alpine belt that extends from Morocco to Tunisia. The belt resulted mainly from the eastward retreat of the Tethyan slab and from the drift of continental fragments, some of which finally collided with the north African margin. In this study we report the recent discovery of metamorphic diamonds (5-30 μm in size) included in a garnet megacryst and identified by Raman spectroscopy and the characteristic sharp band at 1332 cm-1 for crystalline diamond. The studied megacryst was taken from a weathered actinolitite horizon inserted within a major mylonite-ultramylonite band, which outcrops at the base of an allochtonous oceanic unit thrust onto the African paleomargin. The host garnet is almandine-dominant with a sharp increase in grossular component in the rim and is rich in exsolution of small acicular rutile needles. Major and trace elements show a gradual but significant zonation from core to rim characterized by a decrease in HREE, Y and Mn, typical of a prograde growth in a closed system. Trace element analyses of large prismatic rutile (up to 300 μm) indicate that the host metamorphic rock was a mafic protolith of MORB affinity and the Zr-in-rutile thermometry indicates a temperature range of 724-778°C for rutile growth. U-Pb analyses of these large rutile crystals provide an age of 32.4 ± 3.3 Ma interpreted as dating the prograde subduction stage of the mafic protolith. Minute zircons (≤ 30μm), disseminated in the garnet, display a multifaceted appearance and low Th/U ratios consistent with a metamorphic origin. The lack of HREE depletion in these zircons indicates that their metamorphic growth was not coeval with garnet. U-Pb analyses and Ti-in-zircon thermometry indicate they nucleated at 20.9 ± 2.2 Ma during near isothermal decompression related to exhumation of the UHP units. This study allows bracketing the age of UHP metamorphism in the Western Mediterranean to the Oligocene/early Miocene, thus unambiguously relating UHP metamorphism to the Alpine history. We suggest that the mafic protolith originates from the subducted retreating Calabrian branch of the Tethyan slab, that broke or tore, and which fragments were dragged upward and thrusted onto the North African margin, shortly before the formation of the Edough dome. Exhumation of these UHP units is coeval with the counter clockwise rotation of the Corsica-Sardinia block, which is associated to the extensional opening of the Ligurian Sea as a result of slab rollback (Faccenna et al., 2001). The early Miocene exhumation of the UHP units, which were detached from the downgoing plate, most likely resulted simultaneously from subduction rollback that was driven by slab pull.

How does recycling of sediment components in arc magmatism really work?

NASA Astrophysics Data System (ADS)

Kelemen, P.; Hacker, B.; Austin, N.

2007-12-01

Past work indicates substantial recycling of a sediment component rich in LILE, Th, Sr, Pb and LREE in arcs. For example, in the relatively well-constrained case of Central America, Plank et al (Geology 02) estimate that 80% of subducted, sedimentary Th is recycled in arc magmas. To understand how such a component is transferred from subducted sediment to arc lava, we examined trace-element variation in (a) mid-crustal (0.4 GPa) contact metamorphic rocks (Austin & Kelemen, Fall 06 AGU) and (b) ultrahigh-pressure (UHP, > 3 GPa) metasediments. Most UHP samples were metamorphosed along subduction-zone geotherms (Hacker, Int Geol Rev 06), but some record substantially higher T (e.g., Erzgebirge & Kokchetav, Massone EPSL 03). Unmelted, mid-crustal metapelites are indistinguishable from pelitic sediments for the entire suite of elements analyzed by ICP-MS at WSU. Melt extraction from the mid-crustal metapelites led to systematic depletion of incompatible elements in high-grade hornfels. Depletion increases with decreasing distance to the contact with a mafic pluton, most clearly at peak T > 750°C. In contrast, although many UHP metapelites record PT above the aqueous fluid-saturated solidus, and have fluid inclusions and/or hydrous phases, compared to pelites they show no detectable depletion of "fluid-mobile" elements such as LILE (Cs, Rb, Ba, U, K), Sr and Pb, no depletion of "fluid-immobile, incompatible" elements such as Th and LREE, and no systematic change in key soluble/insoluble ratios such as Ba/Th or K/Zr up to ~1000 C. Mobility of incompatible elements is evident for T > 1000 C, well above PT for subduction-zone geotherms. Presumably, trace phases rich in LILE, Th and LREE persist to ~1050 C in metapelites at UHP conditions.How can our observations be reconciled with the recycled sediment component in arc lavas? Our preferred hypothesis is that low-density metasediments rise into the mantle wedge when heating yields viscosities low enough for density-driven instabilities (Ringwood JGSL 74; Marsh AJS 76; Gerya & Yuen EPSL 03; Kelemen et al, Treatise on Geochem 03). In the wedge, metasedimentary diapirs heat as they rise, and undergo large degrees of super-adiabatic partial melting which exhaust trace phases, releasing the sediment component observed in arcs.

Genesis of ultra-high pressure garnet pyroxenites in orogenic peridotites and its bearing on the compositional heterogeneity of the Earth's mantle

NASA Astrophysics Data System (ADS)

Varas-Reus, María Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Károly

2018-07-01

We present an integrated geochemical study of ultra-high pressure (UHP) garnet pyroxenites from the Ronda and Beni Bousera peridotite massifs (Betic-Rif Belt, westernmost Mediterranean). Based on their Sr-Nd-Pb-Hf isotopic systematics, we classify UHP garnet pyroxenites into three groups: Group A pyroxenites (Al2O3: 15-17.5 wt.%) have low initial 87Sr/86Sr, relatively high εNd, εHf and 206Pb/204Pb ratios, and variable 207Pb/204Pb and 208Pb/204Pb. Group B pyroxenites (Al2O3 < 14 wt.%) are characterized by high initial 87Sr/86Sr and relatively low εNd, εHf and 206Pb/204Pb ratios. Group C pyroxenites (Al2O3 ∼ 15 wt.%) have depleted radiogenic signatures with relatively low initial 87Sr/86Sr and 206Pb/204Pb, high εNd and εHf, and their 207Pb/204Pb and 208Pb/204Pb ratios are similar to those of Group B pyroxenites. The major and trace element and isotopic compositions of UHP garnet pyroxenites support their derivation from ancient (1.5-3.5 Ga) oceanic crust recycled into the mantle and intimately stirred with peridotites by convection. However, the genesis of these pyroxenites requires also the involvement of recycled continental lower crust with an isotopic composition akin to the lower crustal section of the lithosphere where these UHP garnet pyroxenites now reside in. These oceanic and continental crustal components were stirred in different proportions in the convective mantle, originating pyroxenites with a more marked geochemical imprint of either oceanic (Group A) or continental lower crust (Group B), or hybrid compositions (Group C). The pyroxenite protoliths likely underwent several melting events, one of them related to the formation of the subcontinental lithospheric mantle and continental crust, generating restitic UHP garnet pyroxenites now preserved in the Ronda and Beni Bousera orogenic peridotites. The extent of melting was mostly controlled by the bulk Mg-number (Mg#) of the pyroxenite protoliths, where protoliths with low Mg# experienced higher degrees of partial melting than sources with higher Mg#. Positive Eu and Sr anomalies in bulk rocks, indicative of their origin from cumulitic crustal gabbros, are preserved mostly in high Mg# pyroxenites due to their higher melting temperatures and consequent lower partial melting degrees. The results of this study show that the genesis of UHP garnet pyroxenites in orogenic peridotites requires a new recipe for the marble cake mantle hypothesis, combining significant recycling and stirring of both oceanic and continental lower crust in the Earth's mantle. Furthermore, this study establishes a firm connection between the isotopic signatures of UHP pyroxenite heterogeneities in the mantle and the continental lower crust.

A Chlorine-Centric Perspective on Fluid-Mediated Processes at Convergent Plate Boundaries

NASA Astrophysics Data System (ADS)

Selverstone, J.

2014-12-01

The release and migration of metamorphic fluids from subducting slabs into overlying mantle is widely recognized as a major mechanism in producing arc geochemical signatures and returning fluid-mobile elements to earth's crust and surface environments. Although the magnitudes of many geochemical fluxes are well constrained, the processes whereby mass transfer occurs in different portions of the subduction system are less well known. Chlorine stable isotopes provide a new perspective on some of these processes: Cl is hydrophilic, but decarbonation reactions favor Cl retention in minerals. Cl also shows less isotopic fractionation than other fluid-sensitive systems and may thus preserve evidence of specific fluid sources and/or fluid mixing events. Detailed studies of sedimentary sequences show that individual beds are isotopically homogeneous but large heterogeneities in δ37Cl exist across beds on a cm to m scale and vary as a function of depositional environment. Compositionally correlative medium-, high-, and ultrahigh-pressure metamorphic sequences in the Alps record decreases of 30-50% in Cl contents in the earliest stages of metamorphism, but little change thereafter. No statistically significant change in isotopic composition occurs during prograde metamorphism of individual horizons, and the same large degree of isotopic heterogeneity (up to 6‰) persists throughout the prograde devolatilization history of the rocks. Likewise, analysis of HP/UHP serpentinites and altered oceanic crust show that heterogeneous protolith compositions are preserved during transport to sub-arc depths, despite large-scale devolatilization. However, upward transport of rocks within the subduction channel results in highly localized interaction with isotopically distinct, Cl-bearing fluid packets. Overlying forearc wedge rocks also record heterogeneous and channelized interaction with distinct fluid components with different δ37Cl. Within-layer fluid compartmentalization during continuous devolatilization reactions must thus be reconciled with discontinuous, cross-layer fluid percolation out of the slab and into the wedge. The resulting implications of the chlorine data for recent mechanical models of slab-to-wedge fluid transport will be discussed.

Serpentinite-driven Exhumation of the UHP Lago di Cignana Unit in the Fossil Alpine Plate Interface

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Gilio, M.; Angiboust, S.; Godard, M.; Pettke, T.

2015-12-01

The Lago di Cignana Unit (LCU) is a coesite- [1] and diamond-bearing [2] slice of oceanic-derived eclogites and metasediments recording Alpine UHP metamorphism at 600 °C-3.2 GPa (~110 km depth) [3]. The LCU is tectonically sandwiched between the eclogitic Zermatt-Saas Zone (ZSZ; 540 °C-3.2 GPa) [4] and the blueschist Combin Zone (400 °C-0.9 GPa) [5] along a tectonic structure joining HP units recording a ~1.2 GPa (40 km) pressure difference. So far, the ZSZ has been attributed to normal HP conditions and the mechanism driving exhumation and accretion of the LCU in its present structural position is not fully understood.We performed petrography and bulk-rock trace element analyses of rocks from LCU and ZSZ serpentinites. We observed that, while serpentinites in the core of the ZSZ show normal subduction zone trace elements and REE's patterns, the Ol+Ti-chu+Chl veins and host serpentinites enveloping the LCU are strongly enriched in sediment-derived fluid-mobile elements (U, Th, Nb, Ta, Ce, Y, As, Sb) and REE's: their patterns well match those of the closely associated LCU-UHP rocks.The presence of extremely enriched Ol+Ti-chu+Chl veins in the serpentinites at direct contact with the UHP Lago di Cignana Unit suggests that fluid exchange between serpentinite and LCU crustal rocks occurred at peak metamorphic conditions. Their coupling therefore occurred during subduction burial and/or peak UHP conditions. As such, the buoyancy force originating from the relatively light serpentinites fuelled the exhumation of the Lago di Cignana Unit. In this contest, the tectonic contact between the Zermatt-Saas Zone and the Combin Zone evolved into a true tectonic plate interface surface.1. Reinecke (1998). Lithos 42(3), 147-189; 2. Frezzotti et al. (2011). Nat. Geosci. 4(10), 703-706; 3. Groppo et al. (2009). J. Metam. Geol. 27(3), 207-231; 4. Angiboust et al. (2009). Terra Nova 21(3), 171-180; 5. Reddy et al. (1999). J. Metam. Geol. 17, 573-590.

Multistage evolution of UHT granulites from the southernmost part of the Gföhl Nappe, Bohemian Massif, Lower Austria

NASA Astrophysics Data System (ADS)

Schantl, Philip; Hauzenberger, Christoph; Linner, Manfred

2016-04-01

A detailed petrological investigation has been undertaken in leucocratic kyanite-garnet bearing and mesocratic orthopyroxene bearing granulites from the Dunkelsteiner Wald, Pöchlarn-Wieselburg and Zöbing granulite bodies from the Moldanubian Zone in the Bohemian Massif (Austria). A combination of textural observations, conventional geothermobarometry, phase equilibrium modelling as well as major and trace element analyses in garnet enables us to confirm a multistage Variscan metamorphic history. Chemically homogenous garnet cores with near constant grossular-rich plateaus are considered to reflect garnet growth during an early HP/UHP metamorphic evolution. Crystallographically oriented rutile exsolutions restricted to those grossular-rich garnet cores point to a subsequent isothermal decompression of the HP/UHP rocks. Overgrowing garnet rims show a pronounced zonation and are interpreted as the result of dehydration melting reactions during an isobaric heating phase which could have taken place near the base of an overthickened continental crust, where the previously deeply subducted rocks were exhumed to. For this HP granulite facies event maximum PT conditions of ~1050 °C and 1.6 GPa have been estimated from leucocratic granulites comprising the peak mineral assemblage quartz, ternary feldspar, garnet, kyanite and rutile. The pronounced zoning of garnet rims indicates that the HP granulite facies event must have been short lived since diffusion in this temperature region is usually sufficient fast to homogenize a zoning pattern in garnet. A retrogressive metamorphic stage is documented in these rocks by the replacement of kyanite to sillimanite and the growth of biotite. This retrograde event took place within the granulite facies but at significantly lower pressures and temperatures with ~0.8 GPa and ~760 °C. This final stage of re-equilibration is thought to be linked with a second exhumation phase into middle crustal levels accompanied by intensive mylonitization. Keywords: Bohemian Massif; Moldanubian; granulite; HP/UHP, HP granulite facies, LP granulite facies overprint; Andes type geodynamic model.

New petrological and age data from the eclogite province in the central segment of the Greenlandic Caledonides

NASA Astrophysics Data System (ADS)

Nagel, Thorsten; Fassmer, Kathrin; Froitzheim, Niko; Fonseca, Raul; Sprung, Peter

2017-04-01

The Caledonian orogen in northeastern Greenland is a 1200 km long, west-vergent nappe pile mirroring the much better explored Caledonides in Scandinavia. The Greenlandic orogen has traditionally been viewed as the retro-wedge of the Scandinavian Caledonides, which is generally accepted to be the result of west-directed subduction of the Iapetus oceanic realm and the Baltic continental margin. This concept, however, is challenged by the finding of widely distributed high-pressure metamorphism as well as the large amount of horizontal shortening accommodated in the Greenlandic nappe pile (Gasser 2014, and references therein). While eclogites in Liverpool Land in the very south have been interpreted to belong to a window into Baltica, the vast domains of eclogite-bearing basement in the central segment of the orogen are attributed to the Lauretian continental margin. Existing ages for high-pressure metamorphism in this area using U-Pb-zircon and Sm-Nd-garnet dating scatter at 420-390 Ma with an exceptionally young age of 370-330 Ma found for the so far only ultrahigh-pressure location in a very internal position of the orogen (e.g. Gilotti et al. 2004). Eclogite-facies metamorphism in Greenland seems thus coeval to or even younger than the main Scandian orogeny in Scandinavia. However, the relatively high temperatures of metamorphism leave room for the interpretation of the Sm-Nd ages as cooling ages. We present petrologic and Lu-Hf-garnet-age data from three locations in the central eclogite province in Greenland and discuss the implications for tectonic scenarios. Investigated rocks are high-temperature eclogites/high-pressure mafic granulites, and garnet pyroxenites. Samples from the well-known location Danmarkshavn record ultra-high-pressure metamorphic conditions by means of SiO2-exsolutions in clinopyroxene and thermobarometric results. An eclogite yielded a Lu-Hf garnet-whole-rock age of 360 Ma thus confirming the existing young age for ultrahigh-pressure metamorphism obtained 140 kilometers away. Samples from the two other locations (Sondre Mellemland and Store Koldewey) preserve the typical high-temperature eclogite-facies conditions and yield ages of 385 Ma and 400 Ma, respectively. Our results suggest that ultrahigh-pressure rocks in northeastern Greenland may be much wider distributed than presently known and corroborate the existence of very young isotopic ages in these rocks. They also confirm the existing Sm-Nd ages around 400 Ma in the majority of eclogites leaving us with the puzzling conclusion that the Laurentian and Baltic margins were apparently subducted at the same time in opposite directions. Gasser D (2014): The Caledonides of Greenland, Svalbard and other Arctic areas: status of research and open questions. In Corfu F et al. (2014): New Perspectives on the Caledonides of Scandinavia and Related Areas. GSL SP, 390, 93-129. Gilotti JA, et al. (2004): Devonian to Carboniferous collision in the Greenland Caledonides: U-Pb zircon and Sm-Nd ages of high-pressure and ultrahigh-pressure metamorphism. CMP, 148, 216 - 235.

STRUCTURAL GEOMETRY OF AN EXHUMED UHP TERRANE IN THE EASTERN SULU OROGEN, CHINA: IMPLICATIONS FOR CONTINENTAL COLLISIONAL PROCESSES

NASA Astrophysics Data System (ADS)

Wang, L.; Kusky, T.

2009-12-01

High-precision 1:1,000 mapping of Yangkou Bay, eastern Sulu orogen, defines the structural geometry and history of the world’s most significant UHP (Ultrahigh Pressure) rock exposures. Four stages of folds are recognized in the UHP rocks and associated quartzo-feldspathic gneiss. Eclogite facies rootless F1 and isoclinal F2 folds are preserved locally in coesite-eclogite. Mylonitic to ultramylonitic cosesit-eclogite shear zones separate 5-10-meter-thick nappes of ultramafic-mafic UHP rocks from banded quartzo-feldspathic gneiss. These shear zones are folded, and progressively overprinted by amphibolite and greenschist facies shear zones that become wider with lower grade. The deformation sequences is explained by deep subduction of offscraped thrust slices of oceanic or lower continental crust, caught between the colliding North and South China cratons in the Mesozoic. After these slices were structurally isolated along the plate interface, they were rolled like ball-bearings, in the subduction channel during their exhumation, forming several generations of folds, sequentially lower-grade foliations and lineations, and intruded by several generations of in situ and exotically derived melts. The shear zones formed during different generations of deformation are wider with lower grades, suggesting that deep-crustal/upper mantle deformation operates efficiently (perhaps with more active crystallographic slip systems) than deformation at mid to upper crustal levels.

Coesite-Diamond Assemblage in Ultrahigh Pressure Crustal and Mantle rocks: Evidence for Carbon Recycling

NASA Astrophysics Data System (ADS)

Sobolev, N. V.

2010-12-01

Coesite, a high-pressure polymorph of silica, was first discovered as part of a coesite-eclogite assemblage (coesite, garnet, omphacite) in equilibrium with diamond as diamond inclusion (DI) in Siberian diamond placers (Sobolev et al., 1976, Dokl. Akad. Nauk SSSR, 230: 1442). In recent years, coesite has become a key mineral coexisting with diamond both in kimberlite (DIs) and in UHP metamorphic rocks of the Kokchetav massif, Kazakhstan (diamondiferous gneisses and calcsilicate rocks). In the UHPM rocks of Kokchetav massif, coesite was first detected as inclusions in zircon associated with diamonds (Sobolev et al., 1991, Dokl. Akad. Nauk SSSR, 321: 184), as a result of the initial studies that had identified diamonds as inclusions in garnets and zircons (Sobolev, Shatsky, 1990, Nature, 343: 742). Garnet and omphacitic clinopyroxene are the principal primary minerals associated with coesite and diamond in UHP mantle and crustal rocks. Their compositions plot distinctly within the eclogitic compositional field and substantiate the existence of coesite presence as DIs in eclogitic (E-type) diamonds, as well as sometimes in xenoliths of diamondiferous eclogites (Shatsky et al., 2008, Lithos, 105:289). One of the major significant features of these eclogitic minerals in both UHPM and kimberlitic mantle occurrences is the K2O contents of the clinopyroxenes, reaching 1.6 wt.%, with Na2O and MnO in Ca-Mg-Fe garnets reaching 0.3 and 6.0 wt.%, respectively. Stable isotope data for C in diamonds and O in garnet, pyroxene and coesite have resulted in establishing a very wide range for these isotopes most typical for crustal conditions - i.e., atypical of mantle values. This is clearly shown for coesite DIs (Schulze et al., 2003, Nature, 428:68), garnets from diamondiferous eclogite xenoliths from Siberian kimberlites (Spetsius et al., 2008, Eur. J. Min., 20:375), garnets and clinopyroxenes from UHP calcsilicate diamondiferous rocks of the Kokchetav massif (Sobolev et al., in press, Contr. Min. Petr.). This extensive wide range in δ13C (PDB) for coesite-bearing diamonds, from -28 to +1.5 ‰, along with common crustal δ18O (SMOW) values from the principal rock-forming minerals (garnet and clinopyroxene) and accessory mineral (coesite), is typical for diamondiferous mantle eclogites, crustal UHPM rocks, and DIs. The petrogenetic evidences from all these rocks and minerals are indicative of major subduction of crustal protoliths (Ringwood, 1972, EPSL, 14:233), including the recycling of crustal carbon into diamonds in mantle eclogites, first speculated on by V.S. Sobolev and N.V. Sobolev (1980, Dokl. Akad. Nauk SSSR, 249: 1217).

Two types of gneisses associated with eclogite at Shuanghe in the Dabie terrane: carbon isotope, zircon U-Pb dating and oxygen isotope

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Gong, Bing; Zhao, Zi-Fu; Fu, Bin; Li, Yi-Liang

2003-10-01

There are two types of gneisses, biotite paragneiss and granitic orthogneiss, to be closely associated with UHP eclogite at Shuanghe in the Dabie terrane. Both concentration and isotope composition of bulk carbon in apatite and host gneisses were determined by the EA-MS online technique. Structural carbonate within the apatite was detected by the XRD and FTIR techniques. Significant 13C-depletion was observed in the apatite with δ13C values of -28.6‰ to -22.3‰ and the carbon concentrations of 0.70-4.98 wt.% CO 2 despite a large variation in δ18O from -4.3‰ to +10.6‰ for these gneisses. There is significant heterogeneity in both δ13C and δ18O within the gneisses on the scale of several tens meters, pointing to the presence of secondary processes after the UHP metamorphism. Considerable amounts of carbonate carbon occur in some of the gneisses that were also depleted in 13C primarily, but subjected to overprint of 13C-rich CO 2-bearing fluid after the UHP metamorphism. The 13C-depleted carbon in the gneisses is interpreted to be inherited from their precursors that suffered meteoric-hydrothermal alteration before plate subduction. Both low δ13C values and structural carbonate in the apatite suggest the presence of 13C-poor CO 2 in the UHP metamorphic fluid. The 13C-poor CO 2 is undoubtedly derived from oxidation of organic matter in the subsurface fluid during the prograde UHP metamorphism. Zircons from two samples of the granitic orthogneiss exhibit low δ18O values of -4.1‰ to -1.1‰, demonstrating that its protolith was significantly depleted in 18O prior to magma crystallization. U-Pb discordia datings for the 18O-depleted zircons yield Neoproterozoic ages of 724-768 Ma for the protolith of the granitic orthogneiss, consistent with protolith ages of most eclogites and orthogneisses from the other regions in the Dabie-Sulu orogen. Therefore, the meteoric-hydrothermal alteration is directly dated to occur at mid-Neoproterozoic, and may be correlated with the Rodinia supercontinental breakup and the snowball Earth event. It is thus deduced that the igneous protolith of the granitic orthogneiss and some eclogites would intrude into the older sequences composing the sedimentary protoliths of the biotite paragneiss and some eclogites along the northern margin of the Yangtze plate at mid-Neoproterozoic, and drove local meteoric-hydrothermal circulation systems in which both 13C- and 18O-depleted fluid interacted with the protoliths of these UHP rocks now exposed in the Dabie terrane.

Subduction and exhumation of a continental margin in the Scandinavian Caledonides: Insights from ultrahigh pressure metamorphism, late orogenic basins and 3D numerical modelling

NASA Astrophysics Data System (ADS)

Cuthbert, Simon

2017-04-01

The Scandinavian Caledonides (SC) represents a plate collision zone of Himalayan style and scale. Three fundamental characteristics of this orogen are: (1) early foreland-directed, tectonic transport and stacking of nappes; (2) late, wholesale reversal of tectonic transport; (3) ultrahigh pressure metamorphism of felsic crust derived from the underthrusting plate at several levels in the orogenic wedge and below the main thrust surface, indicating subduction of continental crust into the mantle. The significance of this for crustal evolution is the profound remodeling of continental crust, direct geochemical interaction of such crust and the mantle and the opening of accommodation space trapping large volumes of clastic detritus within the orogen. The orogenic wedge of the SC was derived from the upper crust of the Baltica continental margin (a hyper-extended passive margin), plus terranes derived from an assemblage of outboard arcs and intra-oceanic basins and, at the highest structural level, elements of the Laurentian margin. Nappe emplacement was driven by Scandian ( 430Ma) collision of Baltica with Laurentia, but emerging Middle Ordovician ages for diamond-facies metamorphism for the most outboard (or rifted) elements of Baltica suggest prior collision with an arc or microcontinent. Nappes derived from Baltica continental crust were subducted, in some cases to depths sufficient to form diamond. These then detached from the upper part of the down-going plate along major thrust faults, at which time they ceased to descend and possibly rose along the subduction channel. Subduction of the remaining continental margin continued below these nappes, possibly driven by slab-pull of the previously subducted Iapetus oceanic lithosphere and metamorphic densification of subducted felsic continental margin. 3D numerical modelling based upon a Caledonide-like plate scenario shows that if a continental corner or promontory enters the subduction zone, the continental margin descends to greater depths than for a simple orthogonal collision and its modelled thermal evolution is consistent with UHP metamorphic assemblages recorded in the southern part of the SC. Furthermore, a tear initiates at the promontary tip along the ocean-continent junction and propagates rapidly along the orogen. The buoyant upthrust of the subducted margin can then lead to reversal of the motion vector of the entire subducting continent, which withdraws the subducted lithospheric margin out of the subduction channel ("eduction"). Because of the diachroneity of slab failure, the continent also rotates, which causes the eduction vector to change azimuth over time. These model behaviours are consistent with the late orogenic structural evolution of the southern SC. However, during the final exhumation stage the crust may not have acted entirely coherently, as some eduction models propose: There is evidence that some inboard Baltica crust experienced late, shallow subduction before detaching as giant "flakes" that carried the orogenic wedge piggyback, forelandwards. Eduction and flake-tectonics could have operated coevally; the model system does not preclude this. Finally, the traction of a large educting (or extruding) mass of continental margin against the overlying orogenic wedge may have stretched and ruptured the wedge, resulting in opening of the late-orogenic Old Red Sandstone molasse basins.

Modeling the exhumation path of partially melted ultrahigh-pressure metapelites, North-East Greenland Caledonides

NASA Astrophysics Data System (ADS)

Lang, Helen M.; Gilotti, Jane A.

2015-06-01

Pseudosection modeling constrains the pressure-temperature (P-T) exhumation path of partially melted ultrahigh-pressure (UHP) metapelites exposed in the North-East Greenland UHP terrane. A robust peak P and T estimate of 3.6 GPa and 970 °C based on mineral assemblages in nearby kyanite eclogites is the starting point for the P-T path. Although the peak assemblage for the metapelite is not preserved, the calculated modeled peak assemblage contained substantial clinopyroxene, garnet, phengite, K-feldspar and coesite with minor kyanite and rutile. Combining the pseudosection and observed textures, the decompression path crosses the coesite-quartz transition before reaching the dry phengite dehydration melting reaction where phengite is abruptly consumed. In the range of 2.5 to 2.2 GPa, clinopyroxene is completely consumed and garnet grows to its maximum volume and grossular content, matching the high grossular rims of relict megacrysts. Plagioclase joins the assemblage and the pseudosection predicts up to 12-13 vol.% melt in the supersolidus assemblage, which contained garnet, liquid, K-feldspar, plagioclase, kyanite, quartz and rutile. At this stage, the steep decompression path flattened out and became nearly isobaric. The melt crystallization assemblage that formed when the path crossed the solidus with decreasing temperature contains phengite, garnet, biotite, 2 feldspars, kyanite, quartz and rutile. Therefore, the path must have intersected the solidus at approximately 1.2 GPa, 825 °C. The pseudosection predicts that garnet is consumed on the cooling path, but little evidence of late garnet consumption or other retrograde effects is observed. This may be due to partial melt loss from the rock. Isochemical PT-n and PT-X sections calculated along the P-T path display changes in mineral assemblage and composition that are consistent with preserved assemblages.

Foundering and Exhumation of UHP Terranes: Race Car or School Bus?

NASA Astrophysics Data System (ADS)

Kylander-Clark, A. R.; Hacker, B. R.

2008-12-01

Recent geochronologic data from the giant ultrahigh-pressure (UHP) terrane, in the Western Gneiss Region of Norway, indicate that subduction and exhumation were relatively slow (a few mm/yr), and that the terrane was exhumed to the surface as a relatively thick, coherent body. These conclusions are in stark contrast to those reached in previous studies of some of the best-studied, smaller UHP terranes and suggest that the processes that form and/or exhume small UHP terranes are fundamentally different from the processes that affect large UHP terranes. These differences may be the result of variations in the buoyancy forces of different proportions of subducted felsic crust, mafic crust, and mantle lithosphere. Initial collision occurs via the subduction of smaller portions of continental material, such as microcontinents or ribbon continents. Because the proportion of continental crust is small, the processes involved in early UHP terrane formation are dominated by the oceanic slab; subduction rates are fast because average plate densities are high, and, as a result, subduction angles are steep. Because these smaller, thinner portions of crust are weak, they deform easily and mix readily with the mantle. As the collision matures, thicker and larger portions of continental material-such as a continental margin-are subducted, and the subduction regime changes from one that was ocean dominated to one that is continent dominated. The increased buoyancy of the larger volume of continental crust resists the pull of the leading oceanic lithosphere; subduction shallows and plate rates slow. Because the downgoing continent is thick, it is strong, remains cohesive and has limited interaction with the mantle. Although the subduction regime during early orogenesis is distinct from that during late orogenesis, the degree of mountain building and crustal thickening may be similar in both stages as small volumes and fast flow rates of buoyant material give way to large volumes and slow flow rates.

Image analysis method to quantify the effect of different treatments on the visual meat/shell ratio of half-shelled green lipped mussels (Perna canaliculus).

PubMed

Kim, Min Geun; Alçiçek, Zayde; Balaban, Murat O; Atar, Hasan Huseyin

2014-04-01

Aquacultured green lipped mussel (Perna canaliculus) is the New Zealand export leader of seafood in terms of weight. Different treatments shrink mussel meat differently and affect the consumer perception of half-shelled mussels. In order to quantify this, digital images of half-shelled green lipped mussels subjected to two postharvest treatments (ultrahigh pressure (UHP) and heat treatment (HT)) and raw controls were taken. The ratio of the view area of the meat to that of the shell (labelled as 'visual condition index' (VCI)) was measured using image analysis. A polygonal region of interest was defined on the image to depict the boundary of the meat and to calculate the view area. Raw mussels had a VCI of 85%. HT mussels had a much reduced VCI of 41%, indicating shrinkage of the meat due to heat. UHP treatment used as a shucking method resulted in a VCI of 83%. Since VCI is one measure of quality for the consumer, this quantitative method can be used in the optimization of shucking treatment (HT or UHP). VCI can be used to optimize postharvest treatments to minimize meat shrinkage. This method can also be applied to other shellfish such as oysters and clams. © 2013 Society of Chemical Industry.

Crystallization of Skeletal Diamonds from Graphite and Natural Coal in Presence of Hydrous Fluids at P=8 GPa and T=1400-1500° C

NASA Astrophysics Data System (ADS)

Dobrzhinetskaya, L. F.; Renfro, A. P.; Green, H. W.

2001-12-01

Most metamorphic microdiamonds from crustal UHP rocks of the Kokchetav massive, Kazakhstan are characterized by skeletal-hopper crystals, cuboid-like crystals with cavities "healed over" by graphite, rose-like crystals, and other imperfect morphologies. According to the classical theory of crystal growth at thermodynamic equilibrium, only shapes with a minimum surface energy are stable. Thus imperfect crystallographic forms of most metamorphic diamonds formally may be interpreted as metastable while the presence of other high pressure phases associated with diamond indicates that the rocks have been subjected to UHP metamorphism within the diamond stability field. The classical theory also says that a skeletal-hopper crystal is one that develops under conditions of rapid growth, a high degree of supersaturation and in the presence of impurities. In contrast to these observations, most experiments on diamond synthesis at high P (5-7.7 GPa) and T (1250 - 1900° C) from graphite (Wang et al., 1999; Hong et al., 1999; Yamaoka et al., 2000) and carbonate material (Pal'anov et al., 1999; Sokol et al.,2000) in presence of fluid phase produced perfect octahedral and cube-octahedral diamond crystals. Advanced analytical research on metamorphic diamonds and their inclusions has demonstrated that they were crystallized from a multicomponent COH-rich supercritical fluid phase, the composition of which suggests intermixture of crustal and mantle components (de Corte et al., 1999; Dobrzhinetskaya et al., 2001, Stockhert et al., 2001). We have recently synthesized imperfect diamond crystals (skeletal-hopper morphologies with effect of etching of the diamond surfaces) from graphite and natural coal + 2% Mg(OH)2 as a source for fluid phase. Conditions of experiments are: P=8-8.5 GPa, T=1400-1500° C, t=14 to 136 hours. Our experimental data are in a good agreement with similar experiments conducted by Kanda et al. (1984) who showed that with increasing water content of the system, the morphology of diamond crystals changes progressively from octahedra to crystals with elements of dodecahedra to hollow/hopper and skeletal morphologies. We hypothesize that imperfect morphologies of metamorphic diamonds are due to the presence of OH in the system.

Metamorphic Perspectives of Subduction Zone Volatiles Cycling

NASA Astrophysics Data System (ADS)

Bebout, G. E.

2008-12-01

Field study of HP/UHP metamorphic rocks provides "ground-truthing" for experimental and theoretical petrologic studies estimating extents of deep volatiles subduction, and provides information regarding devolatilization and deep subduction-zone fluid flow that can be used to reconcile estimates of subduction inputs and arc volcanic outputs for volatiles such as H2O, N, and C. Considerable attention has been paid to H2O subduction in various bulk compositions, and, based on calculated phase assemblages, it is thought that a large fraction of the initially structurally bound H2O is subducted to, and beyond, subarc regions in most modern subduction zones (Hacker, 2008, G-cubed). Field studies of HP/UHP mafic and sedimentary rocks demonstrate the impressive retention of volatiles (and fluid-mobile elements) to depths approaching those beneath arcs. At the slab-mantle interface, high-variance lithologies containing hydrous phases such as mica, amphibole, talc, and chlorite could further stabilize H2O to great depth. Trench hydration in sub-crustal parts of oceanic lithosphere could profoundly increase subduction inputs of particularly H2O, and massive flux of H2O-rich fluids from these regions into the slab-mantle interface could lead to extensive metasomatism. Consideration of sedimentary N concentrations and δ15N at ODP Site 1039 (Li and Bebout, 2005, JGR), together with estimates of the N concentration of subducting altered oceanic crust (AOC), indicates that ~42% of the N subducting beneath Nicaragua is returned in the corresponding volcanic arc (Elkins et al., 2006, GCA). Study of N in HP/UHP sedimentary and basaltic rocks indicates that much of the N initially subducted in these lithologies would be retained to depths approaching 100 km and thus available for addition to arcs. The more altered upper part of subducting oceanic crust most likely to contribute to arcs has sediment-like δ15NAir (0 to +10 per mil; Li et al., 2007, GCA), and study of HP/UHP eclogites indicates retention of seafloor N signatures and, in some cases, enrichments in sedimentary N due to forearc metamorphic fluid-rock interactions (Halama et al., this session). A global estimate of C cycling, using seafloor inputs (carbonate and organic matter) and estimates of volcanic CO2 outputs, indicates ~40% return (with large uncertainty) of the subducting C in volcanic gases. This imbalance appears plausible, given the evidence for deep carbonate subduction, in UHP marbles, and the preservation of graphite in UHP metasediments, together seemingly indicating that large fractions of subducting C survive forearc-to-subarc metamorphism. Estimates of return efficiency in the Central America arc, based on data for volcanic gases, are lower and variable along strike (12-29%), quite reasonably explained by de Leeuw et al. (2007, EPSL) as resulting from incomplete decarbonation of subducting sediment and AOC, fluid flow patterns expected given sediment section thickness, and varying degrees of forearc underplating. The attempts to mass-balance C and N across individual arc-trench systems demonstrate valuable integration of information from geophysical, field, petrologic, and geochemical observations. Studies of subduction-zone metamorphic suites can yield constraints on the evolution of deeply subducting rocks and the physicochemical characteristics of fluids released in forearcs and contributing to return flux in arc volcanic gases.

The collision process deciphered form the systematic metamorphic pattern along the Qinling-Dabie-Hongseong collision belt between the North and South China(Korea-China) blocks

NASA Astrophysics Data System (ADS)

Oh, C. W.

2016-12-01

As a last step of formation of the Pangea supercontinent, the North China craton collided with the South China craton during Permo-Triassic time forming the Qinling-Dabie-Sulu collision belt. After the Qinling-Dabie-Sulu collision belt was found, the Imjingang belt in Korean Peninsula was suggested as an extension of the belt but evidences of collision belt such as eclogite and ophiolite, were not found from the belt. Whereas Triassic eclogite (ca. >230 Ma) was found in the Hongseong area and Triassic post collision igneous rocks (with ca. 230 Ma intrusion ages) occurred throughout the Gyeonggi massif locating to the north of the line connecting the Hongseong, Yangpyeong and Odesan areas. These new findings suggest the Permo-Triassic Qinling-Dabie-Sulu collision belt between the North and South China cratons extends into the Hongseong-Yangpyeong-Odesan collision belt in Korean Peninsula. Therefore I would like to suggest the North and South Korea-China cratons instead of the North and South China cratons. The collision had started from Korea at ca. 250 Ma and propagated towards China until late Triassic. The metamorphic conditions change systematically along the collision belt; ultrahigh-temperature metamorphism in the Odesan area (at 245 Ma; 9.0-10.6 kbar, 915-1160°C), high-P/T metamorphism in the Hongseong area (at > 230 Ma; 17.0-21.9 kbar, 835-860°C), ultrahigh-pressure metamorphism in the Dabie and Sulu belts (at 230-220 Ma; 30-40 kbar, 680-880°C), ultrahigh-pressure metamorphism in the Hongan belt (at 225-212 Ma; 31 kbar, 590-650°C) and blueschist facies metamorphism in the Qinling belt. The systematic increasing peak pressure condition and decreasing peak temperature condition from the Odesan to Dabie-Sulu belt, may be due to the increase in the depth of slab break-off towards west, which might be related to the increase of the amounts of subducted oceanic slab towards west. However, after the slab break-off in the Dabie-Sulu area, the depth of slab break-off decreased towards west causing the decrease of peak metamorphic conditions from the Dabie-Sulu to Qinling belt. Post collision igneous activities occurred at 230 Ma in the eastern part of the collision belt between the Odesan and Hongseong area and 215-200 Ma in the Qinling belt.

Paragneiss zircon geochronology and trace element geochemistry, North Qaidam HP/UHP terrane, western China

USGS Publications Warehouse

Mattinson, C.G.; Wooden, J.L.; Zhang, J.X.; Bird, D.K.

2009-01-01

In the southeastern part of the North Qaidam terrane, near Dulan, paragneiss hosts minor peridotite and UHP eclogite. Zircon geochronology and trace element geochemistry of three paragneiss samples (located within a ???3 km transect) indicates that eclogite-facies metamorphism resulted in variable degrees of zircon growth and recrystallization in the three samples. Inherited zircon core age groups at 1.8 and 2.5 Ga suggest that the protoliths of these rocks may have received sediments from the Yangtze or North China cratons. Mineral inclusions, depletion in HREE, and absence of negative Eu anomalies indicate that zircon U-Pb ages of 431 ?? 5 Ma and 426 ?? 4 Ma reflect eclogite-facies zircon growth in two of the samples. Ti-in-zircon thermometry results are tightly grouped at ???660 and ???600 ??C, respectively. Inclusions of metamorphic minerals, scarcity of inherited cores, and lack of isotopic or trace element inheritance demonstrate that significant new metamorphic zircon growth must have occurred. In contrast, zircon in the third sample is dominated by inherited grains, and rims show isotopic and trace element inheritance, suggesting solid-state recrystallization of detrital zircon with only minor new growth. ?? 2009 Elsevier Ltd.

Acoustic emission from a solidifying aluminum-lithium alloy

NASA Technical Reports Server (NTRS)

Henkel, D. P.; Wood, J. D.

1992-01-01

Physical phenomena associated with the solidification of an AA2090 Al-Li alloy have been characterized by AE methods. Repeatable patterns of AE activity as a function of solidification time are recorded and explained for ultrahigh-purity (UHP) aluminum and an Al-4.7 wt pct Cu binary alloy, in addition to the AA2090 Al-Li alloy, by the complementary utilization of thermal, AE, and metallographic methods. One result shows that the solidification of UHP aluminum produces one discrete period of high AE activity as the last 10 percent of solid forms.

Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea.

PubMed

Baldwin, Suzanne L; Monteleone, Brian D; Webb, Laura E; Fitzgerald, Paul G; Grove, Marty; Hill, E June

2004-09-16

As lithospheric plates are subducted, rocks are metamorphosed under high-pressure and ultrahigh-pressure conditions to produce eclogites and eclogite facies metamorphic rocks. Because chemical equilibrium is rarely fully achieved, eclogites may preserve in their distinctive mineral assemblages and textures a record of the pressures, temperatures and deformation the rock was subjected to during subduction and subsequent exhumation. Radioactive parent-daughter isotopic variations within minerals reveal the timing of these events. Here we present in situ zircon U/Pb ion microprobe data that dates the timing of eclogite facies metamorphism in eastern Papua New Guinea at 4.3 +/- 0.4 Myr ago, making this the youngest documented eclogite exposed at the Earth's surface. Eclogite exhumation from depths of approximately 75 km was extremely rapid and occurred at plate tectonic rates (cm yr(-1)). The eclogite was exhumed within a portion of the obliquely convergent Australian-Pacific plate boundary zone, in an extending region located west of the Woodlark basin sea floor spreading centre. Such rapid exhumation (> 1 cm yr(-1)) of high-pressure and, we infer, ultrahigh-pressure rocks is facilitated by extension within transient plate boundary zones associated with rapid oblique plate convergence.

Concepts for diamond exploration in "on/off craton" areas—British Columbia, Canada

NASA Astrophysics Data System (ADS)

Simandl, George J.

2004-09-01

The tectonic setting of British Columbia (BC) differs from classic diamond-bearing intracratonic regions such as the Northwest Territories and South Africa. Nevertheless, several diamond occurrences have been reported in BC. It is also known that parts of the province are underlain by Proterozoic and possibly Archean basement. Because the continents of today are composites of fragments of ancient continents, it is possible that some of the regions underlain by old crystalline basement in eastern British Columbia were associated with a deep crustal keel. The keel may have predated the break-up of the early Neoproterozoic supercontinent called Rodinia and was preserved possibly until the Triassic. Some of these old continental fragments may have been displaced relative to their position of origin and dissociated from their keel, or the keel may have since been destroyed. Such fragments represent favourable exploration grounds in terms of the "Diamondiferous Mantle Root" model (DMR model) if they were intersected by kimberlites or lamproites prior to displacement or destruction of their underlying deep keel. Therefore, extrapolation of fragments of the diamond-bearing Precambrian basement from the Northwest Territories or Alberta to BC provides a sufficient reason for initiating reconnaissance indicator mineral surveys. The "Eclogite Subduction Zone" model (ES model) predicts formation of diamonds at lower pressure (i.e., depth) than required by the DMR model in convergent tectonic settings. Although not proven, this model is supported by thermal modeling of cold subduction zones and recent discoveries of diamonds in areas characterized by convergent tectonic settings. If the ES model is correct, then the parts of BC with a geological history similar to today's "cold" subduction zones, such as Honshu (Japan), or to continental collision zones, such as Kokchetav massif (Kazakhstan) and the Dabie-Sulu Terrane (east central China), may be diamondiferous. The terranes where geological evidences suggest an ultrahigh pressure (UHP) metamorphic event followed by rapid tectonic exhumation (which could have prevented complete resorption of diamonds on their journey to the surface) are worth investigating. If UHP rocks were intercepted at depth by syn- or post-subduction diamond elevators, such as kimberlites, lamproites, lamprophyres, nephelinites or other alkali volcanic rocks of deep-seated origin, the diamond potential of the area would be even higher.

Deformation Enhanced Recrystallization of Titanite: Insight from the Western Gneiss Region Ultrahigh-Pressure Terrane

NASA Astrophysics Data System (ADS)

Gordon, S. M.; Reddy, S. M.; Blatchford, H.; Whitney, D. L.; Kirkland, C. L.; Teyssier, C.; Evans, N. J.; McDonald, B.

2017-12-01

Titanite readily recrystallizes due to metamorphism, deformation, and/or fluids making it an ideal chronometer for tracking the exhumation of high-grade rocks. The Western Gneiss Region (WGR), Norway, is a giant UHP terrane exhumed as a fairly coherent slab. Parts of the WGR underwent little deformation during exhumation; however, meters-scale shear zones, located across the WGR, deformed over a range of pressures, from (U)HP to amphibolite facies. Titanite from quartzofeldpathic gneiss within, directly adjacent to, and 300 m away from a mylonitic shear zone within the southern WGR have been analyzed to track exhumation and investigate effects of deformation on recrystallization and trace-element mobility. EBSD was used to characterize the microstructural evolution of the gneisses, and trace-element concentrations and timing of recrystallization were estimated by split-stream LA-ICPMS. Titanite grain size decreases from outside (>200) to inside (<75 µm) the shear zone. Gneiss in and directly adjacent to the shear zone contain partially to completely recrystallized grains, with 207-corrected 206Pb/238U ages of <405 Ma. Gneiss within the shear zone shows a greater percentage of recrystallized grains. EBSD data indicate that some titanite comprises multiple subgrains within an optically coherent single grain. Subgrains in titanite cores show evidence of inherited radiogenic Pb, whereas subgrains in rims and tails of deformed sigma grains were recrystallized. In a gneiss directly adjacent to the shear zone, optically coherent grains are zoned, with increasing Sr and decreasing Zr from core to rim; titanite subgrains within the shear-zone gneiss are too small to analyze. In comparison, titanite from the gneiss outside the shear zone does not show any internal microstructures or evidence for Scandian recrystallization and has low U and high 204Pb. These results show that most trace elements are unaffected by deformation of titanite; however, Pb is mobile. Deformation thus plays an important role in resetting U-Pb systematics and allows the timing of shear zone development to be linked to the early stages of eclogite exhumation at ca. 405 Ma. Atom-probe analyses of adjacent subgrains, one that has recrystallized and one with an inherited age, will provide insight into trace-element mobility on the nm-scale.

Deformation Enhanced Recrystallization of Titanite: Insight from the Western Gneiss Region Ultrahigh-Pressure Terrane

NASA Astrophysics Data System (ADS)

Gordon, S. M.; Reddy, S. M.; Blatchford, H.; Whitney, D. L.; Kirkland, C. L.; Teyssier, C.; Evans, N. J.; McDonald, B.

2016-12-01

Titanite readily recrystallizes due to metamorphism, deformation, and/or fluids making it an ideal chronometer for tracking the exhumation of high-grade rocks. The Western Gneiss Region (WGR), Norway, is a giant UHP terrane exhumed as a fairly coherent slab. Parts of the WGR underwent little deformation during exhumation; however, meters-scale shear zones, located across the WGR, deformed over a range of pressures, from (U)HP to amphibolite facies. Titanite from quartzofeldpathic gneiss within, directly adjacent to, and 300 m away from a mylonitic shear zone within the southern WGR have been analyzed to track exhumation and investigate effects of deformation on recrystallization and trace-element mobility. EBSD was used to characterize the microstructural evolution of the gneisses, and trace-element concentrations and timing of recrystallization were estimated by split-stream LA-ICPMS. Titanite grain size decreases from outside (>200) to inside (<75 µm) the shear zone. Gneiss in and directly adjacent to the shear zone contain partially to completely recrystallized grains, with 207-corrected 206Pb/238U ages of <405 Ma. Gneiss within the shear zone shows a greater percentage of recrystallized grains. EBSD data indicate that some titanite comprises multiple subgrains within an optically coherent single grain. Subgrains in titanite cores show evidence of inherited radiogenic Pb, whereas subgrains in rims and tails of deformed sigma grains were recrystallized. In a gneiss directly adjacent to the shear zone, optically coherent grains are zoned, with increasing Sr and decreasing Zr from core to rim; titanite subgrains within the shear-zone gneiss are too small to analyze. In comparison, titanite from the gneiss outside the shear zone does not show any internal microstructures or evidence for Scandian recrystallization and has low U and high 204Pb. These results show that most trace elements are unaffected by deformation of titanite; however, Pb is mobile. Deformation thus plays an important role in resetting U-Pb systematics and allows the timing of shear zone development to be linked to the early stages of eclogite exhumation at ca. 405 Ma. Atom-probe analyses of adjacent subgrains, one that has recrystallized and one with an inherited age, will provide insight into trace-element mobility on the nm-scale.

Application of ultra high pressure (UHP) in starch chemistry.

PubMed

Kim, Hyun-Seok; Kim, Byung-Yong; Baik, Moo-Yeol

2012-01-01

Ultra high pressure (UHP) processing is an attractive non-thermal technique for food treatment and preservation at room temperature, with the potential to achieve interesting functional effects. The majority of UHP process applications in food systems have focused on shelf-life extension associated with non-thermal sterilization and a reduction or increase in enzymatic activity. Only a few studies have investigated modifications of structural characteristics and/or protein functionalities. Despite the rapid expansion of UHP applications in food systems, limited information is available on the effects of UHP on the structural and physicochemical properties of starch and/or its chemical derivatives included in most processed foods as major ingredients or minor additives. Starch and its chemical derivatives are responsible for textural and physical properties of food systems, impacting their end-use quality and/or shelf-life. This article reviews UHP processes for native (unmodified) starch granules and their effects on the physicochemical properties of UHP-treated starch. Furthermore, functional roles of UHP in acid-hydrolysis, hydroxypropylation, acetylation, and cross-linking reactions of starch granules, as well as the physicochemical properties of UHP-assisted starch chemical derivatives, are discussed.

Introduction to the structures and processes of subduction zones

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Zhao, Zi-Fu

2017-09-01

Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn-subduction processes and products from post-subduction processes and products. Nevertheless, available results indicate that our definition and understanding of subduction zone processes and products can be advanced by the convergence of observations and interpretations from geochemical, geological, geophysical and geodynamic studies of both oceanic and continental subduction zones. Therefore, insights into subduction zones can be provided by intergration of different approaches from different targets in the near future.

Introduction to the structures and processes of subduction zones

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Zhao, Zi-Fu

2017-09-01

Subduction zones have been the focus of many studies since the advent of plate tectonics in 1960s. Workings within subduction zones beneath volcanic arcs have been of particular interest because they prime the source of arc magmas. The results from magmatic products have been used to decipher the structures and processes of subduction zones. In doing so, many progresses have been made on modern oceanic subduction zones, but less progresses on ancient oceanic subduction zones. On the other hand, continental subduction zones have been studied since findings of coesite in metamorphic rocks of supracrustal origin in 1980s. It turns out that high-pressure to ultrahigh-pressure metamorphic rocks in collisional orogens provide a direct target to investigate the tectonism of subduction zones, whereas oceanic and continental arc volcanic rocks in accretionary orogens provide an indirect target to investigate the geochemistry of subduction zones. Nevertheless, metamorphic dehydration and partial melting at high-pressure to ultrahigh-pressure conditions are tectonically applicable to subduction zone processes at forearc to subarc depths, and crustal metasomatism is the physicochemical mechanism for geochemical transfer from the slab to the mantle in subduction channels. Taken together, these provide us with an excellent opportunity to find how the metamorphic, metasomatic and magmatic products are a function of the structures and processes in both oceanic and continental subduction zones. Because of the change in the thermal structures of subduction zones, different styles of metamorphism, metasomatism and magmatism are produced at convergent plate margins. In addition, juvenile and ancient crustal rocks have often suffered reworking in episodes independent of either accretionary or collisional orogeny, leading to continental rifting metamorphism and thus rifting orogeny for mountain building in intracontinental settings. This brings complexity to distinguish the syn-subduction processes and products from post-subduction processes and products. Nevertheless, available results indicate that our definition and understanding of subduction zone processes and products can be advanced by the convergence of observations and interpretations from geochemical, geological, geophysical and geodynamic studies of both oceanic and continental subduction zones. Therefore, insights into subduction zones can be provided by integration of different approaches from different targets in the near future.

Tracing high-pressure metamorphism in marbles: Phase relations in high-grade aluminous calcite-dolomite marbles from the Greek Rhodope massif in the system CaO-MgO-Al 2O 3-SiO 2-CO 2 and indications of prior aragonite

NASA Astrophysics Data System (ADS)

Proyer, A.; Mposkos, E.; Baziotis, I.; Hoinkes, G.

2008-08-01

Four different types of parageneses of the minerals calcite, dolomite, diopside, forsterite, spinel, amphibole (pargasite), (Ti-)clinohumite and phlogopite were observed in calcite-dolomite marbles collected in the Kimi-Complex of the Rhodope Metamorphic Province (RMP). The presence of former aragonite can be inferred from carbonate inclusions, which, in combination with an analysis of phase relations in the simplified system CaO-MgO-Al 2O 3-SiO 2-CO 2 (CMAS-CO 2) show that the mineral assemblages preserved in these marbles most likely equilibrated at the aragonite-calcite transition, slightly below the coesite stability field, at ca. 720 °C, 25 kbar and aCO 2 ~ 0.01. The thermodynamic model predicts that no matter what activity of CO 2, garnet has to be present in aluminous calcite-dolomite-marble at UHP conditions.

Enticed by the punschrulle: Preliminary investigation of the Seve Nappe Complex's incorporation into the Scandinavian Caledonides via 'vacuum-cleaner' exhumation.

NASA Astrophysics Data System (ADS)

Barnes, Chris; Majka, Jaroslaw; Schneider, David; Bukala, Michal; Walczak, Katarzyna

2017-04-01

Recent discoveries of ultra-high pressure (UHP) metamorphism in the Seve Nappe Complex (SNC) of the Scandinavian Caledonides provide the basis for new investigations into the subduction - exhumation dynamics of the Baltoscandian margin during Caledonian tectonism. Specifically, exhumation of (U)HP complexes during subduction remains enigmatic. The recently proposed 'vacuum-cleaner' model details a method of exhumation for the SNC driven by conditions of underpressure within the subduction channel. This model, however, still requires extensive testing. Metasedimentary rocks hosting eclogite boudins of the SNC in Norrbotten, Sweden, preserve both metre-scale folding and a pervasive foliation which were developed during exhumation, as purposed by previous studies. Thus, the SNC host-rock offers an excellent region to test the vacuum-cleaner exhumation model. Preliminary investigation of the host-rock reveals a regional mineral assemblage of Qz + Ms + Grt + Bt + Ksp + Pl + Czo + Aln + Ttn (+ Tur + St). Garnet inclusions (Qz + Rt + Ms) are interpreted to represent the peak pressure assemblage. Chemical profiles of Grt show homogenization of the cores with thin retrogressive rims. Homogenization of Grt requires temperatures >700°C, interpreted to represent peak temperature conditions. Field observations of exhumation-related folds uncovered an axial-planar alignment of mica within the fold hinges, and an abundance of Aln and Czo requires upper-greenschist to lower-amphibolite facies conditions and presence of fluids. The current host-rock mineral assemblage is representative of retrogressive metamorphism at <550-600°C contemporaneous with deformation. Microstructures of the metasedimentary rocks are variable and strongly correlated with competency of the rock. Competent domains abundant in e.g. Qz, Grt, Czo, Ksp etc. exhibit coarse-grained subgrain and bulging-grain recrystallized Qz and development of micrometer-scale shear bands. Less competent domains, dominated by micas, are characterized by very fine-grained recrystallized Qz, mica (Ms) fish bundles and rotated, pre-kinematic Grt and Tur, illustrating strain localization which accommodated the exhumation of eclogite boudins. Kinematic orientations determined from mica-rich shear zones are variable; rigid eclogite boudins are likely controlling local shear sense. Compositional mapping of white mica reveals a narrow range of composition (61-73% XMs/27-39% XCel) regardless of degree of deformation experienced by the crystal. However, individual grains show patchy Mg-depleted/Al-enriched zones (70-84% XMs/16-30% XCel), which are spatially correlated with Bt-after-Ms reactions. Graphical representation of total Mg + Fe-content vs. excess Si-content of white mica illustrates a strong Tschermak substitution towards Ms end-member composition, with moderate Prl and Ti substitutions also contributing to the overall excess Si-content. Growth of Bt-after-Ms and the associated Tschermak substitution towards Ms-composition suggests a decrease in temperature during retrogressive metamorphism, perhaps marking the transition from lower-amphibolite to upper-greenschist facies. Future work on resolving the timing of exhumation of the SNC will involve in-situ 40Ar/39Ar dating of white mica and U-Pb depth profiling of zircon. This preliminary study regarding the petrology, mineral chemistry, and microstructures of the SNC host-rock in Norrbotten will be crucial for interpreting the geo/thermochronological results and will be instrumental for evaluating the vacuum-cleaner model. This work is financially supported by NCN "CALSUB" research project no. 2014/14/E/ST10/00321.

Optimized ultra-high-pressure-assisted extraction of procyanidins from lychee pericarp improves the antioxidant activity of extracts.

PubMed

Zhang, Ruifen; Su, Dongxiao; Hou, Fangli; Liu, Lei; Huang, Fei; Dong, Lihong; Deng, Yuanyuan; Zhang, Yan; Wei, Zhencheng; Zhang, Mingwei

2017-08-01

To establish optimal ultra-high-pressure (UHP)-assisted extraction conditions for procyanidins from lychee pericarp, a response surface analysis method with four factors and three levels was adopted. The optimum conditions were as follows: 295 MPa pressure, 13 min pressure holding time, 16.0 mL/g liquid-to-solid ratio, and 70% ethanol concentration. Compared with conventional ethanol extraction and ultrasonic-assisted extraction methods, the yields of the total procyanidins, flavonoids, and phenolics extracted using the UHP process were significantly increased; consequently, the oxygen radical absorbance capacity and cellular antioxidant activity of UHP-assisted lychee pericarp extracts were substantially enhanced. LC-MS/MS and high-performance liquid chromatography quantification results for individual phenolic compounds revealed that the yield of procyanidin compounds, including epicatechin, procyanidin A2, and procyanidin B2, from lychee pericarp could be significantly improved by the UHP-assisted extraction process. This UHP-assisted extraction process is thus a practical method for the extraction of procyanidins from lychee pericarp.

Felsic granulite with layers of eclogite facies rocks in the Bohemian Massif; did they share a common metamorphic history?

NASA Astrophysics Data System (ADS)

Jedlicka, Radim; Faryad, Shah Wali

2017-08-01

High pressure granulite and granulite gneiss from the Rychleby Mountains in the East Sudetes form an approximately 7 km long and 0.8 km wide body, which is enclosed by amphibolite facies orthogneiss with a steep foliation. Well preserved felsic granulite is located in the central part of the body, where several small bodies of mafic granulite are also present. In comparison to other high pressure granulites in the Bohemian Massif, which show strong mineral and textural re-equilibration under granulite facies conditions, the mafic granulite samples preserve eclogite facies minerals (garnet, omphacite, kyanite, rutile and phengite) and their field and textural relations indicate that both mafic and felsic granulites shared common metamorphic history during prograde eclogite facies and subsequent granulite facies events. Garnet from both granulite varieties shows prograde compositional zoning and contains inclusions of phengite. Yttrium and REEs in garnet show typical bell-shaped distributions with no annular peaks near the grain rims. Investigation of major and trace elements zoning, including REEs distribution in garnet, was combined with thermodynamic modelling to constrain the early eclogite facies metamorphism and to estimate pressure-temperature conditions of the subsequent granulite facies overprint. The first (U)HP metamorphism occurred along a low geothermal gradient in a subduction-related environment from its initial stage at 0.8 GPa/460 °C and reached pressures up to 2.5 GPa at 550 °C. The subsequent granulite facies overprint (1.6-1.8 GPa/800-880 °C) affected the rocks only partially; by replacement of omphacite into diopside + plagioclase symplectite and by compositional modification of garnet rims. The mineral textures and the preservation of the eclogite facies prograde compositional zoning in garnet cores confirm that the granulite facies overprint was either too short or too faint to cause recrystallisation and homogenisation of the eclogite facies mineral assemblage. The results of this study are compared with other granulite massifs in the Moldanubian Zone. In addition, a possible scenario for the Variscan eclogite and subsequent granulite facies metamorphism in the Bohemian Massif is discussed.

Exhumation of high-pressure rocks beneath the Solund Basin, Western Gneiss Region of Norway

USGS Publications Warehouse

Hacker, B.R.; Andersen, T.B.; Root, D.B.; Mehl, L.; Mattinson, J.M.; Wooden, J.L.

2003-01-01

The Solund-Hyllestad-Lavik area affords an excellent opportunity to understand the ultrahigh-pressure Scandian orogeny because it contains a near-complete record of ophiolite emplacement, high-pressure metamorphism and large-scale extension. In this area, the Upper Allochthon was intruded by the c. 434 Ma Sogneskollen granodiorite and thrust eastward over the Middle/Lower Allochthon, probably in the Wenlockian. The Middle/Lower Allochthon was subducted to c. 50 km depth and the structurally lower Western Gneiss Complex was subducted to eclogite facies conditions at c. 80 km depth by c. 410-400 Ma. Within 100. Exhumation to upper crustal levels was complete by c. 403 Ma. The Solund fault produced the last few km of tectonic exhumation, bringing the near-ultrahigh-pressure rocks to within c. 3 km vertical distance from the low-grade Solund Conglomerate.

Metamorphism, Plate Tectonics, and the Supercontinent Cycle

NASA Astrophysics Data System (ADS)

Brown, Michael

Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian; G-UHTM facies series rocks may be inferred at depth in younger, particularly Cenozoic orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the cyclic formation of supercontinents and their breakup, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those associated with the modern Pacific rim. Medium-temperature eclogite, high-pressure granulite metamorphism (E-HPGM), is also first recognized in the Neoarchean rock record and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E-HPGM belts are complementary to G-UHTM belts and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; they record the low thermal gradients associated with modern subduction. Lawsonite blueschists and eclogites (high-pressure metamorphism, HPM) and ultrahigh pressure metamorphism (UHPM) characterized by coesite (±lawsonite) or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers the low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although perhaps counterintuitive, many HPM-UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts—reflecting a duality of thermal regimes—appears in the record only since the Neoarchean Era. A duality of thermal regimes is the hallmark of modern plate tectonics and the duality of metamorphic belts is the characteristic imprint of plate tectonics in the rock record. The occurrence of both G-UHTM and E-HPGM belts since the Neoarchean manifests the onset of a 'Proterozoic plate tectonics regime', although the style of tectonics likely involved differences. The 'Proterozoic plate tectonics regime' evolved during a Neoproterozoic transition to the 'modern plate tectonics regime' characterized by colder subduction and subduction of continental crust deep into the mantle and its (partial) return from depths of up to 300 km, as chronicled by the appearance of HPM-UHPM in the rock record. The age distribution of metamorphic belts that record extreme conditions of metamorphism is not uniform, and metamorphism occurs in periods that correspond to amalgamation of continental lithosphere into supercratons (e.g. Superia/Sclavia) or supercontinents (e.g. Nuna (Columbia), Rodinia, Gondwana, and Pangea).

Chlorine Isotope Evidence for Syn-Subduction Modification of Serpentinites by Interaction with Sediment-Derived Fluid

NASA Astrophysics Data System (ADS)

Selverstone, J.; Sharp, Z. D.

2012-12-01

High-pressure serpentinites and rodingites and high- to ultrahigh-pressure metasedimentary rocks from the Aosta region, Italy, preserve strikingly different chlorine isotope compositions that can be used to constrain the nature of fluid-rock interactions during subduction. Serpentinites and rodingitized gabbroic dikes subducted to 70-80 km have bulk δ37Cl values between -1.6 and +0.9‰ (median= -0.5‰, n=26 plus 5 replicates; one amphibole-vein outlier at -2.9‰). Serpentinite δ37Cl values are positively correlated with Cr ± Cl contents (r2= 0.97 and 0.58) and negatively correlated with CaO (r2=0.72). BSE imaging and X-ray mapping reveal up to three generations of compositionally distinct serpentine and chlorite in single samples. The youngest generation, which is most abundant, has the lowest chlorine content. Three rodingite samples contain abundant texturally early fluid inclusions. These samples were finely crushed and leached in 18 MΩ H2O to extract water-soluble chlorides. The leachates, which are assumed to record the compositions of the fluid inclusions, have δ37Cl values that are 0.7-1.5‰ lower than the corresponding bulk rock values. Leachate from the outlier amph-magnesite vein is indistinguishable from the bulk value at -2.7‰. There is almost no overlap between the Cl isotope compositions of HP serp/rod samples and associated HP/UHP metasedimentary rocks. Calcmica schists, diamond-bearing Mn nodules, and impure marbles subducted to >130 km and calcmica schists and Mn crusts transported to 70-80 km have δ37Cl values between -4.5 and -1.5‰ (median= -2.7‰, n=25 plus 7 replicates; two outlier points at -0.5‰). Primary fluid inclusions in the diamondiferous samples contain carbonate- and silicate-bearing aqueous fluids with very low chloride contents (Frezzotti et al., 2011, Nature Geosci). Taken together, these data record a history of progressive modification of serpentinites and rodingites by mixing with low-δ37Cl, low-Cl, high-Ca fluids during subduction and metamorphism. Serpentinites with the highest Cr contents have Cl isotopic compositions identical to those of modern seafloor serpentinites (δ37Cl=0.2-0.6‰), consistent with primary serpentinization by seawater (e.g., Barnes et al. 2009, Lithos). Low-Cr serpentinites record significant interaction with a Ca-rich fluid that shifted the rocks to lower δ37Cl values and diluted the original Cr and Cl contents. The fluid was likely derived from continuous devolatilization reactions in associated low-δ37Cl, calcareous metasedimentary rocks. These data have important implications for models of subduction mass transfer associated with antigorite breakdown. If serpentinites are commonly modified by interaction with metasedimentary fluids prior to antigorite dehydration, chemical signatures imparted during deserpentinization will reflect the integrated history of fluid-rock interaction in the subduction channel rather than an endmember "serpentinite signature". The data further suggest that Cl may be hydrophobic in HP/UHP carbonate-bearing aqueous fluids, resulting in generation of low-Cl fluid during metamorphic devolatilization.

Coupling of Oceanic and Continental Crust During Eocene Eclogite-Facies Metamorphism: Evidence From the Monte Rosa Nappe, Western Alps, Italy

NASA Astrophysics Data System (ADS)

Lapen, T. J.; Johnson, C. M.; Baumgartner, L. P.; Skora, S.; Mahlen, N. J.; Beard, B. L.

2006-12-01

Subduction of continental crust to HP-UHP metamorphic conditions requires overcoming density contrasts that are unfavorable to deep burial, whereas exhumation of these rocks can be reasonably explained through buoyancy-assisted transport in the subduction channel to more shallow depths. In the western Alps, both continental and oceanic lithosphere has been subducted to eclogite-facies metamorphic conditions. The burial and exhumation histories of these sections of lithosphere bear directly on the dynamics of subduction and the stacking of units within the subduction channel. We address the burial history of the continental crust with high precision U-Pb rutile and Lu-Hf garnet geochronology of the eclogite-facies Monte Rosa nappe (MR), western Alps, Italy. U-Pb rutile ages from quartz-carbonate-white mica-rutile veins that are hosted within eclogite and schist of the MR, Gressoney Valley, Italy, indicate that it was at eclogite-facies metamorphic conditions at 42.6 +/- 0.6 Ma. The sample area (Indren glacier, Furgg zone; Dal Piaz, 2001) consists of eclogite boudins that are surrounded by micaceous schist. Associated with the eclogite and schist are quartz-carbonate-white mica-rutile veins that formed in tension cracks in the eclogite and along the contact between eclogite and surrounding schist. Intrusion of the veins occurred at eclogite-facies metamorphic conditions (480-570°C, >1.3-1.4 GPa) based on textural relations, oxygen isotope thermometry, and geothermobarometry. Lu-Hf geochronology of garnet from a chloritoid-talc-garnet-phengite-quartz-calcite-pyrite - chalcopyrite bearing boudin within talc-chloritoid whiteschists of the MR, Val d'Ayas, Italy (Chopin and Monie, 1984; Pawlig, 2001) yields an age of 40.54 +/- 0.36 Ma. The talc-chloritoid whiteschists from the area record pressures and temperatures of 1.6-2.4 GPa and 500-530°C (Chopin and Monie, 1984; Le Bayon et al., 2006) indicating near UHP metamorphic conditions. Based on the age, P-T, and textural data, the rutile age likely represents the prograde-leg of the eclogite-facies P-T path whereas the Lu-Hf garnet age likely represents higher grade metamorphic conditions. The timing of eclogite-facies metamorphism in the MR is within the same time interval as the duration of prograde metamorphism (~55-40) recorded in the structurally overlying Zermatt-Saas ophiolite (ZSO; e.g., Amato et al., 1999; Lapen et al., 2003; Mahlen et al., this meeting). In particular, the Lu-Hf garnet age from the MR is identical within error to a relatively young 40.8 +/- 1.8 Ma Lu-Hf garnet-whole rock-cpx age from a structurally low slice of the ZSO at Saas-Fee, Switzerland (Mahlen et al., this meeting). Not only do the ages of eclogite-facies metamorphism overlap between the MR and ZSO, but so do the P-T conditions (e.g., between 1.6-2.8 GPa; 500-600°C). These data, combined with the relative structural positions of the MR and ZSO in the western Alps, suggest that the MR and ZSO were likely juxtaposed within the subduction channel through underplating of the MR beneath the ZSO. The strong negative buoyancy of the MR has likely aided in the exhumation of sections of the ZSO. Therefore, coupling of continental and oceanic terranes in a subduction channel, perhaps a general feature in the western Alps, may be critical in preventing permanent loss of oceanic crust to the mantle.

From P-T-age to secular change and global tectonic regimes (or Essene in reverse - from granulites to blueschists and eclogites over time)

NASA Astrophysics Data System (ADS)

Brown, M.

2006-12-01

Essene's contributions began pre-plate tectonics more than 40 years ago; they range from mineralogy to tectonics, from experiments and thermobarometry to elements and isotopes, and from the Phanerozoic to the Precambrian. Eric is a true polymath! Assessing the P-T conditions and age distribution of crustal metamorphism is an important step in evaluating secular change in tectonic regimes and geodynamics. In general, Archean rocks exhibit moderate-P - moderate-to-high-T facies series metamorphism (greenstone belts and granulite terranes); neither blueschists nor any record of deep continental subduction and return are documented and only one example of granulite facies ultrahigh-temperature metamorphism is reported. Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian, although G-UHTM facies series rocks may be inferred at depth in younger orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the formation and breakup of supercontinents, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those around the modern Pacific rim. Medium-temperature eclogite - high-pressure granulite metamorphism (E-HPGM) also is first recognized in the Neoarchean rock record, and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E- HPGM belts are complementary to G-UHTM belts, and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; lawsonite blueschists and eclogites (high-pressure metamorphism, HPM), and ultrahigh pressure metamorphism (UHPM) characterized by coesite or diamond are predominantly Phanerozoic phenomena. HPM-UHPM registers low thermal gradients and deep subduction of continental crust during the early stage of the collision process in Phanerozoic subduction-to-collision orogens. Although counterintuitive, many HPM-UHPM belts appear to have developed by closure of small ocean basins in the process of accretion of a continental terrane during a period of supercontinent introversion (Wilson cycle ocean basin opening and closing). A duality of metamorphic belts - reflecting a duality of thermal regimes - appears in the record only since the Neoarchean Era. A duality of thermal regimes is the hallmark of modern plate tectonics and the duality of metamorphic belts is the characteristic imprint of plate tectonics in the rock record. The occurrence of both G- UHTM and E-HPGM belts since the Neoarchean manifests the onset of a `Proterozoic plate tectonics regime', although the style of tectonics likely involved differences from modern Earth. Although the style of Proterozoic subduction remains cryptic, the change in tectonic regime whereby interactions between discrete lithospheric plates generated tectonic settings with contrasting thermal regimes was a landmark event in Earth history. The `Proterozoic plate tectonics regime' evolved during a Neoproterozoic transition to the `modern plate tectonics regime' characterized by colder subduction, and subduction of continental crust deep into the mantle and its (partial) return from depths of up to 300 km, as chronicled by the appearance of blueschists and HPM-UHPM in the rock record.

Combined garnet and zircon geochronology and trace elements studies - constraints of the UHP-(U)HT evolution of Orlica-Śnieżnik Dome (NE Bohemian Massif).

NASA Astrophysics Data System (ADS)

Walczak, Katarzyna; Anczkiewicz, Robert; Szczepański, Jacek; Rubatto, Daniela

2017-04-01

The Orlica-Śnieżnik Dome (OSD), located on the NE margin of the Bohemian Massif, is predominantly composed of amphibolite-facies orthogneiss that contain bodies of HP and UHP eclogites and granulites. Numerous geochronological studies have been undertaken to constrain the timing of the ultra-high grade metamorphic event. Despite this, the exact timing of UHP-(U)HT conditions remain dubious (e.g. Brueckner et al., 1991; Anczkiewicz et al., 2007; Bröcker et al., 2009 & 2010). We have utilized garnet and zircon geochronology to provide time constraints on the evolution of the UHT-(U)HP rocks of the OSD. We have combined the ages with trace element analyses in garnet and zircon to better understand the significance of the obtained ages in petrological context. Lu-Hf grt-wr dating of peritectic garnet from two felsic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma, recording peak conditions of 2.7 GPa and 950°C (e.g. Ferrero et al., 2015). In situ U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 342.2 ± 3.4 Ma. HREE partitioning between garnet rim and metamorphic zircon indicate their growth in equilibrium, hence, the U-Pb zircon date constrains the terminal phase of garnet crystallization. Similar ages were obtained from two eclogite bodies from Międzygórze and Nowa Wieś localities; Lu-Hf (grt-cpx-wr) dating provided ages of 346.5 ± 2.4 and 348.1 ± 9.1 Ma for samples from Międzygórze and Nowa Wieś, respectively. The same age (within error) of 346.3 ± 5.2 Ma was reported by Bröcker et al. (2010) for zircon from the Międzygórze eclogite. Comparison of REE concentrations in garnet (this study) and in metamorphic zircon (reported in Bröcker et al., 2010) indicate that garnet and zircon crystallized in equilibrium. Furthermore, M-HREE patterns observed in both garnet and zircon strongly suggest their growth at eclogite facies conditions. Sm-Nd garnet ages obtained for both felsic and mafic granulites and eclogites are identical within error and are consistently younger than corresponding Lu-Hf dates. Sm-Nd grt-wr ages of two samples of felsic granulite provide 332.4 ± 5.2 and 337.6 ± 2.3 Ma, while Sm-Nd grt-cpx age of a mafic granulite provides 336.9 ± 6.0 Ma. Sm-Nd grt-cpx(-wr) ages obtained for three eclogite samples range from 336.2 ± 3.5 to 337.7 ± 2.6 Ma. The foregoing ages are interpreted to reflect cooling through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the evolution of the OSD, characterized by two distinct periods: (1) nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites at 347-342 Ma, and (2) fast, nearly isobaric cooling at 342 - 337 Ma, becoming very rapid towards the end of this period. Anczkiewicz, R. et al. 2007. Lithos, 95, 363-380. Bröcker , M. et al. 2009. Journal of Metamorphic Geology, 27, 385-403. Bröcker, M. et al. 2010. Geological Magazine, 147(3), 339-362. Brueckner, H. K. et al. 1991. Neues Jahrb Mineral Abh, 63, 169-193. Ferrero S. et al. 2015. Geology, 43, 447-450.

The systematic change of metamorphism along the Dabie-Sulu-Hongseong-Odesan collision belt between the North and South China blocks

NASA Astrophysics Data System (ADS)

Oh, C. W.

2013-12-01

As a last step of formation of the Pangea supercontinent, the North China block collided with the South China block during Permo-Triassic time forming the Oinling-Dabie-Sulu collision belt which was identified by the finding of ultrahigh- and high-P/T eclogites along the belt. After the Qiling-Dabie-Sulu collision belt was found, the continuation of the collision belt into Korean Peninsula became a hot issue. Although the Imjingang belt in Korean Peninsula was suggested as an extension of the belt, no evidence of collision belt such as eclogite and ophiolite, was found. Whereas recent studies on Korean Peninsula reveal that Triassic eclogite (ca. > 230 Ma) formed in the Hongseong area and Triassic post collision igneous rocks (with ca. 230 Ma intrusion ages) occurred throughout the Gyeonggi Massif locating to the north of the line connecting the Hongseong, Yangpyeong and Odesan areas. These new findings derive the tectonic model in which the Permo-Triassic Qinling-Dabie-Sulu collision belt between the North and South China blocks extends into the Hongseong-Yangpyeong-Odesan collision belt in Korean Peninsula. The belt may be further extended into the late Paleozoic subduction complex in the Yanji belt in North Korea through the Paleozoic subduction complex in the inner part of SW Japan. The collision had started from Korea at ca. 250 Ma and propagated towards China. The collision completed during late Triassic. The metamorphic conditions systematically change along the collision belt; ultrahigh-temperature metamorphism occurred in the Odesan area (at 245-230Ma; 9.0-10.6 kbar, 915-1160°C), high-P/T metamorphism in the Hongseong area (17.0-21.9 kbar, 835-860°C) and ultrahigh-pressure metamorphism in the Dabie and Sulu belts (30-40 kbar, 680-880°C). This systematic increasing peak pressure condition and decreasing peak temperature condition towards west, may be due to the increase in the depth of slab break-off towards west, which might be related to the increase of the amounts of subducted ocecnic slab towards west. The wide distribution of Permo-Triassic arc-related granitoids in the Yeongnam Massif, southern part of Korean Peninsula and in the southern part of the South China block, indicate the Permo-Triassic subduction along the southern boundary of the South China block which may be due to compression caused by the Permo-Triassic collision between the North and South China blocks. The collision belt divides the Gyeonggi Massif into two parts; the northern and southern parts can be correlated to the North and South China blocks, respectively. The Ogcheon metamorphic belt which locates between the Gyeonggi and Youngnam Massifs in Korean Peninsula, can be correlated to the Nanhua rift which formed at 760 Ma and separated the South China blocks into the Yantze and Cathaysia cratons. In that case, the southern Gyeonggi Massif and Yeongnam Massif can be correlated to the Yangtze and Cathaysia cratons in the South China block, respectively. Recently Neoproterozoic igneous complex which was metamorphosed by the late Silurian intermediate-P/T and early Devonian ultrahigh temperature metamorphism, are recognized in the Hongseong area. These metamorphisms indicate the possibility of Middle Paleozoic collision of Neoproterozoic microcontinent with the northern margin of the South China block.

Diapir versus along-channel ascent of crustal material during plate convergence: constrained by the thermal structure of subduction zones

NASA Astrophysics Data System (ADS)

Liu, M. Q.; Li, Z. H.

2017-12-01

Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. The crustal rocks undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channel; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. Thick overriding continental plate and low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, thin overriding lithosphere and steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge. This may corresponds to the origination of continental arc volcanism from mafic to ultramafic metasomatites in the bottom of the mantle wedge. In addition, the plate convergence rate can also affect the material ascent mode, e.g., diapiric extrusion versus along-channel exhumation, by changing the amount of supracrustal rocks carried into the subduction channels, which further regulate the fluid/melt activity and thermo-rheological properties.

Metamorphic reprocessing of a serpentinized carbonate-bearing peridotite after detachment from the mantle wedge: A P-T path constrained from textures and phase diagrams in the system CaO-MgO-Al 2O 3-SiO 2-CO 2-H 2O

NASA Astrophysics Data System (ADS)

Mposkos, E.; Baziotis, I.; Proyer, A.

2010-08-01

In the central Rhodope mountains of Greece a carbonate-bearing metaperidotite lens ˜ 200 × 500 m in size crops out as part of the high- to ultrahigh-pressure metamorphic Upper Sidironero Complex ˜ 500 m SE of the Gorgona Village, north of Xanthi town. It is composed primarily of coarse grained (3-20 mm in size) olivine and orthopyroxene, medium grained clinohumite and medium to fine grained tremolite, chlorite, dolomite, magnesite, talc, antigorite and various spinel phases. Whole-rock chemistry, mineral textures and compositions, and phase diagram calculations show that the metaperidotite was subjected to a prograde HP metamorphism, isofacial with the surrounding migmatitic gneisses, metapelites and amphibolites. The prograde character of metamorphism is demonstrated by inclusions of talc, antigorite, chlorite, dolomite, magnesite and Ti-clinohumite in ferrit-chromite, olivine, and orthopyroxene, as well as of olivine in orthopyroxene, and by the typical change in composition of zoned spinel minerals from ferrit-chromite in the core to chromian spinel at the rim. The prograde path is characterized by successive growth of amphibole, Ti-clinohumite, olivine and orthopyroxene, followed by the breakdown of Ti-clinohumite to olivine + Mg-ilmenite and of chlorite to olivine + spinel, probably during exhumation. The construction of a partial petrogenetic P- T grid in the system CaO-MgO-Al 2O 3-SiO 2-CO 2-H 2O (CMASCH) for Ca-poor ultramafic bulk compositions has proven highly useful for the reconstruction of the metamorphic evolution and a P- T path, indicating that the use of univariant reactions in mixed volatile systems is highly warranted. The P- T path is clearly constrained to pressures below 1.5-1.7 GPa by the absence of clinopyroxene. These pressures are slightly lower than those recorded in the closely associated Jurassic eclogites and much lower than those recorded in the diamond-bearing gneisses 5 km to the south in the same tectonic unit. The carbonate-bearing metaperidotite from Gorgona probably represents a fragment of the hydrated mantle wedge. This is indicated by the REE compositions which differ from those of ophiolitic peridotites and resemble those of spinel or garnet peridotites of sub-continental origin. The ultramafic slice was incorporated tectonically into the subduction channel, most likely by tectonic erosion in the Early Jurassic, but did not experience ultrahigh-pressure metamorphism like the nearby metapelites that exhumed along the same subduction channel.

Developments in Laser-Ablation Split-Stream Petrochronology

NASA Astrophysics Data System (ADS)

Kylander-Clark, Andrew R.

2017-04-01

One of the biggest challenges in assessing the timing and rates of petrogenesis and deformation is having the ability to match the age of a dated mineral to the conditions at which that mineral grew. This is especially challenging for high-temperature chonometers that can grow and remain stable over a wide range of pressures and temperatures. The development of the laser-ablation split-stream method has afforded the ability to rapidly aquire chemical and chronologic data that are directly linked; as such, timing and rates of processes are better constrained than before. Several examples are given within: 1) Zircon and monazite from a single, coesite-bearing sample from the Western Gneiss Region in western Norway record the entire 30+ Myr history of metamorphism during Caledonian orogenesis, from intial burial, through ultrahigh-pressure (UHP) conditions, and back to crustal levels. Early monazite ( 425 Ma) contains low concentrations of Sr and HREE, consistent with plagioclase and garnet stability during prograde metamorphism. 420-400 Ma ages from monazite (high Sr, increased Eu/Eu*, low HREE) and zircon (increased Eu/Eu*, low HREE) indicate the timing of HP conditions, and monazite with low Sr and high HREE indicates the breakdown of omphacite and garnet at 390 Ma. 2) Titanite is becoming more widely used as chronometer, primarly because laser ablation has made analysis more feasible. Nevertheless, dates produced from titanite can be difficult to interpret because titanite may alter more easily than zircon and monazite. LASS analyses of titanite, combined with X-ray maps and backscattered electron images provide insight into processes involved in growth, recrystallization and dissolution/reprecipitation, and allow us to better interpret ages and the geologic process that they represent. This study presents recrystallized titanite from metamorphic terranes as well as ocillatory-zoned titanite from igneous rocks, and suggests some possible processes that explain the TE/age trends. 3) Detrital zircons have long been used to investigate the location and geology of landforms in the past. By adding chemical information to the age data, a clearer history can be produced. Recent LASS data from Mesozoic sedimentary rocks indicate changes in chemistry of the Sierra Nevada-Peninsular Ranges batholith, as well and the exposure and erosion of distinct units (e.g., ophiolites) over discrete time periods. 4) Isotopic data retrieved in combination with age data across an orogeny or batholith can aid in the understanding of the areal and temporal evolution of both deformation and source rocks over time. This can be done with a number of petrochronometers: Hf in zircon, Nd in titanite and monazite, This study presents examples that show how significant advances can be made in understanding lithosphere evolution using this quick and efficient analytical technique.

Genesis of Ultra-High Pressure Garnet Pyroxenite in Orogenic Peridotites and its bearing on the Isotopic Chemical Heterogeneity in the Mantle Source of Oceanic Basalts

NASA Astrophysics Data System (ADS)

Varas Reus, María Isabel; Garrido, Carlos J.; Marchesi, Claudio; Bosch, Delphine; Hidas, Károly

2017-04-01

The genesis of ultra-high pressure (UHP) garnet pyroxenites in orogenic peridotite massifs and its implications on the formation of chemical heterogeneities in the mantle and on basalt petrogenesis are still not fully understood. Some UHP (diamond-bearing) garnet pyroxenites have isotopic, and major and trace element compositions similar to the recycled oceanic crustal component observed in oceanic basalts [1-6]. These pyroxenites hence provide an exceptional opportunity to investigate in situ the nature and scale of the Earth's mantle chemical heterogeneities. Here, we present an integrated geochemical study of UHP garnet pyroxenites from the Ronda (Betic Belt, S. Spain) and Beni Bousera (Rif Belt, N. Morocco) peridotite massifs. This investigation encompasses, in the same sample, bulk rock major and trace elements, as well as Sr-Nd-Pb-Hf isotopic analyses. According to their Al2O3 content, we classify UHP garnet pyroxenites into three groups that have distinct trace elements and Sr-Nd-Pb-Hf isotopic signatures. Group A pyroxenites (Al2O3: 15 - 17.5 wt. %) are characterized by low initial 87Sr/86Sr, relatively high 143Nd/144Nd, 206Pb/204Pb and 176Hf/177Hf ratios, and highly variable 207Pb/204Pb and 208Pb/204Pb ratios. Group B pyroxenites (Al2O3 < 14 wt. %) have isotopic signatures characterized by relatively high initial 87Sr/86Sr and low 143Nd/144Nd, 206Pb/204Pb and 176Hf/177Hf ratios. Group C pyroxenites (Al2O3 ˜ 15 wt. %) display relatively low initial 87Sr/86Sr and 206Pb/204Pb ratios, high 143Nd/144Nd and 176Hf/177Hf ratios, and 207Pb/204Pb and 208Pb/204Pb ratios similar to Group B pyroxenites. The major and trace element, and isotopic compositions of the studied Ronda and Beni Bousera UHP garnet pyroxenites lend support to the "Marble Cake Mantle" model [7] for the genesis of these pyroxenites. This model envisions the mantle source of oceanic basalts as a mélange of subducted, ancient oceanic crust —-represented by garnet pyroxenites in orogenic peridotites—- intimately mixed with peridotites by mantle convection. The present study reveals, however, that besides this exotic component of ancient recycled oceanic crust, the genesis of these pyroxenites requires a previously unnoticed component of recycled lower continental crust akin to the lower crustal section of the lithosphere where these UHP garnet pyroxenites now reside in. The results of this study provide a new recipe for the marble cake hypothesis for the genesis of UHP garnet pyroxenites in orogenic peridotites. Furthermore, it establishes a connection between the genesis of UHP pyroxenites, the composition of the continental crust and the generation of Earth's mantle heterogeneities. References: [1] Pearson, D. G., Davies, G. R. & Nixon, P. H. (1993). Geochemical constraints on the petrogenesis of diamond facies pyroxenites from the Beni Bousera peridotite massif, North Morocco. Journal of Petrology 34, 125-172. [2] Blichert-Toft, J., Albarède, F. & Kornprobst, J. (1999). Lu-Hf Isotope systematics of garnet pyroxenites from Beni Bousera, Morocco: implications for basalt origin. Science 283, 1303-1306. [3] Garrido, C. J. & Bodinier, J. L. (1999). Diversity of mafic rocks in the Ronda peridotite: Evidence for pervasive melt-rock reaction during heating of subcontinental lithosphere by upwelling asthenosphere. Journal of Petrology 40, 729-754. [4] Marchesi, C., Garrido, C.J., Bosch, D., Bodinier, J.-L., Gervilla, F., Hidas, K., 2013. Mantle refertilization by melts of crustal-derived garnet pyroxenite: Evidence from the Ronda peridotite massif, southern Spain. Earth and Planetary Science Letters 362, 66-75. doi: 10.1016/j.epsl.2012.11.047. [5] Marchesi, C., Dale, C.W., Garrido, C.J., Pearson, D.G., Bosch, D., Bodinier, J.-L., Gervilla, F., Hidas, K., 2014. Fractionation of highly siderophile elements in refertilized mantle: Implications for the Os isotope composition of basalts. Earth and Planetary Science Letters 400, 33-44. doi: 10.1016/j.epsl.2014.05.025 [6] Montanini, A. & Tribuzio, R. (2015). Evolution of recycled crust within the mantle: Constraints from the garnet pyroxenites of the External Ligurian ophiolites (northern Apennines, Italy). Geology 43, 911-914. [7] Allègre, C. J. & Turcotte, D. L. (1986). Implications of a two-component marble-cake mantle. Nature 323, 123-127.

Metamorphic and tectonic evolution of Ceuta peninsula (Internal Rif): new interpretation in the framework of arc and back arc evolution

NASA Astrophysics Data System (ADS)

Homonnay, Emmanuelle; Lardeaux, Jean-Marc; Corsini, Michel; Cenki-Tok, Bénédicte; Bosch, Delphine; Munch, Philippe; Romagny, Adrien; Ouazzani-Touhami, Mohamed

2016-04-01

In the last twenty years, various geophysical investigations have established that the Western Mediterranean opened in a subduction context as a back arc domain. In the Alboran basin the dip of the subduction plane is eastwards or southeastwards depending of considered models. If the geological records of back-arc opening are well-known, the arc-related tectonic and petrologic evolutions are still poorly documented. In order to decipher these markers, we focalised structural, petrological and thermo-chronological studies on the Ceuta peninsula located in the Rif belt, on the western part of the Gibraltar arc to the North of Morocco. The present-day tectonic pile is constituted by: (1) the upper Ceuta unit, composed of High Pressure and High Temperature metapelites retromorphosed under Amphibolite-facies condition, with Ultra-High Pressure relicts, and pyrigarnite and spinel bearing peridotites boudins at its base, (2) the lower Monte Hacho unit, with orthogneisses metamorphosed under Amphibolite-facies conditions. Structural analysis indicates a polyphase tectonic evolution: (1) an earlier deformation phase only observed in the UHP metapelites and characterized by a steep S1 foliation plane, (2) a main deformation phase associated to a pervasive gently dipping S2 foliation plane bearing a L2 stretching lineation and synschistose folds whose axes are parallel to L2 and (3) a late deformation phase which developed S3 foliation plane and L3 stretching lineation coeval with development of narrow normal ductile shear zones. A zone of increasing deformation, several dozen meters wide, is identified as a major ductile shear zone involving the peridotitic lenses at the base of the metapelites of the Ceuta unit and overlaying this upper unit on top of the orthogneisses of the Monte Hacho lower unit. The attitude of mylonitic foliation and stretching and mineral lineations as well as the numerous shear sense indicators observed in the shear zone are consistent with a thrusting toward the NE. Furthermore, biotite-sillimanite bearing S2 foliation affecting the whole of crustal rocks is contemporaneous with the movement on this main ductile thrusting. We combined garnet-biotite and GASP thermo-barometers with thermodynamic modelling (Theriak-Domino) in order to constrain pressure and temperature conditions of D2 and D3 tectono-metamorphic events. P-T conditions of D2 deformation are in the range 7-10kbar and 770-820°C and are compatible with syn-tectonic partial melting. D3 deformation event occurred at 1-7kbar and 400-550°C. These metamorphic conditions reflect abnormally high geothermal gradients during both shortening and thinning and are clearly compatible with the thermal evolution recognized in continental arcs. Preliminary U-Th-Pb (monazite, zircon and xenotime) and previous Ar39/Ar40 (micas) analyses, furnished similar ages around 21 Ma for D2 and D3 events, suggesting a very fast transition from arc to back-arc dynamics.

First occurrence of very low pressure ultra-high temperatures metamorphism in the Khondalite Belt, North China Craton.

NASA Astrophysics Data System (ADS)

Lobjoie, Cyril; Lin, Wei; Trap, Pierre; Goncalves, Philippe; Marquer, Didier

2016-04-01

This study report the first occurrence of very low pressure (<0.4GPa) ultra-high temperatures metamorphism within the Paleoproterozoic Khondalite Belt of the North China Craton. This high grade orogenic domain is mostly composed of garnet +/- spinel +/- sapphirine-bearing migmatites, numerous Grt-bearing granites and marbles. These rocks are intruded by numerous metric to kilometric mafic intrusions. Petrological analyses and phase equilibria diagram modeling were performed on garnet and spinel-bearing and olivine-bearing migmatites. Garnet and spinel-bearing migmatites show a quartz, ternary feldspar, garnet, biotite sillimanite and spinel main assemblage. Pseudosection diagram calculations give suprasolidus P-T conditions around ca. 0.7GPa for ca. 900°C that correspond to the peak temperature conditions. Thermometry using ternary feldspar thermometry gives temperatures estimations at ca. 950-1015°C for a pressure of 0.7GPa. The Olivine-bearing migmatite, located at the contact with a mafic intrusion, shows two main assemblages. The first assemblage that makes the rock matrix consists of a micrographic quartz and feldspar domains associated with biotite, sillimanite and spinel. The second assemblage appears within mm-scale pockets with a complex symplectitic texture. Careful investigation revealed that theses pockets formed after garnet pseudomorphosis, with the development of an Opx-Sp-Crd association. Within this assemblage, an olivine-cordierite and Opx-Crd-Bi-Qtz assemblage occurred as smaller pockets. The petrogenetic grid and pseudosection calculations made for this olivine-bearing migmatite give P-T conditions around 0.35GPa for ca. 950°C that correspond to the peak temperature conditions recorded by the olivine-cordierite assemblage. The succession of reactions with garnet pseudomorphosis into an Opx-Spl-Crd followed by the crystallization of an Ol-Crd assemblage is modelled in the petrogenetic grid calculation and correspond to an isobaric clockwise P-T path. Results from in situ LA-ICP-MS U-Th-Pb dating on monazite performed on the Grt-Spl bearing migmatite suggest a duration of partial melting bracketed between ca. 1932Ma and ca. 1898Ma. Zircon U-Th-Pb SIMS dating yield an age of a ca.1.92-1.94 Ga for the olivine-bearing migmatite and the adjacent gabbroic bodies. This age is interpreted as the timing for the very low pressure UHT metamorphism. This first occurrence of very low pressure UHT metamorphism bring new insight for the understanding of the UHT Khondalite Belt. Implications about spatial and temporal distribution of heat and UHT metamorphism in the orogenic crust are discussed.

Cost-effectiveness analysis of alternative factor VIII products in treatment of haemophilia A.

PubMed

Hay, J W; Ernst, R L; Kessler, C M

1999-05-01

Manufactured factor VIII (FVIII) concentrates of varying purity are available for managing patients with haemophilia A. This study is a cost-effectiveness analysis of ultra-high purity and recombinant (UHP/R) FVIII products relative to intermediate and very-high purity (IP/VHP) preparations. Because the societal (including research and development) costs of FVIII products are unknown and product prices vary with market conditions, we conducted the analysis with treatment cost as a variable quantity. We estimated the largest price premium that could be paid for a UHP/R concentrate relative to an IP/VHP concentrate such that the UHP/R product is the more cost-effective preparation. In the analysis haemophilic patients were assumed to be seropositive for human immunodeficiency virus, seropositive for hepatitis C (HCV), or at risk for seroconversion of hepatitis A (HAV) or hepatitis B (HBV). The results showed that the maximum cost-effective UHP/R price premium is essentially zero if the patient is only at risk of HAV or HBV infection, positive but small for the base-case HCV+ patient, and positive and large for the base-case HIV+ patient having a short life expectancy. Thus UHP/R preparations are not uniformly more cost-effective than IP/VHP products across the spectrum of haemophilic patients' health problems, and the relative cost-effectiveness of the two classes of prepared FVIII products is sensitive to product prices. The methodology employed here can be used in other circumstances where multiple treatments exist for illnesses for which there are significant multiple comorbidities or health risks.

Post-peak metamorphic evolution of the Sumdo eclogite from the Lhasa terrane of southeast Tibet

NASA Astrophysics Data System (ADS)

Cao, Dadi; Cheng, Hao; Zhang, Lingmin; Wang, Ke

2017-08-01

A reconstruction of the pressure-temperature-time (P-T-t) path of high-pressure eclogite-facies rocks in subduction zones may reveal important information about the tectono-metamorphic processes that occur at great depths along the plate interface. The majority of studies have focused on prograde to peak metamorphism of these rocks, whereas after-peak metamorphism has received less attention. Herein, we present a detailed petrological, pseudosection modeling and radiometric dating study of a retrograded eclogite sample from the Sumdo ultrahigh pressure belt of the Lhasa terrane, Tibet. Mineral chemical variations, textural discontinuities and thermodynamic modeling suggest that the eclogite underwent an exhumation-heating period. Petrographic observations and phase equilibria modeling suggest that the garnet cores formed at the pressure peak (∼2.5 GPa and ∼520 °C) within the lawsonite eclogite-facies and garnet rims (∼1.5 GPa and <650 °C) grew during post-peak amphibole eclogite-facies metamorphism. The metamorphic evolution of the Sumdo eclogite is characterized by a clockwise P-T path with a heating stage during early exhumation, a finding that conflicts with previously reported heating-compression P-T paths for the Sumdo eclogite. A garnet-whole rock Lu-Hf age of 266.6 ± 0.7 Ma, which is consistent with the loosely constrained zircon U-Pb age of 261 ± 15 Ma within uncertainty, was obtained for the sample. The peak metamorphic temperature of the sample is lower than the Lu-Hf closure temperature of garnet, which combined with the general core-to-rim decrease in the Mn and Lu concentrations and the occurrence of a second maximum Lu peak in the inner rim, is consistent with the Lu-Hf system skewing to the age of the garnet inner rim. Thus the Lu-Hf age likely reflects late eclogite-facies metamorphism. The new U-Pb and Lu-Hf ages, together with previously published radiometric dating results, suggest that the overall growth of garnet spans an interval of ∼7 million years, which is a minimum estimate of the duration of the eclogite-facies metamorphism of the Sumdo eclogite.

Kinetics of the coesite to quartz transformation

USGS Publications Warehouse

Mosenfelder, J.L.; Bohlen, S.R.

1997-01-01

The survival of coesite in ultrahigh-pressure (UHP) rocks has important implications for the exhumation of subducted crustal rocks. We have conducted experiments to study the mechanism and rate of the coesite ??? quartz transformation using polycrystalline coesite aggregates, fabricated by devitrifying silica glass cylinders containing 2850H/106 Si at 1000??C and 3.6 GPa for 24h. Conditions were adjusted following synthesis to transform the samples at 700-1000??C at pressures 190-410 MPa below the quartz-coesite equilibrium boundary. Reaction proceeds via grain-boundary nucleation and interface-controlled growth, with characteristic reaction textures remarkably similar to those seen in natural UHP rocks. We infer that the experimental reaction mechanism is identical to that in nature, a prerequisite for reliable extrapolation of the rate data. Growth rates obtained by direct measurement differ by up to two orders of magnitude from those estimated by fitting a rate equation to the transformation-time data. Fitting the rates to Turnbull's equation for growth therefore yields two distinct sets of parameters with similar activation energies (242 or 269 kJ/mol) but significantly different pre-exponential constants. Extrapolation based on either set of growth rates suggests that coesite should not be preserved on geologic time scales if it reaches the quartz stability field at temperatures above 375-400??C. The survival of coesite has previously been linked to its inclusion in strong phases, such as garnet, that can sustain a high internal pressure during decompression. Other factors that may play a crucial role in preservation are low fluid availability - possibly even less than that of our nominally "dry" experiments - and the development of transformation stress, which inhibits nucleation and growth. These issues are discussed in the context of our experiments as well as recent observations from natural rocks. ?? 1997 Elsevier Science B.V.

The Chemical Behavior of Fluids Released during Deep Subduction Based on Fluid Inclusions

NASA Astrophysics Data System (ADS)

Frezzotti, M. L.; Ferrando, S.

2014-12-01

We present a review of current research on fluid inclusions in (HP-) UHP metamorphic rocks that, combined with existing experimental research and thermodynamic models, allow us to investigate the chemical and physical properties of fluids released during deep subduction, their solvent and element transport capacity, and the subsequent implications for the element recycling in the mantle wedge. An impressive number of fluid inclusion studies indicate three main populations of fluid inclusions in HP and UHP metamorphic rocks: i) aqueous and/or non-polar gaseous fluid inclusions (FI), ii) multiphase solid inclusions (MSI), and iii) melt inclusions (MI). Chemical data from preserved fluid inclusions in rocks match with and implement "model" fluids by experiments and thermodynamics, revealing a continuity behind the extreme variations of physico-chemical properties of subduction-zone fluids. From fore-arc to sub-arc depths, fluids released by progressive devolatilization reactions from slab lithologies change from relatively diluted chloride-bearing aqueous solutions (± N2), mainly influenced by halide ligands, to (alkali) aluminosilicate-rich aqueous fluids, in which polymerization probably governs the solubility and transport of major (e.g., Si and Al) and trace elements (including C). Fluid inclusion data implement the petrological models explaining deep volatile liberation in subduction zones, and their flux into the mantle wedge.

An exotic terrane in the Sulu UHP region, China

NASA Astrophysics Data System (ADS)

Chu, W.; Zhang, R.; Tsujimori, T.; Liou, J. G.

2004-12-01

The Haiyangsuo region of about 15 km2 along the coast in the NE part of the Triassic Sulu UHP terrane occurs three major rock types: amphibolitized metagabbro, gneiss and granitic dikes. Three different gneisses were observed in the field: A) Light color felsic gneiss is the dominant country rock and contains Qtz, Pl, Ms and Bi. B) Dark color plagioclase-amphibole gneiss occurs as thin layers within country rock; C) Granulite facies rock occurs as discontinuous lens. The amphibolitized metagabbros intrude into the gneisses as massive bodies (several m to hundreds of m in size) and thin dikes. Both metamorphic intrusives and gneisses are cross-cut by granitic dikes. The amphibolitized metagabbro was divided into three types: coronal metagabbro, transitional rock and garnet amphibolite: 1) Coronal metagabbro preserves gabbroic texture and primary assemblage of Opx+Cpx+Pl+Amp+Ilm. Most pyroxene grains are partially rimmed by thin corona of Amp+Ab+Qtz. Garnet occurs as fine-grained coronas at interface between plagioclase, pyroxene or ilmenite. 2) Transitional rocks contain similar assemblage and texture but most orthopyroxenes were partially or totally replaced by Amp+Qtz; garnet increases in content and size. Some gabbroic textures are preserved, but calcic plagioclase was replaced by zoisite, albite and muscovite. 3) Garnet amphibolite occurs at the margins of intrusive bodies and boudins where only minor relict clinopyroxenes preserve. Garnet coronal chains are not clear any more. Granitic dikes show pronounced deformation with mylonitic texture and contain 40-50% quartz porphyroclasts. Zircon separates from 2 metagabbros, 4 gneisses and 1 granitic rock were dated by using Stanford SHRIMP-RG. Metagabbroic zircons are angular and fractured shapes. The upper-intercept ages of gneisses rang from 1730 to about 2400 Ma, indicating variable protoith age. The 2 garnet amphibolites have upper-intercept ages 1734±5Ma and 1735±21Ma respectively. They are much older than the protolith ages (680-850 Ma) of the Sulu eclogite and country rock. At least two possible metamorphic events are indicated by the lower-intercept ages. One metagabbroic rock has a lower-intercept age of 842±37 Ma; this records a garnet amphibolite metamorphic event. One gneiss and one metagabbroic rock yield lower-intercept ages of about 340±25 Ma, suggesting a second metamorphic event. The granitic dike has upper-intercept age 749±43 Ma and lower-intercept age 150±17 Ma. All these petrological and geochronological results indicate that the Haiyangsuo region is not part of the Triassic Sulu UHP terrane.

Tectonic overpressure may reconcile the structural and petrological records of the Adula nappe (Central Alps)

NASA Astrophysics Data System (ADS)

Pleuger, Jan; Podladchikov, Yuri

2014-05-01

The Penninic Alps are the result of progressive underthrusting of oceanic and continental domains below the Adriatic microplate. Situated in the internal part of the Alpine orogen, they expose basement and thinned cover nappes which have been metamorphosed to variable degree, among them several units which were subjected to ultrahigh-pressure metamorphism. Due to the more or less strong nappe-internal deformation of these units, cross sections through the Penninic Alps cannot be restored kinematically by area or line balancing techniques. Instead, such restorations attempt to consistently reconcile geochronological and structural data and petrological pressure-temperature estimates. Pressure data are usually converted into depth assuming that they were lithostatic which puts the ultrahigh-pressure units to subcrustal depths. Tectonic exhumation of a unit from such a depth by whatever mechanism requires a large-scale normal fault with several tens of kilometres of displacement in the hanging wall of the unit. However, for all Penninic ultrahigh-pressure units (Dora Maira unit, Zermatt-Saas zone, Monviso unit, Adula-Cima Lunga nappe), the oldest mappable post-peak-pressure structures are related to top-to-the-foreland shearing, i.e. thrusting. There are two potential solutions to this dilemma. The first one is that either the exhumation was indeed accommodated by a large-scale normal fault which became completely overprinted during later deformational stages. The other one is that peak pressures were not lithostatic. To our knowledge, the first solution is applied to all kinematic models of the Alps so far. In order to explore the feasibility of the second solution, we performed a purely structural restoration of the NFP20-East cross section without lithostatic pressure-to-depth-conversions. This cross-section comprises the ultrahigh-pressure Adula nappe (up to ca. 30 kbar) and relies on quantitative strain data from the overlying units. The result shows that, in accordance with the structural record, the Adula nappe can be restored to maximum depths of up to ca. 60 km. For individual points of the Adula nappe in the restored cross section, corresponding to the sporadic occurences of (ultra)high-pressure rocks, lithostatic pressures are exceeded by petrological peak-pressure data by about 40% to 80%. Such amounts of tectonic overpressure are within the limits of theoretical considerations and numerical modelling results. For the other units comprised in the cross section, and for subsequent tectono-metamorphic stages of the Adula nappe, negligible amounts of overpressure (around 10%) are determined from the restoration. We conclude that (1) the NFP20-East cross section can be kinematically restored by using only structural data, (2) the dilemma mentioned above can be solved by admitting realisting amounts of tectonic overpressure, and (3) significant amounts of overpressure were established only locally and episodically.

From an active continental plate margin to continental collision: New constraints from the petrological, structural and geochronological record of the (ultra) high-P metamorphic Rhodope domain (N-Greece)

NASA Astrophysics Data System (ADS)

Mposkos, E.; Krohe, A.; Wawrzenitz, N.; Romer, R. L.

2012-04-01

The Rhodope domain occupies a key area along the suture between the European and the Apulian/Adriatic plate (Schmid et al., 2008), which collided in the early Tertiary (closure of the Vardar/Axios ocean, cf. Mposkos & Krohe, 2006). An integrated study of the geochronological, tectonic and petrological data of the Rhodope domain provides the unique opportunity resolving a 160 my lasting metamorphic evolution (Jurassic to Miocene) of an active plate margin to a high degree. The Greek Rhodope consists of several composite metamorphic complexes bounded by the Nestos thrust and several normal detachment systems. The PT- and structural records of the complexes constrain metamorphic, magmatic and tectonic processes, associated with subduction along a convergent plate margin including UHP metamorphism, MP to HP metamorphism associated with continental collision, and core complex formation linked to Aegean back arc extension. We focus on the Sidironero Complex that shows a polymetamorphic history. This is documented by SHRIMP and LA-ICP-MS U-Pb zircon ages of ca. 150 Ma from garnet-kyanite gneisses that are interpreted to record the HP/UHP metamorphism (Liati, 2005; Krenn et al., 2010). SHRIMP zircon ages of ca. 51 Ma from an amphibolitized eclogite is interpreted by Liati (2005) to record a second Eocene HP metamorphic event. We present new data from an integrated petrological, geochronological and tectonic study. Granulite facies and upper amphibolite facies metamorphic conditions are recorded by the mineral assemblage Grt-Ky-Bt-Pl-Kfs-Qtz-Rt and Grt-Ky-Bt-Ms-Pl-Qtz-Rt, respectively, in deformed migmatitic metapelites. Deformation occurred under granulite facies conditions. Monazites from the matrix, that formed during the granulite facies deformation, lack core/rim structures and are only locally patchy zoned. Monazite chemical compositions are related to varying reaction partners. Single grains and fractions of few grains yield ID-TIMS U-Pb ages that plot along the concordia between 64 to 60 Ma. One date of 55 Ma might represent Pb-loss during later fluid-induced dissolution-reprecipitation. We discuss the following questions: What is the history of the high-P metamorphic rocks in the Sidironero Complex? Were high-P rocks that have been already exhumed again dragged into the subduction channel? Which rocks from the upper plate are affected by high-P metamorphism evincing that subduction erosion is an important mechanism? We reconsider the significance of the P-T-t evolution in the light of the tectonic processes that took place along the depth extension of a convergent plate interface and during subsequent continental collision along the European/Apulian Suture zone. Krenn et al., 2010. Tectonics 29, TC4001. Liati, A., 2005. Contribution to Mineralogy and Petrology 150, 608-630. Mposkos, E. & Krohe, A. 2006. Canadian Journal of Earth Sciences 43, 1755-1776. Schmid S.M., et al. 2008. Swiss Journal of Geoscience 101, 139-183.

Geochemical and geochronological constraints on the origin and evolution of rocks in the active Woodlark Rift of Papua New Guinea

NASA Astrophysics Data System (ADS)

Zirakparvar, Nasser Alexander

Tectonically active regions provide important natural laboratories to glean information that is applicable to developing a better understanding of the geologic record. One such area of the World is Papua New Guinea, much of which is situated in an active and transient plate boundary zone. The focus of this PhD research is to develop a better understanding of rocks in the active Woodlark Rift, situated in Papua New Guinea's southernmost reaches. In this region, rifting and lithospheric rupture is occurring within a former subduction complex where there is a history of continental subduction and (U)HP metamorphism. The lithostratigraphic units exposed in the Woodlark Rift provide an opportunity to better understand the records of plate boundary processes at many scales from micron-sized domains within individual minerals to regional geological relationships. This thesis is composed of three chapters that are independent of one another but are all related to the overall goal of developing a better understanding of the record of plate boundary processes in the rocks currently exposed in the Woodlark Rift. The first chapter, published in its entirety in Earth and Planetary Science Letters (2011 v. 309, p. 56 - 66), is entitled 'Lu-Hf garnet geochronology applied to plate boundary zones: Insights from the (U)HP terrane exhumed within the Woodlark Rift'. This chapter focuses on the use of the Lu-Hf isotopic system to date garnets in the Woodlark Rift. Major findings of this study are that some of the rocks in the Woodlark Rift preserve a Lu-Hf garnet isotopic record of initial metamorphism and continental subduction occurring in the Late Mesozoic, whereas others only preserve a record of tectonic processes related to lithospheric rupture during the initiation of rifting in the Late Cenozoic. The second chapter is entitled 'Geochemical and geochronological constraints on the origin of rocks in the active Woodlark Rift of Papua New Guinea: Recognizing the dispersed fragments of an active margin'. This chapter uses a panoply of geochronological (U-Pb zircon) and geochemical (Lu-Hf and Sm-Nd isotopes, trace/REEs, and major elements) tools to investigate the origin the major lithostratigraphic units in the Woodlark Rift. Important findings in this chapter include the establishment of a tectonic link between sialic metamorphic rocks in the Woodlark Rift and the remnants of a Late Cretaceous aged bi-modal volcanic province along Australia's northern Queensland coast. This link is important because it identifies another rifted fragment of the former Australian continental margin in Gondwana, and demonstrates the complexity of recognizing the dispersed fragments of active margins. Another important finding of this chapter is that Quaternary aged high silica rhyolites erupted in the western Woodlark Rift have mantle isotopic and geochemical signatures, and are therefore not the extrusive equivalents of partially melted metamorphic rocks found in the lower plates of large metamorphic core complexes. This is important because it signifies that lithospheric rupture has already occurred, despite the fact that mid-ocean ridge basalts are not yet being erupted and there are still topographically prominent metamorphic core complexes in the region. This chapter is not yet published, but is being prepared for submission to Gondwana Research. The third chapter is entitled 'Zircon growth in rapidly evolving plate boundary zones: Evidence from the active Woodlark Rift of Papua New Guinea'. The original purpose of this chapter was simply to use U-Pb dating of zircons from felsic and intermediate gneisses in the Woodlark Rift to understand the history of rocks from (U)HP terranes that don't preserve the (U)HP metamorphic paragenesis. It was soon realized that the types of U-Pb zircon analyses typically performed on a SIMS instrument were going to be insufficient to fully understand the geochemical and geochronological records within zircons from these rocks. Because of this, traditional SIMS analyses for zircons from these rocks are augmented by U-Pb age and elemental depth profiles that elucidate the isotopic and geochemical nature of the sharp boundaries between different aged domains in these polygenetic zircons. The results presented in this chapter demonstrate that zircon U-Pb ages record specific plate boundary events that can be related to the development of the Woodlark Rift, and that traditional assumptions regarding geochemical equilibrium might not hold true in all situations.

Structural styles and zircon ages of the South Tianshan accretionary complex, Atbashi Ridge, Kyrgyzstan: Insights for the anatomy of ocean plate stratigraphy and accretionary processes

NASA Astrophysics Data System (ADS)

Sang, Miao; Xiao, Wenjiao; Orozbaev, Rustam; Bakirov, Apas; Sakiev, Kadyrbek; Pak, Nikolay; Ivleva, Elena; Zhou, Kefa; Ao, Songjian; Qiao, Qingqing; Zhang, Zhixin

2018-03-01

The anatomy of an ancient accretionary complex has a significance for a better understanding of the tectonic processes of accretionary orogens and complex because of its complicated compositions and strong deformation. With a thorough structural and geochronological study of a fossil accretionary complex in the Atbashi Ridge, South Tianshan (Kyrgyzstan), we analyze the structure and architecture of ocean plate stratigraphy in the western Central Asian Orogenic Belt. The architecture of the Atbashi accretionary complex is subdivisible into four lithotectonic assemblages, some of which are mélanges with "block-in-matrix" structure: (1) North Ophiolitic Mélange; (2) High-pressure (HP)/Ultra-high-pressure (UHP) Metamorphic Assemblage; (3) Coherent & Mélange Assemblage; and (4) South Ophiolitic Mélange. Relationships between main units are tectonic contacts presented by faults. The major structures and lithostratigraphy of these units are thrust-fold nappes, thrusted duplexes, and imbricated ocean plate stratigraphy. All these rock units are complicatedly stacked in 3-D with the HP/UHP rocks being obliquely southwestward extruded. Detrital zircon ages of meta-sediments provide robust constraints on their provenance from the Ili-Central Tianshan Arc. The isotopic ages of the youngest components of the four units are Late Permian, Early-Middle Triassic, Early Carboniferous, and Early Triassic, respectively. We present a new tectonic model of the South Tianshan; a general northward subduction polarity led to final closure of the South Tianshan Ocean in the End-Permian to Late Triassic. These results help to resolve the long-standing controversy regarding the subduction polarity and the timing of the final closure of the South Tianshan Ocean. Finally, our work sheds lights on the use of ocean plate stratigraphy in the analysis of the tectonic evolution of accretionary orogens.

Eclogitization on the way up: Lu-Hf garnet chronology of metasomatic ultrahigh-pressure rocks from the Western Gneiss Complex, Norway

NASA Astrophysics Data System (ADS)

Cutts, J.; Smit, M. A.; Vrijmoed, J. C.

2016-12-01

The Western Gneiss Complex (WGC) is a fragment of continental crust that was subjected to high- and ultrahigh pressure (HP; UHP) conditions as a result of Caledonian continental collision (420-400 Ma). Most eclogite lenses and related high-pressure rocks have yielded petrological and chronological results that are consistent with a generalized model of Caledonian continental subduction. A distinct suite of eclogitic rocks - metasomatized (`Caledonized') Fe-Ti meta-peridotites - indicate extreme pressure conditions that do not fit the regional field gradient. The timing of these excursions is critical to their interpretation; however, so far limited age constraints exist for these rocks. In this study, we subject one such rock - the Magerøy orthopyroxene eclogite on the island of Otrøy - to Lu-Hf garnet chronology; a method that provides precise and robust data for garnet even at extreme temperatures. Conventional barometry indicates equilibration of the main garnet-bearing assemblage at c. 4.3 GPa and garnet geochronology yielded a date of c. 390 Ma. This result overlaps with Sm-Nd garnet and U-Pb zircon ages from the nearby diamond-bearing Svartberget peridotite body and leucosomes in its host gneiss. However, the age is ≥ 10 Ma younger than age data for most other eclogite lenses in WGC and corresponds to a time when the terrane was already exhumed to 30-35 km depth. The discrepancy in P-T-t evolution between the bulk of the WGC, and the (ultra-) mafic rocks at Magerøy and Svartberget indicates that the latter rocks reflect localized fluid-induced re-equilibration at pressures higher than lithostatic. The new data provide new support for the occurrence of this phenomenon in subducted continental crust undergoing exhumation and partial melting.

Structural and metamorphic evolution of serpentinites and rodingites recycled in the Alpine subduction wedge

NASA Astrophysics Data System (ADS)

Zanoni, D.; Rebay, G.; Spalla, M. I.

2015-12-01

Hydration-dehydration of mantle rocks affects the viscosity of the mantle wedge and plays a prominent role in subduction zone tectonics, facilitating marble cake-type instead of large-slice dynamics. An accurate structural and petrologic investigation of serpentinites from orogenic belts, supported by their long-lived structural memory, can help to recognize pressure-sensitive mineral assemblages for deciphering their P-prograde and -retrograde tectonic trajectories. The European Alps preserve large volumes of the hydrated upper part of the oceanic lithosphere that represents the main water carrier into the Alpine subduction zone. Therefore, it is important to understand what happens during subduction when these rocks reach P-T conditions proximal to those that trigger the break-down of serpentine, formed during oceanic metamorphism, to produce olivine and clinopyroxene. Rodingites associated with serpentinites are usually derived from metasomatic ocean floor processes but rodingitization can also happen in subduction environments. Multiscale structural and petrologic analyses of serpentinites and enclosed rodingites have been combined to define the HP mineral assemblages in the Zermatt-Saas ophiolites. They record 3 syn-metamorphic stages of ductile deformation during the Alpine cycle, following the ocean floor history that is testified by structural and metamorphic relics in both rock types. D1 and D2 developed under HP to UHP conditions and D3 under lower P conditions. Syn-D2 assemblages in serpentinites and rodingites indicate conditions of 2.5 ± 0.3 GPa and 600 ± 20°C. This interdisciplinary approach shows that the dominant structural and metamorphic imprint of the Zermatt-Saas eclogitized serpentinites and rodingites developed during the Alpine subduction and that subduction-related serpentinite de-hydration occurred exclusively at Pmax conditions, during D2 deformation. In contrast, in the favourable rodingite bulk composition (Ca-rich), hydrated minerals such as vesuvianite are stable up to the estimated P-climax conditions.

Diapir versus along-channel ascent of crustal material during plate convergence: Constrained by the thermal structure of subduction zones

NASA Astrophysics Data System (ADS)

Liu, Ming-Qi; Li, Zhong-Hai; Yang, Shao-Hua

2017-09-01

Subduction channel processes are crucial for understanding the material and energy exchange between the Earth's crust and mantle. Crustal rocks can be subducted to mantle depths, interact with the mantle wedge, and then exhume to the crustal depth again, which is generally considered as the mechanism for the formation of ultrahigh-pressure metamorphic rocks in nature. In addition, the crustal rocks generally undergo dehydration and melting at subarc depths, giving rise to fluids that metasomatize and weaken the overlying mantle wedge. There are generally two ways for the material ascent from subarc depths: one is along subduction channels; the other is through the mantle wedge by diapir. In order to study the conditions and dynamics of these contrasting material ascent modes, systematic petrological-thermo-mechanical numerical models are constructed with variable thicknesses of the overriding and subducting continental plates, ages of the subducting oceanic plate, as well as the plate convergence rates. The model results suggest that the thermal structures of subduction zones control the thermal condition and fluid/melt activity at the slab-mantle interface in subcontinental subduction channels, which further strongly affect the material transportation and ascent mode. The thick overriding continental plate and the low-angle subduction style induced by young subducting oceanic plate both contribute to the formation of relatively cold subduction channels with strong overriding mantle wedge, where the along-channel exhumation occurs exclusively to result in the exhumation of HP-UHP metamorphic rocks. In contrast, the thin overriding lithosphere and the steep subduction style induced by old subducting oceanic plate are the favorable conditions for hot subduction channels, which lead to significant hydration and metasomatism, melting and weakening of the overriding mantle wedge and thus cause the ascent of mantle wedge-derived melts by diapir through the mantle wedge. This may correspond to the origination of continental arc volcanism from mafic to ultramafic metasomatites in the bottom of the mantle wedge. In addition, the plate convergence rate can also affect the material ascent mode, e.g., diapiric extrusion versus along-channel exhumation, by changing the amount of supracrustal rocks carried into the subduction channels, which further regulate the fluid/melt activity and thermo-rheological properties.

Oxygen Fugacity Variation From Mantle Transition Zone To Ocean Ridges Recorded By In Situ Diamond-Bearing Peridotite Of Indus Ophiolite

NASA Astrophysics Data System (ADS)

Das, S.; Basu, A. R.

2017-12-01

Our recently discovered transition zone ( 410 - 660 Km) -derived peridotites in the Indus Ophiolite, Ladakh Himalaya [1] provide a unique opportunity to study changes in oxygen fugacity from shallow mantle beneath ocean ridges to mantle transition zone. We found in situ diamond, graphite pseudomorphs after diamond crystals, hydrocarbon (C - H) and hydrogen (H2) fluid inclusions in ultra-high pressure (UHP) peridotites that occur in the mantle - section of the Indus ophiolite and sourced from the mantle transition zone [2]. Diamond occurs as octahedral inclusion in orthoenstatite of one of these peridotites. The graphite pseudomorphs after diamond crystals and primary hydrocarbon (C-H), and hydrogen (H2) fluids are included in olivine of this rock. Hydrocarbon fluids are also present as inclusions in high pressure clinoenstatite (> 8 GPa). The association of primary hydrocarbon and hydrogen fluid inclusions in the UHP peridotites suggest that their source-environment was highly reduced at the base of the upper mantle. We suggest that during mantle upwelling beneath Neo Tethyan spreading center, the hydrocarbon fluid was oxidized and precipitated diamond. The smaller diamonds converted to graphite at shallower depth due to size, high temperature and elevated oxygen fugacity. This process explains how deep mantle upwelling can oxidize reduced fluid carried from the transition zone to produce H2O - CO2. The H2O - CO2 fluids induce deep melting in the source of the mid oceanic ridge basalts (MORB) that create the oceanic crust. References: [1] Das S, Mukherjee B K, Basu A R, Sen K, Geol Soc London, Sp 412, 271 - 286; 2015. [2] Das S, Basu A R, Mukherjee B K, Geology 45 (8), 755 - 758; 2017.

Surface structure of micro-diamond from ultrahigh-pressure felsic granulite, Bohemian Massif: AFM study of growth and resorption phenomena

NASA Astrophysics Data System (ADS)

Kotková, J.; Klapetek, P.

2012-04-01

Morphology, associated phases and retrogression phenomena of in-situ microdiamonds formed at extreme pressures in ultrahigh-pressure metamorphic terranes represent excellent tools to study character of diamond-forming media at great depths. Well-preserved microdiamonds discovered recently along with coesite in ultrahigh-pressure granulites of the north Bohemian crystalline basement, European Variscan belt (Kotková et al., 2011), provide unique material for such investigations. The diamonds are enclosed in major granulite phases, i.e. garnet both in felsic and intermediate lithologies and in kyanite in the felsic sample, as well as in zircon. Transmitted and reflected light microscopy of the felsic granulite sample, with peak mineral assemblage garnet, kyanite, feldspar and quartz, revealed presence of numerous, 5-20 μm-sized, perfectly preserved diamond crystals enclosed in kyanite grains. In contrast, diamonds within garnet are rare, can reach up to 30 μm in size, and graphite rims as well as polycrystalline graphite aggregates possibly representing complete diamond retrogression are common. We applied atomic force microscopy to study in-situ crystal morphology and surface microtopographic features, representing clues to the conditions and mechanisms of crystal formation as well as diamond resorption and retrogression. Both diamond enclosed in garnet and in kyanite of the felsic granulite occur exclusively as single crystals. The crystals have octahedral crystal shapes with straight but rounded edges and rounded corners. Concentric triangular terraces delimiting a flat triangular table on crystal scale and small micron-sized negatively oriented downward-pointing trigons developed on the octahedron crystal faces. Higher magnification reveals presence of discontinuous elongate hillocks oriented parallel to the octahedron face edge with positively oriented trigons. We suggest that the large-scale triangular terraces represent growth features. In contrast, the rounding of crystal edges and corners and development of negative trigons reflect diamond resorption. According to experimental works, such features are attributed to high temperature resorption, i.e. oxidation above ~ 950°C due to interaction with CO2 and/or H2O-bearing fluids (or fluid-bearing melts). Our results are consistent with presence of supercritical C-O-H fluid in the rocks in subduction zones documented from other ultrahigh-pressure metamorphic terranes, the resorption morphology corresponding rather to the interaction with water-rich than CO2-rich fluids. Kotková J., ÓBrien P., Ziemann M. (2011): Diamond and coesite discovered in Saxony-type granulite: Solution to the Variscan garnet peridotite enigma. Geology, 39, 7, 667-670.

Ediacaran 2,500-km-long synchronous deep continental subduction in the West Gondwana Orogen

NASA Astrophysics Data System (ADS)

Ganade de Araujo, Carlos E.; Rubatto, Daniela; Hermann, Joerg; Cordani, Umberto G.; Caby, Renaud; Basei, Miguel A. S.

2014-10-01

The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.

Development of Ultra-high Purity (UHP) Fe-Based Alloys with High Creep and Oxidation Resistance for A-USC Technology

NASA Astrophysics Data System (ADS)

Hamdani, Fethi; Das, Nishith K.; Shoji, Tetsuo

2018-06-01

The design of ultra-high purity (UHP) Fe-based model alloys for advanced ultra-supercritical (A-USC) technology is attempted in this work. Creep testing has been performed in air at 700 °C and a stress level of 150 MPa. Analysis of the fracture surface and cross section of the crept specimen was performed. To evaluate the oxidation resistance in A-USC conditions, oxidation testing was performed in supercritical water (SCW) at 700 °C and 25 MPa. Weight gain (WG) measurements and meticulous characterization of the oxide scale were carried out. Based on thermodynamics and density functional theory calculations, some reactive elements in the Fe-Cr-Ni system were designated to promote precipitation strengthening and to improve the hydrogen-accelerated oxidation resistance. The addition of a 2 wt pct Mo into Fe-22Cr-22Ni-0.6Nb wt pct-based matrix did not significantly improve the creep resistance. The addition of 0.26 wt pct Zr coupled with cold working was effective for improving creep properties. The Mo-modified model alloy showed almost the same WG value as SUS310, while the Zr-modified alloy showed a higher WG value. Meanwhile, a Cr-enriched continuous oxide layer was formed at the oxidation front of the Zr-modified alloy and SUS310S after exposure to SCW conditions.

Development of Ultra-high Purity (UHP) Fe-Based Alloys with High Creep and Oxidation Resistance for A-USC Technology

NASA Astrophysics Data System (ADS)

Hamdani, Fethi; Das, Nishith K.; Shoji, Tetsuo

2018-03-01

The design of ultra-high purity (UHP) Fe-based model alloys for advanced ultra-supercritical (A-USC) technology is attempted in this work. Creep testing has been performed in air at 700 °C and a stress level of 150 MPa. Analysis of the fracture surface and cross section of the crept specimen was performed. To evaluate the oxidation resistance in A-USC conditions, oxidation testing was performed in supercritical water (SCW) at 700 °C and 25 MPa. Weight gain (WG) measurements and meticulous characterization of the oxide scale were carried out. Based on thermodynamics and density functional theory calculations, some reactive elements in the Fe-Cr-Ni system were designated to promote precipitation strengthening and to improve the hydrogen-accelerated oxidation resistance. The addition of a 2 wt pct Mo into Fe-22Cr-22Ni-0.6Nb wt pct-based matrix did not significantly improve the creep resistance. The addition of 0.26 wt pct Zr coupled with cold working was effective for improving creep properties. The Mo-modified model alloy showed almost the same WG value as SUS310, while the Zr-modified alloy showed a higher WG value. Meanwhile, a Cr-enriched continuous oxide layer was formed at the oxidation front of the Zr-modified alloy and SUS310S after exposure to SCW conditions.

Raman spectroscopy of detrital garnet from the (U)HP terrane of eastern Papua New Guinea

NASA Astrophysics Data System (ADS)

Andò, Sergio; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Malusà, Marco G.; Aliatis, Irene; Vezzoli, Giovanni; Garzanti, Eduardo

2013-04-01

Garnet is one of the most widespread heavy minerals in sediments derived from orogenic systems. Its chemical composition varies systematically with temperature and pressure conditions, and thus provides information on the metamorphic evolution of source areas that is crucial in tectonic and geodynamic reconstructions. Garnet is easily identified in mineral grain mounts and is relatively stable during burial diagenesis. Raman spectroscopy allows rapid determination of garnet compositions in grain mounts or thin sections of sand and sandstone samples, and can be used to assess their density and chemical composition quite accurately ("MIRAGEM" method of Bersani et al., 2009; Andò et al., 2009). In the D'Entrecastreaux Islands of southeastern Papua New Guinea, the world's youngest (U)HP rocks are exposed. There, mafic rocks and their felsic host gneisses were metamorphosed under eclogite facies conditions from late Miocene to Pliocene, before being exhumed from depths of ~90 km (Baldwin et al., 2004, 2008). The eclogite preserves a peak assemblage of garnet, omphacite, rutile, phengite and Si02 (Hill and Baldwin, 1993). A coesite-eclogite has been found in one small island outcrop. In order to sample garnet populations representative of a larger geographical area, we sampled and studied a heavy-mineral-dominated placer sand (HMC 80) from a beach from SE Goodenough Island. Garnet grains in beach sand are associated with blue-green to subordinately green-brown amphibole and minor epidote, omphacitic clinopyroxene, titanite, apatite and rutile. The subordinate low-density fraction is feldspatho-quartzose with high-rank metamorphic rock fragments and biotite (Q62 F35 Lm2; MI 360). Detrital garnets are mostly classified as almandine with relatively high Mg and Ca and lacking Mn, typical of the eclogite facies (Win et al., 2007; type Ci garnets of Mange and Morton 2007; Andò et al., 2013). In well-described stratigraphic sequences within syn-and post-tectonic basins adjacent to orogenic systems, Raman-assisted heavy-mineral studies allow us to detect the first arrival of eclogitic garnet, and thus to assess the minimum age of exhumation and final unroofing of high-pressure rocks (Malusà et al., 2011; Malusà and Garzanti, 2012). However, in the (U)HP terrane of southeastern Papua New Guinea, sediments derived from the actively exhuming D'Entrecasteaux Island core complexes are still being deposited offshore, are rarely preserved sub-aerially, and as such stratigraphic constraints are limited. Raman analysis of detrital garnets from placer sand thus provides invaluable constraints to compare with mineral assemblages preserved in exhumed eclogites. REFERENCES Andò S., Bersani D., Vignola P., Garzanti E. 2009. Raman spectroscopy as an effective tool for high-resolution heavy-mineral analysis: Examples from major Himalayan and Alpine fluvio-deltaic systems. Spectrochim. Acta A73:450-455. Andò S., Morton A., Garzanti E. 2013. Metamorphic grade of source rocks revealed by chemical fingerprints of detrital amphibole and garnet. Geol. Soc. London Spec. Publ. Sediment Provenance Studies in Hydrocarbon Exploration & Production. Baldwin S.L., Monteleone B., Webb L.E., Fitzgerald P.G., Grove M., Hill E.J. 2004. Pliocene eclogite exhumation at plate tectonic rates in eastern Papua New Guinea. Nature 431:263-267. Baldwin S.L., Webb L.E., Monteleone B.D. 2008. Late Miocene coesite-eclogite exhumed in the Woodlark Rift. Geology 36:735-738 Bersani D., Andò S., Vignola P., Moltifiori G., Marino I.G., Lottici P.P., Diella V., 2009. Micro-Raman spectroscopy as a routine tool for garnet analysis. Spectrochim. Acta A73:484-491. Hill E.J., Baldwin S.L. 1993. Exhumation of high-pressure metamorphic rocks during crustal extension in the D'Entrecasteaux region, Papua New Guinea. J. Metam. Geol. 11:261-277. Malusà M.G., Faccenna C., Garzanti E., Polino R. 2011. Divergence in subduction zones and exhumation of high-pressure rocks (Eocene Western Alps). Earth Pl. Sci. Lett. 310:21-32. Malusà M.G., Garzanti E. 2012. Actualistic snapshot of the early Oligocene Alps: the Alps-Apennines knot detangled. Terra Nova 24:1-6. Mange M.A., Morton A.C. 2007. Geochemistry of Heavy Minerals. In: Mange, M.A. & Wright, D.T. (Eds) Heavy Minerals in Use, Developments in Sedimentology 58:345-391. Win K.S., Takeuchi M., Tokiwa T. 2007. Changes in detrital garnet assemblages related to transpressive uplifting associated with strike-slip faulting: an example from the Cretaceous System in Kii Peninsula, southwest Japan. Sedim. Geol. 201:412-431.

Tectono-metamorphic evolution of meta-ophiolitic units along Susa Valley (Italian Western Alps): new suggestions for the exhumation processes

NASA Astrophysics Data System (ADS)

Ghignone, Stefano; Borghi, Alessandro; Balestro, Gianni; Gattiglio, Marco

2017-04-01

In the inner Western Alps, meta-ophiolite units (i.e., the Piemonte Zone) show different stages of the tectono-metamorphic evolution, since the early phases of subduction to the latest exhumation steps. Tectono-metamorphic data collected through the meta-ophiolite units of the Piemonte Zone along the middle Susa Valley allowed to infer new ideas about the exhumation processes that developed in the (U)HP units. In this area, Zermatt-Saas-like meta-ophiolite unit (i.e., the eclogite-facies Internal Piemonte Zone, IPZ) are tectonically overlain by Combin-like ones (i.e., the blueschist-facies External Piemonte Zone, EPZ), through a thick shear zone (i.e., the Susa Shear Zone, SSZ). Metamorphic history was achieved by analyzing basic rocks (metabasalt and Fe-Ti metagabbro) and sedimentary rocks derived from reworking basic rocks in oceanic environment (basic sandstones and conglomerates, and ophiolitic breccia). Different P-T paths were inferred for IPZ and EPZ, according with mineral assemblages and realizations of pseudosections. In the IPZ, four tectono-metamorphic events, developed under variables metamorphic conditions, were recognized. The first (peak-P) event shows (U)HP conditions, defined by the occurrence of relic mineral assemblage (Grt I+ Omp I + Rt). The paragenesis is completed by Zo + Pg pseudomorphs, implying that Lws-eclogite facies were reached. The discovery in Grt (and Rt) relics inclusions of black euhedral pseudomorphs of disordered graphite, suggesting to be derived from original microdiamonds, agree with other petrologic constrains. The second event, marked by the Grt II + Omp II + Ph + Gln + Zo assemblage, developed under epidote-eclogite facies conditions. Following a retrograde and decompressional trajectory, the IPZ was then re-equilibrated under greenschist-facies conditions and a new assemblage (Ab + Chl + Mu + Czo + Ttn + Act) overprinted HP paragenesis. The last event is marked by a weak heating, with crystallization of Bt + Ep + Olig + Hbl (Prg) + Ms. The EPZ shows a different metamorphic evolution, where only two events were recognized. The first event developed under blueschist-facies conditions, with relics of mineral assemblages consisting of Gln + Rt + Ph. Then, a retrograde trajectory re-equilibrated EPZ under greenschist-facies conditions and a new stable mineral assemblage (Ab + Chl + Mu + Ttn + Act + Czo) grew. The inferred P-T path suggests, for the IPZ, a first isothermal exhumation stage, likely driven by buoyancy forces from the base of the orogenic wedge. In the EPZ, HP peak occurs at the same gradient of the second event in the IPZ, suggesting that, during exhumation of the IPZ, the EPZ was still subducted. The strong re-equilibration under greenschist-facies conditions suggests a stage of slow exhumation rate, which can be related to the coupling between IPZ and EPZ.

Detrital zircon provenance from three turbidite depocenters of the Middle-Upper Triassic Songpan-Ganzi complex, central China: Record of collisional tectonics, erosional exhumation, and sediment production

USGS Publications Warehouse

Weislogel, A.L.; Graham, S.A.; Chang, E.Z.; Wooden, J.L.; Gehrels, G.E.

2010-01-01

To test the idea that the voluminous upper Middle to Upper Triassic turbidite strata in the Songpan-Ganzi complex of central China archive a detrital record of Dabie ultrahigh-pressure (UHP) terrane unroofing, we report 2080 single detrital U-Pb zircon ages by sensitive high-resolution ion microprobe-reverse geometry (SHRIMP-RG) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis from 29 eastern Songpan-Ganzi complex sandstone samples. Low (<0.07) Th/U zircons, consistent with crystallization under UHP conditions, are rare in eastern Songpan-Ganzi complex zircon, and U-Pb ages of low Th/U zircons are incompatible with a Dabie terrane source. An unweighted pair group method with arithmetic mean nearest-neighbor analysis of Kolmogorov-Smirnov two-sample test results reveals that the eastern Songpan-Ganzi complex is not a single contiguous turbidite system but is instead composed of three subsidiary depocenters, each associated with distinct sediment sources. The northeastern depocenter contains zircon ages characterized by Paleozoic and bimodally distributed Precambrian zircon populations, which, together with south-to southeast-directed paleocurrent data, indicate derivation from the retro-side of the Qinling-Dabie (Q-D) collisional orogen wedge. In the central depocenter, the dominantly Paleozoic detrital zircon signature and south-to southwest-oriented paleocurrent indicators reflect a profusion of Paleozoic zircon grains. These data are interpreted to reflect an influx of material derived from erosion of Paleozoic supra-UHP rocks of the Dabie terrane in the eastern Qinling-Dabie orogen, which we speculate may have been enhanced by development of a monsoonal climate. This suggests that erosional unroofing played a significant role in the initial phase of UHP exhumation and likely influenced the petrotectonic and structural evolution of the Qinling-Dabie orogen, as evidenced by compressed Triassic isotherms/grads reported in the Huwan shear zone that bounds the Dabie terrane to the north. The central depocenter deposits reflect a later influx of bimodally distributed Precambrian zircon, signifying either a decrease in the influx of Paleozoic zircon grains due to stalled UHP exhumation and/or dilution of the same influx of Paleozoic zircons by spilling of Precambrian zircon from the northeastern depocenter into the central depocenter basin, perhaps due to infilling and bypass of sediment from the northern depocenter or due to initial collapse and constriction of the eastern Songpan-Ganzi complex basin. The southeastern depocenter of the eastern Songpan-Ganzi complex bears significant Paleozoic, Neoproterozoic, and Paleoproterozoic zircon populations derived from the South China block and Yidun arc complex, likely recording nascent uplift of the Longmenshan deformation belt due to impingement of the Yidun arc complex upon the western margin of the South China block. ?? 2010 Geological Society of America.

The influence of pressure on petroleum generation and maturation as suggested by aqueous pyrolysis

USGS Publications Warehouse

Price, L.C.; Wenger, L.M.

1992-01-01

Because fluid pressures are transient in sedimentary basins over geologic time, the effect of increasing fluid pressure on organic-matter metamorphism is difficult to determine, and conflicting opinions exist concerning its influence. Properly-performed aqueous-pyrolysis experiments can closely simulate hydrocarbon generation and maturation in nature, and thus offer an excellent way to study the influence of pressure. Such experiments, carried out on the Retort Phosphatic Shale Member of the Lower Permian Phosphoria Formation (type II-S organic matter) at different constant temperatures, demonstrated that increasing pressure significantly retards all aspects of organic matter metamorphism, including hydrocarbon generation, maturation and thermal destruction. This conclusion results from detailed quantitative and qualitative analyses of all products from hydrocarbon generation, from the C1 to C4 hydrocarbon gases to the asphaltenes, and also from analyses of the reacted rocks. We have documented that our aqueous-pyrolysis experiments closely simulated natural hydrocarbon generation and maturation. Thus the data taken as a function of pressure have relevance to the influence of normal and abnormal fluid pressures as related to: 1) depths and temperatures of mainstage hydrocarbon generation; 2) the thermal destruction of deposits of gas or light oil, or their preservation to unexpectedly high maturation ranks; and 3) the persistence of measurable to moderate concentrations of C15+ hydrocarbons in fine-grained rocks even to ultra-high maturation ranks. ?? 1992.

In Situ UV-Laser Ablation 40Ar/39Ar Muscovite Thermochronology Reveals Excess Argon and 405-399 Ma Age for the Nordfjord-Sogn Detachment Zone, Hornelen region, Norway

NASA Astrophysics Data System (ADS)

Johnston, S. M.; Hacker, B. R.; Eide, E. A.; Hendriks, B.

2006-12-01

The Nordfjord-Sogn Detachment Zone (NSDZ) is a 2-6 km thick, normal-sense shear zone that juxtaposes the eclogite-bearing Western Gneiss Complex in its footwall with Devonian sediments in its hangingwall, and is widely cited as the primary structure responsible for the exhumation of the Norwegian ultrahigh-pressure (UHP) rocks. Critical to our understanding of this crustal-scale detachment, detailed thermochronology places essential constraints on the rates of exhumation and documents spatial variability in the timing of exhumation- related cooling. Regional thermochronology has shown that 40Ar/39Ar muscovite ages increase gradually from 405-390 Ma across the Western Gneiss Complex and into the lower part of the NSDZ, but at higher structural levels within the NSDZ, these ~400 Ma ages are mixed with an older population at 420-418 Ma. Although neither excess argon nor incomplete resetting of argon in these older samples has been ruled out, these results have been interpreted to suggest that extension and exhumation within the NSDZ may have initiated as early as 420 Ma. Here, we investigate these older 40Ar/39Ar muscovite ages by comparing resistance furnace (RF) ages from bulk muscovite separates with in situ UV-laser ablation ages from a suite of 6 samples that transect the NSDZ. RF spectra from 5 of the 6 analyzed samples yield plateau ages that range from 405-399 Ma; in situ ages of these same 5 samples reveal no age zonation within large grains and no differences in ages among texturally different grains. In contrast, the structurally highest sample yields a RF plateau age of 425±6 Ma, and in situ ages of 474-417 Ma in grain cores and c. 400 Ma in grain rims and small grains. On an inverse isochron diagram, these in situ ages define two distinct populations, with grain cores distributed along a line between an excess argon component of 40Ar/36Ar = 660±60 and an age of 404±7 Ma. Analyses from rims and small grains plot in triangle defined by these two apices and an atmospheric 40Ar/36Ar ratio. These results are consistent with the interpretation that the older 40Ar/39Ar muscovite ages from the NSDZ are the result of excess argon. These findings refute the possibility of extension and exhumation as early as 420 Ma along the NSDZ, and suggest that the entire package of NSDZ mylonites was cooled through muscovite closure to argon between 405-399 Ma immediately following UHP metamorphism.

Eclogites and their geodynamic interpretation: a history

NASA Astrophysics Data System (ADS)

Godard, Gaston

2001-09-01

Haüy coined the term eclogite, meaning "chosen rock", in 1822, but de Saussure had already observed rocks of this type in the Alps four decades earlier. Throughout the 19th century, the origin of eclogite remained an enigma, in spite of great progress in our knowledge of this rock. The first chemical analyses, carried out around 1870, showed that its bulk composition was the same as gabbro. Therefore, eclogite was thought to be either an igneous rock of gabbroic composition or a metamorphosed gabbro. This second hypothesis became preferred when progressive transitions were observed between gabbros and eclogites. In 1903, simply by comparing the molar volumes of gabbroic and eclogite parageneses, Becke inferred that eclogite was the high-pressure equivalent of gabbro. In 1920, eclogite was involved in the conception of the metamorphic facies by Eskola. However, a few researchers denied the existence of an eclogite facies, and claimed that high stress instead of high lithostatic pressure could generate eclogites. In the 1960s, consideration of the water pressure parameter also favoured the belief that eclogite was simply the anhydrous equivalent of amphibolite. Finally, eclogite was definitely considered as a high-pressure metamorphic rock following the development of experimental petrology and the application of thermodynamics. In recent years, the discovery of ultrahigh-pressure coesite-bearing rocks in the crust has drastically changed geologists' ideas concerning the limits of eclogite-facies crustal metamorphism. Eclogites have been involved in several geodynamic theories. Around 1900, kimberlite studies favoured the idea that eclogite might be abundant in the interior of the Earth. In 1912, Fermor predicted the existence of a dense eclogite-bearing zone in the mantle. This "eclogite layer" hypothesis was still envisaged as late as 1970. The alternative "peridotite" hypothesis became preferred when experimental investigations demonstrated that the gabbro-to-eclogite transition could not coincide with a sharp Mohorovičić discontinuity. Before plate tectonics, high-pressure belts were interpreted as remnants of ophiolite-bearing "geosynclines", metamorphosed by loading during thrust faulting. After the acceptance of plate tectonics, around 1970, the same high-pressure Alpine-type belts came to be considered as former oceanic crust, transformed into eclogite within subduction zones, and subsequently incorporated into mountain belts. Surprisingly, formation of eclogite in "subsidence" zones (i.e. subduction zones) had already been envisaged as early as 1931 by Holmes, the inventor of a convection-current theory. In the 1980s, many authors tried to apply the model of Alpine-type high-pressure belts to eclogites enclosed within the gneisses of ancient orogens, but the question remains obscure nowadays. These eclogites have been involved in the "in situ versus foreign" controversy and in the unresolved enigma of ultrahigh-pressure metamorphism. The latter came under scrutiny in 1984 after the discovery of coesite and diamond in some eclogite-facies rocks. It has been a matter of considerable interest during the last two decades. Currently, the debate is focused on the geodynamic mechanisms responsible for the exhumation of these rocks, a question that will probably remain unresolved for part of the coming century.

Constraints on the Amount of deeply subducted Water from numerical Models in comparison with natural Samples

NASA Astrophysics Data System (ADS)

Konrad-Schmolke, M.; Halama, R.

2014-12-01

The subduction of hydrated slab mantle to beyond-arc depths is the most important and yet weakly constrained factor in the quantification of the Earth's deep geologic water cycle. During subduction of hydrated oceanic lithosphere, dehydration reactions in the downgoing plate lead to a partitioning of water between upper and lower plate. Water retained in the slab is recycled into the mantle where it controls its rheology and thus plate tectonic velocities. Hence, quantification of the water partitioning in subduction zones is crucial for the understanding of mass transfer between the Earth's surface and the mantle. Combined thermomechanical and thermodynamic models yield quantitative constraints on the water cycle in subduction zones, but unless model results can be linked to natural observations, the reliability of such models remains speculative. We present combined thermomechanical, thermodynamic and geochemical models of active and paleo-subduction zones, whose results can be tested with independent geochemical features in natural rocks. In active subduction zones, evidence for the validity of our model comes from the agreement between modeled and observed across-arc trends of boron concentrations and isotopic compositions in arc volcanic rocks. In the Kamchatkan subduction zone, for example, the model successfully predicts complex geochemical patterns and the spatial distribution of arc volcanoes. In paleo-subduction zones (e.g. Western Gneiss Region and Western Alps), constraints on the water budget and dehydration behavior of the subducting slab come from trace element zoning patterns in ultra-high pressure (UHP) garnets. Distinct enrichments of Cr, Ni and REE in the UHP zones of the garnets can be reconciled by our models that predict intense rehydration and trace element re-enrichment of the eclogites at UHP conditions by fluids released from the underlying slab mantle. Models of present-day subduction zones indicate the presence of 2.5-6 wt.% of water within the uppermost 15 km of the subducted slab mantle. Depending on hydration depth, between 25 and 90% of this water is recycled into the deeper mantle. The Lower Devonian example from the Western Gneiss Region indicates that subduction of water into the Earth's deeper mantle is an active process at least since the middle Paleozoic.

Geochronologic Constraints on the Location of the Sino-Korean/Yangtze Suture and Evolution of the Northern Dabie Shan

NASA Astrophysics Data System (ADS)

Bryant, D. L.; Ayers, J. C.; Gao, S.; Miller, C. F.; Zhang, H.

2002-05-01

The Northern Dabie Complex (NDC) has been proposed to be either a Paleozoic magmatic arc, an exhumed piece of subducted continental crust, or young crust produced almost entirely by Cretaceous extensional magmatism. Ion microprobe zircon 238U-206Pb ages of separates from NDC gneisses center around 689Ma (+/- 31(95%CL)), consistent with the characteristic zircon dates of the Yangtze Craton [1]. Field observations also show that these gneisses, ranging from granitic to dioritic composition, make up a sizeable area ( ~30%) of the NDC. Zircon separates from the Baimajian granitoid, the largest of the widespread Cretaceous intrusions in the NDC, have yielded ages clustered around 677Ma (+/- 79), and 120Ma (+/- 3.4), the latter of which agrees with ion probe Th-Pb monazite ages. The ~700Ma age indicates that this intrusion may be linked with partial melting of underlying Yangtze crust, while the 120Ma age is the age of its crystallization. Granitic intrusions from Sanzushi and Yerenshai in the Dabie ultrahigh-pressure (UHP) region also show clusters of ages at 714Ma (+/- 55) from zircon cores, as well as rims around 250Ma (+/- 38), which is interpreted as the time of collision of the two continental blocks. These age data support the hypothesis set forth by Zhang et al. [2] using Sm-Nd and Pb isotopic data, that the Yangtze block lies beneath the exhumed UHP belt and outcrops as the NDC, which lies between the UHP belt and the Sino-Korean/Yangtze suture. The Baimajian granitoid, however, also shows a range of older zircon core ages from 1.4-2.0Ga, which may represent the early stages of formation of the Yangtze craton. Zhang et al. [2] suggested craton formation at 1.6-2.4Ga but few such ages have been reported for rocks of the Yangtze or Sino-Korean cratons. 1. Hacker, et al. (2000) Journal of Geophysical Research. Vol. 105. p. 13,339. 2. Zhang, et al. (In press) Chemical Geology.

Middle Ordovician subduction of continental crust in the Scandinavian Caledonides: an example from Tjeliken, Seve Nappe Complex, Sweden

NASA Astrophysics Data System (ADS)

Fassmer, Kathrin; Klonowska, Iwona; Walczak, Katarzyna; Andersson, Barbro; Froitzheim, Nikolaus; Majka, Jarosław; Fonseca, Raúl O. C.; Münker, Carsten; Janák, Marian; Whitehouse, Martin

2017-12-01

The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430-400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between 505 and 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet-phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25-27 kbar/680-760 °C for the garnet-phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25-26 kbar/650-700 °C). Metamorphic rims of zircons from the garnet-phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu-Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm-Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction-exhumation cycle.

Ultra-high performance size-exclusion chromatography in polar solvents.

PubMed

Vancoillie, Gertjan; Vergaelen, Maarten; Hoogenboom, Richard

2016-12-23

Size-exclusion chromatography (SEC) is amongst the most widely used polymer characterization methods in both academic and industrial polymer research allowing the determination of molecular weight and distribution parameters, i.e. the dispersity (Ɖ), of unknown polymers. The many advantages, including accuracy, reproducibility and low sample consumption, have contributed to the worldwide success of this analytical technique. The current generation of SEC systems have a stationary phase mostly containing highly porous, styrene-divinylbenzene particles allowing for a size-based separation of various polymers in solution but limiting the flow rate and solvent compatibility. Recently, sub-2μm ethylene-bridged hybrid (BEH) packing materials have become available for SEC analysis. These packing materials can not only withstand much higher pressures up to 15000psi but also show high spatial stability towards different solvents. Combining these BEH columns with the ultra-high performance LC (UHPLC) technology opens up UHP-SEC analysis, showing strongly reduced runtimes and unprecedented solvent compatibility. In this work, this novel characterization technique was compared to conventional SEC using both highly viscous and highly polar solvents as eluent, namely N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF) and methanol, focusing on the suitability of the BEH-columns for analysis of highly functional polymers. The results show a high functional group compatibility comparable with conventional SEC with remarkably short runtimes and enhanced resolution in methanol. Copyright © 2016 Elsevier B.V. All rights reserved.

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

NASA Astrophysics Data System (ADS)

Dai, Lidong; Sun, Wenqing; Li, Heping; Hu, Haiying; Wu, Lei; Jiang, Jianjun

2018-03-01

The electrical conductivity of gneiss samples with different chemical compositions (WA = Na2O + K2O + CaO = 7.12, 7.27 and 7.64 % weight percent) was measured using a complex impedance spectroscopic technique at 623-1073 K and 1.5 GPa and a frequency range of 10-1 to 106 Hz. Simultaneously, a pressure effect on the electrical conductivity was also determined for the WA = 7.12 % gneiss. The results indicated that the gneiss conductivities markedly increase with total alkali and calcium ion content. The sample conductivity and temperature conform to an Arrhenius relationship within a certain temperature range. The influence of pressure on gneiss conductivity is weaker than temperature, although conductivity still increases with pressure. According to various ranges of activation enthalpy (0.35-0.52 and 0.76-0.87 eV) at 1.5 GPa, two main conduction mechanisms are suggested that dominate the electrical conductivity of gneiss: impurity conduction in the lower-temperature region and ionic conduction (charge carriers are K+, Na+ and Ca2+) in the higher-temperature region. The electrical conductivity of gneiss with various chemical compositions cannot be used to interpret the high conductivity anomalies in the Dabie-Sulu ultrahigh-pressure metamorphic belt. However, the conductivity-depth profiles for gneiss may provide an important constraint on the interpretation of field magnetotelluric conductivity results in the regional metamorphic belt.

Subduction-Zone Metamorphic Pathway for Deep Carbon Cycling: Evidence from the Italian Alps and the Tianshan

NASA Astrophysics Data System (ADS)

Bebout, G. E.; Collins, N.; Cook-Kollars, J.; Angiboust, S.; Agard, P.; Scambelluri, M.; John, T.; Kump, L. R.

2013-12-01

Depending on the magnitude of the poorly constrained C flux in ultramafic rocks, on a global basis, sediments and altered oceanic crust (AOC) together deliver 70-95% of the C currently entering subduction zones. We are investigating extents of retention and metamorphic release of C in deeply subducted AOC and carbonate-rich sediment represented by HP/UHP meta-ophiolitic and metasedimentary rocks in the Italian Alps and in the Tianshan. Study of metapelite devolatilization in the same W. Alps suite (Bebout et al., 2013, Chem. Geol.) provides a geochemical framework for study of C behavior along prograde P-T paths similar to those experienced in forearcs of most modern subduction margins. Study of veins in the Tianshan affords examination of C mobility in UHP fluids, in later stages as metabasaltic rocks were fragmented in the subduction channel. Our results for sediments and AOC indicate impressive retention of oxidized C (carbonate) and reduced C (variably metamorphosed organic matter) to depths approaching those beneath arc volcanic fronts. In metasedimentary rocks, extensive isotopic exchange between the oxidized and reduced C resulted in shifts in both reservoirs toward upper mantle compositions. Much of the carbonate in metabasalts has C and O isotopic compositions overlapping with those for carbonate in AOC, with some HP/UHP metamorphic veins showing greater influence of organic C signatures from metasedimentary rocks. Calculations of prograde devolatilization histories using Perple-X demonstrate that, in most forearcs, very little decarbonation occurs in the more carbonate-rich rocks unless they are flushed by H2O-rich fluids from an external source, for example, from the hydrated ultramafic section of subducting slabs (cf. Gorman et al., 2006; G3) or from more nearby rocks experiencing dehydration (e.g., metapelites). A comparison of the most recently published thermal models for modern subduction zones (van Keken et al., 2011, JGR) with calculated and experimentally determined phase relations indicates that significant C loss during devolatilization (and partial melting) should occur as subducting sections traverse depths beneath arcs. The extent of C mobility due to carbonate dissolution remains uncertain. On a global basis, imbalance between subducted C input and C return flux by magmatism (excluding ultramafic inputs, ~40×20% of subducted C return via arcs and ~80×20% by all magmatism; Bebout, 2013, Treat. Geochem.) indicates net modern C return to the mantle, perhaps a reversal of Archean net outgassing (despite more rapid subduction). Global C cycle models predict that relatively small (and geologically plausible) change in the subduction/volcanic C flux could significantly affect atmospheric CO2 levels and thus global climate.

Activation of the E1 Ultra High Pressure Propulsion Test Facility at Stennis Space Center

NASA Technical Reports Server (NTRS)

Messer, Bradley; Messer, Elisabeth; Sewell, Dale; Sass, Jared; Lott, Jeff; Dutreix, Lionel, III

2001-01-01

After a decade of construction and a year of activation the El Ultra High Pressure Propulsion Test Facility at NASA's Stennis Space Center is fully operational. The El UHP Propulsion Test Facility is a multi-cell, multi-purpose component and engine test facility . The facility is capable of delivering cryogenic propellants at low, high, and ultra high pressures with flow rates ranging from a few pounds per second up to two thousand pounds per second. Facility activation is defined as a series of tasks required to transition between completion of construction and facility operational readiness. Activating the El UHP Propulsion Test Facility involved independent system checkouts, propellant system leak checks, fluid and gas sampling, gaseous system blow downs, pressurization and vent system checkouts, valve stability testing, valve tuning cryogenic cold flows, and functional readiness tests.

Deformation and Metasomatic Evolution at the Subduction Plate Interface As Viewed from Study of HP/UHP Metamorphic Rocks

NASA Astrophysics Data System (ADS)

Bebout, G. E.; Penniston-Dorland, S.

2014-12-01

We provide a view of lithologic makeup, deformation, and fluid-rock interaction along the deep forearc to subarc plate interface, based on insights gained from study of HP/UHP metamorphic rocks. Exposures of plate-boundary shear zones on which we base our perspective represent 30-80 km depths and are on Catalina Island and at Monviso, Syros, and New Caledonia. Each contains highly deformed zones with schistose matrix, commonly with a large ultramafic component, containing bodies of less deformed mafic, sedimentary, and ultramafic rocks. These "blocks" have varying geometries, are up to km-scale, and can preserve disparate P-T histories reflecting dynamics of incorporation and entrainment. Sheared matrices contain high-variance, hydrous mineral assemblages in some cases resembling metasomatic zones ("rinds") at block-matrix contacts, and rinds and matrices have homogenized isotopic compositions reflecting extensive fluid-rock interaction. Shearing and related physical juxtaposition of disparate metasomatic rocks can result in mixed or 'hybrid' chemical compositions. The chlorite-, talc-, and amphibole-rich schists developed by these processes can stabilize H2O to great depth and influence its cycling. Fluids (hydrous fluids, silicate melts) released within slabs necessarily interact with highly deformed, lithologically hybridized zones at the plate interface as they ascend to potentially enter mantle wedges. Fluids bearing chemical/isotopic signatures of hybrid rocks appear capable of producing arc magma compositions interpreted as reflecting multiple, chemically distinct fluids sources. Geophysical signatures of these rheologically weak zones are equivocal but many recognize the presence of zones of low seismic velocity at/near the top of slabs and attribute them to hydrated rocks. Whether rocks from this interface buoyantly ascend into mantle wedges, indicated in some theoretical models, remains largely untested by field and geophysical observations.

Minor elements, HREE and d18O distribution in UHP garnets from the Dora-Maira massif (western Alps)

NASA Astrophysics Data System (ADS)

Brunet, F.; Chazot, G.; Vielzeuf, D.; Chopin, C.

2003-04-01

The spatial distribution of minor elements, HREE and δ18O in garnet can be used as a probe of the availability and mobility of those elements and isotopes at the time of crystal growth, provided that the initial record was not significantly modified by intracrystalline diffusion and that growth took place under nearly constant pressure and temperature conditions. Garnets from three different Dora-Maira rock-types have been studied, (1) nearly pure pyrope (GT1) from the magnesian coesite-bearing quartzites, (2) almandine/pyrope dominant garnets (GT2) from jadeite-quartzite veins which crosscut the Mg-quartzite body, (3) almandine/grossular dominant garnets (GT3) from the country-rock gneiss, sampled in the vicinity of the quartzites. In GT1, minor elements are mainly Fe, Na and P. Na and P are incorporated according to a Na^+ + P5+ = Me2+ + Si4+ substitution with P_2O_5 contents up to 2000 to 2500 ppm. HREE concentrations obtained by LA-ICP-MS, vary by 2 orders of magnitude from core to rim. The δ18O ratio (Cameca 1270, Nancy), around 5 ppm (SMOW), is constant within error throughout the analysed crystals. In GT2, the situation is different since HREE concentrations appear remarkably constant within a given crystal and from one crystal to the other. In contrast with GT1, Na in GT2 is partly charge-balanced by yttrium incorporation. The δ18O ratio in GT2 of around 7 ppm is close to that encountered in GT3 (gneiss) between 7 and 8 ppm. In GT3, phosphorus content is close to detection limit (P_2O_5 below 300 ppm). HREE concentrations are highly variable from one crystal to the other and unfortunately, the size of garnet crystals does not allow profiling. Although δ18O ratio in garnet is imposed by the bulk-rock isotopic composition, HREE distribution is dominated by element availability through the fluid composition and/or absence/presence of accessory phases. The decrease in HREE and P concentration from GT1 cores to rims suggest that these elements are preferentially incorporated into garnet. Garnet growth leads to progressive depletion of these elements in the matrix. There is no significant influx of HREE during UHP garnet growth. The homogeneity of the δ18O ratio within garnet crystals is also an indication of UHP growth in a close metamorphic system. Jadeite-quartzite veins have geochemical characteristics close to that of the country-rock gneiss from which they could originate. They would then represent an evidence of Mg-quartzite and country gneiss interaction at UHP.

Sm-Nd Mineral Isochron Age Patterns from Garnet-bearing Peridotite of the Western Gneiss Region, Norwegian Caledonides: Discrete Mantle Events or Continuous Re- equilibration?

NASA Astrophysics Data System (ADS)

Brueckner, H. K.

2007-12-01

The garnet peridotites (and pyroxenites) of the UHP Western Gneiss Region of Norway give Sm-Nd garnet, clinopyroxene, whole rock, orthopyroxene, amphibole ages that range from ca. 1.7 Ga to 424 Ma. Most of these twenty seven ages are much older than the continent-continent collision that transferred these peridoitites from the mantle into the crust (i.e. the 400 Ma Scandian Orogeny) suggesting the garnet peridotites of the WGR are unique relative to those in other UHP terranes, which invariably give ages that overlap the time of UHP metamorphism of the enclosing country rocks. All but the youngest ages given by WGR peridotites reflect processes that occurred deep in the mantle beneath the Baltic Shield, but it is unclear if they date a series of discrete events related to the tectonic evolution of the Baltic Shield or if the ages reflect continuous, but variable, re-equilibration of the Sm-Nd system between phases during the residence of the peridotites in the mantle. Three ages overlap the 1.75 to 1.55 Ga Gothian Orogeny while twelve ages are within error of the 1.2 to 0.9 Ga Sveconorwegian Orogeny. The three youngest ages (438 to 424 Ma) are associated with a younger generation of garnets and may mark the beginning of eclogite-facies metamorphism of Baltica as it was subducted beneath Laurentia during the Scandian Orogeny. However, the remaining nine ages spread more or less continuously between these three major events. The overall pattern on a histogram is a range of ages with a pronounced peak at and near the Sveconorwegian Orogeny. The ages therefore appear to date continuous diffusion between minerals from garnet-bearing assemblages that formed originally during or, less likely, before the Gothian Orogeny interrupted by a pronounced thermal event during the Svconorwegian Orogeny and a recrystallization event during the early stages of the Scandian orogeny. The degree of re-equilibration was probably controlled by the ambient temperature of the peridotite body in the mantle, which was controlled, in turn, by their depth in the mantle and their proximity to hot mantle upwelling during the Sveconorwegian Orogeny.

Petrology and fluid inclusions of garnet-clinopyroxene rocks from the Gondwana suture zone in southern India: Implications for prograde high-pressure metamorphism

NASA Astrophysics Data System (ADS)

Tsunogae, T.

2012-04-01

The Palghat-Cauvery Suture Zone (PCSZ) in the southern granulite terrane, India, which separates Pan-African granulite blocks (e.g., Madurai and Trivandrum Blocks) to the south and Archean terrane (e.g., Salem Block and Dharwar Craton) to the north is regarded as a major suture zone in the Gondwana collisional orogeny. It probably continues westwards to the Betsimisaraka suture in Madagascar, and eastwards into Sri Lanka and possibly into Antarctica. The available geochronological data including U-Pb zircon and EPMA monazite ages indicate that the rocks along the PCSZ underwent an episode of high-grade metamorphism at ca. 530 Ma that broadly coincides with the time of final assembly of the Gondwana supercontinent. Recent investigations on high-grade metamorphic rocks in this region have identified several new occurrences of garnet-clinopyroxene rocks and associated meta-gabbros from Perundurai, Paramati, Aniyapuram, Vadugappatti, and Mahadevi areas in Namakkal region within the central domain of the PCSZ. They occur as elongated boudins of 1 m to 1 km in length within hornblende-biotite orthogneiss. The garnet-clinopyroxene mafic granulites contain coarse-grained (up to several cm) garnet (Alm30-50 Pyr30-40 Grs10-20) and clinopyroxene (XMg = 0.70-0.85) with minor pargasite, plagioclase (An30-40), orthopyroxene (hypersthene), and rutile. Garnet and clinopyroxene are both subidioblastic and contain few inclusions of clinopyroxene (in garnet) and plagioclase. Orthopyroxene occur only as Opx + Pl symplectite between garnet and clinopyroxene in almost all the localities, suggesting the progress of decompressional reaction: Grt + Cpx + Qtz => Opx + Pl, which is a dominant texture in the PCSZ. The prograde mineral assemblage of the rocks is therefore inferred to be Grt + Cpx + Qtz, although quartz was probably totally consumed by the progress of the reaction. The metamorphic P-T calculations using Grt-Cpx-Pl-Qtz geothermobarometers yield T = 850-900°C and P >13 kbar, which is consistent with the occurrence of high-pressure Mg-rich staurolite in Mg-Al-rich rocks from this region. Fluid inclusion study of some garnet-clinopyroxene rock samples identified CO2-rich fluid inclusions trapped as primary phases within garnet, suggesting that prograde high-pressure metamorphism was dominated by CO2-rich fluids. The results therefore confirmed that the PCSZ underwent regional dry high-pressure metamorphism followed by the peak ultrahigh-temperature event probably associated with the continent-continent collisional and suturing history along the PCSZ.

Specific Adaptation of Gas Atomization Processing for Al-Based Alloy Powder for Additive Manufacturing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Iver; Siemon, John

The charge for each gas atomization experiment was provided by Alcoa and consisted of cast blocks cut into 1 inch by 1 inch square rods of the chosen aluminum alloys. The atmosphere in the melting chamber and connected atomization system was evacuated with a mechanical pump prior to backfilling with ultrahigh purity (UHP grade) Ar. The melt was contained in a bottom tapped alumina crucible with an alumina stopper rod to seal the exit while heating to a pouring temperature of 1000 – 1400°C. When the desired superheat was reached, the stopper rod was lifted and melt flowed through pourmore » tube and was atomized with Ar from a 45-22-052-409 gas atomization nozzle (or atomization die), having a jet apex angle of 45 degrees with 22 cylindrical gas jets (each with diameter of 1.32 mm or 0.052 inches) arrayed around the axis of a 10.4 mm central bore. The Ar atomization gas supply regulator pressure was set to produce nozzle manifold pressures for the series of runs at pressures of 250-650 psi. Secondary gas halos of Ar+O 2 and He also were added to the interior of the spray chamber at various downstream locations for additional cooling of the atomized droplets, surface passivation, and to prevent coalescence of the resulting powder.« less

Comparative chronology of Archean HT/UHT crustal metamorphism

NASA Astrophysics Data System (ADS)

Caddick, Mark; Dragovic, Besim; Guevara, Victor

2017-04-01

Attainment of high crustal heat fluxes and consequent partial melting is critical to the stabilization of continental roots. Understanding the processes and timescales behind partial melting of continental crust in the Archean is thus paramount for understanding Archean tectonic modes and how stable cratons formed. High-temperature (HT) to ultrahigh-temperature (UHT) metamorphic rocks can record evidence for dynamic processes that result in advective heat fluxes and a substantial deviation from normal crustal geothermal gradients. Examination of the pressure-temperature conditions and timescales of HT/UHT metamorphism is thus essential to understanding the tectonic processes behind extreme crust heat fluxes and the formation of stable cratonic crust. Here, utilizing both traditional and nontraditional petrologic and geochronologic techniques, we compare the pressure-temperature-time paths of two Neoarchean terranes: the eastern Beartooth Mountains of the Wyoming Craton and the Pikwitonei Granulite Domain of the Superior Province. The Beartooth Mountains of Montana, USA, expose Archean rocks of the Wyoming Craton that are dominated by an ˜2.8 Ga calc-alkaline granitoid batholith known as the Long Lake Magmatic Complex (LLMC). The LLMC contains widespread, up to km-scale metasedimentary roof pendants, with ID-TIMS Sm-Nd garnet geochronology and laser ablation split stream (LASS) monazite geochronology suggesting that metamorphism occurred almost 100 Ma after entrainment by the LLMC [1]. Phase equilibria modeling and Zr-in-rutile thermometry constrain peak pressures and temperatures of ˜6-7 kbar and ˜780-800˚ C. Major element diffusion modeling of garnet suggest that granulite-facies temperatures were only maintained for a short duration, < 2 Ma. In contrast, the Pikwitonei Granulite Domain consists of >150,000 km2 of high-grade metamorphic rocks situated in the NW Superior Province. Phase equilibria modeling and trace element thermometry constrain peak temperatures in the southernmost part of the PGD to ˜760˚ C, while across the vast central and western parts of the PGD, peak temperatures range from 900-1000°C. LASS monazite and zircon ages, combined with ID-TIMS zircon and Sm-Nd garnet ages range from ˜2720 Ma to ˜2600 Ma, and combined with the thermometry, suggest that temperatures of >700˚ C were maintained region-wide for over 100 Ma, and that this was punctuated by thermal perturbations exceeding 900-950˚ C and occurring over substantially shorter timescales. The depths, temperatures and timescales inferred here suggest that although these regions were experiencing metamorphism within ˜100 Ma of each other, the primary driver for this metamorphism was different in each case. Timescale of metamorphism might be the most important constrained parameter here, highlighting the benefit of high resolution isotopic and geospeedometry approaches. [1] Dragovic et al., 2016. Precamb. Res., 283, 24-49. [2] Guevara et al., 2016. AGU abstracts with programs.

Diamond and Unusual Minerals Discovered from the Chromitite in Polar Ural: A First Report

NASA Astrophysics Data System (ADS)

Yang, J.; Bai, W.; Fang, Q.; Meng, F.; Chen, S.; Zhang, Z.

2007-12-01

Ultrahigh pressure (UHP) minerals, such as diamond, coesite, and pseudomorphs of octahedral olivine, and as well as about 80 other mineral species have been recovered from podiform chromitites of the Luobusa ophiolite, southern Tibet, and a new mineral, Luobusaite (Fe0.82Si2), has been approved recently by CNMMN. The UHP minerals from Luobusa are controversial because they have not found in situ and because ophiolites are currently believed to form at shallow levels above oceanic spreading centers. More detailed study and experimental work are needed to understand the origin and significance of these unusual minerals and investigations of other ophiolites are needed to determine if such minerals occur elsewhere. For this purpose, we collected about 1500 kg of chromitite from two orebodies in an ultramafic body in the Polar Urals. Thus far, more than 60 different mineral species have been separated from these ores. The most exciting discovery is the common occurrence of diamond, a typical UHP mineral in the Luobusa chromitites. Diamonds from Ural chromitite are clear, colorless, well-developed crystals with octahedral morphology, generally 0.2-0.3 mm in size. Attached with the diamonds and perhaps also occurring as inclusions within them are many minerals as chromite, MnNiCrFe alloy, native Si and Ta, corundum, zircon, feldspar, garnet, moissanite, confirming their natural origin and suggesting a long residence time in the mantle. Other mineral group include: (1) native elements: Cr, W, Ni, Co, Si, Al and Ta; (2) carbides: SiC and WC; (3) alloys: Cr-Fe, Si-Al-Fe, Ni-Cu, Ag-Au, Ag-Sn, Fe-Si, Fe-P, and Ag-Zn-Sn; (4) oxides: NiCrFe, PbSn, REE, rutile and Si- bearing rutile, ilmenite, corundum, chromite, MgO, and SnO2; (5) silicates: kyanite, pseudomorphs of octahedral olivine, zircon, garnet, feldspar, and quartz,; (6) sulfides of Fe, Ni, Cu, Mo, Pb, Ab, AsFe, FeNi, CuZn, and CoFeNi; and (7) iron groups: native Fe, FeO, and Fe2O3. These minerals are very similar in composition and structure to those reported from the Luobusa chromitites. For examples, some spherules of native iron contain spherical inclusions of FeO, exactly like comparable grains in the Luobusa sample.

Formation and modification of chromitites in the mantle

NASA Astrophysics Data System (ADS)

Arai, Shoji; Miura, Makoto

2016-11-01

Podiform chromitites have long supplied us with unrivaled information on various mantle processes, including the peridotite-magma reaction, deep-seated magmatic evolution, and mantle dynamics. The recent discovery of ultrahigh-pressure (UHP) chromitites not only sheds light on a different aspect of podiform chromitites, but also changes our understanding of the whole picture of podiform chromitite genesis. In addition, new evidence was recently presented for hydrothermal modification/formation chromite/chromitite in the mantle, which is a classical but innovative issue. In this context, we present here an urgently needed comprehensive review of podiform chromitites in the upper mantle. Wall-rock control on podiform chromitite genesis demonstrates that the peridotite-magma reaction at the upper mantle condition is an indispensable process. We may need a large system in the mantle, far larger than the size of outcrops or mining areas, to fulfill the Cr budget requirement for podiform chromitite genesis. The peridotite-magma reaction over a large area may form a melt enriched with Na and other incompatible elements, which mixes with a less evolved magma supplied from the depth to create chromite-oversaturated magma. The incompatible-element-rich magma trapped by the chromite mainly precipitates pargasite and aspidolite (Na analogue of phlogopite), which are stable under upper mantle conditions. Moderately depleted harzburgites, which contain chromite with a moderate Cr# (0.4-0.6) and a small amount of clinopyroxene, are the best reactants for the chromitite-forming reaction, and are the best hosts for podiform chromitites. Arc-type chromitites are dominant in ophiolites, but some are of the mid-ocean ridge type; chromitites may be common beneath the ocean floor, although it has not yet been explored for chromitite. The low-pressure (upper mantle) igneous chromitites were conveyed through mantle convection or subduction down to the mantle transition zone to form ultrahigh-pressure chromitites. Some of these reappear at the shallower mantle, and can coexist with newly formed low-pressure igneous chromitites. High-temperature hydrothermal fluids can dissolve and precipitate chromite, and hydrothermal chromitites (chromitites precipitated from aqueous fluids) are possibly formed within the mantle where the circulation of hydrous fluid is available, e.g., at the mantle wedge.

Remelting of nanogranitoids in UHP felsic granulites from Erzgebirge (Bohemian Massif, Germany)

NASA Astrophysics Data System (ADS)

Acosta-vigil, A.; Stöckhert, B.; Hermann, J.; Yaxley, G.; Cesare, B.; Bartoli, O.

2017-12-01

Crustal melting commonly takes place at pressures ≤ 1.5 GPa. Anatexis at UHP conditions, however, can occur during subduction of continental crust down to mantle depths. Understanding the timing, mechanisms and nature of this process is important as it has major mechanical and geochemical implications. One way to address this problem is through the novel studies of nanogranitoids in migmatites and granulites (Cesare et al. 2015). We have remelted crystallized former melt inclusions (nanogranitoids) trapped in garnets of diamond-bearing UHP felsic granulites from Erzgebirge, Bohemian Massif. These rocks are made of Qtz+Phe+Pl+Grt+Ky+Bt+Dia, and their peak conditions have been estimated at P≥4.5 GPa and T≥1000 ºC. Nanogranitoids appear homogeneously distributed throughout the entire garnet crystals, are 5-50 µm across and often isometric, with partially developed negative crystal shape, and were trapped during garnet growth in the presence of melt. The mineral assemblage within nanogranites consists of Qtz+Pl+Phe+Pg+Phl±Ky±Dia±Gr±Ap±Rt (Stöckhert et al. 2009). Fragments of nanogranitoids-bearing garnets were loaded inside gold capsules, enclosed in SiO2 or C powders that acted as cushion, either dry or with H2O in excess, and subjected to conditions between 975-1100 ºC and 2.5-4.5 GPa for 2-24 hrs. Re-homogenization has not been completely achieved. Nanogranitoids partially melt, melt often coexists with Als, diamond or Gr, and Grt grows into the melt to form a higher #Mg and Ti, ≈5 µm fringe. Preliminary EMP analyses indicate that melts are granitic sensu stricto, with low FeOt+MgO (≈2 wt%), moderate to high in ASI, and high in TiO2 (≈0.4-0.8 wt%), P2O5 (up to 1 wt%) and volatiles (100-EMP totals ≈ 10-15 wt%). These preliminary results suggest that (i) anatexis started in the presence of a H2O-rich fluid phase, (ii) melt was present and equilibrated at quite high T (>850-950 ºC, Hayden & Watson 2007) at or close to peak conditions, (iii) Als and diamond/Gr in nanogranitoids represent trapped minerals, (iv) Grt equilibrated during the retrograde path after entrapment of melt inclusion via volume diffusion due to the very high T of metamorphism. Cesare et al. Lithos 239:186-216. Hayden & Watson EPSL 258:561-568. Stöckhert et al. JMG 27, 673-684.

Geochronology, geochemistry, and petrogenesis of late Permian to early Triassic mafic rocks from Darongshan, South China: Implications for ultrahigh-temperature metamorphism and S-type granite generation

NASA Astrophysics Data System (ADS)

Xu, Wang-Chun; Luo, Bi-Ji; Xu, Ya-Jun; Wang, Lei; Chen, Qi

2018-05-01

The role of the mantle in generating ultrahigh-temperature metamorphism and peraluminous S-type granites, and the extent of crust-mantle interaction are topics fundamental to our understanding of the Earth's evolution. In this study we present geochronological, geochemical, and Sr-Nd-Hf isotopic data for dolerites and mafic volcanic rocks from the Darongshan granite complex belt in western Cathaysia, South China. LA-ICP-MS U-Pb zircon analyses yielded magma crystallization ages of ca. 250-248 Ma for the dolerites, which are coeval with eruption of the mafic volcanic rocks, ultrahigh-temperature metamorphism, and emplacement of S-type granites in the Darongshan granite complex belt. The mafic volcanic rocks are high-K calc-alkaline or shoshonitic, enriched in Th, U, and light rare earth elements, and depleted in Nb, Ta and Ti. The dolerites are characterized by high Fe2O3tot (11.61-20.39 wt%) and TiO2 (1.62-3.17 wt%), and low MgO (1.73-4.38 wt%), Cr (2.8-10.8 ppm) and Ni (2.5-11.4 ppm). Isotopically, the mafic volcanic rocks have negative whole-rock εNd(t) values (-6.7 to -9.0) and high ISr values (0.71232 to 0.71767), which are slightly depleted compared with the dolerite samples (εNd(t) = -10.3 to -10.4 and ISr = 0.71796 to 0.71923). Zircons in the dolerites have εHf(t) values of -7.6 to -10.9. The mafic volcanic rocks are interpreted to have resulted from the partial melting of an enriched lithospheric mantle source with minor crustal contamination during ascent, whereas the dolerites formed by late-stage crystallization of enriched lithospheric mantle-derived magmas after fractionation of olivine and pyroxene. The formation of these mantle-derived mafic rocks may be attributed to transtension along a NE-trending strike-slip fault zone that was related to oblique subduction of the Paleo-Pacific plate beneath South China. Such underplated mafic magmas would provide sufficient heat for the generation of ultrahigh-temperature metamorphism and S-type granites, and act as a mafic end-member for S-type granite genesis.

Oxygen isotopes in garnet and accessory minerals to constrain fluids in subducted crust

NASA Astrophysics Data System (ADS)

Rubatto, Daniela; Gauthiez-Putallaz, Laure; Regis, Daniele; Rosa Scicchitano, Maria; Vho, Alice; Williams, Morgan

2017-04-01

Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. Garnet and U-Pb accessory minerals constitute some of the most robust and ubiquitous minerals in subducted crust and can preserve multiple growth zones that track the metamorphic evolution of the sample they are hosted in. Microbeam investigation of the chemical (major and trace elements) and isotopic composition (oxygen and U-Pb) of garnet and accessory minerals is used to track significant fluid-rock interaction at different stages of the subduction system. This approach requires consideration of the diffusivity of oxygen isotopes particularly in garnet, which has been investigated experimentally. The nature of the protolith and ocean floor alteration is preserved in relict accessory phases within eclogites that have been fully modified at HP conditions (e.g. Monviso and Dora Maira units in the Western Alps). Minerals in the lawsonite-blueschists of the Tavsanli zone in Turkey record pervasive fluid exchange between mafic and sedimentary blocks at the early stage of subduction. High pressure shear zones and lithological boundaries show evidence of intense fluid metasomatism at depth along discontinuities in Monviso and Corsica. In the UHP oceanic crust of the Zermatt-Saas Zone, garnet oxygen isotopes and tourmaline boron isotopes indicate multistage fluid infiltration during prograde metamorphism. Localized exchanges of aqueous fluids are also observed in the subducted continental crust of the Sesia-Lanzo Zone. In most cases analyses of distinct mineral zones enable identification of multiple pulses of fluids during the rock evolution.

Tracing the depositional history of Kalimantan diamonds by zircon provenance and diamond morphology studies

NASA Astrophysics Data System (ADS)

Kueter, Nico; Soesilo, Joko; Fedortchouk, Yana; Nestola, Fabrizio; Belluco, Lorenzo; Troch, Juliana; Wälle, Markus; Guillong, Marcel; Von Quadt, Albrecht; Driesner, Thomas

2016-11-01

Diamonds in alluvial deposits in Southeast Asia are not accompanied by indicator minerals suggesting primary kimberlite or lamproite sources. The Meratus Mountains in Southeast Borneo (Province Kalimantan Selatan, Indonesia) provide the largest known deposit of these so-called "headless" diamond deposits. Proposals for the origin of Kalimantan diamonds include the adjacent Meratus ophiolite complex, ultra-high pressure (UHP) metamorphic terranes, obducted subcontinental lithospheric mantle and undiscovered kimberlite-type sources. Here we report results from detailed sediment provenance analysis of diamond-bearing Quaternary river channel material and from representative outcrops of the oldest known formations within the Alino Group, including the diamond-bearing Campanian-Maastrichtian Manunggul Formation. Optical examination of surfaces of diamonds collected from artisanal miners in the Meratus area (247 stones) and in West Borneo (Sanggau Area, Province Kalimantan Barat; 85 stones) points toward a classical kimberlite-type source for the majority of these diamonds. Some of the diamonds host mineral inclusions suitable for deep single-crystal X-ray diffraction investigation. We determined the depth of formation of two olivines, one coesite and one peridotitic garnet inclusion. Pressure of formation estimates for the peridotitic garnet at independently derived temperatures of 930-1250 °C are between 4.8 and 6.0 GPa. Sediment provenance analysis includes petrography coupled to analyses of detrital garnet and glaucophane. The compositions of these key minerals do not indicate kimberlite-derived material. By analyzing almost 1400 zircons for trace element concentrations with laser ablation ICP-MS (LA-ICP-MS) we tested the mineral's potential as an alternative kimberlite indicator. The screening ultimately resulted in a small subset of ten zircons with a kimberlitic affinity. Subsequent U-Pb dating resulting in Cretaceous ages plus a detailed chemical reflection make a kimberlitic origin unfavorable with respect to the regional geological history. Rather, trace elemental analyses (U, Th and Eu) suggest an eclogitic source for these zircons. The age distribution of detrital zircons allows in general a better understanding of collisional events that formed the Meratus orogen and identifies various North Australian Orogens as potential Pre-Mesozoic sediment sources. Our data support a model whereby the majority of Kalimantan diamonds were emplaced within the North Australian Craton by volcanic processes. Partly re-deposited into paleo-collectors or residing in their primary host, these diamond-deposits spread passively throughout Southeast Asia by terrane migration during the Gondwana breakup. Terrane amalgamation events largely metamorphosed these diamond-bearing lithologies while destroying the indicative mineral content. Orogenic uplift finally liberated their diamond-content into new, autochthonous placer deposits.

Zircon U-Pb Ages from an Ultra-High Temperature Metapelite, Rauer Group, East Antarctica: Implications for Overprints by Grenvillian and Pan-African Events

USGS Publications Warehouse

Wang, Yanbin; Tong, Laixi; Liu, Dunyi

2007-01-01

SHRIMP U-Pb dating of zircon from an ultra-high temperature (UHT, ~1000 °C) granulite-facies metapelite from the Rauer Group, Mather Peninsula, east Antarctica, has yielded evidence for two episodes of metamorphic zircon growth, at ~1.00 Ga and ~530 Ma, and two episodes of magmatism in the source region for the protolith sediment, at ~2.53 and ~2.65 Ga, were identified from the zircon cores. Successive zircon growth at ~1.00 Ga and ~530 Ma records a sequence of distinct, widely spaced high-temperature metamorphic and/or anatectic events related to Grenvillian and Pan-African orogenesis. This study presents the first robust geochronological evidence for the timing of UHT metamorphism of the Rauer Group, supporting arguments that the peak UHT metamorphic event occurred at ~1.00 Ga and was overprinted by a separate high-grade event at ~530 Ma. The new age data indicate that the UHT granulites of the Rauer Group experienced a complex, multi-stage tectonothermal history, which cannot simply be explained via a single Pan-African (~500 Ma) high-grade tectonic event. This is critical in understanding the role of the eastern Prydz Bay region during the assembly of the east Gondwana supercontinent, and the newly recognized inherited Archaean ages (~2.53 and ~2.65 Ga) suggest a close tectonic relationship between the Rauer Group and the adjacent Archaean of the Vestfold Hills

Sapphirine-bearing granulites from the Tongbai orogen, China: Petrology, phase equilibria, zircon U-Pb geochronology and implications for Paleozoic ultrahigh temperature metamorphism

NASA Astrophysics Data System (ADS)

Xiang, Hua; Zhong, Zeng-Qiu; Li, Ye; Qi, Min; Zhou, Han-Wen; Zhang, Li; Zhang, Ze-Ming; Santosh, M.

2014-11-01

We report here for the first time the occurrence of sapphirine-bearing granulites within the Qinling Group of the Qinling-Tongbai orogen and provide robust evidence for extreme crustal metamorphism at ultrahigh-temperature (UHT) conditions. We document the UHT indicator of sapphirine and spinel in a mafic granulite consisting of orthopyroxene, biotite, plagioclase, amphibole and rutile/ilmenite. The ferromagnesian minerals in the sapphirine-bearing granulite have high XMg [Mg/(Mg + Fe)] (orthopyroxene XMg = 0.84-0.95; biotite XMg = 0.81; amphibole XMg = 0.87-0.96). The phase equilibria modeling demonstrates that the early spinel-bearing assemblage is stable at 923-950 °C and 6.7-8.9 kbar, and the peak assemblage of Opx + Pl + Spr/Spl + Amp + Bt + Ilm (+ melt) defines a field at 922-947 °C and 8.4-10.2 kbar. Rutiles have variable Zr concentrations but mostly cluster at ca. 1,500 and 3400 ppm. Zr-in-rutile geothermometry yielded high temperatures of up to 890-940 °C. Zircon U-Pb dating of the granulite constrains the timing of the immediate post-peak and retrograde metamorphic stages as 429 ± 7 Ma and 412 ± 4 Ma, respectively. The UHT metamorphism, together with extensive occurrence of coeval magmatic suites suggests that the Tongbai orogen experienced a Paleozoic Andean-type orogeny probably derived from mid-oceanic ridge subduction of the Qinling Ocean.

Ternary feldspar thermometry of Paleoproterozoic granulites from In-Ouzzal terrane (Western Hoggar, southern Algeria)

NASA Astrophysics Data System (ADS)

Benbatta, A.; Bendaoud, A.; Cenki-Tok, B.; Adjerid, Z.; Lacène, K.; Ouzegane, K.

2017-03-01

The In Ouzzal terrane in western Hoggar (Southern Algeria) preserves evidence of ultrahigh temperature (UHT) crustal metamorphism. It consists in Archean crustal units, composed of orthogneissic domes and greenstone belts, strongly remobilized during the Paleoproterozoic orogeny which was recognized as an UHT event (peak T > 1000 °C and P ≈ 9-12 kbar). This metamorphism was essentially defined locally in Al-Mg granulites, Al-Fe granulites and quartzites outcropping in the Northern part of the In Ouzzal terrane (IOT). In order to test and verify the regional spread of the UHT metamorphism in this terrane, ternary feldspar thermometry on varied rock types (Metanorite, Granulite Al-Mg and Orthogneiss) and samples that crop out in different zones of the In Ouzzal terrane. These rocks contain either perthitic, antiperthitic or mesoperthitic parageneses. Ternary feldspars used in this study have clearly a metamorphic origin. The obtained results combined with previous works show that this UHT metamorphism (>900 °C) affected the whole In Ouzzal crustal block. This is of major importance as for future discussion on the geodynamic context responsible for this regional UHT metamorphism.

Melting of subducted continental crust: Geochemical evidence from Mesozoic granitoids in the Dabie-Sulu orogenic belt, east-central China

NASA Astrophysics Data System (ADS)

Zhao, Zi-Fu; Liu, Zhi-Bin; Chen, Qi

2017-09-01

Syn-collisional and postcollisional granitoids are common in collisional orogens, and they were primarily produced by partial melting of subducted continental crust. This is exemplified by Mesozoic granitoids from the Dabie-Sulu orogenic belt in east-central China. These granitoids were emplaced in small volumes in the Late Triassic (200-206 Ma) and the Late Jurassic (146-167 Ma) but massively in the Early Cretaceous (111-143 Ma). Nevertheless, all of them exhibit arc-like trace element distribution patterns and are enriched in Sr-Nd-Hf isotope compositions, indicating their origination from the ancient continental crust. They commonly contain relict zircons with Neoproterozoic and Triassic U-Pb ages, respectively, consistent with the protolith and metamorphic ages for ultrahigh-pressure (UHP) metaigneous rocks in the Dabie-Sulu orogenic belt. Some granitoids show low zircon δ18O values, and SIMS in-situ O isotope analysis reveals that the relict zircons with Neoproterozoic and Triassic U-Pb ages also commonly exhibit low δ18O values. Neoproterozoic U-Pb ages and low δ18O values are the two diagnostic features that distinguish the subducted South China Block from the obducted North China Block. Thus, the magma source of these Mesozoic granitoids has a genetic link to the subducted continental crust of the South China Block. On the other hand, these granitoids contain relict zircons with Paleoproterozoic and Archean U-Pb ages, which are present in both the South and North China Blocks. Taken together, the Mesozoic granitoids in the Dabie-Sulu orogenic belt and its hanging wall have their magma sources that are predominated by the continental crust of the South China Block with minor contributions from the continental crust of the North China Block. The Triassic continental collision between the South and North China Blocks brought the continental crust into the thickened orogen, where they underwent the three episodes of partial melting in the Late Triassic, Late Jurassic and Early Cretaceous, respectively, for granitic magmatism. While partial melting in the Late Triassic is responsible for syn-exhumation magmatism, the Late Jurassic and Early Cretaceous granitoids are independent of the continental collision and thus belong to postcollisional magmatism.

Monazite, iron oxide and barite exsolutions in apatite aggregates from CCSD drillhole eclogites and their geological implications

NASA Astrophysics Data System (ADS)

Sun, Xiaoming; Tang, Qian; Sun, Weidong; Xu, Li; Zhai, Wei; Liang, Jinlong; Liang, Yeheng; Shen, Kun; Zhang, Zeming; Zhou, Bing; Wang, Fangyue

2007-06-01

We have identified abundant exsolutions in apatite aggregates from eclogitic drillhole samples of the Chinese Continental Scientific Drilling (CCSD) project. Electron microscope and laser Raman spectroscopy analyses show that the apatite is fluorapatite, whereas exsolutions that can be classified into four types: (A) platy to rhombic monazite exsolutions; (B) needle-like hematite exsolutions; (C) irregular magnetite and hematite intergrowths; and (D) needle-like strontian barite exsolutions. The widths and lengths of type A monazite exsolutions range from about 6-10 μm (mostly 6 μm) and about 50-75 μm, respectively. Type B exsolutions are parallel with the C axis of apatite, with widths ranging from 0.5 to 2 μm, with most around 1.5 μm, and lengths that vary dramatically from 6 to 50 μm. Type C exsolutions are also parallel with the C axis of apatite, with lengths of ˜30-150 μm and widths of ˜10 to 50 μm. Type D strontian barite exsolutions coexist mostly with type B hematite exsolutions, with widths of about 9 μm and lengths of about 60-70 μm. Exsolutions of types B, C and D have never been reported in apatites before. Most of the exsolutions are parallel with the C axis of apatite, implying that they were probably exsolved at roughly the same time. Dating by the chemical Th-U-total Pb isochron method (CHIME) yields an U-Pb isochron age of 202 ± 28 Ma for monazite exsolutions, suggesting that these exsolutions were formed during recrystallization and retrograde metamorphism of the exhumed ultrahigh pressure (UHP) rocks. Quartz veins hosting apatite aggregates were probably formed slightly earlier than 202 Ma. Abundant hematite exsolutions, as well as coexistence of magnetite/hematite and barite/hematite in the apatite, suggest that the oxygen fugacity of apatite aggregates is well above the sulfide-sulfur oxide buffer (SSO). Given that quartz veins host these apatite aggregates, they were probably deposited from SiO 2-rich hydrous fluids formed during retrogression of the subducted slab. Such SiO 2-rich hydrous fluids may act as an oxidizing agent, a feasible explanation for the high oxygen fugacity in convergent margin systems.

Earthquakes, fluid pressures and rapid subduction zone metamorphism

NASA Astrophysics Data System (ADS)

Viete, D. R.

2013-12-01

High-pressure/low-temperature (HP/LT) metamorphism is commonly incomplete, meaning that large tracts of rock can remain metastable at blueschist- and eclogite-facies conditions for timescales up to millions of years [1]. When HP/LT metamorphism does take place, it can occur over extremely short durations (<<1 Myr) [1-2]. HP/LT metamorphism must be associated with processes that allow large volumes of rock to remain unaffected over long periods of time, but then suddenly undergo localized metamorphism. Existing models for HP/LT metamorphism have focussed on the role of fluids in providing heat for metamorphism [2] or catalyzing metamorphic reactions [1]. Earthquakes in subduction zone settings can occur to depths of 100s of km. Metamorphic dehydration and the associated development of elevated pore pressures in HP/LT metamorphic rocks has been identified as a cause of earthquake activity at such great depths [3-4]. The process of fracturing/faulting significantly increases rock permeability, causing channelized fluid flow and dissipation of pore pressures [3-4]. Thus, deep subduction zone earthquakes are thought to reflect an evolution in fluid pressure, involving: (1) an initial increase in pore pressure by heating-related dehydration of subduction zone rocks, and (2) rapid relief of pore pressures by faulting and channelized flow. Models for earthquakes at depth in subduction zones have focussed on the in situ effects of dehydration and then sudden escape of fluids from the rock mass following fracturing [3-4]. On the other hand, existing models for rapid and incomplete metamorphism in subduction zones have focussed only on the effects of heating and/or hydration with the arrival of external fluids [1-2]. Significant changes in pressure over very short timescales should result in rapid mineral growth and/or disequilibrium texture development in response to overstepping of mineral reaction boundaries. The repeated process of dehydration-pore pressure development-earthquake-pore pressure relief could conceivably produce a record of episodic HP/LT metamorphism driven by rapid pressure pulses. A new hypothesis is presented for the origins of HP/LT metamorphism: that HP/LT metamorphism is driven by effective pressure pulses caused by localized, earthquake-related modifications to fluid pressures in the subducted slab. In other words, HP/LT metamorphism marks abrupt changes in stress state within the subducted slab, driven by earthquake rupture and fluid flow, and involving a rapid return toward lithostatic pressure from effective pressures well below lithostatic. References: 1. Bjørnerud, MG, Austrheim, H & Lund, MG, 2002. Processes leading to eclogitization (densification) of subducted and tectonically buried crust. Journal of Geophysical Research 107, 2252. 2. Camacho, A, Lee, JKW, Hensen, BJ & Braun, J, 2005. Short-lived orogenic cycles and the eclogitization of cold crust by spasmodic hot fluids. Nature 435, 1191-1196. 3. Green, HW & Houston, H, 1995. The mechanics of deep earthquakes. Annual Reviews of Earth and Planetary Sciences 23, 169-213. 4. Hacker, BR, Peacock, SM, Abers, GA & Holloway, SD, 2003. Subduction factory 2. Are intermediate-depth earthquakes in subducting slabs linked to metamorphic dehydration reactions?. Journal of Geophysical Research 108, 2030.

Joint Inversion of Geochemical Data and Geophysical Logs for Lithology Identification in CCSD Main Hole

NASA Astrophysics Data System (ADS)

Deng, Chengxiang; Pan, Heping; Luo, Miao

2017-12-01

The Chinese Continental Scientific Drilling (CCSD) main hole is located in the Sulu ultrahigh-pressure metamorphic (UHPM) belt, providing significant opportunities for studying the metamorphic strata structure, kinetics process and tectonic evolution. Lithology identification is the primary and crucial stage for above geoscientific researches. To release the burden of log analyst and improve the efficiency of lithology interpretation, many algorithms have been developed to automate the process of lithology prediction. While traditional statistical techniques, such as discriminant analysis and K-nearest neighbors classifier, are incompetent in extracting nonlinear features of metamorphic rocks from complex geophysical log data; artificial intelligence algorithms are capable of solving nonlinear problems, but most of the algorithms suffer from tuning parameters to be global optimum to establish model rather than local optimum, and also encounter challenges in making the balance between training accuracy and generalization ability. Optimization methods have been applied extensively in the inversion of reservoir parameters of sedimentary formations using well logs. However, it is difficult to obtain accurate solution from the logging response equations of optimization method because of the strong overlapping of nonstationary log signals when applied in metamorphic formations. As oxide contents of each kinds of metamorphic rocks are relatively less overlapping, this study explores an approach, set in a metamorphic formation model and using the Broyden Fletcher Goldfarb Shanno (BFGS) optimization algorithm to identify lithology from oxide data. We first incorporate 11 geophysical logs and lab-collected geochemical data of 47 core samples to construct oxide profile of CCSD main hole by using backwards stepwise multiple regression method, which eliminates irrelevant input logs step by step for higher statistical significance and accuracy. Then we establish oxide response equations in accordance with the metamorphic formation model and employ BFGS algorithm to minimize the objective function. Finally, we identify lithology according to the composition content which accounts for the largest proportion. The results show that lithology identified by the method of this paper is consistent with core description. Moreover, this method demonstrates the benefits of using oxide content as an adhesive to connect logging data with lithology, can make the metamorphic formation model more understandable and accurate, and avoid selecting complex formation model and building nonlinear logging response equations.

"Fullerene-like" Raman bands in UHP metamorphic diamonds: Metastable intermediate phases for diamond formation

NASA Astrophysics Data System (ADS)

Harada, Y.; Igarashi, M.; Hashiguchi, Y.; Ogasawara, Y.

2011-12-01

Mysterious Raman bands at 1430-1480 cm-1 suggesting carbon (or carbon-bearing) species have been discovered in UHP metamorphic microdiamonds entirely enclosed in dolomite marble from Kokchetav Massif (Igarashi et al., 2011). Such Raman bands first discovered at some domains in a T-type (see Ishida et al., 2003) diamond in dolomite marble in 2005, but we have not reported this because of the possibility of misidentification by contamination. Later, similar bands were also found in the rim and the core of S-type and R-type. The relative intensities of these Raman bands to diamond (at 1332 cm-1) were 10-40 % in average (max. 90-110 %) and FWHMs are broad (25-45 cm-1). The possibility of the appearance of these Raman bands was low. As we used ordinary polished thin sections (thickness: 25 μm) and the organic materials used in thin section making have Raman bands at ca. 1450 cm-1, we carefully examined observed Raman spectra and the positions of the source materials of these bands to exclude the possibility of contaminations. Examined microdiamond grains are entirely enclosed in the host garnet, and no crack was observed in the host. We conducted 2D Raman mappings at different depths with 2 μm intervals. The result showed that the domains having these Raman bands were located within diamond grains and limited area (1-3 μm). These bands were never detected from outside diamond grains (e.g., host garnet). Thus, the unknown Raman bands at 1430-1480 cm-1 were attributed to some materials inside microdiamonds entirely included in the host garnet. The possibility of contamination was denied. Recently, we found similar Raman bands in the microdiamonds in garnet in Grt-Bt gneiss. Examined microdiamonds are entirely enclosed in garnet grain and no extra phase observed near laser spots in these microdiamond grains under an optical microscope. The Raman bands at 1430-1480 cm-1 were found from 4 microdiamond grains. The peak positions and FWHMs of these bands were as follows: (a) 1433, 31 (b) 1456, 35 (b) 1458, 41 (c) 1461, 31 (e) 1462 cm-1, 44 cm-1. Their intensities to the host diamond were 10-20 % in average. The mappings at different depths also showed very limited source space inside microdiamond grains. Although it is difficult to identify the source materials only by Raman spectroscopy, we considered that the Raman bands could be attributed to some carbon or carbon-bearing species which were relicts as metastable intermediate phases for microdiamond formation under UHP. Fullerenes are speculated as possible carbon materials for those bands. The band at 1470 cm-1 is similar to Ag (2) band of C60 fullerene. The large FWHM and the variation of peak positions at 1430-1480 cm-1 may be caused by aggregations of several species of fullerenes. If our speculation is correct, metamorphic diamond could have the possibility of preservation of intermediate carbon phases in diamond because the duration for diamond growth was much shorter than kimberlitic diamonds. We should pay attentions to such extra materials inside diamonds in order to clarify the real image of the diamond formation.

Amphibole equilibria as monitors of P-T path and process in the exhumation of HP/UHP terranes

NASA Astrophysics Data System (ADS)

Waters, David; Airaghi, Laura; Czertowicz, Thomas

2014-05-01

Recent advances in modelling and the development of refined activity-composition relations allow the calculation of phase diagrams involving complex mineral solid solutions, such as calcic, sodic-calcic and sodic amphiboles (e.g. Diener et al., 2007, J metamorphic Geol.). Amphiboles are commonly found in eclogite facies metabasites, and formed at different metamorphic stages. Such rocks commonly show complex reaction microstructures that reveal their history. The focus in this contribution is on two distinct amphibole types: coarse, post-peak matrix amphibole, and amphibole involved in symplectitic microstructures replacing omphacite. These studies serve as a test of the current activity models and calculation approaches, but more importantly as a framework for understanding the processes and P-T path during exhumation of subducted terranes. Examples are taken from the Western Gneiss Complex of Norway and from the Kaghan Valley (Pakistan), but are more generally applicable to crustal blocks that have exhumed through the P-T 'window' in which comparable petrological features develop. The microstructural types of interest here are: broad irregular interstitial amphibole grains, which commonly merge with a coarse spongy intergrowth of amphibole with quartz and/or albite (most likely replacing omphacite); and a fine-grained symplectite of low-Na clinopyroxene with sodic plagioclase and minor hornblende invading omphacite. Many specimens show these varieties as a sequence, inferred to reflect decreasing pressure (and ultimately, temperature). Amphibole compositions cover a wide range: the most sodic occur in large interstitial grains and fall near the junction of the winchite, barroisite and taramite fields of the IMA classification; they trend towards a pargasitic hornblende, still with significant glaucophane component; spongy amphiboles typically lie on a trend towards lower glaucophane component; symplectite amphibole is generally a common hornblende on a typical trend between actinolite and pargasite, with low glaucophane component. Pressures and temperatures for matrix and spongy amphiboles are constrained by mapping phase compositions and proportions on P-T phase diagrams calculated for a range of water contents in bulk rock and local systems. In HP eclogites they define near-isothermal decompression trajectories from ~20 to ~12 kbar at ~630-670°C. Matrix and spongy amphiboles from UHP eclogites lacking significant hydrous minerals require influx of external fluid in the interval 16-12 kbar. In symplectites conditions are derived from an internal equilibrium among amphibole, pyroxene and plagioclase. In a number of cases the variation along lamellae in a symplectite colony defines a P-T array covering ~60°C of cooling over ~3 kbar decompression down to 12-10 kbar. In many cases amphibole development can be linked to both external and local sources of aqueous fluid. Microstructural and chemical evidence links symplectite formation to the breakdown of phengite. The near-isothermal earlier stages of P-T paths in these slices dominated by continental units suggest that exhumation did not take place in a cold subduction channel, but may reflect a post-collisional mechanism. The lower P-T slope of paths associated with later symplectite arrays may reflect the loss of buoyancy contrast as exhuming slices reach crustal levels.

Chlorine isotope constraints on fluid-rock interactions during subduction and exhumation of the Zermatt-Saas ophiolite

NASA Astrophysics Data System (ADS)

Selverstone, J.; Sharp, Z. D.

2013-10-01

Chlorine isotope compositions of high-pressure (˜2.3 GPa) serpentinite, rodingite, and hydrothermally altered oceanic crust (AOC) differ significantly from high- and ultrahigh-pressure (> 3.2 GPa) metasedimentary rocks in the Aosta region, Italy. Texturally early serpentinites, rodingites, and AOC have bulk δ37Cl values indistinguishable from those of modern seafloor analogues (δ37Cl = -1.0 to +1.0‰). In contrast, serpentinites and AOC samples that recrystallized during exhumation have low δ37Cl values (-2.7 to -0.5‰); 37Cl depletion correlates with progressive changes in bulk chemistry. HP/UHP metasediments have low δ37Cl values (median = -2.5‰) that differ statistically from modern marine sediments (median = -0.6‰). Cl in metasedimentary rocks is concentrated in texturally early minerals, indicating modification of seafloor compositions early in the subduction history. The data constrain fluid sources during both subduction and exhumation-related phases of fluid-rock interaction: (1) marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction. (2) No pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial. (3) Localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel. Most samples, however, preserved protolith signatures during subduction to near-arc depths.

Mineral Reactions Involving Sapphirine and Their Application for Characterization of Metamorphic Conditions

NASA Astrophysics Data System (ADS)

Podlesskii, K. K.

2008-05-01

Assemblages of sapphirine, once considered to be a rare mineral, have in recent years been recognized as important indicators of high-temperature metamorphism. They occur in rocks that have undergone different tectono-metamorphic histories, with the P-T range of formation being estimated from below 700°C and 0.5 GPa to above 1100°C and 1.5 GPa. Sapphirine associated with quartz is attributed exclusively to the highest temperature conditions of crustal metamorphism referred to as ultrahigh-temperatiure metamorphism. Although experimental data involving sapphirine extend over an even wider P-T range, the quantitative interpretation of sapphirine-bearing assemblages remains ambiguous. Thermodynamic properties of magnesian sapphirine end-members have been optimized on the basis of experimentally constrained phase relations with the equation of state developed by Gerya et al., 2004. They differ from the model used in THERMOCALC (Kelsey et al., 2004), and the differences in the estimated stability of assemblages of sapphirine with quartz, kyanite and forsterite, to which a special attention have been paid due to their petrologic importance, look dramatic and may change interpretations of petrogenetic processes.

Partial melting of deeply subducted eclogite from the Sulu orogen in China

PubMed Central

Wang, Lu; Kusky, Timothy M.; Polat, Ali; Wang, Songjie; Jiang, Xingfu; Zong, Keqing; Wang, Junpeng; Deng, Hao; Fu, Jianmin

2014-01-01

We report partial melting of an ultrahigh pressure eclogite in the Mesozoic Sulu orogen, China. Eclogitic migmatite shows successive stages of initial intragranular and grain boundary melt droplets, which grow into a three-dimensional interconnected intergranular network, then segregate and accumulate in pressure shadow areas and then merge to form melt channels and dikes that transport magma to higher in the lithosphere. Here we show, using zircon U–Pb dating and petrological analyses, that partial melting occurred at 228–219 Myr ago, shortly after peak metamorphism at 230 Myr ago. The melts and residues are complimentarily enriched and depleted in light rare earth element (LREE) compared with the original rock. Partial melting of deeply subducted eclogite is an important process in determining the rheological structure and mechanical behaviour of subducted lithosphere and its rapid exhumation, controlling the flow of deep lithospheric material, and for generation of melts from the upper mantle, potentially contributing to arc magmatism and growth of continental crust. PMID:25517619

Integrated in situ U-Pb Age and Hf-O Analyses of Zircon from the Northern Yangtze Block: New Insights into the Neoproterozoic Low-δ18O Magmas in the South China Block

NASA Astrophysics Data System (ADS)

Yang, Y. N.; Wang, X. C.; Li, Q. L.; Li, X. H.

2015-12-01

The oxygen isotopic composition of Neoproterozoic magmas from the northern Yangtze Block holds a key for the origin of large-scale 18O depletion in the HP and UHP metamorphic rocks in the Dabie-Sulu orogenic belt, northern margin of the South China Block. We report here the integrated in situ U-Pb dating and O-Hf isotope analyses of zircon grains from sedimentary and volcanic rocks of the late Neoproterozoic Suixian Group (SG) from the northern Yangtze Block. Detrital zircon grains display age peaks of 0.73-0.74 Ga, 0.79 Ga, and 2.0 Ga. Zircon U-Pb ages together with Hf-O isotopic composition indicate provenance of SG dominantly from proximal Neoproterozoic igneous rock and likely hidden Paleoproterozoic basement along the northern margin of the Yangtze Block. The zircon δ18O values from SG range from 10.5‰ to 1.3‰. Zircon grains with negative δ18O value, typical result of magma-ice interaction, were not identified in this study. The major phase of low-δ18O (< 4‰) magmas initiated at ca. 780 Ma, long before the first glaciation event (< 715 Ma) in the South China Block. Thus caution should be taken when using low-δ18O zircon grains to infer cold climate. Low-δ18O zircon grains have large ranges of ɛHf(t) values, varying from -15.5 to 10.7, concentrating on negative ɛHf(t). This strongly argues against the possibility that the low-δ18O magma was produced by partial melting of high-temperature hydrothermally altered oceanic crust because this model predicted MORB-like Hf isotopes for the resultant low-δ18O magmas. This study emphasizes that high-T water-rock interaction and continental rifting tectonic setting are essential to generate abundant low-δ18O magmas. The important application of our study is to confirm that most of negative-δ18O zircons identified in HP and UHP metamorphic rocks may not have been inherited from their Neoproterozoic protoliths.

Elemental and isotopic (C, O, Sr, Nd) compositions of Late Paleozoic carbonated eclogite and marble from the SW Tianshan UHP belt, NW China: Implications for deep carbon cycle

NASA Astrophysics Data System (ADS)

Zhu, Jianjiang; Zhang, Lifei; Lü, Zeng; Bader, Thomas

2018-03-01

Subduction zones are important for understanding of the global carbon cycle from the surface to deep part of the mantle. The processes involved the metamorphism of carbonate-bearing rocks largely control the fate of carbon and contribute to local carbon isotopic heterogeneities of the mantle. In this study, we present petrological and geochemical results for marbles and carbonated eclogites in the Southwestern Tianshan UHP belt, NW China. Marbles are interlayered with coesite-bearing pelitic schists, and have Sr-Nd isotopic values (εNd (T=320Ma) = -3.7 to -8.9, 87Sr/86Sr (i) = 0.7084-0.7089), typical of marine carbonates. The marbles have dispersed low δ18OVSMOW values (ranging from 14 to 29‰) and unaffected carbon isotope (δ13CVPDB = -0.2-3.6‰), possibly due to infiltration of external H2O-rich fluids. Recycling of these marbles into mantle may play a key role in the carbon budget and contributed to the mantle carbon isotope heterogeneity. The carbonated eclogites have high Sr isotopic compositions (87Sr/86Sr (i) = 0.7077-0.7082) and positive εNd (T = 320 Ma) values (from 7.6 to 8.2), indicative of strong seafloor alteration of their protolith. The carbonates in the carbonated eclogites are mainly dolomite (Fe# = 12-43, Fe# = Fe2+/(Fe2+ + Mg)) that were added into oceanic basalts during seafloor alteration and experienced calcite - dolomite - magnesite transformation during the subduction metamorphic process. The uniformly low δ18O values (∼11.44‰) of carbonates in the carbontaed eclogites can be explained by closed-system equilibrium between carbonate and silicate minerals. The low δ13C values (from -3.3 to -7.7‰) of the carbonated eclogites most likely reflect contribution from organic carbon. Recycling of these carbonated eclogites with C isotope similar to typical mantle reservoirs into mantle may have little effect on the mantle carbon isotope heterogeneity.

Li/B ratio in deep fluids an indicator of their generation depth

NASA Astrophysics Data System (ADS)

Hirajima, Takao; Sengen, Yoshiteru; Nishimura, Koshi; Ohsawa, Shinji

2010-05-01

Deep fluids derived from subducted terrestrial materials significantly affect and cause various physicochemical processes in the subduction zone, e.g., earthquakes in the subducting plate, partial melting in the mantle wedge, which causes island arc volcanism, the exhumation of high pressure metamorphic rocks, and so on (e.g., Schmidt and Poli, 1998). However, nature of deep fluids is still under the deep veil. To evaluate precisely the effect of deep fluids which affect various subduction processes, following aspects concerning the nature of deep fluids should be evaluated well, 1) the depths and the amounts of fluid release, 2) species and compositions of fluids, 3) the fluid paths and scale of motion, and etc. (e.g., Scambelluri and Philippot, 2001). In recent years, the depths and amounts of fluid release become to be evaluated well by synthetic experiments and thermodynamic calculation in the basaltic system (e.g., Schmidt and Poli, 1998; Hacker et al., 2003). The information on species and compositions of fluids can be obtained directly from fluid inclusions trapping in natural HP/UHP metamorphic rocks, but quantitative analyses of their major and trace element composition are still in the hard task. This paper reports the Li-B-Cl ratio of deep fluids extracted from quartz veins/lenses developing parallel to the main foliation of LT/HP type metamorphic rocks crystallized from 20 to 60 km depths in the Sanbagawa belt, Japan. The quartz veins crosscutting the main foliation, i.e., formed during the retrograde stage, are out of scope in this paper. Raman spectroscopy for fluid inclusions in quartz veins/lenses reveals that most inclusions are composed of aqueous liquid and gas species of CO2, CH4 and/or N2. Aqueous bubble was not detected. Microthermometry for them reveals that freezing temperature varies from -15oC to 0oC .Rough negative correlation is detected between the freezing temperature and homogenization temperature (120-450 oC). These results suggest that the fluid inclusions in the studied specimens were produced during multi-stages, probably higher salinity syn-metamorphic ones and lower salinity post-peak metamorphic ones. The deep fluids contained in the quartz veins/lenses were leached into the extra-pure water by the crush leaching technique, mainly following Banks and Yardley (1992) and Bottrell et al. (1988). Composition in the leached fluids was analyzed using gas-chromatography and ICP-MS. All extracted fluids are characterized by significantly lower Cl/(Lix2000+Bx500+Cl) (<0.2) ratio than the value of the modern sea water (ca. 0.8). Li(x2000)/B(x500) ratio of extracted fluids varies from 0.1 to 1.0 and shows a positive correlation with the metamorphic grade of the host rock., i.e., ca. 0.1 in the chlorite zone, ca. 0.2 in the garnet zone, ca. 0.4 in the biotite zone and 0.4-1.0 in the eclogite unit. Literature data of Li-B contents in natural HP metamorphic rocks suggest that Li/B ration of dehydrated fluid released from subducted meta-basalts increases with the metamorphic depth (Marschall et al., 2006; 2007). These evidences suggest that Li/B ratio of deep fluids has a potential evaluating the generated depth, although there remains several factors which control should Li/B ration ratio in the fluid should be clarified.

Diamonds in ophiolitic mantle rocks and podiform chromitites: An unsolved mystery

NASA Astrophysics Data System (ADS)

Yang, J.; Zhang, Z.; Xu, X.; Ba, D.; Bai, W.; Fabg, Q.; Meng, F.; Chen, S.; Robinson, P. T.; Dobrzhinetskaya, L.

2009-05-01

In recent years ultrahigh pressure minerals, such as diamond and coesite, and other unusual minerals were discovered in chromitites of the Luobusa ophiolite in Tibet, and 4 new minerals have been approved by the CNMMN. These results have raised many questionsWhat are the occurrences of the diamonds, what is the source of their carbon and how were they formed? What is the origin of the chromites hosting the diamonds and at what depth did they form? What is the genetic relationship between the diamonds and the host chromitites? In what geological, geophysical and geochemical environments can the diamonds be formed and how are they preserved? The UHP minerals from Luobusa are controversial because they have not been found in situ and because ophiolites are currently believed to form at shallow levels above oceanic spreading centers in suprasubduction zone environments. More detailed study and experimental work are needed to understand the origin and significance of these unusual minerals and investigations of other ophiolites are needed to determine if such minerals occur elsewhere To approach these problems, we have collected two one-ton samples of harzburgite hosting chromitite orebodies in the Luobusa ophiolite in Tibet. The harzburgite samples were taken close to chromitite orebody 31, from which the diamonds, coesite and other unusual minerals were recovered. We processed these two samples in the same manner as the chromitites and discovered numerous diamonds and more than 50 other mineral species. These preliminary results show that the minerals in the harzburgites are similar to those in the chromitites, suggesting a genetic relationship between them. To determine if such UHP and unusual minerals occur elsewhere, we collected about 1.5 t of chromitite from two orebodies in an ultramafic body in the Polar Urals. Thus far, more than 60 different mineral species have been separated from these ores. The most exciting discovery is the common occurrence of diamond, a typical UHP mineral in the Luobusa chromitites. Other minerals include: (1) native elements: Cr, W, Ni, Co, Si, Al and Ta; (2) carbides: SiC and WC; (3) alloys: Cr-Fe, Si-Al-Fe, Ni-Cu, Ag-Au, Ag-Sn, Fe-Si, Fe-P, and Ag-Zn-Sn; (4) oxides: NiCrFe, PbSn, REE, rutile and Si-bearing rutile, ilmenite, corundum, chromite, MgO, and SnO2; (5) silicates: kyanite, pseudomorphs of octahedral olivine, zircon, garnet, feldspar, and quartz,; (6) sulfides of Fe, Ni, Cu, Mo, Pb, Ab, AsFe, FeNi, CuZn, and CoFeNi; and (7) iron groups: native Fe, FeO, and Fe2O3. These minerals are very similar in composition and structure to those reported from the Luobusa chromitites.

A 4.43 Ga Transition from Mega-impact to Habitability Deduced from Microstructural Geochronology of Martian Zircon and Baddeleyite

NASA Astrophysics Data System (ADS)

Moser, D.; Reinhard, D. A.; Larson, D. J.; McCubbin, F. M.; Darling, J.; White, L. F.; Arcuri, G.; Irving, A. J.; Tait, K.; Barker, I.

2017-12-01

The rates at which early planetary surfaces like those of Mars and Earth transitioned to stability within the heavy bombardment epoch are poorly constrained. Here we show through analysis of the shock history of the earliest mineral remnants of Mars crust, specifically the accessory and highly refractory phases zircon and baddeleyite in martian meteorites, that the transition for Mars was relatively rapid and early. The Moon-sized impactor widely believed to have generated the martian hemispheric dichotomy, would have caused catastrophic heating, impact metamorphism and global re-surfacing by magma.This process would either destroy any primordial accessory phases through melting and vaporization, or impart micro- or nano-structural signatures of ultra-high temperature and/or pressure metamorphism on survivor crystals. We have conducted atom probe and/or correlative electron microscopy on intensely shocked and heated zircon and baddeleyite reference samples from Earth and the Moon, as well as from 4.43 Ga grains occurring as crystals and in lithic clasts in six polished surfaces of the Rabt Sbayta suite of martian polymict regolith breccias (NWA 7475, NWA 7034, NWA 7906, Rabt Sbayta 003). The martian population (n=68) shows no micro- or nano-signatures of ultra high temperature or pressure metamorphism. Instead, it exhibits mostly low-grade shock and thermal features consistent with regolith formation at 1.5 Ga and recent low pressure ( 5GPa) launch to Earth. Taken together with the time for decay of the mega-impact heat effects, as well as the 4.50 Ga age estimate for martian mantle solidification (modelled by other workers) our results indicate an early, 70 million year long transition from initiation of the hemispheric dichotomy to establishment of at least one domain of persistently stable and potentially habitable crust. The accelerated deep mantle convection prompted by mega-impact may have also increased the transport rate of volatiles to the Martian exterior during this transition, permitting the inference that early, planet-shaping impacts may ultimately promote habitability pathways in planetary systems.

Ultrahigh pressure extraction of bioactive compounds from plants-A review.

PubMed

Xi, Jun

2017-04-13

Extraction of bioactive compounds from plants is one of the most important research areas for pharmaceutical and food industries. Conventional extraction techniques are usually associated with longer extraction times, lower yields, more organic solvent consumption, and poor extraction efficiency. A novel extraction technique, ultrahigh pressure extraction, has been developed for the extraction of bioactive compounds from plants, in order to shorten the extraction time, decrease the solvent consumption, increase the extraction yields, and enhance the quality of extracts. The mild processing temperature of ultrahigh pressure extraction may lead to an enhanced extraction of thermolabile bioactive ingredients. A critical review is conducted to introduce the different aspects of ultrahigh pressure extraction of plants bioactive compounds, including principles and mechanisms, the important parameters influencing its performance, comparison of ultrahigh pressure extraction with other extraction techniques, advantages, and disadvantages. The future opportunities of ultrahigh pressure extraction are also discussed.

Alpine Serpentinite Geochemistry As Key To Define Timing Of Oceanic Lithosphere Accretion To The Subduction Plate Interface

NASA Astrophysics Data System (ADS)

Gilio, M.; Scambelluri, M.; Agostini, S.; Godard, M.; Pettke, D. T.; Angiboust, S.

2016-12-01

Isotopic (Pb, Sr and B) and trace element (B, Be, As, Sb, U, Th) signatures of serpentinites are useful geochemical tools to assess element exchange and fluid-rock interactions in subduction zone settings. They help to unravel geological history and tectonic evolution of subduction serpentinites and associated meta-oceanic crust. Sedimentary-derived fluid influx within HP plate interface environments strongly enriches serpentinites in As, Sb, B, U and Th and resets their B, Sr and Pb isotopic compositions. This HP metasomatic signature is preserved during exhumation and/or released at higher PT through de-serpentinization, fueling partial melting in the sub-arc mantle and recycling such fingerprint into arc magmas. This study focuses on the subduction recrystallization, geochemical diversity and fluid-rock interaction recorded by high- to ultra-high pressure (HP, UHP) Alpine serpentinites from the subducted oceanic plate (Cignana Unit, Zermatt-Saas Complex, Monviso and Lanzo Ultramafic Massifs). The As and Sb compositions of the HP-UHP Alpine ophiolitic rocks reveal the interaction between serpentinite and crust-derived fluids during their emplacement along the plate interface. This enables to define a hypothetical architecture of the Alpine subduction interface, considering large ultramafic slices. In this scenario, the Lanzo peridotite and serpentinite retain an As-Sb composition comparable to DM and PM: i.e. they experienced little exchange with sediment-derived fluids. Lanzo thus belonged to sections of the subducting plate, afar from the plate interface. Serpentinites from the Lago di Cignana Unit and Monviso and Voltri are richer in As and Sb, showing moderate to strong interaction with sediment- and crust-derived fluids during subduction (i.e. they behaved as open systems). These serpentinite slices accreted at the plate interface and exchanged with slab-derived fluids at different depths during Alpine subduction: Voltri accreted at shallower conditions (50-60 km) than Monviso Unit (around 80 km depth) and Lago di Cignana (about 100 km depth), and exchanged with sedimentary and crustal systems during the entire burial history. Their relatively lower density might act as buoyancy force, triggering the exhumation of much denser lithologies (eclogite and peridotite).

Titanite chronology, thermometry, and speedometry of ultrahigh-temperature (UHT) calc-silicates from south Madagascar: U-Pb dates, Zr temperatures, and lengthscales of trace-element diffusion

NASA Astrophysics Data System (ADS)

Holder, R. M.; Hacker, B. R.

2017-12-01

Calc-silicate rocks are often overlooked as sources of pressure-temperature-time data in granulite-UHT metamorphic terranes due to the strong dependence of calc-silicate mineral assemblages on complex fluid compositions and a lack of thermodynamic data on common high-temperature calc-silicate minerals such as scapolite. In the Ediacaran-Cambrian UHT rocks of southern Madagascar, clinopyroxene-scapolite-feldspar-quartz-zircon-titanite calc-silicate rocks are wide-spread. U-Pb dates of 540-520 Ma from unaltered portions of titanite correspond to cooling of the rocks through upper-amphibolite facies and indicate UHT metamorphism occurred before 540 Ma. Zr concentrations in these domains preserve growth temperatures of 900-950 °C, consistent with peak temperatures calculated by pseudosection modeling of nearby osumilite-bearing gneisses. Younger U-Pb dates (510-490 Ma) correspond to fluid-mediated Pb loss from titanite grains, which occurred below their diffusive Pb-closure temperature, along fractures. The extent of fluid alteration is seen clearly in back-scattered electron images and Zr-, Al-, Fe-, Ce-, and Nb-concentration maps. Laser-ablation depth profiling of idioblastic titanite grains shows preserved Pb diffusion profiles at grain rims, but there is no evidence for Zr diffusion, indicating that it was effectively immobile even at UHT.

On the Preservation of Intergranular Coesite in UHP Eclogite at Yangkou Bay, Sulu belt of eastern China

NASA Astrophysics Data System (ADS)

Wang, L.; Wang, S.; Brown, M.

2016-12-01

In contrast to coesite that occurs as inclusions in zircon and rock-forming minerals, intergranular coesite is preserved in UHP eclogite at Yangkou in the Sulu belt. The survival of intergranular coesite is intriguing because the eclogite experienced phengite growth and partial melting during exhumation. The coesite eclogite occurs as rootless isoclinal fold noses within quartz-rich schist which contains 10-20 vol% phengite, whereas phengite is absent from coesite eclogite in the fold noses. To evaluate the factors that control preservation of intergranular coesite, four samples representative of different stages along the retrograde P-T path were selected for study. For each sample we determined the number of intergranular coesite grains per cm2 and the OH content of garnet and omphacite. As the number of coesite grains decreases, the bulk rock OH content increases from <200 ppm in phengite-free coesite eclogite to 200-260 ppm in phengite-bearing (<5 vol%) coesite eclogite and up to a maximum of 430-438 ppm in quartz eclogite ( 10 vol% phengite). However, the OH content drops to a minimum of 59 ppm in residual eclogite resulting from melt drainage. This trend implies that the volume of fluid increased sufficiently during exhumation to facilitate the growth of phengite and the transformation to quartz of intergranular coesite outside of the fold noses. The fluid is inferred to have been a supercritical fluid probably residual from prograde dehydration but also derived by dissolution of nominally anhydrous minerals. Post-metamorphic-peak deformation combined with fluid percolation along sheared fold limbs induced phengite growth during initial exhumation and then facilitated partial melting. In contrast, fold hinges in competent layers are unfavourable sites for fluid penetration. At Yangkou, the intergranular coesite is preserved in the fold noses where it was protected from both penetrative deformation and fluid ingress. Therefore, the fold noses maintained a relatively dry environment that allowed preservation of the intergranular coesite. Thus, deformation partitioning and strain localization impose local controls on fluid distribution and migration in UHP eclogite. This study informs our understanding of variations in fluid regime during exhumation of deeply subducted continental crust.

An eclogite-bearing continental tectonic slice in the Zermatt-Saas high-pressure ophiolites at Trockener Steg (Zermatt, Swiss Western Alps)

NASA Astrophysics Data System (ADS)

Weber, Sebastian; Bucher, Kurt

2015-09-01

The Theodul Glacier Unit (TGU) at "Trockener Steg" represents a continental slice, embedded within the ophiolitic Zermatt-Saas Zone. The Zermatt-Saas Zone is the remnant of the Piemonte-Liguria oceanic lithosphere, formed in the middle Jurassic and subducted up to eclogite facies conditions in the Early Tertiary. The close spatial association of the TGU to the Zermatt-Saas Zone permits a comparison of the metamorphic evolution of the units by detailed field mapping and a petrological investigation of eclogites. The eclogites from both tectono-metamorphic units can be clearly distinguished by their textures, mineral assemblages and by mineral and bulk-rock composition. Geothermobarometry and computed assemblage stability diagrams for the TGU eclogites indicate P-T conditions of 2.2 ± 0.1 GPa and 580 ± 50 °C. These derived P-T conditions must be considered as minimum peak metamorphic conditions the rocks achieved during subduction. The P-T data are different from those derived for eclogites of Zermatt-Saas Zone adjacent to the Theodul Glacier Unit, that reached maximal burial depths at 2.3-2.4 GPa and 500 ± 50 °C. While the estimates of the eclogites of Zermatt-Saas Zone are in good agreement with some of the previous studies, the contrasting P-T estimates for the TGU eclogites suggest that the Zermatt-Saas complex must be subdivided into several tectonic subunits. The non-uniform peak conditions over the "Trockener Steg" area and the maximum pressures conditions reported from ultra-high pressure localities within Zermatt-Saas Zone suggest, that individual tectonic slices have been assembled after detachment from the slab at the return-point, i.e. along the exhumation path. Detached packages of rocks may range from small tectonic slices up to several kilometer-sized fragments. The TGU is separated from the surrounding rocks of the ophiolite unit by two major tectonic contacts. In addition, the formation of biotite-rich crusts along the basal contact of the TGU is evidence of prolonged fluid channeling along the basal thrust. The presence of hydrous decompression assemblages replacing earlier formed high-pressure mineral assemblages within the studied eclogite suggests that fluids were present throughout most of the TGU exhumation history.

Geochronology of pervasive top-to-the-SE directed deformation in the Caledonian nappe stack, Jämtland, Sweden

NASA Astrophysics Data System (ADS)

Bender, Hagen; Glodny, Johannes; Ring, Uwe; Almqvist, Bjarne S. G.; Grasemann, Bernhard; Stephens, Michael B.

2017-04-01

The Caledonian orogen of Scandinavia is thought to be a Himalaya-style head-on collisional orogen. However, in contrast to the Himalayas, the Caledonides are characterized by various ultrahigh-pressure belts of different ages, which make them a unique orogen on Earth. The Seve Nappe Complex (SNC) in Jämtland (Sweden) holds the key to better understanding the multi-stage tectonometamorphic evolution of a well-studied ultrahigh-pressure belt in the central Scandinavian Caledonides. Leucogranites and migmatic gneisses record an ultrahigh-pressure event at 460 Ma (Brueckner and Van Roermund, 2007; Grimmer et al., 2015), followed by migmatization at 440 Ma (Ladenberger at al. 2014). How those high-grade metamorphic events relate to the nappe structure remains elusive. We use a combined structural and geochronological approach to show that amphibolite- and greenschist-facies foreland-directed, top-to-the-ESE shearing formed the nappe pile consisting of the Köli Nappe overlying the SNC, the various nappes of the SNC, and the underlying units. Furthermore, we present new Rb-Sr internal multi-mineral isochron ages from two east-west transects in central and northern Jämtland. Most isotopic ages, complemented by a dense network of kinematic field data, range between 431 and 427 Ma. These ages are interpreted to reflect the timing of amphibolite-facies top-to-the-ESE-directed nappe stacking. Blackwall formation, i.e., in-situ chemical interaction between ultramafic rocks and felsic gneiss, at the Seve-Köli boundary occurred at 423 Ma, an age interpreted to postdate nappe emplacement. Biotite in top-to-the-ESE greenschist-facies shear bands in the Middle Köli nappe formed at 416 Ma. These new geochronological data show that the nappe assembly postdates deep subduction and subsequent decompression melting. Top-to-the-foreland directed thrusting occurred at 430 Ma and continued for several million years, while amphibolite-facies shear criteria yield older ages than retrograde structures. References: Brueckner and Van Roermund, 2007, J. Geol. Soc. 164, 117-128. Grimmer et al., 2015, Geology 43 (4), 347-350. Ladenberger et al., 2014, Geol. Soc. Spec. Publ. 390, 337-368.

Evaluation of Ultra High Pressure (UHP) Firefighting in a Room-and-Contents Fire

DTIC Science & Technology

2017-03-15

Burn Room and Hangar Temperature Prior to Ignition ............................................... 18 Figure 12. Effect of Temperature on Normalized...Figure 20. Maximum Average Temperature and Heat Flux ......................................................... 22 Figure 21. Effect of Maximum Average...Aspirated Ceiling Temperature .................................... 23 Figure 22. Effect of Maximum Average Floor Heat Flux on Extinguishment Quantity

The importance of intracrustal magmatic heat advection in large hot orogens: the Ediacaran-Cambrian ultrahigh-temperature domain of southern Madagascar.

NASA Astrophysics Data System (ADS)

Holder, R. M.; Hacker, B. R.

2016-12-01

Ultrahigh temperature metamorphism (UHTM) represents the thermal extremes of crustal metamorphism and is integral to our understanding of orogenic systems and continental evolution. The relative importance of advective and radiogenic heating in UHTM is often unclear, however, due to retrogression of UHT mineral assemblages and lack of robust chronology. We report the first observation of osumilite, pseudosections, feldspar thermometry, and monazite LASS U-Th-Pb chronology from the Ediacaran-Cambrian Anosyen domain of southern Madagascar to evaluate P-T-time paths and assess the relative importance of advective and radiogenic heating. Pseudosections of an osumilite-bearing assemblage, a garnet-orthopyroxene gneiss, and a garnet-spinel leucogneiss indicate peak conditions of 930-1010 C, 4-6 kbar; 900-950 C, 6-7 kbar; and 970-1000 C, 4.5-5.5 kbar, respectively. Feldspar thermometry indicates T > 915 ± 30 C. These conditions were reached along a low-P prograde path, as implied by cordierite and sillimanite inclusions in garnet. Monazite and zircon U/Th-Pb dating indicates that prograde metamorphism began 625 Ma and lasted 60 Myr. The timing of peak metamorphism is constrained to a 16 ± 2.5 Myr period between 566 ± 2 and 550 ± 1.5 Ma, by monazite inclusions in pseudomorphs after osumilite and monazite from a leucosome in the same outcrop. Peak T was achieved immediately following emplacement of voluminous charnockites (emplaced 1000-1100 C) and related magmas of the Anosyen Batholith. Crystallization of pegmatite dikes, leucosomes, and smaller plutons during cooling lasted from 550 to 510 Ma. This broad thermal history is also recorded by metamorphic monazite Eu/Eu*, which indicate progressive melt generation and extraction prior to 550 Ma followed by melt accumulation and crystallization after 550 Ma. Although the duration of prograde metamorphism is consistent with radiogenic heating models of large hot orogens, peak T was 100-200 C higher in southern Madagascar than in models, implying that UHTM in southern Madagascar cannot be explained by radiogenic heating alone. We attribute this thermal discrepancy to heat advected by the Anosyen Batholith. Published Nd isotope data (ɛNd = -22) indicate that these magmas were primarily sourced from the even hotter (>1000 C) lower crust of the orogen.

Separation of major catechins from green tea by ultrahigh pressure extraction.

PubMed

Jun, Xi; Shuo, Zhao; Bingbing, Lu; Rui, Zhang; Ye, Li; Deji, Shen; Guofeng, Zhou

2010-02-15

This study presents a novel extraction technique, ultrahigh pressure extraction, to obtain major catechins from green tea leaves. The effects of various high pressure level (100, 200, 300, 400, 500, 600 MPa) on the extract are examined. HPLC chromatographic analyses determine the concentration of four major catechins and caffeine. The extraction yields of active ingredients with ultrahigh pressure extraction (400 MPa pressure) for only 15 min were given the same as those of organic solvent extraction for 2h. These excellent results for the ultrahigh pressure extraction are promising for the future separation of active ingredients from traditional Chinese herbal medicine. Copyright 2009 Elsevier B.V. All rights reserved.

Preservation of Partial Melt Textures in Inclusions in Garnet Megacrysts of Pelitic Paragneiss, UHP Terrane, North-East Greenland Eclogite Province

NASA Astrophysics Data System (ADS)

Lang, H. M.; Gilotti, J. A.

2005-12-01

Although paragneiss is not common in the North-East Greenland Eclogite Province (NEGEP), of the few paragneiss samples collected in the UHP zone, some contain inclusion-rich garnet megacrysts (to 2 cm) in an anatectic matrix. In the matrix, quartz ribbons are segregated from anatectic melt layers and lenses that contain plagioclase, antiperthitic alkali-feldspar, white mica, biotite, small garnets, rutile and minor kyanite. In addition to one-phase and two-phase inclusions of quartz, polycrystalline quartz (no definitive coesite-replacement textures), and phengitic white mica, the garnet megacrysts contain some relatively large polyphase inclusions with all or most of the following phases: kyanite, rutile, phengitic white mica, biotite, quartz, Na-rich plagioclase, K-feldspar and zircon. Textures in these complex, polyphase inclusions suggest that their constituent minerals crystallized from a melt. Crystals are randomly oriented with early crystallizing minerals (kyanite, rutile, micas) forming euhedral grains and later crystallizing minerals (quartz and feldspars) filling the interstitial spaces. The textures and mineral assemblages are consistent with dehydration melting of phengitic white mica + quartz (enclosed in garnet) during decompression of the rocks from UHP metamorphic conditions. Although anatectic minerals in the matrix may have experienced extensive retrograde re-equilibration subsequent to crystallizing from a melt, the minerals trapped in the crystallized melt inclusions in garnet are likely to preserve their original textures and compositions. Microtextures in the melt inclusions and surrounding garnet suggest that partial melting was accompanied by volume expansion and that some melt penetrated garnets. Some radial fractures extend from inclusion margins into surrounding garnet. Individual fractures may have formed by volume expansion on melting or expansion accompanying the coesite-quartz transformation. Small and large polycrystalline quartz inclusions are commonly rimmed by a moat of plagioclase + K-feldspar, which extends into apophyses in garnet. These feldspar rims indicate that the most mobile and volatile-rich portion of the melt was able to penetrate garnets and travel along garnet-inclusion boundaries. Possible melt inclusions have been described in natural garnets from other UHP terranes (Stockert, et al., 2001, Geology; Hwang, et al., 2001, Earth and Planetary Science Letters) and have been produced experimentally (Perchuk, et al., 2005, Terra Nova). In the experiments and at least one of the natural occurrences, patchy microstructures (attributed to high Ca) were observed in BSE images of garnet surrounding the melt inclusions. Although we observe no garnet zoning in BSE images, patchy high-Ca zoning is apparent on X-ray maps of garnet surrounding the melt inclusions in our samples. Small, euhedral, high-Ca garnets are abundant in melt lenses in the matrix, so crystallization or recrystallization of high-Ca garnet surrounding the melt inclusions is not surprising.

The internal structure of eclogite-facies ophiolite complexes: Implications from the Austroalpine outliers within the Zermatt-Saas Zone, Western Alps

NASA Astrophysics Data System (ADS)

Weber, Sebastian; Martinez, Raul

2016-04-01

The Western Alpine Penninic domain is a classical accretionary prism that formed after the closure of the Penninic oceans in the Paleogene. Continental and oceanic nappes were telescoped into the Western Alpine stack associated with continent-continent collision. Within the Western Alpine geologic framework, the ophiolite nappes of the Zermatt-Saas Zone and the Tsate Unit are the remnants of the southern branch of the Piemonte-Liguria ocean basin. In addition, a series of continental basement slices reported as lower Austroalpine outliers have preserved an eclogitic high-pressure imprint, and are tectonically sandwiched between these oceanic nappes. Since the outliers occur at an unusual intra-ophiolitic setting and show a polymetamorphic character, this group of continental slices is of special importance for understanding the tectono-metamorphic evolution of Western Alps. Recently, more geochronological data from the Austroalpine outliers have become available that make it possible to establish a more complete picture of their complex geological history. The Lu-Hf garnet-whole rock ages for prograde growth of garnet fall into the time interval of 52 to 62 Ma (Weber et al., 2015, Fassmer et al. 2015), but are consistently higher than the Lu-Hf garnet-whole rock ages from several other locations throughout the Zermatt-Saas zone that range from 52 to 38 Ma (Skora et al., 2015). This discrepancy suggests that the Austroalpine outliers may have been subducted earlier than the ophiolites of the Zermatt-Saas Zone and therefore have been tectonically emplaced into their present intra-ophiolite position. This points to the possibility that the Zermatt-Saas Zone consists of tectonic subunits, which reached their respective pressure peaks over a prolonged time period, approximately 10-20 Ma. The pressure-temperature estimates from several members of the Austroalpine outliers indicate a complex distribution of metamorphic peak conditions, without ultrahigh-pressure indications. By contrast, the peak conditions derived from the ophiolites of the Zermatt-Saas Zone are uniform, and close to or inside the coesite stability field. These results further underline that the oceanic lithosphere, which experienced its geodynamic evolution as a relatively coherent unit, may contain slices of continental rocks, which in turn show differences in the metamorphic evolution compared to the surrounding ophiolites. Faßmer, K., Obermüller, G., Nagel, T.J., Kirst, F., Froitzheim, N., Sandmann, S., Miladinova, I., Fonseca, R.O.C., Münker, C. (2015): Coherent vs. non-coherent subduction of ophiolite complexes - new insights from the Zermatt-Saas Zone in the Western Alps. GeoBerlin 2015, Berlin, Germany. Skora, S., Mahlen, N. J., Johnson, C. M., Baumgartner, L. P., Lapen, T. J., Beard, B. L., Szilvagyi, E. T., 2015. Evidence for protracted prograde metamorphism followed by rapid exhumation of the Zermatt-Saas Fee ophiolite. Journal of Metamorphic Geology, 33, 711-734. Weber, S., Sandmann, S., Fonseca, R. O. C., Froitzheim, N., Mu¨ nker, C., Bucher, K., 2015. Dating the beginning of Piemonte-Liguria Ocean subduction: Lu-Hf garnet chronometry of eclogites from the Theodul Glacier Unit (Zermatt-Saas Zone, Switzerland). Swiss Journal of Geosciences, 108, 183-199.

Metamorphic records of multiple seismic cycles during subduction

PubMed Central

Hacker, Bradley R.; Seward, Gareth G. E.; Kelley, Chris S.

2018-01-01

Large earthquakes occur in rocks undergoing high-pressure/low-temperature metamorphism during subduction. Rhythmic major-element zoning in garnet is a common product of such metamorphism, and one that must record a fundamental subduction process. We argue that rhythmic major-element zoning in subduction zone garnets from the Franciscan Complex, California, developed in response to growth-dissolution cycles driven by pressure pulses. Using electron probe microanalysis and novel techniques in Raman and synchrotron Fourier transform infrared microspectroscopy, we demonstrate that at least four such pressure pulses, of magnitude 100–350 MPa, occurred over less than 300,000 years. These pressure magnitude and time scale constraints are most consistent with the garnet zoning having resulted from periodic overpressure development-dissipation cycles, related to pore-fluid pressure fluctuations linked to earthquake cycles. This study demonstrates that some metamorphic reactions can track individual earthquake cycles and thereby opens new avenues to the study of seismicity. PMID:29568800

The Friningen Garnet Peridotite (central Swedish Caledonides). A good example of the characteristic PTt path of a cold mantle wedge garnet peridotite

NASA Astrophysics Data System (ADS)

Gilio, Mattia; Clos, Frediano; van Roermund, Herman L. M.

2015-08-01

We present pseudosections of Cr-bearing garnet peridotite that together with new mineral-chemical data allow quantification of the early PT conditions of the original lithospheric mantle assemblage (M1) of the Friningen Garnet Peridotite (FGP) located in the central/middle belt of the Seve Nappe Complex in central Sweden. Results indicate that the early, coarse grained, olivine + orthopyroxene + clinopyroxene + "high Cr" garnet assemblage (M1a) was formed at 1100 ± 100 °C and 5.0 ± 0.5 GPa. These metamorphic conditions were followed by an inferred late Proterozoic exhumation event down to 850-900 °C and 1.5 GPa (M1b). The latter PT estimate is based on the breakdown of high-Cr M1a garnet (Cr# = 0.065) + olivine into an orthopyroxene + clinopyroxene + spinel (Cr# = 0.15-0.25) ± pargasite kelyphite (M1b) and the exsolution of garnet from Al-rich orthopyroxene and clinopyroxene. The M1b kelyphite is overprinted by an early-Caledonian UHPM mineral assemblage (M2; T = 800 °C and P = 3.0 GPa), equivalent to the earlier discovered UHP assemblage within an eclogitic dyke that cross-cuts FGP. In the garnet peridotite M2 is displayed by low-Cr garnet (Cr# = 0.030) growing together with spinel (Cr# = 0.35-0.45), both these minerals form part of the olivine + orthopyroxene + clinopyroxene + garnet + spinel + pargasite M2 assemblage. The formation of plagioclase + diopside symplectites after omphacite and breakdown of kyanite to sapphirine + albite in internal eclogite and the breakdown of M2 olivine + garnet to amphibole + orthopyroxene + spinel assemblages (M3) in garnet peridotite indicate post-UHP isothermal decompression down to 750-800 °C and 0.8-1.0 GPa (= M3). Multiphase solid-and fluid inclusion assemblages composed of Sr-bearing magnesite, dolomite or carbon decorate linear defect structures within M1a-b minerals and/or form subordinate local assemblages together with M2 minerals. The latter are interpreted as evidence for infiltration of early-Caledonian COH-bearing subduction zone fluids. The well-defined PTt-deformation path of the FGP resembles that of a mantle wedge garnet peridotite. The M1 assemblage originates from the base of a cold, old and thick subcontinental lithospheric mantle that is inferred to extend asymmetrically leading to extreme exhumation of FGP down to lithospheric conditions around 1.5 GPa and 850-900 °C. After that the FGP became incorporated into the subducting continental crust of the SNC during "early-Caledonian" subduction (M2) down to UHPM conditions (800 °C/3.0 GPa), subsequently followed by eduction back to sub-crustal levels. As such, FGP is the first locality in the Swedish Caledonides from which two UHP metamorphic events are described, the first event can be related to the formation of an ancient (> 1.0 Ga) lithosphere underneath a craton (Rodinia) and the second is of early-Caledonian age.

Field Demonstration of a Centrifugal Ultra High Pressure (UHP) P-19

DTIC Science & Technology

2010-03-01

States Air Force  Tyndall Air Force Base, FL 32403-5323 DISTRIBUTION A: Approved for public release; distribution unlimited. NOTICE AND SIGNATURE...PUBLICATION IN ACCORDANCE WITH ASSIGNED DISTRIBUTION STATEMENT. ___//SIGNATURE//______________________ ___//SIGNATURE//______________________ R...PROGRAM ELEMENT NUMBER 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 6. AUTHOR(S) 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8

First application of the revised Ti-in-zircon geothermometer to Paleoproterozoic ultrahigh-temperature granulites of Tuguiwula, Inner Mongolia, North China Craton

NASA Astrophysics Data System (ADS)

Liu, S. J.; Li, J. H.; Santosh, M.

2010-02-01

The revised titanium-in-zircon geothermometer was applied to Paleoproterozoic ultrahigh-temperature (UHT) granulites at Tuguiwula, Inner Mongolia, North China Craton. The Tuguiwula granulites contain diagnostic UHT mineral assemblages such as sapphirine + quartz and high alumina orthopyroxene + sillimanite + quartz, suggesting formation under temperatures of ca. 1,000°C and pressures of up to 10 kbar. Here, we report detailed petrographic studies and ICP-MS data on titanium concentration in zircons associated with the UHT assemblages. The zircons associated with sapphirine-spinel-sillimanite-magnetite assemblages have the highest Ti concentration of up to 57 ppm, yielding a temperature of 941°C, and suggesting that the growth of zircons occurred under ultrahigh-temperature conditions. The maximum temperatures obtained by the revised Ti-in-zircon geothermometer is lower than the equilibrium temperature of sapphirine + quartz, indicating an interval of cooling history of the granulites from UHT condition to ca. 940°C. Many of the zircons have Ti concentrations ranging from 10 to 33 ppm, indicating their growth or recrystallization under lower temperatures of ca. 745-870°C. These zircons are interpreted to have recrystallized during the retrograde stage indicated by microstructures such as cordierite rim or corona between spinel and quartz, and orthopyroxene-cordierite symplectite around garnet. Previous geochronological study on the zircons of the Tuguiwula UHT granulites gave a mean U-Pb SHRIMP age of 1.92 Ga. However, based on the Ti-in-zircon geothermometer results reported in this work, and considering the relatively slow thermal relaxation of these rocks, we infer that the timing of peak UHT metamorphism in the Tuguiwula area could be slightly older than 1.92 Ga.

Pressure-temperature evolution of Neoproterozoic metamorphism in the Welayati Formation (Kabul Block), Afghanistan

NASA Astrophysics Data System (ADS)

Collett, Stephen; Faryad, Shah Wali

2015-11-01

The Welayati Formation, consisting of alternating layers of mica-schist and quartzite with lenses of amphibolite, unconformably overlies the Neoarchean Sherdarwaza Formation of the Kabul Block that underwent Paleoproterozoic granulite-facies and Neoproterozoic amphibolite-facies metamorphic events. To analyze metamorphic history of the Welayati Formation and its relations to the underlying Sherdarwaza Formation, petrographic study and pressure-temperature (P-T) pseudosection modeling were applied to staurolite- and kyanite-bearing mica-schists, which crop out to the south of Kabul City. Prograde metamorphism, identified by inclusion trails and chemical zonation in garnet from the micaschists indicates that the rocks underwent burial from around 6.2 kbar at 525 °C to maximum pressure conditions of around 9.5 kbar at temperatures of around 650 °C. Decompression from peak pressures under isothermal or moderate heating conditions are indicated by formation of biotite and plagioclase porphyroblasts which cross-cut and overgrow the dominant foliation. The lack of sillimanite and/or andalusite suggests that cooling and further decompression occurred in the kyanite stability field. The results of this study indicate a single amphibolite-facies metamorphism that based on P-T conditions and age dating correlates well with the Neoproterozoic metamorphism in the underlying Sherdarwaza Formation. The rocks lack any paragenetic evidence for a preceding granulite-facies overprint or subsequent Paleozoic metamorphism. Owing to the position of the Kabul Block, within the India-Eurasia collision zone, partial replacement of the amphibolite-facies minerals in the micaschist could, in addition to retrogression of the Neoproterozoic metamorphism, relate to deformation associated with the Alpine orogeny.

Mesozoic crustal thickening of the eastern North China craton: Evidence from eclogite xenoliths and petrologic implications

NASA Astrophysics Data System (ADS)

Xu, Wenliang; Gao, Shan; Wang, Qinghai; Wang, Dongyan; Liu, Yongsheng

2006-09-01

A suite of xenoliths of eclogite, garnet clinopyroxenite, and felsic gneiss is found in Early Cretaceous high-Mg [Mg# >45, where Mg# = molar 100 × Mg/(Mg + Fetotal)] adakitic intrusions from the Xuzhou-Huaibei (Xu-Huai) region along the southeastern margin of the North China craton. The primary mineral assemblage of garnet + omphacite/augite + quartz + rutile ± pargasite of the eclogite and garnet clinopyroxenite xenoliths defines a minimum pressure of >1.5 GPa, while the estimated peak metamorphic temperatures range from 800 to 1060 °C. An Sm-Nd whole-rock garnet isochron and zircon U-Pb dates show that timing of the eclogite facies metamorphism took place ca. 220 Ma. This Triassic age agrees with the age of eclogites from the Dabie-Sulu ultrahigh-pressure metamorphic (UHPM) belt. The ages of abundant Late Archean to early Paleoproterozoic (2.3 2.6Ga) inherited zircons correspond to the most prominent crustal growth event in the North China craton. In addition, these xenoliths and their host high-Mg adakitic intrusions have complementary major and trace element compositions, suggesting that the adakites formed by partial melting of Archean metabasalts that were the protoliths of the Xu-Huai eclogite and garnet clinopyroxenite xenoliths. Trace element and Sr-Nd isotopic modeling shows that the high-Mg adakitic intrusions can be modeled as melts from ˜40% partial melting of the metabasalts in the eclogite facies, followed by interaction with the convecting mantle and variable degrees of crustal assimilation. Together with the similar zircon age populations between the xenoliths and the host rocks, these lines of evidence strongly suggest their genetic link via thickening, foundering, and partial melting of the Archean North China craton mafic lower crust, followed by adakitic melt-mantle interaction. The crustal thickening resulted from Triassic collision between the Yangtze craton and the North China craton, which produced the Dabie-Sulu UHPM belt in the subducting Yangtze plate and eclogitization of the basaltic crustal root of the overriding North China craton plate. Such processes may have played an important role in generating the high-Mg character of the continental crust.

Is Absence of Evidence of UHPM Evidence of Absence: Did Conditions on Earth Before the Ediacaran Period Allow Formation of UHP Rocks but Only Rarely Their Exhumation?

NASA Astrophysics Data System (ADS)

Brown, M.

2008-12-01

UHPM provides petrologic evidence of transport of continental lithosphere to asthenospheric depth and return of some of these materials to crustal depth. The rock record registers UHPM since the Ediacaran Period, and studies of inclusion assemblages in zircon have increased the evidence of UHPM in Phanerozoic orogens and enabled an assessment of the real estate involved. Plots of apparent thermal gradient vs. age of metamorphism and P vs. age of metamorphism reveal two dramatic changes in inferred thermal environment and inferred depth of metamorphism from which continental lithosphere has been recovered during Earth evolution. First, from the Mesoarchean Era to the Neoproterozoic Era, sutures in subduction-to- collision orogens are marked by eclogite and high-pressure granulite metamorphism (characterized by apparent thermal gradients of 750-350 C/GPa). The P of metamorphism in sutures jumped from <1 GPa during the Eoarchean-Paleoarchean up to 2 GPa during the Paleoproterozoic. Second, from the Cryogenian- Ediacaran to the present, many sutures in subduction-to-collision orogens, and sometimes intracratonic sutures in the overriding plate, are marked by UHPM (characterized by apparent thermal gradients of <350 C/GPa) with P of metamorphism >2.7GPa. Given this pattern of secular change to colder apparent thermal gradients in sutures, the recent discovery of diamonds in zircons of crustal paragenesis in Neoarchean sedimentary rocks is surprising. Maybe UHPM has been possible since the Neoarchean but the evidence was rarely exhumed or if exhumed maybe the evidence was rarely preserved? The Appalachian/Caledonian-Variscide-Altaid and the Cimmerian-Himalayan-Alpine orogenic systems were formed by successive closure of short-lived oceans by transfer and suturing of ribbon-continent terranes derived from the Gondwanan side. Subduction of young ocean lithosphere followed by choking of the subduction channel by arc or terrane collision limited transport of water to the mantle wedge, and suppressed development of small-scale convection, arc magmatism and backarc formation. This allowed the retro- continental margin to remain strong, which favored efficient exhumation of UHPM rocks (Warren et al., 2008, EPSL). How should we interpret the presence of diamonds in detrital zircons (age range 3,050-4,260 Ma) from the Narryer terrane? Menneken et al. (2007, Nature) argue that the age range indicates repeated conditions for diamond formation (or recycling of ancient diamond) and that diamonds imply thick continental lithosphere and crust-mantle interactions since 4,260 Ma! This implies thermal environments and tectonics in the Hadean and Archean Eons similar to the Phanerozoic Eon. However, these ancient zircons originally crystallized from low-T melts (Watson and Harrison, 2006, Science) and the 'age' of the diamonds is only constrained to be > the age of deposition and <3,050 Ma. Williams (2007, Science) suggests that C was introduced as graphite precipitated from COH fluid in fractures/imperfections in zircon prior to deep burial to form diamond during a single event. COH fluid was involved in the formation of diamonds from Phanerozoic UHPM localities, so the hypothesis is viable if an appropriate tectonic model can be developed. I will present a model for the formation and exhumation of an overriding plate source terrane for the diamond-bearing detrital zircons that is consistent with periodic changes in the tectonic regime of Earth (Brown, 2006, Geology), and the geology and likely tectonic setting of the Narryer Terrane-Yilgarn Craton during the Neoarchean. Finally, I will speculate about UMPM during the Proterozoic and exhumation vs. relamination (Hacker et al., Eos, 2007).

Dynamics of subduction, accretion, exhumation and slab roll-back: Mediterranean scenarios

NASA Astrophysics Data System (ADS)

Tirel, C.; Brun, J.; Burov, E. B.; Wortel, M. J.; Lebedev, S.

2010-12-01

A dynamic orogen reveals various tectonic processes brought about by subduction: accretion of oceanic and continental crust, exhumation of UHP-HP rocks, and often, back-arc extension. In the Mediterranean, orogeny is strongly affected by slab retreat, as in the Aegean and Tyrrhenian Seas. In order to examine the different dynamic processes in a self-consistent manner, we perform a parametric study using the fully coupled thermo-mechanical numerical code PARAFLAM. The experiments reproduce a subduction zone in a slab pull mode, with accretion of one (the Tyrrhenian case) and two continental blocks (the Aegean case) that undergo, in sequence, thrusting, burial and exhumation. The modeling shows that despite differences in structure between the two cases, the deformation mechanisms are fundamentally similar and can be described as follows. The accretion of a continental block at the trench beneath the suture zone begins with its burial to UHP-HP conditions and thrusting. Then the continental block is delaminated from its subducting lithosphere. During the subduction-accretion process, the angle of the subducting slab increases due to the buoyancy of the continental block. When the oceanic subduction resumes, the angle of the slab decreases to reach a steady-state position. The Aegean and Tyrrhenian scenarios diverge at this stage, due naturally to the differences of their accretion history. When continental accretion is followed by oceanic subduction only, the continental block that has been accreted and detached stays at close to the trench and does not undergo further deformation, despite the continuing rollback. The extensional deformation is located further within the overriding plate, resulting in continental breakup and the development of an oceanic basin, as in the Tyrrhenian domain. When the continental accretion is followed first by oceanic subduction and then by accretion of another continental block, however, the evolution of the subduction zone is different. The angle of the subducting slab increases again, following the arrival of the second continental block. The first continental block is now disconnected from the trench and is strongly heated by the asthenosphere that rises to just below the Moho. The locus of extension, originally in the overriding plate, moves to the first continental block, resulting in the development of metamorphic core complexes, as in the Aegean domain. Simultaneously, the second continent undergoes burial to UHP-HP conditions, thrusting and exhumation.

Carbonatitic metasomatism in orogenic dunites from Lijiatun in the Sulu UHP terrane, eastern China

NASA Astrophysics Data System (ADS)

Su, Bin; Chen, Yi; Guo, Shun; Chu, Zhu-Yin; Liu, Jing-Bo; Gao, Yi-Jie

2016-10-01

Among orogenic peridotites, dunites suffer the weakest crustal metasomatism at the slab-mantle interface and are the best lithology to trace the origins of orogenic peridotites and their initial geodynamic processes. Petrological and geochemical investigations of the Lijiatun dunites from the Sulu ultrahigh-pressure (UHP) terrane indicate a complex petrogenetic history involving melt extraction and multistage metasomatism (carbonatitic melt and slab-derived fluid). The Lijiatun dunites consist mainly of olivine (Fo = 92.0-92.6, Ca = 42-115 ppm), porphyroblastic orthopyroxene (En = 91.8-92.8), Cr-spinel (Cr# = 50.4-73.0, TiO2 < 0.2 wt.%) and serpentine. They are characterized by refractory bulk-rock compositions with high MgO (45.31-47.07 wt.%) and Mg# (91.5-91.9), and low Al2O3 (0.48-0.70 wt.%), CaO (0.25-0.44 wt.%) and TiO2 (< 0.03 wt.%) contents. Whole-rock platinum group elements (PGE) are similar to those of cratonic mantle peridotites and Re-Os isotopic data suggest that dunites formed in the early Proterozoic ( 2.2 Ga). These data indicate that the Lijiatun dunites were the residues of 30% partial melting and were derived from the subcontinental lithospheric mantle (SCLM) beneath the North China craton (NCC). Subsequent carbonatitic metasomatism is characterized by the formation of olivine-rich (Fo = 91.6-92.6, Ca = 233-311 ppm), clinopyroxene-bearing (Mg# = 95.9-96.7, Ti/Eu = 104-838) veins cutting orthopyroxene porphyroblasts. Based on the occurrence of dolomite, mass-balance calculation and thermodynamic modeling, carbonatitic metasomatism had occurred within the shallow SCLM (low-P and high-T conditions) before dunites were incorporated into the continental subduction channel. These dunites then suffered weak metasomatism by slab-derived fluids, forming pargasitic amphibole after pyroxene. This work indicates that modification of the SCLM beneath the eastern margin of the NCC had already taken place before the Triassic continental subduction. Orogenic peridotites derived from such a lithospheric mantle wedge may be heterogeneously modified prior to their incorporation into the subduction channel, which would set up a barrier for investigation of the mass transfer from the subducted crust to the mantle wedge through orogenic peridotites.

Principles of Metamorphic Petrology

NASA Astrophysics Data System (ADS)

Williams, Michael L.

2009-05-01

The field of metamorphic petrology has seen spectacular advances in the past decade, including new X-ray mapping techniques for characterizing metamorphic rocks and minerals, new internally consistent thermobarometers, new software for constructing and viewing phase diagrams, new methods to date metamorphic processes, and perhaps most significant, revised petrologic databases and the ability to calculate accurate phase diagrams and pseudosections. These tools and techniques provide new power and resolution for constraining pressure-temperature (P-T) histories and tectonic events. Two books have been fundamental for empowering petrologists and structural geologists during the past decade. Frank Spear's Metamorphic Phase Equilibria and Pressure-Temperature-Time Paths, published in 1993, builds on his seminal papers to provide a quantitative framework for P-T path analysis. Spear's book lays the foundation for modern quantitative metamorphic analysis. Cees Passchier and Rudolph Trouw's Microtectonics, published in 2005, with its superb photos and figures, provides the tools and the theory for interpreting deformation textures and inferring deformation processes.

Petrology and zircon U-Pb geochronology of metagabbros from a mafic-ultramafic suite at Aniyapuram: Neoarchean to Early Paleoproterozoic convergent margin magmatism and Middle Neoproterozoic high-grade metamorphism in southern India

NASA Astrophysics Data System (ADS)

Koizumi, Tatsuya; Tsunogae, Toshiaki; Santosh, M.; Tsutsumi, Yukiyasu; Chetty, T. R. K.; Saitoh, Yohsuke

2014-12-01

Several mafic-ultramafic complexes occur within the Palghat-Cauvery Suture Zone (PCSZ) in southern India. The PCSZ is regarded in recent models as the zone along which crustal blocks were amalgamated during the Late Neoproterozoic-Cambrian (550-530 Ma) Gondwana assembly. Here we report petrologic and zircon U-Pb geochronologic data from gabbros associated with the Aniyapuram mafic-ultramafic suite in the central domain of the PCSZ. Geothermobarometry and pseudosection approach in the system NCFMASHTO for the metagabbro (Grt + Cpx + Opx + Hbl + Pl + Qtz + Ilm + Rt) yield peak P-T condition of 9.8-10.6 kbar and 730-790 °C, which was followed by decompression to 6.5-8.0 kbar and ca. 750 °C as inferred from the formation of Opx + Pl symplectite around garnet, probably along a clockwise P-T path. Zircon U-Pb data analyzed by LA-ICP-MS plot along a well-defined discordia with upper and lower intercepts in the concordia at 2436 ± 22 Ma and 731 ± 11 Ma respectively, suggesting Neoarchean-Early Paleoproterozoic magmatic emplacement of the protolith and progressive Pb loss related to the Middle Neoproterozoic (Cryogenian) thermal event (or high-grade metamorphism). These results closely compare with the available Neoarchean magmatic ages of mafic-ultramafic complexes (e.g., Sittampundi, Devanur, Agali Hills, and Kanja Malai) and Middle Neoproterozoic magmatic event (e.g., Manamedu and Kadavur) in the PCSZ and adjacent granulite blocks. The 650 Ma concordia ages obtained from unzoned zircons might indicate the timing of high-grade metamorphism or post-peak hydration event. The P-T conditions obtained from Aniyapuram are significantly lower than the high-pressure and ultrahigh-temperature conditions of the 550-530 Ma final collisional event (P > 14 kbar and T > 950 °C). The Middle Neoproterozoic (ca. 730 Ma or 650 Ma) high-grade metamorphism in Aniyapuram reported for the first time from the PCSZ is possibly associated with magmatism in arc tectonic setting.

Preserved anatectic melt in ultrahigh-temperature (or high pressure?) felsic granulites, Connecticut, US

NASA Astrophysics Data System (ADS)

Ferrero, Silvio; Axler, Jennifer; Ague, Jay J.; Wunder, Bernd; Ziemann, Martin A.

2017-04-01

Polycrystalline inclusions occur in felsic granulites from northeastern Connecticut, US (Axler and Ague, 2015). They sit in the core of garnet porphyroblasts formed during peak metamorphism at T >1000°C and P >1 GPa. The investigated inclusions vary from needle-shaped, with length ≤50 microns and few microns across, to isometric with diameter ≤10 microns. They show a rather constant assemblage which includes quartz, phlogopite, biotite and very often a compositionally variable phase. Raman spectroscopy shows the occasional presence of glass and cristobalite (the latter only when quartz is absent). Crystallized phases and the presence of glass suggest that these inclusions formed originally as droplets of melt trapped during garnet growth, likely as result of partial melting of the original metasedimentary protolith. A prominent feature of the garnet is the presence of rutile needles and ilmenite oriented accordingly to the crystallographic planes of garnet. When elongated in shape, also the polycrystalline inclusions are generally oriented according to the same planes, and occasionally contain rutile and /or ilmenite occur as trapped phases. Re-heating experiments were performed on the polycrystalline inclusions using a piston cylinder apparatus and without adding water to the experimental capsules. Complete re-homogenization was achieved at T 1025-1050°C and P 1.7 GPa, confirming that these inclusions are nanogranites (Ferrero et al., 2015). Re-homogenized inclusions contain a peraluminous glass (ASI=1.36) with ≤6 wt% water, confirmed also via Raman spectroscopy. Its average composition is granitic, with K/Na= 4.37 and rather high FeO (3.70 wt%). Both K-rich character and FeO content are consistent with experimental melts generated at T of 900-1000°C and variable P via melting of metasediments. The investigation of the experimental products furthermore provides novel constraints for the peak conditions (and likely of anatexis) of these granulites. During experiments performed at T 1025-1050°C and P <1.7 GPa melt and garnet interacts forming a new garnet with different composition, thus indicating lack of equilibrium between melt and garnet. Such microstructure is absent in the experiment at P ≥1.7 GPa, suggesting that such P values correspond to the conditions of melting with the simultaneous production of melt and garnet. Such values are more consistent with the water content of re-homogenized inclusions, rather high for melts formed at T>1000°C. Such pressures are remarkably higher than those previously proposed for these rocks, and suggest that they experienced indeed high pressure rather than ultrahigh temperature conditions, a possibility also supported by the widespread presence of pseudomorphs of sillimanite after kyanite. References Axler JA, Ague JJ (2015). Oriented multiphase needles in garnet from ultrahigh-temperature granulites. American Mineralogist, 100, 2254-2271. Ferrero S, Wunder B, Walczak K, Ziemann MA, O'Brien PJ (2015). Preserved near ultrahigh-pressure melt from continental crust subducted to mantle depths. Geology, 43, 447-450.

High-pressure amphibolite facies dynamic metamorphism and the Mesozoic tectonic evolution of an ancient continental margin, east- central Alaska

USGS Publications Warehouse

Dusel-Bacon, C.; Hansen, V.L.; Scala, J.A.

1995-01-01

Ductilely deformed amphibolite facies tectonites comprise two adjacent terranes in east-central Alaska: the northern, structurally higher Taylor Mountain terrane and the southern, structurally lower Lake George subterrane of the Yukon-Tanana terrane. The pressure, temperature, kinematic and age data are interpreted to indicate that the metamorphism of the Taylor Mountain terrane and Lake George subterrane took place during different phases of a latest Palaeozoic through early Mesozoic shortening episode resulting from closure of an ocean basin now represented by klippen of the Seventymile-Slide Mountain terrane. High- to intermediate-pressure metamorphism of the Taylor Mountain terrane took place within a SW-dipping (present-day coordinates) subduction system. High- to intermediate-pressure metamorphism of the Lake George subterrane and the structural contact zone occurred during NW-directed overthrusting of the Taylor Mountain, Seventymile-Slide Mountain and Nisutlin terranes, and imbrication of the continental margin in Jurassic time. -from Authors

Field Evaluation of Ultra-High Pressure Water Systems for Runway Rubber Removal

DTIC Science & Technology

2014-04-01

ER D C/ G SL T R- 14 -1 1 Field Evaluation of Ultra-High Pressure Water Systems for Runway Rubber Removal G eo te ch ni ca l a nd S tr...Field Evaluation of Ultra-High Pressure Water Systems for Runway Rubber Removal Aaron B. Pullen Applied Research Associates, Inc. 421 Oak Avenue...collaboration with Applied Research Associates, Inc. (ARA). Several types of commercial UHPW water blasting systems were tested on an ungrooved portland cement

A Comparison of the Raman Spectra and Crystal Chemistry of Norbergite and Clinohumite at High Pressure

NASA Astrophysics Data System (ADS)

Pease, A. M.; Gramsch, S. A.

2017-12-01

Humite group minerals n(Mg.Fe)2SiO4 - (Mg,Fe)(OH)2 have been suggested as possible candidates for water storage and transport in the mantle, and clinohumite in particular has been proposed as the source of ilmenite lamellae in Alpine ultrahigh pressure metamorphic terranes via its decomposition at high pressure and temperature. In this study, a comparison is made between the Raman spectra of norbergite (n = 1) and clinohumite (n = 4) up to 15 GPa to correlate the structural and vibrational properties of these two members of the group. All observed vibrational modes in the Raman spectra of both minerals increase in frequency with pressure, although the change in frequencies with pressure is much steeper in norbergite than for clinohumite. In norbergite, antisymmetric stretching modes of the SiO4 tetrahedra merge, but no such merging of modes occurs in clinohumite. In addition, the intensity of the antisymmetric stretching mode for clinohumite decreases dramatically in pressure compared to the intensity of the symmetric stretching mode. In the spectra of norbergite, these two modes retain their relative intensities with increasing pressure. The most striking difference between the spectra of norbergite and clinohumite is in the deformation modes of the brucite layer, which within the clinohumite structure retain their intensities with increasing pressure, while these modes are not observed in the spectra of norbergite. The nature of the Raman spectra and their evolution with pressure are correlated with the structural properties of the two minerals in terms of the interactions between olivine and brucite layers and the crystal chemistry of the humite group minerals.

P-T evolution of metasedimentary rocks of the Santa Filomena Complex, Riacho do Pontal Orogen, Borborema Province (NE Brazil): Geothermobarometry and metamorphic modelling

NASA Astrophysics Data System (ADS)

Santos, Felipe H.; Amaral, Wagner S.; Luvizotto, George L.; Martins de Sousa, Daniel F.

2018-03-01

We present in this paper petrologic data and discuss the pressure-temperature (P-T) metamorphic history of the neoproterozoic metasedimentary rocks of the Santa Filomena Complex, Riacho do Pontal Orogen, which is inserted in the southern portion of the Borborema Province (Northeast Brazil). Therefore, the data provide constraints on metamorphic evolution during Neoproterozoic Brasiliano Orogeny in Northeast Brazil. The rocks studied are aluminous schists and paragneisses. Silver-gray and red pelitic schists are intensely deformed, biotite-muscovite rich, contain centimeter-sized garnet, staurolite and kyanite porphyroblasts, and subordinately plagioclase and quartz. Paragneisses are from light gray to dark gray colored, medium to coarse-grained and display a well-spaced foliated matrix of biotite, and kyanite and garnet porphyroblasts. Locally, the schists and paragneisses are migmatized. Pressure-temperature modelling based on thermobarometric calculations indicate that metamorphism reached 643 °C with pressures estimated in 12 kbar. Pre-peak and post-peak metamorphic conditions are constrained by mineralogical and textural relationships: garnet inclusion-rich and inclusion-free (possible of higher T) are documented and the inclusion-rich core probably indicates a Sn-1 foliation that was transposed by Sn. The pre-peak stage most probably occurred close to 500 °C and 8 kbar, in upper greenschist to lower amphibolite facies metamorphism along kyanite stability field. We also propose that post-peak stage was associated with isothermal decompression along a possible path of tectonic exhumation in conditions of 600 °C and 7 kbar. To further evaluate the equilibrium condition, pressure-temperature pseudosections were calculated for the metasedimentary rocks. Thus, the estimated metamorphic peak took place in the upper amphibolite facies. A suggested clockwise pressure-temperature path is compatible with the regional tectonic setting of continent-continent collision which occurred in the Late Neoproterozoic of Borborema Province, during the Brasiliano Orogeny.

Significance of the Nestos Shearzone in the southern Rhodopes (Northern Greece/Southern Bulgaria)

NASA Astrophysics Data System (ADS)

Nagel, T. J.; Schmidt, S.; Froitzheim, N.; Jahn-Awe, S.; Georgiev, N.

2009-04-01

The Nestos Shearzone can be traced over 100 kilometers and separates the two main units of the Rhodopes, the Upper Complex in the hangingwall from the Pangaion-Pirin Unit in the footwall. The Upper Complex consists of mingled continental and oceanic basement rocks, intruded by granitic bodies of Cretaceous and Tertiary age. It underwent at least amphibolite facies conditions during the Alpine orogenic cycle and several localities with preserved high-pressure and/or ultrahigh-pressure rocks have been found. The age of orogenesis and metamorphism is ambiguous and several Mesozoic and Tertiary cycles may be recorded in that unit. The lowermost level immediately on top of the Nestos Shearzone (Sidironero subunit) mainly consists of rocks derived from a Jurassic arc and appears to show the youngest reported (i.e. Eocene) high-grade metamorphism (including ultra-high-pressure conditions and a subsequent migmatic stage). The underlying Pangaion-Pirin Unit beneath the Nestos Shearzone is build of marbles and Variscan gneisses of disputed Mesozoic paleogeographic position. It is intruded by Oligocene granitoids, which also crosscut the Nestos shearzone. The Pangaion-Pirin Unit experienced only blueschist facies and subsequent upper greenschist facies conditions during the Alpine cycle. The Nestos Shearzone is defined by top-to-the-southwest-directed mylonites formed under upper greenschist facies conditions. So far, it has been viewed as a thrust. We present structural and petrological data suggesting that the Nestos Shearzone is instead a major mid-crustal detachment related to late Eo-Oligocene backarc extension. Mylonitisation along the shear zone occurred under greenschist facies conditions and postdates the blueschist facies stage. The shear zone formed between about 40 Ma and 34 Ma as indicated by the age of high temperature conditions in the hangingwall and the age of Oligocene granitoids crosscutting the mylonites. During this time, pronounced extension and basin formation took place in the hangingwall of the Nestos Shearzone. We propose that the brittle Mesta detachment, which bounds the Mesta Graben to the East, roots into the Nestos Shearzone. The metamorphic history of the Pangaion-Pirin Unit as well as the proposed young age of the Nestos Shearzone is in conflict with studies proposing that this unit represents an independent microcontinent (Drama) accreted to the future Rhodopes in late Jurassic or early Cretaceous times. Instead, we hypothesize that the Pangaion-Pirin Unit could be derived from the Apulian plate, which would have far reaching consequences for the structural architecture of the Aegean Sea area.

Origin of peraluminous minerals (corundum, spinel, and sapphirine) in a highly calcic anorthosite from the Sittampundi Layered Complex, Tamil Nadu, India

NASA Astrophysics Data System (ADS)

Karmakar, Shreya; Mukherjee, Subham; Sanyal, Sanjoy; Sengupta, Pulak

2017-08-01

The highly calcic anorthosite (An>95) from the Sittampundi Layered Complex (SLC) develops corundum, spinel and sapphirine that are hitherto not reported from any anorthositic rocks in the world. Petrological observations indicate the following sequence of mineral growth: plagioclasematrix → corundum; clinopyroxene → amphibole; corundum + amphibole → plagioclasecorona + spinel; and spinel + corundum → coronitic sapphirine. Phase relations in the CaO-Na2O-Al2O3-SiO2-H2O (CNASH) system suggest that corundum was presumably developed through vapour present incongruent melting of the highly calcic plagioclase during ultra-high temperature (UHT) metamorphism ( T ≥ 1000 °C, P ≥ 9 kbar). Topological constraints in parts of the Na2O-CaO-MgO-Al2O3-SiO2-H2O (NCMASH) system suggest that subsequent to the UHT metamorphism, aqueous fluid(s) permeated the rock and the assemblage corundum + amphibole + anorthite + clinozoisite was stabilized during high-pressure (HP) metamorphism (11 ± 2 kbar, 750 ± 50 °C). Constraints of the NCMASH topology and thermodynamic and textural modeling study suggest that coronitic plagioclase and spinel formed at the expense of corundum + amphibole during a steeply decompressive retrograde P- T path (7-8 kbar and 700-800 °C) in an open system. Textural modeling studies combined with chemical potential diagrams (μSiO2-μMgO) in the MASH system support the view that sapphirine also formed from due to silica and Mg metasomatism of the precursor spinel ± corundum, on the steeply decompressive retrograde P- T path, prior to onset of significant cooling of the SLC. Extremely channelized fluid flow and large positive solid volume change of the stoichiometrically balanced sapphirine forming reaction explains the localized growth of sapphirine.

Effects of the ultra-high pressure on structure and α-glucosidase inhibition of polysaccharide from Astragalus.

PubMed

Zhu, Zhen-Yuan; Luo, You; Dong, Guo-Ling; Ren, Yuan-Yuan; Chen, Li-Jing; Guo, Ming-Zhu; Wang, Xiao-Ting; Yang, Xue-Ying; Zhang, Yongmin

2016-06-01

A novel homogeneous polysaccharide fraction (APS) was extracted from Astragalus by hot water and purified by Sephadex G-100 and G-75 column. Its molecular weight was 693kDa. APS and APS with ultra-high pressure treatment exhibited significant inhibitory abilities on a-glucosidase, inhibition rate from high to low in order was 400MPa-APS, 300MPa-APS, 500MPa-APS and APS. The inhibition ​percentage of 400MPa-APS (1.5mg/mL) was 49% (max.). This suggested that the inhibitory activity of APS on a-glucosidase was improved by ultra-high pressure treatment. FT-IR, SEM, CD spectra, atomic force microscope and Congo red test analysis of APS and 400MPa-APS showed ultra-high pressure treatment didn't change the preliminary structure but had an effect on its advanced structure. Copyright © 2016 Elsevier B.V. All rights reserved.

Metamorphism within the Chugach accretionary complex on southern Baranof Island, southeastern Alaska

USGS Publications Warehouse

Zumsteg, Cathy L.; Himmelberg, Glen R.; Karl, Susan M.; Haeussler, Peter J.

2003-01-01

On Baranof Island, southeastern Alaska, we identify four metamorphic events that affect rocks associated with the Chugach accretionary complex. This study focuses on the M1 and M4 metamorphic events. Mesozoic schists, gneisses, and migmatitic gneisses exposed near the Kasnyku pluton on central Baranof Island represent the M1 metamorphic rocks. These rocks underwent amphibolite facies metamorphism. Calculated temperatures and pressures range from about 620 to 780 ºC and 5.5 to 6.6 kbar and are compatible with the observed metamorphic mineral assemblages.The M4 metamorphism affected rocks of the Sitka Graywacke on southern Baranof Island, producing extensive biotite and garnet zones as well as andalusite and sillimanite zones at the contacts of the Crawfish Inlet and Redfish Bay plutons. Calculated M4 temperatures and pressures from the andalusite and sillimanite zones range from 575 to 755 ºC and 3.4 to 6.9 kbar. These results fall within the sillimanite stability field, at pressures higher than andalusite stability. These results may indicate the M4 metamorphic event occurred along a P-T path along which the equilibration of aluminosilicate-garnet-plagioclase-quartz did not occur or was not maintained. This interpretation is supported by the occurrence of andalusite and sillimanite within the same sample. We propose the data reflect a clockwise P-T path with peak M4 metamorphism of the sillimanite-bearing samples adjacent to the intrusions at an approximate depth of 15 to 20 km, followed by rapid uplift without reequilibration of garnet-plagioclase-aluminosilicate-quartz.The large extent of the biotite zone, and possibly the garnet zone, suggests that an additional heat source must have existed to regionally metamorphose these rocks during the M4 event. We suggest the M4 regional thermal metamorphism and intrusion of the Crawfish Inlet and Redfish Bay plutons were synchronous and the result of heat flux from a slab window beneath the accretionary complex at that time. If our conclusions regarding the effect of the slab window are correct, the style of metamorphism is different from the Chugach metamorphic complex, which is clearly linked to a slab window. Therefore, our findings would suggest that there is no distinct metamorphic signature for slab window effects.

High-pressure metamorphism in the southern New England Orogen: Implications for long-lived accretionary orogenesis in eastern Australia

NASA Astrophysics Data System (ADS)

Phillips, G.; Offler, R.; Rubatto, D.; Phillips, D.

2015-09-01

New geochemical, metamorphic, and isotopic data are presented from high-pressure metamorphic rocks in the southern New England Orogen (eastern Australia). Conventional and optimal thermobarometry are augmented by U-Pb zircon and 40Ar/39Ar phengite dating to define pressure-temperature-time (P-T-t) histories for the rocks. The P-T-t histories are compared with competing geodynamic models for the Tasmanides, which can be summarized as (i) a retreating orogen model, the Tasmanides formed above a continuous, west dipping, and eastward retreating subduction zone, and (ii) a punctuated orogen model, the Tasmanides formed by several arc accretion, subduction flip, and/or transference events. Whereas both scenarios are potentially supported by the new data, an overlap between the timing of metamorphic recrystallization and key stages of Tasmanides evolution favors a relationship between a single, long-lived subduction zone and the formation, exhumation, and exposure of the high-pressure rocks. By comparison with the retreating orogen model, the following links with the P-T-t histories emerge: (i) exhumation and underplating of oceanic eclogite during the Delamerian Orogeny, (ii) recrystallization of underplated and exhuming high-pressure rocks at amphibolite facies conditions coeval with a period of rollback, and (iii) selective recrystallization of high-pressure rocks at blueschist facies conditions, reflecting metamorphism in a cooled subduction zone. The retreating orogen model can also account for the anomalous location of the Cambrian-Ordovician high-pressure rocks in the Devonian-Carboniferous New England Orogen, where sequential rollback cycles detached and translated parts of the leading edge of the overriding plate to the next, younger orogenic cycle.

Common Pb isotope mapping of UHP metamorphic zones in Dabie orogen, Central China: Implication for Pb isotopic structure of subducted continental crust

NASA Astrophysics Data System (ADS)

Shen, Ji; Wang, Ying; Li, Shu-Guang

2014-10-01

We report Pb isotopic compositions for feldspars separated from 57 orthogneisses and 2 paragneisses from three exhumed UHPM slices representing the North Dabie zone, the Central Dabie zone and the South Dabie zone of the Dabie orogen, central-east China. The feldspars from the gneisses were recrystallized during Triassic continental subduction and UHP metamorphism. Precursors of the orthogneisses are products of Neoproterozoic bimodal magmatic events, those in north Dabie zone emplaced into the lower crust and those in central and south Dabie zones into middle or upper crust, respectively. On a 207Pb/204Pb vs. 206Pb/204Pb diagram, almost all orthogneisses data lie to the left of the 0.23 Ga paleogeochron and plot along the model mantle evolution curve with the major portion of the data plotting below it. On a 208Pb/204Pb vs. 206Pb/204Pb diagram the most of data of north Dabie zone extend in elongate arrays along the lower crustal curve and others extend between the lower crustal curve to near the mantle evolution curve for the plumbotectonics model. This pattern demonstrates that the Pb isotopic evolution of the feldspars essentially ended at 0.23 Ga and the orthogneiss protoliths were principally dominated by reworking of ancient lower crust with some addition of juvenile mantle in the Neoproterozoic rifting tectonic zone. According to geological evolution history of the locally Dabie orogen, a four-stage Pb isotope evolution model including a long time evolution between 2.0 and 0.8 Ga with a lower crust type U/Pb ratio (μ = 5-6) suggests that magmatic emplacement levels of the protoliths of the orthogneisses in the Dabie orogen at 0.8 Ga also play an important role in the Pb evolution of the exhumed UHPM slices, corresponding to their respective Pb characters at ca. 0.8-0.23 Ga. For example, north Dabie zone requires low μ values (3.4-9.6), while central and south Dabie zones require high μ values (10.9-17.2). On the other hand, Pb isotopic mixing between north and central or south Dabie zones during retro-grade metamorphism enhanced by the extensive magmatism in the Cretaceous has also been observed in the 207Pb/204Pb vs. 206Pb/204Pb and 208Pb/204Pb vs. 206Pb/204Pb diagrams. A combined study of common Pb isotopic compositions of Dabie orthogneisses and Sulu UHPM rocks from the Chinese Continental Scientific Drilling project demonstrates that a slab marked by extremely unradiogenic Pb observed in the main hole was absent in the Dabie orogen. However, occurrence of some Mesozoic granitoids with such unradiogenic character in the Dabie orogen suggests that their source may be a buried unradiogenic unit underlying below north Dabie zone. This case study clearly shows that whether the position of the Dabie data relative to the orogen curve of the plumbotectonic model is helpful in understanding the Pb isotopic structure and evolution of subducted continental crust.

Development of inverted metamorphic isograds in the western metamorphic belt, Juneau, Alaska

USGS Publications Warehouse

Himmelberg, G.R.; Brew, D.A.; Ford, A.B.

1991-01-01

An inverted metamorphic gradient is preserved in the western metamorphic belt near Juneau, Alaska. Detailed mapping of pelitic single-mineral isograds, systematic changes in mineral assemblages, and silicate geothermometry indicate that thermal peak metamorphic conditions increase structurally upward over a distance of about 8 km. Silicate geobarometry suggests that the thermal peak metamorphism occurred under pressures of 9-11 kbar. Our preferred interpretation of the cause of the inverted gradient is that it formed during compression of a thickened wedge of relatively wet and cool rocks in response to heat flow associated with the formation and emplacement of tonalite sill magma. -from Authors

Pressure Variations in Metamorphic Rocks: Implications for the Interpretation of Petrographic Observations

NASA Astrophysics Data System (ADS)

Tajčmanová, Lucie

2014-05-01

Metamorphic petrologists and structural geologists, using direct measurements, bring the only direct observational constrains for validating geodynamic models. Therefore, petrological and structural geological observations are essential for the quality and reproducibility of geodynamic reconstructions and models. One of the important assumptions for geodynamic reconstructions arises from the pressure and temperature estimates in the petrology analysis. Pressure is commonly converted to depth through the equation for lithostatic pressure and so the original position of the rock sample within the Earth's interior can be constrained. The current assumption that the studied sample corresponds to uniform pressure may not be correct, and if so, it has serious implications. Increasing evidence from analytical data shows that pressure is not constant even on a grain scale, posing new challenges because, if ignored, it leads to an incorrect use of petrology data in constraining geodynamic models. Well known examples of the preservation of coesite and diamond in a host mineral like garnet show that high pressure inclusions are preserved during decompression. Tajčmanová et al. (2014) has shown that grain-scale pressure variations can develop and that these pressure variations allow compositional zoning in minerals preserved over geological time scales. A new unconventional barometric method based on equilibrium under pressure variations has been developed . Such pressure variations are also connected with differences in fluid pressure in open systems and can be thus observed at all scales. Tajčmanová L., Podladchikov Y., Powell R., Moulas E., Vrijmoed J. and Connolly J. (2014). Grain scale pressure variations and chemical equilibrium in high-grade metamorphic rocks.Journal of Metamorphic Geology, doi:10.1111/jmg.12066 This work was supported by ERC starting grant 335577 to Lucie Tajcmanova

Grain-scale Sr isotope heterogeneity in amphibolite (retrograded UHP eclogite, Dabie terrane): Implications for the origin and flow behavior of retrograde fluids during slab exhumation

NASA Astrophysics Data System (ADS)

Guo, Shun; Yang, Yueheng; Chen, Yi; Su, Bin; Gao, Yijie; Zhang, Lingmin; Liu, Jingbo; Mao, Qian

2016-12-01

To constrain the origin and flow behavior of amphibolite-facies retrograde fluids during slab exhumation, we investigate the textures, trace element contents, and in situ strontium (Sr) isotopic compositions (using LA-MC-ICP-MS) of multiple types of epidote and apatite in the UHP eclogite and amphibolites from the Hualiangting area (Dabie terrane, China). The UHP epidote porphyroblasts in the eclogite (Ep-E), which formed at 28-30 kbar and 660-720 °C, contain high amounts of Sr, Pb, Th, Ba, and light rare earth elements (LREEs) and have a narrow range of initial 87Sr/86Sr ratios (0.70431 ± 0.00012 to 0.70454 ± 0.00010). Two types of amphibolite-facies epidote were recognized in the amphibolites. The first type of epidote (Ep-AI) developed in all the amphibolites and has slightly lower trace element contents than Ep-E. The Ep-AI has a same initial 87Sr/86Sr ratio range as the Ep-E and represents the primary amphibolite-facies retrograde product that is associated with an internally buffered fluid at 8.0-10.3 kbar and 646-674 °C. The other type of epidote (Ep-AII) occurs as irregular fragments, veins/veinlets, or reaction rims on the Ep-AI in certain amphibolites. Elemental X-ray maps reveal the presence of Ep-AI relics in the Ep-AII domains (appearing as a patchy texture), which indicates that Ep-AII most likely formed by the partial replacement of the Ep-AI in the presence of an infiltrating fluid. The distinctly lower trace element contents of Ep-AII are ascribed to element scavenging by a mechanism of dissolution-transport-precipitation during replacement. The Ep-AII in an individual amphibolite exhibits large intra- and inter-grain variations in the initial 87Sr/86Sr ratios (0.70493 ± 0.00030 to 0.70907 ± 0.00022), which are between those of the Ep-AI and granitic gneisses (wall rock of the amphibolites, 0.7097-0.7108). These results verify that the infiltrating fluid was externally derived from granitic gneisses. The matrix apatite in the amphibolites has the same initial 87Sr/86Sr ratio range as the Ep-AI, indicating that the amphibolite-facies fluid involved in the apatite crystallization was also internally derived. We propose that at least two separate stages of fluids were accounted for the amphibolite-facies retrogression of the Hualiangting eclogite. The fluid responsible for the growth of most of the amphibolite minerals was locally derived and behaved in a pervasive manner, whereas the influx of gneiss-derived fluid was transient, episodic, and highly channelized with a longer transport distance (> 60 m). The disparate origins and flow behavior of these fluids significantly influence the water budget and element transfer in exhumed HP-UHP slabs. This study also indicates that examining grain-scale Sr isotopic variations provides key information regarding the isotopic (dis)equilibrium, fluid origins, and fluid-flow regimes in metamorphic or metasomatic rocks that form in subduction-zone environments.

Terapascal static pressure generation with ultrahigh yield strength nanodiamond.

PubMed

Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Solopova, Natalia A; Abakumov, Artem; Turner, Stuart; Hanfland, Michael; Bykova, Elena; Bykov, Maxim; Prescher, Clemens; Prakapenka, Vitali B; Petitgirard, Sylvain; Chuvashova, Irina; Gasharova, Biliana; Mathis, Yves-Laurent; Ershov, Petr; Snigireva, Irina; Snigirev, Anatoly

2016-07-01

Studies of materials' properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications.

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

PubMed Central

Dubrovinskaia, Natalia; Dubrovinsky, Leonid; Solopova, Natalia A.; Abakumov, Artem; Turner, Stuart; Hanfland, Michael; Bykova, Elena; Bykov, Maxim; Prescher, Clemens; Prakapenka, Vitali B.; Petitgirard, Sylvain; Chuvashova, Irina; Gasharova, Biliana; Mathis, Yves-Laurent; Ershov, Petr; Snigireva, Irina; Snigirev, Anatoly

2016-01-01

Studies of materials’ properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications. PMID:27453944

Ultra High Pressure (UHP) Technology (BRIEFING SLIDES)

DTIC Science & Technology

2008-08-25

to operate in close (15 to 30 ft) proximity to burning JP 8 fuel. In these experiments, three to four gallons of 3% Aqueous Film Forming Foam ( AFFF ...technology provides more that 20X improvement in performance. 5 Steam Formation and Foam / Film capping are also major contributors to the extinguishing...insulates the fuel from the flames and acts as a thermal radiation barrier. In addition, the foam puts a film of water on top of the fuel, sealing the

Experimental Investigation of Magnetic Superconducting and other Phase Transitions in Novel f-Electron Materials at Ultra-high Pressures using Designer Diamond Anvils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maple, M. Brian; Jeffries, Jason R.; Ho, Pei-Chun

Pressure is often used as a controlled parameter for the investigation of condensed matter systems. In particular, pressure experiments can provide valuable information into the nature of superconductivity, magnetism, and the coexistence of these two phenomena. Some f-electron, heavy-fermion materials display interesting and novel behavior at moderately low pressures achievable with conventional experimental techniques; however, a growing number of condensed matter systems require ultrahigh pressure techniques, techniques that generate significantly higher pressures than conventional methods, to sufficiently explore their important properties. To that end, we have been funded to develop an ultrahigh pressure diamond anvil cell facility at the Universitymore » of California, San Diego (UCSD) in order to investigate superconductivity, magnetism, non-Fermi liquid behavior, and other phenomena. Our goals for the first year of this grant were as follows: (a) set up and test a suitable refrigerator; (b) set up a laser and spectrometer fluorescence system to determine the pressure within the diamond anvil cell; (c) perform initial resistivity measurements at moderate pressures from room temperature to liquid helium temperatures ({approx}1K); (d) investigate f-electron materials within our current pressure capabilities to find candidate materials for high-pressure studies. During the past year, we have ordered almost all the components required to set up a diamond anvil cell facility at UCSD, we have received and implemented many of the components that have been ordered, we have performed low pressure research on several materials, and we have engaged in a collaborative effort with Sam Weir at Lawrence Livermore National Lab (LLNL) to investigate Au4V under ultrahigh pressure in a designer diamond anvil cell (dDAC). This report serves to highlight the progress we have made towards developing an ultrahigh pressure research facility at UCSD, the research performed in the past year, as well as future directions we plan to pursue.« less

Physicochemical properties and storage stability of soybean protein nanoemulsions prepared by ultra-high pressure homogenization.

PubMed

Xu, Jing; Mukherjee, Dipaloke; Chang, Sam K C

2018-02-01

This study investigated the effects of the ultrahigh pressure homogenization (pressure, protein concentration, oil phase fraction, pH, temperature, and ionic strength) and storage on the properties of nanoemulsions (100-500nm range), which were stabilized by laboratory-prepared soybean protein isolate (SPI), β-conglycinin (7S) and glycinin (11S). The nanoemulsions made with SPI, 7S and 11S proteins exhibited considerable stability over various ionic strengths (0-500mM NaCl), pH (<4 or >7), thermal treatments (30-60°C) and storage (0-45days). The far-UV spectra of SPI, 7S, 11S dispersions, and SPI-, 7S-, 11S protein-stabilized nanoemulsions were analyzed for the protein structural changes following lipid removal. The ultra-high pressure homogenization changed the secondary structure of SPI, 7S, 11S proteins in the nanoemulsions, and enhanced their stability. This study demonstrated that SPI, 7S, and 11S proteins can be used as effective emulsifiers in nanoemulsions prepared by ultra-high pressure homogenization. Copyright © 2017. Published by Elsevier Ltd.

The case for simultaneous deformation, metamorphism and plutonism: an example from Proterozoic rocks in central Arizona

NASA Astrophysics Data System (ADS)

Karlstrom, K. E.; Williams, M. L.

1995-01-01

The syntectonic 1.70 Ga Crazy Basin Monzogranite provides an example of the complex spatial and temporal interactions between metamorphism, deformation, and plutonism. Synchronous plutonism and deformation is indicated by syn-shortening dikes, sills, and veins; parallel magmatic and solid state fabrics; fabrics in xenoliths; and a foliation triple point. Synchronous plutonism and metamorphism is indicated by a systematic increase from 400 °C to 630 °C towards the pluton at a constant pressure of 300 MPa (3 kb). Temperatures are consistent with a conductive cooling model in which a 700 °C pluton was emplaced into country rocks undergoing greenschist facies regional metamorphism. Synchronous deformation and metamorphism is indicated by porphyroblast inclusion geometries that document the synmetamorphic development of the S2 cleavage. The pluton was emplaced adjacent to the Shylock shear zone during progressive shortening. Emplacement of granite as NE-trending sheets was facilitated by temporal partitioning of transpressional convergence into strike-slip and dip-slip components. At the scale of the pluton's aureole and on the relatively rapid time scale of 10 3-10 6 y, regional deformation and metamorphism were punctuated by thermal softening and increased diffusion rates. Data suggests that accretion of Proterozoic arcs in Arizona involved diachronous pluton-enhanced deformation and associated high temperature-low pressure regional metamorphism.

Continental Subduction: Mass Fluxes and Interactions with the Wider Earth System

NASA Astrophysics Data System (ADS)

Cuthbert, S. J.

2011-12-01

Substantial parts of ultra-high pressure (UHP) terrains probably represent subducted passive continental margins (PCM). This contribution reviews and synthesises research on processes operating in such systems and their implication for the wider Earth system. PCM sediments are large repositories of volatiles including hydrates, nitrogen species, carbonates and hydrocarbons. Sediments and upper/ mid-crustal basement are rich in incompatible elements and are fertile for melting. Lower crust may be more mafic and refractory. Juvenile rift-related mafic rocks also have the potential to generate substantial volumes of granitoid melts, especially if they have been hydrated. Exposed UHP terrains demonstrate the return of continental crust from mantle depths, show evidence for substantial fluxes of aqueous fluid, anatexis and, in entrained orogenic peridotites, metasomatism of mantle rocks by crust- derived C-O-H fluids. However, substantial bodies of continental material may never return to the surface as coherent masses of rock, but remain sequestered in the mantle where they melt or become entrained in the deeper mantle circulation. Hence during subduction, PCM's become partitioned by a range of mechanisms. Mechanical partitioning strips away weaker sediment and middle/upper crust, which circulate back up the subduction channel, while denser, stronger transitional pro-crust and lower crust may "stall" near the base of the lithosphere or be irreversibly subducted to join the global mantle circulation. Under certain conditions sediment and upper crustal basement may reach depths for UHPM. Further partitioning takes place by anatexis, which either aids stripping and exhumation of the more melt-prone rock-masses through mechanical softening, or separates melt from residuum so that melt escapes and is accreted to the upper plate leading to "undercrusting", late-orogenic magmatism and further refinement of the crust. Melt that traverses sections of mantle will interact with it causing metasomatism and refertilisation. Partitioning also takes place by solid-fluid and melt-fluid partitioning. Dehydration may take place both during subduction and exhumation, and fluxes between dehydrating and hydrating rock masses influence the internal fluid budget of the orogen (essential for eclogitisation and densification of mafic lithologies). Ascending granitic melts advect dissolved water to shallow levels, or even the atmosphere. Irreversible subduction of PCM sediment carries water plus nitrogen species to the deeper mantle. Decarbonation of voluminous PCM carbonates depends on thermal regime and may release a pulse of CO2 to the atmosphere, but is limited in colder subduction zones hence transferring large volumes of carbon to the deep mantle. This may ultimately be mobilised by melting or dissolution to form fluid media for diamond formation.

Recycling of ancient subduction-modified mantle domains in the Purang ophiolite (southwestern Tibet)

NASA Astrophysics Data System (ADS)

Gong, Xiao-Han; Shi, Ren-Deng; Griffin, W. L.; Huang, Qi-Shuai; Xiong, Qing; Chen, Sheng-Sheng; Zhang, Ming; O'Reilly, Suzanne Y.

2016-10-01

Ophiolites in the Indus-Yarlung Zangbo (IYZ) suture (southern Tibet) have been interpreted as remnants of the Neo-Tethyan lithosphere. However, the discovery of diamonds and super-reducing, ultra-high pressure (SuR-UHP) mineral assemblages (e.g., coesite after stishovite, olivine after wadsleyite, native metals, alloys, and moissanite) in some of these massifs and associated chromitites requires a re-evaluation of their origin and evolution. A new petrological and geochemical study of the Purang ophiolite in the western IYZ suture sheds new lights on these issues. The depleted harzburgites of the Purang massif have low modal contents of clinopyroxene (< 2%), and high Cr# [100*Cr3 +/(Cr3 + + Al3 +)] in spinel (> 40 70) and pyroxenes (> 16 in orthopyroxene, and > 20 in clinopyroxene), suggesting high degrees of melt extraction (> 20%). These features are not consistent with formation in a (ultra-) slow-spreading mid-ocean ridge. These peridotites have high modal contents of orthopyroxene; this, and the extremely high Cr# of spinels in these peridotites, suggests modification in a subduction zone. The clinopyroxene-rich harzburgites and lherzolites contain rare spinel-pyroxene symplectites after garnet. Their clinopyroxenes have low MREE-to-HREE ratios ((Sm/Yb)N < 0.1) at relatively high HREE concentrations, and are Na-rich but Nd-poor. The relatively enrichment of Na but depletion of Nd in clinopyroxene cannot be explained by refertilization with MORB melts but are consistent with an origin from Na-rich subcontinental lithospheric mantle (SCLM). All lines of evidence suggest that these peridotites underwent initial melting in the stability field of garnet-facies peridotites, followed by additional melting in the spinel-facies mantle. Whole-rock Os isotopic compositions of the Purang peridotites give ancient TRD model ages (up to 1.3 Ga), indicating that the formation of these ancient depletion residues predated the opening of Neo-Tethyan Ocean. These observations, together with recent studies on other IYZ peridotites, suggest that the Purang peridotites are genetically unrelated to the associated mafic crust. Instead, they represent ancient SCLM domains, initially formed beneath a continental margin, and then modified by subduction, before they were incorporated into the Neo-Tethyan ocean basin. This model is consistent with the deep-mantle-recycling model for the presence of SuR-UHP phases in the IYZ ophiolites. The infiltration of MORB melts through these ancient depleted peridotites during their final exhumation in a (ultra-) slow-spreading center may have refertilized them to produce the clinopyroxene-rich peridotites.

Recent developments in novel freezing and thawing technologies applied to foods.

PubMed

Wu, Xiao-Fei; Zhang, Min; Adhikari, Benu; Sun, Jincai

2017-11-22

This article reviews the recent developments in novel freezing and thawing technologies applied to foods. These novel technologies improve the quality of frozen and thawed foods and are energy efficient. The novel technologies applied to freezing include pulsed electric field pre-treatment, ultra-low temperature, ultra-rapid freezing, ultra-high pressure and ultrasound. The novel technologies applied to thawing include ultra-high pressure, ultrasound, high voltage electrostatic field (HVEF), and radio frequency. Ultra-low temperature and ultra-rapid freezing promote the formation and uniform distribution of small ice crystals throughout frozen foods. Ultra-high pressure and ultrasound assisted freezing are non-thermal methods and shorten the freezing time and improve product quality. Ultra-high pressure and HVEF thawing generate high heat transfer rates and accelerate the thawing process. Ultrasound and radio frequency thawing can facilitate thawing process by volumetrically generating heat within frozen foods. It is anticipated that these novel technologies will be increasingly used in food industries in the future.

Precipitation of Oriented Rutile and Ilmenite Needles in Garnet, Northeastern Connecticut, USA: Evidence for Extreme Metamorphic Conditions?

NASA Astrophysics Data System (ADS)

Ague, J. J.; Eckert, J. O.

2011-12-01

We report the discovery of oriented needles of rutile and, less commonly, ilmenite in the cores of garnets from northeastern CT, USA. The rocks preserve granulite facies mineral assemblages, form part of the Merrimack Synclinorium, and underwent metamorphism and deformation during the Acadian orogeny. The needles appear identical to those reported from a number of extreme P-T environments worldwide, including UHP metamorphic rocks, high-P granulites, and garnet peridotites. The needles are predominantly oriented along <111> directions in garnet. The long axes of the rutile needles commonly do not go extinct parallel to the cross hairs under cross-polarized light (e.g., Griffin et al., 1971). This anomalous extinction indicates that the needles do not preserve a specific crystallographic relationship with their garnet hosts (e.g., Hwang et al., 2007). The needles range from a few hundred nm to a few um in diameter, and can be mm-scale in length. Micrometer-scale plates of rutile, srilankite and crichtonite have also been observed in some garnets together with the Fe-Ti oxide needles. Several origins for the needles have been proposed in the literature; we investigate the hypothesis that they precipitated in situ from originally Ti-rich garnet. Chemical profiles across garnets indicate that some retain Ti zoning, with elevated-Ti concentrations in the cores dropping to low values in the rims. For these zoned garnets, high-resolution, 2-D chemical mapping using the JEOL JXA-8530F field emission gun electron microprobe at Yale University reveals that the needles are surrounded by well-defined Ti-depletion halos. Chemical profiles also document strong depletions of Cr (which is present in both rutile and ilmenite) directly adjacent to needles. The observed Ti-depletions demonstrate that the needles precipitated from Ti-bearing garnet, probably during cooling and/or decompression associated with exhumation. The rutile precipitates must be largely incoherent with respect to the garnet crystal lattice; consequently, the surface energy penalty for incoherent precipitation was unable to prevent needle formation. Coherent precipitation would in all likelihood have required nontrivial deformation of the lattices of garnet and/or Fe-Ti oxides, and this is inferred to have been energetically less favorable than incoherent precipitation. The Fe-Ti oxide needles suggest that a previously-unrecognized area of extreme T and/or P metamorphism exists in southern New England.

Separating Multiple Episodes of Partial Melting in Polyorogenic Crust: AN Example from the Haiyangsuo Complex, Northern Sulu Belt, Eastern China

NASA Astrophysics Data System (ADS)

Feng, P.; Wang, L.; Brown, M.; Wang, S.

2017-12-01

Determining the timing, mechanism and source of partial melts in polyorogenic crust is challenging. In the Sulu belt, the tectonic affinity of the Haiyangsuo (HYS) complex is controversial due to its polyphase metamorphic history. Here we use detailed field mapping, petrology, microstructural analysis and zircon geochronology to study thin stromatic leucosomes in host granite gneiss, and crosscutting leucogranite dykes to decipher the melting history. Zircon grains from both granite gneiss and thin leucosomes exhibit core-mantle-rim structures. Zircon cores yield protolith ages of 2.86-2.81 Ga, whereas the mantles and rims yield younger metamorphic/melt crystallization ages of ca. 1.82-1.80 Ga. The mantles are characterized by gray luminescence, flat HREE distribution patterns and relatively low Th/U ratios, indicating crystallization during granulite-facies metamorphism. Whereas rims show bright luminescence, steep HREE distribution patterns and higher Th/U ratios, suggesting they crystallized from melt. The mantles and rims have ɛHf (t) of -18.2 to -11.0. Using 176Lu/177Hf = 0.001, these data project back to the array of ɛHf (t) values for the zircon cores. This demonstrates that the thin leucosomes were derived from the gneiss without any mass input from a mantle source. These features are consistent with an origin of the HYS as part of the eastern margin of the NCC prior to juxtaposition with the Sulu belt. Zircons from the leucogranite dykes also show core-mantle-rim structure. Inherited cores yield concordant 206Pb/238U ages of 776-701 Ma consistent with the dominant age range for protoliths of the UHP metamorphic rocks in the Sulu belt. Zircon mantle and rim domains, which both contain multiphase solid inclusions (Kfs + Pl + Qz and Hem + Pl + Qz in mantles and Kfs + Pl + Qz + Bt in rims), yield melt crystallization ages of 226-217 and 169-156 Ma, respectively. High Sr, low Y and Yb contents, high Sr/Y ratios, and the range of ɛNd (t) values (-18.2- -15.0) and initial 87Sr/86Sr ratios (0.7106 - 0.7146) for the leucogranites are consistent with melting of thickened lower continental crust of the Sulu belt. We interpret the dykes to have been emplaced during post-collisional collapse of the orogenic root of this belt in the Middle-Upper Jurassic.

Neoarchean arc magmatism followed by high-temperature, high-pressure metamorphism in the Nilgiri Block, southern India

NASA Astrophysics Data System (ADS)

Samuel, Vinod O.; Sajeev, K.; Hokada, T.; Horie, K.; Itaya, T.

2015-11-01

The Nilgiri Block, southern India is an exhumed lower crust formed through arc magmatic processes in the Neoarchean. The main lithologies in this terrane include charnockites, gneisses, volcanic tuff, metasediments, banded iron formation and mafic-ultramafic bodies. Mafic-ultramafic rocks are present towards the northern and central part of the Nilgiri Block. We examine the evolution of these mafic granulites/metagabbros by phase diagram modeling and U-Pb sensitive high resolution ion microprobe (SHRIMP) dating. They consist of a garnet-clinopyroxene-plagioclase-hornblende-ilmenite ± orthopyroxene ± rutile assemblage. Garnet and clinopyroxene form major constituents with labradorite and orthopyroxene as the main mineral inclusions. Labradorite, identified using Raman analysis, shows typical peaks at 508 cm- 1, 479 cm- 1, 287 cm- 1 and 177 cm- 1. It is stable along with orthopyroxene towards the low-pressure high-temperature region of the granulite facies (M1 stage). Subsequently, orthopyroxene reacted with plagioclase to form the peak garnet + clinopyroxene + rutile assemblage (M2 stage). The final stage is represented by amphibolite facies-hornblende and plagioclase-rim around the garnet-clinopyroxene assemblage (M3 stage). Phase diagram modeling shows that these mafic granulites followed an anticlockwise P-T-t path during their evolution. The initial high-temperature metamorphism (M1 stage) was at 850-900 °C and ~ 9 kbar followed by high-pressure granulite facies metamorphism (M2 stage) at 850-900 °C and 14-15 kbar. U-Pb isotope studies of zircons using SHRIMP revealed late Neoarchean to early paleoproterozoic ages of crystallization and metamorphism respectively. The age data shows that these mafic granulites have undergone arc magmatism at ca. 2539.2 ± 3 Ma and high-temperature, high-pressure metamorphism at ca. 2458.9 ± 8.6 Ma. Thus our results suggests a late Neoarchean arc magmatism followed by early paleoproterozoic high-temperature, high-pressure granulite facies metamorphism due to the crustal thickening and suturing of the Nilgiri Block onto the Dharwar Craton.

Combined Detrital U/Pb Zircon and 40Ar/39Ar Mica Geoochronology to Test Structural Models for a Devonian Orogenic Collapse Basin in the Norwegian Caledonides

NASA Astrophysics Data System (ADS)

Templeton, J.; Anders, M.; Fossen, H.

2014-12-01

The Hornelen basin is the largest of the Devonian 'Old Red' sandstone basins in Norway, comprising 25 km of alluvial-fluvial deposits which are organized into basin-wide, coarsening-upward megacycles. Hornelen sits with several smaller basins in the hanging wall a major extensional shear zone along which the ultra-high pressure metamorphic core of subducted Baltican crust was rapidly exhumed during the extensional collapse of the Caledonian orogeny. The timing of orogenic collapse corresponds closely to the timing of the basins, which are loosely constrained by sparse trace-fossil assemblages to a mid-Devonian age. Further, the basins are now in brittle fault contact with the underlying mylonitic shear zone and the metamorphic core, implying that they are the upper-crustal expression of large-scale extension and deep-crustal exhumation. Two distinct structural models have been proposed for Hornelen to account for these observations. The strike-slip model juxtaposes different source terranes across the basin-controlling fault and predicts spatially changing provenance within chronostratigraphic units. The supradetachment model links the filling of the basin directly to unroofing of the metamorphic core on a low-angle detachment fault, and predicts basin-wide changes in provenance through time with progressive exhumation of the metamorphic hinterland. We present an extensive new provenance dataset, spanning the Hornelen basin strata through space and time. Detrital zircon U/Pb ages from 18 new samples comprise three distinct populations (1.6, 1.0, and 0.43 Ga) with the Caledonian-aged zircons (ca 0.43 Ga) present mainly along the northern margin of the basin, representing an Upper Allochthon source not found on the southern or eastern margins of the basin. Juxtaposition of different source terranes across the basin supports the strike-slip model. 40Ar/39Ar detrital white mica from the same sample set documents a younging of the dominant age peak from 432 Ma in the oldest sediments to 401 Ma in the youngest units, but does not document any difference between northern and southern mica sources. This trend supports the supradetachment model, but may also be explained by passive, isostatically-driven erosional unroofing of the overthickened orogenic crust.

Ultrahigh-pressure polyamorphism in GeO2 glass with coordination number >6

NASA Astrophysics Data System (ADS)

Kono, Yoshio; Kenney-Benson, Curtis; Ikuta, Daijo; Shibazaki, Yuki; Wang, Yanbin; Shen, Guoyin

2016-03-01

Knowledge of pressure-induced structural changes in glasses is important in various scientific fields as well as in engineering and industry. However, polyamorphism in glasses under high pressure remains poorly understood because of experimental challenges. Here we report new experimental findings of ultrahigh-pressure polyamorphism in GeO2 glass, investigated using a newly developed double-stage large-volume cell. The Ge-O coordination number (CN) is found to remain constant at ∼6 between 22.6 and 37.9 GPa. At higher pressures, CN begins to increase rapidly and reaches 7.4 at 91.7 GPa. This transformation begins when the oxygen-packing fraction in GeO2 glass is close to the maximal dense-packing state (the Kepler conjecture = ∼0.74), which provides new insights into structural changes in network-forming glasses and liquids with CN higher than 6 at ultrahigh-pressure conditions.

Oligo-Miocene thinning of the Beni Bousera peridotites and their Variscan crustal host rocks, Internal Rif, Morocco

NASA Astrophysics Data System (ADS)

Gueydan, Frédéric; Pitra, Pavel; Afiri, Abdelkhaleq; Poujol, Marc; Essaifi, Abderrahim; Paquette, Jean-Louis

2015-06-01

Deciphering Variscan versus Alpine history in the Internal Rif system is a key to constrain the tectonic evolution of the Alboran domain and hence the geodynamics of the western Mediterranean system during the Cenozoic. This study focuses on the evolution of the metamorphic envelope of the Beni Bousera massif and its relation to the underlying peridotites. Combining structural geology, metamorphic petrology, and laser ablation inductively coupled plasma mass spectrometry U-Th-Pb dating of monazite, this study contributes to the understanding of the tectonic history of the western Internal Rif. The regional foliation (S2) is characterized by low pressure-high temperature (LP-HT) mineral assemblages and obliterates a former foliation (S1) developed along a Barrovian (medium pressure-medium temperature, MP-MT) metamorphic gradient. The dating of some metamorphic monazite grains from a micaschist and a migmatitic gneiss demonstrates that the crustal envelope of the peridotite recorded two distinct tectonometamorphic episodes. Data from monazite inclusions in S1 garnet suggest that the first event, D1, is older than 250-170 Ma and likely related to the Variscan collision, in agreement with the Barrovian type of the metamorphic gradient. The second event, D2, is Alpine in age (at circa 21 Ma) and corresponds to a strong lithosphere thinning allowing subsequent subcontinental mantle exhumation. Such a tectonic context provides an explanation for the LP-HT metamorphic gradient that is recorded in the regional foliation of the western Betic-Rif system. This extension is probably related to a subduction slab rollback in the western end of the Mediterranean realm during the Oligo-Miocene times. No evidence for a Tertiary high pressure/low temperature metamorphism has been identified in the studied area.

Potential Impacts of Ultra-High-Pressure (UHP) Technology of National Fire Protection Agency (NFPA) Standard 403 (POSTPRINT)

DTIC Science & Technology

2007-06-25

AFFF tests, and one-tenth the NFPA 403 standard. r 2007 Elsevier Ltd. All rights reserved. Keywords: Aqueous film forming foam ( AFFF ...proven to reduce water- aqueous film forming foam ( AFFF ) agent quantities 2–3 times over conventional water- foam systems on 325–480m2 (3500–5200 ft2...and combined agent firefighting systems (CAFFS) have proven to enhance the performance of firefighting equipment using water and aqueous

Mechanisms of Superplastic Deformation of Nanocrystalline Silicon Carbide Ceramics

DTIC Science & Technology

2012-08-01

These included the following: standard hot isostatic pressing (HIP), spark plasma sintering , ultra-high pressure HIP, and a multianvil pressure...96.8 2270 Multianvil apparatus 1200 3000 94.8 1130 Note: SPS = spark plasma sintering . 2 Figure 1. Ultra-high pressure HIP; 1600 °C, 980...strain rate sensitivity and flow stress. 15. SUBJECT TERMS silicon carbide, nanostructure, sintering , hot isostatic pressing, hardness 16. SECURITY

Oman metamorphic sole formation reveals early subduction dynamics

NASA Astrophysics Data System (ADS)

Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Plunder, Alexis; Ildefonse, Benoît; Yamato, Philippe; Prigent, Cécile

2016-04-01

Metamorphic soles correspond to m to ~500m thick tectonic slices welded beneath most of the large-scale ophiolites. They typically show a steep inverted metamorphic structure where the pressure and temperature conditions of crystallization increase upward (from 500±100°C at 0.5±0.2 GPa to 800±100°C at 1.0±0.2 GPa), with isograds subparallel to the contact with the overlying ophiolitic peridotite. The proportion of mafic rocks in metamorphic soles also increases from the bottom (meta-sediments rich) to the top (approaching the ophiolite peridotites). These soles are interpreted as the result of heat transfer from the incipient mantle wedge toward the nascent slab (associated with large-scale fluid transfer and possible shear heating) during the first My of intra-oceanic subduction (as indicated by radiometric ages). Metamorphic soles provide therefore major constraints on early subduction dynamics (i.e., thermal structure, fluid migration and rheology along the nascent slab interface). We present a detailed structural and petrological study of the metamorphic sole from 4 major cross-sections along the Oman ophiolite. We show precise pressure-temperature estimates obtained by pseudosection modelling and EBSD measurements performed on both the garnet-bearing and garnet-free high-grade sole. Results allow quantification of the micro-scale deformation and highlight differences in pressure-temperature-deformation conditions between the 4 different locations, showing that the inverted metamorphic gradient through the sole is not continuous in all locations. Based on these new constraints, we suggest a new tectonic-petrological model for the formation of metamorphic soles below ophiolites. This model involves the stacking of several homogeneous slivers of oceanic crust leading to the present-day structure of the sole. In this view, these thrusts are the result of rheological contrasts between the sole and the peridotite as the plate interface progressively cools down. These slivers later underwent several stages of retrogression (partly mediated by ascending fluids from the slab) from amphibolite- to prehnite/pumpellite-facies conditions.

High-pressure granulites in the Fuping Complex of the central North China Craton: Metamorphic P-T-t evolution and tectonic implications

NASA Astrophysics Data System (ADS)

Qian, Jiahui; Yin, Changqing; Zhang, Jian; Ma, Li; Wang, Luojuan

2018-04-01

Mafic granulites in the Fuping Complex occur as lenses or boudins within high-grade TTG (Trondhjemite-Tonalite-Granodiorite) gneisses. Petrographic observations reveal four generations of mineral assemblage in the granulites: an inclusion assemblage of hornblende + plagioclase + ilmenite + quartz within garnet core; an inferred peak assemblage composed of garnet ± hornblende + plagioclase + clinopyroxene + rutile/ilmenite + quartz; a decompression assemblage characterized by symplectites of clinopyroxene ± orthopyroxene + plagioclase, coronae of plagioclase ± clinopyroxene ± hornblende around embayed garnet porphyroblasts or a two-pyroxene association; and a late amphibolite-facies retrogressive assemblage. Two representative samples were used for pseudosection modeling in NCFMASHTO model system to determine their metamorphic evolution. The results show that these granulites experienced a high-pressure stage of metamorphism with peak P-T conditions of 12-13 kbar and 760-800 °C (Pmax) and a post-peak history under P-T conditions of ∼9.0 kbar and 805-835 °C (Tmax), indicating a nearly isothermal decompression process (ITD) with a slight heating. Metamorphic evolution from the Pmax to the Tmax is predicted to be dominated by garnet breakdown through continuous metamorphic reactions of garnet + quartz ± diopside = hornblende + plagioclase + liquid and garnet + quartz + hornblende = plagioclase + diopside + liquid + orthopyroxene. Further metamorphic evolution after the Tmax is dominated by cooling, suggesting that high-pressure (HP) granulites may also exist in the Fuping Complex. Metamorphic zircons in the Fuping HP mafic granulites have left inclined REE patterns, Ti contents of 1.68-6.88 ppm and crystallization temperatures of 602-712 °C. SIMS zircon U-Pb dating on these zircons yields 207Pb/206Pb ages of 1891 ± 14 Ma and 1849 ± 6 Ma, interpreted to represent the cooling stage of metamorphism. The P-T-t evolution of the Fuping HP mafic granulites records well the protracted Paleoproterozoic orogenic event occurred in the central North China Craton.

Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

NASA Astrophysics Data System (ADS)

Rubatto, Daniela; Ferrando, Simona; Compagnoni, Roberto; Lombardo, Bruno

2010-04-01

The age of high-pressure metamorphism is crucial to identify a suitable tectonic model for the vast Variscan orogeny. Banded H P granulites from the Gesso-Stura Terrain in the Argentera Massif, Italy, have been recently described (Ferrando et al., 2008) relicts of high-pressure metamorphism in the western part of the Variscan orogen. Bulk rock chemistry of representative lithologies reveals intermediate silica contents and calc-alkaline affinity of the various cumulate layers. Enrichment in incompatible elements denotes a significant crustal component in line with intrusion during Ordovician rifting. Magmatic zircon cores from a Pl-rich layer yield scattered ages indicating a minimum protolith age of 486 ± 7 Ma. Carboniferous zircons (340.7 ± 4.2 and 336.3 ± 4.1 Ma) are found in a Pl-rich and a Pl-poor layer, respectively. Their zoning, chemical composition (low Th/U, flat HREE pattern and Ti-in-zircon temperature) and deformation indicate that they formed during the high-pressure event before decompression and mylonitisation. The proposed age for high-pressure metamorphism in the Argentera Massif proves that subduction preceded anatexis by less than 20 Ma. The new data allow a first-order comparison with the Bohemian Massif, which is located at the eastern termination of the Variscan orogen. Similarities in evolution at either end of the orogen support a Himalayan-type tectonic model for the entire European Variscides.

Age, temperature and pressure of metamorphism in the Tasriwine Ophiolite Complex, Sirwa, Morocco

NASA Astrophysics Data System (ADS)

Samson, S. D.; Inglis, J.; Hefferan, K. P.; Admou, H.; Saquaque, A.

2013-12-01

Sm-Nd garnet-whole rock geochronology and phase equilbria modeling have been used to determine the age and conditions of regional metamorphism within the Tasriwine ophiolite complex,Sirwa, Morocco. Pressure and temperature estimates obtained using a NaCaKFMASHT phase diagram (pseudosection) and garnet core and rim compositions predict that garnet growth began at ~0.72GPa and ~615°C and ended at ~0.8GPa and ~640°C. A bulk garnet Sm-Nd age of 645.6 × 1.6 Ma, calculated from a four point isochron that combines whole rock, garnet full dissolution and two successively more aggressive partial dissolutions, provides a precise date for garnet formation and regional metamorphism. The age is nearly 20 million years younger than a previous age estimate of regional metamorphism of 663 × 14 Ma based upon a SHRIMP U-Pb date from rims on zircon from the Irri migmatite. The new data provide further constraints on the age and nature of regional metamorphism in the Anti-Atlas mountains and emphasizes that garnet growth during regional metamorphism may not necessarily coincide with magmatism/anatexis which predominate the signature witnessed by previous U-Pb studies. The ability to couple PT estimates for garnet formation with high precision Sm- Nd geochronology highlights the utility of garnet studies for uncovering the detailed metamorphic history of the Anti-Atlas mountain belt.

Distribution, facies, ages, and proposed tectonic associations of regionally metamorphosed rocks in east- and south-central Alaska

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Csejtey, Bela; Foster, Helen L.; Doyle, Elizabeth O.; Nokleberg, Warren J.; Plafker, George

1993-01-01

Most of the exposed bedrock in east- and south-central Alaska has been regionally metamorphosed and deformed during Mesozoic and early Cenozoic time. All the regionally metamorphosed rocks are assigned to metamorphic-facies units on the basis of their temperature and pressure conditions and metamorphic age. North of the McKinley and Denali faults, the crystalline rocks of the Yukon- Tanana upland and central Alaska Range compose a sequence of dynamothermally metamorphosed Paleozoic and older(?) metasedimentary rocks and metamorphosed products of a Devonian and Mississippian continental-margin magmatic arc. This sequence was extensively intruded by postmetamorphic mid-Cretaceous and younger granitoids. Many metamorphic-unit boundaries in the Yukon-Tanana upland are low-angle faults that juxtapose units of differing metamorphic grade, which indicates that metamorphism predated final emplacement of the fault-bounded units. In some places, the relation of metamorphic grade across a fault is best explained by contractional faulting; in other places, it is suggestive of extensional faulting.Near the United States-Canadian border in the central Yukon- Tanana upland, metamorphism, plutonism, and thrusting occurred during a latest Triassic and Early Jurassic event that presumably resulted from the accretion of a terrane that had affinities to the Stikinia terrane onto the continental margin of North America. Elsewhere in the Yukon-Tanana upland, metamorphic rocks give predominantly late Early Cretaceous isotopic ages. These ages are interpreted to date either the timing of a subsequent Early Cretaceous episode of crustal thickening and metamorphism or, assuming that these other areas were also originally heated during the latest Triassic to Early Jurassic and remained buried, the timing of their uplift and cooling. This uplift and cooling may have resulted from extension.South of the McKinley and Denali faults and north of the Border Ranges fault system, medium-grade metamorphism across much of the southern Peninsular and Wrangellia terranes was early to synkinematic with the intrusion of tonalitic and granodioritic plutons of primarily Early and Middle Jurassic age in the Peninsular terrane and Late Jurassic age in the Wrangellia terrane. Areas metamorphosed during the Jurassic episode that crop out near the Border Ranges fault system were subsequently retrograded and deformed in Cretaceous and early Tertiary time during accretion of younger units to the south. North of the Jurassic metamorphic and plutonic complex, low-grade metamorphism affected the rest of the Wrangellia terrane sometime during Jurassic and (or) Cretaceous time.North of the Wrangellia terrane and immediately south of the McKinley and Denali faults, flyschoid rocks, which were deposited within a basin that separated the Wrangellia terrane from the western margin of North America, form a northeastward-tapering wedge. Within the western half of the wedge, flysch and structurally interleaved tectonic fragments were highly deformed and weakly metamorphosed; much of the metamorphism and deformation probably occurred sometime during mid- to Late Cretaceous time. In the eastern half of the wedge, flyschoid rocks form an intermediate-pressure Barrovian sequence (Maclaren metamorphic belt). Metamorphism of the Maclaren metamorphic belt was synkinematic with the Late Cretaceous to earliest Tertiary intrusion of foliated plutons of intermediate composition. Isotopic data suggest metamorphism extended into the early Tertiary and was accompanied by rapid uplift and cooling. Low- to medium-grade metamorphism throughout the wedge was probably associated with the accretion of the outboard Wrangellia terrane, as has been proposed for the Maclaren metamorphic belt.South of the Border Ranges fault system lie variably metamorphosed sequences of oceanic rocks that comprise the successively accreted Chugach, Yakutat, Ghost Rocks, and Prince William terranes. The Chugach terrane consists of three successively accreted sequences of differing metamorphic histories. Metamorphism in all the sequences was associated with north-directed underthrusting beneath either the combined Peninsular-Wrangellia terrane or the older and inner parts of the Chugach terrane. These sequences, from innermost to outermost are: (1) intermediate- to highpressure, transitional greenschist- to blueschist-facies metabasalt and metasedimentary rocks that were metamorphosed during the Early and Middle Jurassic; (2) prehnite-pumpellyite-facies melange that was metamorphosed sometime during the Jurassic and Cretaceous; and (3) low-pressure prehnite-pumpellyite- or greenschist- facies flysch and metavolcanic rocks that were initially metamorphosed during latest Cretaceous to early Tertiary time and, in the eastern Chugach Mountains, were subsequently overprinted by low-pressure amphibolite-facies metamorphism that accompanied widespread intrusion during Eocene time. A similar low-pressure-facies series also developed within melange and flysch of the Yakutat terrane; these rocks are also intruded by Eocene plutons and are correlated with similar rocks of the Chugach terrane.Seaward of the Chugach terrane are the strongly deformed but weakly metamorphosed (prehnite-pumpellyite-facies) deep-sea metasedimentary rocks and oceanic metavolcanic rocks of the Ghost Rocks and Prince William terranes. Metamorphism and deformation occurred during underthrusting of these terranes beneath the Chugach terrane in early Tertiary time and predated, perhaps by very little, intrusion by early Tertiary granitoids.

Increasing the graduation rates of minority medical students.

PubMed

Payne, J L; Nowacki, C M; Girotti, J A; Townsel, J; Plagge, J C; Beckham, T W

1986-05-01

The University of Illinois College of Medicine has operated a program since 1969 to recruit minority students into the college and to increase the graduation rates of these students once they enroll. Known as the Medical Opportunities Program (MOP) until 1978, the program was expanded in 1978 and renamed the Urban Health Program (UHP). The authors of the present paper discuss the results of these programs, particularly the effect of granting minority students delays in completing graduation requirements. The MOP (1969 through 1978) increased graduation rates for minority students from 55 percent for those who graduated on time to 81 percent for both on-time and delayed graduates. Under the first seven years of the UHP (1979 through 1985), more minority students have been offered places, and more have enrolled than in the 10 years of the MOP. The retention rate under the UHP, if it holds, will be higher than that under the MOP. For the combined MOP-UHP period, the retention rate for minority students was 88 percent; 69.8 percent of the graduates were on time, and 30.2 were delayed.

Metamorphic records for subduction erosion and subsequent underplating processes revealed by garnet-staurolite-muscovite schists in central Qiangtang, Tibet

NASA Astrophysics Data System (ADS)

Zhang, Xiu-Zheng; Dong, Yong-Sheng; Wang, Qiang; Dan, Wei; Zhang, Chunfu; Xu, Wang; Huang, Ming-Liang

2017-01-01

Subduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological, geochemical, and geophysical observations at modern convergent plate margins. So far, not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion. Here we first revealed metamorphic records for a subduction erosion process based on our study of the Late Paleozoic garnet-staurolite-muscovite schists in the central Qiangtang block, Tibet. Provenance analyses suggest that the protoliths of garnet-staurolite-muscovite schists have the Northern Qiangtang-affinity and were deposited in an active continental margin setting. Mineral inclusion data show that the early metamorphic stage (M1) recorded blueschist facies pressure-temperature (P-T) conditions of 0.8-1.1 GPa and 402-441°C, indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high-pressure/low-temperature metamorphism. The peak metamorphic stage (M2) recorded amphibolite facies P-T conditions of 0.3-0.5 GPa and 470-520°C. The 40Ar/39Ar cooling ages (263-259 Ma) yielded from muscovite suggest the amphibolite facies metamorphism (>263 Ma) occurred at oceanic subduction stage. The distinctly staged metamorphism defines a clockwise and warming decompression P-T-t path which reveals an underplating process following the early subduction erosion. During the tectonic process, the eroded low-density material escaped from the cold subduction channel and rise upward into the warm middle-lower crust of the upper plate, undergoing amphibolite facies metamorphism. Our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the Paleo-Tethys Ocean.

Tremor activity inhibited by well-drained conditions above a megathrust

PubMed Central

Nakajima, Junichi; Hasegawa, Akira

2016-01-01

Tremor occurs on megathrusts under conditions of near-lithostatic pore-fluid pressures and extremely weakened shear strengths. Although metamorphic reactions in the slab liberate large amounts of fluids, the mechanism for enhancing pore-fluid pressures along the megathrust to near-lithostatic values remains poorly understood. Here we show anti-correlation between low-frequency earthquake (LFE) activity and properties that are markers of the degree of metamorphism above the megathrust, whereby LFEs occur beneath the unmetamorphosed overlying plate but are rare or limited below portions that are metamorphosed. The extent of metamorphism in the overlying plate is likely controlled by along-strike contrasts in permeability. Undrained conditions are required for pore-fluid pressures to be enhanced to near-lithostatic values and for shear strength to reduce sufficiently for LFE generation, whereas well-drained conditions reduce pore-fluid pressures at the megathrust and LFEs no longer occur at the somewhat strengthened megathrust. Our observations suggest that undrained conditions are a key factor for the genesis of LFEs. PMID:27991588

Neoarchean high-pressure metamorphism from the northern margin of the Palghat-Cauvery Suture Zone, southern India: Petrology and zircon SHRIMP geochronology

NASA Astrophysics Data System (ADS)

Saitoh, Yohsuke; Tsunogae, Toshiaki; Santosh, M.; Chetty, T. R. K.; Horie, Kenji

2011-08-01

We report the metamorphic pressure-temperature ( P- T) history of mafic granulites from two localities in southern India, one from Kanja Malai in the northern margin and the other from Perundurai in the central domain of the Palghat-Cauvery Suture Zone (PCSZ). The PCSZ is described in recent models as the trace of the suture along which crustal blocks were amalgamated within the Gondwana supercontinent during Late Neoproterozoic-Cambrian. The mafic granulite from Kanja Malai yields P- T conditions of 750-800 °C and 8-12 kbar reflecting the partially retrograded conditions following a peak high-pressure (HP) metamorphic event. The common Grt + Cpx + Qtz assemblage in these rocks and lack of decompression texture suggest that peak metamorphism was probably buffered by Grt + Cpx + Opx + Pl + Qtz assemblage, following which the rocks were exhumed through a gradual P- T decrease. The mafic granulite from Perundurai (Grt + Cpx + Pl) contains Opx + Pl symplectite commonly occurring between garnet and clinopyroxene, suggesting the progress of reaction: Grt + Cpx + Qtz → Opx + Pl, with the Grt + Cpx + Qtz representing the peak metamorphic assemblage. The reaction microstructures and calculated P- T conditions suggest that the mafic granulites from Perundurai underwent peak HP metamorphism at P > 12 kbar and T = 800-900 °C and subsequent isothermal decompression along a clockwise P- T path, in contrast to the P- T path inferred for Kanja Malai. The contrasting P- T paths obtained from the two localities suggest that whereas Perundurai is a part of the metamorphic orogen developed within the PCSZ during Gondwana assembly, the high-pressure granulites of Kanja Malai belong to a different orogenic regime. In order to evaluate this aspect further, we analyzed zircons in a charnockite and garnet-bearing quartzo-feldspathic gneiss associated with the HP granulites from Kanja Malai which yielded mean 207Pb/ 206Pb magmatic protolith emplacement ages of 2536.1 ± 1.4 Ma and 2532.4 ± 3.7 Ma, and peak metamorphic ages of 2477.6 ± 1.8 Ma and 2483.9 ± 2.5 Ma, respectively. These results closely compare with the available magmatic (2530-2540 Ma) and metamorphic (2470-2480 Ma) ages reported from charnockites in the Salem Block at the southern fringe of the Archean Dharwar craton, immediately north of the PCSZ. The Neoarchean/Paleoproterozoic ages obtained from Kanja Malai correlate with the tectonic history at the margin of the Archean craton. Although no age data are available for the Perundurai mafic granulite, the close correspondence of their P- T data and exhumation path with those reported for Late Neoproterozoic-Cambrian HP-UHT metamorphism within the PCSZ suggest that these rocks form part of the Gondwana-forming orogen.

Metamorphism and partial melting of ordinary chondrites: Calculated phase equilibria

NASA Astrophysics Data System (ADS)

Johnson, T. E.; Benedix, G. K.; Bland, P. A.

2016-01-01

Constraining the metamorphic pressures (P) and temperatures (T) recorded by meteorites is key to understanding the size and thermal history of their asteroid parent bodies. New thermodynamic models calibrated to very low P for minerals and melt in terrestrial mantle peridotite permit quantitative investigation of high-T metamorphism in ordinary chondrites using phase equilibria modelling. Isochemical P-T phase diagrams based on the average composition of H, L and LL chondrite falls and contoured for the composition and abundance of olivine, ortho- and clinopyroxene, plagioclase and chromite provide a good match with values measured in so-called equilibrated (petrologic type 4-6) samples. Some compositional variables, in particular Al in orthopyroxene and Na in clinopyroxene, exhibit a strong pressure dependence when considered over a range of several kilobars, providing a means of recognising meteorites derived from the cores of asteroids with radii of several hundred kilometres, if such bodies existed at that time. At the low pressures (<1 kbar) that typify thermal metamorphism, several compositional variables are good thermometers. Although those based on Fe-Mg exchange are likely to have been reset during slow cooling, those based on coupled substitution, in particular Ca and Al in orthopyroxene and Na in clinopyroxene, are less susceptible to retrograde diffusion and are potentially more faithful recorders of peak conditions. The intersection of isopleths of these variables may allow pressures to be quantified, even at low P, permitting constraints on the minimum size of parent asteroid bodies. The phase diagrams predict the onset of partial melting at 1050-1100 °C by incongruent reactions consuming plagioclase, clinopyroxene and orthopyroxene, whose compositions change abruptly as melting proceeds. These predictions match natural observations well and support the view that type 7 chondrites represent a suprasolidus continuation of the established petrologic types at the extremes of thermal metamorphism. The results suggest phase equilibria modelling has potential as a powerful quantitative tool in investigating, for example, progressive oxidation during metamorphism, the degree of melting and melt loss or accumulation required to produce the spectrum of differentiated meteorites, and whether the onion shell or rubble pile model best explains the metamorphic evolution of asteroid parent bodies in the early solar system.

1.45 Ga granulites in the southwestern Grenville province: Geologic setting, P-T conditions, and U-Pb geochronology

NASA Astrophysics Data System (ADS)

Ketchum, J. W. F.; Jamieson, R. A.; Heaman, L. M.; Culshaw, N. G.; Krogh, T. E.

1994-03-01

In the southwestern Grenville province, the parautochthonous Britt domain includes a variety of pre-Grenvillian metamorphic and plutonic rocks that were reworked at upper amphibolite facies during the Grenvillian orogeny. Near Pointe-au-Baril, Ontario, a crustal block containing pre-Grenvillian granulite facies mineral assemblages and pre-Grenvillian to early Grenvillian tectonic fabrics has been identified. The block is bounded on the northwest and southeast by extensional shear zones that may have isolated it from regional late Gren- villian deformation. Multiequilibria pressure-temperature (P-T) calculations for orthopyroxene-bearing mafic rocks suggest conditions of 625-700 °C and 7.2-8.4 kbar for the pre-Grenvillian metamorphism. The granulite facies assemblages were locally overprinted during higher pressure Grenvillian metamorphism, which peaked at 720-775 °C and 10.8-11.5 kbar. U-Pb zircon data from migmatitic, mafic supracrustal gneiss indicate metamorphism and leucosome development at ca. 1450-1430 Ma, in agreement with other pre-Grenvillian metamorphic ages for the Central gneiss belt and Grenville Front tectonic zone. An expanding data base on pre-Grenvillian events in the southwestern Grenville province indicates that high-grade metamorphism at ca. 1450-1430 Ma affected a large region of crust and was coeval with widespread felsic to intermediate plutonism.

Late Cretaceous tectonothermal evolution of the southern Lhasa terrane, South Tibet: Consequence of a Mesozoic Andean-type orogeny

NASA Astrophysics Data System (ADS)

Dong, Xin; Zhang, Ze-ming; Klemd, Reiner; He, Zhen-yu; Tian, Zuo-lin

2018-04-01

The Lhasa terrane of the southern Tibetan Plateau participated in a Mesozoic Andean-type orogeny caused by the northward subduction of the Neo-Tethyan oceanic lithosphere. However, metamorphic rocks, which can unravel details of the geodynamic evolution, are rare and only exposed in the south-eastern part of the Lhasa terrane. Therefore, we conducted a detailed petrological, geochemical and U-Pb zircon geochronological study of the late Cretaceous metamorphic rocks and associated gabbros from the Nyemo inlier of the southern Lhasa terrane. The Nyemo metamorphic rocks including gneisses, schists, marbles and calc-silicate rocks, experienced peak amphibolite-facies contact metamorphism under P-T conditions of 3.5-4.0 kbar and 642-657 °C with a very high geothermal gradient of 45-50 °C/km, revealing a distinct deflection from the steady-state geotherm during low-pressure metamorphism. Inherited magmatic zircon cores from the metamorphic rocks yielded protolith ages of 197-194 Ma, while overgrowth zircon rims yielded metamorphic ages of ca. 86 Ma. Whole-rock chemistry and zircon Hf isotopes suggest that the protoliths of the gneisses and schists are andesites and tuffs of the early Jurassic Sangri Group, which were derived from a depleted mantle source of a continental arc affinity. The coeval intimately-associated gabbro (ca. 86 Ma) crystallized under P-T conditions of 3.5-5.3 kbar and 914-970 °C, supplying the heat flux high enough to cause the contact metamorphism of the Sangri Group rock types. We propose that the intrusion of the gabbro and a simultaneous pressure increase of up to 4.0 kbar, which is related to crustal thickening due to crustal overthrusting and the intrusion of mafic material, resulted in the late Cretaceous metamorphism of the early Jurassic Sangri Group during an Andean-type orogeny. Furthermore the Nyemo metamorphic rocks, which have previously been considered to represent slivers of the Precambrian metamorphic basement of the Lhasa terrane, are late Cretaceous metamorphic supracrustal rocks.

Validation of the activity expansion method with ultrahigh pressure shock equations of state

NASA Astrophysics Data System (ADS)

Rogers, Forrest J.; Young, David A.

1997-11-01

Laser shock experiments have recently been used to measure the equation of state (EOS) of matter in the ultrahigh pressure region between condensed matter and a weakly coupled plasma. Some ultrahigh pressure data from nuclear-generated shocks are also available. Matter at these conditions has proven very difficult to treat theoretically. The many-body activity expansion method (ACTEX) has been used for some time to calculate EOS and opacity data in this region, for use in modeling inertial confinement fusion and stellar interior plasmas. In the present work, we carry out a detailed comparison with the available experimental data in order to validate the method. The agreement is good, showing that ACTEX adequately describes strongly shocked matter.

Reconstruction of multiple P-T-t stages from retrogressed mafic rocks: Subduction versus collision in the Southern Brasília orogen (SE Brazil)

NASA Astrophysics Data System (ADS)

Tedeschi, Mahyra; Lanari, Pierre; Rubatto, Daniela; Pedrosa-Soares, Antônio; Hermann, Jörg; Dussin, Ivo; Pinheiro, Marco Aurélio P.; Bouvier, Anne-Sophie; Baumgartner, Lukas

2017-12-01

The identification of markers of subduction zones in orogenic belts requires the estimation of paleo-geothermal gradients through pressure-temperature-time (P-T-t) estimates in mafic rocks that potentially derive from former oceanic units once. However, such markers are rare in supracrustal sequences specially in deeply eroded and weathered Precambrian orogens, and reconstructing their metamorphic history is challenging because they are commonly retrogressed and only preserve a few mineral relicts of high-pressure metamorphism. Metamorphosed mafic rocks from Pouso Alegre region of the Neoproterozoic Southern Brasília Orogen outcrop as rare lenses within continental gneisses. They have previously been classified as retrograde eclogites, based on the presence of garnet and the characteristic symplectitic texture replacing omphacite. These rocks were interpreted to mark the suture zone between the Paranapanema and São Francisco cratons. To test the possible record of eclogitic conditions in the Pouso Alegre mafic rocks, samples including the surrounding felsic rocks have been investigated using quantitative compositional mapping, forward thermodynamic modeling and in-situ dating of accessory minerals to refine their P-T-t history. In the metamorphosed mafic rocks, the peak pressure assemblage of garnet and omphacite (Jd20, reconstructed composition) formed at 690 ± 35 °C and 13.5 ± 3.0 kbar, whereas local retrogression into symplectite or corona occurred at 595 ± 25 °C and 4.8 ± 1.5 kbar. The two reactions were coupled and thus took place at the same time. A zircon U-Pb age of 603 ± 7 Ma was obtained for metamorphic rims and linked to the retrogression stage. Monazite and metamorphic zircon U-Th-Pb ages for the surrounding rocks are at ca. 630 Ma and linked to peak pressure conditions similar to the one recorded by the mafic rocks. The low maximal pressure of 14 kbar and the high geothermal gradient do not necessarily support subduction process-related metamorphism but, more likely, metamorphism related to continental collision.

Quantifying the timescales of Archean UHT metamorphism through U-Pb monazite and zircon petrochronology

NASA Astrophysics Data System (ADS)

Guevara, V.; MacLennan, S. A.; Schoene, B.; Dragovic, B.; Caddick, M. J.; Kylander-Clark, A. R.; Couëslan, C. G.

2016-12-01

Unraveling the timescales of metamorphism is crucial to understanding the mechanisms behind mass/heat transfer through Earth's crust. Though such mechanisms and their durations are becoming well constrained in modern (Phanerozoic) settings, the drivers of metamorphism in the ancient geologic record remain more enigmatic. The development of accessory phase petrochronology has allowed metamorphic evolution to be closely linked to isotopic dates, ultimately improving quantification of metamorphic durations. While in-situ petrochronological methods preserve textural and spatial context, they often lack the temporal resolution required to accurately quantify metamorphic duration in Archean terranes. Here we combine in-situ U-Pb monazite (mnz) and zircon (zrn) laser ablation split-stream (LASS) and high-precision ID-TIMS-TEA petrochronology of distinct grain domains to resolve the timescales of ultrahigh temperature (UHT) metamorphism in the Archean Pikwitonei granulite domain (PGD). The PGD encompasses >1.5x105 km2 of granulite-facies rocks on the NW edge of the Superior Province. Themodynamic modelling of a pelite from the western part of the PGD suggests peak P-T conditions of >8 kbar, 900-940 °C and UHT decompression to 8 kbar followed by cooling. LASS analysis of zrn inclusions in garnet (grt) yields a date of 2701 Ma, with Ti in zrn thermometry yielding T of 800-900 °C. LASS analysis of mnz yields dates of 2720-2680 Ma for low HREE domains with no to shallow negative Eu anomalies, suggestive of growth during plagioclase (plg) breakdown and grt stability. ID-TIMS analysis of a mnz fragment with a strong negative Eu anomaly, suggestive of growth during plg stability, gives a concordant 207Pb/206Pb date of 2666 Ma, consistent with LASS results of 2660-2640 Ma for chemically similar domains. ID-TIMS analyses of zrn rims yield a range of 207Pb/206Pb dates from 2671 to 2656 Ma (±<1 Ma). Ti in zrn yields 800 °C for these rims, indicating they grew at similar T. Together, these data indicate a metamorphic cycle in the PGD to/from UHT over a minimum of 35 Ma, with at least 12 Ma of slow cooling near 800 °C in the lower crust following UHT decompression. This evolution is inconsistent with punctuated thermal pulses due to focused fluid flow or magmatism, instead requiring a long-lived source of crustal heating.

PTt path in metamorphic rocks of the Khoy region (northwest Iran) and their tectonic significance for Cretaceous Tertiary continental collision

NASA Astrophysics Data System (ADS)

Azizi, H.; Moinevaziri, H.; Mohajjel, M.; Yagobpoor, A.

2006-06-01

Metamorphic rocks in the Khoy region are exposed between obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic age to the northeast. The Qom formation (Oligocene-Miocene) with a basal conglomerate transgressively overlies all of these rocks. The metamorphic rocks consist of both metasediments and metabasites. The metasediments are micaschist, garnet-staurolite schist and garnet-staurolite sillimanite schist with some meta-arkose, marble and quartzite. The metabasites are metamorphosed to greenschist and amphibolite facies from a basaltic and gabbroic protolith of tholeiitic and calc-alkaline rocks. Geothermobarometry based on the equivalence of minerals stability and their paragenesis in these rocks and microprobe analyses by several different methods indicate that metamorphism occurred in a temperature range between 450 and 680 °C at 5.5 and 7.5 kb pressure. Rims of minerals reveal a considerable decrease of pressure (<2 kb) and insignificant decrease of temperature. The PTt path of this metamorphism is normal. The MFG line passes above the triple junction of Al 2SiO 5 polymorphs, and the average geothermal gradient during metamorphism was from 27 to 37 °C/km, which is more concordant with the temperature regime of collision zones. We infer that crustal thickening during post-Cretaceous (possibly Eocene) collision of the Arabian plate and the Azerbaijan-Albourz block was the main factor that caused the metamorphism in the studied area.

Metamorphic sole formation and early plate interface rheology: Insights from Griggs apparatus experiments

NASA Astrophysics Data System (ADS)

Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Hirth, Greg; Yamato, Philippe; Ildefonse, Benoît; Prigent, Cécile

2016-04-01

Metamorphic soles correspond to m to ~500 m thick highly strained metamorphic rock units found beneath mylonitic banded peridotites at the base of large-scale ophiolites, as exemplified in Oman. Metamorphic soles are mainly composed of metabasalts deriving from the downgoing oceanic lithosphere and metamorphosed up to granulite-facies conditions by heat transfer from the mantle wedge. Pressure-temperature peak conditions are usually estimated at 1.0±0.2 GPa and 800±100°C. The absence of HP-LT metamorphism overprint implies that metamorphic soles have been formed and exhumed during subduction infancy. In this view, metamorphic soles were strongly deformed during their accretion to the mantle wedge (corresponding, now, to the base of the ophiolite). Therefore, metamorphic soles and banded peridotites are direct witnesses of the dynamics of early subduction zones, in terms of thermal structure, fluid migration and rheology evolution across the nascent slab interface. Based on fieldwork and EBSD analyses, we present a detailed (micro-) structural study performed on samples coming from the Sumeini window, the better-preserved cross-section of the metamorphic sole of Oman. Large differences are found in the deformation (CPO, grain size, aspect ratio) of clinopyroxene, amphibole and plagioclase, related to mineralogical changes linked with the distance to the peridotite contact (e.g., hardening due to the appearance of garnet and clinopyroxene). To model the incipient slab interface in laboratory, we carried out 5 hydrostatic annealing and simple-shear experiments on Griggs solid-medium apparatus. Deformation experiments were conducted at axial strain rates of 10-6 s-1. Fine-grained amphibolite was synthetized by adding 1 wt.% water to a (Mid-Ocean Ridge) basalt powder as a proxy for the metamorphic sole (amphibole + plagioclase + clinopyroxene ± garnet assemblage). To synthetize garnet, 2 experiments were carried out in hydrostatic conditions and with deformation at 800°C with confining pressure of 2 GPa. Another simple-shear experiment has been carried out at 800°C and 1 GPa with fined-grained natural garnet. With the aim of mimicking the early slab interface (between the metamorphic sole and banded peridotites at the base of the ophiolite), 2 simple-shear deformation experiments with 2 layers have been carried out at 800°C and confining pressure of 1 GPa. The bottom layer was made of hydrated basalt powder and the top layer was made of olivine. Fined-grained garnet-free amphibolite is significantly weaker than dunite but the appearance of harder minerals in the amphibolite (garnet and clinopyroxene) has major implications on its rheological evolution. These results allow liking field observations of strain localization at the interface to the metamorphic sole formation.

Tectono-metamorphic evolution of the Chinese Altai, central Asia: new insights from microstructures

NASA Astrophysics Data System (ADS)

Jiang, Yingde; Zhang, Jian; Schulmann, Karel; Sun, Min; Zhao, Guochun

2013-04-01

The Altai Orogen, extending from Russia, through northeast Kazakhstan and northwest China, to western and southern Mongolia, occupies a pivotal position in understanding the accretionary process of the Central Asian Orogenic Belt and has drawn much attention in recent years. However, its orogenic evolution remains poorly constrained, because previous studies were mainly focused on the geochronological and geochemical signatures and much less work has been done on metamorphic and structural studies. Metamorphic rocks widely occur in the southern Altai Range and have previously been separated into high-T/low-P and medium-P types. Recent studies demonstrated that these two kinds of rocks may have similar protoliths, i.e. early Paleozoic arc-related assemblages, but experienced different metamorphic histories. The development of biotite, garnet, staurolite and kyanite metamorphic zonal sequences in the low- to medium- grade rocks, demonstrate typical medium-pressure metamorphism that has been suggested as a major consequence of the orogenesis. The high-T/low-P metamorphism, represented by the growth of garnet+cordierite+sillimanite+k-feldspar and was accompanied by extensive anatexis, remains its tectonic significance poorly constrained. Field structural investigation in the Chinese Altai reveals that the high-T/low-P metamorphic rocks have major S-L fabrics (defined by the strongly aligned biotite and sillimanite) exactly in the same orientations as those developed in the associated medium-P grade rocks. Geochronological studies constrain the major fabrics in both kinds of rocks developed during mid-Devonian, coeval with the strong magmatism in the region. Micro-structural investigation on both kinds of rocks show similar prograde metamorphic history featured by clockwise P-T path evolution. Phase equilibrium modeling in the MnNCKFMASH system indicates that the development of major fabrics in the medium-P metamorphic rocks mainly recorded the notable increase of pressure and that in the high-T rocks was featured by the significant increase of temperature. The pressure increase could attribute to the progressive crustal thickening that may be correlated to the accretionary regime of the southern Altai in the mid-Devonian and the high temperature conditions most likely imply a significant heat input from the deep depth, consistent with the syn-chronologically emplacement of juvenile magmas on a large scale. Our study indicates the development of high-T metamorphism was genetically linked with that of the medium-P metamorphism and suggests that the crustal thickening during the orogenic process of the Altai region was accompanied by large heat input. This study is supported by Hong Kong Research Grant Council (HKU705311P and HKU704712P), National Science Foundation of China (41273048), IGCP #592 Project "Continental construction in Central Asia" and Research grant of State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (SKLIG-KF-12-06) .

The timing of metamorphism in the Odenwald-Spessart basement, Mid-German Crystalline Zone

NASA Astrophysics Data System (ADS)

Will, T. M.; Schulz, B.; Schmädicke, E.

2017-07-01

New in situ electron microprobe monazite and white mica 40Ar/39Ar step heating ages support the proposition that the Odenwald-Spessart basement, Mid-German Crystalline Zone, consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition. The monazite ages constrain tectonothermal events at 430 ± 43 Ma, 349 ± 14 Ma, 331 ± 16 Ma and 317 ± 12 Ma/316 ± 4 Ma, and the 40Ar/39Ar analyses provide white mica ages of 322 ± 3 Ma and 324 ± 3 Ma. Granulite-facies metamorphism occurred in the western Odenwald at c. 430 and 349 Ma, and amphibolite-facies metamorphism affected the eastern Odenwald and the central Spessart basements between c. 324 and 316 Ma. We interpret these data to indicate that the Otzberg-Michelbach Fault Zone, which separates the eastern Odenwald-Spessart basement from the Western Odenwald basement, is part of the Rheic Suture, which marks the position of a major Variscan plate boundary separating Gondwana- and Avalonia-derived crustal terranes. The age of the Carboniferous granulite-facies event in the western Odenwald overlaps with the minimum age of eclogite-facies metamorphism in the adjacent eastern Odenwald. The granulite- and eclogite-facies rocks experienced contrasting pressure-temperature paths but occur in close spatial proximity, being separated by the Rheic Suture. As high-pressure and high-temperature metamorphisms are of similar age, we interpret the Odenwald-Spessart basement as a paired metamorphic belt and propose that the adjacent high-pressure and high-temperature rocks were metamorphosed in the same subduction zone system. Juxtaposition of these rocks occurred during the final stages of the Variscan orogeny along the Rheic Suture.

The use of ultra-high pressure liquid chromatography with tandem mass spectrometric detection of analysis of agrochemical residues and mycotoxines in food - challenges and applications

USDA-ARS?s Scientific Manuscript database

In the field of food contaminant analysis, the most significant development of recent years has been the integration of ultra-high pressure liquid chromatography (UHPLC), coupled to tandem quadrupole mass spectrometry (MS/MS), into analytical applications. In this review, we describe the emergence o...

A Transmission Electron Microscope Study of Experimentally Shocked Pregraphitic Carbon

NASA Technical Reports Server (NTRS)

Rietmeijer, Frans J. M.

1995-01-01

A transmission electron microscope study of experimental shock metamorphism in natural pre-graphitic carbon simulates the response of the most common natural carbons to increased shock pressure. The d-spacings of this carbon are insensitive to the shock pressure and have no apparent diagnostic value, but progressive comminution occurs in response to increased shock pressure up to 59.6 GPa. The function, P = 869.1 x (size(sub minimum )(exp -0.83), describes the relationship between the minimum root-mean-square subgrain size (nm) and shock pressure (GPa). While a subgrain texture of natural pregraphitic carbons carries little information when pre-shock textures are unknown, this texture may go unnoticed as a shock metamorphic feature.

Migmatization and low-pressure overprinting metamorphism as record of two pre-Cretaceous tectonic episodes in the Santander Massif of the Andean basement in northern Colombia (NW South America)

NASA Astrophysics Data System (ADS)

Zuluaga, C. A.; Amaya, S.; Urueña, C.; Bernet, M.

2017-03-01

The core of the Santander Massif in the northern Andes of Colombia is dominated by migmatitic gneisses with a < 1.71 Ga protolith and was affected by continuous interactions of oceanic plates to the west and the northwestern corner of the South American continental plate. The exposed metamorphic core of the massif offers a unique opportunity to understand the tectonic evolution of northwestern South America. We present new metamorphic petrology and geochemistry data from the Bucaramanga Gneiss in the Santander Massif to document part of this tectonic evolution from late Proterozoic to Jurassic times. Metapelitic migmatite gneiss, quartz-feldspathic gneiss, and amphibolite from the Bucaramanga Gneiss recorded metamorphic peak conditions in the range of 660-850 °C at pressures of > 7.5 kbar. Lithologies are overprinted by low-pressure metamorphism, related to extensive Jurassic intrusions and linked with growth of cordierite and equilibration of low-pressure mineral assemblages, recorded metamorphic conditions are < 750 °C and < 6.5 kbar. Observed leucosomes display significant compositional variations and can be grouped in three groups: i) Group One leucosomes with high total REE content, high LREE/HREE, and negative Eu anomaly, ii) Group Two leucosomes with low total REE, low LREE/HREE, and positive Eu anomalies, and iii) Group Three leucosomes with relatively low LREE/HREE and strong positive Eu anomaly. Geochemical data support the interpretation that Group Two leucosomes crystallized from melts originated in a partial melting event affecting mostly pelitic and quartz-feldspathic lithologies with fluid-present melting reactions. The evaluation of mesosomes (amphibolite, pelitic and quartz-feldspathic rocks) as potential protoliths or restites indicates that at least two pelitic samples of the analyzed lithologies have characteristics consistent with the occurrence of fluid-present melting reactions involving quartz and feldspar. The leucosomes produced by crystallization of modified partial melts contrast with several other leucosomes that were injected; however, in some cases the melts crystallized as injected leucosomes show consistent geochemistry with partial melting of lithologies geochemically similar to the ones observed in the unit. The migmatization and the low pressure metamorphic overprint are related here to two main tectonic events: an early Paleozoic tectonic pulse produced by subduction of the oceanic crust of the Iapetus Ocean beneath northwestern Gondwana, and an Upper Triassic to Lower Jurassic tectonic pulse produced by subduction of oceanic crust of the proto-Pacific ocean beneath western Pangaea.

Ultrahigh vacuum/high pressure chamber for surface x-ray diffraction experiments

NASA Astrophysics Data System (ADS)

Bernard, P.; Peters, K.; Alvarez, J.; Ferrer, S.

1999-02-01

We describe an ultrahigh vacuum chamber that can be internally pressurized to several bars and that is designed to perform surface x-ray diffraction experiments on solid-gas interfaces. The chamber has a cylindrical beryllium window that serves as the entrance and exit for the x rays. The sample surface can be ion bombarded with an ancillary ion gun and annealed to 1200 K.

Characterization of Organic Materials in the Xenolithic Clasts in Sharps (H3.4) Meteorite Using Micro-Raman Spectroscopy

NASA Technical Reports Server (NTRS)

Chan, Q. H. S.; Zolensky, M. E.; Bodnar, R. J.; Kebukawa, Y.

2015-01-01

Graphitization of carbon is an irreversible process which alters the structure of graphitic materials in response to the increase in metamorphic grade (temperature and/or pressure). Carbonaceous materials offer a reliable geothermometer as their Raman spectra change systematically with increasing metamorphic grade. In this study, we identified carbonaceous materials in the xenolithic clasts in Sharps and interpreted their metamorphic history by revealing the structural organization (order) of the polyaromatic organic phases using micro-Raman spectroscopy.

Characterization of Organic Materials in the Xenolithic Clasts in Sharps (H3.4) Meteorite Using Microraman Spectroscopy

NASA Technical Reports Server (NTRS)

Chan, Q. H. S.; Zolensky, M. E.; Bodnar, R. J.; Kebukawa, Y.

2015-01-01

Graphitization of carbon is an irreversible process which alters the structure of graphitic materials in response to the increase in metamorphic grade (temperature and/or pressure). Carbonaceous materials offer a reliable geothermometer as their Raman spectra change systematically with increasing metamorphic grade [1-3]. In this study, we identified carbonaceous materials in the xenolithic clasts in Sharps and interpreted their metamorphic history by revealing the structural organization (order) of the polyaromatic organic phases using µ-Raman spectroscopy.

Interaction force and motion estimators facilitating impedance control of the upper limb rehabilitation robot.

PubMed

Mancisidor, Aitziber; Zubizarreta, Asier; Cabanes, Itziar; Bengoa, Pablo; Jung, Je Hyung

2017-07-01

In order to enhance the performance of rehabilitation robots, it is imperative to know both force and motion caused by the interaction between user and robot. However, common direct measurement of both signals through force and motion sensors not only increases the complexity of the system but also impedes affordability of the system. As an alternative of the direct measurement, in this work, we present new force and motion estimators for the proper control of the upper-limb rehabilitation Universal Haptic Pantograph (UHP) robot. The estimators are based on the kinematic and dynamic model of the UHP and the use of signals measured by means of common low-cost sensors. In order to demonstrate the effectiveness of the estimators, several experimental tests were carried out. The force and impedance control of the UHP was implemented first by directly measuring the interaction force using accurate extra sensors and the robot performance was compared to the case where the proposed estimators replace the direct measured values. The experimental results reveal that the controller based on the estimators has similar performance to that using direct measurement (less than 1 N difference in root mean square error between two cases), indicating that the proposed force and motion estimators can facilitate implementation of interactive controller for the UHP in robotmediated rehabilitation trainings.

Petrogenetic grids for sapphirine-bearing granulites

NASA Astrophysics Data System (ADS)

Podlesskii, Konstantin K.

2010-05-01

Phase relations involving sapphirine, garnet, spinel, orthopyroxene, olivine, cordierite, alumina silicates, corundum, and quartz have been calculated in the system FeO-MgO-Al2O3-SiO2 based on internally consitent thermodynamic properties of both the end-member minerals and the solid solutions (Gerya et al., 2004; Podlesskii et al., 2008). The derived P-T diagrams imply stable invariant points and stability fields of key assemblages that differ from those proposed by other authors (Kelsey et al., 2004; Harley 2008). The sapphirine + quartz assemblage, which is widely recognized as indicative of ultrahigh-temperature metamorphism, can be stable down to 835° C and ~6 kbar. The sapphirine + kyanite assemblage has been found stable at temperatures below 860° C and 11.3 kbar, whereas the sapphirine + forsterite assemblage may be stable below 800° C only under specific conditions of a very low activity of water. The existing constraints on the thermodynamic properties of sapphirine are considered insufficient to make decisive conclusions about metamorphic conditions. Granulites containing the sapphirine + quartz assemblage have been investigated with the microprobe to apply both the conventional thermobarometry and thermometry based on Ti contents of quartz (TitaniQ, Wark & Watson, 2006). The results demonstrate that, in some cases, this assemblage might have formed at relatively low temperatures during retrograde stages of metamorphism. The research has been supported by the RFBR grant 09-05-00193. References Gerya,T.V., Perchuk,L.L., & Podlesskii,K.K. In: Zharikov,V.A. & Fed'kin,V.V. (eds.) Experimental Mineralogy: Some Results on the Century's Frontier. Moscow: Nauka, Vol. 2, 188-206 (2004). Harley,S.L. Refining the P-T records of UHT crustal metamorphism. Journal of Metamorphic Geology, 26, 125-154 (2008). Kelsey,D.E., White,R.W., Holland,T.J.B., & Powell,R. Journal of Metamorphic Geology, 22, 559-578 (2004). Podlesskii,K.K., Aranovich,L.Y., Gerya,T.V., & Kosyakova,N.A. Sapphirine-bearing assemblages in the system MgO-Al2O3-SiO2: A continuing ambiguity. European Journal of Mineralogy, 20, 721-734 (2008). Wark,D.A. & Watson,E.B. TitaniQ: a titanium-in-quartz geothermometer. Contributions to Mineralogy and Petrology, 152, 743-754 (2006).

Ultrahigh vacuum gauge having two collector electrodes

NASA Technical Reports Server (NTRS)

Torney, F. L., Jr. (Inventor)

1967-01-01

A gauge for measuring ultrahigh vacuums with great accuracy is described. It provides a means for ionizing the gas whose pressure is being measured, and consists of a collector electrode, a suppressor, radiation shielding, and a second collector.

Beyond sixfold coordinated Si in SiO2 glass at ultrahigh pressures

PubMed Central

Prescher, Clemens; Prakapenka, Vitali B.; Stefanski, Johannes; Jahn, Sandro; Skinner, Lawrie B.; Wang, Yanbin

2017-01-01

We investigated the structure of SiO2 glass up to 172 GPa using high-energy X-ray diffraction. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We show that SiO2 first undergoes a change in Si–O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. Si–O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si–O coordination. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures. PMID:28874582

Beyond sixfold coordinated Si in SiO2 glass at ultrahigh pressures.

PubMed

Prescher, Clemens; Prakapenka, Vitali B; Stefanski, Johannes; Jahn, Sandro; Skinner, Lawrie B; Wang, Yanbin

2017-09-19

We investigated the structure of SiO 2 glass up to 172 GPa using high-energy X-ray diffraction. The combination of a multichannel collimator with diamond anvil cells enabled the measurement of structural changes in silica glass with total X-ray diffraction to previously unachievable pressures. We show that SiO 2 first undergoes a change in Si-O coordination number from fourfold to sixfold between 15 and 50 GPa, in agreement with previous investigations. Above 50 GPa, the estimated coordination number continuously increases from 6 to 6.8 at 172 GPa. Si-O bond length shows first an increase due to the fourfold to sixfold coordination change and then a smaller linear decrease up to 172 GPa. We reconcile the changes in relation to the oxygen-packing fraction, showing that oxygen packing decreases at ultrahigh pressures to accommodate the higher than sixfold Si-O coordination. These results give experimental insight into the structural changes of silicate glasses as analogue materials for silicate melts at ultrahigh pressures.

Long distance transport of eclogite and blueschist during early Pacific Ocean subduction rollback

NASA Astrophysics Data System (ADS)

Tamblyn, Renee; Hand, Martin; Kelsey, David; Phillips, Glen; Anczkiewicz, Robert

2017-04-01

The Tasmanides in eastern Australia represent a period of continental crustal growth on the western margin of the Pacific Ocean associated with slab rollback from the Cambrian until the Triassic. During rollback numerical models predict that subduction products can become trapped in the forearc (Geyra et al., 2002), and can migrate with the trench as it retreats. In a long-lived subduction controlled regime such as the Tasmanides, this should result in an accumulation of subduction products with protracted geochronological and metamorphic histories. U-Pb, Lu-Hf, Sm-Nd and Ar-Ar geochronology and phase equilibria modelling of lawsonite-eclogite and garnet blueschist in the Southern New England Fold Belt in Australia demonstrate that high-P low-T rocks remained within a subduction setting for c. 40 Ma, from c. 500 to 460 Ma. High-P metamorphic rocks initially formed close to the Australian cratonic margin during the late Cambrian, and were subsequently transported over 1500 Ma oceanward, during which time subducted material continued to accumulate, resulting in the development of complex mélange which records eclogite and blueschist metamorphism and partial exhumation over 40 Ma. The duration of refrigerated metamorphism approximates the extensional evolution of the upper plate which culminated in the development of the Lachlan Fold Belt. The protracted record of eclogite and blueschist metamorphism indicates that rapid exhumation is not necessarily required for preservation of high-pressure metamorphic rocks from subduction systems. Reference: Gerya, T. V., Stockhert, B., & Perchuk, A. L. (2002). Exhumation of high-pressure metamorphic rocks in a subduction channel: A numerical simulation. Tectonics, 21(6), 6-1-6-19. doi:10.1029/2002tc001406

Unconventional Hydrocarbon Development Hazards Within the Central United States. Report 1: Overview and Potential Risk to Infrastructure

DTIC Science & Technology

2015-08-01

of the injection purpose, i.e., secondary oil and gas recovery, disposal of waste fluids, geothermal energy, and/or UHP hydraulic fracturing...activities such as reservoir impoundment, mining, wastewater injection, geothermal systems and CO2 capture have been linked directly to induced...activities, e.g., deep fluid injection, geothermal injection, and/or UHP wells, that critically affect deep lithologies and alter the existing mechanical

Urban Health Project: A Sustainable and Successful Community Internship Program for Medical Students.

PubMed

Roberts, Kasey; Park, Thomas; Elder, Nancy C; Regan, Saundra; Theodore, Sarah N; Mitchell, Monica J; Johnson, Yolanda N

2015-11-01

Urban Health Project (UHP) is a mission and vision-driven summer internship at the University of Cincinnati College of Medicine that places first-year medical students at local community agencies that work with underserved populations. At the completion of their internship, students write Final Intern Reflections (FIRs). Final Intern Reflections written from 1987 to 2012 were read and coded to both predetermined categories derived from the UHP mission and vision statements and new categories created from the data themselves. Comments relating to UHP's mission and vision were found in 47% and 36% of FIRs, respectively. Positive experiences outweighed negative by a factor of eight. Interns reported the following benefits: educational (53%), valuable (25%), rewarding (25%), new (10%), unique (6%), and life-changing (5%). Urban Health Project is successful in providing medical students with enriching experiences with underserved populations that have the potential to change their understanding of vulnerable populations.

Hydrothermal alteration and timing of gold mineralisation in the Rumbia Complex, Southeast Arm of Sulawesi, Indonesia

NASA Astrophysics Data System (ADS)

Mawaleda, Musri; Suparka, Emmy; Idham Abdullah, Chalid; Indro Basuki, Nurcahyo; Forster, Marnie; Jamal; Kaharuddin

2017-06-01

The Rumbia Mountains, which in this study named Rumbia schist Complex is an east-west oriented, composed by a high-pressure/low-temperature, and a medium-pressure/low-temperature metamorphic rocks. Identified as mica schist, glauchopane schist, and green schist. Rumbia complex known as the location of gold deposits prospects discovered by local communities since 2007. The results of research showed that the metamorphic rocks are as hosts. There are two phase of gold mineralization that occurs in this area, namely: 1) Associated with tectonic deformation and metamorphic rocks exhumation, and 2) gold-related hydrothermal deposits. Radiometric age dating used 40Ar/39Ar geochronology, indicate that the first of gold mineralisation in the Rumbia Complex occurred ∼23 million years ago, and the second gold mineralisation were subsequently overprinting at 7 million years ago.

Metamorphic and structural evidence for significant vertical displacement along the Ross Lake fault zone, a major orogen-parallel shear zone in the Cordillera of western North America

USGS Publications Warehouse

Baldwin, J.A.; Whitney, D.L.; Hurlow, H.A.

1997-01-01

Results of an investigation of the petrology and structure of the Skymo complex and adjacent terranes constrain the amount, timing, and sense of motion on a segment of the > 600-km-long Late Cretaceous - early Tertiary Ross Lake fault zone (RLFZ), a major orogen-parallel shear zone in the Cordillera of western North America. In the study area in the North Cascades, Washington state, the RLFZ accommodated significant pre-middle Eocene vertical displacement, and it juxtaposes the Skymo complex with upper amphibolite facies (650??-690??C and 6-7 kbar) Skagit Gneiss of the North Cascades crystalline core to the SW and andalusite-bearing phyllite of the Little Jack terrane (Intermontane superterrane) to the NE. The two main lithologic units of the Skymo complex, a primitive mafic intrusion and a fault-bounded block of granulite facies metasedimentary rocks, are unique in the North Cascades. Granulite facies conditions were attained during high-temperature (> 800??C), low pressure (??? 4 kbar) contact metamorphism associated with intrusion of the mafic magma. P-T estimates and reaction textures in garnet-orthopyroxene gneiss suggest that contact metamorphism followed earlier, higher pressure regional metamorphism. There is no evidence that the Skagit Gneiss experienced high-T - low-P contact metamorphism. In the Little Jack terrane, however, texturally late cordierite ?? spinel and partial replacement of andalusite by sillimanite near the terrane's fault contact with Skymo gabbro suggest that the Little Jack terrane experienced high-T (??? 600??C) - low-P (??? 4 kbar) contact metamorphism following earlier low-grade regional metamorphism. Similarities in the protoliths of metasedimentary rocks in the Skymo and Little Jack indicate that they may be part of the same terrane. Differences in pressure estimates for the Little Jack versus Skymo for regional metamorphism that preceded contact metamorphism indicate vertical displacement of ??? 10 km (west side up) on the strand of the RLFZ that now separates the two structural blocks. High-angle faults in the study area are dextral-reverse mylonitic shear zones that experienced later brittle normal slip. Vertical motion on these shear zones before intrusion of Skymo gabbro can account for metamorphic discontinuities indicated by P-T results. The terranes have also been internally deformed by nonintersecting but coeval dextral and sinistral shear zones that formed after the terranes were brought together in the RLFZ and intruded by Eocene dikes. These results show that the RLFZ has accommodated significant vertical displacement but perhaps no more than tens of kilometers of early Tertiary lateral movement. Structural evidence for earlier, large-magnitude strike-slip displacement is not preserved.

Techniques for measuring ultrahigh-pressure Hugoniot equation of state on a three-stage gas gun

NASA Astrophysics Data System (ADS)

Wang, Xiang; Hu, Jianbo; Dai, Chengda; Wang, Qiangsong; Bo, Jingsong; Tan, Hua; Yu, Yuying

2011-06-01

A three-stage gas gun was developed by mounting an extending launcher tube on a two-stage gas gun, and was successfully applied to perform ultrahigh-pressure Hugoniot measurements for Ta and Pt by using this three-stage gun. Here we introduced the three-stag gas gun launcher and Hugoniot measurement techniques, including shock front shape diagnosis, shock wave velocity and impact velocity measurement as well as numerical simulation. By using this three-stage gun, Ta or Pt impactors were launched up to ~10 km/s, and the Hugoniot data were respectively measured with high accuracy up to 750 GPa for Ta and 1TPa for Pt. It is demonstrated that the three-stage gas gun is a promising technique for studying the ultrahigh-pressure properties of materials, which never before obtained by utilizing two-stage light-gas-gun.

Metamorphic P-T conditions and CO2 influx history of medium-grade metapelites from Karakorum, Trans-Himalaya, India

NASA Astrophysics Data System (ADS)

Sachan, Himanshu K.; Santosh, M.; Prakash, Divya; Kharya, Aditya; Chandra Singh, P.; Rai, Santosh K.

2016-07-01

The medium grade metapelites of Pangong-Tso area in the trans-Himalayan region underwent sillimanite-grade metamorphism initiated during the Cretaceous, associated with the collision of the Kohistan arc and the Indian plate with Asia. This paper present results from a petrological and fluid inclusion study to understand the metamorphic P-T conditions and fluid history of these rocks. The calculated phase equilibria in the Na2O-CaO-K2O-FeO-MgO-MnO-Al2O3-SiO2-H2O-TiO2 (NCKFMMnASHT) system suggest P-T conditions of 8 kbar and 650 °C for the peak metamorphic event. Primary fluid inclusions occur in staurolite and garnet, whereas quartz carries mostly secondary fluid inclusions. The trapped fluids in primary inclusions show initial melting temperatures in the range of -56.9 to -56.6 °C, suggesting nearly pure CO2 composition. The secondary fluids are of mixed carbonic-aqueous nature. The re-equilibrated inclusions show annular morphology as well as necking phenomena. The CO2 isochores for the primary inclusions indicate pressures of 6.1-6.7 kbar, suggesting that the CO2-rich fluids were trapped during post-peak exhumation of the rocks, or that synmetamorphic carbonic fluids underwent density reversal during isothermal decompression. The secondary CO2-H2O fluids must have been trapped during the late exhumation stage, as their isochores define further lower pressures of 4.8 kbar. The morphology of re-equilibrated fluid inclusions and the rapid decrease in pressure are consistent with a near-isothermal decompression trajectory following the peak metamorphism. The carbonic fluids were probably derived locally from decarbonation reactions of the associated carbonate rocks during metamorphism or from a deep-seated reservoir through Karakorum fault.

The effect of thermal resetting and recrystallisation on white mica 40Ar/39Ar ages during retrograde metamorphism on Syros, Greece

NASA Astrophysics Data System (ADS)

Uunk, Bertram; Wijbrans, Jan; Brouwer, Fraukje

2015-04-01

White mica 40Ar/39Ar dating is a proven powerful tool for constraining timing of metamorphism, deformation and exhumation. However, in high-pressure metamorphic rocks, dating often results in wide age ranges which are not in agreement with constraints from other isotopic systems, indicating that geological and chemical processes complicate straightforward 40Ar/39Ar dating. In this research project, white mica ages from rocks of the Cycladic Blueschist Unit on Syros, Greece with contrasting rheology and strain mechanisms are compared, in order to better understand the role of deformation, recrystallization and fluid flow on 40Ar/39Ar ages of white mica during retrograde metamorphism. Resulting ages vary along different sections on the island, inconsistent with other isotopic constraints on eclogite-blueschist metamorphism (55-50 Ma) and greenschist overprinting (41-30 Ma). Two end-member models are possible: 1) Results represent continuous crystallization of white mica while moving from blueschist to greenschist conditions in the metamorphic P-T loop, or 2) white mica equilibrated in eclogite-blueschist conditions and their diffusion systematics were progressively perturbed during greenschist overprinting. The single grain fusion analyses yielded contrasting age distributions, which indicate contrasts in degree of re-equilibration during retrograde metamorphism. Step wise heating of larger grain populations resulted in flat plateau shapes, providing no evidence for partial resetting. Electron microprobe measurements of Si per formula unit, as a proxy for pressure during crystallisation, do not explain age variation within sections or on the island scale. The previously unreported north-south age trend and age ranges per sample, as shown only in the 40Ar/39Ar system of the metapelitic and marble lithologies, contains key information that will allow us to test between different scenarios for age formation. Excess argon infiltration at this stage seems to have been of minor importance. Our new approach should lead to a better understanding of the interplay of these processes during and after HP metamorphism.

Developing an inverted Barrovian sequence; insights from monazite petrochronology

NASA Astrophysics Data System (ADS)

Mottram, Catherine M.; Warren, Clare J.; Regis, Daniele; Roberts, Nick M. W.; Harris, Nigel B. W.; Argles, Tom W.; Parrish, Randall R.

2014-10-01

In the Himalayan region of Sikkim, the well-developed inverted metamorphic sequence of the Main Central Thrust (MCT) zone is folded, thus exposing several transects through the structure that reached similar metamorphic grades at different times. In-situ LA-ICP-MS U-Th-Pb monazite ages, linked to pressure-temperature conditions via trace-element reaction fingerprints, allow key aspects of the evolution of the thrust zone to be understood for the first time. The ages show that peak metamorphic conditions were reached earliest in the structurally highest part of the inverted metamorphic sequence, in the Greater Himalayan Sequence (GHS) in the hanging wall of the MCT. Monazite in this unit grew over a prolonged period between ∼37 and 16 Ma in the southerly leading-edge of the thrust zone and between ∼37 and 14.5 Ma in the northern rear-edge of the thrust zone, at peak metamorphic conditions of ∼790 °C and 10 kbar. Monazite ages in Lesser Himalayan Sequence (LHS) footwall rocks show that identical metamorphic conditions were reached ∼4-6 Ma apart along the ∼60 km separating samples along the MCT transport direction. Upper LHS footwall rocks reached peak metamorphic conditions of ∼655 °C and 9 kbar between ∼21 and 16 Ma in the more southerly-exposed transect and ∼14.5-12 Ma in the northern transect. Similarly, lower LHS footwall rocks reached peak metamorphic conditions of ∼580 °C and 8.5 kbar at ∼16 Ma in the south, and 9-10 Ma in the north. In the southern transect, the timing of partial melting in the GHS hanging wall (∼23-19.5 Ma) overlaps with the timing of prograde metamorphism (∼21 Ma) in the LHS footwall, confirming that the hanging wall may have provided the heat necessary for the metamorphism of the footwall. Overall, the data provide robust evidence for progressively downwards-penetrating deformation and accretion of original LHS footwall material to the GHS hanging wall over a period of ∼5 Ma. These processes appear to have occurred several times during the prolonged ductile evolution of the thrust. The preserved inverted metamorphic sequence therefore documents the formation of sequential 'paleo-thrusts' through time, cutting down from the original locus of MCT movement at the LHS-GHS protolith boundary and forming at successively lower pressure and temperature conditions. The petrochronologic methods applied here constrain a complex temporal and thermal deformation history, and demonstrate that inverted metamorphic sequences can preserve a rich record of the duration of progressive ductile thrusting.

Solvent-free iodination of organic molecules using the I(2)/urea-H(2)O(2) reagent system.

PubMed

Pavlinac, Jasminka; Zupan, Marko; Stavber, Stojan

2007-02-21

Introduction of iodine under solvent-free conditions into several aromatic compounds activated toward electrophilic functionalization was found to proceed efficiently using elemental iodine in the presence of a solid oxidizer, the urea-H(2)O(2) (UHP) adduct. Two types of iodo-functionalization through an electrophilic process were observed: iodination of an aromatic ring, and side-chain iodo-functionalization in the case of arylalkyl ketones. Two reaction routes were established based on the required substrate : iodine : oxidizer ratio for the most efficient iodo-transformation, and the role of UHP was elucidated in each route. The first, requiring a 1 : 0.5 : 0.6 stoichiometric ratio of substrate to iodine to UHP, followed the atom economy concept in regard to iodine and was valid in the case of aniline, 4-t-Bu-phenol, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene, 1,2,3-trimethoxy benzene, 1,2,4-trimethoxy benzene, 1,3,5-trimethoxy benzene, 1-indanone and 1-tetralone. The second reaction route, where a 1 : 1 : 1 stoichiometric ratio of substrate : I(2) : UHP was needed for efficient iodination, was suitable for side-chain iodo-functionalization of acetophenone and methoxy-substituted acetophenones. Moreover, addition of iodine to 1-octene and some phenylacetylenic derivatives was found to proceed efficiently without the presence of any oxidizer and solvent at room temperature.

Late Carboniferous high-pressure metamorphism of the Kassan Metamorphic Complex (Kyrgyz Tianshan) and assembly of the SW Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Mühlberg, M.; Hegner, E.; Klemd, R.; Pfänder, J. A.; Kaliwoda, M.; Biske, Y. S.

2016-11-01

High-pressure (HP) metamorphism of the Kassan Metamorphic Complex (KMC) in the western Kyrgyz Tianshan has been related to either late Ordovician or late Carboniferous-Permian subduction processes. We report Sm-Nd ages for retrogressed eclogite samples and 40Ar/39Ar cooling ages for enclosing garnet-muscovite samples from the KMC as new age constraints on HP metamorphism and rock exhumation. These data will be used for an upgraded paleogeographic model for late Paleozoic crustal consolidation in the southwestern Central Asian Orogenic Belt. The retrogressed eclogite samples have transitional alkaline to tholeiitic affinity and trace-element patterns consistent with protoliths derived from garnet-bearing mantle sources at rifting plate margins. Geothermobarometric data for a retrogressed eclogite sample indicate peak-metamorphic conditions of 540 ± 30 °C at 1.6 ± 0.1 GPa. Samples from different lithotectonic units of the KMC provide coherent Sm-Nd garnet-whole rock ages of 317 ± 4 Ma and 316 ± 3 Ma (2σ). The prograde major-element zoning in the mm-sized garnets in combination with the moderate peak-metamorphic temperature, support our interpretation of the Sm-Nd garnet ages as unambiguous evidence for late Carboniferous HP metamorphism. The Sm-Nd garnet growth ages overlap within-error with the 40Ar/39Ar mica cooling ages of 314 ± 2 Ma and 313 ± 2 Ma (2σ) indicating rapid uplift of the subduction complex after peak metamorphism. The ca. 317-313 Ma HP-exhumation event of the KMC is contemporaneous with those of the Atbashi and Akeyazi (ca. 500 km east in NW China) HP complexes and implies similar collision histories at the South Tianshan Suture to the east and west of the Talas-Fergana Fault (TFF). The exhumation of the KMC and Atbashi HP complexes overlaps with the initiation of the TFF (Rolland et al., 2013) suggesting incipient separation of the Chatkal and Atbashi complexes during rock exhumation and early plate collision.

Subduction of Proterozoic to Late Triassic continental basement in the Guatemala suture zone: A petrological and geochronological study of high-pressure metagranitoids from the Chuacús complex

NASA Astrophysics Data System (ADS)

Maldonado, Roberto; Ortega-Gutiérrez, Fernando; Ortíz-Joya, Guillermo A.

2018-05-01

Many continental subduction complexes contain abundant granitic rocks coexisting with minor volumes of eclogite-facies rocks. Characterization of granitic protoliths is crucial to decipher the origin of subducted continental crust, whereas knowledge of its metamorphic evolution is required to constrain the mechanisms of burial and exhumation. In this work we present geochronological and petrological evidence that demonstrate the occurrence of a subducted Proterozoic to Late Triassic granitic basement in the Chuacús complex of central Guatemala. Metagranitoids exposed in this area are interlayered with eclogite and other high-pressure rocks, and their structure is considerably variable due to strain partitioning during deformation. Laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon data from two ferroan metagranites yield protolith crystallization ages of ca. 1.1 Ga and their trace-element abundances suggest an origin related to intraplate magmatism, while a high-silica, peraluminous metagranite is dated at 1.0 Ga and was probably originated by partial melting of a high-grade continental crust. On the other hand, two megacrystic to augen metagranitoids yield protolith crystallization ages of ca. 224 Ma, which are identical within errors to the protolith age of hosted eclogitic metabasites. Their high incompatible trace element abundances together with the observed spatial-temporal relationships with mafic protoliths suggest that Late Triassic bimodal magmatism in the Chuacús complex was probably originated in a within-plate setting. Regardless of their age or structure, the studied metagranites preserve evidences for high-pressure metamorphic equilibration, such as the occurrence of Ca-rich garnet (XCa up to 0.52) in association with phengite (Si contents of up to 3.4 pfu) and rutile. The integration of Zr-in-rutile thermometry and phengite barometry allows the peak metamorphic conditions to be constrained at 640-680 °C and 13 kbar. This pressure-temperature estimate indicates that metagranitoids underwent high-pressure metamorphism but equilibrated at significantly lower pressures than associated eclogite-facies rocks, and, therefore, they do not necessarily share a common high-pressure metamorphic evolution. The new data show that the Chuacús complex in the study area represents a Proterozoic (1.1-1.0 Ga) to Late Triassic (220 Ma) continental basement that was subducted, and consequently metamorphosed under high-pressure conditions, during the Cretaceous evolution of the North America-Caribbean plate boundary.

The Reaction Titanite+Kyanite=Anorthite+Rutile and Titanite-Rutile Barometry in Eclogites

USGS Publications Warehouse

Manning, C.F.; Bohlen, S.R.

1991-01-01

Titanite and rutile are a common mineral pair in eclogites, and many equilibria involving these phases are potentially useful in estimating pressures of metamorphism. We have reversed one such reaction, {Mathematical expression} using a piston-cylinder apparatus. Titanite+kyanite is the high-pressure assemblage and our results locate the equilibrium between 15.5 15.9, 17.7-17.9, 18.8-19.0, and 20.0-20.2 kb at 900, 1000, 1050, and 1100??C, respectively. The experiments require a positive dP/dT of between 20.5 and 23.5 bars/??C for the reaction. We use the reversed equilibrium and two other reactions, {Mathematical expression} and {Mathematical expression} to calculate metamorphic conditions for three eclogite localities. Using these reactions in conjunction with garnet-clinopyroxene Fe2+-Mg exchange equilibria, conditions of metamorphism were 16 kb and 750??C for kyaniteeclogites from Glenelg, Scotland, 21 kb and 625??C for eclogite-facies mica schists from the Tauern Window, Austria, and 46 kb and 850??C for eclogite-facies biotite gneisses from the Kokchetav Massif, USSR. For the Scottish and Austrian eclogites, the pressures derived from the titanite-rutile reactions provide additional constraints on pressures for these localities, leading to precise estimates of metamorphic conditions. In the case of the Soviet Union eclogites, the results show that the silicate-oxide assemblage is consistent with the remarkable occurrence of diamond inclusions in the garnets. The results of this study suggest that titanite and rutile stably coexist in many eclogites and that titanite solid solutions are ideal or nearly so. ?? 1991 Springer-Verlag.

Stepwise exhumation of the Triassic Lanling high-pressure metamorphic belt in Central Qiangtang, Tibet: Insights from a coupled study of metamorphism, deformation, and geochronology

NASA Astrophysics Data System (ADS)

Liang, Xiao; Wang, Genhou; Yang, Bo; Ran, Hao; Zheng, Yilong; Du, Jinxue; Li, Lingui

2017-04-01

The E-W trending Central Qiangtang metamorphic belt (CQMB) is correlated to the Triassic orogeny of the Paleo-Tethys Ocean prior to Cenozoic growth of the Tibetan Plateau. The well-exposed Lanling high-pressure, low-temperature (HP-LT) metamorphic complex was chosen to decipher the process by which it was exhumed, which thereby provides insights into the origin of the CQMB and Qiangtang terrane. After a detailed petrological and structural mapping, three distinct N-S-trending metamorphic domains were distinguished. Microscopic observations show that core domain garnet (Grt)-bearing blueschist was exhumed in a heating plus depressurization trajectory after peak eclogitic conditions, which is more evident in syntectonic vein form porphyroblastic garnets with zoning typical of a prograde path. Grt-free blueschist of the mantle domain probably underwent an exhumation path of temperature increasing and dehydration, as evidenced by pervasive epidote veins. The compilation of radiometric results of high-pressure mineral separates in Lanling and Central Qiantang, and reassessments on the published phengite data sets of Lanling using Arrhenius plots allow a two-step exhumation model to be formulated. It is suggested that core domain eclogitic rocks were brought onto mantle domain blueschist facies level starting at 244-230 Ma, with exhumation continuing to 227-223.4 Ma, and subsequently were exhumed together starting at 223-220 Ma, reaching lower greenschist facies conditions generally after 222-217 Ma. These new observations indicate that the CQMB formed as a Triassic autochthonous accretionary complex resulting from the northward subdcution of the Paleo-Tethys Ocean and that HP-LT rocks therein were very probably exhumed in an extensional regime.

A coupled model between mechanical deformation and chemical diffusion: An explanation for the preservation of chemical zonation in plagioclase at high temperatures

NASA Astrophysics Data System (ADS)

Zhong, Xin; Vrijmoed, Johannes; Moulas, Evangelos; Tajcmanová, Lucie

2016-04-01

Compositional zoning in metamorphic minerals have been generally recognized as an important geological feature to decipher the metamorphic history of rocks. The observed chemical zoning of, e.g. garnet, is commonly interpreted as disequilibrium between the fractionated inner core and the surrounding matrix. However, chemically zoned minerals were also observed in high grade rocks (T>800 degree C) where the duration of metamorphic processes was independently dated to take several Ma. This implies that temperature may not be the only factor that controls diffusion timescales, and grain scale pressure variation was proposed to be a complementary factor that may significantly contribute to the formation and preservation of chemical zoning in high temperature metamorphic minerals [Tajcmanová 2013, 2015]. Here, a coupled model is developed to simulate viscous deformation and chemical diffusion. The numerical approach considers the conservation of mass, momentum, and a constitutive relation developed from equilibrium thermodynamics. A compressible viscoelastic rheology is applied, which associates the volumetric change triggered by deformation and diffusion to a change of pressure. The numerical model is applied to the chemically zoned plagioclase rim described by [Tajcmanová 2014]. The diffusion process operating during the plagioclase rim formation can lead to a development of a pressure gradient. Such a pressure gradient, if maintained during ongoing viscous relaxation, can lead to the preservation of the observed chemical zonation in minerals. An important dimensionless number, the Deborah number, is defined as the ratio between the Maxwell viscoelastic relaxation time and the characteristic diffusion time. It characterizes the relative influence between the maintenance of grain scale pressure variation and chemical diffusion. Two extreme regimes are shown: the mechanically-controlled regime (high Deborah number) and diffusion-controlled regime (low Deborah number). In the mechanically-controlled regime, the grain scale pressure variation and thus the chemical zonation can be maintained due to slow viscous relaxation. Furthermore, by utilizing experimental flow laws and diffusion coefficients, the Deborah number is estimated in a variety of physical conditions. References Tajcmanová, L., Y. Podladchikov, R. Powell, E. Moulas, J.C. Vrijmoed, and J.A.D. Connolly, 2014. Journal of Metamorphic Geology, 32(2):195-207. Tajcmanová, L., J.C. Vrijmoed, and E. Moulas, 2015. Lithos, 216-217:338-351.

Cretaceous crust beneath SW Borneo: U-Pb dating of zircons from metamorphic and granitic rocks

NASA Astrophysics Data System (ADS)

Davies, L.; Hall, R.; Armstrong, R.

2012-12-01

Metamorphic basement rocks from SW Borneo are undated but have been suggested to be Palaeozoic. This study shows they record low pressure 'Buchan-type' metamorphism and U-Pb SHRIMP dating of zircons indicates a mid-Cretaceous (volcaniclastic) protolith. SW Borneo is the southeast promontory of Sundaland, the continental core of SE Asia. It has no sedimentary cover and the exposed basement has been widely assumed to be a crustal fragment from the Indochina-China margin. Metamorphic rocks of the Pinoh Group in Kalimantan (Indonesian Borneo) are intruded by granitoid rocks of Jurassic-Cretaceous age, based on K-Ar dating, suggesting emplacement mainly between 130 and 80 Ma. The Pinoh metamorphic rocks have been described as a suite of pelitic schists, slates, phyllites, and hornfelses, and have not been dated, although they have been correlated with rocks elsewhere in Borneo of supposed Palaeozoic age. Pelitic schists contain biotite, chlorite, cordierite, andalusite, quartz, plagioclase and in some cases high-Mn almandine-rich garnet. Many have a shear fabric associated with biotite and fibrolite intergrowth. Contact metamorphism due to intrusion of the granitoid rocks produced hornfelses with abundant andalusite and cordierite porphyroblasts. Granitoids range from alkali-granite to tonalite and contain abundant hornblende and biotite, with rare white mica. Zircons from granitoid rocks exhibit sector- and concentric- zoning; some have xenocrystic cores mantled by magmatic zircon. There are four important age populations at c. 112, 98, 84 and 84 Ma broadly confirming earlier dating studies. There is a single granite body with a Jurassic age (186 ± 2.3 Ma). Zircons from pelitic metamorphic rocks are typically euhedral, with no evidence of rounding or resorbing of grains; a few preserve volcanic textures. They record older ages than those from igneous rocks; U-Pb ages are Cretaceous with a major population between 134 and 110 Ma. A single sample contains Proterozoic and Phanerozoic zircons. The metamorphic rocks from SW Borneo are not an ancient core to the island as previously assumed. We propose that extensive arc volcanism produced fine grained volcanogenic sediments during the Early Cretaceous deposited on, or reworking, older crust. These sediments were subjected to low pressure 'Buchan-type' metamorphism soon after deposition. Magmatism continued into the Late Cretaceous, resulting in contact metamorphism.

Stacking and metamorphism of continuous segments of subducted lithosphere in a high-pressure wedge: The example of Alpine Corsica (France)

NASA Astrophysics Data System (ADS)

Vitale Brovarone, Alberto; Beyssac, Olivier; Malavieille, Jacques; Molli, Giancarlo; Beltrando, Marco; Compagnoni, Roberto

2013-01-01

Alpine Corsica consists of a stack of variably metamorphosed units of continental and Tethys-derived rocks. It represents an excellent example of high-pressure (HP) orogenic belt, such as the Western Alps, exposed over a small and accessible area. Compared to the Western Alps, the geology of Alpine Corsica is poorly unraveled. During the 1970s-80s, based on either lithostratigraphic or metamorphic field observations, various classifications of the belt have been proposed, but these classifications have been rarely matched together. Furthermore, through time, the internal complexity of large domains has been progressively left aside in the frame of large-scale geodynamic reconstructions. As a consequence, major open questions on the internal structure of the belt have remained unsolved. Apart from a few local studies, Alpine Corsica has not benefited of modern developments in petrology and basin research. This feature results in several uncertainties when combining lithostratigraphic and metamorphic patterns and, consequently, in the definition of an exhaustive architecture of the belt. In this paper we provide a review on the geology of Alpine Corsica, paying particular attention to the available lithostratigraphic and metamorphic classifications of the metamorphic terranes. These data are completed by a new and exhaustive metamorphic dataset obtained by means of thermometry based on Raman Spectroscopy of Carbonaceous Material (RSCM). This technique provides reliable insights on the peak temperature of the metamorphic history for CM-bearing metasediments. A detailed metamorphic characterization of metasediments, which have been previously largely ignored due to retrogression or to the lack of diagnostic mineralogy, is thus obtained and fruitfully coupled with the available lithostratigraphic data. Nine main tectono-metamorphic units are defined, from subgreenschist (ca. 280-300 °C) to the lawsonite-eclogite-facies (ca. 500-550 °C) condition. These units are homogeneous in metamorphism, laterally continuous and have characteristic lithostratigraphic features. This study also suggests a direct link between the pre-orogenic extensional setting and the present-day compressional structure of Alpine Corsica, indicating that large sections of subducted lithosphere were subducted and exhumed as coherent domains. These features provide important insight on the mechanism of stacking and exhumation of HP rocks, and make Alpine Corsica a unique reference for mountain-building processes in Tethyan-type orogens.

A Manganin Thin Film Ultra-High Pressure Sensor for Microscale Detonation Pressure Measurement

PubMed Central

Zhang, Guodong; Zhao, Yulong; Zhao, Yun; Wang, Xinchen; Ren, Wei; Li, Hui; Zhao, You

2018-01-01

With the development of energetic materials (EMs) and microelectromechanical systems (MEMS) initiating explosive devices, the measurement of detonation pressure generated by EMs in the microscale has become a pressing need. This paper develops a manganin thin film ultra-high pressure sensor based on MEMS technology for measuring the output pressure from micro-detonator. A reliable coefficient is proposed for designing the sensor’s sensitive element better. The sensor employs sandwich structure: the substrate uses a 0.5 mm thick alumina ceramic, the manganin sensitive element with a size of 0.2 mm × 0.1 mm × 2 μm and copper electrodes of 2 μm thick are sputtered sequentially on the substrate, and a 25 μm thick insulating layer of polyimide is wrapped on the sensitive element. The static test shows that the piezoresistive coefficient of manganin thin film is 0.0125 GPa−1. The dynamic experiment indicates that the detonation pressure of micro-detonator is 12.66 GPa, and the response time of the sensor is 37 ns. In a word, the sensor developed in this study is suitable for measuring ultra-high pressure in microscale and has a shorter response time than that of foil-like manganin gauges. Simultaneously, this study could be beneficial to research on ultra-high-pressure sensors with smaller size. PMID:29494519

The Cycladic Blueschist Belt in the Central Aegean Sea: Resolving the Interplay between Alpine Orogeny and Back-arc Extension

NASA Astrophysics Data System (ADS)

Avigad, D.

2007-12-01

The Aegean Sea, formed via extensional tectonics and floored by an attenuated continental crust, overprinted and dissected a once-continuous Alpine orogenic belt that stretched from mainland Greece to Anatolia. The Cycladic islands, in the central Aegean region, mainly comprise HP-LT metamorphic rocks (and their greenschist-facies derivatives) whose P-T conditions range at 12-15 kbars and 450-500 °C, straddling the blueschist-eclogite facies boundary. The protoliths are supracrustals metavolcanics and volcanoclastics alongside thick marble units that were deposited on the Pindos basin margin. Locally, such as on Syros and Sifnos, kilometer-thick, blueschist and eclogite-facies rocks are preserved intact allowing to explore the bottom of the orogenic edifice. 40Ar/39Ar ages of ~45Ma have been repeatedly obtained on Si rich phengites assessing the Eocene timing of the high-pressure metamorphism and crustal thickening. Upon decompression, the high- pressure rocks were overprinted in the greenschist-facies but locally as on Naxos migmatites were formed on the expense of eclogites at mid-crustal depth, at ~20 Ma. A series of granitoids penetrated the exhumed rock units during the Middle Miocene (until ~10Ma) in relation to whole-lithosphere back-arc extension.//The Cycladic blueschist belt, in the core of the extending Aegean region, is a suitable site to analyze the interplay between Mediterranean-type back-arc extension and the exhumation of the high-pressure metamorphic rocks. The Cycladic blueschist unit is sandwiched between lower pressure rocks: it is topped by greenschist- and amphibolite facies metamorphic rocks comprising metavolcanics interleaved with metamorphosed ultrabasic slices. The tectonic contact is a low-angle extensional detachment of significant lateral dimension and kinematic markers usually portray top-to-the-North sense of motion. Being stitched by mid-Miocene granitoids this is the oldest extensional discontinuity observed in the central Aegean. Where the original architecture of the Alpine orogenic belt was not severely obliterated, such as on Evia, a basal unit (Almyropotamos window) is exposed below the Cycladic blueschists unit. Within the basal unit, the presence of relict glaucophane and Si-rich phengite attest for a LT-HP metamorphism, but carbonates still preserve Lutetian nummullites indicating the basal unit metamorphism outlasted the Middle Eocene as well as cooling of the overlying Cycladic blueschists. The Cycladic blueschist unit is thus allochtonous on a regional scale: it was accreted into the orogenic wedge sometimes after the mid-Eocene. The time interval between the Eocene peak of eclogite metamorphism and the onset of back-arc extension in the Oligo-Miocene involved thrusting and contraction. In the central Aegean, the entire inventory of extensional structures operated subsequently to the emplacement of the Cycladic blueschist unit onto lower pressure sequences implying whole-lithosphere back-arc extension overprinted an Alpine orogen containing eclogites at relatively shallow structural levels. This resembles the mode of occurrence of eclogites in other mountain belts where back-arc extension played no role. Remarkably, despite significant crustal stretching only minor lateral metamorphic breaks can be identified in the Cyclades and the 12-15 kbar level of the former orogen are pervasively exposed over much of the archipelago.

QEMSCAN+LAICPMS: a new tool for petrochronology and sedimentary provenance analysis

NASA Astrophysics Data System (ADS)

Vermeesch, Pieter; Rittner, Martin; Omma, Jenny

2017-04-01

Only a relatively small number of rock-forming minerals contain sufficiently high concentrations of naturally occurring radioactive parent isotopes and sufficiently low background concentrations of the corresponding daughter isotopes to be suitable for geochronology. The first step in most geochronological studies is to extract these datable minerals from the host rock using a combination of magnetic and density separation techniques, a process that is tedious and time consuming. We here present a new method to avoid mineral separation by coupling a QEMSCAN electron microscope to an LA-ICP-MS instrument. Given a polished hand specimen, a petrographic thin section, or a grain mount, the QEMSCAN+LAICPMS method produces chemical and mineralogical maps from which the X-Y coordinates of the datable mineral are extracted. These coordinates are subsequently passed on to the laser ablation system for isotopic and, hence, geochronological analysis. QEMSCAN+LAICPMS can be applied to a wide range of problems in igneous, metamorphic and sedimentary geology, as is illustrated with three case studies. In the first case study, a 3 × 4 cm slab of polished granite from the L'Erée pluton in Guernsey is scanned for zircon. This yields 23 U-Pb ages resulting in a concordia age of 615 ± 2 Ma. The second case study re-investigates a paragneiss from an ultra-high pressure terrane in the Qaidam Basin (Qinghai, China) that was previously analysed by conventional petrography, electron microscopy and SIMS zircon U-Pb analysis. In this example, the QEMSCAN revealed 107 small (20 μm) metamorphic zircons that were analysed by LA-ICP-MS to constrain the 430 Ma age of peak metamorphism. The third and final case study investigates the mineralogy and geochronology of sedimentary rocks of the Ordovician Sarah Formation (Saudi Arabia). We analysed 44 outcrop samples and a further 35 subsurface samples, resulting in a dataset comprising 10,000 detrital zircon U-Pb ages and 79 heavy mineral compositions and petrographic analyses. Jointly considering this enormous dataset by 3-way multidimensional scaling paints a remarkably simple picture of sandstone compositions that are determined by a combination of provenance and diagenesis. In conclusion, the QEMSCAN+LAICPMS method represents an efficient and cost effective way to obtain chemical and isotopic compositions on the same sample, which improves both the quantity and quality of geological data.

Newly discovered Late Triassic Baqing eclogite in central Tibet indicates an anticlockwise West-East Qiangtang collision.

PubMed

Zhang, Yu-Xiu; Jin, Xin; Zhang, Kai-Jun; Sun, Wei-Dong; Liu, Jian-Ming; Zhou, Xiao-Yao; Yan, Li-Long

2018-01-17

The Triassic eclogite-bearing central Qiangtang metamorphic belt (CQMB) in the northern Tibetan Plateau has been debated whether it is a metamorphic core complex underthrust from the Jinsha Paleo-Tethys or an in-situ Shuanghu suture. The CQMB is thus a key issue to elucidate the crustal architecture of the northern Tibetan Plateau, the tectonics of the eastern Tethys, and the petrogenesis of Cenozoic high-K magmatism. We here report the newly discovered Baqing eclogite along the eastern extension of the CQMB near the Baqing town, central Tibet. These eclogites are characterized by the garnet + omphacite + rutile + phengite + quartz assemblages. Primary eclogite-facies metamorphic pressure-temperature estimates yield consistent minimum pressure of 25 ± 1 kbar at 730 ± 60 °C. U-Pb dating on zircons that contain inclusions (garnet + omphacite + rutile + phengite) gave eclogite-facies metamorphic ages of 223 Ma. The geochemical continental crustal signature and the presence of Paleozoic cores in the zircons indicate that the Baqing eclogite formed by continental subduction and marks an eastward-younging anticlockwise West-East Qiangtang collision along the Shuanghu suture from the Middle to Late Triassic.

Detailed thermal fingerprinting of obduction-related processes: insights from Northern New Caledonia

NASA Astrophysics Data System (ADS)

Vitale Brovarone, A.; Agard, P.; Monié, P.; Chauvet, A.

2012-04-01

Northern New Caledonia comprises large and continuous units of high-pressure metamorphic rocks formed in response to the Eocene subduction of a continental margin, classically viewed as a northern extension of the Norfolk ridge, below an oceanic island-arc system (well-exposed in southern New Caledonia) [1, 2]. Metamorphic conditions increase gradually towards the east, providing a continuous window on prograde metamorphism from low-grade, lawsonite-bearing assemblages to epidote-bearing eclogite [3, 4, 5]. Unfortunately, available P-T constraints are mostly restricted to metamafics, but are almost completely lacking in metasediments, which represent the dominant lithology in these mainly continental-derived units. This is due both to the lack of diagnostic mineral assemblages in the metasedimentary lower grade units and to the intense late retrogression affecting the higher-grade metasediments. We herein present an extensive thermometric dataset (encompassing the area from Hienghene to the south and from Koumac to Pouébo) obtained via Raman Spectroscopy of Carbonaceous Material (RSCM), which provides quantitative estimates of the peak metamorphic temperature of CM-bearing metasediments in the range ~200-650°C [6, 7]. Metamorphic conditions vary from about 200 °C in the lower-grade units and progressively increase toward the east to about 550 °C in the eclogite facies unit. Sharp metamorphic gaps are nevertheless found across some major tectonic boundaries (such as the Gendarmerie fault zone). Importantly, the main metamorphic units defined by means of our dataset do not always match with previous studies. This dataset also provides useful insights on the architecture of the high-pressure belt in Northern New Caledonia, where structures are poorly exposed due to thick vegetation. [1] Cluzel, D., Aitchison, J.C., Picard, C., 2001. Tectonic accretion and underplating of mafic terranes in the Late Eocene intraoceanic forearc of New Caledonia (Southwest Pacific): geodynamic implications. Tectonophysics 340 (1-2), 23-59. [2] Ulrich, M., Picard C., Guillot S., Chauvel C., Cluzel D., Meffre S. (2010) The New Caledonia Ophiolite : multiple Stage of melting and refertilisation process as indicators of ridge to subduction formation. Lithos. doi 10.1016/j.lithos.2009.12.011. [3] Brothers, R. N. & Blake, M. C., 1972. Tertiary plate tectonics and high-pressure metamorphism in New Caledonia. Tectonophysics, 17, 359-391. [4] Fitzherbert, J. A., Clarke, G. L. & Powell, R., 2003. Lawsonite- omphacite bearing metabasites of the Pam Peninsula, NE New Caledonia: Evidence for disrupted blueschist to eclogite facies conditions. Journal of Petrology, 44, 1805-1831. [5] Spandler, C., & Hermann, J., 2006. High-pressure veins in eclogite from New Caledonia and their significance for fluid migration in subduction zones. Lithos, 89 (1-2). pp. 135-153. ISSN 1872-6143 [6] Beyssac, O., Goffé, B., Chopin, C. & Rouzaud, J.N., 2002. Raman spectra of carbonaceous material in metasediments: a new geothermometer. J. Metamorph. Geol., 20, 859-871. [7] Lahfid, A., Beyssac, O., Deville, E., Negro, F., Chopin, C. & Goffé, B., 2010. Evolution of the Raman spectrum of carbonaceous material in low-grade metasediments of the Glarus Alps (Switzerland). Terra Nova, 22: 354-360. doi: 10.1111/j.1365-3121.2010.00956.x

Petrological evolution of subducted rodingite from seafloor metamorphism to dehydration of enclosing antigorite-serpentinite (Cerro del Almirez massif, southern Spain)

NASA Astrophysics Data System (ADS)

Laborda-López, Casto; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Gómez-Pugnaire, María Teresa; Garrido, Carlos J.; Jabaloy-Sánchez, Antonio; Padrón-Navarta, José Alberto

2016-04-01

Rodingites are common rocks associated with serpentinites in exhumed terrains that experienced subduction and high pressure metamorphism. However, the response of these rocks to devolatilization and redox reactions in subduction settings is not well constrained. In the Cerro del Almirez ultramafic massif (southern Spain) rodingites constitute about 1-2% of the total volume of exposed rocks. Metarodingites are enclosed in antigorite-serpentinite and chlorite-harzburgite separated by a transitional zone that represents the front of prograde serpentinite-dehydration in a paleo-subduction setting (Padrón-Navarta et al., 2011). Metarodingites occur as boudin lenses, 1 to 20 m in length and 30 cm to 2 m in thickness. During serpentinization of peridotite host rocks, dolerites and basalts precursor of rodingites underwent intense seafloor metasomatism, causing the enrichment in Ca and remobilization of Na and K. Subsequent metamorphism during subduction transformed the original igneous and seafloor metamorphic mineralogy into an assemblage of garnet (Ti-rich hydrogrossular), diopside, chlorite, and epidote. During prograde metamorphism, garnet composition changed towards higher andradite contents. High-pressure transformation of enclosing antigorite-serpentinite to chlorite-harzburgite released fluids which induced breakdown of garnet to epidote in metarodingites. Ti liberation by this latter reaction produced abundant titanite. Released fluids also triggered the formation of amphibole by alkalis addition. Highly recrystallized metarodingites in chlorite-harzburgite present a new generation of idiomorphic garnet with composition equal to 10-30% pyrope, 30-40% grossular and 35-55% almandine + spessartine. This garnet has titanite inclusions in the core and rutile inclusions in the rim. The contact between metarodingites and ultramafic rocks consists of a metasomatic zone (blackwall) with variable thickness (7 to 40 cm) constituted by chlorite, diopside, and titanite. Close to the contact with the blackwall, antigorite-serpentinite is very rich in diopside, olivine and Ti-clinohumite. In this study we present a thermodynamic model of phase relationships in rodingites and transitional blackwalls during their metamorphic history. We mainly aim to establish the evolution of P-T conditions experienced by metarodingites during subduction and the influence of fluids in the formation of mineral assemblages at different metamorphic stages. REFERENCES Padrón-Navarta, J.A., López Sánchez-Vizcaíno, V., Garrido, C.J., Gómez-Pugnaire, M.T., (2011): Metamorphic record of high-pressure dehydration of antigorite serpentinite to chlorite harzburgite in a subduction setting (Cerro Del Almirez, Nevado-Filábride Complex, Southern Spain). Journal of Petrology, 52, 2047-2078.

Thermobarometric constraints on mid-Cretaceous to late Cretaceous metamorphic events in the western metamorphic belt of the Coast Mountains complex near Petersburg, southeastern Alaska

USGS Publications Warehouse

Himmelberg, Glen R.; Brew, David A.

2005-01-01

The western metamorphic belt is part of the Coast Mountains Complex of southeastern Alaska and western Canada. This complex formed as a result of mid-Cretaceous through middle Eocene crustal shortening between the previously amalgamated Wrangellia and Alexander terranes (Insular superterrane) and previously accreted terranes of the North American continental margin (Intermontane superterrane). The western metamorphic belt, which ranges from a few kilometers to several tens of kilometers in width, records a complex sequence of contact-metamorphic and regional metamorphic events, the most significant of which are designated M1R, M2C-R, and M3R. The M1R regional metamorphic event ranged in grade from subgreenschist to greenschist facies and was overprinted by the M2C-R and M3R metamorphic events. The M2C-R metamorphic event is recorded in discrete contact-metamorphic aureoles and regional metamorphic-mineral assemblages related to tonalite-granodiorite plutons of the Admiralty-Revillagigedo plutonic belt. The M3R metamorphic belt, which is adjacent to the M2C-R belt, is characterized by regional Barrovian isograds of garnet, staurolite, kyanite, and sillimanite. Using the THERMOCALC program, pressure-temperature (P-T) conditions for the M2C-R metamorphic event are estimated to be in the ranges 5.3-7.5 kbars and 525-640 deg.C and for the M3R metamorphic event in the ranges 9.4-12.6 kbars and 730-895 deg.C. The M2C-R metamorphic event occurred at approximately 90 Ma, but the timing of the M3R metamorphic event is poorly documented and uncertain. On the basis of an 40Ar/39Ar age on actinolitic amphibole and a Sm-Nd age on garnet core, the timing of metamorphism might be constrained between 90+/-1 and 80+/-9 Ma, although the Sm-Nd age of 80+/-9 m.y. possibly reflects postpeak growth. Thermobarometric data suggest that the two events occurred at different crustal levels and followed different P-T paths. No evidence exists that M2C-R metamorphic-mineral assemblages were overprinted by the M3R metamorphic event, as proposed by some workers. Juxtaposition of the two belts of rocks probably occurred along the Coast shear zone during uplift and exhumation of the Coast Mountains.

Metamorphic and geochronogical study of the Triassic El Oro metamorphic complex, Ecuador: Implications for high-temperature metamorphism in a forearc zone

NASA Astrophysics Data System (ADS)

Riel, N.; Guillot, S.; Jaillard, E.; Martelat, J.-E.; Paquette, J.-L.; Schwartz, S.; Goncalves, P.; Duclaux, G.; Thebaud, N.; Lanari, P.; Janots, E.; Yuquilema, J.

2013-01-01

In the forearc of the Andean active margin in southwest Ecuador, the El Oro metamorphic complex exhibits a well exposed tilted forearc section partially migmatized. We used Raman spectroscopy on carbonaceous matter (RSCM) thermometry and pseudosections coupled with mineralogical and textural studies to constrain the pressure-temperature (P-T) evolution of the El Oro metamorphic complex during Triassic times. Our results show that anatexis of the continental crust occurred by white-mica and biotite dehydration melting along a 10 km thick crustal domain (from 4.5 to 8 kbar) with increasing temperature from 650 to 700 °C. In the biotite dehydration melting zone, temperature was buffered at 750-820 °C in a 5 km thick layer. The estimated average thermal gradient during peak metamorphism is of 30 °C/km within the migmatitic domain can be partitioned into two apparent gradients parts. The upper part from surface to 7 km depth records a 40-45 °C/km gradient. The lower part records a quasi-adiabatic geotherm with a 10 °C/km gradient consistent with an isothermal melting zone. Migmatites U-Th-Pb geochronology yielded zircon and monazite ages of 229.3 ± 2.1 Ma and 224.5 ± 2.3 Ma, respectively. This thermal event generated S-type magmatism (the Marcabeli granitoid) and was immediately followed by underplating of the high-pressure low-temperature (HP-LT) Arenillas-Panupalí unit at 225.8 ± 1.8 Ma. The association of high-temperature low-pressure (HT-LP) migmatites with HP-LT unit constitutes a new example of a paired metamorphic belt along the South American margin. We propose that in addition to crustal thinning, underplating of the Piedras gabbroic unit before 230 Ma provided the heat source necessary to foster crustal anatexis. Furthermore, its MORB signature shows that the asthenosphere was involved as the source of the heat anomaly. S-type felsic magmatism is widespread during this time and suggests that a large-scale thermal anomaly affected a large part of the South American margin during the late Triassic. We propose that crustal anatexis is related to an anomaly that arose during subduction of the Panthalassa ocean under the South American margin. Slab verticalization or slab break-off can be invoked as the origin of the upwelling of the asthenosphere.

Detrital-zircon fission-track geochronology of the Lower Cenozoic sediments, NW Himalayan foreland basin: Clues for exhumation and denudation of the Himalaya during the India-Asia collision

NASA Astrophysics Data System (ADS)

Jain, A.; Lal, N.; Suelmani, B.; Awasthi, A. K.; Singh, S.; Kumar, R.

2007-12-01

Detrital-zircon fission-track geochronology of the synorogenically-deposited Subathu-Dagshai-Kasauli-Lower Siwalik Formations of the Sub-Himalayan Lower Cenozoic foreland basin reflects progressive effects of the Himalayan tectonometamorphic events on the Proterozoic-Paleozoic source rock as a consequence of the India-Asia collision. The oldest transgressive marine Subathu Formation (57.0-41.5 Ma) contains a very dominant 302.4 ± 21.9 Ma old detrital zircon FT suite with a few determinable 520.0 Ma grains. This old suite was derived by mild erosion of the Zircon Partially Annealed Zone (ZPAZ) of 240-180 oC, which affected the Himalayan Proterozoic basement and its Tethyan sedimentary cover as a consequence of first imprint of the collision. In addition, 50.0 Ma old detrital zircons in this formation were derived possibly from the Indus Tsangpo Suture Zone and the Trans-Himalayan Ladakh Batholith. Sudden source rock changes and unroofing are manifested in the overlying fluvial Dagshai (~30-20 Ma) and Kasauli (20-13 Ma) molassic sediments, which are characterised by dominant 30.0 and 25.0 Ma old youngest zircon FT peaks, respectively. A distinct unconformity spanning for about 10 Myr gets established between the Subathu-Dagshai formations on the basis of detrital- zircon FT ages. Molassic sedimentation since ~30 Ma coincides with the depletion of detritus from the suture zone, and the bulk derivation from the main Higher Himalayan source rock, which has undergone sequentially the UHP-HP-amphibolite facies metamorphism (53-40 Ma) in the extreme north and widespread Eo- and Neo-Himalayan tectonothermal events in the middle. Strength of the Pre-Himalayan Peaks (PHP) >50 Ma in these younger sediments gradually decreases with the intensification of the Himalayan thermal events till the end of the Kasauli sedimentation. Widespread Eo- and Neo-Himalayan metamorphic events (40.0-30.0 and 25.0-15.0 Ma) have almost remobilised the provenance and obliterated most of the evidences of the Pre-Himalayan Peaks in zircon FT ages and appear to be responsible for incoming of the Himalayan (HP) ~30.0 Ma and Young Himalayan Peaks (YHP) of ~15.0 Ma, respectively; the latter appears only between 13.0 and 11.0 Ma sedimentation of the Lower Siwalik Formation. Three distinct metamorphic events get recognised in source area of the Himalayan Metamorphic Belt. Though the Dagshai-Kasauli-Lower Siwalik sequence records uninterrupted fluvial sedimentation since 30 Ma, distinct breaks in zircon FT ages ~5.0-7.0 Myr at the beginning of each formation records pulsative exhumation of the source area in response to the collision between India and Asia.

Investigating the response of biotite to impact metamorphism: Examples from the Steen River impact structure, Canada

NASA Astrophysics Data System (ADS)

Walton, E. L.; Sharp, T. G.; Hu, J.; Tschauner, O.

2018-01-01

Impact metamorphic effects from quartz and feldspar and to a lesser extent olivine and pyroxene have been studied in detail. Comparatively, studies documenting shock effects in other minerals, such as double chain inosilicates, phyllosilicates, carbonates, and sulfates, are lacking. In this study, we investigate impact metamorphism recorded in crystalline basement rocks from the Steen River impact structure (SRIS), a 25 km diameter complex crater in NW Alberta, Canada. An array of advanced analytical techniques was used to characterize the breakdown of biotite in two distinct settings: along the margins of localized regions of shock melting and within granitic target rocks entrained as clasts in a breccia. In response to elevated temperature gradients along shock vein margins, biotite transformed at high pressure to an almandine-Ca/Fe majorite-rich garnet with a density of 4.2 g cm-3. The shock-produced garnets are poikilitic, with oxide and silicate glass inclusions. Areas interstitial to garnets are vesiculated, in support of models for the formation of shock veins via oscillatory slip, with deformation continuing during pressure release. Biotite within granitic clasts entrained within the hot breccia matrix thermally decomposed at ambient pressure to produce a fine-grained mineral assemblage of orthopyroxene + sanidine + titanomagnetite. These minerals are aligned to the (001) cleavage plane of the original crystal. In this and previous work, the transformation of an inosilicate (pargasite) and a phyllosilicate (biotite) to form garnet, an easily identifiable, robust mineral, has been documented. We contend that in deeply eroded astroblemes, high-pressure minerals that form within or in the environs of shock veins may serve as one of the possibly few surviving indicators of impact metamorphism.

Metamorphic geology: Why should we care?

NASA Astrophysics Data System (ADS)

Tajcmanova, Lucie; Moulas, Evangelos; Vrijmoed, Johannes

2016-04-01

Estimation of pressure-temperature (P-T) from petrographic observations in metamorphic rocks has become a common practice in petrology studies during the last 50 years. This data then often serves as a key input in geodynamic reconstructions and thus directly influences our understanding of lithospheric processes. Such an approach might have led the metamorphic geology field to a certain level of quiescence. Obtaining high-quality analytical data from metamorphic rocks has become a standard part of geology studies. The numerical tools for geodynamic reconstructions have evolved to a great extend as well. Furthermore, the increasing demand on using the Earth's interior for sustainable energy or nuclear waste disposal requires a better understanding of the physical processes involved in fluid-rock interaction. However, nowadays, metamorphic data have apparently lost their importance in the "bigger picture" of the Earth sciences. Interestingly, the suppression of the metamorphic geology discipline limits the potential for understanding the aforementioned physical processes that could have been exploited. In fact, those phenomena must be considered in the development of new generations of fully coupled numerical codes that involve reacting materials with changing porosity while obeying conservation of mass, momentum and energy. In our contribution, we would like to discuss the current role of metamorphic geology. We will bring food for thoughts and specifically touch upon the following questions: How can we revitalize metamorphic geology? How can we increase the importance of it? How can metamorphic geology contribute to societal issues?

Collision in the Central Alps: 2. Exhumation of high-pressure fragments

NASA Astrophysics Data System (ADS)

Brouwer, F. M.; Burri, T.; Berger, A.; Engi, M.

2003-04-01

In the Central Alps high-pressure metamorphic rocks are confined to but a few tectonic units. In the Adula nappe pressures range from about 12 kbar in the north, to 20 kbar in the south [1]. The Southern Steep Belt (SSB) is a high-strain zone at the contact between rocks deriving from Apulia and Eurasia. The SSB contains a tectonic composite of ortho and paragneisses, with widespread bands and lenses of mafic and ultramafic composition. Many of the mafic fragments are garnet-amphibolites or eclogites, with a highly variable degree of retrogression. Our petrological studies indicate that the HP rocks in the SSB show extensive variation in metamorphic pressure. In mafic fragments, pressures retained by assemblages predating the amphibolite facies overprint range from 8 to 21 kbar, while pressure estimates for some peridotites are >30 kbar. Some HP fragments show evidence of substantial heating during decompression. New Lu-Hf and Sm-Nd geochronology, in conjunction with previously published data, indicates a spread in ages obtained from the high-pressure metamorphic assemblage. Thermal models based on simplified kinematics produce computed PTt histories that resemble those documented in individual HP fragments [2]. The SSB is interpreted to represent an exhumed part of a Tectonic Accretion Channel (TAC, cf. [3]), assembled of numerous, relatively small fragments which reflect a variety of paths. The different residence times and exhumation rates reflect a protracted history of subduction and extrusion, in which the fragments moved independently from their current neighbours. Combination of thermal modelling and field-based studies improve our conceptual thinking on the dynamics of exhumation of high-pressure rocks in a convergent orogen. [1] Heinrich (1986) J. Pet. 27: 123-154 [2] Roselle et al. (2002) Amer. J. Sci. 302: 381-409 [3] Engi et al. (2001) Geology 29: 1143-1146

Pressure variations in the Monte Rosa nappe, Western Alps

NASA Astrophysics Data System (ADS)

Luisier, Cindy; Vaughan-Hammon, Joshua; Baumgartner, Lukas; Schmalholz, Stefan

2017-04-01

The Monte Rosa nappe is part of the Penninic nappe stack of the Western Alps. It represents the southern-most European continental basement involved in the alpine orogeny. It consists of a pre-Variscan basement complex, made of mostly metapelites and paragneisses, which were intruded by a Permian-age granitic body (Pawlig, 2001). The nappe is heterogeneously deformed, with localized high strain domains separating low strain domains. The metamorphic record is tightly linked to deformation. Different thermodynamic data bases and approaches were used in the past to estimate the peak alpine metamorphic conditions. They range from 1.2 to 2.7 GPa and 490 to 650˚C, based on metagranite, metapelite, metamafic and whiteschist assemblages. The peak alpine metamorphic assemblage of zoisite, phengite and albite symplectites pseudomorphing magmatic plagioclase is preserved only in the less deformed portions of the nappe. Phengite, garnet and titanite coronas surrounding biotite, quartz and igneous K-feldspar make up the rest of the rock. The metagranite locally grades into 10 to 50 meters whiteschist bodies, consisting of talc-chloritoid-kyanite-phengite-quartz, which can contain carbonate and garnet. Their chemistry is interpreted as a metasomatic product of the late magmatic hydrothermal alteration of the granite, whereas their mineralogy results from the alpine high pressure metamorphism (Pawlig and Baumgartner, 2001; Luisier et al., 2015). We performed a phase petrology and textural study to consistently estimate peak alpine metamorphic conditions in the granite and the related whiteschists. Textural observations were used to select the best-preserved high-pressure metagranite samples. Inherited magmatic feldspar textures indicate that jadeite was never formed in these granites, confirmed independently by Si in phengite barometer (1.2 to 1.5 GPa). Note that the granite contains the phengite buffer assemblage of Massonne and Schreyer (1987). Thermodynamic calculations using internally consistent thermodynamic database on whiteschists result in a minimum P of 2.2 GPa at T of 550 to 570˚C and a water activity close to 1, unlike previous water activities proposed (Le Bayon et al., 2006). Peak alpine pressures and temperatures calculated for the metagranite and associated whiteschists hence result in significant different pressure estimates, corroborating previous results from the literature. The possible explanations for such pressure variations are i) slight underestimation of the metagranite peak pressure, due to water-undersaturation conditions, however a pressure as high as 2 GPa is unlikely, or ii) heterogeneous stress conditions, due to rheologically contrasting lithologies, consisting of weak whiteschist inclusions within strong, undeformed metagranites. References Le Bayon et al., 2006: Contrib. Mineral. Petrol. 151, 395-412 Luisier et al., 2015: GSA conference abstract Massonne and Schreyer, 1987: Contrib. Mineral. Petrol. 96, 212-224 Pawlig, S. 2001: PhD thesis, University of Mainz (Germany) Pawlig and Baumgartner, 2001: SMPM 81,329-346

Significance of the Nestos Shearzone in the southern Rhodopes (Northern Greece/Southern Bulgaria)

NASA Astrophysics Data System (ADS)

Nagel, Thorsten; Schmidt, Silke; Janak, Marian; Jahn-Awe, Silke; Froitzheim, Niko; Georgiev, Neven

2010-05-01

The Nestos Shearzone can be traced over 100 kilometers and separates the two main units of the Rhodopes, the Rhodope Terrane in the hangingwall from the Pangaion-Pirin Unit in the footwall. The Rhodope Terrane consists of mingled continental and oceanic basement rocks, intruded by granitic bodies of Cenozoic age. It underwent at least amphibolite facies conditions during the Alpine orogenic cycle and several localities with preserved highpressure and/or ultrahigh-pressure rocks have been found. The age of orogenesis and metamorphism is ambiguous and several Mesozoic and Tertiary cycles may be recorded in that unit. The lowermost level immediately on top of the Nestos Shearzone (Sidironero subunit) mainly consists of rocks derived from a Jurassic arc and appears to show the youngest reported (i.e. Eocene) high-grade metamorphism (including ultra-high-pressure conditions and a subsequent migmatic stage). The underlying Pangaion-Pirin Unit beneath the Nestos Shearzone is build of marbles and Variscan gneisses of disputed Mesozoic paleogeographic position. It is intruded by Oligocene granitoids, which also crosscut the Nestos Shearzone. The Pangaion-Pirin Unit experienced a clockwise PT-path culminating at upper greenschist facies conditions during the Alpine cycle. The Nestos Shearzone is defined by top-to-the-southwest-directed mylonites formed under upper greenschist facies conditions. So far, it has been viewed as a thrust. We present structural and petrological data suggesting that the Nestos Shearzone instead represents a major detachment horizon related to late Eo-Oligocene normal faults in the overlying units. Mylonitisation along the shear zone occurred under conditions postdating peak pressures. The shear zone formed between about 40 Ma and 34 Ma as indicated by the age of high temperature conditions in the hangingwall and the age of Oligocene granitoids crosscutting the mylonites. During this time, pronounced extension and basin formation took place in the hangingwall of the Nestos Shearzone. We propose that the brittle Mesta detachment, which bounds the Mesta Graben to the East, roots into the Nestos Shearzone. Themetamorphic history of the Pangaion-Pirin Unit as well as the proposed young age of the Nestos Shearzone is in conflict with studies proposing that this unit represents an independent microcontinent (Drama) accreted to the future Rhodopes in late Jurassic or early Cretaceous times. Instead, we propose that the Pangaion-Pirin Unit could be derived from the Apulian plate, which would have far reaching consequences for the structural architecture of the Hellenic orogen.

Mobility of partially molten crust, heat and mass transfer, and the stabilization of continents

NASA Astrophysics Data System (ADS)

Teyssier, Christian; Whitney, Donna L.; Rey, Patrice F.

2017-04-01

The core of orogens typically consists of migmatite terrains and associated crustal-derived granite bodies (typically leucogranite) that represent former partially molten crust. Metamorphic investigations indicate that migmatites crystallize at low pressure (cordierite stability) but also contain inclusions of refractory material (mafic, aluminous) that preserve evidence of crystallization at high pressure (HP), including HP granulite and eclogite (1.0-1.5 GPa), and in some cases ultrahigh pressure (2.5-3.0 GPa) when the continental crust was subducted (i.e. Norwegian Caledonides). These observations indicate that the partially molten crust originates in the deep crust or at mantle depths, traverses the entire orogenic crust, and crystallizes at shallow depth, in some cases at the near-surface ( 2 km depth) based on low-T thermochronology. Metamorphic assemblages generally show that this nearly isothermal decompression is rapid based on disequilibrium textures (symplectites). Therefore, the mobility of partially molten crust results in one of the most significant heat and mass transfer mechanisms in orogens. Field relations also indicate that emplacement of partially molten crust is the youngest major event in orogeny, and tectonic activity essentially ceases after the partially molten crust is exhumed. This suggests that flow and emplacement of partially molten crust stabilize the orogenic crust and signal the end of orogeny. Numerical modeling (open source software Underworld; Moresi et al., 2007, PEPI 163) provides useful insight into the mechanisms of exhumation of partially molten crust. For example, extension of thickened crust with T-dependent viscosity shows that extension of the shallow crust initially drives the mobility of the lowest viscosity crust (T>700°C), which begins to flow in a channel toward the zone of extension. This convergent flow generates channel collision and the formation of a double-dome of foliation (two subdomes separated by a steep high strain zone). In turn, the rapid exhumation of low-viscosity deep crust within and between the two subdomes enhances localization of extension in the shallow crust; the positive feedback between exhumation of low-viscosity crust and localization of shallow crust extension explains the exhuming power of migmatite domes, the rapid isothermal decompression of dome rocks (order of 1.0-1.5 GPa), and the crystallization of melt at shallow depth followed by rapid cooling. Modeling results indicate that the mobility of low-viscosity (partially molten) crust is a major process for transferring heat and mass during the late stages of orogeny.

Effect of ultra-high pressure on small animals, tardigrades and Artemia

NASA Astrophysics Data System (ADS)

Ono, Fumihisa; Mori, Yoshihisa; Takarabe, Kenichi; Fujii, Akiko; Saigusa, Masayuki; Matsushima, Yasushi; Yamazaki, Daisuke; Ito, Eiji; Galas, Simon; Saini, Naurang L.

2016-12-01

This research shows that small animals, tardigrades (Milnesium tardigradum) in tun (dehydrated) state and Artemia salina cists (dried eggs) can tolerate the very high hydrostatic pressure of 7.5 GPa. It was really surprising that living organisms can survive after exposure to such a high pressure. We extended these studies to the extremely high pressure of 20 GPa by using a Kawai-type octahedral anvil press. After exposure to this pressure for 30 min, the tardigrades were soaked in pure water and investigated under a microscope. Their bodies regained metabolic state and no serious injury could be seen. But they were not alive. A few of Artemia eggs went part of the way to hatching after soaked in sea water, but they never grew any further. Comparing with the case of blue-green alga, these animals are weaker under ultra-high pressure.

Control of Hydrogen Environment Embrittlement of Ultra-High Strength Steel for Naval Application

DTIC Science & Technology

2005-07-01

load cracking behavior of maraging steels in hydrogen. Corrosion , 29, 1973, 299-304. D.A. Jones, A.F. Jankowski and G.A. Davidson, "Diffusion of...short crack case. This behavior is relevant to small surface cracks in coated UHSS components such as a landing gear. IV.B. Effect of Steel Composition ...PRESSURE (k N /m 2) Figure 26. The effect of H2 pressure on the HEAC growth rate for a ultra-high strength 18Ni Maraging steel stressed in a highly

Exhumation rates of high pressure metamorphic rocks in subduction channels: The effect of Rheology

NASA Astrophysics Data System (ADS)

Gerya, T. V.; Stöckhert, B.

2002-04-01

Exhumation of high-pressure metamorphic rocks can take place with typical plate velocities of cm/year. This is consistent with a model of forced flow in a subduction channel. The (micro)structural record of exhumed metamorphic rocks indicates that stresses are generally too low to drive deformation of the bulk material by dislocation creep, according to a power-law rheology. Instead deformation appears to be localized in low-strength shear zones, and is dominated by dissolution precipitation creep or fluid assisted granular flow, implying a Newtonian rheology. 1D modeling shows that the effective rheology of the material in the subduction channel has a significant influence on the rate of exhumation. When the subduction flux either equals or exceeds the return flux, the maximum exhumation rate for Newtonian behavior of the material is at least twice as high (~1/3 of the subduction burial rate) compared to that for power-law creep (~1/6 of the subduction burial rate).

Intermediate P/T-type regional metamorphism of the Isua Supracrustal Belt, southern west Greenland: The oldest Pacific-type orogenic belt?

NASA Astrophysics Data System (ADS)

Arai, Tatsuyuki; Omori, Soichi; Komiya, Tsuyoshi; Maruyama, Shigenori

2015-11-01

The 3.7-3.8 Ga Isua Supracrustal Belt (ISB), southwest Greenland, might be the oldest accretionary complex on Earth. Regional metamorphism of the ISB has a potential to constrain the tectonothermal history of the Earth during the Eoarchean. Chemical and modal analyses of metabasite in the study area (i.e., the northeast part of the ISB) show that the metamorphic grade increases from greenschist facies in the northern part of the study area to amphibolite facies in the southern part. To determine the precise metamorphic P-T ranges, isochemical phase diagrams of minerals of metabasite were made using Perple_X. A synthesis of the estimated metamorphic P-T ranges of the ISB indicates that both the metamorphic pressure and temperature increase systematically to the south in the study area from 3 kbar and 380 °C to 6 kbar and 560 °C. The monotonous metamorphic P-T change suggests that the northeast part of the ISB preserves regional metamorphism resulting from the subduction of an accretionary complex although the ISB experienced metamorphic overprints during the Neoarchean. Both the presence of the regional metamorphism and an accretionary complex having originating at subduction zone suggest that the ISB may be the oldest Pacific-type orogenic belt. The progressive metamorphism can be considered as a record of intermediate-P/T type geothermal gradient at the subduction zone in the Eoarchean. Intermediate-P/T type geothermal gradient is typical at the current zones of subducting young oceanic crust, such as in the case of the Philippine Sea Plate in the southwest part of Japan. Considering the fact that almost all metamorphisms in the Archean are greenschist-amphibolite facies, the intermediate-P/T type geothermal gradient at the ISB might have been worldwide in the Archean. This would indicate that the subduction of young micro-plates was common because of the vigorous convection of hot mantle in the Archean.

Modélisation magnétotellurique de la structure géologique profonde de l’unité granulitique de l’In Ouzzal (Hoggar occidental)

NASA Astrophysics Data System (ADS)

Bouzid, Abderrezak; Akacem, Nouredine; Hamoudi, Mohamed; Ouzegane, Khadidja; Abtout, Abdeslam; Kienast, Jean-Robert

2008-11-01

Magnetotelluric modeling of the deep geologic structure of In Ouzzal Granulitic Unit (western Hoggar). The In Ouzzal Granulitic Unit (IOGU) or In Ouzzal Terrane (IOT) is an Archaean block belonging to the Hoggar terrane mosaic. It has been reworked during the Eburnean and is characterized by ultrahigh temperature metamorphism of the structures, which are likely to be old dome and basin structures. The aim of this study, based on a survey of 12 magnetotelluric (MT) soundings, was to characterize the IOGU deep lateral boundaries and to see if it is possible to reconstruct some of these old dome and basin structures after their transformation by metamorphism and deformation. MT data analysis and modeling show that IOGU boundaries extend downwards, at least down to the crust's basement, and may represent suture zones. Inside the terrane, the MT observations do not allow separation between dome and basin structures, because these features are severely stretched. However, the main MT transverse response feature is a deeply rooted great accident, which may be interpreted as a major fault that separates IOGU into two compartments.

Punctuated HT/UHT metamorphism during prolonged Archean orogenesis in the Pikwitonei Granulite Domain revealed by garnet petrochronology

NASA Astrophysics Data System (ADS)

Dragovic, Besim; Guevara, Victor; Caddick, Mark; Couëslan, Chris; Baxter, Ethan

2017-04-01

Fundamental to every modern continent's early (Archean) history is the generation of high temperature conditions required to produce the dense, strong, relatively anhydrous rocks that comprise most of Earth's stable cratonic crust. While the thermal gradients supported in Archean terranes are better understood, the timescales over which these conditions occur are more enigmatic. Garnet petrochronology allows for the interrogation of a semi-continuous record of these tectonometamorphic conditions, by linking pressure-temperature-fluid conditions (using phase equilibria modeling, trace element thermometry, stable isotope geochemistry) to a precise chronologic/chronometric record (e.g. high-precision Sm-Nd geochronology, geospeedometry of major and trace element diffusion profiles). Here, we utilize techniques from this burgeoning field of study to elucidate the rates and conditions of high temperature/ultra-high temperature (HT/UHT) metamorphism in the 2.7 Ga Pikwitonei Granulite Domain (PGD). The PGD represents over 150,000 km2 of dominantly granulite-facies metamorphic rocks situated at the NW edge of the Superior Province. Peak temperatures in the region range from 760°C in the southernmost part of the PGD, to 900-960˚C in the central/western PGD ( 40-60 km apart). Previous studies have suggested that metamorphism was long-lived in the region, occurring over 100 Ma, from 2.71-2.60 Ga [1, 2, 3]. High-precision garnet geochronology on microsampled garnets provides a detailed growth history of several lithologies across the region. Where necessary, bulk garnet analysis (i.e. dating based upon multiple whole garnet crystals rather than portions thereof) was also performed. While cooling from HT/UHT will result in some degree of intra-mineral age resetting, a detailed isotopic study of a range of large garnet porphyroblasts from the PGD (those which would be variably reset depending on peak T, grain size, and initial cooling rate) can retain information about both prograde, peak, and initial cooling history of the region. For example, fifteen Sm-Nd garnet ages were determined from a 7cm garnet from the southern PGD (peak T of 760˚C). The initiation of garnet growth was calculated to be 2666 ± 3 Ma, with the termination of garnet growth at 2610 ± 2 Ma, providing a growth duration of 56 ± 3 Ma. Across the larger, hotter, central and western parts of the PGD (peak T of 900-960˚C), major element zoning is preserved in garnets from throughout these localities, implying ultrahigh-temperature conditions over significantly shorter timescales. This suggests that while HT metamorphic conditions can be maintained region-wide for tens of Myr, punctuated UHT conditions that last for Myr to sub-Myr timescales occur locally. By integrating these petrochronological techniques to decipher P-T conditions and timescales, on samples from across the PGD, we seek to provide insight into the mechanisms for diachronous crustal heating and the formation of stable cratonic lithosphere. [1] Smit et al., 2013. EPSL, 381, 222-233. [2] Heaman et al., 2011. Can. J. Earth. Sci., 48, 205-245. [3] Guevara et al., 2016. AGU abstracts with programs

Pan-African granulites of central Dronning Maud Land and Mozambique: A comparison within the East-African-Antarctic orogen

USGS Publications Warehouse

Engvik, A.K.; Elevevold, S.; Jacobs, J.; Tveten, E.; de Azevedo, S.; Njange, F.

2007-01-01

Granulite-facies metamorphism is extensively reported in Late Neoproterozoic/Early Palaeozoic time during formation of the East-African-Antarctic orogen (EAAO). Metamorphic data acquired from the Pan-African orogen of central Dronning Maud Land (cDML) are compared with data from northern Mozambique. The metamorphic rocks of cDML are characterised by Opx±Grt-bearing gneisses and Sil+Kfs-bearing metapelites which indicate medium-P granulite-facies metamorphism. Peak conditions, which are estimated to 800-900ºC at pressures up to 1.0 GPa, were followed by near-isothermal decompression during late Pan-African extension and exhumation. Granulite-facies lithologies are widespread in northern Mozambique, and Grt+Cpx-bearing assemblages show that high-P granulite-facies conditions with PT reaching 1.55 GPa and 900ºC were reached during the Pan-African orogeny. Garnet is replaced by symplectites of Pl+Opx+Mag indicating isothermal decompression, and the subsequent formation of Pl+amphibole-coronas suggests cooling into amphibolite facies. It is concluded that high-T metamorphism was pervasive in EAAO in Late Neoproterozoic/Early Paleozoic time, strongly overprinting evidences of earlier metamorphic assemblages.

Urea Hydrogen Peroxide Reduces the Numbers of Lactobacilli, Nourishes Yeast, and Leaves No Residues in the Ethanol Fermentation

PubMed Central

Narendranath, N. V.; Thomas, K. C.; Ingledew, W. M.

2000-01-01

Urea hydrogen peroxide (UHP) at a concentration of 30 to 32 mmol/liter reduced the numbers of five Lactobacillus spp. (Lactobacillus plantarum, L. paracasei, Lactobacillus sp. strain 3, L. rhamnosus, and L. fermentum) from ∼107 to ∼102 CFU/ml in a 2-h preincubation at 30°C of normal-gravity wheat mash at ∼21 g of dissolved solids per ml containing normal levels of suspended grain particles. Fermentation was completed 36 h after inoculation of Saccharomyces cerevisiae in the presence of UHP, even when wheat mash was deliberately contaminated (infected) with L. paracasei at ∼107 CFU/ml. There were no significant differences in the maximum ethanol produced between treatments when urea hydrogen peroxide was used to kill the bacteria and controls (in which no bacteria were added). However, the presence of L. paracasei at ∼107 CFU/ml without added agent resulted in a 5.84% reduction in the maximum ethanol produced compared to the control. The bactericidal activity of UHP is greatly affected by the presence of particulate matter. In fact, only 2 mmol of urea hydrogen peroxide per liter was required for disinfection when mashes had little or no particulate matter present. No significant differences were observed in the decomposition of hydrogen peroxide in normal-gravity wheat mash at 30°C whether the bactericidal agent was added as H2O2 or as urea hydrogen peroxide. NADH peroxidase activity (involved in degrading H2O2) increased significantly (P = 0.05) in the presence of 0.75 mM hydrogen peroxide (sublethal level) in all five strains of lactobacilli tested but did not persist in cells regrown in the absence of H2O2. H2O2-resistant mutants were not expected or found when lethal levels of H2O2 or UHP were used. Contaminating lactobacilli can be effectively managed by UHP, a compound which when used at ca. 30 mmol/liter happens to provide near-optimum levels of assimilable nitrogen and oxygen that aid in vigorous fermentation performance by yeast. PMID:11010858

Chemical and oxygen isotope zonings in garnet from subducted continental crust record mineral replacement and metasomatism

NASA Astrophysics Data System (ADS)

Vho, Alice; Rubatto, Daniela; Regis, Daniele; Baumgartner, Lukas; Bouvier, Anne-Sophie

2017-04-01

Garnet is a key mineral in metamorphic petrology for constraining pressure, temperature and time paths. Garnet can preserve multiple growth stages due to its wide P-T stability field and the relatively slow diffusivity for major and trace elements at sub-solidus temperatures. Pressure-temperature-time-fluid paths of the host rock may be reconstructed by combining metamorphic petrology with microscale trace element and oxygen isotope measurements in garnet. Subduction zones represent relevant geological settings for geochemical investigation of element exchanges during aqueous fluid-rock interactions. The Sesia Zone consists of a complex continental sequence containing a variety of mono-metamorphic and poly-metamorphic lithologies such as metagranitoids, sediments and mafic boudins. The precursor Varisican-Permian amphibolite-facies basement (6-9 kbar 650-850°C; Lardeaux and Spalla, 1991; Robyr et al., 2013) experienced high pressure metamorphism (15-22 kbar 500-550°C; Regis, et al. 2014; Robyr et al., 2013) during Alpine subduction. In different lithologies of the Internal Complex (Eclogitic Micaschist Complex), including metabasites from the Ivozio Complex, Ti-rich metasediments from Val Malone and pre-Alpine Mn-quartzites associated to metagabbros from Cima Bonze, garnet is abundant and shows a variety of complex textures that cannot be reconciled with typical growth zoning, but indicate resorption and replacement processes and possible metasomatism. In-situ, microscale oxygen isotopes analysis of garnet zones was performed by ion microprobe with the SwissSIMS Cameca IMS 1280-HR at University of Lausanne and SHRIMP-SI at the Australian National University. Each sample has a distinct δ18O composition, and the δ18O values show different degrees of variation between domains. Homogeneously low values of < 5‰ are measured in the garnets from the Ivozio Complex metagabbro. Intragrain variations of up to 3.5‰ in the porphyroblasts from Val Malone metasediments, and variations up to 6.5‰ in Cima Bonze garnets suggest significant metasomatic replacement from external fluids. The combination of oxygen isotopes, trace element geochemistry and P-T modelling allows reconstructing the major stages of metasomatism, as well as identifying the nature of the fluid interacting with the rock at each metamorphic stage. REFERENCES Lardeaux, J. M., & Spalla, M. I. (1991). From granulites to eclogites in the Sesia zone (Italian Western Alps): A record of the opening and closure of the Piedmont ocean. Journal of Metamorphic Geology, 9, 35-59. Regis, D., Rubatto, D., Darling, J., Cenki-Tok, B., Zucali, M., & Engi, M. (2014). Multiple metamorphic stages within an eclogite-facies terrane (Sesia Zone, Western Alps) revealed by Th-U-Pb petrochronology. Journal of Petrology, 55(7), 1429-1456. Robyr, M., Darbellay, B., & Baumgartner, L. P. (2014). Matrix-dependent garnet growth in polymetamorphic rocks of the Sesia zone, Italian Alps. Journal of Metamorphic Geology, 32(1), 3-24.

High-pressure/low-temperature metamorphism in the collision zone between the Chilenia and Cuyania microcontinents (western Precordillera, Argentina)

NASA Astrophysics Data System (ADS)

Boedo, F. L.; Willner, A. P.; Vujovich, G. I.; Massonne, H.-J.

2016-12-01

In central-western Argentina, an Early Paleozoic belt including mafic-ultramafic bodies, marine metasedimentary rocks and high-pressure rocks occur along the western margin of the Precordillera and in the Frontal Cordillera. First pressure-temperature estimates are presented here for low-grade rocks of the southern sector of this belt based on two metasedimentary and one metabasaltic sample from the Peñasco Formation. Peak metamorphic conditions resulted within the range of 345-395 °C and 7.0-9.3 kbar within the high-pressure greenschist facies. The corresponding low metamorphic gradient of 13 °C/km is comparable with subduction related geothermal gradients. Comparison between these results and data from other localities of the same collision zone (Guarguaraz and Colohuincul complexes) confirms a collision between Chilenia and the composite margin of western Gondwana and suggests a stronger crustal thickening in the south of the belt, causing exhumation of more deeply buried sequences. During the Early Paleozoic a long-lived marine sedimentation coupled with the intrusion of MORB-like basalts occurred along a stable margin before the collision event. This contrasts with the almost contemporaneous sedimentation registered during accretion in accretionary prism settings and additionally proves the development of a collision zone along western Precordillera and the eastern Frontal Cordillera as well as the existence of Chilenia as a separate microcontinent.

Decoding a protracted zircon geochronological record in ultrahigh temperature granulite, and persistence of partial melting in the crust, Rogaland, Norway

NASA Astrophysics Data System (ADS)

Laurent, Antonin T.; Bingen, Bernard; Duchene, Stephanie; Whitehouse, Martin J.; Seydoux-Guillaume, Anne-magali; Bosse, Valerie

2018-04-01

This contribution evaluates the relation between protracted zircon geochronological signal and protracted crustal melting in the course of polyphase high to ultrahigh temperature (UHT; T > 900 °C) granulite facies metamorphism. New U-Pb, oxygen isotope, trace element, ion imaging and cathodoluminescence (CL) imaging data in zircon are reported from five samples from Rogaland, South Norway. The data reveal that the spread of apparent age captured by zircon, between 1040 and 930 Ma, results both from open-system growth and closed-system post-crystallization disturbance. Post-crystallization disturbance is evidenced by inverse age zoning induced by solid-state recrystallization of metamict cores that received an alpha dose above 35 × 1017 α g-1. Zircon neocrystallization is documented by CL-dark domains displaying O isotope open-system behaviour. In UHT samples, O isotopic ratios are homogenous (δ18O = 8.91 ± 0.08‰), pointing to high-temperature diffusion. Scanning ion imaging of these CL-dark domains did not reveal unsupported radiogenic Pb. The continuous geochronological signal retrieved from the CL-dark zircon in UHT samples is similar to that of monazite for the two recognized metamorphic phases (M1: 1040-990 Ma; M2: 940-930 Ma). A specific zircon-forming event is identified in the orthopyroxene and UHT zone with a probability peak at ca. 975 Ma, lasting until ca. 955 Ma. Coupling U-Pb geochronology and Ti-in-zircon thermometry provides firm evidence of protracted melting lasting up to 110 My (1040-930 Ma) in the UHT zone, 85 My (ca. 1040-955 Ma) in the orthopyroxene zone and some 40 My (ca. 1040-1000 Ma) in the regional basement. These results demonstrate the persistence of melt over long timescales in the crust, punctuated by two UHT incursions.

P-T paths of ophiolite-related metamorphic rocks from the Dinaride ophiolite zone in Bosnia

NASA Astrophysics Data System (ADS)

Balen, Dražen; Massonne, Hans-Joachim; Koller, Friedrich; Theye, Thomas; Opitz, Joachim; Hrvatović, Hazim; Premužak, Lucija

2017-04-01

The Dinarides, an Alpine mountain chain in south-eastern Europe, is characterized by complex fold, thrust, and imbricate structures. Partially dismembered ophiolites, a regular part of the Inner Dinarides, are considered as separate ultramafic massifs. The large Krivaja-Konjuh ultramafic massif (KKUM) within the Dinaride Ophiolite Zone (DOZ), composed of tectonic spinel lherzolite, occurs as NE-dipping thrust sheet underlain by gradually decreasing, up to 1200 m thick, high- to medium-grade metamorphic rocks. The metamorphic rocks geochemically resemble MORB-like rocks with tholeiitic signature. Such metamorphic rocks, which originated from cumulate gabbro and/or troctolite, are mainly represented by granulite and amphibolite varieties (subordinate eclogite and epidote-amphibolite facies metamafic rocks are also present) with various proportions of amphibole, plagioclase, pyroxenes (diopside and hypersthene), garnet, corundum, sapphirine, spinel and quartz. These rocks vary in textures (granoblastic, porphyroblastic and nematoblastic) and grain size (coarse- to fine-grain varieties). Conventional thermobarometry of garnet- and clinopyroxene-bearing amphibolites directly beneath the contact to the overlying peridotite resulted in peak pressure (P) - temperature (T) conditions of 10-12 kbar (depth of ca. 35-40 km) and 745-830°C. Those amphibolites without clinopyroxene but with garnet experienced peak conditions of 7 kbar and 630°C. Amphibole + plagioclase amphibolite gave temperatures of 670-730 °C and lowermost-grade amphibolites yielded peak temperatures of 550°C. These estimates are thought to reflect the metamorphic conditions during the Late Jurassic obduction of the hot upper mantle part of the KKUM onto the ophiolite mélange. The hot obducted ultramafic fragments acted as a heat source for metamorphism that transformed cumulate gabbroic protolith into high- to medium-grade amphibolites and granulites. P-T pseudosections constructed for various metamorphic rock types in the MnNCFMASHTO system, contoured by mineral isopleths and modes, combined with chemical zonation of garnet (elucidated by X-ray mapping), succession of accessory Ti-minerals (ilmenite -> rutile -> titanite) and textural features (particularly occurrence of complex kelyphite textures around garnet and clinopyroxene) gave us important clues for P-T paths (re)constructions. The petrographic details and mineral chemistry point to composite clockwise P-T paths characterized by high-temperature high-pressure conditions (ca. 20 kbar, 700 °C for garnet- and amphibole-bearing metaperidotite), followed by significant pressure decrease to medium-pressure values accompanied by temperature increase to > 830 °C. Such a composite P-T path can be interpreted in the frame of Late Jurassic to Early Cretaceous regional geodynamic processes that involve collision at the edge of the Adriatic microplate, intra-oceanic NE-dipping subduction and underplating of mafic cumulate rocks under the hot upper mantle part of the KKUM and subsequent erosional events. Processes of the final emplacement of the KKUM metamorphic rocks must have been terminated in Early Cretaceous times as indicated by amphibolite fragments in the adjacent Pogari Formation overlying the ophiolite mélange. Support by the Croatian Science Foundation (IP-2014-09-9541) is acknowledged.

In situ study of maize starch gelatinization under ultra-high hydrostatic pressure using X-ray diffraction.

PubMed

Yang, Zhi; Gu, Qinfen; Hemar, Yacine

2013-08-14

The gelatinization of waxy (very low amylose) and high-amylose maize starches by ultra-high hydrostatic pressure (up to 6 GPa) was investigated in situ using synchrotron X-ray powder diffraction on samples held in a diamond anvil cell (DAC). The starch pastes, made by mixing starch and water in a 1:1 ratio, were pressurized and measured at room temperature. X-ray diffraction pattern showed that at 2.7 GPa waxy starch, which displayed A-type XRD pattern at atmospheric pressure, exhibited a faint B-type-like pattern. The B-type crystalline structures of high-amylose starch were not affected even when 1.5 GPa pressure was applied. However, both waxy and high-amylose maize starches can be fully gelatinized at 5.9 GPa and 5.1 GPa, respectively. In the case of waxy maize starch, upon release of pressure (to atmospheric pressure) crystalline structure appeared as a result of amylopectin aggregation. Copyright © 2013 Elsevier Ltd. All rights reserved.

Flavor characterization of sugar-added pennywort (Centella asiatica L.) juices treated with ultra-high pressure and thermal processes.

PubMed

Apichartsrangkoon, Arunee; Wongfhun, Pronprapa; Gordon, Michael H

2009-01-01

The flavor characteristics of pennywort juices with added sugar treated by ultra-high pressure, pasteurization, and sterilization were investigated using solid phase microextraction combined with gas chromatography-mass spectrometry. It was found that sesquiterpene hydrocarbons comprised the major class of volatile components present and the juices had a characteristic aroma due to the presence of volatiles including beta-caryophyllene and humulene and alpha-copaene. In comparison with heated juices, HPP-treated samples could retain more volatile compounds such as linalool and geraniol similar to those present in fresh juice, whereas some volatiles such as alpha-terpinene and ketone class were apparently formed by thermal treatment. All processing operations produced juice that was not significantly different in the concentration of total volatiles. Practical Application: Pennywort juice is considered a nutraceutical drink for health benefits. Therefore, to preserve all aroma and active components in this juice, a nonthermal process such as ultra-high pressure should be a more appropriate technique for retention of its nutritive values than pasteurization and sterilization.

Linking monazite geochronology with fluid infiltration and metamorphic histories: Nature and experiment

NASA Astrophysics Data System (ADS)

Shazia, J. R.; Harlov, D. E.; Suzuki, K.; Kim, S. W.; Girish-Kumar, M.; Hayasaka, Y.; Ishwar-Kumar, C.; Windley, B. F.; Sajeev, K.

2015-11-01

Migmatised metapelites from the Kodaikanal region, central Madurai Block, southern India have undergone ultrahigh-temperature metamorphism (950-1000 °C; 7-8 kbar). In-situ electron microprobe Th-U-Pb isochron (CHIME) dating of monazites in a leucosome and surrounding silica-saturated and silica-poor restites from the same outcrop indicates three principal ages that can be linked to the evolutionary history of these rocks. Monazite grains from the silica-saturated restite have well-defined, inherited cores with thick rims that yield an age of ca. 1684 Ma. This either dates the metamorphism of the original metapelite or is a detrital age of inherited monazite. Monazite grains from the silica-poor restite, thick rims from the silica-saturated restite, and monazite cores from the leucosome have ages ranging from 520 to 540 Ma suggesting a mean age of 530 Ma within the error bars. In the leucosome the altered rim of the monazite gives an age of ca. 502 Ma. Alteration takes the form of Th-depleted lobes of monazite with sharp curvilinear boundaries extending from the monazite grain rim into the core. We have replicated experimentally these altered rims in a monazite-leucosome experiment at 800 °C and 2 kbar. This experiment, coupled with earlier published monazite-fluid experiments involving high pH alkali-bearing fluids at high P-T, helps to confirm the idea that alkali-bearing fluids, in the melt and along grain boundaries during crystallization, were responsible for the formation of the altered monazite grain rims via the process of coupled dissolution-reprecipitation.

Partial eclogitization of the Ambolten gabbro-norite, north-east Greenland Caledonides

USGS Publications Warehouse

Gilotti, J.A.; Elvevold, S.

1998-01-01

Partially eclogitized igneous bodies composed of gabbro, leucogabbro, anorthosite and cross-cutting diabase dikes are well represented in the North-East Greenland Eclogite Province. A 200 x 100 meter intrusive body on Ambolten Island (78?? 20' N, 19?? 15' W) records a prograde transition from gabbro-norite to eclogite facies coronitic metagabro-norite surrounded by hydrated margins of undeformed to strongly foliated amphibolite. Igneous plagioclase + olivine + enstatite + augite + oxides convert to eclogite facies assemblages consisting of garnet, omphacite, diopside, enstatite, kyanite, zoisite, rutile and pargasitic amphibole through several coronitic reactions. Relict cumulus plagioclase laths are replaced by an outer corona of garnet, an inner corona of omphacite and an internal region of sodic plagioclase, garnet, kyanite, omphacite and zoisite. Olivine and intercumulus pyroxene are partly replaced by metamorphic pyroxenes and amphibole. The corona structures, zoning patterns, diversity of mineral compositions in a single thin section, and preservation of metastable asemblages are characteristic of diffusion-controlled metamorphism. The most extreme disequilibrium is found in static amphibolites, where igneous pyroxenes, plagioclase domains with eclogite facies, assemblages, and matrix amphibole coexist. Complete eclogitization was not attained at Ambolten due to a lack of fluids needed to drive diffusion during prograde and retrograde metamorphism. The P-T conditions of the high-pressure metamorphism are estimated at ??? 750??C and > 18 kbar. Well-equilibrated, foliated amphibolites from the margin of the gabbro-norite supports our contention that the entire North-East Greenland Eclogite Province experienced Caledonian high-pressure metamorphism, even though no eclogite facies assemblages have been found in the quartzofeldspathic host gneisses to date.

Origin and geodynamic significance of the early Mesozoic Weiya LP and HT granulites from the Chinese Eastern Tianshan

NASA Astrophysics Data System (ADS)

Mao, Ling-Juan; He, Zhen-Yu; Zhang, Ze-Ming; Klemd, Reiner; Xiang, Hua; Tian, Zuo-Lin; Zong, Ke-Qing

2015-12-01

The Chinese Tianshan in the southwestern part of the Central Asian Orogenic Belt (CAOB) is characterized by a variety of high-grade metamorphic rocks, which provide critical constraints for understanding the geodynamic evolution of the CAOB. In this paper, we present detailed petrological and zircon U-Pb geochronological studies of the Weiya low-pressure and high-temperature (LP-HT) granulites of the Chinese Eastern Tianshan. These granulites were previously considered to be a product of a regional metamorphic orogenic event. Due to different bulk-rock chemistries the Weiya granulites, which occur as lenses within the contact metamorphic aureole of the Weiya granitic ring complex, have a variety of felsic-pelitic and mafic granulites with different textural equilibrium mineral assemblages including garnet-cordierite-sillimanite-bearing granulites, cordierite-sillimanite-bearing granulites, cordierite-orthopyroxene-bearing granulites, and orthopyroxene-clinopyroxene-bearing granulites. Average P-T thermobarometric calculations and conventional geothermobarometry indicates that the Weiya granulites underwent early prograde metamorphism under conditions of 600-650 °C at 3.2-4.2 kbar and peak metamorphism of 750-840 °C at 2.9-6.3 kbar, indicating a rather high geothermal gradient of ca. 60 °C/km. Zircon U-Pb LA-ICP-MS dating revealed metamorphic ages between 244 ± 1 to 237 ± 3 Ma, which are in accordance with the crystallization age of the Weiya granitic ring complex. We suggest that the formation of the Weiya granulites was related to contemporaneous granitic magmatism instead of a regional metamorphic orogenic event. In addition, a Late Devonian metamorphic age of ca. 380 Ma was recorded in zircon mantle domains from two pelitic samples which is consistent with the metamorphic age of the Xingxingxia metamorphic complex in the Chinese Eastern Tianshan. This suggests that the mantle domains of the zircon grains of the Weiya granulites probably formed during the Late Devonian regional metamorphism and were overprinted by the Early Triassic contact metamorphism. Therefore, Early Triassic geodynamic models for the southwestern part of the CAOB, which are based on a previously suggested regional metamorphic orogenic event of the Weiya granulites, need to be viewed with caution.

Age and composition of the UHP garnet peridotites in the Dabie orogenic belt (central China) record complex crust-mantle interaction in continental margin

NASA Astrophysics Data System (ADS)

Zhao, Y.; Zheng, J.; Wang, B.

2017-12-01

The Dabie-Sulu UHP belt was created by the collision between the North and South China cratons in Middle Triassic time (240-225 Ma). There are lots of garnet-bearing ultramafic body occurs as a lens in the belt. Age and composition of the Maowu garnet peridotites in the Dabie orogenic belt are reported. The garnet harzburgites are main moderately refractory (Mg#Ol=92) and minor fertile (Mg#Ol=88) with high Ni (2344-2603 ppm) and low Al2O3 (0.35-0.54 wt.%), CaO (0.76-2.19 wt.%) and TiO2 (˜0.01 wt.%). Zircons in the harzburgites mainly document metamorphism at 230 ± 2 Ma, 275 ± 5 Ma, 357 ± 4 Ma, and complex minor populations of ages including: 1.8 Ga, 1.3 Ga, and Neoproterozic-early Paleozoic ages (901-420 Ma). The early Meszosic and late Paleozoic zircons have similar trace-element patterns and ranges in ɛHf(t) (+0.6 to +3.4), Th/U ratio (0.2-0.7) and Hf depleted-mantle model ages (TDM ) mainly cluster in the interval 1.2-0.9 Ga. In contrast, the Paleo-Mesoproterozoic zircons have negative ɛHf(t) (-24.9 to -2.7) and oldest Hf TDM = 3.4Ga. Zircons of Neoproterozic-early Paleozoic have a wide range of Hf depleted-mantle model ages (2.4-0.7Ga) and ɛHf(t) (-15.3 to +9.5). Above of the all, we suggest that the Maowu garnet harzburgites are interpreted as a fragment of the metasomatized ancient lithospheric mantle beneath the southern margin of the North China Craton. They experienced the Proterozoic thermal event (1.9-1.8Ga), which is coeval with the assembly of the supercontinent Columbia. And then 1.3Ga mantle metasomatism with asthenospheric materials resulted in the final breakup of the Columbia supercontinent. Neoproterozic-early Paleozoic (901-420 Ma), deep parts of the south margin of the craton were metasomatized during the assembly and breakup of the Rodinia supercontinent. Then, the southern margin of the craton occurred oceanic crust subduction ( 357 Ma), subsequent continental deep subduction and final continent-continent collision in Triassic.

Metamorphic P-T-t path retrieved from metapelites in the southeastern Taihua metamorphic complex, and the Paleoproterozoic tectonic evolution of the southern North China Craton

NASA Astrophysics Data System (ADS)

Lu, Jun-Sheng; Zhai, Ming-Guo; Lu, Lin-Sheng; Wang, Hao Y. C.; Chen, Hong-Xu; Peng, Tao; Wu, Chun-Ming; Zhao, Tai-Ping

2017-02-01

The Taihua metamorphic complex in the southern part of the North China Craton is composed of tonalite-trondhjemite-granodiorite (TTG) gneisses, amphibolites, metapelitic gneisses, marbles, quartzites, and banded iron formations (BIFs). The protoliths of the complex have ages ranging from ∼2.1 to ∼2.9 Ga and was metamorphosed under the upper amphibolite to granulite facies conditions with NWW-SEE-striking gneissosity. Metapelitites from the Wugang area have three stages of metamorphic mineral assemblages. The prograde metamorphic mineral assemblage (M1) includes biotite + plagioclase + quartz + ilmenite preserved as inclusions in garnet porphyroblasts. The peak mineral assemblage (M2) consists of garnet porphyroblasts and matrix minerals of sillimanite + biotite + plagioclase + quartz + K-feldspar + ilmenite + rutile + pyrite. The retrograde mineral assemblage (M3), biotite + plagioclase + quartz, occurs as symplectic assemblages surrounding embayed garnet porphyroblasts. Garnet porphyroblasts are chemically zoned. Pseudosection calculated in the NCKFMASHTO model system suggests that mantles of garnet porphyroblasts define high-pressure granulites facies P-T conditions of 12.2 kbar and 830 °C, whereas garnet rims record P-T conditions of 10.2 kbar and 840 °C. Integrating the prograde mineral assemblages, zoning of garnet porphyroblasts with symplectic assemblages, a clockwise metamorphic P-T path can be retrieved. High resolution SIMS U-Pb dating and LA-ICP-MS trace element measurements of the metamorphic zircons demonstrate that metapelites in Wugang possibly record the peak or near peak metamorphic ages of ∼1.92 Ga. Furthermore, 40Ar/39Ar dating of biotite in metapelites suggests that the cooling of the Taihua complex may have lasted until ∼1.83 Ga. Therefore, a long-lived Palaeoproterozoic metamorphic event may define a slow exhumation process. Field relationship and new metamorphic data for the Taihua metamorphic complex does not support the previous model in which the Tran-North China Craton (TNCO) was formed through the collision between the East and West blocks.

Pseudo- and real-inverted metamorphism caused by the superposition and extrusion of a stack of nappes: a case study of the Southern Brasília Orogen, Brazil

NASA Astrophysics Data System (ADS)

da Motta, Rafael Gonçalves; Moraes, Renato

2017-10-01

The Southern Brasília Orogen is a Neoproterozoic belt that occurs along the southernmost border of the São Francisco Craton where the Andrelândia Nappe System represents the subducted sedimentary domain and is divided into three allochthonous groups, of which the ages and P-T conditions of metamorphism are studied here. The basal unit, the Andrelândia Nappe, exhibits an inverted metamorphic pattern. The base of the structure, composed of staurolite, garnet, biotite, kyanite, quartz, and muscovite, marks the metamorphic peak, whereas at the top, the association of the metamorphic peak does not contain staurolite. The Liberdade Nappe, the middle unit, presents a normal metamorphic pattern; its base, close to the Andrelândia Nappe, shows paragneiss with evidence of in situ partial melting, and towards the top, coarse-grained staurolite schist is found. The staurolite-out and melt-in isograds are coincident and parallel to the main foliation. Thus, the shear zone that limits the nappes is syn-metamorphic, reheating the underlying Andrelândia Nappe and influencing the establishment of metamorphic inversion. This suggestion is supported by the monazite chemical ages, which indicates that the Andrelândia Nappe metamorphic peak (586 ± 15 Ma) is younger than that of the Liberdade Nappe (622.3 ± 7.6 Ma). The upper unit, the Serra da Natureza Klippe, bears a typical high-pressure granulite mineral assemblage that is composed of kyanite, garnet, K-feldspar, rutile, and leucosome, as well as a metamorphic peak at 604.5 ± 6.1 Ma. This tectonic assembly, with inverted and non-inverted metamorphic patterns and generation of klippen structures, is consistent with exhumation models and a strong indentor located in the lower continental crust.

Eclogites and garnet clinopyroxenites in the Anrakhai complex, Central Asian Orogenic Belt, Southern Kazakhstan: P-T evolution, protoliths and some geodynamic implications

NASA Astrophysics Data System (ADS)

Pilitsyna, Anfisa V.; Tretyakov, Andrey A.; Degtyarev, Kirill E.; Cuthbert, Simon J.; Batanova, Valentina G.; Kovalchuk, Elena V.

2018-03-01

The Anrakhai Metamorphic Complex (AMC), located in the SE part of the Chu-Ili Mountains of Southern Kazakhstan in the western part of Central Asian Orogenic Belt, exhibits occurrences of HP metamorphic rocks in the form of eclogites and garnet clinopyroxenites with peak metamorphic conditions of 750-850° and 15-19 kbar estimated with both conventional geothermobarometric methods and phase diagram modeling. P-T estimates as well as intimate field relations evidently imply a common metamorphic history for eclogites and garnet clinopyroxenites of the AMC. These high-pressure, medium temperature eclogite facies P-T conditions are indicative of a collision or subduction tectonic setting. Major and trace element geochemistry suggests that they probably had a common magmatic origin as part of a suite of differentiated tholeiitic intrusions. Furthermore, distinctive mineral and chemical compositions of these eclogites and garnet clinopyroxenites correspond to the Fe-Ti type of ultramafic rocks suggesting that they may have been derivatives of intraplate tholeiitic melts, introduced into continental crust before HP metamorphism.

Spatiotemporal evolution of magmatic pulses and regional metamorphism during a Cretaceous flare-up event: Constraints from the Ryoke belt (Mikawa area, central Japan)

NASA Astrophysics Data System (ADS)

Takatsuka, Kota; Kawakami, Tetsuo; Skrzypek, Etienne; Sakata, Shuhei; Obayashi, Hideyuki; Hirata, Takafumi

2018-05-01

The spatiotemporal relationship between granitoid intrusions and low-pressure/temperature type regional metamorphism in the Ryoke belt (Mikawa area) is investigated to understand the tectono-thermal evolution of the upper- to middle-crust during a Cretaceous flare-up event at the Eurasian active continental margin. Three plutono-metamorphic stages are recognized; (1) 99-84 Ma: intrusion of granitoids (99-95 Ma pulse) into the upper crust and high-T regional metamorphism reaching sillimanite-grade (97.0 ± 4.4 Ma to 88.5 ± 2.5 Ma) in the middle crust, (2) 81-75 Ma: intrusion of gneissose granitoids (81-75 Ma Ma pulse) into the middle crust at 19-24 km depth, and (3) 75-69 Ma: voluminous intrusions of massive to weakly-foliated granitoids (75-69 Ma pulse) at 9-13 km depth and formation of contact metamorphic aureoles. Cooling of the highest-grade metamorphic zone below the wet solidus of granitic rocks is estimated at 88.5 ± 2.5 Ma. At ca. 75 Ma, the upper-middle crustal section underwent northward tilting, resulting in the exhumation of regional metamorphic zones to 9-13 km depth. Although the highest-grade metamorphic rocks and the 99-95 Ma pulse granitoids preserve similar U-Pb zircon ages, the absence of spatial association suggests that the regional metamorphic zones were mainly produced by a transient thermal anomaly in the mantle and thermal conduction through the crust, supplemented by localized advection due to granitoid intrusions. The successive emplacement of granitoids into shallow, deep and shallow levels of the crust was probably controlled by the combination of change in thermal structure of the crust and tectonics during granitoid intrusions.

Phase equilibria modelling and zircon dating for Precambrian metapelites from Xinghuadukou Group in Lvlin Forest of Erguna Massif, NE China

NASA Astrophysics Data System (ADS)

Xu, Jiulei; Zheng, Changqing; Tajcmanova, Lucie; Zhong, Xin; Xu, Xuechun; Han, Xiaomeng; Wang, Zhaoyuan

2017-04-01

Xinghuadukou Group, the basement metamorphic complex of Erguna Massif in NE China, is considered to be Mesoproterozoic with Sm-Nd age of 1157±32 Ma. However, the new zircon data from these metamorphic supracrustal rocks in Lvlin Forest show that they formed in Neoproterozoic with the age of 800 Ma. Old zircon age with 2.5 Ga, 2.0 Ga and 1.8 Ga, indicate that the Erguna Massif had an affinity to both Columbia and Rodinia continents. Furthermore, we also present 500 Ma metamorphic age in micashists and 500 Ma age of adjacent granitoids that might have thermally influenced its surrounding. No detailed studies have been undertaken on the metamorphic evolution of the Xinghuadukou Complex. The typical paragneissic mineral assemblage of garnet sillimanite mica schist is Grt+Sil+Bt+Mus+Qtz±Kfs. (Zhou et al., 2011) proposed that the Xinghuadukou Complex appears to have undergone similar granulite facies metamorphic conditions based on the similarity of mineral assemblages to the Mashan Complex in the Jiamusi Massif, NE China. However, the new phase equilibria modelling result shows that these rocks are high amphibolite facies product with 650℃. We can easily find K-feldspar formed by partial melting due to the consuming of muscovite. Also the remaining muscovite is directly connected with a fluid channel in thin sections which indicate that the remaining muscovite formed from retrograde with the existence of fluid. The zoned garnet has low MgO and high CaO content in rims and high MgO and low CaO content in core. It seems that this garnet has high pressure and low temperature (HP-LT) in rims and low pressure and high temperature (LP-HT) in core which would point to an anti-clockwise metamorphic evolution. Zhou, J.B., Wilde, S.A., Zhang, X.Z., Zhao, G.C., Liu, F.L., Qiao, D.W., Ren, S.M. and Liu, J.H., 2011b. A> 1300km late Pan-African metamorphic belt in NE China: new evidence from the Xing'an block and its tectonic implications. Tectonophysics, 509(3): 280-292.

The problem of the age and structural position of the Blyb metamorphic complex (Fore Range zone, Great Caucasus) granitoids.

NASA Astrophysics Data System (ADS)

Kamzolkin, Vladimir; Latyshev, Anton; Ivanov, Stanislav

2016-04-01

The Blyb metamorphic complex (BMC) of the Fore Range zone is one of the most high-grade metamorphosed element of the Great Caucasus fold belt. Determination of the timing and the mechanism of formation of the Fore Range fold-thrust structures are not possible without investigation of the BMC located at the basement of its section. At the same time, the conceptions about its structure and age are outdated and need revision. Somin (2011) determined the age of the protolith and metamorphism of the Blyb complex as the Late Devonian - Early Carboniferous. We have recently shown that the BMC has not the dome, as previously thought, but nappe structure (Vidjapin, Kamzolkin, 2015), and is metamorphically coherent with the peak metamorphism pressures up to 22 kbar (Kamzolkin et al., 2015; Konilov et al., 2013). Considering the age and structure of the Blyb complex it is necessary to revise the age of granitoid intrusions and their relations with gneisses and schists, which constitute the main part of the section of the complex. Most authors (Gamkrelidze, Shengelia, 2007; Lavrischev, 2002; Baranov, 1967) adheres to Early Paleozoic age of intrusives, which is doubtful, considering the younger age of metamorphic rocks. We suppose, that the intrusive bodies broke through a BMC nappe structure during the exhumation of the complex (Perchuk, 1991) at the Devonian - Carboniferous boundary. Seemingly, the massive monzodiorites body (Lavrischev, 2002), intruding garnet-muscovite schists and amphibolite gneisses of the Blyb complex and cut by the Main Caucasian fault (MCF), are younger. Given the timing of termination of the MCF movement activity as the Middle Jurassic (Greater Caucasus..., 2005), their age should be in the Early Carboniferous - Middle Jurassic interval. At the same time, on the modern geological map (Lavrischev, 2002) monzodiorites body is assigned to the Middle Paleozoic. The study of the BMC granitoids and monzodiorites will help in determining of the mechanism and age of exhumation of the Blyb metamorphic complex high-pressure rocks. The reported study was partially supported by RFBR, research projects No. 16-35-00571mol_a; 16-05-01012a

Zircon (Hf, O isotopes) as melt indicator: Melt infiltration and abundant new zircon growth within melt rich layers of granulite-facies lenses versus solid-state recrystallization in hosting amphibolite-facies gneisses (central Erzgebirge, Bohemian Massif)

NASA Astrophysics Data System (ADS)

Tichomirowa, Marion; Whitehouse, Martin; Gerdes, Axel; Schulz, Bernhard

2018-03-01

In the central Erzgebirge within the Bohemian Massif, lenses of high pressure and ultrahigh pressure felsic granulites occur within meta-sedimentary and meta-igneous amphibolite-facies felsic rocks. In the felsic granulite, melt rich parts and restite form alternating layers, and were identified by petrology and bulk rock geochemistry. Mineral assemblages representing the peak P-T conditions were best preserved in melanocratic restite layers. In contrast, in the melt rich leucocratic layers, garnet and related HP minerals as kyanite are almost completely resorbed. Both layers display differences in accessory minerals: melanosomes have frequent and large monazite and Fe-Ti-minerals but lack xenotime and apatite; leucosomes have abundant apatite and xenotime while monazite is rare. Here we present a detailed petrographic study of zircon grains (abundance, size, morphology, inclusions) in granulite-facies and amphibolite-facies felsic gneisses, along with their oxygen and hafnium isotope compositions. Our data complement earlier Usbnd Pb ages and trace element data (REE, Y, Hf, U) on zircons from the same rocks (Tichomirowa et al., 2005). Our results show that the degree of melting determines the behaviour of zircon in different layers of the granulites and associated amphibolite-facies rocks. In restite layers of the granulite lenses, small, inherited, and resorbed zircon grains are preserved and new zircon formation is very limited. In contrast, new zircons abundantly grew in the melt rich leucocratic layers. In these layers, the new zircons (Usbnd Pb age, trace elements, Hf, O isotopes) best preserve the information on peak metamorphic conditions due to intense corrosion of other metamorphic minerals. The new zircons often contain inherited cores. Compared to cores, the new zircons and rims show similar or slightly lower Hf isotope values, slightly higher Hf model ages, and decreased oxygen isotope ratios. The isotope compositions (Hf, O) of new zircons indicate partial Hf isotope homogenization in the melt, and melt infiltration from an external source. New zircon was most likely formed by a peritectic reaction with melt above the wet solidus (peritectic zircon). Conversely, the amphibolite-facies host gneisses lack indications of significant melt production. Pre-metamorphic zircons experienced mainly solid-state recrystallization and variable Pb loss with only minor new zircon formation. However, subtle changes in cathodoluminescence pattern, in the Hf and O isotopes, and in the Lu/Hf, Yb/Hf ratios of zircons suggest that small volumes of melt were locally present. In difference to granulites, melt was internally produced. The detection of low degree melts (inferred from zircon geochemistry) is extremely important for the rheology because these amphibolite-facies rocks could act as large scale ductile shear zones. The new zircon data support a different P-T path for closely spaced amphibolite- and granulite-facies rocks.

Shock metamorphism of planetary silicate rocks and sediments: Proposal for an updated classification system

NASA Astrophysics Data System (ADS)

Stöffler, Dieter; Hamann, Christopher; Metzler, Knut

2018-01-01

We reevaluate the systematics and geologic setting of terrestrial, lunar, Martian, and asteroidal "impactites" resulting from single or multiple impacts. For impactites derived from silicate rocks and sediments, we propose a unified and updated system of progressive shock metamorphism. "Shock-metamorphosed rocks" occur as lithic clasts or melt particles in proximal impactites at impact craters, and rarely in distal impactites. They represent a wide range of metamorphism, typically ranging from unshocked to shock melted. As the degree of shock metamorphism, at a given shock pressure, depends primarily on the mineralogical composition and the porosity of a rock or sediment sample, different shock classification systems are required for different types of planetary rocks and sediments. We define shock classification systems for eight rock and sediment classes which are assigned to three major groups of rocks and sediments (1) crystalline rocks with classes F, M, A, and U; (2) chondritic rocks (class C); and (3) sedimentary rocks and sediments with classes SR, SE, and RE. The abbreviations stand for felsic (F), mafic (M), anorthositic (A), ultramafic (U), sedimentary rocks (SR), unconsolidated sediments (SE), and regoliths (RE). In each class, the progressive stages of shock metamorphism are denominated S1 to Sx. These progressive shock stages are introduced as: S1-S7 for F, S1-S7 for M, S1-S6 for A, S1-S7 for U, S1-S7 for C, S1-S7 for SR, S1-S5 for SE, and S1-S6 for RE. S1 stands for "unshocked" and Sx (variable between S5 and S7) stands for "whole rock melting." We propose a sequence of symbols characterizing the degree of shock metamorphism of a sample, i.e., F-S1 to F-S7 with the option to add the tabulated pressure ranges (in GPa) in parentheses.

Role of DNA protection and repair in resistance of Bacillus subtilis spores to ultrahigh shock pressures simulating hypervelocity impacts.

PubMed

Moeller, Ralf; Horneck, Gerda; Rabbow, Elke; Reitz, Günther; Meyer, Cornelia; Hornemann, Ulrich; Stöffler, Dieter

2008-11-01

Impact-induced ejections of rocks from planetary surfaces are frequent events in the early history of the terrestrial planets and have been considered as a possible first step in the potential interplanetary transfer of microorganisms. Spores of Bacillus subtilis were used as a model system to study the effects of a simulated impact-caused ejection on rock-colonizing microorganisms using a high-explosive plane wave setup. Embedded in different types of rock material, spores were subjected to extremely high shock pressures (5 to 50 GPa) lasting for fractions of microseconds to seconds. Nearly exponential pressure response curves were obtained for spore survival and linear dependency for the induction of sporulation-defective mutants. Spores of strains defective in major small, acid-soluble spore proteins (SASP) (alpha/beta-type SASP) that largely protect the spore DNA and spores of strains deficient in nonhomologous-end-joining DNA repair were significantly more sensitive to the applied shock pressure than were wild-type spores. These results indicate that DNA may be the sensitive target of spores exposed to ultrahigh shock pressures. To assess the nature of the critical physical parameter responsible for spore inactivation by ultrahigh shock pressures, the resulting peak temperature was varied by lowering the preshock temperature, changing the rock composition and porosity, or increasing the water content of the samples. Increased peak temperatures led to increased spore inactivation and reduced mutation rates. The data suggested that besides the potential mechanical stress exerted by the shock pressure, the accompanying high peak temperatures were a critical stress parameter that spores had to cope with.

Regional fluid and metal mobility in the Dalradian metamorphic belt, Southern Grampian Highlands, Scotland

NASA Astrophysics Data System (ADS)

Craw, D.

1990-10-01

A prominent set of veins was formed during post-metamorphic deformation of the Caledonian Dalradian metamorphic belt. These veins are concentrated in dilational zones in fold hinges, but apophyses follow schistosity and fold axial surface fractures. The veins are most common in the cores of regional structures, especially the Dalradian Downbend and consist of quartz, calcite, chlorite and metallic sulphides and oxides. Metals, including gold, have been concentrated in the veins. The fluid which formed the veins was low salinity (1 5 wt% NaCl and KCl) CO2-bearing (3 16 wt% CO2) water of metamorphic origin. The fluid varies slightly in composition within and between samples, but is essentially uniform in composition over several hundred km2. Vein formation occurred at about 350±50 °C and 200 300 MPa pressure. Further quartz mineralization occurred in some dilational zones at lower temperatures (160 180 °C). This later mineralization was accompanied by CO2 immiscibility. Dilution and oxidation of the metamorphic fluid occurred due to mixing with meteoric water as the rocks passed through the brittle-ductile transition. A similar metamorphic fluid is thought to have been responsible for gold mineralization in the nearby Tyndrum Fault at a later stage in the Dalradian uplift.

Fi Investigations On Hp-Rocks From The Lower Engadine Window New Insights On Its Late Tectono-Metamorphic Evolution

NASA Astrophysics Data System (ADS)

Bertle, R. J.; Götzinger, M. A.; Koller, F.

2003-04-01

Fluid inclusions studies in metamorphic rocks allow to reconstruct not only the chemistry of the fluids enabling and/or supporting metamorphic reactions but also the late metamorphic evolution of orogenesis. Therefore late, discordant quarz-calcite veins were investigated using FI-techniques. The Engadine Window which is exposed at the Swiss-Austrian-border exposes the penninic units of the Western Alps as a tectonic window within the Austroalpine nappes of the Eastern Alps. The nappes of the Engadine window underwent metamorphism and deformation during Tertiary times (THÖNI 1981, BERTLE 2000). The highest unit (Fimber unit) and the core of the window (= Zone of Pfunds) suffered HP-LT-metamorphism. P-T-conditions for parts of the Zone of Pfunds at the region of Piz Mundin are at 13-15 kbar at 380^oC (BOUSQUET et al. 2002) indicated by the occurrence of carpholite and glaucophane. The late metamorphic history is not very well constrained. There exist only a few FI-data published in an abstract by STÖCKHERT et al. 1990 and some unpublished data in RING 1989. During the ongoing mapping campaign of the first author samples from the Fimber unit and the Zone of Pfunds were collected and investigated using a LINKHAM freezing-cooling-stage. The investigated veins are discordant in respect to the main-foliation of the rocks and show nice cristalls of quarz, calcite and sometimes feldspar (adularia). Structural data implie that the investigated veins correspond to a set of ac-joints that correlate to the late updoming of the large "Engadiner Gewölbe" (Engadin anticlinal structure, MATTMÜLLER 1996). All investigated veins (from all tectonic units) show the same relationship to the anticlinal structure. FI-investigations show, that a large amount of the primary FI are decrepitated, however it was possible to find enough to provide a serious statistical data set. FI from Piz Mundin in the core of the Engadine window exhibit at the base of the vein quarz at the contact to the host rock (blueschist) epidote-clinozoisite cristalls. Futheron amphibole is visible. It is common at the base of the vein quarz and decreases towards the middle of the vein. FI are H2O-rich and indicate high pressure of trapping. Quarzes from the upper most part of the Zone of Pfunds from S of Zeblasjoch (W of Samnaun Dorf) show two main groups of primary FI which could be differentiated at room temperature: homogenous FI and such with a bubble. All FI were frozen at max. temperatures of ca. -56 ^oC. Bigger FI show cracking due to cristallisation pressure (build up of "wings"), the cracks however closed again during heating, so that the FI remained closed. Initial melting started between -20 ^oC (first recristallisation signs) and -9 ^oC, final melting was observable at -1 ^oC to 0 ^oC. Then the FI was a.) homogenous or b.) showed a bubble. Homogenisation Temp. of the inclusions with bubble were in the range of 70 to 150 ^oC , most of them between 70 and 80 ^oC and 110 - 125 ^oC. The data indicate a more or less pure H_2O-system for the FI under high pressure. Assuming a cristallisation temperature of the cristalls of about 200 to 250 ^oC and a density of the FI between 0,97 and 1,0 g/cm^3 pressures of 2,5 to 4,5 Kbar are indicated. The same P-T-conditions (same chemistry and melting & homog. Temp.) could be derived from FI in quarz from the Salaaser Kopf (Idalpe) for the late metamorphic evolution of the Fimber unit, indicating that the late metamorphic history of both units is the same. It is concluded that opening of the veins and first cristallisation of vein quarz corresponds to the first signs of updoming of the Engadine anticlinal structure. Updoming of the anticline started when the whole nappe stack was covered by the Austroalpine nappes. Therefore FI show such high pressures for trapping of the fluid. Acknowledgements: Data partly result from FWF-project P. 15278 "Bündnerschieferakkretion in the westlichen Ostalpen". Financal support is greatly acknowledged. References: BERTLE, R. J. 2000: Zur Geologie und Geochronologie um Alp Trida (Samnaun/Schweiz) einschließlich ingenieurgeologischer Fragen der Gebirgsauflösung und des Permafrosts. - Unpubl. Msc-Thesis. Univ. Wien, 395 S. BOUSQUET, R., GOFFÉ, B., VIDAL, O., OBERHÄNSLI, R. & PATRIAT, M. 2002: The tectono-metamorphic history of the Valaisan domain from the Western to the Central Alps: new constraints on the evolution of the Alps. - Geol. Soc. America Bull., 114/2, S. 207-225. KÜSTER, M. &STÖCKHERT, B. 1997: Density changes of fluid inclusions in high-pressure low-temperature metamorphic rocks from Crete: A thermobarometric approach based on the creep strength of the host minerals. Lithos, 41, S. 151-167. MATTMÜLLER, C. R. 1996: Geometrische Untersuchung des Inntalgewölbes. - Jahrb. Geol. B.-A., 139/1, S. 45-69, Wien 1996. RING, U. 1989: Tectonogenesis of the Penninic/Austroalpine Boundary Zone: The Arosa Zone (Grisons Rätikon area, Swiss-Austrian Alps). - Unpubl. Phd.-Thesis., 177 p., Tübingen. STOECKHERT, B., RÖSSNER, G., KÜSTER, M., HEIDER, M., GUNDLACH, K. &RICHTER, D.K. 1990: High-Pressure Metamorphism of the Mesozoic Sediments in the Lower Engadine Window, Eastern Alps. - Terra Abstracts, 2, S. 34, 1990. THÖNI, M. 1981: Degree and Evolution of the Alpine Metamorphism in the Austroalpine Unit W of the Hohe Tauern in the light of K/Ar and Rb/Sr Age Determinations on Micas. - Jahrb. Geol. B.-A., 124/1, S. 111-174, Wien 1981.

Ultra-high speed visualization of the flashing instability under vacuum conditions

NASA Astrophysics Data System (ADS)

Hernández Sánchez, Jose Federico; Al-Ghamdi, Tariq; Thoroddsen, Sigurdur T.

2017-11-01

We investigated experimentally the flashing instability of a jet of perfluoro-n-hexane (PFnH) released into a low-pressure environment. Using a ultra-high speed camera we observed the jet fragmentation occurring close to the nozzle. Using a fixed total driving pressure, we decreased systematically the vacuum pressure, investigating the transition from a laminar jet to a fully flashing jet. Our high temporal resolution allowed to visualize the detailed dynamics of external flash-boiling for the first time. We identified different mechanisms of jet break-up. At chamber pressures lower than the vapor pressure the laminar jet evolves to a meandering stream. In this stage, bubbles start to nucleate and violently expand upstream the nozzle. At lower vacuum pressures the initially cylindrical jet elongates, forming a liquid sheet that breaks in branches and later in drops. At very low pressures both mechanisms are responsible for the jet breaking. We calculated the size distribution of the ejected droplets, their individual trajectories, velocities as well as the spray angle as a function of the dimensionless vacuum pressure.

First principles study of iron-bearing MgO under ultrahigh pressure

NASA Astrophysics Data System (ADS)

Umemoto, K.; Hsu, H.

2017-12-01

Understanding of minerals under ultrahigh pressure is essential to model interiors of super-Earths. Chemical compositions of the super-Earths are expected to be similar to those of the Earth. Computational studies on Mg-Si-O ternary systems under ultrahigh pressures, which are difficult to be achieved by diamond-anvil-cell experiments, have been intensively performed (e.g., [1] for MgO, [2,3] for SiO2, and [4,5] for MgSiO3). However, as far as we know, these studies have been restricted to pure Mg-Si-O systems. In the mantles of super-Earths, we expect that there should be impurities as in the Earth's mantle. Among candidates of impurities, iron is especially important to model interiors of super-Earths. Here, we investigate iron-bearing MgO under ultrahigh pressures by first principles. We clarify effects of iron on the phase transition of MgO and thermodynamic quantities by first principles. The role of the 3d electrons will be elucidated. [1] Z. Wu, R. M. Wentzcovitch, K. Umemoto, B. Li, K. Hirose, and J. C. Zheng, J. Geophys. Res. 113, B06204 (2008). [2] S. Q. Wu, K. Umemoto, M. Ji, C. Z. Wang, K. M. Ho, and R. M. Wentzcovitch, Phys. Rev. B 83, 184102 (2011). [3] T. Tsuchiya and J. Tsuchiya, Proc. Nat. Acad. Sci. 108, 1252 (2011) [4] S. Q. Wu, M. Ji, C. Z. Wang, M. C. Nguye, X. Zhao, K. Umemoto, R. M. Wentzcovitch, and K. M. Ho, J. Phys.: Condens. Matter 26, 035402 (2014). [5] H. Niu, A. R. Oganov, X.-C. Chen, and D. Li, Sci. Rep. 5, 18347 (2015).

Timing and duration of Variscan high-pressure metamorphism in the French Massif Central: A multimethod geochronological study from the Najac Massif

NASA Astrophysics Data System (ADS)

Lotout, Caroline; Pitra, Pavel; Poujol, Marc; Anczkiewicz, Robert; Van Den Driessche, Jean

2018-05-01

Accurate dating of eclogite-facies metamorphism is of paramount importance in order to understand the tectonic evolution of an orogen. An eclogite sample from the Najac Massif (French Massif Central, Variscan belt) displays a zircon-bearing garnet-omphacite-amphibole-rutile-quartz peak assemblage. Pseudosection modeling suggests peak pressure conditions of 15-20 kbar, 560-630 °C. Eclogite-facies garnet displays Lu-enriched cores and Sm-rich rims and yields a Lu-Hf age of 382.8 ± 1.0 Ma and a Sm-Nd age of 376.7 ± 3.3 Ma. The ages are interpreted as marking the beginning of the prograde garnet growth during the initial stages of the eclogite-facies metamorphism, and the high-pressure (and temperature) peak reached by the rock, respectively. Zircon grains display chondrite-normalized REE spectra with variably negative, positive or no Eu anomalies and are characterized by either enriched or flat HREE patterns. However, they yield a well constrained in situ LA-ICP-MS U-Pb age of 385.5 ± 2.3 Ma, despite this REE pattern variability. Zr zonation in garnet, Y content in zircon and the diversity of zircon HREE spectra may suggest that zircon crystallized prior to and during incipient garnet growth on the prograde P-T path, recording the initial stages of the eclogite-facies conditions. Consequently, the zircon age of 385.5 ± 2.3 Ma, comparable within error with the Lu-Hf age obtained on garnet, is interpreted as dating the beginning of the eclogite-facies metamorphism. Accordingly, the duration of the prograde part of the eclogite-facies event is estimated at 6.1 ± 4.3 Myr. Subsequent exhumation is constrained by an apatite U-Pb age at 369 ± 13 Ma.

Flexible Ferroelectric Sensors with Ultrahigh Pressure Sensitivity and Linear Response over Exceptionally Broad Pressure Range.

PubMed

Lee, Youngoh; Park, Jonghwa; Cho, Soowon; Shin, Young-Eun; Lee, Hochan; Kim, Jinyoung; Myoung, Jinyoung; Cho, Seungse; Kang, Saewon; Baig, Chunggi; Ko, Hyunhyub

2018-04-24

Flexible pressure sensors with a high sensitivity over a broad linear range can simplify wearable sensing systems without additional signal processing for the linear output, enabling device miniaturization and low power consumption. Here, we demonstrate a flexible ferroelectric sensor with ultrahigh pressure sensitivity and linear response over an exceptionally broad pressure range based on the material and structural design of ferroelectric composites with a multilayer interlocked microdome geometry. Due to the stress concentration between interlocked microdome arrays and increased contact area in the multilayer design, the flexible ferroelectric sensors could perceive static/dynamic pressure with high sensitivity (47.7 kPa -1 , 1.3 Pa minimum detection). In addition, efficient stress distribution between stacked multilayers enables linear sensing over exceptionally broad pressure range (0.0013-353 kPa) with fast response time (20 ms) and high reliability over 5000 repetitive cycles even at an extremely high pressure of 272 kPa. Our sensor can be used to monitor diverse stimuli from a low to a high pressure range including weak gas flow, acoustic sound, wrist pulse pressure, respiration, and foot pressure with a single device.

Phase Equilibria Modeling of Coesite Eclogite from the Sulu Belt, Eastern China

NASA Astrophysics Data System (ADS)

Xia, B.; Brown, M.; Wang, L.; Wang, S.; Piccoli, P. M.

2016-12-01

Modeling of phase equilibria and tectonic processes are essential components to understand controls on P-T paths of UHPM rocks. However, diffusion at higher temperatures (> 700 °C), and issues with determination of Fe3+ in minerals and estimating H2O contents limit our ability to determine prograde, peak P and retrograde P-T data. Also, the lack of an appropriate activity-composition model for melt in basic rocks has limited the application of phase equilibria modeling to understand partial melting associated with exhumation. Here we apply phase equilibria modeling to coesite eclogite from Yangkou to assess the influence of Fe3+ and fluid during metamorphism, monitor reactions and phase relations in eclogite during deep subduction and exhumation and investigate partial melting at HP conditions. The modeling used the THERMOCALC software and the new internally consistent thermodynamic dataset for basic rocks (http://www.metamorph.geo.uni-mainz.de/thermocalc/dataset6/index.html). Here we investigate bimineralic (gt+omp+coe/qz+ru/ilm), phengite-bearing (gt+omp+phen (2 samples, <5 vol% and >5 vol%) +coe/qz+ru/ilm) and kyanite-bearing (gt+omp+phen+ky+coe/qz+ru/ilm) eclogites. Coesite in the matrix is the hallmark of the Yangkou eclogite. For each sample, we use an iterative process to estimate the H2O and O content in the bulk composition, and then calculate a P-T pseudosection. The results suggest that some prograde information (670-770 °C, > 3.0 GPa) is retained in large garnet cores in bimineralic and phengite-bearing eclogite. The peak P-T conditions are a challenge because in the field of gt+omp+coe/qz±phen+H2O at T > 750 °C and P > 3.5 GPa mode and compositional changes are small. However, isopleths of Si in phengite suggest that the peak P could have been > 5-6 GPa. Re-equilibration of garnet and omphacite compositions occurred during exhumation, yielding P-T conditions of 700-790 °C at 3.1-2.0 GPa. Amphibolite facies metamorphism occurred at 630-710 °C, 1.3-1.2 GPa. The retrograde P-T path passes through the suprasolidus field; however, the melt produced is very low (< 5 mol%). Our work provides new quantitative P-T data for UHP eclogite in the Sulu belt and contributes to further understanding of the processes that affect deeply subducted continental crust.

Microbial diversity in ultra-high-pressure rocks and fluids from the Chinese Continental Scientific Drilling Project in China.

PubMed

Zhang, Gengxin; Dong, Hailiang; Xu, Zhiqin; Zhao, Donggao; Zhang, Chuanlun

2005-06-01

Microbial communities in ultra-high-pressure (UHP) rocks and drilling fluids from the Chinese Continental Scientific Drilling Project were characterized. The rocks had a porosity of 1 to 3.5% and a permeability of approximately 0.5 mDarcy. Abundant fluid and gas inclusions were present in the minerals. The rocks contained significant amounts of Fe2O3, FeO, P2O5, and nitrate (3 to 16 ppm). Acridine orange direct counting and phospholipid fatty acid analysis indicated that the total counts in the rocks and the fluids were 5.2 x 10(3) to 2.4 x 10(4) cells/g and 3.5 x 10(8) to 4.2 x 10(9) cells/g, respectively. Enrichment assays resulted in successful growth of thermophilic and alkaliphilic bacteria from the fluids, and some of these bacteria reduced Fe(III) to magnetite. 16S rRNA gene analyses indicated that the rocks were dominated by sequences similar to sequences of Proteobacteria and that most organisms were related to nitrate reducers from a saline, alkaline, cold habitat; however, some phylotypes were either members of a novel lineage or closely related to uncultured clones. The bacterial communities in the fluids were more diverse and included Proteobacteria, Bacteroidetes, gram-positive bacteria, Planctomycetes, and Candidatus taxa. The archaeal diversity was lower, and most sequences were not related to any known cultivated species. Some archaeal sequences were 90 to 95% similar to sequences recovered from ocean sediments or other subsurface environments. Some archaeal sequences from the drilling fluids were >93% similar to sequences of Sulfolobus solfataricus, and the thermophilic nature was consistent with the in situ temperature. We inferred that the microbes in the UHP rocks reside in fluid and gas inclusions, whereas those in the drilling fluids may be derived from subsurface fluids.

Microbial Diversity in Ultra-High-Pressure Rocks and Fluids from the Chinese Continental Scientific Drilling Project in China

PubMed Central

Zhang, Gengxin; Dong, Hailiang; Xu, Zhiqin; Zhao, Donggao; Zhang, Chuanlun

2005-01-01

Microbial communities in ultra-high-pressure (UHP) rocks and drilling fluids from the Chinese Continental Scientific Drilling Project were characterized. The rocks had a porosity of 1 to 3.5% and a permeability of ∼0.5 mDarcy. Abundant fluid and gas inclusions were present in the minerals. The rocks contained significant amounts of Fe2O3, FeO, P2O5, and nitrate (3 to 16 ppm). Acridine orange direct counting and phospholipid fatty acid analysis indicated that the total counts in the rocks and the fluids were 5.2 × 103 to 2.4 × 104 cells/g and 3.5 × 108 to 4.2 × 109 cells/g, respectively. Enrichment assays resulted in successful growth of thermophilic and alkaliphilic bacteria from the fluids, and some of these bacteria reduced Fe(III) to magnetite. 16S rRNA gene analyses indicated that the rocks were dominated by sequences similar to sequences of Proteobacteria and that most organisms were related to nitrate reducers from a saline, alkaline, cold habitat; however, some phylotypes were either members of a novel lineage or closely related to uncultured clones. The bacterial communities in the fluids were more diverse and included Proteobacteria, Bacteroidetes, gram-positive bacteria, Planctomycetes, and Candidatus taxa. The archaeal diversity was lower, and most sequences were not related to any known cultivated species. Some archaeal sequences were 90 to 95% similar to sequences recovered from ocean sediments or other subsurface environments. Some archaeal sequences from the drilling fluids were >93% similar to sequences of Sulfolobus solfataricus, and the thermophilic nature was consistent with the in situ temperature. We inferred that the microbes in the UHP rocks reside in fluid and gas inclusions, whereas those in the drilling fluids may be derived from subsurface fluids. PMID:15933024

Tectono-metamorphic evolution of the Jomolhari massif: Variations in timing of syn-collisional metamorphism across western Bhutan

NASA Astrophysics Data System (ADS)

Regis, Daniele; Warren, Clare J.; Young, David; Roberts, Nick M. W.

2014-03-01

Our current understanding of the rates and timescales of mountain-building processes is largely based on information recorded in U-bearing accessory minerals such as monazite, which is found in low abundance but which hosts the majority of the trace element budget. Monazite petrochronology was used to investigate the timing of crustal melting in migmatitic metasedimentary rocks from the Jomolhari massif (NW Bhutan). The samples were metamorphosed at upper amphibolite to granulite facies conditions (~ 0.85 GPa, ~ 800 °C), after an earlier High-Pressure stage (P > 1.4 GPa), and underwent partial melting through dehydration melting reactions involving muscovite and biotite. In order to link the timing of monazite growth/dissolution to the pressure-temperature (P-T) evolution of the samples, we identified 'chemical fingerprints' in major and accessory phases that were used to back-trace specific metamorphic reactions. Variations in Eu anomaly and Ti in garnet were linked to the growth and dissolution of major phases (e.g. growth of K-feldspar and dehydration melting of muscovite/biotite). Differences in M/HREE and Y from garnet core to rim were instead related to apatite breakdown and monazite-forming reactions. Chemically zoned monazite crystals reacted multiple times during the metamorphic evolution suggesting that the Jomolhari massif experienced a prolonged high-temperature metamorphic evolution from 36 Ma to 18 Ma, significantly different from the P-T-time path recorded in other portions of the Greater Himalayan Sequence (GHS) in Bhutan. Our data demonstrate unequivocally that the GHS in Bhutan consists of units that experienced independent high-grade histories and that were juxtaposed across different tectonic structures during exhumation. The GHS may have been exhumed in response to (pulsed) mid-crustal flow but cannot be considered a coherent block.

Metamorphic reactions in the Chaunskij mesosiderite

NASA Astrophysics Data System (ADS)

Petaev, M. I.; Brearley, A. J.

1994-07-01

The Chaunskij meteorite, found in 1985, recently has been found to be the most highly metamorphosed, shock-modified, and metal-rich mesosiderite. It contains approximately 10 vol% mono- and polymineralic troilite-phosphate-silicate inclusions, micrometers to centimeters in size. Two dominant silicate lithologies have been found in the inclusions. The primary 'igneous' lithology, making up the largest inclusion studied, is generally a microophitic fine-grained aggregate of pyroxene, plagioclase, and minor silica, with scattered coarser-grained granoblastic spots enriched in silica and troilite. The secondary 'metamorphic' lithology occurs as separate small inclusions and as larger areas in intimate contact with the 'igneous' lithology, separated by highly irregular boundaries from each other, in the largest inclusion. In small inclusions the metamorphic lithology consists of a fine-grained hornfelsic to granoblastic aggregate of cordierite, orthopyroxene, quartz, and whitlockite with variable amounts of opaque minerals. In the largest inclusion the metamorphic lithology is a generally granoblastic to poikiloblastic aggregate of cordierite and quartz with minor amounts of other minerals. The Opx-Chr mineral thermometer and the Cord-Sp barometer have been applied to estimate the conditions of Chaunskij metamorphism. The data for 16 Opx-Chr pairs from different inclusions and lithologies correspond to a temperature of 590 +/- 30 C. The data for 9 Cord-Chr pairs from different inclusions correspond to a pressure of 6.0 +/- 0.2 kbar. While the composition of spinel in Chaunskij much richer in Cr than were the spinels used to calibrate Cord-Sp barometer the estimated pressure is consistent with the occurrence in the igneous lithology of two small pyroxene grains enriched in the CaAl2SiO6 molecule, coexisting with quartz and plagioclase. This mineral assemblage is unstable below approximately 5 kbar at 600 C.

Fore arc tectonothermal evolution of the El Oro metamorphic province (Ecuador) during the Mesozoic

NASA Astrophysics Data System (ADS)

Riel, Nicolas; Martelat, Jean-Emmanuel; Guillot, Stéphane; Jaillard, Etienne; Monié, Patrick; Yuquilema, Jonatan; Duclaux, Guillaume; Mercier, Jonathan

2014-10-01

The El Oro metamorphic province of SW Ecuador is a composite massif made of juxtaposed terranes of both continental and oceanic affinity that has been located in a fore-arc position since Late Paleozoic times. Various geochemical, geochronological, and metamorphic studies have been undertaken on the El Oro metamorphic province, providing an understanding of the origin and age of the distinct units. However, the internal structures and geodynamic evolution of this area remain poorly understood. Our structural analysis and thermal modeling in the El Oro metamorphic province show that this fore-arc zone underwent four main geological events. (1) During Triassic times (230-225 Ma), the emplacement of the Piedras gabbroic unit at crustal-root level ( 9 kbar) triggered partial melting of the metasedimentary sequence under an E-W extensional regime at pressure-temperature conditions ranging from 4.5 to 8.5 kbar and from 650 to 900°C for the migmatitic unit. (2) At 226 Ma, the tectonic underplating of the Arenillas-Panupalí oceanic unit (9 kbar and 300°C) thermally sealed the fore-arc region. (3) Around the Jurassic-Cretaceous boundary, the shift from trench-normal to trench-parallel subduction triggered the exhumation and underplating of the high-pressure, oceanic Raspas Ophiolitic Complex (18 kbar and 600°C) beneath the El Oro Group (130-120 Ma). This was followed by the opening of a NE-SW pull-apart basin, which tilted the massif along an E-W subhorizontal axis (110 Ma). (4) In Late Cretaceous times, an N-S compressional event generated heterogeneous deformation due to the presence of the Cretaceous Celica volcanic arc, which acted as a buttress and predominantly affected the central and eastern part of the massif.

Trace element behavior and P-T-t evolution during partial melting of exhumed eclogite in the North Qaidam UHPM belt (NW China): Implications for adakite genesis

NASA Astrophysics Data System (ADS)

Zhang, Guibin; Niu, Yaoling; Song, Shuguang; Zhang, Lifei; Tian, Zuolin; Christy, Andrew G.; Han, Lei

2015-06-01

We have studied trace element behavior and timing of decompression melting of UHP rocks during exhumation recorded in the magmatic products, i.e., the melt phase (leucosomes), cumulate (garnetite) and residue (amphibolitized eclogite) from a single outcrop in the south Dulan area, North Qaidam UHPM belt, NW China. Two distinct episodes of partial melting are recognized. First, Grt-free tonalitic-trondhjemitic leucosome melts with higher silica crystallized at 424.0 ± 2.7 Ma. Garnets grew in the leucosome melt but fractionated out to form garnetite cumulates along with Ti-rich phases (rutile and titanite), strengthening the adakitic signature of the leucosome. Later Grt-bearing leucosome melts with an age of 412.4 ± 2.9 Ma cross-cut boudins and layers of amphibolitized eclogite. Geochemical investigation of bulk-rocks and in situ minerals verifies the genetic relationship between the amphibolitized eclogite and the tonalitic-trondhjemitic melts. Zircons from the amphibolitized eclogite have older (> 700 Ma) protolith ages, with subsequent eclogite-facies metamorphism, retrograde granulite-facies overprinting and partial melting. Phase modeling and Zr-in-rutile thermometry calculations in combination with zircon geochronology reveal the evolution P-T-t path for the exhumation and the partial melting of the deeply subducted continental crust at the North Qaidam subduction zone in the Early Paleozoic.

New Caledonia a classic example of an arc continent collision

NASA Astrophysics Data System (ADS)

Aitchison, J.

2011-12-01

The SW Pacific island of New Caledonia presents a classic example of an arc-continent collision. This event occurred in the Late Eocene when elements of an intra-oceanic island arc system, the Loyalty-D'Entrecasteaux arc, which stretched SSE from near Papua New Guinea east of New Caledonia to offshore New Zealand, collided with micro-continental fragments that had rifted off eastern Gondwana (Australia) in the late Cretaceous. Intervening Late Cretaceous to Paleogene oceanic crust of the South Loyalty Basin was eliminated through eastward subduction beneath this west-facing intra-oceanic island arc. As with many arc-continent collisions elsewhere collision was accompanied by ophiolite emplacement. The erosional remnants of which are extensive in New Caledonia. Collision led to subduction flip, followed by extensive rollback in front of the newly established east-facing Vitiaz arc. Post-collisional magmatism occurred after slab break-off and is represented by small-scale granitoid intrusions. Additional important features of New Caledonia include the presence of a regionally extensive UHP metamorphic terrain consisting of blueschists and eclogites that formed during the subduction process and were rapidly exhumed as a result of the collision Not only was collision and associated orogeny short-lived this collision system has not been overprinted by any major subsequent collision. New Caledonia thus provides an exceptional location for the study of processes related to arc-continent collision in general.

Evaluation of dopants in hydrogen to reduce hydrogen permeation in candidate Stirling engine heater head tube alloys at 760 deg and 820 deg

NASA Technical Reports Server (NTRS)

Misencik, J. A.

1982-01-01

Alloy tubes filled with hydrogen doped with various amounts of carbon monoxide, carbon dioxide, ethane, ethylene, methane, ammonia, or water were heated in a diesel fuel-fired Stirling engine simulator materials test rig for 100 hours at 21 MPa and 760 or 820 C to determine the effectiveness of the dopants in reducing hydrogen permeation through the hot tube walls. Ultra high purity (UHP) hydrogen was used for comparison. The tube alloys were N-155, A-286, Incoloy 800, Nitronic 40, 19-9DL, 316 stainless steel, Inconel 718, and HS-188. Carbon dioxide and carbon monoxide in the concentration range 0.2 to 5 vol % were most effective in reducing hydrogen permeation through the hot tube walls for all alloys. Ethane, ethylene, methane, ammonia, and water at the concentrations investigated were not effective in reducing the permeation below that achieved with UHP hydrogen. One series of tests were conducted with UHP hydrogen in carburized tubes. Carburization of the tubes prior to exposure reduced permeation to values similar to those for carbon monoxide; however, carbon dioxide was the most effective dopant.

An Ultrahigh CO2-Loaded Silicalite-1 Zeolite: Structural Stability and Physical Properties at High Pressures and Temperatures.

PubMed

Marqueño, Tomas; Santamaria-Perez, David; Ruiz-Fuertes, Javier; Chuliá-Jordán, Raquel; Jordá, Jose L; Rey, Fernando; McGuire, Chris; Kavner, Abby; MacLeod, Simon; Daisenberger, Dominik; Popescu, Catalin; Rodriguez-Hernandez, Placida; Muñoz, Alfonso

2018-06-04

We report the formation of an ultrahigh CO 2 -loaded pure-SiO 2 silicalite-1 structure at high pressure (0.7 GPa) from the interaction of empty zeolite and fluid CO 2 medium. The CO 2 -filled structure was characterized in situ by means of synchrotron powder X-ray diffraction. Rietveld refinements and Fourier recycling allowed the location of 16 guest carbon dioxide molecules per unit cell within the straight and sinusoidal channels of the porous framework to be analyzed. The complete filling of pores by CO 2 molecules favors structural stability under compression, avoiding pressure-induced amorphization below 20 GPa, and significantly reduces the compressibility of the system compared to that of the parental empty one. The structure of CO 2 -loaded silicalite-1 was also monitored at high pressures and temperatures, and its thermal expansivity was estimated.

Ultrahigh hydrostatic pressure extraction of flavonoids from Epimedium koreanum Nakai

NASA Astrophysics Data System (ADS)

Hou, Lili; Zhang, Shouqin; Dou, Jianpeng; Zhu, Junjie; Liang, Qing

2011-02-01

Herba Epimedii is one of the most famous Chinese herbal medicines listed in the Pharmacopoeia of the People's Republic of China, as one of the representatives of traditional Chinese herb, it has been widely applied in the field of invigorate the kidney and strengthen 'Yang'. The attention to Epimedium extract has more and more increased in recent years. In this work, a novel extraction technique, ultra-high hydrostatic pressure extraction (UPE) technology was applied to extract the total flavonoids of E. koreanum. Three factors (pressure, ethanol concentration and extraction time) were chosen as the variables of extraction experiments, and the optimum UPE conditions were pressure 350 MPa; ethanol concentration 50% (v/v); extraction time 5 min. Compared with Supercritical CO2 extraction, Reflux extraction and Ultrasonic-assisted extraction, UPE has excellent advantages (shorter extraction time, higher yield, better antioxidant activity, lower energy consumption and eco-friendly).

Water permeability of nanoporous graphene at realistic pressures for reverse osmosis desalination

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen-Tanugi, David; Grossman, Jeffrey C.

Nanoporous graphene (NPG) shows tremendous promise as an ultra-permeable membrane for water desalination thanks to its atomic thickness and precise sieving properties. However, a significant gap exists in the literature between the ideal conditions assumed for NPG desalination and the physical environment inherent to reverse osmosis (RO) systems. In particular, the water permeability of NPG has been calculated previously based on very high pressures (1000–2000 bars). Does NPG maintain its ultrahigh water permeability under real-world RO pressures (<100 bars)? Here, we answer this question by drawing results from molecular dynamics simulations. Our results indicate that NPG maintains its ultrahigh permeabilitymore » even at low pressures, allowing a permeate water flux of 6.0 l/h-bar per pore, or equivalently 1041 ± 20 l/m{sup 2}-h-bar assuming a nanopore density of 1.7 × 10{sup 13} cm{sup −2}.« less

New Equation of State Models for Hydrodynamic Applications

NASA Astrophysics Data System (ADS)

Young, David A.; Barbee, Troy W., III; Rogers, Forrest J.

1997-07-01

Accurate models of the equation of state of matter at high pressures and temperatures are increasingly required for hydrodynamic simulations. We have developed two new approaches to accurate EOS modeling: 1) ab initio phonons from electron band structure theory for condensed matter and 2) the ACTEX dense plasma model for ultrahigh pressure shocks. We have studied the diamond and high pressure phases of carbon with the ab initio model and find good agreement between theory and experiment for shock Hugoniots, isotherms, and isobars. The theory also predicts a comprehensive phase diagram for carbon. For ultrahigh pressure shock states, we have studied the comparison of ACTEX theory with experiments for deuterium, beryllium, polystyrene, water, aluminum, and silicon dioxide. The agreement is good, showing that complex multispecies plasmas are treated adequately by the theory. These models will be useful in improving the numerical EOS tables used by hydrodynamic codes.

Effect of extra-column volume on practical chromatographic parameters of sub-2-μm particle-packed columns in ultra-high pressure liquid chromatography.

PubMed

Wu, Naijun; Bradley, Ashley C; Welch, Christopher J; Zhang, Li

2012-08-01

Effects of extra-column volume on apparent separation parameters were studied in ultra-high pressure liquid chromatography with columns and inlet connection tubings of various internal diameters (id) using 50-mm long columns packed with 1.8-μm particles under isocratic conditions. The results showed that apparent retention factors were on average 5, 11, 18, and 41% lower than those corrected with extra-column volumes for 4.6-, 3.0-, 2.1-, and 1.0-mm id columns, respectively, when the extra-column volume (11.3 μL) was kept constant. Also, apparent pressures were 31, 16, 12, and 10% higher than those corrected with pressures from extra-column volumes for 4.6-, 3.0-, 2.1-, and 1.0-mm id columns at the respective optimum flow rate for a typical ultra-high pressure liquid chromatography system. The loss in apparent efficiency increased dramatically from 4.6- to 3.0- to 2.1- to 1.0-mm id columns, less significantly as retention factors increased. The column efficiency was significantly improved as the inlet tubing id was decreased for a given column. The results suggest that maximum ratio of extra-column volume to column void volume should be approximately 1:10 for column porosity more than 0.6 and a retention factor more than 5, where 80% or higher of theoretically predicted efficiency could be achieved. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Geological implications of a permeability-depth curve for the continental crust

USGS Publications Warehouse

Ingebritsen, S.E.; Manning, C.E.

1999-01-01

The decrease in permeability (k) of the continental crust with depth (z), as constrained by geothermal data and calculated fluid flux during metamorphism, is given by log k = -14 - 3.2 log z, where A is in meters squared and z is in kilometers. At moderate to great crustal depths (>???5 km), this curve is defined mainly by data from prograde metamorphic systems, and is thus applicable to orogenic belts where the crust is being thickened and/or heated; lower permeabilities may occur in stable cratonic regions. This k-z relation implies that typical metamorphic fluid flux values of ???10-11 m/s are consistent with fluid pressures significantly above hydrostatic values. The k-z curve also predicts that metamorphic CO2 flux from large orogens may be sufficient to cause significant climatic effects, if retrograde carbonation reactions are minimal, and suggests a significant capacity for diffuse degassing of Earth (1015-1016 g/yr) in tectonically active regions.

Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar

NASA Astrophysics Data System (ADS)

Maw Maw Win; Enami, Masaki; Kato, Takenori

2016-03-01

The high temperature (T)/pressure (P) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet-biotite-plagioclase-sillimanite-quartz assemblage and its partial system suggest equilibrium P/T conditions of 0.6-1.0 GPa/780-850 °C for the peak metamorphic stage, and 0.3-0.5 GPa/600-680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments-I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th-U-total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6-49.9 ± 7.9, 37.8 ± 1.0-38.1 ± 1.7, 28.0 ± 0.8-28.8 ± 1.6, and 23.7 ± 1.3 Ma (2σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.

Ultrahigh pressure extraction of lignan compounds from Dysosma versipellis and purification by high-speed counter-current chromatography.

PubMed

Zhu, Qing; Liu, Feng; Xu, Meixia; Lin, Xiaojing; Wang, Xiao

2012-09-15

Ultrahigh pressure extraction (UPE) was employed to extract podophyllotoxin and 4'-demethylpodophyllotoxin from Dysosma versipellis. The effects of extraction parameters including extraction solvents, pressure, time and solid/liquid ratio were investigated using a High Hydrostatic Pressure Processor. The optimal condition for UPE of the target compounds was 80% methanol, 200 MPa of pressure, 1 min of extraction time and 1:12 (g/mL) of solid/liquid ratio. Podophyllotoxin and 4'-demethylpodophyllotoxin in the crude extract were purified by high-speed counter-current chromatography (HSCCC) with a two-phase solvent system composed of petroleum ether-ethyl acetate-methanol-water (10:10:8:12, v/v), and the fractions were analyzed by HPLC, ESI-MS and (1)H NMR. As a result, 73.7 mg podophyllotoxin and 16.5mg 4'-demethylpodophyllotoxin with purities over 96% were obtained from 260 mg crude sample in one-step separation. Copyright © 2012 Elsevier B.V. All rights reserved.

40Ar/39Ar thermochronology of mesoproterozoic metamorphism in the Colorado Front Range

USGS Publications Warehouse

Shaw, C.A.; Snee, L.W.; Selverstone, J.; Reed, J.C.

1999-01-01

A low-pressure metamorphic episode in the Colorado Front Range has been identified by the presence of staurolite, andalusite, cordierite, and garnet porphyroblasts overprinting earlier assemblages. The overprinting assemblages and reaction textures are most consistent with porphyroblast growth on a prograde metamorphic path with peak temperatures exceeding ~525??C. Twenty-eight 40Ar/39Ar dates on hornblende, muscovite, biotite, and microcline were used to infer the age and thermal conditions of metamorphism. Muscovite and biotite 40Ar/39Ar ages fall mainly in the interval 1400-1340 Ma, consistent with cooling through the closure temperature interval of micas (~400??-300??C) after about 1400 Ma. In contrast, hornblende apparent ages (T(c)~500??-550??C) between 1600 and 1390 Ma reflect variable retention of radiogenic argon. Forward modeling of argon diffusion shows that the distribution of hornblende and mica ages is consistent with the partial resetting of argon systematics ca. 1400 Ma by a thermal pulse reaching maximum temperatures around 550??C and decaying within <20 m.yr. These temperatures match the conditions inferred from the overprinting assemblage; thus, muscovite and biotite ages are interpreted to date the cooling phase of this metamorphic event. This late metamorphism is broadly coeval with the intrusion of ca. 1400-Ma granitic plutons in the study area and throughout the southwestern United States. However, thermal effects are observed far from pluton margins, suggesting pervasive, regional crustal heating rather than restricted contact metamorphism. Our results suggest that ca. 1400-Ma metamorphism and plutonism are manifestations of a regional thermal episode that both partially melted the lower crust and pervasively metamorphosed middle crustal rocks.

Adakitic (tonalitic-trondhjemitic) magmas resulting from eclogite decompression and dehydration melting during exhumation in response to continental collision

NASA Astrophysics Data System (ADS)

Song, Shuguang; Niu, Yaoling; Su, Li; Wei, Chunjing; Zhang, Lifei

2014-04-01

Modern adakite or adakitic rocks are thought to result from partial melting of younger and thus warmer subducting ocean crust in subduction zones, with the melt interacting with or without mantle wedge peridotite during ascent, or from melting of thickened mafic lower crust. Here we show that adakitic (tonalitic-trondhjemitic) melts can also be produced by eclogite decompression during exhumation of subducted and metamorphosed oceanic/continental crust in response to continental collision, as exemplified by the adakitic rocks genetically associated with the early Paleozoic North Qaidam ultra-high pressure metamorphic (UHPM) belt on the northern margin of the Greater Tibetan Plateau. We present field evidence for partial melting of eclogite and its products, including adakitic melt, volumetrically significant plutons evolved from the melt, cumulate rocks precipitated from the melt, and associated granulitic residues. This “adakitic assemblage” records a clear progression from eclogite decompression and heating to partial melting, to melt fractionation and ascent/percolation in response to exhumation of the UHPM package. The garnetite and garnet-rich layers in the adakitic assemblage are of cumulate origin from the adakitic melt at high pressure, and accommodate much of the Nb-Ta-Ti. Zircon SHRIMP U-Pb dating shows that partial melting of the eclogite took place at ∼435-410 Ma, which postdates the seafloor subduction (>440 Ma) and temporally overlaps the UHPM (∼440-425 Ma). While the geological context and the timing of adakite melt formation we observe differ from the prevailing models, our observations and documentations demonstrate that eclogite melting during UHPM exhumation may be important in contributing to crustal growth.

A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A

USGS Publications Warehouse

Jackson, J.C.; Horton, J. Wright; Chou, I.-Ming; Belkin, H.E.

2006-01-01

A shock-induced polymorph (TiO2II) of anatase and rutile has been identified in breccias from the late Eocene Chesapeake Bay impact structure. The breccia samples are from a recent, partially cored test hole in the central uplift at Cape Charles, Virginia. The drill cores from 744 to 823 m depth consist of suevitic crystalline-clast breccia and brecciated cataclastic gneiss in which the TiO2 phases anatase and rutile are common accessory minerals. Electron-microprobe imaging and laser Raman spectroscopy of TiO2 crystals, and powder X-ray diffraction (XRD) of mineral concentrates, confirm that a high-pressure, ??-PbO2 structured polymorph of TiO2 (TiO2II) coexists with anatase and rutile in matrix-hosted crystals and in inclusions within chlorite. Raman spectra of this polymorph include strong bands at wavenumbers (cm-1) 175, 281, 315, 342, 356, 425, 531, 571, and 604; they appear with anatase bands at 397, 515, and 634 cm-1, and rutile bands at 441 and 608 cm-1. XRD patterns reveal 12 lines from the polymorph that do not significantly interfere with those of anatase or rutile, and are consistent with the TiO2II that was first reported to occur naturally as a shock-induced phase in rutile from the Ries crater in Germany. The recognition here of a second natural shock-induced occurrence of TiO2II suggests that its presence in rocks that have not been subjected to ultrahigh-pressure regional metamorphism can be a diagnostic indicator for confirmation of suspected impact structures.

Carbon Retention and Isotopic Evolution in Deeply Subducted Sediments: Evidence from the Italian Alps

NASA Astrophysics Data System (ADS)

Cook-Kollars, J.; Bebout, G. E.; Agard, P.; Angiboust, S.

2012-12-01

Subduction-zone metamorphism of oceanic crust and carbonate-rich seafloor sediments plays an important regulatory role in the global C cycle by controlling the fraction of subducting C entering long-term storage in the mantle and the fraction of subducting C emitted into the atmosphere in arc volcanic gases. Modeling studies suggest that the extent of decarbonation of subducting sediments could be strongly affected by extents of infiltration by external H2O-rich fluids and that, in cool subduction zones, the dehydration of subducting oceanic slabs may not release sufficient H2O to cause significant decarbonation of overlying sediments [Gorman et al. (2006), G-cubed; Hacker (2008), G-cubed]. Metasedimentary suites in the Western Alps (sampled from the Schistes Lustres, Zermatt-Saas ophiolite, and at Lago di Cignana) were subducted to depths corresponding to 1.5-3.2 GPa, over a range of peak temperatures of 350-600°C, and are associated with HP/UHP-metamorphosed Jurassic ophiolitic rocks [Agard et al. (2001), Bull. soc. geol. France; Frezzotti et al. (2011), Nature Geoscience]. These metasedimentary suites are composed of interlayered metapelites and metacarbonates and represent a range of peak P-T conditions experienced in modern, relatively cool subduction zones. Integrated petrologic and isotopic study of these rocks allows an analysis of decarbonation and isotopic exchange among oxidized and reduced C reservoirs along prograde subduction-zone P-T paths. Petrographic work on Schistes Lustres metacarbonates indicates only minor occurrences of calc-silicate phases, consistent with the rocks having experienced only very minor decarbonation during prograde metamorphism. Carbonate δ13CVPDB values (-1.5 to 1‰) are similar to values typical of marine carbonates. Higher grade, UHP-metamorphosed carbonates at Cignana show mineralogic evidence of decarbonation; however, the δ13C of the calcite in these samples remains similar to that of marine carbonate. With increasing grade, metapelitic carbonaceous matter shows an increase in δ13CVPDB, ranging from about -25‰ in low-grade Schistes Lustres samples to -16‰ in the highest-grade Cignana samples. Carbonate in the entire suite shows decrease in δ18OSMOW, from marine carbonate values > 25‰ to values of 17-22‰ independent of the carbonate content of the rocks. This shift could possibly be explained by isotopic exchange with silicate phases in the same rocks [Henry et al. (1996), Chem. Geol.]. Metapelitic rocks in this suite experienced moderate amounts of dehydration (20-50%) largely related to breakdown of chlorite and carpholite [Bebout et al. (in press), Chem. Geol. (abstract in this session); Angiboust and Agard (2010), Lithos], conceivably providing a source for infiltrating H2O-rich fluids producing negative shifts in calcite δ18O in interlayered metacarbonates. These results indicate that relatively little decarbonation occurred in carbonate-bearing sediments subducted to depths greater than 100 km, arguing against any model of extensive decarbonation driven by infiltration of the sediments by H2O-rich fluids released from mafic and ultramafic parts of the underlying subducting slab. This study provides field evidence for the efficient retention of C in subducting shale-carbonate sequences through forearc depths, potentially affecting the C budget and isotopic evolution of the deeper mantle.

Oxygen isotope thermometry of quartz-Al2SiO5veins in high-grade metamorphic rocks on Naxos island (Greece)

NASA Astrophysics Data System (ADS)

Putlitz, Benita; Valley, John; Matthews, Alan; Katzir, Yaron

2002-04-01

Diffusion models predict that peak metamorphic temperatures are best recorded by the oxygen isotope fractionation between minerals in a bi-mineralic rock in which a refractory accessory mineral with slow oxygen diffusion rate is modally minor to a mineral with a faster diffusion rate. This premise is demonstrated for high-grade metamorphism on the island of Naxos, Greece, where quartz-kyanite oxygen isotope thermometry from veins in high-grade metamorphic pelites gives temperatures of 635-690 °C. These temperatures are in excellent agreement with independent thermometry for the regional M2 peak metamorphic conditions and show that the vein minerals isotopically equilibrated at the peak of metamorphism. Quartz-sillimanite fractionations in the same veins give similar temperatures (680+/-35 °C) and suggest that the veins grew near to the kyanite-sillimanite boundary, corresponding to pressures of 6.5 to 7.5 kbar for temperatures of 635-685 °C. By contrast, quartz-kyanite and quartz-biotite pairs in the host rocks yield lower temperature estimates than the veins (590-600 and 350-550 °C, respectively). These lower apparent temperatures are also predicted from calculations of diffusional resetting in the polyphase host-rock system. The data demonstrate that bimineralic vein assemblages can be used as accurate thermometers in high-temperature rocks whereas retrograde exchange remains a major problem in many polymineralic rocks.

Carbonation by fluid-rock interactions at high-pressure conditions: Implications for carbon cycling in subduction zones

NASA Astrophysics Data System (ADS)

Piccoli, Francesca; Vitale Brovarone, Alberto; Beyssac, Olivier; Martinez, Isabelle; Ague, Jay J.; Chaduteau, Carine

2016-07-01

Carbonate-bearing lithologies are the main carbon carrier into subduction zones. Their evolution during metamorphism largely controls the fate of carbon, regulating its fluxes between shallow and deep reservoirs. Recent estimates predict that almost all subducted carbon is transferred into the crust and lithospheric mantle during subduction metamorphism via decarbonation and dissolution reactions at high-pressure conditions. Here we report the occurrence of eclogite-facies marbles associated with metasomatic systems in Alpine Corsica (France). The occurrence of these marbles along major fluid-conduits as well as textural, geochemical and isotopic data indicating fluid-mineral reactions are compelling evidence for the precipitation of these carbonate-rich assemblages from carbonic fluids during metamorphism. The discovery of metasomatic marbles brings new insights into the fate of carbonic fluids formed in subducting slabs. We infer that rock carbonation can occur at high-pressure conditions by either vein-injection or chemical replacement mechanisms. This indicates that carbonic fluids produced by decarbonation reactions and carbonate dissolution may not be directly transferred to the mantle wedge, but can interact with slab and mantle-forming rocks. Rock-carbonation by fluid-rock interactions may have an important impact on the residence time of carbon and oxygen in subduction zones and lithospheric mantle reservoirs as well as carbonate isotopic signatures in subduction zones. Furthermore, carbonation may modulate the emission of CO2 at volcanic arcs over geological time scales.

Advanced Photonic Sensors Enabled by Semiconductor Bonding

DTIC Science & Technology

2010-05-31

a dry scroll backing pump to maintain the high differential pressure between the UV gun and the sample/analysis chamber. We also replaced the...semiconductor materials in an ultra-high vacuum (UHV) environment where the properties of the interface can be controlled with atomic-level precision. Such...year research program, we designed and constructed a unique system capable of fusion bonding two wafers in an ultra-high vacuum environment. This system

Characterising the metamorphic discontinuity across the Main Central Thrust Zone of eastern-central Nepal

NASA Astrophysics Data System (ADS)

Wang, Jiamin; Zhang, Jinjiang; Wei, Chunjing; Rai, SantaMan; Wang, Meng; Qian, Jiahui

2015-04-01

The Main Central Thrust Zone (MCTZ) is a top-to-south shear zone that has exhumed the high-grade Himalayan metamorphic core during the orogeny. Identifying the location of the MCTZ is a major challenge and the characteristics of the metamorphic discontinuity remain under debate. To clarify this issue, petrologic and thermobarometric studies were carried out on metapelites and metapsammites that were collected from the basal Nyalam transect in eastern-central Nepal. Results reveal that the metamorphic discontinuity across the MCTZ is characterised by a continuous increase in peak P-T conditions toward higher structural levels, a relatively high field temperature gradient (25-50 °C km-1) and different types of P-T paths. Specifically, representative rocks in the MCTZ record sub-solidus peak conditions (637 ± 16 °C and 9.2 ± 1.0 kbar) and a hairpin-type P-T path. The lower GHC rocks record supra-solidus peak conditions (690 ± 32 °C and 10.3 + 1.1/-1.4 kbar) and a prograde loading path with a small segment of decompression. The presence of a high field pressure gradient across the MCTZ is debatable in the Nyalam transect due to the large uncertainties in pressure estimates. Comparison between obtained P-T results and model predictions indicates that a multiple thrusting process dominated exhumation of the MCTZ and lower GHC rocks, while crustal flow contributed partly to exhumation of the lower GHC rocks.

Mesozoic thermal history and timing of structural events for the Yukon-Tanana Upland, east-central Alaska: 40Ar/39Ar data from metamorphic and plutonic rocks

USGS Publications Warehouse

Dusel-Bacon, C.; Lanphere, M.A.; Sharp, W.D.; Layer, P.W.; Hansen, V.L.

2002-01-01

We present new 40Ar/39Ar ages for hornblende, muscovite, and biotite from metamorphic and plutonic rocks from the Yukon-Tanana Upland, Alaska. Integration of our data with published 40Ar/39Ar, kinematic, and metamorphic pressure (P) and temperature (T) data confirms and refines the complex interaction of metamorphism and tectonism proposed for the region. The oldest metamorphic episode(s) postdates Middle Permian magmatism and predates the intrusion of Late Triassic (215-212 Ma) granitoids into the Fortymile River assemblage (Taylor Mountain assemblage of previous papers). In the eastern Eagle quadrangle, rapid and widespread Early Jurassic cooling is indicated by ???188-186 Ma 40Ar/39Ar plateau ages for hornblende from plutons that intrude the Fortymile River assemblage, and for metamorphic minerals from the Fortymile River assemblage and the structurally underlying Nasina assemblage. We interpret these Early Jurassic ages to represent cooling resulting from northwest-directed contraction that emplaced the Fortymile River assemblage onto the Nasina assemblage to the north as well as the Lake George assemblage to the south. This cooling was the final stage of a continuum of subduction-related contraction that produced crustal thickening, intermediate- to high-P metamorphism within both the Fortymile River assemblage and the structurally underlying Lake George assemblage, and Late Triassic and Early Jurassic plutonism in the Fortymile River and Nasina assemblages. Although a few metamorphic samples from the Lake George assemblage yield Jurassic 40Ar/39Ar cooling ages, most yield Early Cretaceous 40Ar/39Ar ages: hornblende ???135-115 Ma, and muscovite and biotite ???110-108 Ma. We interpret the Early Cretaceous metamorphic cooling, in most areas, to have resulted from regional extension and exhumation of the lower plate, previously tectonically thickened during Early Jurassic and older convergence.

Synchronous formation of the metamorphic sole and igneous crust of the Semail ophiolite: New constraints on the tectonic evolution during ophiolite formation from high-precision U-Pb zircon geochronology

NASA Astrophysics Data System (ADS)

Rioux, Matthew; Garber, Joshua; Bauer, Ann; Bowring, Samuel; Searle, Michael; Kelemen, Peter; Hacker, Bradley

2016-10-01

The Semail (Oman-United Arab Emirates) and other Tethyan-type ophiolites are underlain by a sole consisting of greenschist- to granulite-facies metamorphic rocks. As preserved remnants of the underthrust plate, sole exposures can be used to better understand the formation and obduction of ophiolites. Early models envisioned that the metamorphic sole of the Semail ophiolite formed as a result of thrusting of the hot ophiolite lithosphere over adjacent oceanic crust during initial emplacement; however, calculated pressures from granulite-facies mineral assemblages in the sole suggest the metamorphic rocks formed at >35 km depth, and are too high to be explained by the currently preserved thickness of ophiolite crust and mantle (up to 15-20 km). We have used high-precision U-Pb zircon dating to study the formation and evolution of the metamorphic sole at two well-studied localities. Our previous research and new results show that the ophiolite crust formed from 96.12-95.50 Ma. Our new dates from the Sumeini and Wadi Tayin sole localities indicate peak metamorphism at 96.16 and 94.82 Ma (±0.022 to 0.035 Ma), respectively. The dates from the Sumeini sole locality show for the first time that the metamorphic rocks formed either prior to or during formation of the ophiolite crust, and were later juxtaposed with the base of the ophiolite. These data, combined with existing geochemical constraints, are best explained by formation of the ophiolite in a supra-subduction zone setting, with metamorphism of the sole rocks occurring in a subducted slab. The 1.3 Ma difference between the Wadi Tayin and Sumeini dates indicates that, in contrast to current models, the highest-grade rocks at different sole localities underwent metamorphism, and may have returned up the subduction channel, at different times.

Nanowire growth kinetics in aberration corrected environmental transmission electron microscopy

DOE PAGES

Chou, Yi -Chia; Panciera, Federico; Reuter, Mark C.; ...

2016-03-15

Here, we visualize atomic level dynamics during Si nanowire growth using aberration corrected environmental transmission electron microscopy, and compare with lower pressure results from ultra-high vacuum microscopy. We discuss the importance of higher pressure observations for understanding growth mechanisms and describe protocols to minimize effects of the higher pressure background gas.

Monazite behaviours during high-temperature metamorphism: a case study from Dinggye region, Tibetan Himalaya

NASA Astrophysics Data System (ADS)

Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Shi-Ran; Zhang, Jin-Jiang

2017-04-01

Monazite is a key accessory mineral for metamorphic geochronology, but its growth mechanisms during melt-bearing high-temperature metamorphism is not well understood. Therefore, the petrology, pressure-temperature and timing of metamorphism have been investigated in pelitic and psammitic granulites from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent an isothermal decompression process from pressure conditions of >10 kbar to <5 kbar with constant temperatures of 750-830°C, and recorded three metamorphic stages of kyanite-grade (M1), sillimanite-grade (M2) and cordierite-spinel grade (M3). Monazite and zircon crystals were analyzed for ages by microbeam techniques either in mounts or thin sections. Ages were linked to specific conditions of mineral growth by comprehensive studies on zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural correlations with coexisting minerals. The results show that inherited domains (500-400 Ma) are common in monazite even at granulite-facies conditions. Few monazites formed at the M1-stage ( 30-29 Ma) and recorded heterogeneous Th, Y, and HREE compositions, which formed by recrystallization related to muscovite dehydration melting reaction. These monazite grains were protected from dissolution or lateral overprinting mainly by the armour effect of matrix crystals (biotite and quartz). Most monazite grains formed at the M3-stage (21-19 Ma) through either dissolution-reprecipitation or recrystallization that was related to biotite dehydration melting reaction. These monazite grains record HREE and Y signatures in local equilibrium with different reactions involving either garnet breakdown or peritectic garnet growth. Another peak of monazite growth occurs during melt crystallization ( 15 Ma), and these monazites are unzoned and have homogeneous compositions. Our results documented the widespread recrystallization to account for monazite growth during high-temperature metamorphism and related melting reactions that trigger monazite recrystallization. In a regional sense, our P-T-t data along with published data indicate that the pre-M1 eclogite-facies metamorphism occurred at 39-30 Ma in the Dinggye Himalaya. Our results are in favour of a steady exhumation of the GHC rocks since Oligocene that was contributed by partial melting. Key words: U-Th-Pb geochronology, Monazite, Recrystallization, Pelitic granulite, Himalaya

Unconventional barometry and rheometry: new quantification approaches for mechanically-controlled microstructures

NASA Astrophysics Data System (ADS)

Tajcmanova, L.; Moulas, E.; Vrijmoed, J.; Podladchikov, Y.

2016-12-01

Estimation of pressure-temperature (P-T) from petrographic observations in metamorphic rocks has become a common practice in petrology studies during the last 50 years. This data often serves as a key input in geodynamic reconstructions and thus directly influences our understanding of lithospheric processes. Such an approach might have led the metamorphic geology field to a certain level of quiescence. In the classical view of metamorphic quantification approaches, fast viscous relaxation (and therefore constant pressure across the rock microstructure) is assumed, with chemical diffusion being the limiting factor in equilibration. Recently, we have focused on the other possible scenario - fast chemical diffusion and slow viscous relaxation - and brings an alternative interpretation of chemical zoning found in high-grade rocks. The aim has been to provide insight into the role of mechanically maintained pressure variations on multi-component chemical zoning in minerals. Furthermore, we used the pressure information from the mechanically-controlled microstructure for rheological constrains. We show an unconventional way of relating the direct microstructural observations in rocks to the nonlinearity of rheology at time scales unattainable by laboratory measurements. Our analysis documents that mechanically controlled microstructures that have been preserved over geological times can be used to deduce flow-law parameters and in turn estimate stress levels of minerals in their natural environment. The development of the new quantification approaches has opened new horizons in understanding the phase transformations in the Earth's lithosphere. Furthermore, the new data generated can serve as a food for thought for the next generation of fully coupled numerical codes that involve reacting materials while respecting conservation of mass, momentum and energy.

Thermal contraints on high-pressure granulite metamorphism of supracrustal rocks

NASA Technical Reports Server (NTRS)

Ashwal, L. D.; Morgan, P.; Leslie, W. W.

1983-01-01

The circumstances leading to the formation and exposure at the Earth's surface of supracrustal granulites are examined. These are defined as sediments, volcanics, and other rock units which originally formed at the surface of the Earth, were metamorphosed to high-pressure granulite facies (T = 700-900 C, P = 5-10 kbar), and reexposed at the Earth's surface, in many cases underlain by normal thicknesses of continental crust (30-40 km). Five possible heating mechanisms to account for granulite metamorphism of supracrustal rocks are discussed: magnetic heating, thermal relaxation of perturbed temperature profiles following underthrusting of the continental crust, thermal relaxation after underthrusting of thin slivers of supracrustal rocks below continental crust of normal thickness, major preheating of the upper plate, and shear heating caused by frictional stress along the thrust plane.

Ar/Ar geochronology in the western Tianshan (northwestern China): from Carboniferous (ultra)high-pressure metamorphism and thrusting to Permian strike-slip deformation and fluid ingress

NASA Astrophysics Data System (ADS)

de Jong, K.; Wang, B.; Ruffet, G.; Shu, L. S.; Faure, M.

2012-04-01

The Tianshan belt (northwestern China) is a major tectonic element of the southern Central Asian Orogenic Belt that contains a number of ophiolitic mélanges and (ultra)high-pressure metamorphic belts formed after closure of oceanic and back-arc basins that resulted in terrane collisions. Deciphering its tectonic evolution is thus crucial for understanding the amalgamation of Central Asia. We produce robust 40Ar/39Ar laser-probe evidence that the Tianshan is a Late Palaeozoic (ultra)high-pressure metamorphic collision belt, not a Triassic one, as suggested by some SHRIMP zircon ages in recent literature. Instead of trying to date the peak pressure conditions we focused on 40Ar/39Ar analysis of white mica formed during retrograde recrystallisation when the (ultra)high-pressure metamorphic rocks of the Changawuzi-Kekesu complex were exhumed. Exhumation was coeval with their northward thrusting over the southern margin of the Yili terrane, the easternmost element of the Kazakhstan composite super-terrane, which produced main phase tectonic structures. The Yili terrane comprises a Proterozoic basement covered by metasediments, intruded by Early Carboniferous granites when it formed part of a continental margin arc. During the Permian deformation was partitioned in vertical brittle-ductile strike-slip fault zones that reactivated these suture zones and in which bimodal magmatism was concentrated. We also investigate the effects of these events on the isotopic ages of mica. 40Ar/39Ar laser-probe dating of white mica reveals that the strongest retrogressed blueschists immediately above the basal thrust fault of the Changawuzi-Kekesu belt gave the youngest plateau age of 316 ± 2 Ma (1σ). White mica in greenschist-facies metamorphic quartzite from the ductilely deformed metasedimentary cover of the Yili terrane's crystalline basement, taken at about 1 km below the thrust contact with the overlying Changawuzi-Kekesu belt, yielded a plateau age of 323 ± 1 Ma (1σ). Elsewhere, such metasediments yielded plateau ages (1σ) of 253 ± 1 (muscovite) and 252 ± 1 (biotite) Ma, whereas biotite from an undeformed ca. 340 Ma-old granite intruding the Yili terrane's southern margin gave a 263 ± 1 Ma plateau age (1σ). The 263-252-Ma-old samples were taken between 2 and 5 km across strike from the Permian Qingbulak-Nalati strike-slip fault, and within the 15-20 km wide zone with steeply dipping tectonic fabrics used by intruding Permian granites, and associated mineralisations. We interpret these Permian ages by recrystallisation of the mica by (late magmatic?) fluid flow channeled into these steep zones. Laser-probe dating of mylonite whole-rock samples from the North Tianshan - Main Tianshan strike-slip fault zone yielded 40Ar/39Ar spectra with step ages in the 255-285 Ma range, which date the movement on this ductile shear zone. The picture is emerging that a convective fluid system partly driven by magmatic heat, existed in a strongly fractured and weakened crust with an elevated heat flow, leading to regional-scale isotope resetting. We suggest that surprisingly young isotopic ages for early orogenic (ultra)high-pressure metamorphism are similarly due to fluid-mediated recrystallisation, leading to the erroneous view that the Tianshan is a Triassic orogenic belt.

Archaean and Palaeoproterozoic metamorphic events in the Orekhov-Pavlograd compressional zone, Ukrainian Shield

NASA Astrophysics Data System (ADS)

Yurchenko, A. V.

2012-04-01

The Orekhov-Pavlograd zone (OPZ) is located between the Mesoarchaean-Neoarchaean Middle Dnieper Province and the Mesoarchaean-Palaeoproterozoic Azov Province in the eastern Ukrainian Shield. The OPZ consists of Archaean and Palaeoproterozoic high-grade metamorphic rocks. According U-Pb isotope analyses Archaean methaigneous rocks have age of 3.5-3.3 Ga, and latest AR events dated form both individual grains and metamorphic rims in the tonalite and the granitic vein occurred at about 2.88 Ga ego. Paleoproterozoic zircons from a hornblende granulite have a concordia age of 2.08 Ga [1]. P-T conditions of the 3.5-3.3 Ga processes calculated from the Ti content in zircon are of 730-760°C. Metamorphic event dated as 2.88 Ga is more preserved and detected in some amphibolites after mafic dykes. According to different methods of hornblende-plagioclase geothermometry along with Al- and Ti-geobarometry of hornblende, the amphibolites have formed at temperature of 735-749 °C and pressure of 5.2 to 7.8 kbar. P-T conditions of Paleoproterozoic metamorphic processes have been calculated for a Paleoproterozoic high-Al paragneiss and mafic rocks. On the base of the computer software THERIAK-DOMINO [2], near-isothermal decompression from ca. 8.5 to 6.0 kbar at 650 °C and then to 5.8 kbar at 740 °C has been determined for small irregular garnet grains (grs 4-7% and XMg 0.36-0.37) associated with the same biotite and plagioclase. P-T conditions obtained by means of the P-T pseudosection calculation are identical within errors to those defined by the Grt + Bt + Pl + Ozt geothermometer by [3] and the geobarometer by [4], T = 675 °C and P = 5.6 kbar. Temperature and pressure calculated for assemblage Grt-Pl-Opx-Amph-Ilm-Ru (mafic rock) by using the TWEEQU method shows: 1) high values of pressure and temperature (ca. 7 kbar and 800 °C) are linked with the first metamorphic event with Opx-Cpx assemblage, 2) moderate values (ca. 5 kbar and ca. 600 °C) are referred to the second metamorphic event when amphibole was crystallized instead of orthopyroxene. The latest metamorphic reworking took place at P = 3.3-4 kbar and T = ca. 600 °C. The resulting Paleoproterozoic P-T-t path suggests a clockwise P-T evolution of the OPZ area. Preferences: 1. S.B.Lobach-Zhuchenko, Yu.S.Egorova, A.V.Yurchenko, V.V.Balagansky, G.V.Artemenko, V.P.Chekulaev, N.A.Arestova, 2009. Mineralogical Journal (Kiev), 31 (1): 3-10. 2. de Capitani, C., 2005. THERIAK - DOMINO User's Guide, Version 1402005, http://titan. minpet.unibas.ch/minpet/theriak/theruser.html (04/2007). 3. Ferry, J.M., Spear, F.S., 1978. Experimental calibration of the partitioning of Fe and Mg between biotite and garnet. Contrib. Mineral. Petrol. 66, 113-117. 4. Koziol, A.M., Newton, R.C., 1989. Grossular activity-composition relationship in ternary garnets determined by reversed displaced-equilibrium experiments. Contrib. Mineral. Petrol. 103, 423-433.

Metamorphic sole formation reveals plate interface rheology during early subduction

NASA Astrophysics Data System (ADS)

Mathieu, S.; Agard, P.; Dubacq, B.; Plunder, A.; Prigent, C.

2015-12-01

Metamorphic soles are m to ~500m thick tectonic slices welded beneath most large ophiolites. They correspond to highly to mildly deformed portions of oceanic lithosphere metamorphosed at amphibolite to granulite facies peak conditions. Metamorphic soles are interpreted as formed ≤1-2Ma after intraoceanic subduction initiation by heat transfer from the hot, incipient mantle wegde to the underthrusting lower plate. Their early accretion and exhumation together with the future ophiolite implies at least one jump of the subduction plate interface from above to below the metamorphic sole. Metamorphic soles thus represent one of the few remnants of the very early evolution of the subduction plate interface and provide major constraints on the thermal structure and the effective rheology of the crust and mantle along the nascent slab interface.We herein present a structural and petrological detailed description of the Oman and Turkey metamorphic soles. Both soles present a steep inverted metamorphic structure, with isograds subparallel to the peridotite contact, in which the proportion of mafic rocks, pressure and temperature conditions increase upward. They comprise, as most metamorphic soles worldwide, two main units: (1) a high-grade unit adjacent to the overlying peridotite composed of granulitized to amphibolized metabasalts, with rare metasedimentary interlayers (~800±100ºC at 10±2kbar) and (2) a low-grade greenschist facies unit composed of metasedimentary rocks with rare metatuffs (~500±100ºC at 5±2kbar). We provide for the first time refined P-T peak condition estimations by means of pseudosection modelling and maximum temperature constraints for the Oman low-grade sole by RAMAN thermometry. In order to quantify micro-scale deformations trough the sole, we also present EBSD data on the Oman garnet-bearing and garnet-free high-grade sole.With these new constraints, we finally propose a new conceptual mechanical model for metamorphic sole formation. This model excludes the presence of a continuous inverted metamorphic gradient through the sole but implies the stacking of several homogeneous slivers to constitute the present structure of the sole. These successive thrusts are the result of rheological changes as the plate interface progressively cools.

New evidence for an old idea: Geochronological constraints for a paired metamorphic belt in the central European Variscides

NASA Astrophysics Data System (ADS)

Will, T. M.; Schmädicke, E.; Ling, X.-X.; Li, X.-H.; Li, Q.-L.

2018-03-01

New geochronological data reveal a prolonged tectonothermal evolution of the Variscan Odenwald-Spessart basement, being part of the Mid-German Crystalline Zone in central Europe. We report the results from (i) secondary ion mass spectrometry (SIMS) U-Pb dating of zircon, rutile and monazite, (ii) SIMS zircon oxygen isotope analyses, (iii) laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) zircon Lu-Hf isotope analyses and, (iv) LA-ICPMS zircon and rutile trace element data for a suite of metamorphic rocks (five amphibolite- and eclogite-facies mafic meta-igneous rocks and one granulite-facies paragneiss). The protoliths of the mafic rocks formed from juvenile as well as depleted mantle sources in distinct tectonic environments at different times. Magmatism took place at a divergent oceanic margin (possibly in a back-arc setting) at 460 Ma, in an intraoceanic basin at ca. 445 Ma and at a continental margin at 329 Ma. Regardless of lithology, zircon in eclogite, amphibolite and high-temperature paragneiss provide almost identical Carboniferous ages of 333.7 ± 4.1 Ma (eclogite), 329.1 ± 1.8 to 328.4 ± 8.9 Ma (amphibolite), and 334.0 ± 2.0 Ma (paragneiss), respectively. Rutile yielded ages of 328.6 ± 4.7 and 321.4 ± 7.0 Ma in eclogite and amphibolite, and monazite in high-temperature paragneiss grew at 330.1 ± 2.4 Ma (all ages are quoted at the 2σ level). The data constrain coeval high-pressure eclogite- and high-temperature granulite-facies metamorphism of the Odenwald-Spessart basement at ca. 330 Ma. Amphibolite-facies conditions were attained shortly afterwards. The lower plate eclogite formed in a fossil subduction zone and the upper plate high-temperature, low-pressure rocks are the remains of an eroded Carboniferous magmatic arc. The close proximity of tectonically juxtaposed units of such radically different metamorphic conditions and thermal gradients is characteristic for a paired metamorphic belt sensu Miyashiro (1961). Thus, the Odenwald-Spessart basement represents the first recognised paired metamorphic belt in the European Variscides.

Ultra-high speed vacuum pump system with first stage turbofan and second stage turbomolecular pump

DOEpatents

Jostlein, Hans

2006-04-04

An ultra-high speed vacuum pump evacuation system includes a first stage ultra-high speed turbofan and a second stage conventional turbomolecular pump. The turbofan is either connected in series to a chamber to be evacuated, or is optionally disposed entirely within the chamber. The turbofan employs large diameter rotor blades operating at high linear blade velocity to impart an ultra-high pumping speed to a fluid. The second stage turbomolecular pump is fluidly connected downstream from the first stage turbofan. In operation, the first stage turbofan operates in a pre-existing vacuum, with the fluid asserting only small axial forces upon the rotor blades. The turbofan imparts a velocity to fluid particles towards an outlet at a high volume rate, but moderate compression ratio. The second stage conventional turbomolecular pump then compresses the fluid to pressures for evacuation by a roughing pump.

The Effect of O2, H2O, and N2 on the Fatigue Crack Growth Behavior of an Alpha + Beta Titanium Alloy at 24 C and 177 C

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Piascik, Robert S.

2001-01-01

To study the effects of atmospheric species on the fatigue crack growth behavior of an a+B titanium alloy (Ti 6-2-2-2-2) at room temperature and 177 C, fatigue tests were performed in laboratory air, ultrahigh vacuum, and high purity water vapor, oxygen, nitrogen and helium at various partial pressures. Accelerated fatigue crack growth rates in laboratory air compared to ultrahigh vacuum are linked to the damaging effects of both water vapor and oxygen. Observations of the fatigue crack growth behavior in ultrahigh purity environments, along with surface film analysis using X-ray photoelectron spectroscopy (XPS), suggest that multiple crack-tip processes govern the damaging effects of air. Three possible mechanisms are proposed: 1) at low pressure (less than 10(exp -1) Pa), accelerated da/dN is likely due to monolayer adsorption on crack-tip surfaces presumably resulting in decreased bond strengths at the fatigue crack tip, 2) for pressures greater than 10(exp -1) Pa, accelerated da/dN in oxygen may result from oxidation at the crack tip limiting reversible slip, and 3) in water vapor, absorption of atomic hydrogen at the reactive crack tip resulting in process zone embrittlement.

Near-isothermal conditions in the middle and lower crust induced by melt migration.

PubMed

Depine, Gabriela V; Andronicos, Christopher L; Phipps-Morgan, Jason

2008-03-06

The thermal structure of the crust strongly influences deformation, metamorphism and plutonism. Models for the geothermal gradient in stable crust predict a steady increase of temperature with depth. This thermal structure, however, is incompatible with observations from high-temperature metamorphic terranes exhumed in orogens. Global compilations of peak conditions in high-temperature metamorphic terranes define relatively narrow ranges of peak temperatures over a wide range in pressure, for both isothermal decompression and isobaric cooling paths. Here we develop simple one-dimensional thermal models that include the effects of melt migration. These models show that long-lived plutonism results in a quasi-steady-state geotherm with a rapid temperature increase in the upper crust and nearly isothermal conditions in the middle and lower crust. The models also predict that the upward advection of heat by melt generates granulite facies metamorphism, and widespread andalusite-sillimanite metamorphism in the upper crust. Once the quasi-steady-state thermal profile is reached, the middle and lower crust are greatly weakened due to high temperatures and anatectic conditions, thus setting the stage for gravitational collapse, exhumation and isothermal decompression after the onset of plutonism. Near-isothermal conditions in the middle and lower crust result from the thermal buffering effect of dehydration melting reactions that, in part, control the shape of the geotherm.

Degassing procedure for ultrahigh vacuum

NASA Technical Reports Server (NTRS)

Moore, B. C.

1979-01-01

Calculations based on diffusion coefficients and degassing rates for stainless-steel vacuum chambers indicate that baking at lower temperatures for longer periods give lower ultimate pressures than rapid baking at high temperatures. Process could reduce pressures in chambers for particle accelerators, fusion reactors, material research, and other applications.

Highly informative multiclass profiling of lipids by ultra-high performance liquid chromatography - Low resolution (quadrupole) mass spectrometry by using electrospray ionization and atmospheric pressure chemical ionization interfaces.

PubMed

Beccaria, Marco; Inferrera, Veronica; Rigano, Francesca; Gorynski, Krzysztof; Purcaro, Giorgia; Pawliszyn, Janusz; Dugo, Paola; Mondello, Luigi

2017-08-04

A simple, fast, and versatile method, using an ultra-high performance liquid chromatography system coupled with a low resolution (single quadrupole) mass spectrometer was optimized to perform multiclass lipid profiling of human plasma. Particular attention was made to develop a method suitable for both electrospray ionization and atmospheric pressure chemical ionization interfaces (sequentially in positive- and negative-ion mode), without any modification of the chromatographic conditions (mobile phase, flow-rate, gradient, etc.). Emphasis was given to the extrapolation of the structural information based on the fragmentation pattern obtained using atmospheric pressure chemical ionization interface, under each different ionization condition, highlighting the complementary information obtained using the electrospray ionization interface, of support for related molecule ions identification. Furthermore, mass spectra of phosphatidylserine and phosphatidylinositol obtained using the atmospheric pressure chemical ionization interface are reported and discussed for the first time. Copyright © 2017 Elsevier B.V. All rights reserved.

X-ray diffraction investigation of amorphous calcium phosphate and hydroxyapatite under ultra-high hydrostatic pressure

NASA Astrophysics Data System (ADS)

Lam, Elisa; Gu, Qinfen; Swedlund, Peter J.; Marchesseau, Sylvie; Hemar, Yacine

2015-11-01

The changes in the crystal structures of synthetically prepared amorphous calcium phosphate (ACP) and hydroxyapatite (HAP) in water (1:1 mass ratio) were studied by synchrotron X-ray diffraction (XRD) under ultra-high hydrostatic pressures as high as 2.34 GPa for ACP and 4 GPa for HAP. At ambient pressure, the XRD patterns of the ACP and HAP samples in capillary tubes and their environmental scanning electron micrographs indicated amorphous and crystalline characteristics for ACP and HAP, respectively. At pressures greater than 0.25 GPa, an additional broad peak was observed in the XRD pattern of the ACP phase, indicating a partial phase transition from an amorphous phase to a new high-pressure amorphous phase. The peak areas and positions of the ACP phase, as obtained through fitting of the experimental data, indicated that the ACP exhibited increased pseudo-crystalline behavior at pressures greater than 0.96 GPa. Conversely, no structural changes were observed for the HAP phase up to the highest applied pressure of 4 GPa. For HAP, a unit-cell reduction during compression was evidenced by a reduction in both refined lattice parameters a and c. Both ACP and HAP reverted to their original structures when the pressure was fully released to ambient pressure.

A nanofiber based artificial electronic skin with high pressure sensitivity and 3D conformability

NASA Astrophysics Data System (ADS)

Zhong, Weibin; Liu, Qiongzhen; Wu, Yongzhi; Wang, Yuedan; Qing, Xing; Li, Mufang; Liu, Ke; Wang, Wenwen; Wang, Dong

2016-06-01

Pressure sensors with 3D conformability are highly desirable components for artificial electronic skin or e-textiles that can mimic natural skin, especially for application in real-time monitoring of human physiological signals. Here, a nanofiber based electronic skin with ultra-high pressure sensitivity and 3D conformability is designed and built by interlocking two elastic patterned nanofibrous membranes. The patterned membrane is facilely prepared by casting conductive nanofiber ink into a silicon mould to form an array of semi-spheroid-like protuberances. The protuberances composed of intertwined elastic POE nanofibers and PPy@PVA-co-PE nanofibers afford a tunable effective elastic modulus that is capable of capturing varied strains and stresses, thereby contributing to a high sensitivity for pressure sensing. This electronic skin-like sensor demonstrates an ultra-high sensitivity (1.24 kPa-1) below 150 Pa with a detection limit as low as about 1.3 Pa. The pixelated sensor array and a RGB-LED light are then assembled into a circuit and show a feasibility for visual detection of spatial pressure. Furthermore, a nanofiber based proof-of-concept wireless pressure sensor with a bluetooth module as a signal transmitter is proposed and has demonstrated great promise for wireless monitoring of human physiological signals, indicating a potential for large scale wearable electronic devices or e-skin.Pressure sensors with 3D conformability are highly desirable components for artificial electronic skin or e-textiles that can mimic natural skin, especially for application in real-time monitoring of human physiological signals. Here, a nanofiber based electronic skin with ultra-high pressure sensitivity and 3D conformability is designed and built by interlocking two elastic patterned nanofibrous membranes. The patterned membrane is facilely prepared by casting conductive nanofiber ink into a silicon mould to form an array of semi-spheroid-like protuberances. The protuberances composed of intertwined elastic POE nanofibers and PPy@PVA-co-PE nanofibers afford a tunable effective elastic modulus that is capable of capturing varied strains and stresses, thereby contributing to a high sensitivity for pressure sensing. This electronic skin-like sensor demonstrates an ultra-high sensitivity (1.24 kPa-1) below 150 Pa with a detection limit as low as about 1.3 Pa. The pixelated sensor array and a RGB-LED light are then assembled into a circuit and show a feasibility for visual detection of spatial pressure. Furthermore, a nanofiber based proof-of-concept wireless pressure sensor with a bluetooth module as a signal transmitter is proposed and has demonstrated great promise for wireless monitoring of human physiological signals, indicating a potential for large scale wearable electronic devices or e-skin. Electronic supplementary information (ESI) available. See DOI: 10.1039/c6nr02678h

PT conditions of metamorphism in the Wami River granulite complex, central coastal Tanzania: implications for Pan-African geotectonics in the Mozambique Belt of eastern Africa

NASA Astrophysics Data System (ADS)

Maboko, M. A. H.

1997-02-01

Solid-solution equilibria for gamet-clinopyroxene pairs in the early Pan-African Wami River granulite complex of central coastal Tanzania indicate metamorphic recrystallization at a temperature of about 700°C and a pressure of 8-9 kb, corresponding to metamorphism at a depth of 30-40 km. This suggests that granulite formation was preceded by an anomalous regional crustal thickening, similar to the crustal doubling that accompanies Phanerozoic continent-continent collisions of the Himalaya type. The analogy prompts the interpretation of the Wami River granulite complex, and possibly the rest of the granulite complexes in the Mozambique Belt, as slices of the underthrusted plate, which were accreted to the present day African plate following a continent-continent collision during early Pan-African time.

An inverted metamorphic field gradient in the central Brooks Range, Alaska and implications for exhumation of high-pressure/low-temperature metamorphic rocks

USGS Publications Warehouse

Patrick, B.; Till, A.B.; Dinklage, W.S.

1994-01-01

During exhumation of the Brooks Range internal zone, amphibolite-facies rocks were emplaced atop the blueschist/greenschist facies schist belt. The resultant inverted metamorphic field gradient is mappable as a series of isograds encountered as one traverses up structural section. Amphibolite-facies metamorphism occurred at ??? 110 Ma as determined from 40Ar 39Ar analysis of hornblende. This contrasts with 40Ar 39Ar phengite cooling ages from the uderlying schist belt, which are clearly older (by 17-22 m.y.). Fabrics in both the amphibolite-facies rocks and schist belt are characterized by repeated cycles of N-vergent crenulation and transposition that was likely associated with out-of-sequence ductile thrusting in the internal zone of the Brooks Range orogen. Contractional deformation occurred in an overall environment of foreland-directed tectonic transport, broadly synchronous with exhumation of the internal zone, and shortening within the thin-skinned fold and thrust belt. These data are inconsistent with a recently postulated mid-Cretaceous episode of lithospheric extension in northern Alaska. ?? 1994.

Metamorphism, P-T-t Conditions of Formation, and Prospects for the Practical Use of Al2SiO5 Polymorphs, Chloritoid, and Staurolite (Yenisei Ridge)

NASA Astrophysics Data System (ADS)

Kozlov, P. S.

2017-12-01

The Yenisei Ridge is an accretion-collisional orogen located in the southwestern frame of the Siberian Craton in the interfluve between Podkamennaya Tunguska, Angara, Kan, and Yenisei rivers. The Precambrian mono- and polymetamorphic complexes composed predominantly of the Mesoarchean-Neoproterozoic metapelitic rocks have been studied. Based on the typification of metamorphic complexes by pressure, temperature, metamorphic gradient, as well as age of metamorphism, the location scheme of the fields of the Precambrian sedimentary-metamorphic rock which are prospective for searching deposits of high-alumina metamorphic minerals (andalusite, kyanite, and sillimanite, chloritoid, and staurolite) in the Trans-Angara segment of the Yenisei Region, was compiled. The Teya sillimanite and Panimbinsk andalusite deposits, which are confined to the fields of regional metamorphic complexes of iron-alumina metapelites of the And-Sill facies series, are recommended as a priority for the organization of prospecting works and the subsequent involvement to the metallurgical industry. These metapelites are classified as monomineral. Owing to widespread occurrence and abundance of andalusite and sillimanite, the above deposits have significant inferred resources. Stratiform deposits of garnet-staurolite and chloritoid high-alumina rocks are still insufficiently studied and should be investigated further. The prospects for the possible use of high-alumina andalusite and sillimanite together with Middle Tatarka and Kiya nepheline syenite massifs and the bauxites of the Chadobets uplift, already being explored in the region, for production of aluminum oxide, silumin, and aluminum, as well as, the prospects for the expansion of the raw material base of the Boguchansk Electrometallurgical Complex, brought into operation in 2016 in the Lower Angara region, are considered.

Mapping age and trace elements using laser ablation split-stream (LASS) ICPMS

NASA Astrophysics Data System (ADS)

Kylander-Clark, A. R.; Hacker, B. R.; Cottle, J. M.

2012-12-01

One of the biggest challenges in the determination of the timing and rates of metamorphic processes is tying the age of a particular mineral to the conditions (i.e., pressure, temperature, fluid composition) at which that phase grew. Conventional microbeam techniques increase our understanding of crustal evolution by enabling this linkage; e.g., x-ray maps of monazite allow us to pinpoint grain segments that grew under a different set of conditions, cathodoluminescence images of zircon reveal zoning patterns and hence targets for dating different metamorphic and/or igneous events, and rare-earth element (REE) transects across garnet reveal the budget of a variety of trace elements during a metamorphic episode, to name but a few. More recent advances in LA-ICPMS and SIMS have allowed the ability to produce age maps or trace element maps—thus further our understanding of crystallization processes—but not both. Here we employ laser ablation split-stream (LASS) to quantitatively image the age, and trace element signature of datable phases such as zircon, monazite, titanite, and rutile in metamorphic rocks on the micron scale. By mapping the age and TE signature of a metamorphic phase, we can better interpret the metamorphic stage at which all portions of that phase grew, and relate it to other phases/portions of phases within that rock, such as garnet. For example, zircons and monazites from from eclogites reveal complex zoning in REEs indicating growth prior to, during, and post eclogite-facies metamorphism; those zones correspond to distinct age domains. Metamorphosed titanite reveals differences in diffusivities of TEs in inherited portions of the grain; e.g., Pb-loss is more prominent than diffusion of REEs, which in turn diffuse faster than higher charged ions, such as Th.

Can the Metamorphic Basement of Northwestern Guatemala be Correlated with the Chuacús Complex?

NASA Astrophysics Data System (ADS)

Cacao, N.; Martens, U.

2007-05-01

The Chuacús complex constitutes a northward concave metamorphic belt that stretches ca. 150 km south of the Cuilco-Chixoy-Polochic (CCP) fault system in central and central-eastern Guatemala. It represents the basement of the southern edge of the Maya block, being well exposed in the sierra de Chuacús and the sierra de Las Minas. It is composed of high-Al metapelites, amphibolites, quartzofeldspathic gneisses, and migmatites. In central Guatemala the Chuacús complex contains ubiquitous epidote-amphibolite mineral associations, and local relics of eclogite reveal a previous high-pressure metamorphic event. North of the CCP, in the Sierra de Los Cuchumatanes area of western Guatemala, metamorphic rocks have been considered the equivalent of the Chuacús complex and hence been given the name Western Chuacús group, These rocks, which were intruded by granitic rocks and later mylonitized, include chloritic schist and gneiss, biotite-garnet schist, migmatites, and amphibolites. No eclogitic relics have been found within metamorphic rocks in northwestern Guatemala. Petrographic analyses of garnet-biotite schist reveal abundant retrogression and the formation of abundant zeolite-bearing veins associated with intrusion. Although metamorphic conditions in the greenschist and amphibolite facies are similar to those in the sierra de Chuacús, the association with deformed intrusive granites is unique for western Guatemala. Hence a correlation with metasediments intruded by the Rabinal granite in the San Gabriel area of Baja Verapaz seems more feasible than a correlation with the Chuacús complex. This idea is supported by reintegration of the Cenozoic left-lateral displacement along the CCP, which would place the metamorphic basement of western Guatemala north of Baja Verapaz, adjacent to metasediments intruded by granites in the San Gabriel-Rabinal area.

High pressure reaction cell and transfer mechanism for ultrahigh vacuum spectroscopic chambers

NASA Astrophysics Data System (ADS)

Nelson, A. E.; Schulz, K. H.

2000-06-01

A novel high pressure reaction cell and sample transfer mechanism for ultrahigh vacuum (UHV) spectroscopic chambers is described. The design employs a unique modification of a commercial load-lock transfer system to emulate a tractable microreactor. The reaction cell has an operating pressure range of <1×10-4 to 1000 Torr and can be evacuated to UHV conditions to enable sample transfer into the spectroscopic chamber. Additionally, a newly designed sample holder equipped with electrical and thermocouple contacts is described. The sample holder is capable of resistive specimen heating to 400 and 800 °C with current requirements of 14 A (2 V) and 25 A (3.5 V), respectively. The design enables thorough material science characterization of catalytic reactions and the surface chemistry of catalytic materials without exposing the specimen to atmospheric contaminants. The system is constructed primarily from readily available commercial equipment allowing its rapid implementation into existing laboratories.

Thermomagnetic and thermoelectric properties of semiconductors (PbTe, PbSe) at ultrahigh pressures

NASA Astrophysics Data System (ADS)

Ovsyannikov, Sergey V.; Shchennikov, Vladimir V.

2004-02-01

The longitudinal and transverse thermomagnetic Nernst-Ettingshausen (LNE, TNE) effects and the Maggi-Reghi-Leduc (MRL) effect were measured on PbTe and PbSe micro-samples at ultrahigh pressures upto 20 GPa. Values of the mobility of charge carriers as well as the scattering parameter were estimated both for the low- and high-pressure phase of PbTe and PbSe. At about 3 GPa, the maxima of both Nernst-Ettingshausen effects and magnetoresistance (MR) (and hence of the mobility of charge carriers μ), attributed to the gapless state of PbTe and PbSe were established. The TNE effect was found to be the largest among the effects measured, while the MRL was hardly visible even at the highest mobility values of the charge carriers. The possibilities for using thermomagnetic effects in micro-device technologies are discussed.

Metamorphic style and development of the blueschist- to eclogite-facies rocks, Cyclades, Greece

NASA Astrophysics Data System (ADS)

Schumacher, J. C.; Brady, J. B.; Cheney, J. T.

2008-07-01

The island of Syros, Greece is part of the Attic-Cycladic blueschist belt, formed during Mesozoic Eurasia-Africa subduction. The rocks of Syros can be broadly divided into three tectono-stratigraphic units: (I) metamorphosed sedimentary and volcanic rocks (marble-schist sequence), (II) remnants of oceanic crust with fault-bounded packages of blueschist/eclogite-facies mafic rocks and serpentinite (mafic-ultramafic rocks) and (III) the Vari gneiss, which is a tectonic klippe. Low-temperature, high-pressure assemblages are found on several islands in the Cyclades. The best preserved of these rocks are on Syros and Sifnos islands. Mineral compositions and peak metamorphic assemblages are similar on both islands. Both islands are considered to share similar P-T histories with highest-pressure mineral assemblages reflecting conditions of at least 15 kbar and about 500°C.

The metamorphic record of subduction-accretion processes in the Neoarchaean: the Nuuk region, southern West Greenland.

NASA Astrophysics Data System (ADS)

Dziggel, Annika; Kolb, Jochen

2013-04-01

The Nuuk region of southern West Greenland exposes an exceptionally well preserved section through Archaean mid- to lower continental crust, and therefore provides a natural laboratory to study the tectonic processes in the Archaean. The area mainly consists of amphibolite to granulite facies TTG gneisses, narrow supracrustal belts, and minor late-tectonic granites. It is made up of several distinct terranes, including, from NW to SE, the Færingehavn, Tre Brødre, and Tasiusarsuaq terranes. Extensive high-grade metamorphism and a clockwise PT evolution of the Færingehavn terrane in the Neoarchaean (2.72-2.71 Ga) have been interpreted as a result of crustal thickening and thrusting of the Tasiusarsuaq terrane on top of the Tre Brødre and Færingehavn terranes (Nutman and Friend, 2007). Prior to final collision, the Tasiusarsuaq terrane (the upper plate in a plate tectonic model) underwent a prolonged period of compressive deformation between 2.8 and 2.72 Ga (Kolb et al., 2012). The structural evolution was associated with near-isobaric cooling from medium-pressure granulite facies conditions of ca. 850°C and 7.5 kbar to amphibolite facies conditions of ca. 700°C and 6.5-7 kbar (Dziggel et al., 2012). Despite this long period of crustal convergence, there is no evidence for exhumation and/or loading, pointing to a rheologically weak and unstable Archaean crust perhaps due to low density differences and ongoing melt extraction. Rocks of the structurally underlying Færingehavn terrane record a distinctly different metamorphic evolution. Although generally more strongly retrogressed, relict higher-pressure mineral assemblages in mafic granulites and felsic gneisses record conditions of > 8-9 kbar and >= 750°C, indicating burial to depths of at least 30 km along an apparent geothermal gradient of 20-25°C/km. The peak of metamorphism was followed by isothermal decompression at ca. 2.715 Ga (Nutman and Friend, 2007), indicating rapid exhumation of lower crustal rocks during, or shortly after, the main accretionary event. The existence of dual thermal regimes with contrasting PT paths, as well as the good correlation between the timing of collision, high-pressure metamorphism and rapid exhumation are all consistent with plate-tectonic processes operating in the Neoarchaean. However, the crustal convergence in the Nuuk region was not associated with the extreme crustal thickening observed in many younger orogenic belts, and this likely reflects the generally higher mantle temperatures in the Neoarchaean. The prolonged period of crustal convergence prior to final collision may further indicate that the convergence rates in the Archaean were rather low. Dziggel, A., Diener, J.F.A., Stoltz, N.B., Kolb, J., 2012. Role of H2O in the formation of garnet coronas during near-isobaric cooling of mafic granulites: the Tasiusarsuaq terrane, southern West Greenland. Journal of Metamorphic Geology, 30, 957-972. Kolb, J., Kokfelt, T.F., Dziggel, A., 2012. Geodynamic setting and deformation history of an Archaean terrane at mid-crustal level: the Tasiusarsuaq terrane of southern West Greenland. Precambrian Research, 212-213, 34-56. Nutman, A.P. & Friend, C.R.L., 2007. Adjacent terranes with ca. 2715 and 2650 Ma high-pressure metamorphic assemblages in the Nuuk region of the North Atlantic Craton, southern West Greenland: Complexities of Neoarchaean collisional orogeny. Precambrian Research, 155, 159-203.

Successful Cleaning and Study of Contamination of Si(001) in Ultrahigh Vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gheorghe, N. G.; Lungu, G. A.; Husanu, M. A.

2011-10-03

This paper presents the very first surface physics experiment performed in ultrahigh vacuum (UHV) in Romania, using a new molecular beam epitaxy (MBE) installation. Cleaning of a Si(001) wafer was achieved by using a very simple technique: sequences of annealing at 900-1000 deg. C in ultrahigh vacuum: low 10{sup -8} mbar, with a base pressure of 1.5x10{sup -10} mbar. The preparation procedure is quite reproducible and allows repeated cleaning of the Si(001) after contamination in ultrahigh vacuum. The Si(001) single crystal surface is characterized by low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED), and Auger electron spectroscopymore » (AES). The latter technique is utilized in order to investigate the sample contamination by the residual gas in the UHV chamber, as determined by a residual gas analyzer (RGA). Unambiguous assignment of oxidized and unoxidized silicon is provided; also, an important feature is that the LVV Auger peak at 90-92 eV cannot be solely attributed to clean Si (i.e. Si surrounded only by Si), but also to silicon atoms bounded with carbon. Even with a sum of partial pressures of oxygen and carbon containing molecules in the range of 5x10{sup -10} mbar, the sample is contaminated very quickly, having a (1/e) lifetime of about 76 minutes.« less

FUNDAMENTAL PROPERTIES OF ULTRA HIGH PERFORMANCE-STRAIN HARDENING CEMENTITIOUS COMPOSITES AND USAGE FOR REPAIR

NASA Astrophysics Data System (ADS)

Kunieda, Minoru; Shimizu, Kosuke; Eguchi, Teruyuki; Ueda, Naoshi; Nakamura, Hikaru

This paper presents the fundamental properties of Ultra High Performance-Strain Hardening Cementitious Composites (UHP-SHCC), which were depeloped for repair applications. In particular, mechanical properties such as tensile response, shrinkage and bond strength were investigated experimentally. Protective performance of the material such as air permeability, water permeability and penetration of chloride ion was also confirmed comparing to that of ordinary concrete. This paper also introduces the usage of the material in repair of concrete st ructures. Laboratory tests concerining the deterioration induced by corrosion were conducted. The UHP-SHCC that coverd the RC beam resisted not only crack opening along the rebar due to corrosion but also crack opening due to loading tests.

The lower-temperature-pressure stability of pyrope in the presence of quartz in the system MgO-Al2O3-SiO2

NASA Astrophysics Data System (ADS)

Cheng, N.; Jenkins, D. M.

2017-12-01

Pyrope (Mg3Al2Si3O12) is the dominant component in garnets from type A eclogites. Determining the lower-pressure-temperature (P-T) stability of pyrope in the presence of quartz helps put constraints on the stability of quartz-bearing eclogites and therefore the depths to which crustal rocks in high pressure/ultra-high pressure (HP/UHP) terranes can be transferred. It also defines the lower-pressure stability of the nearly pure pyrope-bearing quartzites of the Dora Maira massif of the Western Alps (Chopin, 1984, Contrib. Min. Pet.). Aside from the approximate boundary proposed by Hensen & Essene (1971, Contrib. Min. Pet.), there has been no detailed study of the lower P-T stability of pyrope + quartz. A reversed determination of the reaction 3 enstatite + 2 kyanite = 2 pyrope + 2 quartz has been done in the system MgO-Al2O3-SiO2 over the P-T range of 900-1100 °C and 1.6-2.5 GPa for durations of 24 hours. Double capsules, one using pure enstatite and the other Al-rich (10 wt% Al2O3) enstatite in the starting mixtures, were used to obtain reversals on the Al content in the orthopyroxene (Opx). Experiments were done using a ½-inch diameter piston-cylinder press and NaCl-pyrex-MgO pressure media. Run products were analyzed using powder XRD and electron microprobe. Reaction direction was readily determined from peak height changes on XRD patterns. The reaction has been bracketed at 1.65 GPa at 1100 °C with > 12 wt% Al2O3 in Opx; 2.05 GPa at 1000 °C with 10 wt% Al2O3 in Opx; and 2.4 GPa at 930 °C with 5 wt% Al2O3 in Opx. The reaction boundary is slightly curved to higher P with increasing T caused by increasing Al in Opx. The boundary observed in this study is about 100 °C or 0.4 GPa higher than previously proposed by Hensen & Essene (1971) and 70-170 °C or 0.6-0.7 GPa higher than the boundary calculated in this system using THERMOCALC ds6.22 (Holland & Powell, 2011, J. Meta. Geol.) and about 1-4 wt% higher Al2O3 contents in Opx. Higher pressure runs in the field of coesite are being done using a multi-anvil press to extend these results to the lower T range reported for many UHP terranes. Minor extrapolation of the present data to lower T puts the absolute minimum depth for pyrope-quartzites in Dora Maira at 95 km (3.0 GPa) at 800°C; even greater depths are expected for the reaction of pyrope + quartz + H2O to talc-bearing assemblages.

The extending lithosphere (Arthur Holmes Medal Lecture)

NASA Astrophysics Data System (ADS)

Brun, Jean-Pierre

2017-04-01

Extension of the lithosphere gives birth to a wide range of structures, with characteristic widths between 10 and 1000 km, which includes continental rifts, passive margins, oceanic rifts, core complexes, or back-arc basins. Because the rheology of rocks strongly depends on temperature, this variety of extensional structures falls in two broad categories of extending lithospheres according to the initial Moho temperature TM. "Cold extending systems", with TM < 750°C and mantle-dominated strength, lead to narrow rifts and, if extension is maintained long enough, to passive margins and then mantle core complexes. "Hot extending systems", with TM > 750°C and crustal-dominated strength, lead, depending on strain rate, to either wide rifts or metamorphic core complexes. A much less quoted product of extension is the exhumation of high-pressure (HP ) metamorphic rocks occurring in domains of back-arc extension driven by slab rollback (e.g. Aegean; Appennines-Calabrian) or when the subduction upper plate undergoes extension for plate kinematics reasons (e.g. Norwegian Caledonides; Papua New Guinea). In these tectonic environments, well-documented pressure-temperature-time (P - T - t) paths of HP rocks show a two-stage retrogression path whose the first part corresponds to an isothermal large pressure drop ΔP proportional to the maximum pressure Pmax recorded by the rocks. This linear relation between ΔP and Pmax, which likely results from a stress switch between compression and extension at the onset of exhumation, is in fact observed in all HP metamorphism provinces worldwide, suggesting that the exhumation of HP rocks in extension is a general process rather than an uncommon case. In summary, the modes and products of extension are so diverse that, taken all together, they constitute a very versatile natural laboratory to decipher the rheological complexities of the continental lithosphere and their mechanical implications.

Slab dehydration recorded in subducted serpentine sea-mount

NASA Astrophysics Data System (ADS)

Okamoto, K.; Fukumura, S.; Ishimori, C.; Jung, H.

2014-12-01

It has been considered that there is a correlation between the double seismic zones and metamorphic dehydration reaction in deep slab. The lower seismic plane of the double seismic zone is considered to be located on the 600 oC isotherm in the subducting lithosphere. Antigorite terminal reaction is highly temperature sensitive around 600 oC. Therefore it has been proposed that the oceanic lithosphere was hydrated forming serpentine prior to subduction, then serpentine was decomposed to release fluid causing dehydration embrittlement in the slab. In order to unravel relation between dehydration and seismic deformation, we have investigated dehydration process of natural metamorphic rocks recording very cold geothermal history in the crust and lithosphere in the slab. Metamorphic olivine after antigorite has been described in Italian Alps and also from the Mt. Shiraga, Japan [1]. However, the olivine was formed with talc and fluid by antigorite breakdown reaction in pressures lower than 1.5 GPa. Spinifex olivine with opx in the Cerro del Almirez [2], is the product at pressures (P > 1.5 GPa) relevant to the lower seismic plane beneath Northeast Japan. It clearly indicates the presence of large amount of water facilitate crystallization of elongated olivine with opx. It is also supported by LPO pattern of olivines determined by EBSD. Fine-grained olivine-rich samples shows that Type-C fabric pattern is dominant, suggesting deformation under water-rich condition [3]. With metamorphic olivines, chlorite was also recrystallized, suggesting that water would be transported farther down to deep. The estimated dehydration reaction has a negative P-T slope at pressures higher than 1.5 GPa. The reaction is volume reducing reaction and the olivine-opx spinifex texture was formed under volume reducing reaction. In the warm slab beneath SW Japan, the reaction has a positive slope in P-T space and forms olivine+talc+fluid. From microstrucral and petrological analysis of the Serpentinite in the Sambagawa high P/T metamorphic rocks, we found that the olivine with talc, is preserved mainly in the vein along the shear crack in mylonitized serpentinite. References: [1] K. Okamoto et al., Geochemistry, 46 205-215 (2013). [2] V. Trommsdorff et al., CMP, 132, 139-148 (1998). [3] Jung H, Karato S., Science 293, 1460-1463 (2001)

An ultrahigh pressure homogenization technique for easily exfoliating few-layer phosphorene from bulk black phosphorus

NASA Astrophysics Data System (ADS)

Guan, Qing-Qing; Zhou, Hua-Jing; Ning, Ping; Lian, Pei-Chao; Wang, Bo; He, Liang; Chai, Xin-Sheng

2018-05-01

We have developed an easy and efficient method for exfoliating few-layer sheets of black phosphorus (BP) in N-methyl-2-pyrrolidone, using ultra-high pressure homogenization (UPH). The BP was first exfoliated into sheets that were a few atomic layers thick, using a homogenizer for only 30 min. Next, a double centrifugation procedure was used to separate the material into few-layer nanosheets that were examined by X-ray diffraction, atomic force microscopy (AFM), transmission electron microscopy (TEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) spectroscopy. The results show that the products are specimens of phosphorene that are only a few-layer thick.

Implementation of high slurry concentration and sonication to pack high-efficiency, meter-long capillary ultrahigh pressure liquid chromatography columns.

PubMed

Godinho, Justin M; Reising, Arved E; Tallarek, Ulrich; Jorgenson, James W

2016-09-02

Slurry packing capillary columns for ultrahigh pressure liquid chromatography is complicated by many interdependent experimental variables. Previous results have suggested that combination of high slurry concentration and sonication during packing would create homogeneous bed microstructures and yield highly efficient capillary columns. Herein, the effect of sonication while packing very high slurry concentrations is presented. A series of six, 1m×75μm internal diameter columns were packed with 200mg/mL slurries of 2.02μm bridged-ethyl hybrid silica particles. Three of the columns underwent sonication during packing and yielded highly efficient separations with reduced plate heights as low as 1.05. Copyright © 2016 Elsevier B.V. All rights reserved.

Ultra-High Pressure Driver and Nozzle Survivability in the RDHWT/MARIAH II Hypersonic Wind Tunnel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Costantino, M.; Brown, G.; Raman, K.

2000-06-02

An ultra-high pressure device provides a high enthalpy (> 2500 kJ/kg), low entropy (< 5 kJ/kg-K) air source for the RDHWT/MARIAH II Program Medium Scale Hypersonic Wind Tunnel. The design uses stagnation conditions of 2300 MPa (330,000 Psi) and 750 K (900 F) in a radial configuration of intensifiers around an axial manifold to deliver pure air at 100 kg/s mass flow rates for run times suitable for aerodynamic, combustion, and test and evaluation applications. Helium injection upstream of the nozzle throat reduces the throat wall recovery temperature to about 1200 K and reduces the oxygen concentration at the nozzlemore » wall.« less

Super earth interiors and validity of Birch's Law for ultra-high pressure metals and ionic solids

NASA Astrophysics Data System (ADS)

Ware, Lucas Andrew

2015-01-01

Super Earths, recently detected by the Kepler Mission, expand the ensemble of known terrestrial planets beyond our Solar System's limited group. Birch's Law and velocity-density systematics have been crucial in constraining our knowledge of the composition of Earth's mantle and core. Recently published static diamond anvil cell experimental measurements of sound velocities in iron, a key deep element in most super Earth models, are inconsistent with each other with regard to the validity of Birch's Law. We examine the range of validity of Birch's Law for several metallic elements, including iron, and ionic solids shocked with a two-stage light gas gun into the ultra-high pressure, temperature fluid state and make comparisons to the recent static data.

Ultrahigh-Sensitivity Piezoresistive Pressure Sensors for Detection of Tiny Pressure.

PubMed

Li, Hongwei; Wu, Kunjie; Xu, Zeyang; Wang, Zhongwu; Meng, Yancheng; Li, Liqiang

2018-06-20

High-sensitivity pressure sensors are crucial for the ultrasensitive touch technology and E-skin, especially at the tiny-pressure range below 100 Pa. However, it is highly challenging to substantially promote sensitivity beyond the current level at several to 200 kPa -1 and to improve the detection limit lower than 0.1 Pa, which is significant for the development of pressure sensors toward ultrasensitive and highly precise detection. Here, we develop an efficient strategy to greatly improve the sensitivity near to 2000 kPa -1 using short-channel coplanar device structure and sharp microstructure, which is systematically proposed for the first time and rationalized by the mathematic calculation and analysis. Significantly, benefiting from the ultrahigh sensitivity, the detection limit is improved to be as small as 0.075 Pa. The sensitivity and detection limit are both superior to the current levels and far surpass the function of human skin. Furthermore, the sensor shows fast response time (50 μs), excellent reproducibility and stability, and low power consumption. Remarkably, the sensor shows excellent detection capacity in the tiny-pressure range, including light-emitting diode switching with a pressure of 7 Pa, ringtone (2-20 Pa) recognition, and ultrasensitive (0.1 Pa) electronic glove. This work represents a performance and strategic progress in the field of pressure sensing.

Study on the Pressure Pulsation inside Runner with Splitter Blades in Ultra-High Head Turbine

NASA Astrophysics Data System (ADS)

Meng, L.; Zhang, S. P.; Zhou, L. J.; Wang, Z. W.

2014-03-01

Runners with splitter blades were used widely for the high efficiency and stability. In this paper, the unsteady simulation of an ultra-high head turbine at the best efficiency point, 50% and 75% discharge points were established, to analyze the pressure pulsation in the vaneless space, rotating domain and the draft tube. First of all, runners with different length splitter blades and without splitter blades were compared to learn the efficiency and the pressure distribution on the blade surface. And then the amplitude of the pressure pulsation was analysed. The peak efficiency of the runner with splitter blades is remarkably higher than that of the corresponding impeller without splitter blades. And the efficiency of the turbine is the highest when the length ratio of the splitter blades is 0.75 times the main blades. The pressure pulsation characteristics were also influenced, because the amplitudes of the pulsation induced by the RSI phenomenon were changed as a result of more blades. At last, the best design plan of the length of the splitter blades (length ratio=0.825) was obtained, which improved the pressure pulsation characteristics without significant prejudice to the efficiency.

Deep subduction of hot young oceanic slab required by the Syros eclogites

NASA Astrophysics Data System (ADS)

Flemetakis, Stamatis; Moulas, Evangelos; Kostopoulos, Dimitrios; Chatzitheodoridis, Elias

2014-05-01

The Cycladic islands of Syros and Siphnos, Aegean Sea, Greece, represent subducted IAT and BABB remnants of the Neotethyan Pindos Ocean. Garnet porphyroblasts (Ø=1mm) in a glaucophane-zoisite eclogite from Kini locality on Syros are compositionally zoned and display a unique prograde heating path from a high-pressure greenschist-facies core with high XSps and low Mg# via a blueschist-facies mantle with moderate XSps and Mg# to an eclogite-facies rim with low XSps and high Mg#. The outermost 35 μm of the garnet rims show flat XSps with rapidly increasing outwards Mg#. Na-Act-Chl-Ph rimmed by Gln mark the greenschist-blueschist facies transition, whereas Pg rimmed by Omp and the incoming of Rt at the expense of Ttn signify the blueschist-eclogite facies transition. Raman barometry of quartz inclusions in the eclogitic garnet rims coupled with elastic modelling of the garnet host [1], and Zr-in-Rt and Grt-Cpx-Ph thermobarometry revealed near-UHP P-T conditions of the order of 2.6 GPa/660°C (maximum residual pressure was 0.8-0.9GPa). By contrast, the greenschist-blueschist transition lies at ~0.75 GPa/355°C. This pressure is in excellent agreement with the position of the albite = jadeite + quartz boundary calculated at 350°C using the observed omphacite composition corrected for jadeite activity (Koons & Thompson, 1985) [2]. As a result, Cpx inclusions in garnet core signify the early entrance of garnet in the subduction zone history of the slab. Furthermore, the early growth of garnet (in lower pressures) observed in eclogites from Syros lies in great agreement with published slab-geotherms that indicate hot subduction and show a precocious garnet growth (Baxter and Caddick, 2013) [3]. The complete absence of lawsonite and the great abundance of zoisite crystals, based on the stability fields of both minerals (Poli et al., 2009) [4], further constrain the P-T trajectory of the slab. Our new P-T estimates match published T distributions on the slab surface calculated for a subduction velocity of 3 cm/yr, a subduction angle of 30° and an age of incoming lithosphere of ~20 Ma with a shear stress of 80 MPa at the slab-mantle interface [5]. The above are in excellent agreement with published isotopic work on zircons and garnets from Syros eclogites suggesting crystallisation from magmas derived from a depleted mantle at ~80 Ma and constraining the event of eclogitic metamorphism at ~55 Ma. Diffusion modelling of the garnet outermost rims suggests a brief heating pulse of only ~1,000 years at peak T. [1] Van der Molen (1981) Tectonophysics 73, 323-342 .[2] Koons and Thompson (1985) Chemical Geology 50, 3-30. [3] Baxter and Caddick (2013) Geology 41, 6, 643-646. [4] Poli et al. (2009) Earth and Planetary Science Letters 278, 350-360. [5] Peacock (1993) Geol. Soc. Am. Bull. 105, 684-694 .

Evolution of metamorphic fluids in shear zones: The record from the emeralds of Habachtal, Tauern Window, Austria

NASA Astrophysics Data System (ADS)

Nwe, Y. Y.; Grundmann, G.

1990-11-01

Fluid inclusions in emeralds from the Habachtal, Central Tauern Window, have been studied by microthermometry. Results allow a detailed reconstruction of trapping history and evolution of the metamorphic fluids during the Middle Alpine Tauernkristallisation metamorphic event and some of the subsequent cooling period. Five different types of fluid inclusions, corresponding to at least five trapping periods, have been distinguished. In general, the earliest primary (type 1) inclusions, which occur as negative crystals or thin long tubes, are represented by low salinity ( < 10 wt. % NaCl equivalent) aqueous fluids with or without CO 2 with up to XCO 2 ≈ 0.04. Later primary type 2 inclusions are distinguished by different morphologies and distribution patterns. Lower salinity CO 2-free brines and CO 2-bearing denser inclusions with higher CO 2 contents (up to XCO 2 ≈ 0.11) are characteristic of this stage. The type 2 inclusions may also occur as pseudosecondary arrays. The effects of necking have been studied, and found to be considerable in the type 1 primary inclusions. This mechanism has occasionally resulted in the appearance of almost pure CO 2 fluids. The possibility of fluid immiscibility has been examined, and rejected, for the apparent "coexistence" of primary brine and CO 2-bearing inclusions. Instead, mixing of fluids which fluctuated between two different compositions is proposed. The fluctuation was probably due to the sequence of hydration reactions during the Tauernkristallisation. Maximum trapping pressures (3.6 kbar) obtained for stage 1 of the Tauernkristallisation are thought to represent a situation where sublithostatic fluid pressures exested in shear zones during the crystallisation period of many of the emerald cores and coexisting biotite and actinolite. Maximum fluid pressures of 7 kbar were obtained from the type 2 inclusions. This is similar to pressure estimates obtained from mineral equilibria. At least four phases of deformation are indicated by the trapping history. A pressure-temperature-time path for the Tauernkristallisation and the subsequent cooling/uplift period has been constructed for the Habachtal area, using the maximum pressure estimates obtained in this work together with previously existing data. In the cooling period, fluid pressures lower than the lithostatic load again prevailed. This difference, about 1-2 kbar, was probably due to late stage fracturing and/or the development of an open system. At least two more phases of minor deformation and three more stages of entrapment have been defined for this period. During this time, fluids gradually evolved towards more CO 2-poor, and less saline compositions. The present work shows that the possibility of fluctuations in fluid pressures must be considered seriously when attempting to define the PT cooling path from fluid inclusions in metamorphic rocks, especially those in shear zones. Postulations of retrograde PT paths based on fluid inclusions alone may result in pressure estimates which are too low.

Telescoping metamorphic isograds: Evidence from 40Ar/39A dating in the Orange-Milford belt, southern Connecticut

USGS Publications Warehouse

Kunk, Michael J.; Walsh, Gregory J.; Growdon, Martha L.; Wintsch, Robert P.

2013-01-01

New 40Ar/39Ar ages for hornblende and muscovite from the Orange-Milford belt in southern Connecticut reflect cooling from Acadian amphibolite facies metamorphism between ∼380 to 360 Ma followed by retrograde recrystallization of fabric-forming muscovite and chlorite during lower greenschist facies Alleghanian transpression at ∼280 Ma. Reported field temperature and pressure gradients are improbably high for these rocks and a NW metamorphic field gradient climbing from chlorite-grade to staurolite-grade occurs over less than 5 km. Simple tilting cannot account for this compressed isograd spacing given the geothermal gradient of ∼20 °C/km present at the time of regional metamorphism. However, post-metamorphic transpression could effectively telescope the isograds by stretching the belt at an oblique angle to the isograd traces. Textures in the field and in thin section reveal several older prograde schistosities overprinted by lower greenschist facies fabrics. The late cleavages commonly occur at the scale of ∼100 μm and these samples contain multiple age populations of white mica. 40Ar/39Ar analysis of these poly-metamorphic samples with mixed muscovite populations yield climbing or U-shaped age spectra. The ages of the low temperature steps are late Paleozoic, while the ages of the older steps are late Devonian. These results support our petrologic interpretation that the younger cleavage developed under metamorphic conditions below the closure temperature for Ar diffusion in muscovite, that is, in the lower greenschist facies. The correlation of a younger regionally reproducible age population with a pervasive retrograde muscovite ± chlorite cleavage reveals an Alleghanian (∼280 Ma) overprint on the Acadian metamorphic gradient (∼380 Ma). Outcrop-scale structures including drag folds and imbricate boudins suggest that Alleghanian deformation and cleavage development occurred in response to dextral transpression along a northeast striking boundary. Alleghanian oblique collision of accreting terranes from the northeast would have resulted in northeast-southwest dextral transpression against the New York promontory. This deformation was responsible for crystallization of pervasive retrograde muscovite + chlorite cleavages and associated telescoping of the Acadian metamorphic isograds in southern Connecticut at ∼280 Ma.

Subduction starts by stripping slabs

NASA Astrophysics Data System (ADS)

Soret, Mathieu; Agard, Philippe; Dubacq, Benoît; Prigent, Cécile; Plunder, Alexis; Yamato, Philippe; Guillot, Stéphane

2017-04-01

Metamorphic soles correspond to tectonic slices welded beneath most large-scale ophiolites. These slivers of oceanic crust metamorphosed up to granulite facies conditions are interpreted as having formed during the first My of intra-oceanic subduction from heat transfer from the incipient mantle wedge towards the top of the subducting plate. Our study reappraises the formation of metamorphic sole through detailed field and petrological work on three classical key sections across the Semail ophiolite (Oman and United Arab Emirates). Geothermobarometry and thermodynamic modelling show that metamorphic soles do not record a continuous temperature gradient, as expected from simple heating by the upper plate or by shear heating and proposed by previous studies. The upper, high-temperature metamorphic sole is subdivided in at least two units, testifying to the stepwise formation, detachment and accretion of successive slices from the downgoing slab to the mylonitic base of the ophiolite. Estimated peak pressure-temperature conditions through the metamorphic sole are, from top to bottom, 850˚C - 1GPa, 725°C - 0.8 GPa and 530°C - 0.5 GPa. These estimates appear constant within each unit but separated by a gap of 100 to 200˚C and 0.2 GPa. Despite being separated by hundreds of kilometres below the Semail ophiolite and having contrasting locations with respect to the ophiolite ridge axis, metamorphic soles show no evidence for significant petrological variations along strike. These constraints allow to refine the tectonic-petrological model for the genesis of metamorphic soles, formed through the stepwise stacking of several homogeneous slivers of oceanic crust and its sedimentary cover. Metamorphic soles do not so much result from downward heat transfer (ironing effect) but rather from progressive metamorphism during strain localization and cooling of the plate interface. The successive thrusts are the result of rheological contrasts between the sole (initially at the subducting slab) and the peridotite above as the plate interface progressively cools down. These findings have implications for the thickness, the scale and the coupling state at the plate interface during the early history of subduction/obduction systems.

Pre-Alpine contrasting tectono-metamorphic evolutions within the Southern Steep Belt, Central Alps

NASA Astrophysics Data System (ADS)

Roda, Manuel; Zucali, Michele; Li, Zheng-Xiang; Spalla, Maria Iole; Yao, Weihua

2018-06-01

In the Southern Steep Belt, Italian Central Alps, relicts of the pre-Alpine continental crust are preserved. Between Valtellina and Val Camonica, a poly-metamorphic rock association occurs, which belongs to the Austroalpine units and includes two classically subdivided units: the Languard-Campo nappe (LCN) and the Tonale Series (TS). The outcropping rocks are low to medium grade muscovite, biotite and minor staurolite-bearing gneisses and micaschists, which include interlayered garnet- and biotite-bearing amphibolites, marbles, quartzites and pegmatites, as well as sillimanite-bearing gneisses and micaschists. Permian intrusives (granitoids, diorites and minor gabbros) emplaced in the metamorphic rocks. We performed a detailed structural, petrological and geochronological analysis focusing on the two main lithotypes, namely, staurolite-bearing micaschists and sillimanite-bearing paragneisses, to reconstruct the Variscan and Permian-Triassic history of this crustal section. The reconstruction of the tectono-metamorphic evolution allows for the distinction between two different tectono-metamorphic units during the early pre-Alpine evolution (D1) and predates the Permian intrusives, which comprise rocks from both TS and LCN. In the staurolite-bearing micaschists, D1 developed under amphibolite facies conditions (P = 0.7-1.1 GPa, T = 580-660 °C), while in the sillimanite-bearing paragneisses formed under granulite facies conditions (P = 0.6-1.0 GPa, T> 780 °C). The two tectono-metamorphic units coupled together during the second pre-Alpine stage (D2) under granulite-amphibolite facies conditions at a lower pressure (P = 0.4-0.6 GPa, T = 620-750 °C) forming a single tectono-metamorphic unit (Languard-Tonale Tectono-Metamorphic Unit), which comprised the previously distinguished LCN and TS. Geochronological analyses on zircon rims indicate ages ranging between 250 and 275 Ma for D2, contemporaneous with the emplacement of Permian intrusives. This event developed under a high thermal state, which is compatible with an extensional tectonic setting that occurred during the exhumation of the Languard-Tonale Tectono-Metamorphic Unit. The extensional regime is interpreted as being responsible for the thinning of the Adriatic continental lithosphere during the Permian, which may be related to an early rifting phase of Pangea.

A New Model of the Early Paleozoic Tectonics and Evolutionary History in the Northern Qinling, China

NASA Astrophysics Data System (ADS)

Dong, Yunpeng; Zhang, Guowei; Yang, Zhao; Qu, Hongjun; Liu, Xiaoming

2010-05-01

The Qinling Orogenic Belt extends from the Qinling Mountains in the west to the Dabie Mountains in the east. It lies between the North China and South China Blocks, and is bounded on the north by the Lushan fault and on the south by the Mianlue-Bashan-Xiangguang fault (Zhang et al., 2000). The Qinling Orogenic Belt itself is divided into the North and South Qinling Terranes by the Shangdan suture zone. Although the Shangdan zone is thought to represent the major suture separating the two blocks, there still exists debate about the timing and mechanism of convergence between these two blocks. For instance, some authors suggested an Early Paleozoic collision between the North China Block and South China Block (Ren et al., 1991; Kroner et al., 1993; Zhai et al., 1998). Others postulated left-lateral strike-slip faulting along the Shangdan suture at ca. 315 Ma and inferred a pre-Devonian collision between the two blocks (Mattauer et al., 1985; Xu et al., 1988). Geochemistry of fine-grained sediments in the Qinling Mountains was used to argue for a Silurian-Devonian collision (Gao et al., 1995). A Late Triassic collision has also been proposed (Sengor, 1985; Hsu et al., 1987; Wang et al., 1989), based on the formation of ultrahigh-pressure metamorphic rocks in the easternmost part of the Qinling Orogenic Belt at ~230 Ma (e.g., Li et al., 1993; Ames et al., 1996). Paleomagnetic data favor a Late Triassic-Middle Jurassic amalgamation of the North China and South China Blocks (Zhao and Coe, 1987; Enkin et al., 1992). It is clear that most authors thought that the Qinling Mountains are a collisional orogen, even they have different methods about the timing of the orogeny. Based on new detailed investigations, we propose a new model of the Early Paleozoic Tectonics and Evolutionary History between the North China and South China Blocks along the Shangdan Suture. The Shangdan suture is marked by a great number of ophiolites, island-arc volcanic rocks and other related rock assemblages. Our new geological and geochemical data revealed a lot of ophiolitic mélanges along the Shangdan suture, such as the Guojiagou, Ziyu, Xiaowangjian, Yanwan, Tangzang, Guanzizhen and Wushan areas from east to west. The ophiolite assemblage in Guojiagou, Ziyu area consists mainly of some blocks of E-MORB type and IAB-type basalts, while the pillow lavas from Xiaowangjian are IAB-type basalts. The basalts from the ophiolite assemblages in Yanwan, Tangzang and Wushan areas possess E-MORB geochemical compositions. The zircons of gabbro from Yanwan ophiolite mélange yield an U-Pb age of 516±3.8 Ma, which represents the formation age of the Yanwan ophiolite. Meanwhile, the basalts in the Guanzizhen ophiolite mélange show N-MORB type geochemical signature, and the zircons from gabbro yield a U-Pb age of 471±1.4 Ma, which constraints the formation age of the mature oceanic crust. Additionally, there also exists a U-Pb age of 523±26 Ma (Lu et al.,2003) and Cambrian-Ordovician radiolarites from the interlayed silicarites within the volcanic rock in the Guojiagou ophiolite mélange (Cui et al., 1995). All these geochemical and geochronological evidences indicate that there existed an oceanic basin and its subduction, which separated the Northern China Block from the Southern China Block during 523 -471 Ma. Accordant with this ocean and its subduction, there had been existed an active continental margin, island-arc setting on the north side of the Shangdan ophiolite mélange which were marked by a series of moderate-basic intrude igneous mass along the Sifangtai-Lajimiao area (Li et al., 1993) and the Fushui area (Dong et al., 1997). In addition to, there also exist a great number of subduction-collisional granites intruding into island-arc basement along the active continental margin. Zircons from the Fushui intrusion yield a U-Pb age of 514±1.3 Ma (Chen et al., 2004), which constraints the time of the subduction. Above all, more and more data suggest that there exists a back-arc basin on the northern side of the island-arc terrain. To the east, it is presented by the Erlangping group in Xixia area, which consists mainly of clastic sediments, carbonatites and basic volcanic rocks. The geochemistry of the basalts show that they were formed in a back-arc basin setting (Sun et al.,1996), and the radiolarites from the interlayed silicalites show the Orovician-Silurian age (Wang et al., 1995). Our new investigation reveals some new tectonic assemblages exposed in the Yinggerzui area, Qinghusi area to the west. The detailed geochemical studies indicate that they were formed in a back-arc basin. All above evidences suggest that there had existed an Early Paleozoic subduction system, which consists of a subduction trench, island-Arc and back-arc basin along the northern Qinling zone. It is also indicated that the Paleo-ocean had been evolved into a complete evolutionary process including initial spreading (E-MORB ophiolite), maturated extension (N-MORB ophiolite) and subduction (Island-arc volcanic rocks). However, it is notable that there are large scale of Devonian clastic sediments distributing on the south of the Shangdan suture, and the pre-Mesozoic rocks in the South Qinling without any metamorphism or just underwent the low-greenschist facies metamorphism in some places, which are very different from the North Qinling Terrane consisting mainly of Precambrian rocks and evolving into an amphibolite facies metamorphism at ~1.0 Ga and greenschist facies metamorphism at ~400 Ma (Liu et al., 1993; Zhang et al., 1994). Accordingly, it is prefer that there only occurred a subduction of the Shangdan oceanic crust from south to north along the Shangdan suture on the south of the Northern Qinling Terrane. However, the Piaochi and the Anjiping granites possessing the sym-collisional type granite geochemistry and formation age of 450-486 (Chen et al., 1991; zhang et al., 1996) indicate that there occurred a collisional event between the North Qinling Island-arc Terrane and the Northern China Block caused by closing of the Early Paleozoic back-arc basin. Additionally, the studies of the metamorphism show that there are two zones of high / ultra-high pressure metamorphic rocks outcropping along the both side of the Northern Qingling island-arc terrane. On the north, it is characterized by eclogite and coesite outcropping in the Guanpo area, and the metamorphic zircon U-Pb age of 507±38 Ma and 509±12 Ma by means of SHRIM (Yang et al., 2002). Meanwhile, there also exist some high pressure basic granulite (Liu et al., 1995) and felsic granulite (Liu et al., 1996) distributing in the Xigou fault on the south margin of the Northern Qingling island-arc terrane. Zircon U-Pb ages of 485±3.3 Ma by means of LA－ICP－MS method (Chen et al., 2004) and 518±12 Ma by means of SHRIM (Liu et al., 2003) constrain the time of the metamorphism. All these metamorphic data suggest the Northern Qingling island-arc terrane had been evolved into a deep subduction event during 485-518 Ma. Based on all above evidences, we infer a new model about the tectonics and evolutionary history of the Norhtern Qinling Terrane. It is emphasized that the Early Paleozoic tectonics between the North China and Southern China Blocks had existed an ocean, island-arc and back-arc basin, and evolved into four stages of evolutionary stages: 1) initial spreading along the Shangdan zone during 516-523 Ma; 2) maturated ocean along the Shangdan zone during 516-471 Ma; 3) subduction along the south side of the Northern Qinling Terrane and formation of the Back-arc basin along the north side of the Northern Qinling Terrane during518-514; 4) closing of the back-arc basin, collision between the Northern Qingling island-arc terrane and the Northern China Block, and deep subduction of the Northern Qingling island-arc terrane during 518-485Ma. This work was supported by NSFC (40772140 & 40972140)

An Evaluation of Ultra-High Pressure Regulator for Robotic Lunar Landing Spacecraft

NASA Technical Reports Server (NTRS)

Burnside, Christopher; Trinh, Huu; Pedersen, Kevin

2011-01-01

The Robotic Lunar Lander Development (RLLD) Project Office at NASA Marshall Space Flight Center (MSFC) has studied several lunar surface science mission concepts. These missions focus on spacecraft carrying multiple science instruments and power systems that will allow extended operations on the lunar surface. Initial trade studies of launch vehicle options for these mission concepts indicate that the spacecraft design will be significantly mass-constrained. To minimize mass and facilitate efficient packaging, the notional propulsion system for these landers has a baseline of an ultra-high pressure (10,000 psig) helium pressurization system that has been used on Defense missiles. The qualified regulator is capable of short duration use; however, the hardware has not been previously tested at NASA spacecraft requirements with longer duration. Hence, technical risks exist in using this missile-based propulsion component for spacecraft applications. A 10,000-psig helium pressure regulator test activity is being carried out as part of risk reduction testing for MSFC RLLD project. The goal of the test activity is to assess the feasibility of commercial off-the-shelf ultra-high pressure regulator by testing with a representative flight mission profile. Slam-start, gas blowdown, water expulsion, lock-up, and leak tests are also performed on the regulator to assess performance under various operating conditions. The preliminary test results indicated that the regulator can regulate helium to a stable outlet pressure of 740 psig within the +/- 5% tolerance band and maintain a lock-up pressure less than +5% for all tests conducted. Numerous leak tests demonstrated leakage less than 10-3 standard cubic centimeters per second (SCCS) for internal seat leakage at lock-up and less than10-5 SCCS for external leakage through the regulator ambient reference cavity. The successful tests have shown the potential for 10,000 psig helium systems in NASA spacecraft and have reduced risk associated with hardware availability and hardware ability to meet RLL mission requirements.

Metamorphic density controls on early-stage subduction dynamics

NASA Astrophysics Data System (ADS)

Duesterhoeft, Erik; Oberhänsli, Roland; Bousquet, Romain

2013-04-01

Subduction is primarily driven by the densification of the downgoing oceanic slab, due to dynamic P-T-fields in subduction zones. It is crucial to unravel slab densification induced by metamorphic reactions to understand the influence on plate dynamics. By analyzing the density and metamorphic structure of subduction zones, we may gain knowledge about the driving, metamorphic processes in a subduction zone like the eclogitization (i.e., the transformation of a MORB to an eclogite), the breakdown of hydrous minerals and the release of fluid or the generation of partial melts. We have therefore developed a 2D subduction zone model down to 250 km that is based on thermodynamic equilibrium assemblage computations. Our model computes the "metamorphic density" of rocks as a function of pressure, temperature and chemical composition using the Theriak-Domino software package at different time stages. We have used this model to investigate how the hydration, dehydration, partial melting and fractionation processes of rocks all influence the metamorphic density and greatly depend on the temperature field within subduction systems. These processes are commonly neglected by other approaches (e.g., gravitational or thermomechanical in nature) reproducing the density distribution within this tectonic setting. The process of eclogitization is assumed as being important to subduction dynamics, based on the very high density (3.6 g/cm3) of eclogitic rocks. The eclogitization in a MORB-type crust is possible only if the rock reaches the garnet phase stability field. This process is primarily temperature driven. Our model demonstrates that the initiation of eclogitization of the slab is not the only significant process that makes the descending slab denser and is responsible for the slab pull force. Indeed, our results show that the densification of the downgoing lithospheric mantle (due to an increase of pressure) starts in the early subduction stage and makes a significant contribution to the slab pull, where eclogitization does not occur. Thus, the lithospheric mantle acts as additional ballast below the sinking slab shortly after the initiation of subduction. Our calculation shows that the dogma of eclogitized basaltic, oceanic crust as the driving force of slab pull is overestimated during the early stage of subduction. These results improve our understanding of the force budget for slab pull during the intial and early stage of subduction. Therefore, the complex metamorphic structure of a slab and mantle wedge has an important impact on the development and dynamics of subduction zones. Further Reading: Duesterhoeft, Oberhänsli & Bousquet (2013), submitted to Earth and Planetary Science Letters

Ultrahigh-yield growth of GaN via halogen-free vapor-phase epitaxy

NASA Astrophysics Data System (ADS)

Nakamura, Daisuke; Kimura, Taishi

2018-06-01

The material yield of Ga during GaN growth via halogen-free vapor-phase epitaxy (HF-VPE) was systematically investigated and found to be much higher than that obtained using conventional hydride VPE. This is attributed to the much lower process pressure and shorter seed-to-source distance, owing to the inherent chemical reactions and corresponding reactor design used for HF-VPE growth. Ultrahigh-yield GaN growth was demonstrated on a 4-in.-diameter sapphire seed substrate.

The matrices of unequilibrated ordinary chondrites - Implications for the origin and history of chondrites

NASA Technical Reports Server (NTRS)

Huss, G. R.; Keil, K.; Taylor, G. J.

1981-01-01

The matrices of 16 unequilibrated chondrites were examined by optical microscopy, an electron microprobe, and a scanning electron microscope. The fine-grained, opaque, silicate matrix of type 3 unequilibrated chondrites was compositionally, mineralogically, and texturally different from the chondrules and their fragments; it may be the low temperature condensate proposed by Larimer and Anders (1967, 1970). Each meteorite has been metamorphosed by a combination of processes including thermal metamorphism and the passage of shock waves; the appearance of each chondrite results from the temperature and pressure conditions which formed it, and subsequent metamorphic alterations.

Comparative thermometry on pelitic rocks and marbles of the Llano uplift, Texas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Letargo, C.M.R.; Lamb, W.M.

1992-01-01

The Llano Uplift in central Texas is a Grenville-aged metamorphic complex consisting of amphibolite facies assemblages whose development has been attributed to the emplacement of granite plutons between 1.0--1.1 Ga. Temperatures have been obtained from garnet-biotite, garnet-ilmenite, and calcite-dolomite pairs as well as from various silicate equilibria. Application of these geothermometers yield consistent results and are thus indicative of peak conditions attending the amphibolite facies metamorphism. Temperature determined using garnet-biotite and garnet-ilmenite thermometry compare favorably with calcite-dolomite temperatures obtained from marbles in contact with granite plutons in the southeastern part of the uplift. The highest calcite-dolomite temperatures of [approximately]600 Cmore » are obtained from marbles containing an isobarically invariant assemblage consisting of calcite + dolomite + diopside + tremolite + forsterite. At pressures of 2--3 kbar, this isobarically invariant assemblage will be stable at a temperature range of [approximately]600--650 C. Also in close proximity to granites in the southeast uplift is the assemblage muscovite + quartz + k-feldspar + sillimanite [approximately] andalusite which indicate T 650 C and P 2.5 kbar. Assemblages consisting of garnet + sillimanite + quartz + plagioclase (GASP) and garnet + rutile + ilmenite + plagioclase + quartz (GRIPS) are currently being studied to provide additional constraints on pressures of amphibolite facies metamorphism.« less

The thermoluminescence sensitivity-metamorphism relationship in ordinary chondrites - Experimental data on the mechanism and implications for terrestrial systems

NASA Technical Reports Server (NTRS)

Guimon, R. K.; Sears, D. W. G.; Lofgren, G. E.

1986-01-01

Hydrothermal annealing experiments have been performed on samples of the Sharps meteorite in order to investigate the mechanism responsible for the metamorphism-related, 10-to-the-5th-fold range in the thermoluminescence (TL) sensitivity in ordinary chondrites. Duplicate 50 mg samples of meteorite were annealed under the following conditions: (1) 168 h at 785 C and 1 kbar; (2) the same time, temperature and pressure, but with 2 wt pct water; (3) 174 h at 855 C and 0.77 kbar with 2 wt pct water and 2 molal sodium disilicate (NadiSi); (4) the same time, temperature and pressure as the preceding samples, but with 10 wt pct H2O and 2 molal NadiSi. Samples annealed under the first three sets of conditions showed little or no change in their TL sensitivities, however the samples annealed with 10 wt pct water and 2 molal NadiSi showed a three-fold to 10-fold increase in TL sensitivity, and the temperature of the TL peak was suggestive of feldspar in the high-temperature form. It is suggested that these data are consistent with the TL sensitivity-metamorphism relationship in ordinary chondrites being due to the formation of the TL phosphor, feldspar, by the crystallization of chondrule glass.

The continental Etirol-Levaz slice (Western Alps, Italy): Tectonometamorphic evolution of an extensional allochthon

NASA Astrophysics Data System (ADS)

Ewerling, Kathrin; Obermüller, Gerrit; Kirst, Frederik; Froitzheim, Nikolaus; Nagel, Thorsten; Sandmann, Sascha

2013-04-01

The Etirol-Levaz slice (ELS) in the western Valtournenche of Italy is a continental fragment trapped between two oceanic units, the eclogite-facies Zermatt-Saas Zone in the footwall and the greenschist-facies Combin Zone in the hanging wall. It has been interpreted as an extensional allochthon derived from the Adriatic continental margin and stranded inside the Piemont-Ligurian oceanic domain during Jurassic rifting (Dal Piaz et al., 2001; Beltrando et al., 2010). The slice consists of Variscan high-grade gneisses, micaschists and metabasics overprinted under eclogite-facies conditions during Early Tertiary Alpine subduction. Eclogites generally consist of garnet + omphacite ± epidote ± amphibole ± phengite ± quartz. We investigate their metamorphic history using equilibrium phase diagrams, mineral compositions, and textural relations between prograde, peak, and retrograde phases. In sample FD328, garnets have compositions of Alm52-61 Grs18-41 Prp5-22 Sps0.5-2 and typical growth zoning. Some garnet grains are brittlely fractured, strongly corroded and overgrown by epidote. Amphibole occurs as a major phase in the matrix and shows a progressive evolution from glaucophane in the core to pargasitic hornblende towards the rim. Sample FD329 with a particular Ca-rich bulk composition (18.3 wt% Ca) displays two distinct garnet generations. Perfectly euhedral cores show compositions of Grs42-45 Alm47-51 Prp3-6 Sps2-7 and typical prograde growth zoning. These cores are overgrown by irregularly shaped rims characterised by an initial rise in Mn and the Fe-Mg ratio. Omphacite in this sample with jadeite-contents of 19-28 mol% apparently has been fractured and annealed by jadeite-poor (7-12 mol%) omphacite suggesting brittle behaviour at eclogite-facies conditions or two high-pressure stages with lower metamorphic conditions in between. We discuss whether the ELS experienced the same monocyclic metamorphic history as the Zermatt-Saas Zone or not. Some of our observations suggest that the ELS experienced two independent stages of high-pressure metamorphism during the Alpine orogeny, e.g. as proposed by Rubatto et al. (2011) for the Sesia Nappe. A lower-pressure stage in between might have been associated with brittle fracturing of high-pressure phases like garnet, glaucophane, and omphacite while the second generations of these minerals might indicate a new stage of increasing pressures and/or temperatures. References Beltrando, M., Rubatto, D. & Manatschal, G. (2010): From passive margins to orogens: The link between ocean-continent transition zones and (ultra)high-pressure metamorphism. Geology, 6, 559-562. Dal Piaz, G.V., Cortiana, G., Del Moro, A., Martin, S., Pennacchioni, G. & Tartarotti, P. (2001): Tertiary age and paleostructural inferences of the eclogitic imprint in the Austroalpine outliers and Zermatt-Saas ophiolite, western Alps. Int. J. Earth Sci., 90, 668-684. Rubatto, D., Regis, D., Hermann, J., Boston, K., Engi, M., Beltrando, M. & McAlpine, S.R.B. (2011): Yo-yo subduction recorded by accessory minerals in the Italian Western Alps. Nature Geoscience, 4, 338-342.

Age and P-T Conditions of the Gridino eclogite in the Belomorian Province, Russia

NASA Astrophysics Data System (ADS)

Yu, Huanglu; Zhang, Lifei; Guo, Jinghui

2017-04-01

The Russian Belomorian eclogite was once regarded as Archean in age and the oldest eclogite in the world. However, its Archean age is disputed. The Gridino ecogite, the abundant eclogite in Belomorian province, is located in the southwest of the Paleoproterozoic Lapland-Kola collisional orogeny, and occurs as boudins and metamorphosed dykes within the tonalite-trondhjemite-granodiorite (TTG) gneisses. Zircons from these eclogites have magmatic cores and metamorphic rims. Metamorphic rims, which contain typical metamorphic mineral inclusions of omphacite and garnet, and are characterized by low Th/U ratios (< 0.035) and flat HREE patterns, yield a U-Pb age of ca. 1.90 Ga. The δ18O values of 6.23 to 6.80 ‰ of zircon rims are acquired during the eclogite-facies metamorphism. On the contrary, zircon cores display higher Th/U ratios 0.18-0.45, negative Eu anomalies and strong enrichment in HREE and have Neoarchean U-Pb ages of ca. 2.70 Ga. δ18O values of 5.64 to 6.07 ‰ suggest the possibility of crystallization from slightly evolved mantle-derived magmas. A three-stage metamorphic evolution has been recognized in the Gridino eclogite based on phase equilibria modeling: prograde epidote amphibolite facies, peak eclogite facies and retrogressed high-pressure granulite facies. The peak metamorphic P-T conditions (790-815 °C, 21-22 kbar) give an apparent geothermal gradient of 11-12 °C/km for Lapland-Kola collisional orogeny during Paleoproterozoic. The Gridino eclogite is not Archean, but the known oldest Paleoproterozoic eclogite, which may respond to the assembly of Columbia supercontinent.

Detrital, metamorphic and metasomatic tourmaline in high-pressure metasediments from Syros (Greece): intra-grain boron isotope patterns determined by secondary-ion mass spectrometry

NASA Astrophysics Data System (ADS)

Marschall, Horst R.; Altherr, Rainer; Kalt, Angelika; Ludwig, Thomas

2008-06-01

The boron isotopic composition of zoned tourmaline in two metasediments from the island of Syros, determined by secondary-ion mass spectrometry (SIMS), reflects the sedimentary and metamorphic record of the rocks. Tourmaline from a silicate-bearing marble contains small (≤20 μm) detrital cores with highly variable δ 11B values (-10.7 to +3.6‰), pointing to a heterogeneous protolith derived from multiple sources. The sedimentary B isotopic record survived the entire metamorphic cycle with peak temperatures of ˜500°C. Prograde to peak metamorphic rims are homogeneous and similar among all analysed grains ( δ 11B ≈ +0.9‰). The varying δ 11B values of detrital cores in the siliceous marble demonstrate that in situ B isotope analysis of tourmaline by SIMS is a potentially powerful tool for provenance studies not only in sediments but also in metasediments. A meta-tuffitic blueschist bears abundant tourmaline with dravitic cores of detrital or authigenic origin ( δ 11B ≈ -3.3‰), and prograde to peak metamorphic overgrowth zones (-1.6‰). Fe-rich rims, formed during influx of B-bearing fluids under retrograde conditions, show strongly increasing δ 11B values (up to +7.7‰) towards the margins of the grains. The δ 11B values of metamorphic tourmaline from Syros, formed in mixed terrigenous-marine sediments, reflect the B signal blended from these two different sources, and was probably not altered by dehydration during subduction.

Peak Metamorphic Temperature Profile across Eastern Belt Franciscan, Northern California Coast Ranges

NASA Astrophysics Data System (ADS)

Schmidt, W. L.; Platt, J. P.

2017-12-01

Previous work done on metamorphic temperatures across the lawsonite-albite to blueschist facies rocks of the Eastern Belt of the Franciscan accretionary complex has relied on a combination of many methods, and suggests that temperature broadly increases from west to east. The Taliaferro Metamorphic Complex is an exception to this pattern and shows higher pressures, and possibly higher temperatures, than its surroundings. The exact location and nature of the faults separating accreted packets in the Eastern Belt is somewhat controversial. A recently calibrated low-temperature laser Raman geothermometer for use on carbonaceous material provides a uniform method of estimating peak metamorphic temperature across the eastern Franciscan and is here used to identify the position of major tectonic boundaries. Temperatures were obtained from exposures in Thomes Creek, Cottonwood Creek, Grindstone Creek, and the middle fork of the Eel River. Peak T in the South Fork Mountain Schist, the highest grade and easternmost unit in the Franciscan, is 310-375°C, whereas in immediately underlying lawsonite-albite facies rocks below the Log Springs thrust, peak T is 270 - 300°C. The Taliaferro Metamorphic Complex reached a peak temperature of 336°C, whereas the surrounding lawsonite-albite facies rocks yield peak temperatures as low as 232°C. Preliminary temperature profiles clearly allow the major faults bounding the Taliaferro Metamorphic Complex and the South Fork Mountain Schist to be located. Extension of the temperature profile has the potential to reveal further detail within these units and the lower grade rocks surrounding them.

New data for paleoprotherozoic PGE-bearing anorthosite of Kandalaksha massif (Baltic shield): U-Pb and Sm-Nd ages

NASA Astrophysics Data System (ADS)

Steshenko, Ekaterina; Bayanova, Tamara; Serov, Pavel

2015-04-01

The aims of this researches were to study the isotope U-Pb age of zircon and rutile and Sm-Nd (rock forming and sulphide minerals) on Kandalaksha anorthosite massif due to study of polimetamorphic history. In marginal zone firstly have been obtained the presence of sulphide mineralization with PGE (Chashchin, Petrov , 2013). Kandalaksha massif is located in the N-E part of Baltic shield and consists of three parts. Marginal zone (mesocratic metanorite) lies at the base of the massif. Main zone is composed of leucocratic metagabbro. The upper zone is alteration of mataanorthosite and leucocratic metagabbro. All rocks were subjected to granulate polymetamorphism. Two fractions of single grains from anorthosite of the massif gave precise U-Pb age, which is equal to 2450± 3 Ma. Leucocratic gabbro-norite were dated by U-Pb method, with age up to 2230 ± 10 Ma. This age reflects the time of granulite metamorphism according to data of (Mitrofanov, Nirovich, 2003). Two fractions of rutile have been analyzed by U-Pb method and reflect age of 1700 ± 10 Ma. It is known that the closure temperature of U-Pb system rutile is 400-450 ° C (Mezger et.al., 1989), thus cooling processes of massif rocks to these temperatures was about 1.7 Ga. These data reflect one of the stages of metamorphic alteration of the massif. Three stages of metamorphism are distinguished by Sm-Nd method. Isotope Sm-Nd dating on Cpx-WR line gives the age of 2311 Ma which suggested of high pressure granulite metamorphism. Moreover Cpx-Pl line reflect the age 1908 Ma of low pressure granulite metamorphism. Also two-points (Grt-Rt) Sm-Nd isochrone yield the age 1687 Ma of the last metamorphic alterations in Kandalaksha anorthosite massif. Model Sm-Nd age of the leucocratic gabbro-norite is 2796 Ma with positive ɛNd (+0.32). It means that the source of gabbro-norite was mantle reservoir. All investigations are devoted to memory of academician PAS F. MItrofanov which was a leader of scientific school for geology, geochemistry and metallogenesis of ore deposits. The studies are contribution by RFBR OFI-M 13-05-12055, 13-05-00493, Department of Earth Sciences RAS (programs 2 and 4), and IGCP-SIDA 599.

The single grain fusion dating approach: Determining the factors that control white mica 40Ar/39Ar age formation during HP metamorphism of the Cycladic Blueschist Unit, Greece

NASA Astrophysics Data System (ADS)

Uunk, Bertram; Wijbrans, Jan; Brouwer, Fraukje

2017-04-01

White mica 40Ar/39Ar dating is a proven powerful tool for constraining the timing and rate of metamorphism, deformation and exhumation. However, for high-pressure metamorphic rocks dating often results in wide age ranges, which are not in agreement with constraints from other isotopic systems, indicating that geological and chemical processes complicate straightforward 40Ar/39Ar dating. Despite hosting one of the largest geochronological datasets in the world, the Cycladic Blueschist Unit in Greece is presently one of the focal areas in the discussion on the interpretation of metamorphic 40Ar/39Ar ages. Previous phengite multi grain step heating experiments commonly yielded undulating age spectra ranging between 20 - 60 Ma. While some studies attempt to assign geological significance to these ages, others argue the ages are geologically meaningless and the result of the interplay between partial diffusive resetting and continued crystallization. By taking an alternative approach of multiple single grain fusion experiments, this study investigates age heterogeneity between samples of contrasting metamorphic facies, rheology and strain from the Cycladic islands of Syros and Sifnos. Comparing the size and shape of single grain fusion age distributions at the grain, rock, outcrop and island scale allows determination of the scale at which different age-forming processes operate. Resulting ages show a previously unreported consistent variation between different outcrops, moving from the eclogite-blueschist facies (55-45 Ma) to greenschist overprinting (40-30 Ma). This indicates that outcrop scale homogeneous resetting is the dominant processes for age formation in the CBU. Single grain age variation at the sample and outcrop scale is only limited to 10 Ma, indicating a smaller but observable role for local age perturbing processes of incomplete resetting, continued (re)crystallization or infiltration of excess argon. Some of the partially overprinted samples show homogeneous single grain age populations, indicating at least a partial role for efficient resetting by thermally activated diffusion at the outcrop scale. Traditional multi grain step heating experiments on the same samples yield flat plateaus for various single grain age distributions, indicating that age heterogeneities resolved by single grain fusion dating are mixed to a meaningless average in step heating experiments. In contrast, our approach leads to a better understanding of the processes responsible for age formation during high pressure metamorphism.

P-T-t paths from polyphased garnets of the Yenisey Ridge: evidence for three tectonothermal events along the western margin of Siberian craton

NASA Astrophysics Data System (ADS)

Likhanov, Igor

2015-04-01

Studies of pelitic gneisses and schists within the Yenisey regional shear zone (Garevka complex) at the western margin of the Siberian craton provide important constraints on the tectonothermal events and geodynamic processes in the Yenisey Ridge. In situ U-Th-Pb geochronology of monazite and xenotime from different growth zones of the garnet porphyroblasts coupled with P-T path calculations derived from garnet zoning patterns records three superimposed metamorphic event [1]. The different field gradients reflect contrasting tectonic settings. The first stage occurred as a result of the Grenville-age orogeny during late Meso-early Neoproterozoic (1050-850 Ma) and was marked by low-pressure zoned metamorphism at c. 4.8-5.0 kbar and 565-580 °C with a metamorphic field gradient of dT/dZ = 20-30 °C/km. At the second stage, the rocks experienced middle Neoproterozoic (801-793 Ma) collision-related medium-pressure metamorphism at c. 7.7-7.9 kbar and 630 °C with dT/dZ < 10 °C/km. The final stage evolved as a synexhumation retrograde metamorphism (785-776 Ma) at c. 4.8-5.4 kbar and 500 °C with dT/dZ < 14 °C/km and recorded uplift of the rocks to upper crustal levels in shear zones. The duration of post-collisional thrust exhumation does not exceed 16 Myr, which gives an exhumation rate of the metamorphic rocks of about 500-700 m/Myr [2]. This is in good agreement with the rate of exhumation (400 m/Myr) calculated for coeval collision-related metamorphic events in the Teya complex of the Yenisey Ridge [3] resulted from crustal thickening due to overthrusting [4] and also agrees with the results of thermomechanical numerical modeling (350 m/Myr) [5]. The final stages of collisional orogeny were followed by the development of rift-related bimodal dyke swarms of the Baikal-Yenisey belt, resulting from Neoproterozoic (790-780 Ma) extensional processes along the western margin of the Siberian craton and the onset of Rodinia's breakup [6]. Post-Grenville metamorphic episodes of regional crust evolution are correlated with the synchronous succession and similar style of the later tectonometamorphic events within the Valhalla orogen along the Arctic margin of Rodinia [7,8] and supports the spatial proximity of Siberia and North Atlantic cratons (Laurentia, Baltica, Svalbard) at c. 800 Ma, as indicated by the Neoproterozoic paleocontinental reconstructions of the classic Rodinia configuration [9,10]. [1] Likhanov et al. (2013) Petrology 21, 561-578. [2] Likhanov et al. (2014) J. Asian Earth Sci., http://dx.doi.org/10.1016/j.jseaes.2014.10.026. [3] Likhanov et al. (2011) Russ. Geol. Geophys. 52, 1256-1269. [4] Likhanov & Reverdatto (2011) Int. Geol. Rev. 53, 802-845. [5] Likhanov et al. (2004) J. Metamorph. Geol. 22, 743-762. [6] Likhanov et al. (2013) Dokl. Earth Sci. 450, 613-617. [7] Cutts et al. (2010) J. Metamorph. Geol. 28, 249-267. [8] Cawood et al. (2010) Geology 38, 99-102. [9] Dalziel et al. (2000) J. Geol. 108, 499-513. [10] Torsvik (2003) Science 300, 1379-1381.

An ultrahigh vacuum multipurpose specimen chamber with sample introduction system for in situ transmission electron microscopy investigations

NASA Technical Reports Server (NTRS)

Heinemann, K.; Poppa, H.

1986-01-01

A commercial transmission electron microscope (TEM), with flat-plate upper pole piece configuration of the objective lens, and top-entry specimen introduction was modified by introducing an ultrahigh vacuum (UHV) specimen chamber for in situ TEM experimentation. The pumping and design principles and special features of this UHV chamber, which makes it possible to obtain 5 x 10 to the -10th mbar pressure at the site of the specimen, while maintaining the airlock system that allows operation in the 10 to the -10th mbar range within 15 min after specimen change, are described. Design operating pressures and image quality (resolution of metal particles smaller than 1 nm in size) were achieved. Schematic drawings and design dimensions are included.

Oblique wedge extrusion of UHP/HP complexes in the Late Triassic: structural analysis and zircon ages of the Atbashi Complex, South Tianshan, Kyrgyzstan

NASA Astrophysics Data System (ADS)

Sang, Miao; Xiao, Wenjiao; Bakirov, Apas

2017-04-01

The exhumation and tectonic emplacement of eclogites and blueschists takes place in forearc accretionary complexes by either forearc- or backarc-directed extrusion, but few examples have been well analysed in detail. Here we present an example of oblique wedge extrusion of UHP/HP rocks in the Atbashi accretionary complex of the Kyrgyz South Tianshan. The Atbashi Eclogite-Blueschist Complex (AEBC) is a conventional, formal name for the Atbashi Formation that contains pelitic to siliceous schists alternating with HP/UHP eclogites and blueschists. The main belt of the AEBC strikes SW-NE mostly parallel to the Atbashi-Inylchek Fault. Our field mapping and structural analysis demonstrate that the Atbashi Eclogite-Blueschist Complex is situated in a complicated duplex formed by a northerly dextral transpression system and a southerly sinistral transtension system, both of which contain a series of strike-slip duplexese at several scales. The two shear systems suggest that the Atbashi Complex underwent a unique oblique south- westward extrusion with a general plunge to the NE, the horizontal projection of which is sub-parallel to the strike of the major structures. This indicates that the Atbashi Complex was extruded obliquely southwestwards during eastward penetration of the southern tip of the Yili- Central Tianshan Arc of the Kazakhstan Orocline during the Late Triassic. Also, to constrain the extrusion of the AEBC and to place it in its temporal framework during docking of the Tarim Craton to the southern margin of the Ili-Tianshan Arc, we report new zircon U-Pb isotopic data for four eclogites and one garnet-bearing quartz-schist, in order to document the timing event during extrusion. The youngest ages of the eclogites and the garnet-bearing quartz-schist may be Late Triassic of 217-221 Ma and 223.9 Ma, respectively, suggesting that the main extrusion was later than previously proposed and that the final orogenesis was not completed until the Late Triassic. The HP/UHP rocks have an oblique plunge to the NE and extrusion took place south-westwards during escape tectonics along the South Tianshan accretionary wedge in the Late Triassic. Our work shows that the movement of HP/UHP rocks had a 3D style with an arc-parallel structure, and sheds light on earlier 2D models with either forearc- or backarc-directed extrusions, which indicates that more systematic structural and geochronological work is needed to characterize the accretionary tectonics of many orogens around the world. Our data on the timing of extrusion and emplacement of the Atbashi Eclogite-Blueschist Complex also help to resolve the long-standing controversy about the time of terminal orogeny of the Central Asian Orogenic Belt.

Low Pressure-High Temperature Metamorphism and the Advection of Heat to the Continental Crust: A Case Study from Northwest New Guinea

NASA Astrophysics Data System (ADS)

Jost, B.; Webb, M.; White, L. T.

2017-12-01

In northwest New Guinea, Palaeozoic basement rocks forming part of the northern margin of the Australian continent are exposed in a rugged mountain range. This remote and understudied region provides a unique window into the complex Palaeozoic evolution and tectonic history of this region, which we help unravel with new field, petrographic, geochemical, and geochronological data. The basement rocks consist of extensive meta-turbidites that were subject to low pressure-high temperature metamorphism along their eastern margin. They are cross-cut by predominantly acidic granitoids. U-Pb zircon dating reveals that these granitoids intruded in three episodes in the Devonian-Carboniferous, the Carboniferous, and the Triassic. The first episode has not previously been reported in the region. The granitoids are strongly peraluminous, suggesting that partial melting of the meta-sedimentary country rock contributed to their petrogenesis (S-type). The occurrence and character of country rock xenoliths and migmatites supports this interpretation. Equilibrium thermodynamic modelling of the metapelites and the migmatites indicates that a substantial amount of heat was added to the lower and middle crust to cause partial melting and regional metamorphism at relatively low pressure. We propose repeated intrusion of hot magma as the mechanism responsible for advecting the necessary heat from the mantle. This likely occurred in an active continental margin setting during the Devonian-Carboniferous and the Triassic, possibly separated by an interval of magmatic quiescence during most of the Permian. New biostratigraphic and low-temperature thermochronological data reveal very recent Pliocene-Pleistocene uplift and unroofing of these basement rocks.

Generation and stabilization of whey-based monodisperse naoemulsions using ultra-high pressure homogenization and small amphipathic co-emulsifier combinations

USDA-ARS?s Scientific Manuscript database

Ultra-high-pressure homogenization (UHPH) was used to generate monodisperse stable peanut oil nanoemulsions within a desired nanosize range (<100 nm) (DNR) stabilized using combinations of whey protein concentrate (WPC), sodium dodecyl sulfate, Triton X-100 (X100), and zwitterionic sulfobetaine-base...

Processes of deep terrestrial mantles and cores

NASA Technical Reports Server (NTRS)

Jeanloz, Raymond

1991-01-01

Ultrahigh pressure experiments are currently focused on revealing processes occurring deep inside planets. This is in addition to the traditional emphasis on the constitution of planetary interiors, such as the identification of the high pressure perovskite phase of (Mg,Fe)SiO3 as the predominant mineral inside the Earth, and probably Venus. For example, experiments show that the mechanism of geochemical differentiation, separation of partial melts, differs fundamentally in the lower mantles of Earth and Venus than at near surface conditions. In addition to structural transformations, changes in chemical bonding caused by pressure can also be significant for planetary interiors. Measurements of AC and DC electrical conductivity can be obtained at ultrahigh pressures and temperatures, to greater than 80 GPa and 3000 K simultaneously, using the laser heated diamond cell. Anhydrous lower mantle assemblages (perovskite + or - oxide phases) exhibit an electrical conductivity that depends strongly on Fe content. Contrary to traditional assumptions, temperature affects the conductivity of lower mantle assemblages relatively little. The Earth's deep focus seismicity can be explained by the recycling of water into the mantle.

An ionization gauge for ultrahigh vacuum measurement based on a carbon nanotube cathode

NASA Astrophysics Data System (ADS)

Zhang, Huzhong; Cheng, Yongjun; Sun, Jian; Wang, Yongjun; Xi, Zhenhua; Dong, Meng; Li, Detian

2017-10-01

This work reports on the complete design and the properties of an ionization gauge based on a carbon nanotube cathode, which can measure ultrahigh vacuum without thermal effects. The gauge is composed of a pressure sensor and an electronic controller. This pressure sensor is constructed based on a hot-cathode ionization gauge, where the traditional hot filament is replaced by an electron source prepared with multi-wall nanotubes. Besides, an electronic controller was developed for bias voltage supply, low current detection, and pressure indication. The gauge was calibrated in the pressure range of 10-8 to 10-4 Pa in a XHV/UHV calibration apparatus. The gauge shows good linear characteristics in different gases. The calibrated sensitivity is 0.035 Pa-1 in N2, and the standard deviation of the sensitivity is about 1.1%. In addition, the stability of the sensitivity was learned in a long period. The standard deviation of the sensitivity factor "S" during one year is 2.0% for Ar and 1.6% for N2.

Nature and probable age of metamorphism in northern New Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grambling, J.A.; Daniel, C.D.; Dallmeyer, R.D.

1993-02-01

Metamorphic conditions near the Al[sub 2]SiO[sub 5] triple point are unusually common in northern New Mexico. This observation is supported by mineralogy (Ky + And + Sil, Cld + Sil, Sil + Pg + Qz) and Grt-Bt-Pl-Ms thermobarometry (4--5 kb and 500--550 C). Isograds cut across tight folds (overturned to the north) in the Pecos, Rio Mora, Truchas and Picuris areas. Some deformation also accompanied or preceded metamorphism in the Rincon and Cimarron ranges. P-T paths derived from zoning in Grt and Pl, in Mn-andalusite, and the textural transition Ky to Sil to And reflect up to 2 kb ofmore » decompression, at constant temperature in the more southerly ranges but during cooling toward the north. These 500--550 C rocks are in direct contact with gneisses in the Rincon and Cimarron Ranges. Metaplutonic gneisses record hornblende pressures of 6--8 kb. Metasedimentary gneisses are migmatitic. Assemblages include Sil + Kfs, Hc + Qz and Alm + Bt + Sil, whereas Grt-Sil-Pl-Bt yields 6.5--7 kb and 700--725 C. Pressures increase northward from the Cimarrron Mountains. The gneisses display retrograde P-T paths with 2.5--3 kb of decompression and cooling through the Al[sub 2]SiO[sub 5] triple point. Geometric relationships between gneisses and 500--550 C rocks are best constrained in the Cimarron Mountains, where a folded but initially low-angle contact separates the two metamorphic grades. Gneisses are structurally beneath this contact. Other regions may display a similar geometry. The structurally-highest gneisses are locally mylonitic, suggesting that contacts between gneisses and 500--550 C rocks are ductile shear zones. Monazite U-Pb ages from gneisses of the Cimarron Range are 1420-1425 Ma, whereas hornblende argon ages are 1,395--1,397 Ma.« less

Development and application of laser microprobe techniques for oxygen isotope analysis of silicates, and, fluid/rock interaction during and after granulite-facies metamorphism, highland southwestern complex, Sri Lanka

DOE Office of Scientific and Technical Information (OSTI.GOV)

Elsenheimer, D.W.

1992-01-01

The extent of fluid/rock interaction within the crust is a function of crustal depth, with large hydrothermal systems common in the brittle, hydrostatically pressured upper crust, but restricted fluid flow in the lithostatically pressured lower crust. To quantify this fluid/rock interaction, a Nd-YAG/CO[sub 2] laser microprobe system was constructed to analyze oxygen isotope ratios in silicates. Developed protocols produce high precision in [sigma][sup 18]O ([+-]0.2, 1[sigma]) and accuracy comparable to conventional extraction techniques on samples of feldspar and quartz as small as 0.3mg. Analysis of sub-millimeter domains in quartz and feldspar in granite from the Isle of Skye, Scotland, revealsmore » complex intragranular zonation. Contrasting heterogeneous and homogeneous [sigma][sup 18]O zonation patterns are revealed in samples <10m apart. These differences suggest fluid flow and isotopic exchange was highly heterogeneous. It has been proposed that granulite-facies metamorphism in the Highland Southwestern Complex (HSWC), Sri Lanka, resulted from the pervasive influx of CO[sub 2], with the marbles and calc-silicates within the HSWC a proposed fluid source. The petrologic and stable isotopic characteristic of HSWC marbles are inconsistent with extensive decarbonation. Wollastonite calc-silicates occur as deformed bands and as post-metamorphis veins with isotopic compositions that suggest vein fluids that are at least in part magmatic. Post-metamorphic magmatic activity is responsible for the formation of secondary disseminated graphite growth in the HSWC. This graphite has magmatic isotopic compositions and is associated with vein graphite and amphibolite-granulite facies transitions zones. Similar features in Kerela Khondalite Belt, South India, may suggest a common metamorphic history for the two terranes.« less

Ultrahigh vacuum process for the deposition of nanotubes and nanowires

DOEpatents

Das, Biswajit; Lee, Myung B

2015-02-03

A system and method A method of growing an elongate nanoelement from a growth surface includes: a) cleaning a growth surface on a base element; b) providing an ultrahigh vacuum reaction environment over the cleaned growth surface; c) generating a reactive gas of an atomic material to be used in forming the nanoelement; d) projecting a stream of the reactive gas at the growth surface within the reactive environment while maintaining a vacuum of at most 1.times.10.sup.-4 Pascal; e) growing the elongate nanoelement from the growth surface within the environment while maintaining the pressure of step c); f) after a desired length of nanoelement is attained within the environment, stopping direction of reactive gas into the environment; and g) returning the environment to an ultrahigh vacuum condition.

The next chapter in experimental petrology: Metamorphic dehydration of polycrystalline gypsum captured in 3D microtomographic time series datasets

NASA Astrophysics Data System (ADS)

Bedford, John; Fusseis, Florian; Leclere, Henry; Wheeler, John; Faulkner, Dan

2016-04-01

Nucleation and growth of new minerals in response to disequilibrium is the most fundamental metamorphic process. However, our current kinetic models of metamorphic reactions are largely based on inference from fossil mineral assemblages, rather than from direct observation. The experimental investigation of metamorphism has also been limited, typically to concealed vessels that restrict the possibility of direct microstructural monitoring. Here we present one of the first time series datasets that captures a metamorphic reaction, dehydration of polycrystalline gypsum to form hemihydrate, in a series of three dimensional x-ray microtomographic datasets. We achieved this by installing an x-ray transparent hydrothermal cell (Fusseis et al., 2014, J. Synchrotron Rad. 21, 251-253) in the microtomography beamline 2BM at the Advanced Photon Source (USA). In the cell, we heated a millimetre-sized sample of Volterra Alabaster to 388 K while applying an effective pressure of 5 MPa. Using hard x-rays that penetrate the pressure vessel, we imaged the specimen 40 times while it reacted for approximately 10 hours. Each microtomographic dataset was acquired in 300 seconds without interrupting the reaction. Our absorption microtomographic data have a voxel size of 1.3 μm, which suffices to analyse the reaction progress in 4D. Gypsum can clearly be distinguished from hemihydrate and pores, which form due to the large negative solid volume change. On the resolved scale, the first hemihydrate needles appear after about 2 hours. Our data allow tracking of individual needles throughout the entire experiment. We quantified their growth rates by measuring their circumference. While individual grains grow at different rates, they all start slowly during the initial nucleation stage, then accelerate and grow steadily between about 200 and 400 minutes before reaction rate decelerates again. Hemihydrate needles are surrounded by porous haloes, which grow with the needles, link up and eventually encapsulate the remaining gypsum crystals. The reaction appears to be homogenously distributed throughout the sample and we find no evidence for metamorphic overpressure. We used an advanced machine learning algorithm (http://fiji.sc/Trainable_Weka_Segmentation) to segment the porosity from the microtomographic data and quantify it in Fiji (Schindelin et al., 2012, Nature Methods 9, 676-682). The porosity evolution follows the grain growth curves and reaches 23%, which indicates that the dehydration reaction is 80% complete. Our 4D data provide a unique opportunity not only to explore evolving reaction microtextures in spectacular visualisations but also to test general metamorphic theory. Our data, which track the entire reaction history from nucleation through to interaction with surrounding grains raise several questions. While individual grains grow quicker than others, why do, when grain growth is normalised against final grain size, all grains have a very similar growth history? This is not currently explained by an Avrami type model, and an alternative model for metamorphic reaction kinetics may be based on our data. Do metamorphic transport distances change during the reaction as the pore structure evolves? What controls the orientation of hemihydrate needles? In this presentation we present not only the images and data highlighting these questions, but also explore possible answers.

Fluid-induced Crystallization of Majoritic Garnet During Deep Continental Subduction (Western Gneiss Region, Norway)

NASA Astrophysics Data System (ADS)

Scambelluri, M.; Pettke, T.; van Roermund, H. L.

2008-12-01

In ultrahigh pressure (UHP) rocks, garnet containing pyroxene exsolutions derives from breakdown of majorite crystallized at depths > 200 km. Presence of microdiamonds in some of these rocks [1], including those of the Western Gneiss Region (WGR) of Norway [2], may suggest a fluid-bearing environment for the genesis of majorite. The WGR UHP gneisses host garnet peridotite and websterite recording uplift from extraordinary depths prior to uptake in a subducting slab [2]. These ultramafic rocks (islands of Otrøy and Bardane) derive from depleted Archean transition-zone mantle (350 km depth) upwelled and accreted to a cratonic lithosphere (M2 stage). Evidence for this are decimetric garnets (grt) preserved in Otrøy, hosting up to 20 volume% orthopyroxene (opx) and clinopyroxene (cpx) exsolved from precursor majoritic garnet (M1 stage). The pyroxene lamellae (20-30 ¥ìm thick, hundreds of ¥ìm long) [3] were exsolved under high-T, as shown by the garnet/cpx REE distribution [4]. This Archean-mid Proterozoic record is overprinted by the 425- 390 Ma Scandian continental subduction (M3 stage), forming new grt + cpx + opx + phlogopite (phl) + spinel (sp) that contain diamond-bearing micro-inclusions witnessing deep COH subduction fluids [2]. Here we document formation of new majoritic garnet in the M3 assemblage and in veins at Bardane [5]. Textural characteristics, together with the LREE and LILE enrichments of the M3 minerals, indicate that the new majorite is linked to infiltration of subduction fluids during renewed burial towards sub-lithospheric depths. It represents the deepest occurrence of fluid-related microstructures in mantle rocks. The new majoritic garnet crystallized at grain boundaries and in micro-veins at 7 Gpa and 900-1000 °C. It hosts thin pyroxene needles (5 mm thick, 100 mm long) exsolved under comparatively low-T, as indicated by the garnet/cpx REE distribution. The trace element signature of the majorite-bearing subduction assemblage is LREE- (cpx La/Yb = 220) and LILE-enriched (appreciable Li, B, Rb, Ba, Pb, U, Th in cpx and phl), to indicate addition of crustal components. The interstitial and vein M3 majoritic garnet has flat REE patterns (La 1xChondrite; La/Yb= 0.35) and lacks the LREE depletion characteristic of common grt. The px component of majorite thus allows LREE and subordinate LILE storage in this mineral, which becomes a relevant trace element repository in the deep mantle. The REE enriched signature of M3 majorite contrasts the depleted nature of M1 (+ M2) grt: this indicates the presence of two generations of majorite in these rocks and suggests the re-fertilization of initially depleted peridotite by subduction fluid at 200 km depth. Distinct generations of majoritic garnet thus survive in the same terrain, displaying distinct textures, compositions, and exsolution T. The majorite microstructures and compositions enable to discriminate between crystallization environments: hot sub- cratonic lithosphere vs. colder subduction settings. 1 Mposkos ED, Kostopoulos DK, 2001, EPSL 192, 497- 506; 2 Van Roermund HLM. et al., 2002, Geology 30, 959-962; 3 Van Roermund HLM, Drury M., 1998, Terra Nova 10, 295-301; 4 Spengler D. et al., 2006, Nature 440, 913-917; 5 Scambelluri M. et al., 2008, Geology 36, 59-62.

The behaviour of monazite at high temperature and high stress in the lower crust

NASA Astrophysics Data System (ADS)

Clark, Chris; Taylor, Richard; Erickson, Timmons; Reddy, Steven; Fougerouse, Denis; Fitzsimons, Ian; Hand, Martin

2017-04-01

Monazite is fast becoming the go to geochronometer for establishing the timing of metamorphic, deformational and hydrothermal events in crustal rocks. This is principally due to monazite forming in rocks that are petrologically useful (e.g. metapelites), it's susceptibility to recrystallization (both fluid and deformation driven) and the suite of trace elements it incorporates during growth. In dry conditions (i.e. the melt-depleted lower crust) monazite has a high closure temperature. It therefore has the ability to record the timing of prograde to peak metamorphic conditions. The reactivity of monazite in the presence of fluid allows the timing of post-peak fluid and melt crystallisation events to be constrained. Under high-stress monazite will recrystallise, forming new crystals that can be used to constrain the age of deformational events - this feature is particularly useful as high-grade reworking of lower crustal rocks often leave no geochronological record within other accessory minerals (e.g. zircon). However, it has long been recognised that monazite can record a cryptic range and/or distribution of ages that are difficult reconcile with how we traditionally believe the lower crust responds to deformational events - e.g. the anhydrous nature of lower crustal rocks and the preservation of granulite facies mineral assemblages. Here we present datasets collected by a suite of microanalytical techniques on monazite grains from lower-crustal rocks that have experienced deformation, fluid-rock interaction and ultrahigh temperature metamorphism. To better understand how monazite behaves in these environments we integrate electron probe, electron backscatter diffraction, laser ablation split stream petrochronology, transmission electron microscopy and Atom Probe Tomography datasets to image and quantify behaviour of key elements from the micro- to the nanoscale. When used sequentially, these techniques provide a detailed view of the processes that re-distribute U-Th-REE-Y-Pb at the nanoscale. Understanding how monazite behaves under different stress and thermal conditions is the key to using this geochronometer to develop and refine event chronologies in the lower crust.

Development of a 45kpsi ultrahigh pressure liquid chromatography instrument for gradient separations of peptides using long microcapillary columns and sub-2μm particles.

PubMed

Grinias, Kaitlin M; Godinho, Justin M; Franklin, Edward G; Stobaugh, Jordan T; Jorgenson, James W

2016-10-21

Commercial chromatographic instrumentation for bottom-up proteomics is often inadequate to resolve the number of peptides in many samples. This has inspired a number of complex approaches to increase peak capacity, including various multidimensional approaches, and reliance on advancements in mass spectrometry. One-dimensional reversed phase separations are limited by the pressure capabilities of commercial instruments and prevent the realization of greater separation power in terms of speed and resolution inherent to smaller sorbents and ultrahigh pressure liquid chromatography. Many applications with complex samples could benefit from the increased separation performance of long capillary columns packed with sub-2μm sorbents. Here, we introduce a system that operates at a constant pressure and is capable of separations at pressures up to 45kpsi. The system consists of a commercially available capillary liquid chromatography instrument, for sample management and gradient creation, and is modified with a storage loop and isolated pneumatic amplifier pump for elevated separation pressure. The system's performance is assessed with a complex peptide mixture and a range of microcapillary columns packed with sub-2μm C18 particles. Copyright © 2016 Elsevier B.V. All rights reserved.

Incorporating Cutting Edge Scientific Results from the Margins-Geoprisms Program into the Undergraduate Curriculum: The Subduction Factory

NASA Astrophysics Data System (ADS)

Penniston-Dorland, S.; Stern, R. J.; Edwards, B. R.; Kincaid, C. R.

2014-12-01

The NSF-MARGINS Program funded a decade of research on continental margin processes. The NSF-GeoPRISMS Mini-lesson Project, funded by NSF-TUES, is designed to integrate fundamental results from the MARGINS program into open-source college-level curriculum. Three Subduction Factory (SubFac) mini-lessons were developed as part of this project. These include hands-on examinations of data sets representing 3 key components of the subduction zone system: 1) Heat transfer in the subducted slab; 2) Metamorphic processes happening at the plate interface; and 3) Typical magmatic products of arc systems above subduction zones. Module 1: "Slab Temperatures Control Melting in Subduction Zones, What Controls Slab Temperature?" allows students to work in groups using beads rolling down slopes as an analog for the mathematics of heat flow. Using this hands-on, exploration-based approach, students develop an intuition for the mathematics of heatflow and learn about heat conduction and advection in the subduction zone environment. Module 2: "Subduction zone metamorphism" introduces students to the metamorphic rocks that form as the subducted slab descends and the mineral reactions that characterize subduction-related metamorphism. This module includes a suite of metamorphic rocks available for instructors to use in a lab, and exercises in which students compare pressure-temperature estimates obtained from metamorphic rocks to predictions from thermal models. Module 3: "Central American Arc Volcanoes, Petrology and Geochemistry" introduces students to basic concepts in igneous petrology using the Central American volcanic arc, a MARGINS Subduction Factory focus site, as an example. The module relates data from two different volcanoes - basaltic Cerro Negro (Nicaragua) and andesitic Ilopango (El Salvador) including hand sample observations and major element geochemistry - to explore processes of mantle and crustal melting and differentiation in arc volcanism.

Shear heating and metamorphism in subduction zones, 1. Thermal models

NASA Astrophysics Data System (ADS)

Kohn, M. J.; Castro, A. E.; Spear, F. S.

2017-12-01

Popular thermal-mechanical models of modern subduction systems are 100-500 °C colder at c. 50 km depth than pressure-temperature (P-T) conditions determined from exhumed metamorphic rocks. This discrepancy has been ascribed by some to profound bias in the rock record, i.e. metamorphic rocks reflect only anomalously warm subduction, not normal subduction. Accurately inferring subduction zone thermal structure, whether from models or rocks, is crucial for predicting depths of seismicity, fluid release, and sub-arc melting conditions. Here, we show that adding realistic shear stresses to thermal models implies P-T conditions quantitatively consistent with those recorded by exhumed metamorphic rocks, suggesting that metamorphic rock P-T conditions are not anomalously warm. Heat flow measurements from subduction zone fore-arcs typically indicate effective coefficients of friction (µ) ranging from 0.025 to 0.1. We included these coefficients of friction in analytical models of subduction zone interface temperatures. Using global averages of subducting plate age (50 Ma), subduction velocity (6 cm/yr), and subducting plate geometry (central Chile), temperatures at 50 km depth (1.5 GPa) increase by c. 200 °C for µ=0.025 to 700 °C for µ=0.1. However, at high temperatures, thermal softening will reduce frictional heating, and temperatures will not increase as much with depth. Including initial weakening of materials ranging from wet quartz (c. 300 °C) to diabase (c. 600 °C) in the analytical models produces concave-upward P-T distributions on P-T diagrams, with temperatures c. 100 to 500 °C higher than models with no shear heating. The absolute P-T conditions and concave-upward shape of the shear-heating + thermal softening models almost perfectly matches the distribution of P-T conditions derived from a compilation of exhumed metamorphic rocks. Numerical models of modern subduction zones that include shear heating also overlap metamorphic data. Thus, excepting the very hottest examples, exhumed metamorphic rocks represent the products of normal, not anomalous, subduction. Consequently numerous geochemical, petrologic, and geophysical interpretations that have been founded on models that lack shear heating must be re-evaluated.

Proterozoic orogens in southern Peninsular India: Contiguities and complexities

NASA Astrophysics Data System (ADS)

Chetty, T. R. K.; Santosh, M.

2013-12-01

The Precambrian terranes of southern Peninsular India have been central to discussions on the history of formation and breakup of supercontinents. Of particular interest are the Proterozoic high grade metamorphic orogens at the southern and eastern margins of the Indian shield, skirting the 3.4 Ga Dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics, but also carry imprints of the tectonic framework related to the assembly of the major Neoproterozoic supercontinents - Rodinia and Gondwana. These Proterozoic orogens are described as Southern Granulite Terrane (SGT) in the southern tip and the Eastern Ghats Mobile Belt (EGMB) in the eastern domains of the peninsula. The contiguity of these orogens is broken for a distance of ˜400 km and disappears in the Bay of Bengal. These orogens expose windows of middle to lower crust with well-preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths.Recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems, some of which represent collisional sutures. The SGT and EGMB carry several important features such as fold-thrust tectonics, regional granulite facies metamorphism of up to ultrahigh-temperature conditions in some cases, multiple P-T paths, development of lithospheric shear zones, emplacement of ophiolites, presence of alkaline and anorthositic complexes, development of crustal-scale "flower structures", transpressional strains, and reactivation tectonics. A heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified. Both EGMB and SGT share a common transpressional deformation history during the latest Neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics. Our synthesis of the spatial distribution, geometry, kinematics and the transpressional strain of the shear zone systems provides insights into the tectono-metamorphic history of the Proterozoic orogens of southern India and their contiguity and complexities. Recent understanding of subduction, accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in Earth history, although the major and common structural architecture was built during the final assembly of the Gondwana supercontinent.

Timing and duration of garnet granulite metamorphism in magmatic arc crust, Fiordland, New Zealand

USGS Publications Warehouse

Stowell, H.; Tulloch, A.; Zuluaga, C.; Koenig, A.

2010-01-01

Pembroke Granulite from Fiordland, New Zealand provides a window into the mid- to lower crust of magmatic arcs. Garnet Sm-Nd and zircon U-Pb ages constrain the timing and duration of high-P partial melting that produced trondhjemitic high Sr/Y magma. Trace element zoning in large, euhedral garnet is compatible with little post growth modification and supports the interpretation that garnet Sm-Nd ages of 126.1??2.0 and 122.6??2.0. Ma date crystal growth. Integration of the garnet ages with U-Pb zircon ages elucidates a history of intrusion(?) and a protracted period of high-temperature metamorphism and partial melting. The oldest zircon ages of 163 to 150. Ma reflect inheritance or intrusion and a cluster of zircon ages ca. 134. Ma date orthopyroxene-bearing mineral assemblages that may be magmatic or metamorphic in origin. Zircon and garnet ages from unmelted gneiss and garnet reaction zones record garnet granulite facies metamorphism at 128 to 126. Ma. Peritectic garnet and additional zircon ages from trondhjemite veins and garnet reaction zones indicate that garnet growth and partial melting lasted until ca. 123. Ma. Two single fraction garnet ages and young zircon ages suggest continued high-temperature re-equilibration until ca. 95. Ma. Phase diagram sections constrain orthopyroxene assemblages to <0.6 GPa @ 650??C, peak garnet granulite facies metamorphic conditions to 680-815??C @ 1.1-1.4. GPa, and a P-T path with a P increase of???0.5. GPa. These sections are compatible with water contents???0.28wt.%, local dehydration during garnet granulite metamorphism, and <0.3. GPa P increases during garnet growth. Results demonstrate the utility of integrated U-Pb zircon and Sm-Nd garnet ages, and phase diagram sections for understanding the nature, duration, and conditions of deep crustal metamorphism and melting. Geochronologic and thermobarometric data for garnet granulite indicate that thickening of arc crust, which caused high-pressure metamorphism in northern Fiordland, must have occurred prior to 126. Ma, that loading occurred at a rate of ca. 0.06. GPa/m.y., and that garnet granulite metamorphism lasted 3-7m.y. Locally-derived partial melts formed and crystallized in considerably less than 10 and perhaps as little as 3m.y. ?? 2010 Elsevier B.V.

Microstructural evidence for dissolution precipitation creep in high pressure metamorphic serpentinites from subduction zones

NASA Astrophysics Data System (ADS)

Wassmann, S.; Trepmann, C.; Krohe, A.; Stoeckhert, B.

2009-12-01

Serpentinite is generally believed to constitute weak material in subduction zones and to play an essential role for the development of a subduction channel. Information on deformation mechanisms and appropriate rheological models to describe these large scale flow processes is obtained from natural serpentinites exhumed from ancient subduction zones. In this study, we investigate the microstructural record of serpentinites exposed in the Zermatt-Saas-Zone, Western Alps. The metamorphic mineral assemblage comprises antigorite, forsterite, diopside, tremolite, chlorite, oxide phases, and in places titanclinohumite. Original mantle minerals are only locally preserved as relics. The conditions of Alpine metamorphism can be estimated from associated eclogites; the pressures are mostly between 1.5 and 2.5 GPa at temperatures of c. 500-600°C. The serpentinites show a complex structure with several generations of folds and foliations. An early foliation is defined by the combined shape and crystallographic preferred orientation (SPO and CPO) of antigorite and metamorphic diopside. These patterns are undistinguishable from the SPO and CPO of the same minerals in strain shadows, where the CPO must be developed by oriented growth from an aqueous solution. Therefore we suspect that the SPO and CPO in the polyphase matrix layers also result from oriented growth. Also, there is no microstructural evidence for any crystal plastic deformation of diopside. In places, antigorite flakes with SPO and CPO are overgrown by single crystals or aggregates of metamorphic forsterite, locally titanoclinohumite, and tremolite. The aggregates of forsterite exhibit a foam structure without CPO. All microfabrics indicate that dissolution precipitation creep was predominant in the investigated serpentinites, and most finite strain was accumulated by this mechanism. We see no evidence for a significant contribution of dislocation creep, both based on microstructure and on the CPO patterns. This does not preclude dislocation creep and a power law rheology to hold for higher stress levels, as expected for short episodes of postseismic creep. For the long term flow of serpentinites in subduction zones, however, Newtonian behaviour and a low viscosity are indicated.

Argon behaviour in an inverted Barrovian sequence, Sikkim Himalaya: The consequences of temperature and timescale on 40Ar/39Ar mica geochronology

NASA Astrophysics Data System (ADS)

Mottram, Catherine M.; Warren, Clare J.; Halton, Alison M.; Kelley, Simon P.; Harris, Nigel B. W.

2015-12-01

40Ar/39Ar dating of metamorphic rocks sometimes yields complicated datasets which are difficult to interpret in terms of timescales of the metamorphic cycle. Single-grain fusion and step-heating data were obtained for rocks sampled through a major thrust-sense shear zone (the Main Central Thrust) and the associated inverted metamorphic zone in the Sikkim region of the eastern Himalaya. This transect provides a natural laboratory to explore factors influencing apparent 40Ar/39Ar ages in similar lithologies at a variety of metamorphic pressure and temperature (P-T) conditions. The 40Ar/39Ar dataset records progressively younger apparent age populations and a decrease in within-sample dispersion with increasing temperature through the sequence. The white mica populations span 2-9 Ma within each sample in the structurally lower levels (garnet grade) but only 0-3 Ma at structurally higher levels (kyanite-sillimanite grade). Mean white mica single-grain fusion population ages vary from 16.2 ± 3.9 Ma (2σ) to 13.2 ± 1.3 Ma (2σ) from lowest to highest levels. White mica step-heating data from the same samples yields plateau ages from 14.27 ± 0.13 Ma to 12.96 ± 0.05 Ma. Biotite yield older apparent age populations with mean single-grain fusion dates varying from 74.7 ± 11.8 Ma (2σ) at the lowest structural levels to 18.6 ± 4.7 Ma (2σ) at the highest structural levels; the step-heating plateaux are commonly disturbed. Temperatures > 600 °C at pressures of 0.4-0.8 GPa sustained over > 5 Ma, appear to be required for white mica and biotite ages to be consistent with diffusive, open-system cooling. At lower temperatures, and/or over shorter metamorphic timescales, more 40Ar is retained than results from simple diffusion models suggest. Diffusion modelling of Ar in white mica from the highest structural levels suggests that the high-temperature rocks cooled at a rate of 50-80 °C Ma- 1, consistent with rapid thrusting, extrusion and exhumation along the Main Central Thrust during the mid-Miocene.

Geology of Precambrian rocks and isotope geochemistry of shear zones in the Big Narrows area, northern Front Range, Colorado

USGS Publications Warehouse

Abbott, Jeffrey T.

1970-01-01

Rocks within the Big Narrows and Poudre Park quadrangles located in the northern Front Range of Colorado are Precambrian metasedimentary and metaigneous schists and gneisses and plutonic igneous rocks. These are locally mantled by extensive late Tertiary and Quaternary fluvial gravels. The southern boundary of the Log Cabin batholith lies within the area studied. A detailed chronology of polyphase deformation, metamorphism and plutonism has been established. Early isoclinal folding (F1) was followed by a major period of plastic deformation (F2), sillimanite-microcline grade regional metamorphism, migmatization and synkinematic Boulder Creek granodiorite plutonism (1.7 b.y.). Macroscopic doubly plunging antiformal and synformal structures were developed. P-T conditions at the peak of metamorphism were probably about 670?C and 4.5 Kb. Water pressures may locally have differed from load pressures. The 1.4 b.y. Silver Plume granite plutonism was post kinematic and on the basis of petrographic and field criteria can be divided into three facies. Emplacement was by forcible injection and assimilation. Microscopic and mesoscopic folds which postdate the formation of the characteristic mineral phases during the 1.7 b.y. metamorphism are correlated with the emplacement of the Silver Plume Log Cabin batholith. Extensive retrograde metamorphism was associated with this event. A major period of mylonitization postdates Silver Plume plutonism and produced large E-W and NE trending shear zones. A detailed study of the Rb/Sr isotope geochemistry of the layered mylonites demonstrated that the mylonitization and associated re- crystallization homogenized the Rb87/Sr 86 ratios. Whole-rock dating techniques applied to the layered mylonites indicate a probable age of 1.2 b.y. Petrographic studies suggest that the mylonitization-recrystallization process produced hornfels facies assemblages in the adjacent metasediments. Minor Laramide faulting, mineralization and igneous activity occurred within this area. A sinuous band of gravel deposits trending into the Livermore embayment and lying well above the present drainage is believed to represent a late Tertiary course of the Cache La Poudre river.

Crustal shortening and thickening in Neoarchean granite-greenstone belts: A case study from the link between the ∼2.7 Ga Elu and Hope Bay belts, northeast Slave craton, Canada

NASA Astrophysics Data System (ADS)

Mvondo, Hubert; Lentz, Dave; Bardoux, Marc

2017-11-01

The Elu Link between the ∼2.7 Ga Hope Bay and Elu belts in the northeast Bathurst Block of the Slave craton comprises supracrustal and intrusive rocks variably deformed by three tectono-metamorphic events (D1-D3). The geometry of D1 structures formed during prograde metamorphism is uncertain, because of subsequent overprint. D2 occurred in two stages predating (D2a) and postdating (D2b) peak metamorphism. D1 and D2a were thrusting events inferred from peak metamorphic pressures of ∼6.7 kbar (670 MPa) retained by a garnet orthogneiss. The latter is diagnostic of thrust tectonism in Archean granite-greenstone belts with no characteristic thrust faults. Unlike D2a, D2b was a vertical general flattening event prevailing during the formation of magmatic domes and interdomal folds that form the main strain patterns of the belts. This was followed by the formation of buckled F3 folds associated with D3 vertical constriction. The switch from thrust to vertical tectonics during peak metamorphism and subsequent deformation resulted in intense recrystallization that explains the poor preservation and scarcity of early-formed shears, including thrust zones. A tectonic process, combining D1+D2a thrust stacking, sagduction, and vertical stretching during D2b and D3, is suggested to explain crustal thickening in the Elu Link and terrains of similar ages.

Dating Paleogene Subduction in the Alborán Domain (Alpujárride Complex, S. Spain)

NASA Astrophysics Data System (ADS)

Williams, J. R.; Ashley, K.; Loewy, S. L.; Platt, J. P.

2016-12-01

The multimineral 87Rb/86Sr method has been used in recent studies to date subduction in high-pressure (HP) metamorphic belts of the Mediterranean region. In the Alpujárride Complex, the largest tectonic unit of the Alborán Domain, southern Spain, the timing of burial and HP metamorphism is controversial, with published 40Ar/39Ar white mica ages that range from 48Ma to 25Ma. Dating the HP event is complicated by a pervasive high-temperature (HT) metamorphic overprint (23-19Ma) associated with late-orogenic extension. We have identified 5 rock samples for 87Rb/86Sr dating which preserve a HP equilibrium assemblage: a garnet-staurolite-chloritoid schist, two calcareous Mg-chloritoid schists and two calcareous phyllites with previous 40Ar/39Ar ages of 48Ma and 41Ma. Improved constraints on the time gap between HP and HT metamorphism are important to test geodynamic models of the Alborán Domain, which range from prolonged thickening of continental lithosphere followed by extensional collapse, to punctuated subduction followed by back-arc extension. Furthermore, determining the onset and duration of HP metamorphism has broad implications for whether the Alborán Domain formed in the context of a single Alpine belt, or a separate and local accretionary setting. Lastly, this study will test the advantages and limitations of the 87Rb/86Sr method in a HP domain with a late HT overprint, a very common issue in orogenic systems.

Small-volume, ultrahigh-vacuum-compatible high-pressure reaction cell for combined kinetic and in situ IR spectroscopic measurements on planar model catalysts

NASA Astrophysics Data System (ADS)

Zhao, Z.; Diemant, T.; Häring, T.; Rauscher, H.; Behm, R. J.

2005-12-01

We describe the design and performance of a high-pressure reaction cell for simultaneous kinetic and in situ infrared reflection (IR) spectroscopic measurements on model catalysts at elevated pressures, between 10-3 and 103mbars, which can be operated both as batch reactor and as flow reactor with defined gas flow. The cell is attached to an ultrahigh-vacuum (UHV) system, which is used for sample preparation and also contains facilities for sample characterization. Specific for this design is the combination of a small cell volume, which allows kinetic measurements with high sensitivity under batch or continuous flow conditions, the complete isolation of the cell from the UHV part during UHV measurements, continuous temperature control during both UHV and high-pressure operation, and rapid transfer between UHV and high-pressure stage. Gas dosing is performed by a designed gas-handling system, which allows operation as flow reactor with calibrated gas flows at adjustable pressures. To study the kinetics of reactions on the model catalysts, a quadrupole mass spectrometer is connected to the high-pressure cell. IR measurements are possible in situ by polarization-modulation infrared reflection-absorption spectroscopy, which also allows measurements at elevated pressures. The performance of the setup is demonstrated by test measurements on the kinetics for CO oxidation and the CO adsorption on a Au /TiO2/Ru(0001) model catalyst film at 1-50 mbar total pressure.

Ginsenoside extraction from Panax quinquefolium L. (American ginseng) root by using ultrahigh pressure.

PubMed

Zhang, Shouqin; Chen, Ruizhan; Wu, Hua; Wang, Changzheng

2006-04-11

A new method of ultrahigh pressure extraction (UPE) was used to extract the ginsenosides from Panax quinquefolium L. (American ginseng) root at room temperature. Several solvents, including water, ethanol, methanol, and n-butanol were used in the UPE. The ginsenosides were quantified by a HPLC equipped with UV-vis detector. The results showed that ethanol is the most efficient solvent among the used ones. Compared with other methods, i.e., Soxhlet extraction, heat reflux extraction, ultrasound-assisted extraction, microwave-assisted extraction, and supercritical CO2 extraction, the UPE has the highest extraction yield in the shortest time. The extraction yield of 0.861% ginsenoside-Rc in 2 min was achieved by the UPE, while the yields of 0.284% and 0.661% were obtained in several hours by supercritical CO2 extraction and the heat reflux extraction, respectively.

Phenylpropanoid-substituted procyanidins and tentatively identified procyanidin glycosides from hawthorn (Crataegus spp.).

PubMed

Sendker, Jandirk; Petereit, Frank; Lautenschläger, Marcus; Hellenbrand, Nils; Hensel, Andreas

2013-01-01

The rational use of hawthorn leafs and flowers from Crataegus spp. for declining cardiac performance is mainly due to flavon-C-glycosides and oligomeric procyanidins (OPC). From OPC-enriched extracts from different batches, a dimeric phenylpropanoid-substituted procyanidin (cinchonain II b, 1) was isolated and characterized by MS, CD, and NMR. Also the presence of higher oligomeric cinchonains (degree of polymerization 3 to 8) in hawthorn extracts was shown by a specific ultrahigh-pressure liquid chromatography-ESI-qTOF-MS method. Interestingly, strong evidence for the occurrence of oligomeric procyanidin hexosides was found by ultrahigh-pressure liquid chromatography-ESI-qTOF-MS analysis which additionally revealed the presence of peaks indicative of dimeric procyanidin hexosides by their exact mass, which were clearly distinguishable from the cinchonain II type peaks. Georg Thieme Verlag KG Stuttgart · New York.

A simple dual online ultra-high pressure liquid chromatography system (sDO-UHPLC) for high throughput proteome analysis.

PubMed

Lee, Hangyeore; Mun, Dong-Gi; Bae, Jingi; Kim, Hokeun; Oh, Se Yeon; Park, Young Soo; Lee, Jae-Hyuk; Lee, Sang-Won

2015-08-21

We report a new and simple design of a fully automated dual-online ultra-high pressure liquid chromatography system. The system employs only two nano-volume switching valves (a two-position four port valve and a two-position ten port valve) that direct solvent flows from two binary nano-pumps for parallel operation of two analytical columns and two solid phase extraction (SPE) columns. Despite the simple design, the sDO-UHPLC offers many advantageous features that include high duty cycle, back flushing sample injection for fast and narrow zone sample injection, online desalting, high separation resolution and high intra/inter-column reproducibility. This system was applied to analyze proteome samples not only in high throughput deep proteome profiling experiments but also in high throughput MRM experiments.

Fluid and mass transfer at subduction interfaces-The field metamorphic record

NASA Astrophysics Data System (ADS)

Bebout, Gray E.; Penniston-Dorland, Sarah C.

2016-01-01

The interface between subducting oceanic slabs and the hanging wall is a structurally and lithologically complex region. Chemically disparate lithologies (sedimentary, mafic and ultramafic rocks) and mechanical mixtures thereof show heterogeneous deformation. These lithologies are tectonically juxtaposed at mm to km scales, particularly in more intensely sheared regions (mélange zones, which act as fluid channelways). This juxtaposition, commonly in the presence of a mobile fluid phase, offers up huge potential for mass transfer and related metasomatic alteration. Fluids in this setting appear capable of transporting mass over scales of kms, along flow paths with widely varying geometries and P-T trajectories. Current models of arc magmatism require km-scale migration of fluids from the interface into mantle wedge magma source regions and implicit in these models is the transport of any fluids generated in the subducting slab along and ultimately through the subduction interface. Field and geochemical studies of high- and ultrahigh-pressure metamorphic rocks elucidate the sources and compositions of fluids in subduction interfaces and the interplay between deformation and fluid and mass transfer in this region. Recent geophysical studies of the subduction interface - its thickness, mineralogy, density, and H2O content - indicate that its rheology greatly influences the ways in which the subducting plate is coupled with the hanging wall. Field investigation of the magnitude and styles of fluid-rock interaction in metamorphic rocks representing "seismogenic zone" depths (and greater) yields insight regarding the roles of fluids and elevated fluid pore pressure in the weakening of plate interface rocks and the deformation leading to seismic events. From a geochemical perspective, the plate interface contributes to shaping the "slab signature" observed in studies of the composition of arc volcanic rocks. Understanding the production of fluids with hybridized chemical/isotopic compositions could improve models aimed at identifying the relative contributions of end-member rock reservoirs through analyses of arc volcanic rocks. Production of rocks rich in hydrous minerals, along the subduction interface, could stabilize H2O to great depths in subduction zones and influence deep-Earth H2O cycling. Enhancement of decarbonation reactions and dissolution by fluid infiltration facilitated by deformation at the interface could influence the C flux from subducting slabs entering the sub-arc mantle wedge and various forearc reservoirs. In this paper, we consider records of fluid and mass transfer at localities representing various depths and structural expressions of evolving paleo-interfaces, ranging widely in structural character, the rock types involved (ultramafic, mafic, sedimentary), and the rheology of these rocks. We stress commonalities in styles of fluid and mass transfer as related to deformation style and the associated geometries of fluid mobility at subduction interfaces. Variations in thermal structure among individual margins will lead to significant differences in not only the rheology of subducting rocks, and thus seismicity, but also the profiles of devolatilization and melting, through the forearc and subarc, and the element/mineral solubilities in any aqueous fluids or silicate melts that are produced. One key factor in considering fluid and mass transfer in the subduction interface, influencing C cycling and other chemical additions to arcs, is the uncertain degree to which sub-crustal ultramafic rocks in downgoing slabs are hydrated and release H2O-rich fluids.

High-beta spherical tokamak startup in TS-4 merging experiment by use of toroidal field ramp-up

NASA Astrophysics Data System (ADS)

Kaminou, Yasuhiro; , Toru, II; Kato, Joji; Inomoto, Michiaki; Ono, Yasushi; TS Group Team; National InstituteFusion Science Collaboration

2014-10-01

We demonstrated the formation method of an ultrahigh-beta spherical tokamak by use of a field-reversed configuration and a spheromak in TS-4 device (R ~ 0.5 m, A ~ 1.5, Ip ~ 30-100 kA, B ~ 100 mT). This method is composed of the following steps: 1. Two spheromaks are merged together and a high-beta spheromak or FRC is formed by reconnection heating. 2. External toroidal magnetic field is added (current rising time ~50 μs), and spherical tokamak-like configuration is formed. In this way, the ultrahigh-beta ST is formed. The ultrahigh-beta ST formed by FRC has a diamagnetic toroidal field, and it presumed to be in a second-stable state for ballooning stability, and the one formed by spheromak has a weak paramagnetic toroidal magnetic field, while a spheormak has a strong paramagnetic toroidal magnetic field. This diamagnetic current derives from inductive electric field by ramping up the external toroidal magnetic field, and the diamagnetic current sustains high thermal pressure of the ultrahigh-beta spherical tokamak. And the beta of the ultrahigh-beta ST formed by FRC reaches about 50%. To sustain the high-beta state, 0.6 MW neutral beam injection and center solenoid coils are installed to the TS-4 device. In the poster, we report the experimental results of ultrahigh-beta spherical tokamak startup and sustainment by NBI and CS current driving experiment.

On the role of horizontal displacements in the exhumation of high pressure metamorphic rocks

NASA Astrophysics Data System (ADS)

Brun, J.-P.; Tirel, C.; Philippon, M.; Burov, E.; Faccenna, C.; Gueydan, F.; Lebedev, S.

2012-04-01

High pressure metamorphic rocks exposed in the core of many mountain belts correspond to various types of upper crustal materials that have been buried to mantle depths and, soon after, brought back to surface at mean displacement rates up to few cm/y, comparable to those of plate boundaries. The vertical component of HP rock exhumation velocity back to surface is commonly well constrained by pressure estimates from petrology and geochronological data whereas the horizontal component remains generally difficult or impossible to estimate. Consequently, most available models, if not all, attempt to simulate exhumation with a minimal horizontal component of displacement. Such models, require that the viscosity of HP rocks is low and/or the erosion rate large -i.e. at least equal to the rate of exhumation. However, in some regions like the Aegean, where the exhumation of blueschists and eclogites is driven by slab rollback, it can be shown that the horizontal component of exhumation related displacement, obtained from map view restoration, is 5 to 7 times larger than the vertical one, deduced from metamorphic pressure estimates. Using finite element models performed with FLAMAR, we show that such a situation simply results from the subduction of small continental blocks (< 500km) that stimulate subduction rollback. The continental block is dragged downward and sheared off the downgoing mantle slab by buoyancy force. Exhumation of the crustal block occurs through a one step Caterpillar-type walk, with the block's tail slipping along a basal décollement, approaching the head and making a large buckle, which then unrolls at surface as soon as the entire block is delaminated. Finally, the crustal block emplaces at surface in the space created by trench retreat. This process of exhumation requires neither rheological weakening of HP rocks nor high rates of erosion.

Matrix deformation mechanisms in HP-LT tectonic mélanges — Microstructural record of jadeite blueschist from the Franciscan Complex, California

NASA Astrophysics Data System (ADS)

Wassmann, Sara; Stöckhert, Bernhard

2012-09-01

Exhumed high pressure-low temperature metamorphic mélanges of tectonic origin are believed to reflect high strain accumulated in large scale interplate shear zones during subduction. Rigid blocks of widely varying size are embedded in a weak matrix, which takes up the deformation and controls the rheology of the composite. The microfabrics of a highly deformed jadeite-blueschist from the Franciscan Complex, California, are investigated to help understand deformation mechanisms at depth. The specimen shows a transposed foliation with dismembered fold hinges and boudinage structures. Several generations of open fractures have been sealed to become veins at high-pressure metamorphic conditions. The shape of these veins, frequently restricted to specific layers, indicates distributed host rock deformation during and after sealing. Small cracks in jadeite and lawsonite are healed, with tiny quartz inclusions aligned along the former fracture surface. Large jadeite porphyroblasts show strain caps and strain shadows. Open fractures are sealed by quartz and new jadeite epitactically grown on the broken host. Monophase glaucophane aggregates consist of undeformed needles with a diameter between 0.1 and 2 μm, grown after formation of isoclinal folds. Only quartz microfabrics indicate some stage of crystal-plastic deformation, followed by annealing and grain growth. Aragonite in the latest vein generation shows retrogression to calcite along its rims. The entire deformation happened under HP-LT metamorphic conditions in the stability field of jadeite and quartz, at temperatures between 300 and 450 °C and pressures exceeding 1-1.4 GPa. The microfabrics indicate that dissolution precipitation creep was the predominant deformation mechanism, accompanied by brittle failure and vein formation at quasi-lithostatic pore fluid pressure. This indicates low flow strength and, combined with high strain rates expected for localized deformation between the plates, a very low viscosity of material in the interplate shear zone at a depth > 30-45 km.

Pan-African metamorphic evolution in the southern Yaounde Group (Oubanguide Complex, Cameroon) as revealed by EMP-monazite dating and thermobarometry of garnet metapelites

NASA Astrophysics Data System (ADS)

Owona, Sebastien; Schulz, Bernhard; Ratschbacher, Lothar; Mvondo Ondoa, Joseph; Ekodeck, Georges E.; Tchoua, Félix M.; Affaton, Pascal

2011-01-01

Garnet-bearing micaschists and paragneisses of the Yaounde Group in the Pan-African Central African Orogenic Belt in Cameroon underwent a polyphase structural evolution with the deformation stages D 1-D 2, D 3 and D 4. The garnet-bearing assemblages crystallized in course of the deformation stage D 1-D 2 which led to the formation of the regional main foliation S 2. In XCa- XMg coordinates one can distinguish several zonation trends in the garnet porphyroblasts. Zonation trends with increasing XMg and variably decreasing XCa signalize a garnet growth during prograde metamorphism. Intermineral microstructures provided criteria for local equilibria and a structurally controlled application of geothermobarometers based on cation exchange and net transfer reactions. The syndeformational P- T path sections calculated from cores and rims of garnets in individual samples partly overlap and align along clockwise P- T trends. The P- T evolution started at ˜450 °C/7 kbar, passed high-pressure conditions at 11-12 kbar at variable temperatures (600-700 °C) and involved a marked decompression toward 6-7 kbar at high temperatures (700-750 °C). Th-U-Pb dating of metamorphic monazite by electron microprobe (EMP-CHIME method) in eight samples revealed a single period of crystallization between 613 ± 33 Ma and 586 ± 15 Ma. The EMP-monazite age populations between 613 ± 33 Ma enclosed in garnet and 605 ± 12 Ma in the matrix apparently bracket the high temperature-intermediate pressure stage at the end of the prograde P- T path. The younger monazites crystallized still at amphibolite-facies conditions during subsequent retrogression. The Pan-African overall clockwise P- T evolution in the Yaounde Group with its syndeformational high pressure stages and marked pressure variations is typical of the parts of orogens which underwent contractional crustal thickening by stacking of nappe units during continental collision and/or during subduction-related accretionary processes.

Microdiamonds from the European Variscan Orogenic Belt

NASA Astrophysics Data System (ADS)

Kotkova, J.; Jakubova, P.; Whitehouse, M.; Fedortchouk, Y.

2014-12-01

Diamond, along with coesite, has been discovered recently in the continental crustal rocks of the European Variscan orogenic belt, namely the Bohemian Massif (BM). In addition to the garnet-phengite gneiss in Germany, western BM, microdiamond occurs in major rock forming minerals - garnet, kyanite - and in zircon in ultrahigh-pressure rocks overprinted under high-pressure granulite facies conditions (c. 16-20 kbar, c. 1000°C) in the northern and eastern BM. Well-preserved 10-30 μm-sized microdiamonds from northern BM exhibit diverse morphologies (SEM data) depending upon the host rock type. Octahedral diamond occurs in felsic garnet-kyanite-feldspar-quartz rock (metasediment), whereas intermediate garnet-clinopyroxene-feldspar-quartz rock contains a cubo-octahedral variety. Diamond morphology can be thus controlled by solid impurities available in the medium of crystallization (K- vs. Ca-bearing fluids or melts), as shown by experiments. Pointed-bottom negatively oriented trigonal etch pits on the octahedral diamond faces developed due to diamond resorption at CO2-dominated environment (less than 50 wt % of H2O, experimental data), possibly by action of a residual fluid. SIMS determined δ13C values range from -22 to -21 ‰ for the felsic rock and from - 26 to - 33 for the intermediate one, corresponding to the typical range of organic carbon δ13C and inconsistent with a significant mantle carbon (δ13C ~ - 5 ‰) input. Diamond-bearing domains in zircon, also analysed by SIMS, yielded a Variscan U-Pb age of c. 340 Ma. The present stage of knowledge allows us to conclude that (i) metamorphic diamonds in the BM occur in lithologies of metasedimentary character, and their carbon source was organic; (ii) crustal-derived CO2-rich fluids with impurities played an important role in diamond formation and dissolution; (iii) diamonds formed during the Variscan orogenic cycle and (iv) diamonds are best preserved in the external domain of the Variscan orogenic belt.

Mechanics of lung ventilation in a post-metamorphic salamander, Ambystoma Tigrinum.

PubMed

Simons, R S; Bennett, W O; Brainerd, E L

2000-03-01

The mechanics of lung ventilation in frogs and aquatic salamanders has been well characterized, whereas lung ventilation in terrestrial-phase (post-metamorphic) salamanders has received little attention. We used electromyography (EMG), X-ray videography, standard videography and buccal and body cavity pressure measurements to characterize the ventilation mechanics of adult (post-metamorphic) tiger salamanders (Ambystoma tigrinum). Three results emerged: (i) under terrestrial conditions or when floating at the surface of the water, adult A. tigrinum breathed through their nares using a two-stroke buccal pump; (ii) in addition to this narial two-stroke pump, adult tiger salamanders also gulped air in through their mouths using a modified two-stroke buccal pump when in an aquatic environment; and (iii) exhalation in adult tiger salamanders is active during aquatic gulping breaths, whereas exhalation appears to be passive during terrestrial breathing at rest. Active exhalation in aquatic breaths is indicated by an increase in body cavity pressure during exhalation and associated EMG activity in the lateral hypaxial musculature, particularly the M. transversus abdominis. In terrestrial breathing, no EMG activity in the lateral hypaxial muscles is generally present, and body cavity pressure decreases during exhalation. In aquatic breaths, tidal volume is larger than in terrestrial breaths, and breathing frequency is much lower (approximately 1 breath 10 min(-)(1 )versus 4-6 breaths min(-)(1)). The use of hypaxial muscles to power active exhalation in the aquatic environment may result from the need for more complete exhalation and larger tidal volumes when breathing infrequently. This hypothesis is supported by previous findings that terrestrial frogs ventilate their lungs with small tidal volumes and exhale passively, whereas aquatic frogs and salamanders use large tidal volumes and and exhale actively.

The origin of oceanic crust and metabasic rocks protolith, the Luk Ulo Mélange Complex, Indonesia

NASA Astrophysics Data System (ADS)

Permana, H.; Munasri; Mukti, Maruf M.; Nurhidayati, A. U.; Aribowo, S.

2018-02-01

The Luk Ulo Mélange Complex (LUMC) is composed of tectonic slices of rocks that surrounded by scaly clay matrix. These rocks consist of serpentinite, gabbro, diabase, and basalt, eclogite, blueschist, amphibolite, schist, gneiss, phylite and slate, granite, chert, red limestone, claystone and sandstone. The LUMC was formed since Paleocene to Eocene, gradually uplifted of HP-UHP metabasic-metapelite (P: 20-27kbar; T: 410-628°C) to near surface mixed with hemipelagic sedimentary rocks. The metamorphic rocks were formed during 101-125 Ma (Early Cretaceous) within 70 to 100 km depth and ∼6°C/km thermal gradient. It took about 50-57 Myr for these rocks to reach the near surface during Paleocene-Eocene, with an uplift rate at ∼1.4-1.8 km/year to form the mélange complex. The low thermal gradient was due to subduction of old and cold oceanic crust. The subducted oceanic crust (MORB) as protolith of Cretaceous metabasic rocks must be older than Cretaceous. The data show that the basalt of oceanic crust is Cretaceous (130-81 Ma) comparable to the age of the cherts (Early to Late Cretaceous). Therefore, we consider that neither oceanic crust exposed in LUMC nor all of part of the old oceanic crust is the protolith of LUMC metabasic subducted beneath the Eurasian Plate. These oceanic rocks possibly originated or part of the edge of micro-continental that merged as a part of the LUMC during the collision with the Eurasian margin.

Plate interface rheological switches during subduction infancy: Control on slab penetration and metamorphic sole formation

NASA Astrophysics Data System (ADS)

Agard, P.; Yamato, P.; Soret, M.; Prigent, C.; Guillot, S.; Plunder, A.; Dubacq, B.; Chauvet, A.; Monié, P.

2016-10-01

Subduction infancy corresponds to the first few million years following subduction initiation, when slabs start their descent into the mantle. It coincides with the transient (yet systematic) transfer of material from the top of the slab to the upper plate, as witnessed by metamorphic soles welded beneath obducted ophiolites. Combining structure-lithology-pressure-temperature-time data from metamorphic soles with flow laws derived from experimental rock mechanics, this study highlights two main successive rheological switches across the subduction interface (mantle wedge vs. basalts, then mantle wedge vs. sediments; at ∼800 °C and ∼600 °C, respectively), during which interplate mechanical coupling is maximized by the existence of transiently similar rheologies across the plate contact. We propose that these rheological switches hinder slab penetration and are responsible for slicing the top of the slab and welding crustal pieces (high- then low-temperature metamorphic soles) to the base of the mantle wedge during subduction infancy. This mechanism has implications for the rheological properties of the crust and mantle (and for transient episodes of accretion/exhumation of HP-LT rocks in mature subduction systems) and highlights the role of fluids in enabling subduction to overcome the early resistance to slab penetration.

Resetting of RbSr ages of volcanic rocks by low-grade burial metamorphism

USGS Publications Warehouse

Asmeroma, Y.; Damon, P.; Shafiqullah, M.; Dickinson, W.R.; Zartman, R.E.

1991-01-01

We report a nine-point RbSr whole-rock isochron age of 70??3 Ma (MSWD 3.97) for Mid-Jurassic volcanic rocks. The same rocks have also been dated by the UThPb method on zircon, giving a crystallization age of 166 ?? 11 Ma, over twice as old as the RbSr age. The data demonstrate that whole-rock RbSr ages of volcanic rocks, even lava flows with SiO2 content as low as 57 wt.%, are susceptible to complete resetting. The rocks range in composition from rhyodacite tuffs to andesite lavas. The complete breakdown of all major minerals that contain Rb and Sr resulted in an alteration mineral assemblage consisting of phengite, albite, secondary quartz, and minor amounts of chlorite and epidote. Phengite is the K-bearing product of the breakdown of biotite and K-feldspar. Pressure during low-grade metamorphism of the volcanic rocks, estimated from phengite composition to have been in the range of 4 to 6 kbar, points to thrust-related burial as the main cause of resetting. Consequently, such reset isochrons may date large-scale events such as regional thrusting and metamorphism. The coherent resetting of the RbSr isochron suggests large-scale pervasive fluid movement during thrust-related burial metamorphism. ?? 1991.

Metamorphic Proteins: Emergence of Dual Protein Folds from One Primary Sequence.

PubMed

Lella, Muralikrishna; Mahalakshmi, Radhakrishnan

2017-06-20

Every amino acid exhibits a different propensity for distinct structural conformations. Hence, decoding how the primary amino acid sequence undergoes the transition to a defined secondary structure and its final three-dimensional fold is presently considered predictable with reasonable certainty. However, protein sequences that defy the first principles of secondary structure prediction (they attain two different folds) have recently been discovered. Such proteins, aptly named metamorphic proteins, decrease the conformational constraint by increasing flexibility in the secondary structure and thereby result in efficient functionality. In this review, we discuss the major factors driving the conformational switch related both to protein sequence and to structure using illustrative examples. We discuss the concept of an evolutionary transition in sequence and structure, the functional impact of the tertiary fold, and the pressure of intrinsic and external factors that give rise to metamorphic proteins. We mainly focus on the major components of protein architecture, namely, the α-helix and β-sheet segments, which are involved in conformational switching within the same or highly similar sequences. These chameleonic sequences are widespread in both cytosolic and membrane proteins, and these folds are equally important for protein structure and function. We discuss the implications of metamorphic proteins and chameleonic peptide sequences in de novo peptide design.

Combined garnet and zircon geochronology of the ultra-high temperature metamorphism: Constraints on the rise of the Orlica-Śnieżnik Dome, NE Bohemian Massif, SW Poland

NASA Astrophysics Data System (ADS)

Walczak, Katarzyna; Anczkiewicz, Robert; Szczepański, Jacek; Rubatto, Daniela; Košler, Jan

2017-11-01

Garnet and zircon geochronology combined with trace element partitioning and petrological studies provide tight constraints on evolution of the UHT-(U)HP terrain of the Orlica-Śnieżnik Dome (OSD) in the NE Bohemian massif. Lu-Hf dating of peritectic garnet from two mesocratic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma recording peak 2.5 GPa pressure and 950 °C temperature. In situ, U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 341.9 ± 3.4 Ma. Ti-in-zircon thermometry indicates crystallization at 810-860 °C pointing to zircon formation on the retrograde path. Lu partitioning between garnet rim and zircon suggest equilibrium growth and thus U-Pb zircon age constrain the terminal phase of garnet crystallization which lasted about 6 Ma. All Sm-Nd garnet ages obtained for mesocratic and mafic granulites are identical and consistently younger than the corresponding Lu-Hf dates. They are interpreted as reflecting cooling of granulites through the Sm-Nd closure temperature at about 337 Ma. The estimated PTt path documents the ca. 10 Ma evolution cycle of the OSD characterized by two distinct periods: (1) 347 - > 342 Ma period corresponds to nearly isothermal decompression resulting from crustal scale folding and vertical extrusion of granulites, and (2) at > 342-337 Ma which corresponds to a fast, nearly isobaric cooling.

The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India

NASA Astrophysics Data System (ADS)

Das, Kaushik; Tomioka, Naotaka; Bose, Sankar; Ando, Jun-ichi; Ohnishi, Ichiro

2017-06-01

We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91-1.94Fe0.06-0.07Ca<0.01) (P0.99-1.00O4)(OH0.02-0.17F0.98-0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites ( 1000 °C, 8-9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800-850 °C, 6-6.5 kbar) as deduced from their pressure -temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with high X Mg and/or fO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.

Molecular Retrofitting Adapts a Metal–Organic Framework to Extreme Pressure

DOE PAGES

Kapustin, Eugene A.; Lee, Seungkyu; Alshammari, Ahmad S.; ...

2017-06-07

Despite numerous studies on chemical and thermal stability of metal-organic frameworks (MOFs), mechanical stability remains largely undeveloped. No strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure, to date. We show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4'-biphenyldicarboxylate (BPDC) linker as a "girder" to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structuremore » from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kapustin, Eugene A.; Lee, Seungkyu; Alshammari, Ahmad S.

Despite numerous studies on chemical and thermal stability of metal-organic frameworks (MOFs), mechanical stability remains largely undeveloped. No strategy exists to control the mechanical deformation of MOFs under ultrahigh pressure, to date. We show that the mechanically unstable MOF-520 can be retrofitted by precise placement of a rigid 4,4'-biphenyldicarboxylate (BPDC) linker as a "girder" to afford a mechanically robust framework: MOF-520-BPDC. This retrofitting alters how the structure deforms under ultrahigh pressure and thus leads to a drastic enhancement of its mechanical robustness. While in the parent MOF-520 the pressure transmitting medium molecules diffuse into the pore and expand the structuremore » from the inside upon compression, the girder in the new retrofitted MOF-520-BPDC prevents the framework from expansion by linking two adjacent secondary building units together. As a result, the modified MOF is stable under hydrostatic compression in a diamond-anvil cell up to 5.5 gigapascal. The increased mechanical stability of MOF-520-BPDC prohibits the typical amorphization observed for MOFs in this pressure range. Direct correlation between the orientation of these girders within the framework and its linear strain was estimated, providing new insights for the design of MOFs with optimized mechanical properties.« less

Pore Fluid Extraction by Reactive Solitary Waves in 3-D

NASA Astrophysics Data System (ADS)

Omlin, Samuel; Malvoisin, Benjamin; Podladchikov, Yury Y.

2017-09-01

In the lower crust, viscous compaction is known to produce solitary porosity and fluid pressure waves. Metamorphic (de)volatilization reactions can also induce porosity changes in response to the propagating fluid pressure anomalies. Here we present results from high-resolution simulations using Graphic Processing Unit parallel processing with a model that includes both viscous (de)compaction and reaction-induced porosity changes. Reactive porosity waves propagate in a manner similar to viscous porosity waves, but through a different mechanism involving fluid release and trap in the solid by reaction. These waves self-generate from red noise or an ellipsoidal porosity anomaly with the same characteristic size and abandon their source region to propagate at constant velocity. Two waves traveling at different velocities pass through each other in a soliton-like fashion. Reactive porosity waves thus provide an additional mechanism for fluid extraction at shallow depths with implications for ore formation, diagenesis, metamorphic veins formation, and fluid extraction from subduction zones.

Découverte et signification d'une paragenèse à ilménite zincifère dans les métapélites des Jebilet centrales (Maroc)Occurrence and significance of zincian ilmenite in low-pressure metapelites from central Jebilet (Morocco)

NASA Astrophysics Data System (ADS)

Essaifi, Abderrahim; Ballèvre, Michel; Marignac, Christian; Capdevila, Ramon

2001-10-01

A zincian ilmenite paragenesis is found in metapelites from a contact metamorphic zone (central Jebilet, Morocco) induced by the emplacement of microgranitic intrusions. The zincian ilmenite is mainly preserved in syntectonic andalusite porphyroblasts. The growth of zincian ilmenite is related either to sphalerite breakdown during prograde metamorphism, or to the pervasive flow of a mineralizing fluid within the metapelites. The chlorine-rich fluid carried zinc and other metals leached in the microgranites, during its flow to discharge zones which were probably the Jebilet sulfide deposits.

Prograde and retrograde metamorphic processes in high-pressure subduction zone serpentinites from East Thessaly, Greece

NASA Astrophysics Data System (ADS)

Koutsovitis, Petros

2016-04-01

The East Thessaly region, Central Greece, includes metaophiolitic mélange formations which extend from the eastern foothills of Mt. Olympus and Ossa, throughout the Agia basin, Mt. Mavrovouni (Sklithro region), South Pelion and reaching up to northeast Othris (regions of Aerino and Velestino). They appear in the form of dispersed and deformed thrust sheets having been variably emplaced onto Mesozoic platform series rocks of the Pelagonian tectonostratigraphic zone[1]. These formations consist mainly of serpentinites, as well as metasediments, metagabbros, metadolerites, rodingites, ophicalcites, talc-schists and chromitites. Based upon petrographic observations, mineral chemistry data and XRD patterns, the subduction zone-related serpentinites from the regions of Potamia, Anavra, Aetolofos and Kalochori-Chasanbali (Agia basin), as well as from the regions of Aerino and Velestino, are characterized by the progressive transformation of lizardite to antigorite and are distinguished into two groups. The first group includes serpentinites from the metaophiolitic formations of Potamia, Anavra, Aerino and Velestino, which are marked by destibillization of lizardite to antigorite, mostly along the grain boundaries of the lizardite mesh textured relics. The presence of lizardite and antigorite in almost equal amounts indicates medium-temperature blueschist facies metamorphic conditions (˜340-370 ° C; P≈10-11 kbar)[2,3,4]. The second serpentinite group appears in the regions of Aetolofos and Kalochori, characterized by the predominance of antigorite, the minor occurrence of lizardite and the complete replacement of spinel by Cr-magnetite. The absence of metamorphic olivine suggests that these serpentinites were most likely formed at slightly higher temperature and pressure conditions compared to the first serpentinite group, corresponding to medium or high temperature blueschist facies metamorphism (˜360-380 ° C; P≈12 kbar)[2,3,4]. These metamorphic conditions are highly comparable with the P-T estimates from the East Thessaly metabasic rocks (˜350 ° C; P≈10-11 kbars)[5], suggesting that the entire metaophiolitic formation underwent blueschist facies metamorphism, comparable with high-pressure metaophiolitic formations appearing in Evia, Attica and the Cyclades. The East Thessaly serpentinites exhibit significantly high PM-normalized Pb, U enrichments and rather high Cs, La, As and Sb concentrations, which are comparable with subduction-related serpentinites, formed after mantle wedge peridotite hydration, and that have interacted with sedimentary derived fluids [2,6,7,8]. These serpentinites were also partly affected by de-serpentinization retrograde metamorphism (estimated at P<8 kbar and T<350 ° C) which is noticed by the following: secondary crosscuting antigorite veins occasionally with chlorite, coronas of chlorite along Cr-magnetite crystals, appearance of secondary calcite veins and talc. In the Kalochori-Chasanbali area, intense carbonization processes formed ophicalcite breccias enveloped by imbricated serpentinites[9], whereas talc-rich serpentinites appear in the region of Sklithro. Retrograde metamorphism may have occurred during exhumation, possibly within a serpentinite channel[8]. In addition, their retrograde history can also be indirectly identified through the study of their rodingite intrusions and more specifically through the formation of late-stage vesuvianite-rich dykes at low-moderate temperature conditions (T=250-300 oC) and subsequent derodingitization processes, forming metarodingites. The latter include abundant high-Mg replacive chlorite formed by continuous serpentinization which provided Mg2+ to the infiltrating fluids, causing the partial breakdown of Ca-bearing minerals. References. [1] Pe-Piper & Piper 2002: Borntraeger, Stuttgart, 1-645; [2] Lafay et al 2013: Chem Geol 343, 38-54; [3] Schwartz et al 2013: Lithos 178, 197-210; [4] Guillot, et al 2015: Tectonophysics 646, 1-19; [5] Perraki et al 2002: Geologica Carpathica 53, 164-165; [6] Deschamps, et al 2013: Lithos 178, 96-127; [7] Hattori & Guillot, 2007: G-Cubed 8 (9); [8] Barnes et al 2014: Chemi Geol 389, 29-47; [9] Melfos et al 2009: Geoph. Res. Abst, 11.

Ultra-High Pressure Homogenization improves oxidative stability and interfacial properties of soy protein isolate-stabilized emulsions.

PubMed

Fernandez-Avila, C; Trujillo, A J

2016-10-15

Ultra-High Pressure Homogenization (100-300MPa) has great potential for technological, microbiological and nutritional aspects of fluid processing. Its effect on the oxidative stability and interfacial properties of oil-in-water emulsions prepared with 4% (w/v) of soy protein isolate and soybean oil (10 and 20%, v/v) were studied and compared to emulsions treated by conventional homogenization (15MPa). Emulsions were characterized by particle size, emulsifying activity index, surface protein concentration at the interface and by transmission electron microscopy. Primary and secondary lipid oxidation products were evaluated in emulsions upon storage. Emulsions with 20% oil treated at 100 and 200MPa exhibited the most oxidative stability due to higher amount of oil and protein surface load at the interface. This manuscript addresses the improvement in oxidative stability in emulsions treated by UHPH when compared to conventional emulsions. Copyright © 2016 Elsevier Ltd. All rights reserved.

Ultra-high vacuum compatible induction-heated rod casting furnace

NASA Astrophysics Data System (ADS)

Bauer, A.; Neubauer, A.; Münzer, W.; Regnat, A.; Benka, G.; Meven, M.; Pedersen, B.; Pfleiderer, C.

2016-06-01

We report the design of a radio-frequency induction-heated rod casting furnace that permits the preparation of polycrystalline ingots of intermetallic compounds under ultra-high vacuum compatible conditions. The central part of the system is a bespoke water-cooled Hukin crucible supporting a casting mold. Depending on the choice of the mold, typical rods have a diameter between 6 mm and 10 mm and a length up to 90 mm, suitable for single-crystal growth by means of float-zoning. The setup is all-metal sealed and may be baked out. We find that the resulting ultra-high vacuum represents an important precondition for processing compounds with high vapor pressures under a high-purity argon atmosphere up to 3 bars. Using the rod casting furnace, we succeeded to prepare large high-quality single crystals of two half-Heusler compounds, namely, the itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb.

Ultra-high vacuum compatible induction-heated rod casting furnace.

PubMed

Bauer, A; Neubauer, A; Münzer, W; Regnat, A; Benka, G; Meven, M; Pedersen, B; Pfleiderer, C

2016-06-01

We report the design of a radio-frequency induction-heated rod casting furnace that permits the preparation of polycrystalline ingots of intermetallic compounds under ultra-high vacuum compatible conditions. The central part of the system is a bespoke water-cooled Hukin crucible supporting a casting mold. Depending on the choice of the mold, typical rods have a diameter between 6 mm and 10 mm and a length up to 90 mm, suitable for single-crystal growth by means of float-zoning. The setup is all-metal sealed and may be baked out. We find that the resulting ultra-high vacuum represents an important precondition for processing compounds with high vapor pressures under a high-purity argon atmosphere up to 3 bars. Using the rod casting furnace, we succeeded to prepare large high-quality single crystals of two half-Heusler compounds, namely, the itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb.

The Genesis of tectonically and hydrothermally controlled industry mineral deposits: A geochemical and structural study

NASA Astrophysics Data System (ADS)

Wölfler, Anke; Prochaska, Walter; Henjes-Kunst, Friedhelm; Fritz, Harald

2010-05-01

The study aims to investigate the role of hydrothermal fluids in the formation of talc and magnesite deposits. These deposits occur in manifold geological and tectonical settings such as stockworks and veins within ultramafite hostrocks and monomineralic lenses within marine platform sediments. Along shear zones talc mineralizations may occur as a result of tectonical and hydrothermal activity. To understand the role of the fluids for the genesis of the mineralization, deposits in different geological and tectonical settings are investigated: Talc mineralization within in magnesite in low-grade palaeozoic nappe complexes (Gemerska Poloma, Slovakia): The magnesite body lies within the Gemer unit of the Inner Carpathians consisting of Middle Triassic metacarbonates and Upper Triassic pelagic limestones and radiolarites. The talc mineralization is bound to crosscutting veins. Two metamorphic events can be distinguished, one during Variscan orogeny and one related to the Alpine orogeny leading to the formation of talc along faults in an Mg carbonate body (Radvanec et al, 2004).The origin of the fluids as well as the tectonic events leading to the mineralization is still widely unknown. Talc mineralization in shearzones within Palaeozoic meta sedimentary rocks (Sa Matta, Sardinia): Variscan granitoids intruded Palaeozoic meta sedimentary rocks and were overprinted be NE striking tectonic structures that host talc mineralizations. The origin of Mg and fluids leading to the mineralization is still not answered satisfactorily (Grillo and Prochaska, 2007) and thus a tectonic model for the genesis of the talc deposit is missing. Talc mineralization within UHP pre-Alpine continental crust (Val Chisone, Italy): The talc deposit forms part of the Dora-Maira Massif. Geologicaly the massif derived from a Variscan basement that includes post-Variscan intrusions. The talc mineralization occurs as a sheetlike, conformable body. A possible tectonic emplacement of talc along shear surfaces was proposed by Sandrone & Zucchetti, 1988. Magnesite and talc bearing shearzones in ultramafic hostrocks (Lahnaslampi & Horsmanaho, Finland): Both deposits are situated in the Proterozoic schist belt where the talc-magnesite rocks at Lahnaslampi are associated with minor serpentine breccias. The steatitization took place in two different stages: During prograde metamorphism with H2O-dominated solutions and at declining temperature and pressure in the presence of CO2-bearing fluids that resulted in the main steatitization along tectonic structures. A combined geological, petrological and geochronological is chosen to resolve mechanism of mineralisation within the different tectonic setting. Different phases of mineral formation are first distinguished by pertrological and structural field work and then dated by radiometric techniques. Fluid species and chemical environment during mineralisation is resolved by geochemical techniques and stable isotope studies. References Grillo, S., Prochaska, W. (2007): Fluid Chemistry and Stable Isotope Evidence of Shearzone related Talc and Chlorite Mineralizations in Central Sardinia-Italy, In: Conference Abstracts SGA-Meeting. Radvanec, M., Koděra, P., Prochaska, W. (2004): Mg replacement of the Gemerska Poloma talk-magnesite deposit, Western Carpathians, Slovakia. Acta Petrologica Sinica, 20, 773-790. Sandrone, Zucchetti (1988): Geology of the Italian high-quality cosmetic talc from the Pinerolo district (Western Alps). Zuffar' Days - Symposium held in Cagliari, 10-15

The dynamics of serpentinite dehydration reactions in subduction zones: Constrains from the Cerro del Almirez ultramafic massif (Betic Cordillera, SE Spain)

NASA Astrophysics Data System (ADS)

Dilissen, Nicole; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Padrón-Navarta, José Alberto

2015-04-01

Arc volcanism, earthquakes and subduction dynamics are controlled by fluids from downgoing slabs and their effect on the melting and rheology of the overlying mantle wedge. High pressure dehydration of serpentinite in the slab and the subduction channel is considered as one of the main sources of fluids in subduction zones. Even though this metamorphic reaction is essential in subduction activities, the behavior of the fluids, the kinetics and thermodynamics during the breakdown reaction are still poorly understood. The Cerro del Almirez (Nevado-Filábride Complex, Betic Cordillera, SE Spain) uniquely preserves the dehydration front from antigorite serpentinite to chlorite-harzburgite and constitutes a unique natural laboratory to investigate high-pressure dehydration of serpentinite. This reaction occurred in a subduction setting releasing up to 13 wt% of water, contributing significantly to the supply of fluids to the overlying mantle wedge. A key to the understanding of the metamorphic conditions prevailing during serpentinite dehydration is to study the two prominent textures -granofels and spinifex-like chlorite harzburgite- occurring in this reaction product. The detailed texture differences in the Chl-harzburgite can provide insights into diverse kinetic and thermodynamic conditions of this dehydration reaction due to variations in effective pressure and drainage conditions. It has been proposed that difference in overpressure (P') and deviation from growth equilibrium, i.e. overstepping, is responsible for these two types of textures [Padrón-Navarta et al., 2011]. The magnitude and duration of P' is highly dependent on dehydration kinetics [Connolly, 1997]. The fast pressure drop, with spinifex-texture as a product, can be linked to draining events expected after hydrofracturing, which are recorded in grain size reduction zones in this massif. According to this hypothesis, mapping of textural variation in Chl-harzburgite might be used as a proxy to investigate the hydrodynamics of serpentinite dehydration reaction. During an intensive detailed field mapping of a well-exposed area of ca. 0.87 km2 in the W-SW part of the massif, we mapped textural variations of Chl-harzburgite every three to ten meters. Granofels and spinifex lenses occur within scales of decimetres to decametres. These spatial scale constrains can be linked to temporal scales of the reactions and to the spatial and temporal variation of fluid release during dehydration of serpentinite. REFERENCES Connolly, J. A. D. (1997), Devolatilization-generated fluid pressure and deformation-propagated fluid flow during prograde regional metamorphism, J. Geophys. Res.-Solid Earth, 102(B8), 18149-18173, doi:10.1029/97jb00731. Padrón-Navarta, J. A., V. López Sánchez-Vizcaíno, C. J. Garrido, and M. T. Gómez-Pugnaire (2011), Metamorphic record of high-pressure dehydration of antigorite serpentinite to chlorite harzburgite in a subduction setting (Cerro del Almirez, Nevado-Filábride Complex, southern Spain), Journal of Petrology, 52(10), 2047-2078.

Inheritance, Variscan tectonometamorphic evolution and Permian to Mesozoic rejuvenations in the metamorphic basement complexes of the Romanian Carpathians revealed by monazite microprobe geochronology

NASA Astrophysics Data System (ADS)

Săbău, Gavril; Negulescu, Elena

2014-05-01

Monazite U-Th-Pb chemical dating reaches an acceptable compromise between precision and accuracy on one side, and spatial resolution and textural constraints on the other side. Thus it has a powerful potential in testing the coherence of individual metamorphic basement units, and enabling correlations among them. Yet, sensitivity and specificity issues in monazite response to thermotectonic events, especially in the case of superposed effects, remain still unclear. Monazite dating at informative to detailed scale in the main metamorphic basement units of the Carpathians resulted in complex age spectra. In the main, the spectra are dominated by the most pervasive thermal and structural overprint, as checked against independent geochronological data. Post-peak age resetting is mostly present, but statistically subordinate. Resetting in case of superposed events is correlated with the degree of textural and paragenetic overprinting, inheritances being always indicated by more or less well-defined age clusters. The lack of relict ages correlating with prograde structural and porphyroblast zonation patterns is indicative for juvenile formations. Age data distribution in the Carpathians allowed distinction of pre-Variscan events, syn-metamorphic Variscan tectonic stacking of juvenile and reworked basement, post-Variscan differential tectonic uplift, as well as prograde metamorphic units ranging down to Upper Cretaceous ages. In the South Carpathians, the Alpine Danubian domain consists of several Variscan and Alpine thrust sheets containing a metamorphic complex dominated by Upper Proterozoic to Lower Cambrian metamorphic and magmatic ages (Lainici-Păiuş), and several complexes with metamorphic overprints ranging from Carboniferous to Lower Permian. Any correlation among these units, as well as geotectonic models placing a Lower Paleozoic oceanic domain between pre-existing Lainici-Păiuş and Drăgşan terranes are precluded by the age data. Other basement of the South Carpathians contain lower Paleozoic or older units intruded by Ordovician granitoids, imbricated with juvenile Variscan slivers, the structural sequence differing in individual basement complexes. So, in the Leaota Massif the lowermost term of the sequence is prograde Variscan, tectonically overlain by reworked lower Paleozoic gneisses, supporting thrust sheets with very low- to low-grade Variscan schists. In the Făgăraş Massif a lower Paleozoic (Cumpăna) complex bearing a strong Variscan overprint, straddles Variscan juvenile rocks, and the lowermost visible structural level is assumed by upper Carboniferous to Permian juvenile medium-grade metamorphic schists. In the Lotru Metamorphic Suite of the Alpine Getic Nappe, the Variscan stacking is overprinted by post-orogenic differential uplift, documented by the correlation among younging ages, structural and metamorphic low-pressure overprints, recording often higher metamorphic temperatures. The most spectacular structure is Upper Jurassic in age, contains high-grade metamorphic rocks and peraluminous anatectic granitoids, is outlined by a deformed boundary evolving from ductile to brittle regime during cooling, and induces a thermal overprint in the neighbouring rocks. In the basement units thrust over the Getic Nappe, the Sibişel unit yielded Permian prograde peak metamorphic ages and Triassic post-peak overprints, while an adjacent gneissic unit (Laz) delivered an exclusively Cretaceous age pattern. Unexpectedly young metamorphic ages resulted also for the East Carpathians and the Apuseni Mountains. While most of the ages obtained so far correspond to Variscan retrogression of older basement units, the lowermost structural unit of the infra-Bucovinian nappe system in the East Carpathians yielded Upper Cretaceous metamorphic ages in apparently monometamorphic medium-grade schists. In the Apuseni Mountains, schists of the Baia de Arieş Unit display an Upper Jurassic age spectrum, corresponding to a clearly prograde medium-grade event. The ages recorded not only question some of the currently accepted correlations among basement units, but urge to reconsideration of the way in which the basement-cover relationships are interpreted and extrapolated.

Rapid and quantitative determination of 10 major active components in Lonicera japonica Thunb. by ultrahigh pressure extraction-HPLC/DAD

NASA Astrophysics Data System (ADS)

Fan, Li; Lin, Changhu; Duan, Wenjuan; Wang, Xiao; Liu, Jianhua; Liu, Feng

2015-01-01

An ultrahigh pressure extraction (UPE)-high performance liquid chromatography (HPLC)/diode array detector (DAD) method was established to evaluate the quality of Lonicera japonica Thunb. Ten active components, including neochlorogenic acid, chlorogenic acid, 4-dicaffeoylquinic acid, caffeic acid, rutin, luteoloside, isochlorogenic acid B, isochlorogenic acid A, isochlorogenic acid C, and quercetin, were qualitatively evaluated and quantitatively determined. Scanning electron microscope images elucidated the bud surface microstructure and extraction mechanism. The optimal extraction conditions of the UPE were 60% methanol solution, 400 MPa of extraction pressure, 3 min of extraction time, and 1:30 (g/mL) solid:liquid ratio. Under the optimized conditions, the total extraction yield of 10 active components was 57.62 mg/g. All the components showed good linearity (r2 ≥ 0.9994) and recoveries. This method was successfully applied to quantify 10 components in 22 batches of L. japonica samples from different areas. Compared with heat reflux extraction and ultrasonic-assisted extraction, UPE can be considered as an alternative extraction technique for fast extraction of active ingredient from L. japonica.

Multi-Objective Optimization of a Turbofan for an Advanced, Single-Aisle Transport

NASA Technical Reports Server (NTRS)

Berton, Jeffrey J.; Guynn, Mark D.

2012-01-01

Considerable interest surrounds the design of the next generation of single-aisle commercial transports in the Boeing 737 and Airbus A320 class. Aircraft designers will depend on advanced, next-generation turbofan engines to power these airplanes. The focus of this study is to apply single- and multi-objective optimization algorithms to the conceptual design of ultrahigh bypass turbofan engines for this class of aircraft, using NASA s Subsonic Fixed Wing Project metrics as multidisciplinary objectives for optimization. The independent design variables investigated include three continuous variables: sea level static thrust, wing reference area, and aerodynamic design point fan pressure ratio, and four discrete variables: overall pressure ratio, fan drive system architecture (i.e., direct- or gear-driven), bypass nozzle architecture (i.e., fixed- or variable geometry), and the high- and low-pressure compressor work split. Ramp weight, fuel burn, noise, and emissions are the parameters treated as dependent objective functions. These optimized solutions provide insight to the ultrahigh bypass engine design process and provide information to NASA program management to help guide its technology development efforts.

Pseudolinear gradient ultrahigh-pressure liquid chromatography using an injection valve assembly.

PubMed

Xiang, Yanqiao; Liu, Yansheng; Stearns, Stanley D; Plistil, Alex; Brisbin, Martin P; Lee, Milton L

2006-02-01

The use of ultrahigh pressures in liquid chromatography (UHPLC) imposes stringent requirements on hardware such as pumps, valves, injectors, connecting tubing, and columns. One of the most difficult components of the UHPLC system to develop has been the sample injector. Static-split injection, which can be performed at pressures up to 6900 bar (100,000 psi), consumes a large sample volume and is very irreproducible. A pressure-balanced injection valve provided better reproducibility, shorter injection time, reduced sample consumption, and greater ease of use; however, it could only withstand pressures up to approximately 1000 bar (15,000 psi). In this study, a new injection valve assembly that can operate at pressures as high as 2070 bar (30,000 psi) was evaluated for UHPLC. This assembly contains six miniature electronically controlled needle valves to provide accurate and precise volumes for introduction into the capillary LC column. It was found that sample volumes as small as several tenths of a nanoliter can be injected, which are comparable to the results obtained from the static-split injector. The reproducibilities of retention time, efficiency, and peak area were investigated, and the results showed that the relative standard deviations of these parameters were small enough for quantitative analyses. Separation experiments using the UHPLC system with this new injection valve assembly showed that this new injector is suitable for both isocratic and gradient operation modes. A newly designed capillary connector was used at a pressure as high as 2070 bar (30,000 psi).

Dewaterability of five sewage sludges in Guangzhou conditioned with Fenton's reagent/lime and pilot-scale experiments using ultrahigh pressure filtration system.

PubMed

Liang, Jialin; Huang, Shaosong; Dai, Yongkang; Li, Lei; Sun, Shuiyu

2015-11-01

Sludge conditioning with Fenton's reagent and lime is a valid method for sludge dewatering. This study investigated the influence of different organic matter content sludge on sludge dewatering and discussed the main mechanism of sludge conditioning by combined Fenton's reagent and lime. The results indicated that the specific resistance to filterability (SRF) of sludge was reduced efficiently by approximately 90%, when conditioned with Fenton's reagent and lime. Through single factor experiments, the optimal conditioning combinations were found. In addition, the relationship between VSS% and consumption of the reagents was detected. Furthermore, it was also demonstrated that the SRF and filtrate TOC values had a significant correlation with VSS% of sludge (including raw and conditioned). The main mechanism of sludge dewatering was also investigated. Firstly, it revealed that the dewaterability of sludge was closely correlated to extracellular polymeric substances (EPS) and bound water contents. Secondly, the results of scanning electron microscopy (SEM) stated that sludge particles were to be smaller and thinner after conditioning. And this structure could easily form outflow channels for releasing free water. Additionally, with the ultrahigh pressure filtration system, the water content of sludge cake conditioned with Fenton's reagent and lime could be reduced to below 50%. Moreover, the economic assessment shows that Fenton's reagent and lime combined with ultrahigh pressure filtration system can be an economical and viable technology for sewage sludge dewatering. Finally, three types of sludge were classified: (1) Fast to dewater; (2) Moderately fast to dewater; (3) Slow to dewater sludge. Copyright © 2015 Elsevier Ltd. All rights reserved.

The effect of pressure and mobile phase velocity on the retention properties of small analytes and large biomolecules in ultra-high pressure liquid chromatography.

PubMed

Fekete, Szabolcs; Veuthey, Jean-Luc; McCalley, David V; Guillarme, Davy

2012-12-28

A possible complication of ultra-high pressure liquid chromatography (UHPLC) is related to the effect of pressure and mobile phase velocity on the retention properties of the analytes. In the present work, numerous model compounds have been selected including small molecules, peptides, and proteins (such as monoclonal antibodies). Two instrumental setups were considered to attain elevated pressure drops, firstly the use of a post-column restrictor capillary at low mobile phase flow rate (pure effect of pressure) and secondly the increase of mobile phase flow rate without restrictor (i.e. a combined effect of pressure and frictional heating). In both conditions, the goal was to assess differences in retention behaviour, depending on the type or character of the analyte. An important conclusion is that the effect of pressure and mobile phase velocity on retention varied in proportion with the size of the molecule and in some cases showed very different behaviour. In isocratic mode, the pure effect of pressure (experiments with a post-column restrictor capillary) induces an increase in retention by 25-100% on small molecules (MW<300 g/mol), 150% for peptides (~1.3 kDa), 800% for insulin (~6 kDa) and up to >3000% for myoglobin (~17 kDa) for an increase in pressure from 100 bar up to 1100 bar. The important effect observed for the isocratic elution of proteins is probably related to conformational changes of the protein in addition to the effect of molecular size. Working in gradient elution mode, the pressure related effects on retention were found to be less pronounced but still present (an increase of apparent retention factor between 0.2 and 2.5 was observed). Copyright © 2012 Elsevier B.V. All rights reserved.

Ultra-high Strength Nanostructured Mg

DTIC Science & Technology

2014-03-31

27709-2211 Nanostructured Mg and Mg alloys, Mg metallic glass, Cryomilling, Powder consolidation, Spark plasma sintering , Deformation mechanisms REPORT...mechanically milled powder and high pressure on spark plasma sintering of Mg-Cu-Gd metallic glasses; (9) microstructure and mechanical behavior of Mg-10Li-3Al...pressure on spark plasma sintering of Mg– Cu–Gd metallic glasses, Acta Materialia , (07 2013): 4414. doi: Baolong Zheng, Ying Li, Weizong Xu

A transient fault-valve mechanism operating in upper crustal level, Sierras Pampeanas, Argentina

NASA Astrophysics Data System (ADS)

Japas, María Silvia; Urbina, Nilda Esther; Sruoga, Patricia; Garro, José Matías; Ibañes, Oscar

2016-11-01

Located in the Sierras Pampeanas (the broken-foreland of the Pampean flat slab segment in the southern Central Andes), the Cerro Tiporco volcanic field shows Neogene hydrothermal activity linked to migration of arc-magmatism into the foreland. Late Neogene deposits comprise epithermal vein systems emplaced in Precambrian-Early Palaeozoic igneous-metamorphic basement, Late Miocene sedimentary rocks and Early Pliocene volcaniclastic rocks. Mineralization consists of calcareous onyx, aragonite and calcite veins as well as travertine deposits. Onyx and aragonite occur as fill of low-displacement nearly vertical reverse-sinistral faults striking NW, and nearly horizontal dilatant fractures. The latter consist of load-removal induced fractures affecting the igneous-metamorphic rocks, as well as bedding planes in the Late Miocene sediments. The presence of veins recording multiple fracture episodes and crack-and-seal growth of veins suggests relatively low differential stress and supralithostatic fluid pressure, as well as cyclic changes in pore pressure and high mineral-deposition/fracture-opening ratio. These conditions support a mechanism of fault-valve behaviour during onyx and aragonite vein emplacement. The fault-valve mechanism involves fractures associated with impermeable barriers between environments with different fluid pressure. Faulting generated an appreciable directional permeability triggering fluid migration from the highest to the lowest pressure region, with subsequent deposition and sealing that started a new pressurization-faulting-sealing cycle. Late aragonite and calcite veins suggest a change in kinematics indicating the onset of tectonic-load conditions.

Pyrite deformation and connections to gold mobility: Insight from micro-structural analysis and trace element mapping

NASA Astrophysics Data System (ADS)

Dubosq, R.; Lawley, C. J. M.; Rogowitz, A.; Schneider, D. A.; Jackson, S.

2018-06-01

The metamorphic transition of pyrite to pyrrhotite results in the liberation of lattice-bound and nano-particulate metals initially hosted within early sulphide minerals. This process forms the basis for the metamorphic-driven Au-upgrading model applied to many orogenic Au deposits, however the role of syn-metamorphic pyrite deformation in controlling the retention and release of Au and related pathfinder elements is poorly understood. The lower amphibolite facies metamorphic mineral assemblage (Act-Bt-Pl-Ep-Alm ± Cal ± Qz ± Ilm; 550 °C) of Canada's giant Detour Lake deposit falls within the range of pressure-temperature conditions (450 °C) for crystal plastic deformation of pyrite. We have applied a complementary approach of electron backscatter diffraction (EBSD) mapping and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) 2D element mapping on pyrite from the Detour Lake deposit. Chemical element maps document an early generation of Au-rich sieve textured pyrite domains and a later stage of syn-metamorphic oscillatory-zoned Au-poor pyrite. Both pyrite types are cut by Au-rich fractures as a consequence of remobilization of Au with trace element enrichment of first-row transition elements, post-transition metals, chalcogens and metalloids during a late brittle deformation stage. However, similar enrichment in trace elements and Au can be observed along low-angle grain boundaries within otherwise Au-poor pyrite, indicating that heterogeneous microstructural misorientation patterns and higher strain domains are also relatively Au-rich. We therefore propose that the close spatial relationship between pyrite and Au at the microscale, features typical of orogenic Au deposits, reflects the entrapment of Au within deformation-induced microstructures in pyrite rather than the release of Au during the metamorphic transition from pyrite to pyrrhotite. Moreover, mass balance calculations at the deposit scale suggest that only a small percentage of Au could have been sourced from pyrite and instead point to the role of substructures in pyrite as depositional traps for Au during syn-metamorphic deformation- and fluid-assisted diffusion Au-upgrading.

Provenance and metamorphic PT conditions of Cryogenian-Ediacaran metasediments from the Kid metamorphic complex, Sinai, NE Arabian-Nubian Shield: Insights from detrital zircon geochemistry and mineral chemistry

NASA Astrophysics Data System (ADS)

El-Bialy, Mohammed Z.; Ali, Kamal A.; Abu El-Enen, Mahrous M.; Ahmed, Ahmed H.

2015-12-01

The Malhaq and Um Zariq formations occupy the northern part of the Neoproterozoic Kid metamorphic complex of SE Sinai, NE Arabian-Nubian Shield. This study presents new mineral chemistry data and LA-ICP-MS analyses of the trace element concentrations on zircons separated from metapelites from these formations. The detrital zircons of Um Zariq Formation are more enriched in ΣREE, whereas Malhaq Formation zircons are markedly HREE-enriched with strongly fractionated HREE patterns. The quite differences in the overall slope and size of the Eu and Ce anomalies between REE patterns of the two zircon suites provide a robust indication of different sources. The Ti-in-zircon thermometer has revealed that the zircons separated from Malhaq Formation were crystallized within the 916-1018 °C range, while those from Um Zariq Formation exhibit higher range of crystallization temperatures (1084-1154 °C). The detrital zircons of Malhaq Formation were derived mainly from mafic source rocks (basalt and dolerite), whereas Um Zariq Formation zircons have varied and more evolved parent rocks. Most of the investigated zircons from both formations are concluded to be unaltered magmatic that were lately crystallized from a high LREE/HREE melt. All the studied detrital zircon grains show typical trace elements features of crustal-derived zircons. All of the Um Zariq Formation and most of Malhaq Formation detrital zircons are geochemically discriminated as continental zircons. Both formation metapelites record similar, overlapping peak metamorphic temperatures (537-602 °C and 550-579 °C, respectively), and pressures (3.83-4.93 kbar and 3.69-4.07 kbar, respectively). The geothermal gradient, at the peak metamorphic conditions, was quite high (37-41 °C/km) corresponding to metamorphism at burial depth of 14-16 km. The peak regional metamorphism of Um Zariq and Malhaq formations is concluded to be generated during extensional regime and thinning of the lithosphere in an island arc setting with heat flow from the underlying arc granitoids.

Detrital zircons from the Tananao metamorphic complex of Taiwan: Implications for sediment provenance and Mesozoic tectonics

NASA Astrophysics Data System (ADS)

Yui, T. F.; Maki, K.; Lan, C. Y.; Hirata, T.; Chu, H. T.; Kon, Y.; Yokoyama, T. D.; Jahn, B. M.; Ernst, W. G.

2012-05-01

Taiwan formed during the Plio-Pleistocene collision of Eurasia with the outboard Luzon arc. Its pre-Tertiary basement, the Tananao metamorphic complex, consists of the western Tailuko belt and the eastern Yuli belt. These circum-Pacific belts have been correlated with the high-temperature/low-pressure (HT/LP) Ryoke belt and the high-pressure/low-temperature (HP/LT) Sanbagawa belt of Japan, respectively. To test this correlation and to reveal the architecture and plate-tectonic history of the Tananao metamorphic basement, detrital zircons were separated from 7 metasedimentary rock samples for U-Pb dating by LA-ICPMS techniques. Results of the present study, coupled with previous data, show that (1) the Tailuko belt consists of a Late Jurassic to earliest Cretaceous accretionary complex sutured against a Permian-Early Jurassic marble ± metabasaltic terrane, invaded in the north by scattered Late Cretaceous granitic plutons; the latter as well as minor Upper Cretaceous cover strata probably formed in a circum-Pacific forearc; (2) the Yuli belt is a mid- to Late Cretaceous accretionary complex containing HP thrust sheets that were emplaced attending the Late Cenozoic Eurasian plate-Luzon arc collision; (3) these two Late Mesozoic belts are not coeval, and in part were overprinted by low-grade metamorphism during the Plio-Pleistocene collision; (4) accreted clastic sediments of the Tailuko belt contain mainly Phanerozoic detrital zircons, indicating that terrigenous sediments were mainly sourced from western Cathaysia, whereas in contrast, clastic rocks of the Yuli accretionary complex contain a significant amount of Paleoproterozoic and distinctive Neoproterozoic zircons, probably derived from the North China craton and the Yangtze block ± eastern Cathaysia, as a result of continent uplift/exhumation after the Permo-Triassic South China-North China collision; and (5) the Late Jurassic-Late Cretaceous formation of the Tananao basement complex precludes the possibility that the early Yanshanian (Early Jurassic) granitoids in southern China represent a landward arc contemporaneous with the later, outboard Tananao accretionary event.

Preliminary geologic map of the Winchester 7.5' quadrangle, Riverside County, California

USGS Publications Warehouse

Morton, Douglas M.

2003-01-01

The Winchester quadrangle is located in the northern part of the Peninsular Ranges Province within the central part of the Perris block, a relatively stable, rectangular in plan view, area located between the Elsinore and San Jacinto fault zones (see location map). The quadrangle is underlain by Cretaceous and older basement rocks. Cretaceous plutonic rocks are part of the composite Peninsular Ranges batholith, which indicates wide variety of granitic rocks, ranging from granite to gabbro. Parts of three major plutonic complexes are within the quadrangle, the Lakeview Mountains pluton, the Domenigoni Valley pluton and the Paloma Valley ring complex. In the northern part of the quadrangle is the southern part of the Lakeview Mountains pluton, a large composite body, most of which lies in the quadrangle to the north. In the center part of the quadrangle is the eastern part of the Domenigoni Valley pluton, which consists of massive biotite-hornblende granodiorite and tonalite; some tonalite in the southern part of the pluton has a relatively pronounced foliation produced by oriented biotite and hornblende. Common to abundant equant-shaped, mafic inclusions occur through out the pluton except in the outermost part where inclusions are absent. The pluton was passively emplaced by piecemeal stoping of a variety of older rocks and the eastern contact is well exposed in the quadrangle. Associated with the Domenigoni Valley pluton is a swarm of latite dikes; the majority of these dikes occur in the Winchester quadrangle, but they extend into the Romoland quadrangle to the west. The latite dikes intrude both the pluton and adjacent metamorphic rocks, most are foliated, and most have a well developed lineation defined by oriented biotite and/or hornblende crystals. Dikes intruding the pluton were emplaced in northwest striking joints; and dikes intruding the metamorphic rocks were emplaced along foliation planes. In the eastern part of the quadrangle a Cretaceous age suture juxtaposes low-metamorphic grade Mesozoic rocks against high-metamorphic grade gneissic-textured Mesozoic rocks. Juxtaposition occurred when the high-metamorphic grade rocks were at upper amphibolite grade temperatures, and produced a steep thermal gradient in the low-metamorphic grade Mesozoic rocks. Age of suturing and attendant metamorphism, based on metamorphic mineral ages, is about 100 Ma (L. Snee, personal communication, 2002). The suture zone appears to vary in thickness, and includes within it a number of metadunite bodies and related rocks. Prebatholithic rocks of Mesozoic age include a wide variety of sedimentary rocks of greenschist or lower metamorphic grade, in the western and central part of the quadrangle, and upper amphibolite grade near the eastern edge of the quadrangle. The metamorphic grade increases from greenschist to upper amphibolite grade over a distance of less than two miles; andalusite and sillimanite isograds are closely spaced near the suture. Metamorphism was Buchan type of relatively high temperature and relatively low pressure (Schwarcz, 1969). Common lithologies of the low metamorphic grade suite include phyllite, lithic greywacke, impure quartzite, meta-arkose, and interlayered quartzite and phyllite. Most of the layering and foliation in the metamorphic rocks is the result of intense structural transposition. Relic bedding appears to be restricted to very local occurrences in hinges of slip folds. The upper amphibolite grade, gneissic-textured Mesozoic rocks consist of sillimanite-biotite gneiss, black amphibolite, and impure quartzite. Anatectic gneiss containing igneous textured segregations of quartz and feldspar is commonly inter leaved with biotite gneiss.

Petrologic and zircon U-Pb geochronological characteristics of the pelitic granulites from the Badu Complex of the Cathaysia Block, South China

NASA Astrophysics Data System (ADS)

Zhao, Lei; Zhou, Xiwen; Zhai, Mingguo; Liu, Bo; Cui, Xiahong

2018-06-01

The recognition of the Indosinian Orogeny in the South China block has been controversial and difficult because of strong weathering and thick cover. High temperature (HT) and high pressure (HP) metamorphic rocks related to this orogeny were considered to be absent from this orogenic belt until the recent discovery of eclogite and granulite facies meta-igneous rocks, occurring as lenses within the meta-sedimentary rocks of the Badu Complex. However, metamorphic state of these meta-sedimentary rocks is still not clear. Besides, there have been no geochronological data of HT pelitic granulites previously reported from the Badu Complex. This paper presents petrographic characteristics and zircon geochronological results on the newly discovered kyanite garnet gneiss, pyroxene garnet gneiss and the HT pelitic granulites (sillimanite garnet gneiss). Mineral assemblages are garnet + sillimanite + ternary feldspar + plagioclase + quartz + biotite for the HT pelitic granulite, kyanite + ternary feldspar + garnet + sillimanite + plagioclase + quartz + biotite for the kyanite garnet gneiss, and garnet + biotite + pyroxene + plagioclase + ternary feldspar + quartz for the pyroxene garnet gneiss, respectively. Decompressional coronas around garnet grains can be observed in all these pelitic rocks. Typical granulite facies mineral assemblages and reaction textures suggest that these rocks experienced HP granulite facies metamorphism and overprinted decompression along a clockwise P-T loop. Results from integrated U-Pb dating and REE analysis indicate the growth of metamorphic zircons from depleted heavy REE sources (100-50 chondrite) compared with detrital zircons derived from granitic sources (typically > 1000 chondrite). Metamorphic zircons in HP granulite exhibit no or subdued negative Eu anomalies, which perhaps indicate zircon overgrowth under eclogite facies conditions. The zircon overgrowth ages range from 250 to 235 Ma, suggesting that HP granulite (eclogite) to granulite facies metamorphism of these supracrustal rocks occurred in the Early-Middle Triassic. Based on the presence of HP granulite facies pelitic rocks, it is inferred that significant underthrusting was involved during the Indosinian Orogeny which introduced these supracrustal rocks to lower crustal levels.

Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdağ Massif, NW Turkey

NASA Astrophysics Data System (ADS)

Şengün, Fırat; Zack, Thomas

2016-08-01

In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdağ Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdağ Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdağ Massif are dominated by subchondritic Nb/Ta (11-19) and Zr/Hf ratios (20-33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17-18 whereas the rims exhibit relatively high Nb/Ta ratios of 19-23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe-Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 °C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdağ metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the İzmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdağ metamorphic sequence resulting from southerly directed compression during the collision.

Geochronology of high-pressure granulites from the Czech part of the Zlote Unit (Bohemian Massif)

NASA Astrophysics Data System (ADS)

Lange, U.; Bröcker, M.; Trapp, E.

2003-04-01

At the NE margin of the Bohemian Massif, granulites occur in the Zlote Unit which is exposed in the border region between Poland and the Czech Republic [e.g. 1, 3]. On the Polish side, outcrop conditions are rather poor. Besides some isolated blocks, granulites are restricted to a very small occurrence near Stary Gieraltow. This exposure has attracted much attention due to findings of presumed coesite pseudomorphs, as inferred from radial fractures around polycrystalline quartz inclusions in garnet [1]. Peak metamorphic conditions were estimated between 21 and 28 kbar at 800 to 1000 °C [2]. Better outcrop conditions of the same tectonic unit are found on the Czech side in the Rychleby Mts [3]. The focus of this study is on the geochronology of granulites from this occurrence. By means of Sm-Nd (garnet, cpx, whole rock) and single grain U-Pb dating of zircon, we have studied felsic and mafic granulites collected near the location Cerveny Dul. A felsic granulite yielded a Sm-Nd age of 337 +/- 4 Ma (two grain-size fractions of garnet, whole rock). Two mafic granulites provided Sm-Nd ages (two grain-size fractions of garnet, cpx and/or whole rock) of 357 +/- 10 Ma and 351 +/- 10 Ma, respectively. The new Sm-Nd results are in good agreement with metamorphic ages reported for other Bohemian granulites and further document the significance of HP-HT metamorphism at c. 350-340 Ma. Single-grain zircon dating of air-abraded grains provided concordant results. Zircons from a mafic granulite yielded an age of 362 +/- 1 Ma. A similar result was reported for a mafic granulite from Stary Gieraltow, based on conventional multigrain analyses of zircon [2]. This age is considered to approximate the timing of crystallisation from a melt. However, it remains unclear whether this process took place before or during early stages of high-pressure metamorphism. The studied felsic granulite yielded a range in zircon ages between 390 to 330 Ma, indicating the presence of inherited magmatic grains and the influence of anatectic processes post-dating the pressure peak. [1] Bakun-Czubarow (1992): Arch. Mineral. 48, 3-25; [2] Klemd, R. &Bröcker, M. (1999): Contrib. Mineral. Petrol. 136, 358-373; [3] Pouba, Z., Padera, K. &Fiala, J. (1985): N. Jahrb. Mineral., Abh. 151, 29-52

Metamorphic P-T conditions across the Chugach Metamorphic Complex (Alaska)—A record of focussed exhumation during transpression

NASA Astrophysics Data System (ADS)

Bruand, Emilie; Gasser, Deta; Stüwe, Kurt

2014-03-01

The Chugach Metamorphic Complex (CMC) is a large high-grade metamorphic complex that developed in the Eocene within the Chugach accretionary complex along the margin of Alaska where subduction is still ongoing. The CMC has a conspicuous asymmetric structure with a migmatitic zone flanked in the north and west by amphibolite facies schists and in the south by a metabasite belt. To the north and south, major, crustal-scale fault zones juxtapose the Chugach terrane against much lower-grade and less-deformed sequences belonging to different terranes. Curiously these crustal-scale structures are known to have largely strike slip motion posing the question as to the nature of the exhumation of the high-grade complex between them. However, P-T conditions which would allow an estimation of the amount of exhumation were lacking for large parts of the complex. This paper presents petrographic descriptions, biotite-garnet thermometry, RSCM thermometry, average P-T calculations and pseudosection modelling from three major across-strike transects covering the complex from west to south-east. Our results reveal that, both temperature and pressure vary substantially across the complex. More specifically, peak metamorphic conditions evolve from 4-7 kbar and ~ 550-650 °C in the northern schist zone to 5-11 kbar and ~ 650-750 °C in the migmatite zone in the south of the complex. The higher pressure estimates in the south of the complex indicate that focussed exhumation must have occurred in this area and was probably initiated by the subduction of a high topographic relief (intra-oceanic arc or ridge subduction) and the accretion of the metabasite belt in the south. Exhumation of the CMC occurred in an overall transpressive strain regime, with strike-slip deformation concentrated along the northern Border Range fault zone and thrusting and exhumation focussed within the southern migmatite zone and splay faults of the Contact fault zone. The T/P ratios in the southern migmatite zone indicate that the thermal perturbation of the migmatites is less than previously inferred. These new results, associated with the structural data and the accretion of a metabasite belt in the south of the complex, seem incompatible with the existing ridge-subduction models.

Liquid gallium rotary electric contract

NASA Technical Reports Server (NTRS)

Przybyszewski, J. S.

1969-01-01

Due to its low vapor pressure, gallium, when substituted for mercury in a liquid slip ring system, transmits substantial amounts of electrical current to rotating components in an ultrahigh vacuum. It features low electrical loss, little or no wear, and long maintenance-free life.

Regional and contact metamorphism within the Moy Intrusive Complex, Grampian Highlands, Scotland

NASA Astrophysics Data System (ADS)

Zaleski, E.

1985-04-01

In central Scotland, the Moy Intrusive Complex consists of (1) the Main Phase — syntectonic peraluminous granodiorite to granite emplaced at c. 455 Ma, intruded by (2) the Finglack Alaskite — post-tectonic leucocratic granite emplaced at 407+/-5 Ma. The Main Phase was emplaced into country rocks at amphibolite facies temperatures. Rb-Sr dates and a compositional spectrum of decreasing celadonite content in Main Phase muscovite suggest the persistence of c. 550° C temperatures for c. 30 Ma but with a declining pressure regime, i.e. isothermal uplift. The Finglack Alaskite was intruded at high structural level, leading to the development of a contact metamorphic aureole in the Main Phase. The thermal effects of contact metamorphism include intergrowths of andalusite, biotite and feldspar in pseudomorphs after muscovite. This is associated with recrystallized granoblastic quartz. Muscovite breakdown and reaction with adjacent biotite, quartz and feldspar, i.e. a function of local mineral assemblage rather than bulk rock composition, is postulated to explain the occurrence of metamorphic andalusite in a granitoid rock. The Main Phase pluton of the Moy Intrusive Complex lies within a NNE trending belt of c. 450 Ma Caledonian tectonic and magmatic activity paralleling the Moine Thrust, and extending from northern Scotland to the Highland Boundary Fault. Syntectonic ‘S-type’ magmatism with upper crustal source areas implies crustal thickening and suggests an intracratonic orogeny.

Structures of dolomite at ultrahigh pressure and their influence on the deep carbon cycle

PubMed Central

Merlini, Marco; Crichton, Wilson A.; Hanfland, Michael; Gemmi, Mauro; Müller, Harald; Kupenko, Ilya; Dubrovinsky, Leonid

2012-01-01

Carbon-bearing solids, fluids, and melts in the Earth's deep interior may play an important role in the long-term carbon cycle. Here we apply synchrotron X-ray single crystal micro-diffraction techniques to identify and characterize the high-pressure polymorphs of dolomite. Dolomite-II, observed above 17 GPa, is triclinic, and its structure is topologically related to CaCO3-II. It transforms above 35 GPa to dolomite-III, also triclinic, which features carbon in [3 + 1] coordination at the highest pressures investigated (60 GPa). The structure is therefore representative of an intermediate between the low-pressure carbonates and the predicted ultra-high pressure carbonates, with carbon in tetrahedral coordination. Dolomite-III does not decompose up to the melting point (2,600 K at 43 GPa) and its thermodynamic stability demonstrates that this complex phase can transport carbon to depths of at least up to 1,700 km. Dolomite-III, therefore, is a likely occurring phase in areas containing recycled crustal slabs, which are more oxidized and Ca-enriched than the primitive lower mantle. Indeed, these phases may play an important role as carbon carriers in the whole mantle carbon cycling. As such, they are expected to participate in the fundamental petrological processes which, through carbon-bearing fluids and carbonate melts, will return carbon back to the Earth’s surface. PMID:22869705

Ab initio elastic properties of talc from 0 to 12 GPa: Interpretation of seismic velocities at mantle pressures and prediction of auxetic behaviour at low pressure

NASA Astrophysics Data System (ADS)

Mainprice, David; Le Page, Yvon; Rodgers, John; Jouanna, Paul

2008-10-01

Talc is a hydrous magnesium rich layered silicate that is widely disseminated in the Earth from the seafloor to over 100 km depth, in ultra-high pressure metamorphism of oceanic crust. In this paper we determine the single crystal elastic constants at pressures from 0 to 12 GPa of talc triclinic ( C 1¯) and monoclinic (C2/ c) polytypes using ab initio methods. We find that talc has an extraordinarily high elastic anisotropy at zero pressure that reduces with increasing pressure. The exceptional anisotropy is complemented by a negative Poisson's ratio for many directions in crystal space. Calculations show that talc is not only one of very few common minerals to exhibit auxetic behaviour, but the magnitude of this effect may be the largest reported so far for a mineral. The compression (Vp) and shear (Vs) wave velocity anisotropy is 80% and 85% for the triclinic polytype. At pressures where talc is known be stable in the Earth (up to 5 GPa) the Vp and Vs anisotropy is reduced to about 40% for both velocities, which is still a very high value. Vp is slow parallel to the c-axis and fast perpendicular to it. This remains unchanged with increasing pressure and is observed in both polytypes. The shear wave splitting (difference between fast and slow S-wave velocities) at low pressure has high values in the plane normal to the c-axis, with a maximum near the a*-axis in the triclinic and the b-axis in the monoclinic polytype. The c-axis is the direction of minimum splitting. The pattern of shear wave splitting does not change significantly with pressure. The volume fraction of talc varies between 11 and 41% for hydrated mantle rocks, but the lack of data on the crystallographic preferred orientation (CPO) precludes a detailed analysis of the impact of talc on seismic anisotropy in subduction zones. However, it is highly likely that CPO can easily develop in zones of deformation due to the platy habit of talc crystals. For random aggregates of talc, the isotropic Vp, Vs and Vp/Vs ratio have significantly lower values than those of antigorite and may explain low-velocity regions in the mantle wedge. Vp/Vs ratios are more complex in anisotropic media because there are fast and slow S-waves, resulting in Vp/Vs1 and Vp/Vs2 ratios for every propagation direction, making interpretation difficult in deformed polycrystalline talc with a CPO. Talc on the subduction plate boundary can strongly influence guided wave velocity as CPO would develop in this region of intense shearing. The very low coefficient of friction (< 0.1) of talc above 100 °C could also explain silent earthquakes at shallow depths ( ca 30 km) along the subduction plate boundaries, frequently responsible for tsunami.

The development of a portable ultrahigh vacuum chamber via silicon block.

PubMed

Chuang, Ho-Chiao; Huang, Chia-Shiuan

2014-05-01

This paper describes a nonmetallic, light weight portable chamber for ultra-high vacuum (UHV) applications. The chamber consists of a processed silicon block anodically bonding five polished Pyrex glass windows and a Pyrex glass adapter, without using any screws, bolts or vacuum adhesives. The design features provide an alternative chamber for UHV applications which require nonmetallic components. We have cyclically baked the chamber up to 180 °C for 160 h and have achieved an ultimate pressure of 1.4 × 10(-9) Torr (limited by our pumping station), with no leak detected. Both Pyrex glass windows and Pyrex glass adapter have been used successfully.

An experimental assessment of the quartz-in-epidote barometer

NASA Astrophysics Data System (ADS)

Cisneros, M.; Ashley, K.

2017-12-01

We focus on quantifying the suitability of a quartz-in-epidote (qtz-in-ep) solid mineral barometer because theoretical calculations applying an isotropic elastic model suggest that qtz-in-ep inclusion pressures (Pincl) exhibit minimal temperature dependence, with the potential to elucidate the growth conditions of epidote in geologic environments with poor PT constraints (e.g., skarn deposits, retrograde metamorphic rocks). We carried-out heating experiments and compare Raman spectroscopic shifts in the 464 cm-1 band of quartz (and therefore Pincl) with modeled Pincl for three epidotes derived from samples with well constrained PT conditions: 1) FT-1E from Frosnitztal Tal (Pincl = 6.8 kbar), 2) LdC-31C from Lago-di-Cignana (Pincl = 2.6 kbar), and 3) HF-14C from the Upper Schieferhuelle in Western Tauern (Pincl = 0.74 kbar). At elevated temperatures, we encountered difficulties in separating the quartz 464 cm-1 Raman peak and shoulder epidote peaks due to the convergence resulting from the T-sensitivity of the quartz band. Our low pressure HF14C quartz peaks were particularly difficult to fit at elevated temperatures and displayed lower entrapment pressures (Pent) than modelled Pent for most entrapment temperatures (Tent); however, experimental Pent for samples FT-1E and LdC-31C match modelled Pent extremely well. Ambient quartz inclusion pressures are consistent with previously constrained PT conditions: 1) FT-1E: Pent = 21.5 (Tent = 625 ºC), 2) LdC-31C: Pent= 11.7 kbar (Tent = 550 ºC), 3) HF-14C: Pent = 7.4 kbar (Tent= 500 ºC). Reference PT conditions for these samples are as follows: 1) FT-1E: P = 20 - 24 kbar, T = 625 ºC, 2) LdC-31C: P = 32 - 34 kbar, T = 550 ºC, 3) HF-14C: P = 7 - 8 kbar, T = 500 ºC. Qtz-in-ep pressures from sample LdC-31C are consistent with early, low-P vein epidote precipitation that pre-dates high-P metamorphism or low-P retrogression in the Lago-di-Cignana region. Our work successfully demonstrates that a qtz-in-ep barometer can be used for accurate, robust entrapment pressure estimates of rocks from moderate to high pressure metamorphic terranes. Furthermore, our work suggests that other anisotropic mineral pairs may be suitable for Raman thermobarometry without the need to carry-out heating experiments to apply temperature-dependent Pent corrections.