Metamorphic and tectonic evolution of the Greater Himalayan Crystalline Complex in Nyalam region, south Tibet

NASA Astrophysics Data System (ADS)

Wang, Jia-Min; Zhang, Jin-Jiang; Rubatto, Daniela

2016-04-01

Recent studies evoke dispute whether the Himalayan metamorphic core - Greater Himalayan Crystalline Complex (GHC) - was exhumed as a lateral crustal flow or a critical taper wedge during the India-Asia collision. This contribution investigated the evolution of the GHC in the Nyalam region, south Tibet, with comprehensive studies on structural kinematics, metamorphic petrology and geochronology. The GHC in the Nyalam region can be divided into the lower and upper GHC. Phase equilibria modelling and conventional thermobarometric results show that peak temperature conditions are lower in the lower GHC (~660-700°C) and higher in the upper GHC (~740-780°C), whereas corresponding pressure conditions at peak-T decrease from ~9-13 kbar to ~4 kbar northward. Monazite, zircon and rutile U-Pb dating results reveal two distinct blocks within the GHC of the Nyalam region. The upper GHC underwent higher degree of partial melting (15-25%, via muscovite dehydration melting) that initiated at ~32 Ma, peaked at ~29 Ma to 25 Ma, possibly ended at ~20 Ma. The lower GHC underwent lower degree of melting (0-10%) that lasted from 19 to 16 Ma, which was produced mainly via H2O-saturated melting. At different times, both the upper and lower blocks underwent initial slow cooling (35 ± 8 and 10 ± 5°C/Myr, respectively) and subsequent rapid cooling (120 ± 40°C/Myr). The established timescale of metamorphism suggests that high-temperature metamorphism within the GHC lasted a long duration (~15 Myr), whereas duration of partial melting lasted for ~3 Myr in the lower GHC and lasted for 7-12 Myr in the upper GHC. The documented diachronous metamorphism and discontinuity of peak P-T conditions implies the presence of the Nyalam Thrust in the study area. This thrust is probably connected to the other thrusts in Nepal and Sikkim Himalaya, which extends over ~800 km and is named the "High Himalayan Thrust". Timing of activity along this thrust is at ~25-16 Ma, which is coeval with active

Multiple tectonic mode switches indicate short-duration heat pulses in a Mio-Pliocene metamorphic core complex, West Papua, Indonesia

NASA Astrophysics Data System (ADS)

White, L. T.; Hall, R.; Gunawan, I.

2017-12-01

The Wandaman Peninsula is a narrow (<20 km), but mountainous (>2 km) promontory in remote western New Guinea. The peninsula is almost entirely composed of medium- to high-grade metamorphic rocks considered to be associated with a Mio-Pliocene metamorphic core complex. Previous work has shown that the uplift and exhumation of the core complex has potentially brought some extremely young eclogite to the surface. These might be comparable to the world's youngest (4.3 Ma) eclogites found in the D'Entrecasteaux Islands at the opposite end of New Guinea. We show that tectonic history of this region is complex. This is because the metamorphic sequences in the Wandaman Peninsula record multiple phases of deformation, all within the last few million years. This is demonstrated through methodical collation of cross-cutting relations from field and microstructural studies across the peninsula. The first phase of deformation and metamorphism is associated with crustal extension and partial melting that took place at 5-7 Ma according to new U-Pb data from metamorphic zircons. This extensional phase ceased after a tectonic mode switch and the region was shortened. This is demonstrated by two phases of folding (1. recumbent and 2. open) that overprint the earlier extensional fabrics. All previous structures were later overprinted by brittle extensional faults and uplift. This extensional phase is still taking place today, as is indicated by submerged forests exposed along the coastline associated with recent earthquakes and hot springs. The sequence of metamorphic rocks that are exposed in the Wandaman Peninsula show that stress and thermal conditions can change rapidly. If we consider that the present is a key to the past, then such results can identify the duration of deformation and metamorphic events more accurately than in much older orogenic systems.

Late Cretaceous to Paleocene metamorphism and magmatism in the Funeral Mountains metamorphic core complex, Death Valley, California

USGS Publications Warehouse

Mattinson, C.G.; Colgan, J.P.; Metcalf, J.R.; Miller, E.L.; Wooden, J.L.

2007-01-01

Amphibolite-facies Proterozoic metasedimentary rocks below the low-angle Ceno-zoic Boundary Canyon Detachment record deep crustal processes related to Meso-zoic crustal thickening and subsequent extension. A 91.5 ?? 1.4 Ma Th-Pb SHRIMP-RG (sensitive high-resolution ion microprobe-reverse geometry) monazite age from garnet-kyanite-staurolite schist constrains the age of prograde metamorphism in the lower plate. Between the Boundary Canyon Detachment and the structurally deeper, subparallel Monarch Spring fault, prograde metamorphic fabrics are overprinted by a pervasive greenschist-facies retrogression, high-strain subhorizontal mylonitic foliation, and a prominent WNW-ESE stretching lineation parallel to corrugations on the Boundary Canyon Detachment. Granitic pegmatite dikes are deformed, rotated into parallelism, and boudinaged within the mylonitic foliation. High-U zircons from one muscovite granite dike yield an 85.8 ?? 1.4 Ma age. Below the Monarch Spring fault, retrogression is minor, and amphibolite-facies mineral elongation lineations plunge gently north to northeast. Multiple generations of variably deformed dikes, sills, and leucosomal segregations indicate a more complex history of partial melting and intrusion compared to that above the Monarch Spring fault, but thermobarometry on garnet amphibolites above and below the Monarch Spring fault record similar peak conditions of 620-680 ??C and 7-9 kbar, indicating minor (<3-5 km) structural omission across the Monarch Spring fault. Discordant SHRIMP-RG U-Pb zircon ages and 75-88 Ma Th-Pb monazite ages from leucosomal segregations in paragneisses suggest that partial melting of Proterozoic sedimentary protoliths was a source for the structurally higher 86 Ma pegmatites. Two weakly deformed two-mica leucogranite dikes that cut the high-grademetamorphic fabrics below the Monarch Spring fault yield 62.3 ?? 2.6 and 61.7 ?? 4.7 Ma U-Pb zircon ages, and contain 1.5-1.7 Ga cores. The similarity of metamorphic

Geologic and Geochronologic Studies of the Early Proterozoic Kanektok Metamorphic Complex of Southwestern Alaska

USGS Publications Warehouse

Turner, Donald L.; Forbes, Robert B.; Aleinikoff, John N.; McDougall, Ian; Hedge, Carl E.; Wilson, Frederic H.; Layer, Paul W.; Hults, Chad P.

2009-01-01

The Kanektok complex of southwestern Alaska appears to be a rootless terrane of early Proterozoic sedimentary, volcanic, and intrusive rocks which were metamorphosed to amphibolite and granulite facies and later underwent a pervasive late Mesozoic thermal event accompanied by granitic plutonism and greenschist facies metamorphism of overlying sediments. The terrane is structurally complex and exhibits characteristics generally attributed to mantled gneiss domes. U-Th-Pb analyses of zircon and sphene from a core zone granitic orthogneiss indicate that the orthogneiss protolith crystallized about 2.05 b.y. ago and that the protolithic sedimentary, volcanic and granitic intrusive rocks of the core zone were metamorphosed to granulite and amphibolite facies about 1.77 b.y. ago. A Rb-Sr study of 13 whole-rock samples also suggests metamorphism of an early Proterozoic [Paleoproterozoic] protolith at 1.77 Ga, although the data are scattered and difficult to interpret. Seventy-seven conventional 40K/40Ar mineral ages were determined for 58 rocks distributed throughout the outcrop area of the complex. Analysis of the K-Ar data indicate that nearly all of these ages have been totally or partially reset by a pervasive late Mesozoic thermal event accompanied by granitic plutonism and greenschist facies metamorphism. Several biotites gave apparent K-Ar ages over 2 Ga. These ages appear to be controlled by excess radiogenic 40Ar produced by the degassing protolith during the 1.77 Ga metamorphism and incorporated by the biotites when they were at temperatures at which Ar could diffuse through the lattice. Five amphibolites yielded apparent Precambrian 40K/40Ar hornblende ages. There is no evidence that these hornblende ages have been increased by excess argon. The oldest 40K/40Ar hornblende age of 1.77 Ga is identical to the sphene 207Pb/206Pb orthogneiss age and to the Rb-Sr 'isochron' age for six of the 13 whole-rock samples. The younger hornblende ages are interpreted as

Deciphering the tectonometamorphis history of the Anarak Metamorphic Complex, Central Iran

NASA Astrophysics Data System (ADS)

Zanchetta, Stefano; Malaspina, Nadia; Zanchi, Andrea; Martin, Silvana; Benciolini, Luca; Berra, Fabrizio; Javadi, Hamid Reza; Koohpeyma, Meysam; Ghasemi, Mohammad R.; Sheikholeslami, Mohammad Reza

2014-05-01

The Cimmerian orogeny shaped the southern margin of Eurasia during the Late Permian and the Triassic. Several microplates, detached from Gondwana in the Early Permian, migrated northward to be accreted to the Eurasia margin. In the reconstruction of such orogenic event Iran is a key area. The occurrence of several "ophiolites" belt of various age, from Paleozoic to Cretaceous, poses several questions on the possibility that a single rather than multiple Paleotethys sutures occur between Eurasia and Iran. In this scenario the Anarak region in Central Iran still represents a conundrum. Contrasting geochronological, paleontological, paleomagnetic data and reported field evidence suggest different origins for the Anarak Metamorphic Complex (AMC). The AMC is either interpreted to be part of microplate of Gondwanan affinity, a relic of an accretionary wedge developed at the Eurasia margin during the Paleothetys subduction or part of the Cimmerian suture zone, occurring in NE Iran, displaced to central Iran by counterclockwise rotation of the central Iranian blocks from the Triassic. Our field structural data, petrographic and geochemical data, carried out in the frame of the DARIUS PROGRAMME, indicate that the AMC is not a single coherent block, but it consists of several units (Morghab, Chah Gorbeh, Patyar, Palhavand Gneiss, Lakh Marble, Doshak and dismembered "ophiolites") which display different tectonometamorphic evolutions. The Morghab and Chah Gorbeh units share a common history and they preserve, as a peculiar feature within metabasites, a prograde metamorphism with sin- to post-deformation growth of blueschists facies assemblages on pre-existing greenschist facies mineralogical associations. LT-HP metamorphism responsible for the growth of sodic amphibole has been recognized also within marble lenses at the southern limit of the Chah Gorbeh unit. Finally, evidence of LT-HP metamorphism also occur in the metabasites and possibly also in the serpentinites that form

Metamorphic core complexes: Expression of crustal extension by ductile-brittle shearing of the geologic column

NASA Technical Reports Server (NTRS)

Davis, G. H.

1985-01-01

Metamorphic core complexes and detachment fault terranes in the American Southwest are products of stretching of continental crust in the Tertiary. The physical and geometric properties of the structures, fault rocks, and contact relationships that developed as a consequence of the extension are especially well displayed in southeastern Arizona. The structures and fault rocks, as a system, reflect a ductile-through-brittle continuum of deformation, with individual structures and faults rocks showing remarkably coordinated strain and displacement patterns. Careful mapping and analysis of the structural system has led to the realization that strain and displacement were partitioned across a host of structures, through a spectrum of scales, in rocks of progressively changing rheology. By integrating observations made in different parts of the extensional system, especially at different inferred depth levels, it has been possible to construct a descriptive/kinematic model of the progressive deformation that achieved continental crustal extension in general, and the development of metamorphic core complexes in particular.

Deciphering igneous and metamorphic events in high-grade rocks of the Wilmington complex, Delaware: Morphology, cathodoluminescence and backscattered electron zoning, and SHRIMP U-Pb geochronology of zircon and monazite

USGS Publications Warehouse

Aleinikoff, J.N.; Schenck, W.S.; Plank, M.O.; Srogi, L.A.; Fanning, C.M.; Kamo, S.L.; Bosbyshell, H.

2006-01-01

High-grade rocks of the Wilmington Complex, northern Delaware and adjacent Maryland and Pennsylvania, contain morphologically complex zircons that formed through both igneous and metamorphic processes during the development of an island-arc complex and suturing of the arc to Laurentia. The arc complex has been divided into several members, the protoliths of which include both intrusive and extrusive rocks. Metasedimentary rocks are interlayered with the complex and are believed to be the infrastructure upon which the arc was built. In the Wilmingto n Complex rocks, both igneous and metamorphic zircons occur as elongate and equant forms. Chemical zoning, shown by cathodoluminescence (CL), includes both concentric, oscillatory patterns, indicative of igneous origin, and patchwork and sector patterns, suggestive of metamorphic growth. Metamorphic monazites are chemically homogeneous, or show oscillatory or spotted chemical zoning in backscattered electron images. U-Pb geochronology by sensitive high resolution ion microprobe (SHRIMP) was used to date complexly zoned zircon and monazite. All but one member of the Wilmington Complex crystallized in the Ordovician between ca. 475 and 485 Ma; these rocks were intruded by a suite of gabbro-to-granite plutonic rocks at 434 ?? Ma. Detrital zircons in metavolcanic and metasedimentary units were derived predominantly from 0.9 to 1.4 Ga (Grenvillian) basement, presumably of Laurentian origin. Amphibolite to granulite facies metamorphism of the Wilmington Complex, recorded by ages of metamorphic zircon (428 ?? 4 and 432 ?? 6 Ma) and monazite (429 ?? 2 and 426 ?? 3 Ma), occurred contemporaneously with emplacement of the younger plutonic rocks. On the basis of varying CL zoning patterns and external morphologies, metamorphic zircons formed by different processes (presumably controlled by rock chemistry) at slightly different times and temperatures during prograde metamorphism. In addition, at least three other thermal episodes are

Structure and metamorphism of the Franciscan Complex, Mt. Hamilton area, Northern California

USGS Publications Warehouse

Blake, M.C.; Wentworth, C.M.

1999-01-01

Truncation of metamorphic isograds and fold axes within coherent terranes of Franciscan metagraywacke by intervening zones of melange indicate that the melange is tectonic and formed after the subduction-related metamorphism and folding. These relations are expressed in two terranes of blueschist-facies rocks of the Franciscan Complex in the Mt. Hamilton area, northern California-the Jurassic Yolla Bolly terrane and the structurally underlying Cretaceous Burnt Hills terrane. Local preservation in both terranes of basal radiolarian chert and oceanic basalt beneath continent-derived metagraywacke and argillite demonstrates thrust repetition within the coherent terranes, although these relations are scarce near Mt. Hamilton. The metagraywackes range from albite-pumpellyite blueschists to those containing well-crystallized jadeitic pyroxene, and a jadeite-in isograd can be defined in parts of the area. Primary bedding defines locally coherent structural orientations and folds within the metagraywacke units. These units are crosscut by thin zones of tectonic melange containing blocks of high-grade blueschist, serpentinite, and other exotic rocks, and a broader, but otherwise identical melange zone marks the discordant boundary between the two terranes.

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

Distribution and characteristics of metamorphic belts in the south- eastern Alaska part of the North American Cordillera

USGS Publications Warehouse

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

1992-01-01

The Cordilleran orogen in south-eastern Alaska includes 14 distinct metamorphic belts that make up three major metamorphic complexes, from east to west: the Coast plutonic-metamorphic complex; the Glacier Bay-Chichagof plutonic-metamorphic complex; and the Chugach plutonic-metamorphic complex. Each of these complexes is related to a major subduction event. The metamorphic history of the Coast complex is lengthy and is related to the Late Cretaceous collision of the Alexander and Wrangellia terranes and the Gravina overlap assemblage to the west against the Stikine terrane to the east. The metamorphic history of the Glacier Bay-Chichagof complex is relatively simple and is related to the roots of a Late Jurassic to late Early Cretaceous island arc. The metamorphic history of the Chugach is complicated and developed during and after the Late Cretaceous collision of the Chugach terrane with the Wrangellia and Alexander terranes. -from Authors

Carbon, hydrogen, and oxygen isotope studies of the regional metamorphic complex at Naxos, Greece

USGS Publications Warehouse

Rye, R.O.; Schuiling, R.D.; Rye, D.M.; Jansen, J.B.H.

1976-01-01

At Naxos, Greece, a migmatite dome is surrounded by schists and marbles of decreasing metamorphic grade. Sillimanite, kyanite, biotite, chlorite, and glaucophane zones are recognized at successively greater distances from the migmatite dome. Quartz-muscovite and quartz-biotite oxygen isotope and mineralogie temperatures range from 350 to 700??C. The metamorphic complex can be divided into multiple schist-rich (including migmatites) and marblerich zones. The ??18O values of silicate minerals in migmatite and schist units and quartz segregations in the schist-rich zones decrease with increase in metamorphic grades. The calculated ??18OH2O values of the metamorphic fluids in the schist-rich zones decrease from about 15??? in the lower grades to an average of about 8.5??? in the migmatite. The ??D values of OH-minerals (muscovite, biotite, chlorite, and glaucophane) in the schist-rich zones also decrease with increase in grade. The calculated ??DH2O values for the metamorphic fluid decrease from -5??? in the glaucophane zone to an average of about -70??? in the migmatite. The ??D values of water in fluid inclusions in quartz segregations in the higher grade rocks are consistent with this trend. The??18O values of silicate minerals and quartz segregations in marble-rich zones are usually very large and were controlled by exchange with the adjacent marbles. The ??D values of the OH minerals in some marble-rich zones may reflect the value of water contained in the rocks prior to metamorphism. Detailed data on 20 marble units show systematic variations of ??18O values which depend upon metamorphic grade. Below the 540??C isograd very steep ??18O gradients at the margins and large ??18O values in the interior of the marbles indicate that oxygen isotope exchange with the adjacent schist units was usually limited to the margins of the marbles with more exchange occurring in the stratigraphic bottom than in the top margins. Above the 540??C isograd lower ??18O values occur in

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

Unliganded Thyroid Hormone Receptor Regulates Metamorphic Timing via the Recruitment of Histone Deacetylase Complexes

PubMed Central

2014-01-01

Anuran metamorphosis involves a complex series of tissue transformations that change an aquatic tadpole to a terrestrial frog and resembles the postembryonic perinatal period in mammals. Thyroid hormone (TH) plays a causative role in amphibian metamorphosis and its effect is mediated by TH receptors (TRs). Molecular analyses during Xenopus development have shown that unliganded TR recruits histone deacetylase (HDAC)-containing N-CoR/SMRT complexes and causes histone deacetylation at target genes while liganded TR leads to increased histone acetylations and altered histone methylations at target genes. Transgenic studies involving mutant TR-cofactors have shown that corepressor recruitment by unliganded TR is required to ensure proper timing of the onset of metamorphosis while coactivator levels influence the rate of metamorphic progression. In addition, a number of factors that can influence cellular free TH levels appear to contribute the timing of metamorphic transformations of different organs by regulating the levels of unliganded vs. liganded TR in an organ-specific manner. Thus, the recruitment of HDAC-containing corepressor complexes by unliganded TR likely controls both the timing of the initiation of metamorphosis and the temporal regulation of organ-specific transformations. Similar mechanisms likely mediate TR function in mammals as the maturation of many organs during postembryonic development is dependent upon TH and resembles organ metamorphosis in amphibians. PMID:23962846

Structures, microfabrics and textures of the Cordilleran-type Rechnitz metamorphic core complex, Eastern Alps☆

PubMed Central

Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai; Genser, Johann

2013-01-01

Rechnitz window group represents a Cordilleran-style metamorphic core complex, which is almost entirely located within nearly contemporaneous Neogene sediments at the transition zone between the Eastern Alps and the Neogene Pannonian basin. Two tectonic units are distinguished within the Rechnitz metamorphic core complex (RMCC): (1) a lower unit mainly composed of Mesozoic metasediments, and (2) an upper unit mainly composed of ophiolite remnants. Both units are metamorphosed within greenschist facies conditions during earliest Miocene followed by exhumation and cooling. The internal structure of the RMCC is characterized by the following succession of structure-forming events: (1) blueschist relics of Paleocene/Eocene age formed as a result of subduction (D1), (2) ductile nappe stacking (D2) of an ophiolite nappe over a distant passive margin succession (ca. E–W to WNW–ESE oriented stretching lineation), (3) greenschist facies-grade metamorphism annealing dominant in the lower unit, and (4) ductile low-angle normal faulting (D3) (with mainly NE–SW oriented stretching lineation), and (5) ca. E to NE-vergent folding (D4). The microfabrics are related to mostly ductile nappe stacking to ductile low-angle normal faulting. Paleopiezometry in conjunction with P–T estimates yield high strain rates of 10− 11 to 10− 13 s− 1, depending on the temperature (400–350 °C) and choice of piezometer and flow law calibration. Progressive microstructures and texture analysis indicate an overprint of the high-temperature fabrics (D2) by the low-temperature deformation (D3). Phengitic mica from the Paleocene/Eocene high-pressure metamorphism remained stable during D2 ductile deformation as well as preserved within late stages of final sub-greenschist facies shearing. Chlorite geothermometry yields two temperature groups, 376–328 °C, and 306–132 °C. Chlorite is seemingly accessible to late-stage resetting. The RMCC underwent an earlier large-scale coaxial

The behaviour of monazite from greenschist facies phyllites to anatectic gneisses: An example from the Chugach Metamorphic Complex, southern Alaska

PubMed Central

Gasser, Deta; Bruand, Emilie; Rubatto, Daniela; Stüwe, Kurt

2012-01-01

Monazite is a common accessory mineral in various metamorphic and magmatic rocks, and is widely used for U–Pb geochronology. However, linking monazite U–Pb ages with the PT evolution of the rock is not always straightforward. We investigated the behaviour of monazite in a metasedimentary sequence ranging from greenschist facies phyllites into upper amphibolites facies anatectic gneisses, which is exposed in the Eocene Chugach Metamorphic Complex of southern Alaska. We investigated textures, chemical compositions and U–Pb dates of monazite grains in samples of differing bulk rock composition and metamorphic grade, with particular focus on the relationship between monazite and other REE-bearing minerals such as allanite and xenotime. In the greenschist facies phyllites, detrital and metamorphic allanite is present, whereas monazite is absent. In lower amphibolites facies schists (~ 550–650 °C and ≥ 3.4 kbar), small, medium-Y monazite is wide-spread (Mnz1), indicating monazite growth prior and/or simultaneous with growth of garnet and andalusite. In anatectic gneisses, new low-Y, high-Th monazite (Mnz2) crystallised from partial melts, and a third, high-Y, low-Th monazite generation (Mnz3) formed during initial cooling and garnet resorption. U–Pb SHRIMP analysis of the second and third monazite generations yields ages of ~ 55–50 Ma. Monazite became unstable and was overgrown by allanite and/or allanite/epidote/apatite coronas within retrograde muscovite- and/or chlorite-bearing shear zones. This study documents polyphase, complex monazite growth and dissolution during a single, relatively short-lived metamorphic cycle. PMID:26525358

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes in central Iran: New geological data, relationships and tectonic implications

NASA Astrophysics Data System (ADS)

Bagheri, Sasan; Stampfli, Gérard M.

2008-04-01

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes occupy the NW part of the Central-East Iranian Microcontinent and are juxtaposed with the Great Kavir block and Sanandaj-Sirjan zone. Our recent findings redefine the origin of these complexes, so far attributed to the Precambrian-Early Paleozoic orogenic episodes, and now directly related to the tectonic evolution of the Paleo-Tethys Ocean. This tectonic evolution was initiated by Late Ordovician-Early Devonian rifting events and terminated in the Triassic by the Eocimmerian collision event due to the docking of the Cimmerian blocks with the Asiatic Turan block. The "Variscan accretionary complex" is a new name we proposed for the most widely distributed metamorphic rocks connected to the Anarak and Jandaq complexes. This accretionary complex exposed from SW of Jandaq to the Anarak and Kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal-sea ophiolitic remnants, including gabbro-basalts with a supra-subduction-geochemical signature. New 40Ar/ 39Ar ages are obtained as 333-320 Ma for the metamorphism of this sequence under greenschist to amphibolite facies. Moreover, the limy intercalations in the volcano-sedimentary part of this complex in Godar-e-Siah yielded Upper Devonian-Tournaisian conodonts. The northeastern part of this complex in the Jandaq area was intruded by 215 ± 15 Ma arc to collisional granite and pegmatites dated by ID-TIMS and its metamorphic rocks are characterized by some 40Ar/ 39Ar radiometric ages of 163-156 Ma. The "Variscan" accretionary complex was northwardly accreted to the Airekan granitic terrane dated at 549 ± 15 Ma. Later, from the Late Carboniferous to Triassic, huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the Anarak and Kabudan. This new period of accretion is supported by the 280-230 Ma 40Ar/ 39Ar ages for the Anarak mild high-pressure metamorphic rocks and a 262 Ma U

Metamorphic belts of Anatolia

NASA Astrophysics Data System (ADS)

Oberhänsli, Roland; Prouteau, Amaury; Candan, Osman; Bousquet, Romain

2015-04-01

Investigating metamorphic rocks from high-pressure/low-temperature (HP/LT) belts that formed during the closure of several oceanic branches, building up the present Anatolia continental micro-plate gives insight to the palaeogeography of the Neotethys Ocean in Anatolia. Two coherent HP/LT metamorphic belts, the Tavşanlı Zone (distal Gondwana margin) and the Ören-Afyon-Bolkardağ Zone (proximal Gondwana margin), parallel their non-metamorphosed equivalent (the Tauride Carbonate Platform) from the Aegean coast in NW Anatolia to southern Central Anatolia. P-T conditions and timing of metamorphism in the Ören-Afyon-Bolkardağ Zone (>70?-65 Ma; 0.8-1.2 GPa/330-420°C) contrast those published for the overlying Tavşanlı Zone (88-78 Ma; 2.4 GPa/500 °C). These belts trace the southern Neotethys suture connecting the Vardar suture in the Hellenides to the Inner Tauride suture along the southern border of the Kirşehir Complex in Central Anatolia. Eastwards, these belts are capped by the Oligo-Miocene Sivas Basin. Another HP/LT metamorphic belt, in the Alanya and Bitlis regions, outlines the southern flank of the Tauride Carbonate Platform. In the Alanya Nappes, south of the Taurides, eclogites and blueschists yielded metamorphic ages around 82-80 Ma (zircon U-Pb and phengite Ar-Ar data). The Alanya-Bitlis HP belt testifies an additional suture not comparable to the northerly Tavşanlı and Ören-Afyon belts, thus implying an additional oceanic branch of the Neotethys. The most likely eastern lateral continuation of this HP belt is the Bitlis Massif, in SE Turkey. There, eclogites (1.9-2.4 GPa/480-540°C) occur within calc-arenitic meta-sediments and in gneisses of the metamorphic (Barrovian-type) basement. Zircon U-Pb ages revealed 84.4-82.4 Ma for peak metamorphism. Carpholite-bearing HP/LT metasediments representing the stratigraphic cover of the Bitlis Massif underwent 0.8-1.2 GPa/340-400°C at 79-74 Ma (Ar-Ar on white mica). These conditions compares to the Tav

Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines): additional evidence for a Paleozoic age of a metamorphic complex in the Philippine island arc

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

Knittel, U.; Daniels, U.

1987-02-01

The Sr-isotopic composition of marbles from the Puerto Galera area (Mindoro, Philippines) is compatible with either a Tertiary or a Paleozoic age. The former is considered as unlikely because nonmetamorphic sediments of that age overlie the metamorphic complex. This implies that the metamorphic complex does not represent the basement of the Philippine arc but is an accreted terrane.

Submarine hydrothermal metamorphism of the Del Puerto ophiolite, California.

USGS Publications Warehouse

Evarts, R.C.; Schiffman, P.

1983-01-01

Metamorphic zonation overprinted on the volcanic member and overlying volcanogenic sediments of the ophiolite complex increases downward in grade and is characterized by the sequential appearance with depth of zeolites, ferric pumpellyite and pistacitic epidote. Metamorphic assemblages of the plutonic member of the complex are characterized by the presence of calcic amphibole. The overprinting represents the effects of hydrothermal metamorphism resulting from the massive interaction between hot igneous rocks and convecting sea-water in a submarine environment. A thermal gradient of 100oC/km is postulated to account for the zonal recrystallization effects in the volcanic member. The diversity and sporadic distribution of mineral assemblages in the amphibole zone are considered due to the limited availability of H2O in the deeper part of the complex. Details of the zonation and representative microprobe analyses are tabulated.-M.S.

Protolith and metamorphic ages of the Haiyangsuo Complex, eastern China: A non-UHP exotic tectonic slab in the Sulu ultrahigh-pressure terrane

USGS Publications Warehouse

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

2006-01-01

The Haiyangsuo Complex in the NE Sulu ultrahigh-pressure (UHP) terrane has discontinuous, coastal exposures of Late Archean gneiss with amphibolitized granulite, amphibolite, Paleoproterozoic metagabbroic intrusives, and Cretaceous granitic dikes over an area of about 15 km2. The U-Pb SHRIMP dating of zircons indicates that theprotolith age of a garnet-biotite gneiss is >2500 Ma, whereas the granulite-facie metamorphism occurred at around 1800 Ma. A gabbroic intrusion was dated at ???1730 Ma, and the formation of amphibolite-facies assemblages in both metagabbro and granulite occurred at ???340-460 Ma. Petrologic and geochronological data indicate that these various rocks show no evidence of Triassic eclogite-facies metamorphism and Neoproterozoic protolith ages that are characteristics of Sulu-Dabie HP-UHP rocks, except Neoproterozoic inherited ages from post-collisional Jurassic granitic dikes. Haiyangsuo retrograde granulites with amphibolite-facies assemblages within the gneiss preserve relict garnet formed during granulite-facies metamorphism at ???1.85 Ga. The Paleoproterozoic metamorphic events are almost coeval with gabbroic intrusions. The granulite-bearing gneiss unit and gabbro-dominated unit of the Haiyangsuo Complex were intruded by thin granitic dikes at about 160 Ma, which is coeval with post-collisional granitic intrusions in the Sulu terrane. We suggest that the Haiyangsuo Complex may represent a fragment of the Jiao-Liao-Ji Paleoproterozoic terrane developed at the eastern margin of the Sino-Korean basement, which was juxtaposed with the Sulu terrane prior to Jurassic granitic activity and regional deformation. ?? Springer-Verlag 2006.

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

The grand tour of the Ruby-East Humboldt metamorphic core complex, northeastern Nevada: Part 1 - Introduction & road log

USGS Publications Warehouse

Snoke, A.W.; Howard, K.A.; McGrew, A.J.; Burton, B.R.; Barnes, C.G.; Peters, M.T.; Wright, J.E.

1997-01-01

The purpose of this geological excursion is to provide an overview of the multiphase developmental history of the Ruby Mountains and East Humboldt Range, northeastern Nevada. Although these mountain ranges are commonly cited as a classic example of a Cordilleran metamorphic core complex developed through large-magnitude, mid-Tertiary crustal extension, a preceding polyphase Mesozoic contractional history is also well preserved in the ranges. An early phase of this history involved Late Jurassic two-mica granitic magmatism, high-temperature but relatively low-pressure metamorphism, and polyphase deformation in the central Ruby Mountains. In the northern Ruby Mountains and East Humboldt Range, a Late Cretaceous history of crustal shortening, metamorphism, and magmatism is manifested by fold-nappes (involving Archean basement rocks in the northern East Humboldt Range), widespread migmatization, injection of monzogranitic and leucogranitic magmas, all coupled with sillimanite-grade metamorphism. Following Late Cretaceous contraction, a protracted extensional deformation partially overprinted these areas during the Cenozoic. This extensional history may have begun as early as the Late Cretaceous or as late as the mid-Eocene. Late Eocene and Oligocene magmatism occurred at various levels in the crust yielding mafic to felsic orthogneisses in the deep crust, a composite granitic pluton in the upper crust, and volcanic rocks at the surface. Movement along a west-rooted, extensional shear zone in the Oligocene and early Miocene led to core-complex exhumation. The shear zone produced mylonitic rocks about 1 km thick at deep crustal levels, and an overprint of brittle detachment faulting at shallower levels as unroofing proceeded. Megabreccias and other synextensional sedimentary deposits are locally preserved in a tilted, upper Eocene through Miocene stratigraphic sequence. Neogene magmatism included the emplacement of basalt dikes and eruption of rhyolitic rocks. Subsequent

Anatomy of a metamorphic core complex: seismic refraction/wide-angle reflection profiling in southeastern California and western Arizona

USGS Publications Warehouse

McCarthy, J.; Larkin, S.P.; Fuis, G.S.; Simpson, R.W.; Howard, K.A.

1991-01-01

The metamorphic core complex belt in southeastern California and western Arizona is a NW-SE trending zone of unusually large Tertiary extension and uplift. Midcrustal rocks exposed in this belt raise questions about the crustal thickness, crustal structure, and the tectonic evolution of the region. Three seismic refraction/wide-angle reflection profiles were collected to address these issues. The results presented here, which focus on the Whipple and Buckskin-Rawhide mountains, yield a consistent three-dimensiional image of this part of the metamorphic core complex belt. The final model consists of a thin veneer (<2 km) of upper plate and fractured lower plate rocks (1.5-5.5 km s-1) overlying a fairly homogeneous basement (~6.0 km s-1) and a localized high-velocity (6.4 km s -1) body situated beneath the western Whipple Mountains. A prominent midcrustal reflection is identified beneath the Whipple and Buckskin Rawhide mountains between 10 and 20km depth. -from Authors

A tectonic linkage between the Rodelide orogen (Sierra Leone) and the St. Lucie metamorphic complex in the Florida subsurface

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

Dallmeyer, R.D.

1989-03-01

Hornblende concentrates prepared from cuttings from two deep test wells penetrating the complex display internally concordant {sup 40}Ar/{sup 39}Ar incremental-release spectra defining plateau ages of 510.8 {plus minus} 1.1 Ma and 513.1 {plus minus} 1.8 Ma, which are interpreted to date post-metamorphic cooling through temperatures required for intracrystalline argon retention. The Kasila Group constitutes the western segment of the Rokelide orogen in Sierra Leone. Four hornblende concentrations prepared for amphibolite within the Kasila Group yield {sup 40}Ar/{sup 39}Ar plateau ages of 505.0 {plus minus} 5.2, 508.2 {plus minus} 2.1, 510.5 {plus minus} 2.6, and 546.1 {plus minus} 6.8 Ma. Theymore » are interpreted to date post-metamorphic cooling through appropriate argon closure temperature following a ca. 550-560 Ma, Pan-African II phase of tectonothermal activity. A biotite concentrate from paragneiss within the Kasila Group displays an internally concordant {sup 40}/Ar{sup 39}Ar release spectrum defining a plateau age of 524.7 {plus minus} 1.3 Ma, which likely reflects slight contamination with extraneous (excess) argon. Muscovite from the Marampa Group yields a {sup 40}Ar/{sup 39}Ar plateau age of 561.1 {plus minus} 2.3 Ma, which is interpreted to date cooling through appropriate argon closure temperatures. Although these temperatures are generally considered to be lower than those for hornblenede, the muscovite records an older cooling age, suggesting that the Marampa Group experienced slightly earlier post-metamorphic uplift and cooling relative to the Kasila Group. Lithologic comparison combined with similarities in post-metamorphic thermal evolution suggest that the St. Lucie Metamorphic Complex originated within the Rockelide orogen. This and other lithotectonic elements of the Suwannee terrane appear to represent a fragment of Gondwana which accreted to Laurentia during late Paleozoic amalgamation of Pangea.« less

Thermal history of a metamorphic core complex

NASA Astrophysics Data System (ADS)

Dokka, R. K.; Mahaffie, M. J.; Snoke, A. W.

Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

Thermal history of a metamorphic core complex

NASA Technical Reports Server (NTRS)

Dokka, R. K.; Mahaffie, M. J.; Snoke, A. W.

1985-01-01

Fission track (FT) thermochronology studies of lower plate rocks of the Ruby Mountains-East Humbolt Range metamorphic core complex provide important constraints on the timing an nature of major middle Tertiary extension of northeast Nevada. Rocks analyzed include several varieties of mylonitic orthogneiss as well as amphibolitic orthognesses from the non-mylonitic infrastructural core. Oligocene-age porphyritic biotite granodiorite of the Harrison Pass pluton was also studied. The minerals dated include apatite, zircon, and sphene and were obtained from the same rocks that have been previously studied. FT ages are concordant and range in age from 26.4 Ma to 23.8 Ma, with all showing overlap at 1 sigma between 25.4 to 23.4 Ma. Concordancy of all FT ages from all structural levels indicates that the lower plate cooled rapidly from temperatures above approx. 285 C (assumed sphene closure temperature (2)) to below approx. 150 C (assumed apatite closure temperature) near the beginning of the Miocene. This suggests that the lower plate cooled at a rate of at least approx. 36 deg C/Ma during this event. Rapid cooling of the region is considered to reflect large-scale tectonic denudation (intracrustal thinning), the vertical complement to intense crustal extension. FT data firmly establish the upper limit on the timing of mylonitization during detachment faulting and also coincide with the age of extensive landscape disruption.

Interactions between plutonism and detachments during metamorphic core complex formation, Serifos Island (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Rabillard, Aurélien; Arbaret, Laurent; Jolivet, Laurent; Le Breton, Nicole; Gumiaux, Charles; Augier, Romain; Grasemann, Bernhard

2015-06-01

In order to better understand the interactions between plutonic activity and strain localization during metamorphic core complex formation, the Miocene granodioritic pluton of Serifos (Cyclades, Greece) is studied. This pluton (11.6-9.5 Ma) intruded the Cycladic Blueschists during thinning of the Aegean domain along a system of low-angle normal faults belonging to the south dipping West Cycladic Detachment System (WCDS). Based on structural fieldwork, together with microstructural observations and anisotropy of magnetic susceptibility, we recognize a continuum of deformation from magmatic to brittle conditions within the magmatic body. This succession of deformation events is kinematically compatible with the development of the WCDS. The architecture of the pluton shows a marked asymmetry resulting from its interaction with the detachments. We propose a tectonic scenario for the emplacement of Serifos pluton and its subsequent cooling during the Aegean extension: (1) A first stage corresponds to the metamorphic core complex initiation and associated southwestward shearing along the Meghàlo Livadhi detachment. (2) In the second stage, the Serifos pluton has intruded the dome at shallow crustal level, piercing through the ductile/brittle Meghàlo Livadhi detachment. Southwest directed extensional deformation was contemporaneously transferred upward in the crust along the more localized Kàvos Kiklopas detachment. (3) The third stage was marked by synmagmatic extensional deformation and strain localization at the contact between the pluton and the host rocks resulting in nucleation of narrow shear zones, which (4) continued to develop after the pluton solidification.

Tectono-metamorphic evolution of high-P/T and low-P/T metamorphic rocks in the Tia Complex, southern New England Fold Belt, eastern Australia: Insights from K-Ar chronology

NASA Astrophysics Data System (ADS)

Fukui, Shiro; Tsujimori, Tatsuki; Watanabe, Teruo; Itaya, Tetsumaru

2012-10-01

The Tia Complex in the southern New England Fold Belt is a poly-metamorphosed Late Paleozoic accretionary complex. It consists mainly of high-P/low-T type pumpellyite-actinolite facies (rare blueschist facies) schists, phyllite and serpentinite (T = 300 °C and P = 5 kbar), and low-P/high-T type amphibolite facies schist and gneiss (T = 600 °C and P < 5 kbar) associated with granodioritic plutons (Tia granodiorite). White mica and biotite K-Ar ages distinguish Carboniferous subduction zone metamorphism and Permian granitic intrusions, respectively. The systematic K-Ar age mapping along a N-S traverse of the Tia Complex exhibits a gradual change. The white mica ages become younger from the lowest-grade zone (339 Ma) to the highest-grade zone (259 Ma). In contrast, Si content of muscovite changes drastically only in the highest-grade zone. The regional changes of white mica K-Ar ages and chemical compositions of micas indicate argon depletion from precursor high-P/low-T type phengitic white mica during the thermal overprinting and recrystallization by granitoids intrusions. Our new K-Ar ages and available geological data postulate a model of the eastward rollback of a subduction zone in Early Permian. The eastward shift of a subduction zone system and subsequent magmatic activities of high-Mg andesite and adakite might explain formation of S-type granitoids (Hillgrove suite) and coeval low-P/high-T type metamorphism in the Tia Complex.

Time and duration of metamorphism and exhumation of the central Rhodopian core complex, Bulgaria

NASA Astrophysics Data System (ADS)

Ovtcharova, M.; von Quadt, A.; Peytcheva, I.; Neubauer, F.; Heinrich, C. A.; Kaiser, M.

2003-04-01

The evolution of central Rhodopian dome (Bulgaria) is interpreted in terms of an extensional collapse of thickened crust (Ivanov at al., 2000). U-Pb isotope dating (single Zr and Mnz), Rb-Sr (W.R., Bt and Ap) and Ar-Ar (on Bt) were carried out on different rocks from the central Rhodope, Bulgaria, to constrain the timing and duration of the metamorphism and exhumation of the core complex. The beginning of extensional stage is marked by intrusion of earliest non-penetratively deformed granite bodies at 53Ma (U-Pb on single Zr and Mnz). The late Alpine extensional evolution of the massif is marked by a detachment system connected with exhumation of the migmatites in the core part of the dome (lower plate). U-Pb analyses on Mnz and Zr from mesosome and discordant leucosome yield a Variscan protolith age of the gneiss (311 Ma) and Eocene age (37Ma) of crystallization of the newly formed anatectic melt that corresponds with the peak of the Alpine metamorphic event (P 4.5-6kbar and T 720-750^oC; Georgieva et al., 2002). Rb-Sr mineral system of the weakly deformed gneisses from lower plate of the core complex gives evidence for a cooling age of 34.5±0.34Ma. This result is confirmed by Ar-Ar on Bt from the same rock: 35.5±0.4Ma. Ar-Ar data on biotite from gneisses of the upper plate yield an age of 34.9±0.6Ma. The same age is reflected by an Rb-Sr isochron (W.R., Bt and Ap) of 35.22±0.35Ma. The post-collisional extension was followed by graben depressions filled with sediments of Eocene-Oligocene age and active volcanism and ore mineralization (Zn-Pb and Cu-Pb-Zn ore deposits). Connected with the most intensively "stretched" sections of the extensional system is emplacement of rhyolitic dikes at 32.8±0.41Ma (U-Pb on single Zr, Xe). The available data constrain narrow time bracket between timing of high-grade metamorphism event (37Ma, >600^oC), cooling (35Ma, 300ºC) of the core complex and volcanic activity (32Ma) that corresponds with rapid exhumation tectonic regime

Late Mesoproterozoic to Early Paleozoic history of metamorphic basement from the southeastern Chiapas Massif Complex, Mexico, and implications for the evolution of NW Gondwana

NASA Astrophysics Data System (ADS)

Weber, Bodo; González-Guzmán, Reneé; Manjarrez-Juárez, Román; Cisneros de León, Alejandro; Martens, Uwe; Solari, Luigi; Hecht, Lutz; Valencia, Victor

2018-02-01

In this paper, U-Pb zircon geochronology, Lu-Hf and Sm-Nd isotope systematics, geochemistry and geothermobarometry of metaigneous basement rocks exposed in the southeastern Chiapas Massif Complex are presented. Geologic mapping of the newly defined "El Triunfo Complex" located at the southeastern edge of the Chiapas Massif reveals (1) partial melting of a metamorphic basement mainly constituted by mafic metaigneous rocks (Candelaria unit), (2) an Ediacaran metasedimentary sequence (Jocote unit), and (3) occurrence of massif-type anorthosite. All these units are intruded by undeformed Ordovician plutonic rocks of the Motozintla suite. Pressure and temperature estimates using Ca-amphiboles, plagioclase and phengite revealed prograde metamorphism that reached peak conditions at 650 °C and 6 kbar, sufficient for partial melting under water saturated conditions. Relict rutile in titanite and clinopyroxene in amphibolite further indicate a previous metamorphic event at higher P-T conditions. U-Pb zircon ages from felsic orthogneiss boudins hosted in deformed amphibolite and migmatite yield crystallization ages of 1.0 Ga, indicating that dry granitic protoliths represent remnants of Rodinia-type basement. Additionally, a mid-Tonian ( 920 Ma) metamorphic overprint is suggested by recrystallized zircon from a banded gneiss. Zircon from folded amphibolite samples yield mainly Ordovician ages ranging from 457 to 444 Ma that are indistinguishable from the age of the undeformed Motozintla plutonic suite. Similar ages between igneous- and metamorphic- zircon suggest a coeval formation during a high-grade metamorphic event, in which textural discrepancies are explained in terms of differing zircon formation mechanisms such as sub-solidus recrystallization and precipitation from anatectic melts. In addition, some amphibolite samples contain inherited zircon yielding Stenian-Tonian ages around 1.0 Ga. Lu-Hf and Sm-Nd isotopes and geochemical data indicate that the protoliths of

Dry Snow Metamorphism

DTIC Science & Technology

2012-09-19

behavior of snow during metamorphism and grain sintering using mathematical models. 2 Approach Our approach involved the collection and...examination of both types of specimens at various stages of metamorphism using the SEM and micro-CT. More specifically, the above approach involved...than 10ºC·m-1). 5. High-resolution images and X-ray spectra of snow specimens at various metamorphism stages were obtained using an SEM and EDS. 6

Metamorphic facies map of Southeastern Alaska; distribution, facies, and ages of regionally metamorphosed rocks

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Brew, D.A.; Douglass, S.L.

1996-01-01

Nearly all of the bedrock in Southeastern Alaska has been metamorphosed, much of it under medium-grade conditions during metamorphic episodes that were associated with widespread plutonism. The oldest metamorphisms affected probable arc rocks near southern Prince of Wales Island and occurred during early and middle Paleozoic orogenies. The predominant period of metamorphism and associated plutonism occurred during Early Cretaceous to early Tertiary time and resulted in the development of the Coast plutonic-metamorphic complex that extends along the inboard half of Southeastern Alaska. Middle Tertiary regional thermal metamorphism affected a large part of Baranof Island.

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.

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.

Metamorphism in the Potomac composite terrane, Virginia-Maryland

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

Drake, A.A. Jr.

1985-01-01

Metamorphic rocks in the Potomac Valley occur in three allochthon-precursory melange pairs unconformably overlain by the Popes Head Formation which is at greenschist facies of metamorphism. The highest motif, the Piney Branch Complex and Yorkshire Formation are also in the greenschist facies. The middle motif, consists of the Peters Creek Schist and the Sykesville Formation. Quartzose schists and metagraywacke of the Peters Creek contain serpentinite debris and have had a complex metamorphic history: Barrovian prograde to amphibolite facies (with sillimanite), a localized retrograde event producing chlorite phyllonite, and a later greenschist prograde event. The Sykeville is at biotite +/- garnetmore » grade and contains deformed olistoliths of Peters Creek, including phyllonite, at various grades. The lower motif consists of the Annandale Group (pelitic schists and metasandstone) and Indian Run Formation. The Annandale has experienced two greenschist metamorphisms. The Indian Run is at biotite +/- garnet grade and contains previously metamorphosed and deformed olistoliths of Annandale. The allochthons have had different histories, but after stacking they were metamorphosed with their melanges and the Popes Head to biotite grade. The Popes Head has experienced three phases of folding, the earliest synkinematic with Occoquan emplacement. These fold phases are superposed on earlier structures in the older rocks and are probably of Late Cambrian age (Penobscotian). Earlier deformation is probably of Late Proterozoic age (Cadomian). Neither of these deformations is recognized in North American rocks.« less

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

Tectono-stratigraphy and low-grade metamorphism of Late Permian and Early Jurassic accretionary complexes within the Kurosegawa belt, Southwest Japan: Implications for mechanisms of crustal displacement within active continental margin

NASA Astrophysics Data System (ADS)

Hara, Hidetoshi; Kurihara, Toshiyuki; Mori, Hiroshi

2013-04-01

We characterize the tectono-stratigraphic architecture and low-grade metamorphism of the accretionary complex preserved in the Kurosegawa belt of the Kitagawa district in eastern Shikoku, Southwest Japan, in order to understand its internal structure, tectono-metamorphic evolution, and assessments of displacement of continental fragments within the complex. We report the first ever documented occurrence of an Early Jurassic radiolarian assemblage within the accretionary complex of the Kurosegawa belt that has been previously classified as the Late Permian accretionary complex, thus providing a revised age interpretation for these rocks. The accretionary complex is subdivided into four distinct tectono-stratigraphic units: Late Permian mélange and phyllite units, and Early Jurassic mélange and sandstone units. The stratigraphy of these four units is structurally repeated due to an E-W striking, steeply dipping regional fault. We characterized low-grade metamorphism of the accretionary complex via illite crystallinity and Raman spectroscopy of carbonaceous material. The estimated pattern of low-grade metamorphism showed pronounced variability within the complex and revealed no discernible spatial trends. The primary thermal structure in these rocks was overprinted by later tectonic events. Based on geological and thermal structure, we conclude that continental fragments within the Kurosegawa belt were structurally translated into both the Late Permian and Early Jurassic accretionary complexes, which comprise a highly deformed zone affected by strike-slip tectonics during the Early Cretaceous. Different models have been proposed to explain the initial structural evolution of the Kurosegawa belt (i.e., micro-continent collision and klippe tectonic models). Even if we presuppose either model, the available geological evidence requires a new interpretation, whereby primary geological structures are overprinted and reconfigured by later tectonic events.

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

Postmylonitic deformation in the Raft River metamorphic core complex, northwestern Utah: Evidence of a rolling hinge

NASA Astrophysics Data System (ADS)

Manning, Andrew H.; Bartley, John M.

1994-06-01

Much of the recent debate over low-angle normal faults exposed in metamorphic core complexes has centered on the rolling hinge model. The model predicts tilting of seismogenic high-angle normal faults to lower dips by footwall deformation in response to isostatic forces caused by footwall exhumation. This shallow brittle deformation should visibly overprint the mylonitic fabric in the footwall of a metamorphic core complex. The predicted style and magnitude of rolling hinge strain depends upon the macroscopic mechanism by which the footwall deforms. Two end-members have been proposed: subvertical simple shear and flexural failure. Each mechanism should generate a distinctive pattern of structures that strike perpendicular to the regional extension direction. Subvertical simple shear (SVSS) should generate subvertical faults and kink bands with a shear sense antithetic to the detachment. For an SVSS hinge, the hinge-related strain magnitude should depend only on initial fault dip; rolling hinge structures should shorten the mylonitic foliation by >13% for an initial fault dip of >30°. In flexural failure the footwall behaves as a flexed elastic beam that partially fails in response to bending stresses. Resulting structures include conjugate faults and kink bands that both extend and contract the mylonitic foliation. Extensional sets could predominate as a result of superposition of far-field and flexural stresses. Strain magnitudes do not depend on fault dip but depend on the thickness and radius of curvature of the flexed footwall beam and vary with location within that beam. Postmylonitic structures were examined in the footwall of the Raft River metamorphic core complex in northwestern Utah to test these predictions. Observed structures strike perpendicular to the regional extension direction and include joints, normal faults, tension-gash arrays, and both extensional and contractional kink bands. Aside from the subvertical joints, the extensional structures dip

Chronology of paleozoic metamorphism and deformation in the Blue Ridge thrust complex, North Carolina and Tennessee

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

Goldberg, S.A.; Dallmeyer, R.D.

1997-05-01

The Blue Ridge province in northwestern North Carolina and northeastern Tennessee records a multiphase collisional and accretionary history from the Mesoproterozoic through the Paleozoic. To constrain the tectonothermal evolution in this region, radiometric ages have been determined for 23 regionally metamorphosed amphibolites, granitic gneisses, and pelitic schists and from mylonites along shear zones that bound thrust sheets and within an internal shear zone. The garnet ages from the Pumpkin Patch a thrust sheet (458, 455, and 451 Ma) are similar to those from the structurally overlying Spruce Pine thrust sheet (460, 456, 455, and 450 Ma). Both thrust sheets exhibitmore » similar upper amphibolite-facies conditions. Because of the high closure temperature for garnet, the garnet ages are interpreted to date growth at or near the peak of Taconic metamorphism. Devonian metamorphic ages are recognized in the Spruce Pine thrust sheet, where Sm-Nd and Rb-Sr garnet ages of 386 and 393 Ma and mineral isochron ages of 397 {+-} 14 and 375 {+-} 27 Ma are preserved. Hornblendes record similar {sup 40}Ar/{sup 39}Ar, Sm-Nd, and Rb-Sr ages of 398 to 379 Ma. Devonian {sup 40}Ar/{sup 39}Ar hornblende ages are also recorded in the structurally lower Pumpkin Patch thrust sheet. The Devonian mineral ages are interpreted to date a discrete tectonothermal event, as opposed to uplift and slow cooling from an Ordovician metamorphic event. The Mississippian mylonitization is interpreted to represent thrusting and initial assembly of crystalline sheets associated with the Alleghanian orogeny. The composite thrust stack of the Blue Ridge complex was subsequently thrust northwestward along the Linville Falls fault during middle Alleghanian orogeny (about 300 Ma).« less

Modelling Metamorphism by Abstract Interpretation

NASA Astrophysics Data System (ADS)

Dalla Preda, Mila; Giacobazzi, Roberto; Debray, Saumya; Coogan, Kevin; Townsend, Gregg M.

Metamorphic malware apply semantics-preserving transformations to their own code in order to foil detection systems based on signature matching. In this paper we consider the problem of automatically extract metamorphic signatures from these malware. We introduce a semantics for self-modifying code, later called phase semantics, and prove its correctness by showing that it is an abstract interpretation of the standard trace semantics. Phase semantics precisely models the metamorphic code behavior by providing a set of traces of programs which correspond to the possible evolutions of the metamorphic code during execution. We show that metamorphic signatures can be automatically extracted by abstract interpretation of the phase semantics, and that regular metamorphism can be modelled as finite state automata abstraction of the phase semantics.

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

Jurassic to Miocene magmatism and metamorphism in the Mogok metamorphic belt and the India-Eurasia collision in Myanmar

NASA Astrophysics Data System (ADS)

Barley, M. E.; Pickard, A. L.; Zaw, Khin; Rak, P.; Doyle, M. G.

2003-06-01

Situated south of the eastern Himalayan syntaxis at the western margin of the Shan-Thai terrane the high-grade Mogok metamorphic belt (MMB) in Myanmar occupies a key position in the tectonic evolution of Southeast Asia. The first sensitive high-resolution ion microprobe U-Pb in zircon geochronology for the MMB shows that strongly deformed granitic orthogneisses near Mandalay contain Jurassic (˜170 Ma) zircons that have partly recrystallized during ˜43 Ma high-grade metamorphism. A hornblende syenite from Mandalay Hill also contains Jurassic zircons with evidence of Eocene metamorphic recrystallization rimmed by thin zones of 30.9 ± 0.7 Ma magmatic zircon. The relative abundance of Jurassic zircons in these rocks is consistent with suggestions that southern Eurasia had an Andean-type margin at that time. Mid-Cretaceous to earliest Eocene (120 to 50 Ma) I-type granitoids in the MMB, Myeik Archipelago, and Western Myanmar confirm that prior to the collision of India, an up to 200 km wide magmatic belt extended along the Eurasian margin from Pakistan to Sumatra. Metamorphic overgrowths to zircons in the orthogneiss near Mandalay date a period of Eocene (˜43 Ma) high-grade metamorphism possibly during crustal thickening related to the initial collision between India and Eurasia (at 65 to 55 Ma). This was followed by emplacement of syntectonic hornblende syenites and leucogranites between 35 and 23 Ma. Similar syntectonic syenites and leucogranites intruded the Ailao Shan-Red River shear belt in southern China and Vietnam during the Eocene-Oligocene to Miocene, and the Wang Chao and Three Pagodas faults in northern Thailand (that most likely link with the MMB) were also active at this time. The complex history of Eocene to early Miocene metamorphism, deformation, and magmatism in the MMB provides evidence that it may have played a key role in the network of deformation zones that accommodated strain during the northwards movement of India and resulting extrusion or

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.

Structural analysis and deformation characteristics of the Yingba metamorphic core complex, northwestern margin of the North China craton, NE Asia

NASA Astrophysics Data System (ADS)

Yin, Congyuan; Zhang, Bo; Han, Bao-Fu; Zhang, Jinjiang; Wang, Yang; Ai, Sheng

2017-01-01

The presence of the Yingba (Yinggete-Bagemaode) metamorphic core complex (MCC) is confirmed near the Sino-Mongolian border in China. We report its structural evolution and the rheological features of ductile shear zones within this complex. Three deformations (Ds, Dm, and Db) since the Late Jurassic are identified. Ds is characterized by ductile structures that resulted from early NW-oriented, low-angle, extensional ductile shearing. Dm is associated with partial melting and magmatic diapirism, which accelerated the formation of the dome-like geometry of the Yingba MCC. Synchronously with or slightly subsequently to Ds and Dm, the Yingba MCC was subjected to brittle, extensional faulting (Db), which was accompanied by the exhumation of the lower crust and the formation of supracrustal basins. The ductile shearing (Ds) developed under greenschist-to amphibolite-facies metamorphic conditions (400-650 °C), as indicated by microstructures in quartz and feldspar, quartz [c] axis fabrics, and two-feldspar geothermometry. The mean kinematic vorticity estimates of 48-62% show a pure shear-preferred flow during Ds. The Yingba MCC provides an excellent sample that recorded an intermediate to high temperature shearing, which also implies the widely extensional regime in northeastern Asia at that time.

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 magmatism and metamorphism at the Malayer area, Western Iran

NASA Astrophysics Data System (ADS)

Ahadnejad, V.; Valizadeh, M. V.; Esmaeily, D.

2009-04-01

The Malayer area is located in the NW-SE aligned Sanandaj-Sirjan metamorphic belt, western Iran and consists mainly of Mesozoic schists so-called Hamadan Phyllites, Jurassic to Tertiary intrusive rocks and related contact metamorphic aureoles, aplites and pegmatites. The Sanandj-Sirjan Zone is produced by oblique collisional event between Arabian plate and Central Iran microcontinent. Highest level of regional metamorphism in the area is greenschist facies and injection of felsic magmas is caused contact metamorphism. Magmatism is consist of a general northwest trend large felsic to intermediate intrusive bodies. The main trend of structural features i.e. faults, fractures and other structural features is NW-SE. The Malayer granitoid complex is ellipsoid in shape and has NW-SE foliation especially at the corners of the intrusions. Petrography of the magmatic rocks revealed recrystallization of quartz and feldspars, bending of biotite, and aligment of minerals paralle to the main trend of magmatic and metamorphic country rocks. These indicated that intrusion of felsic magma is coincide to the regional metamorphism and is syn-tectoinc. Non-extensive contact metamorphism aureoles and rareness of pegmatite and aplite in the area are interpreted as injection of felsic magmas into the high-strain metamorphic zone. The regional metamorphic rocks mainly consist of meta-sandstone, slate, phyllite, schist. These gray to dark metasedimentary rocks are consist of quartz, muscovite, turmaline, epidote, biotite and chlorite. Sheeted minerals form extended schistosity and study of porphyroblast-matrix relationships shows that injection of granitic magma into the country rocks is syn to post-tectonic. Syn-tectonic indicating porphyroblast growth synchronous with the development of the external fabric. The thermal contact area of the granite can be observed in the contact margin of granite and regional metamorphic rocks, where it produced hornfelses, andalusit-garnet schists and

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

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

The post collisional metamorphic evolution from Ultra High Temperature to Amphibolite facies metamorphism in the Odesan area during the Triassic collision between the North and South China cratons.

NASA Astrophysics Data System (ADS)

Lee, Byung Choon; Oh, Chang Whan; Kim, Tae Sung; Yi, Kee Wook

2015-04-01

The Odaesan Gneiss Complex (OGC) is the eastern end of the Hongseong-Odesan collision belt in Korean Peninsula which is the extension of the Dabie-Sulu collision belt between the North and South China blocks. The OGC mainly consists of banded and migmatitic gneiss with porphyritic granitoid and amphibolite. The banded gneiss can be subdivided into garnet-biotite and garnet-orthopyroxene banded gneisses. The highest metamorphic P/T conditions of the migmatitic and garnet-biotite banded gneiss were 760-820°C/6.3-7.2kbar and 810-840°C/7.2-7.8kbar respectively. On the other hand, the garnet-orthopyroxene banded gneiss records 940-950°C/10.5-10.7kbar that is corresponded to UHT metamorphic condition. These data indicate that the peak UHT metamorphic condition of the study area was preserved only within the garnet-orthopyroxene banded gneiss because its lower water content than other gneisses and UHT metamorphic mineral assemblage was completely replaced by the granulite facies metamorphism in other gneisses due to their higher water content than the garnet-orthopyroxene banded gneiss. Finally all gneisses experienced amphibolite facies retrograde metamorphism which is observed locally within rocks, such as garnet rim and surrounding area. The peak UHT metamorphism is estimated to occur at ca. 250-230 Ma using SHRIMP zircon U-Pb age dating and was caused by the heat supplied from asthenospheric mantle through the opening formed by slab break-off during early post collision stage. The calculated metamorphic conditions represent that geothermal gradient of the study area during the post collision stage was 86°C/kbar indicating the regional low-P/T metamorphic event. Besides the Triassic metamorphic age, two Paleoproterozoic metamorphic ages of ca. 1930 and 1886 Ma are also recognized by the SHRIMP age dating from the banded gneisses and Paleoproterozoic emplacement age of ca. 1847 Ma is identified from the porphyritic granitoid which formed in the within plate tectonic

Oxygen and hydrogen isotopic composition of the fluid during formation of anthophyllite metaultramafic rocks in the Sysert metamorphic complex, central Urals

NASA Astrophysics Data System (ADS)

Murzin, V. V.

2014-12-01

The oxygen (δ18O) and hydrogen (δD) isotopic composition of H2O-bearing minerals was studied for the ore-bearing amphibole metaultramafic rocks, which are the products of the early regional (435 ± 44 Ma) and late local (260 ± 6 Ma) silicic metasomatose in the Sysert metamorphic complex. The gold-sulfide mineralization of the Karas'evogorskoe deposit and anthophyllite-asbestos bodies of the Tersut deposit are related to the regional and local metasomatose combined with plagiogranitization and potassium granitization, respectively. The H2O-bearing minerals of metasomatites (anthophyllite, tremolite, talc) of the Karas'evogorskoe and Tersut deposits are characterized by heavier δ18O (9.8 to 12.2 and 7.6 to 9.4‰, respectively) and lighter ·D (87 to -91 and -56 to -67‰, respectively) values. The calculated isotopic composition of the fluid in equilibrium with these minerals indicates a heterogeneous source of water for the fluids related to the formation of metasomatites and the metamorphic origin of fluids. During the regional metasomatose, this fluid was a result of equilibrium of the deep fluid with volcanosedimentary rocks enriched in the heavy oxygen isotope. At the local metasomatose, the metamorphic fluid was formed by interaction of magmatic water produced by potassium granitization with ultramafic rocks.

Metamorphic brines and no surficial fluids trapped in the detachment footwall of a Metamorphic Core Complex (Nevado-Filábride units, Betics, Spain)

NASA Astrophysics Data System (ADS)

Dyja-Person, Vanessa; Tarantola, Alexandre; Richard, Antonin; Hibsch, Christian; Siebenaller, Luc; Boiron, Marie-Christine; Cathelineau, Michel; Boulvais, Philippe

2018-03-01

The ductile-brittle transition zone in extensional regimes can play the role of a hydrogeological barrier. Quartz veins developed within an orthogneiss body located in the detachment footwall of a Metamorphic Core Complex (MCC) in the Nevado-Filábride units (Betics, Spain). The detachment footwall is composed mainly of gneisses, schists and metacarbonates from the Bédar-Macael sub-unit. Schist and metacarbonate bodies show evidence of ductile deformation at the time the gneiss was already undergoing brittle deformation and vein opening during exhumation. The vein system provides the opportunity to investigate the origin, composition and PVTX conditions of the fluids that circulated in the detachment footwall while the footwall units were crossing the ductile-brittle transition. The analysis of fluid inclusions reveals the presence of a single type of fluid: 30-40 mass% NaCl > KCl > CaCl2 > MgCl2 brines, with trace amounts of CO2 and N2 and tens to thousands of ppm of metals such as Fe, Sr, Li, Zn, Ba, Pb and Cu. δDfluid values between -39.8 and -16.7‰ and δ18Ofluid values between 4.4 and 11.7 ± 0.5‰ show that the brines have undergone protracted interaction with the host orthogneissic body. Coupled salinity and Cl/Br ratios (200 to 4400) indicate that the brines originate from dissolution of Triassic metaevaporites by metamorphic fluids variably enriched in Br by interaction with graphitic schists. This study highlights the absence of any record of surficial fluids within the veins, despite the brittle deformation conditions prevailing in this orthogneiss body. The fact that fluids from the detachment footwall were isolated from surficial fluid reservoirs may result from the presence of overlying schists and metacarbonates that continued to be affected by ductile deformation during vein formation in the gneiss, preventing downward circulation of surface-derived fluids.

Meteoric water in metamorphic core complexes

NASA Astrophysics Data System (ADS)

Teyssier, Christian; Mulch, Andreas

2015-04-01

The trace of surface water has been found in all detachment shear zones that bound the Cordilleran metamorphic core complexes of North America. DeltaD values of mica fish in detachment mylonites demonstrate that these synkinematic minerals grew in the presence of meteoric water. Typically deltaD values are very negative (-120 to -160 per mil) corresponding to deltaD values of water that are < -100 per mil given the temperature of water-mica isotopic equilibration (300-500C). From British Columbia (Canada) to Nevada (USA) detachment systems bound a series of core complexes: the Thor-Odin, Valhalla, Kettle-Okanogan, Bitterroot -Anaconda, Pioneer, Raft River, Ruby Mountain, and Snake Range. The bounding shear zones range in thickness from ~100 m to ~1 km, and within the shear zones, meteoric water signature is recognized over 10s to 100s of meters beneath the detachment fault. The age of shearing ranges generally from Eocene in the N (~50-45 Ma) to Oligo-Miocene in the S (25-15 Ma). DeltaD water values derived from mica fish in shear zones are consistent with supradetachment basin records of the same age brackets and can be used for paleoaltimetry if coeval isotopic records from near sea level are available. Results show that a wave of topography (typically 4000-5000 m) developed from N to S along the Cordillera belt from Eocene to Miocene, accompanied by the propagation of extensional deformation and volcanic activity. In addition, each detachment system informs a particular extensional detachment process. For example, the thick Thor-Odin detachment shear zone provides sufficient age resolution to indicate the downward propagation of shearing and the progressive incorporation of footwall rocks into the hanging wall. The Kettle detachment provides a clear illustration of the dependence of fluid circulation on dynamic recrystallization processes. The Raft River system consists of a thick Eocene shear zone that was overprinted by Miocene shearing; channels of meteoric

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.

Late Vendian Complexes in the Structure of Metamorphic Basement of the Fore Range Zone, Greater Caucasus

NASA Astrophysics Data System (ADS)

Kamzolkin, V. A.; Latyshev, A. V.; Vidyapin, Yu. P.; Somin, M. L.; Smul'skaya, A. I.; Ivanov, S. D.

2018-05-01

The paper presents new data on the composition, age, and relationships (with host and overlying deposits) of intrusive rocks in the basement of the Fore Range zone (Greater Caucasus), in the Malaya Laba River Basin. The evolutionary features of intrusive units located within the Blyb metamorphic complex are described. It is shown for the first time that the lower levels of this complex are, in a structural sense, outcrops of the Late Vendian basement. The basement is composed of the Balkan Formation and a massif of quartz metadiorites that intrudes it; for the rocks of this massif, ages ranging from 549 ± 7.4 to 574.1 ± 6.7 Ma are obtained for three U-Pb datings by the SHRIMP-II method. The Herzyinan magmatic event is represented by a group of granodiorite intrusions penetrating the Blyb complex on a series of faults extending along its boundary with the Main Range zone. The obtained estimate for the U-Pb age of one of the intrusions (319 ± 3.8 Ma) corresponds to the end of the Serpukhovian stage of the Early Carboniferous.

Mayer Kangri metamorphic complexes in Central Qiangtang (Tibet, western China): implications for the Triassic-early Jurassic tectonics associated with the Paleo-Tethys Ocean

NASA Astrophysics Data System (ADS)

Wang, Yixuan; Liang, Xiao; Wang, Genhou; Yuan, Guoli; Bons, Paul D.

2018-03-01

The Mesozoic orogeny in Central Qiangtang Metamorphic Belt, northern Tibet, provides important insights into the geological evolution of the Paleo-Tethys Ocean. However, the Triassic-early Jurassic tectonics, particularly those associated with the continental collisionstage, remains poorly constrained. Here we present results from geological mapping, structural analysis, P-T data, and Ar-Ar geochronology of the Mayer Kangri metamorphic complex. Our data reveal an E-W-trending, 2 km wide dome-like structure associated with four successive tectonic events during the Middle Triassic and Early Jurassic. Field observations indicate that amphibolite and phengite schist complexes in this complex are separated from the overlying lower greenschist mélange by normal faulting with an evident dextral shearing component. Open antiform-like S2 foliation of the footwall phengite schist truncates the approximately north-dipping structures of the overlying mélange. Microtextures and mineral chemistry of amphibole reveal three stages of growth: Geothermobarometric estimates yield temperatures and pressures of 524 °C and 0.88 GPa for pargasite cores, 386 °C and 0.34 GPa for actinolite mantles, and 404 °C and 0.76 GPa for winchite rims. Peak blueschist metamorphism in the phengite schist occurred at 0.7-1.1 GPa and 400 °C. Our Ar-Ar dating of amphibole reveals rim-ward decreasing in age bands, including 242.4-241.2 Ma, ≥202.6-196.8, and 192.9-189.8 Ma. The results provide evidence for four distinct phases of Mesozoic tectonic evolution in Central Qiangtang: (1) northward oceanic subduction beneath North Qiangtang ( 244-220 Ma); (2) syn-collisional slab-break off (223-202 Ma); (3) early collisional extension driven by buoyant extrusion flow from depth ( 202.6-197 Ma); and (4) post-collision contraction and reburial (195.6-188.7 Ma).

Textural and isotopic development of marble assemblages during the Barrovian-style M2 metamorphic event, Naxos, Greece

NASA Astrophysics Data System (ADS)

Baker, Judy; Matthews, Alan

1994-03-01

A detailed petrological analysis of the marble assemblages observed within the M2 metamorphic complex on Naxos is presented. Two distinct periods of mineral growth are documented; the first is associated with prograde M2 metamorphism and the second with retrograde M2 metamorphism occurring during ductile extensional thinning of the complex. The textural and miner-alogical characteristics and the carbon and oxygen isotope compositions of each generation are described, and the P-T-X CO 2 conditions at which these two mineral generations were stable, and the compositions of the fluids present during metamorphism are characterised. Whereas the low variance and stable isotope compositions of prograde siliceous dolomite assemblages are consistent with internally buffered fluid evolution, the retrograde mineral generation is shown to have grown as a result of the infiltration of a water-rich fluid phase that transported silica, Al2O3, Na2O and FeO into the host rocks. This observation, together with the stable isotope compositions of the retrograde calcite, and the fact that occurrences of veins of this type are limited to marbles in the highest grade areas ( T>600° C) of the metamorphic complex, suggests that the fluids responsible for vein formation were generated during the crystallisation of melts as the metamorphic complex cooled from peak temperatures. The existence of this second generation of minerals has significant implications for previous studies of heat transport by fluid flow on Naxos, because many of the unusually low δ18O compositions of pelites at high grades may be ascribable to the effects of interaction with retrograde M2 fluids, rather than with prograde fluids.

Multi-scale characterization of pore evolution in a combustion metamorphic complex, Hatrurim basin, Israel: Combining (ultra) small-angle neutron scattering and image analysis

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

Wang, Hsiu-Wen; Anovitz, Lawrence; Burg, Avihu

Backscattered scanning electron micrograph and ultra small- and small-angle neutron scattering data have been combined to provide statistically meaningful data on the pore/grain structure and pore evolution of combustion metamorphic complexes from the Hatrurim basin, Israel. Three processes, anti-sintering roughening, alteration of protolith (dehydration, decarbonation, and oxidation) and crystallization of high-temperature minerals, occurred simultaneously, leading to significant changes in observed pore/grain structures. Pore structures in the protoliths, and in lowand high-grade metamorphic rocks show surface (Ds) and mass (Dm) pore fractal geometries with gradual increases in both Ds and Dm values as a function of metamorphic grade. This suggests thatmore » increases in pore volume and formation of less branching pore networks are accompanied by a roughening of pore/grain interfaces. Additionally, pore evolution during combustion metamorphism is also characterized by reduced contributions from small-scale pores to the cumulative porosity in the high-grade rocks. At high temperatures, small-scale pores may be preferentially closed by the formation of high-temperature minerals, producing a rougher morphology with increasing temperature. Alternatively, large-scale pores may develop at the expense of small-scale pores. These observations (pore fractal geometry and cumulative porosity) indicate that the evolution of pore/grain structures is correlated with the growth of high-temperature phases and is a consequence of the energy balance between pore/grain surface energy and energy arising from heterogeneous phase contacts. The apparent pore volume density further suggests that the localized time/temperature development of the high-grade Hatrurim rocks is not simply an extension of that of the low-grade rocks. The former likely represents the "hot spots (burning foci)" in the overall metamorphic terrain while the latter may represent contact aureoles.« less

High-P metamorphic rocks from the Himalaya and their tectonic implication ? a review

NASA Astrophysics Data System (ADS)

Jan, M. Qasim

The suture zones bordering the Indian subcontinent on the E, N and W are characterized in several places by the occurrence of ophiolitic complexes and tectonic melanges. High-P metamorphic rocks have recently been discovered in the melanges in Burma, Naga Hills, southern Tibet, eastern and western Ladakh, Kohistan (Jijal, Allai, Shangla) and Khost (Afghanistan). The development of these rocks has an important bearing on the plate tectonics of the Himalaya. The High-P metamorphic rocks belong to prehnite-pumpellyite, blueschist and high-P greenschist facies but extensive garnet-granulites have developed at 35 km depth in Jijal. In the Indus-Zangbo suture zone (IZS) the high-P metamorphism is complemented to the N by low- or medium-P metamorphism and calc-alkaline magmatism in Tibet, Ladakh as well as Kohistan. High-P metamorphism in Jijal has been dated at 104 Ma, in Shangla at 70-100 Ma and in western Ladakh during mid-Cretaceous. Elsewhere, the timing of the high-P metamorphism is not known but a Cretaceous age is inferred. Since collision along the IZS occurred during Eocene, the high-P metamorphism is therefore related to the northwards subduction of the neo-Tethyan lithosphere under Tibet or late Mesozoic magmatic arcs. The timing of high-P metamorphism coincides with the breakup of India from Gondwanaland and its rapid northwards movement, whereas the tectonic melanges may principally have formed during Eocene collision and obduction.

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.

Tectonic evolution of kid metamorphic complex and the recognition of Najd fault system in South East Sinai, Egypt

NASA Astrophysics Data System (ADS)

Sultan, Yasser M.; El-Shafei, Mohamed K.; Arnous, Mohamed O.

2017-03-01

A low-to medium-grade metamorphic belt of a volcano-sedimentary succession occurs in the eastern side of South Sinai as a part of the northernmost extension of the Arabian-Nubian Shield in Egypt. The belt is known as the Kid metamorphic complex. It is considered as one of the major belt among the other exposed metamorphic belts in South Sinai. Here, we detect and investigate the signature of the Najd Fault system in South Sinai based on detailed structural analysis in field and digital image processing. The enhanced satellite image and the geo-spatial distributions confirm that the Kid belt is essentially composed of nine Precambrian units. Field relations and geometrical analysis of the measured structural data revealed that the study area underwent four successive deformational phases (D1-D4). D1 is an upright tight to isoclinal large-scale folds that caused few F1 small-scale folds and a steeply dipping S1 axial plane foliation. The second deformational event D2 produced dominant of sub-horizontal S2 foliation planes accompanied with recumbent isoclinal folds and NW-SE trending L2 lineations. The main sense during D2 was top-to-the-NW with local reversals to the SE. The third folding generations F3 is recorded as axial plane S3-surfaces and is characterized by open concentric folding that overprinting both F1 and F2 folds and has a flexural-slip mechanism. F3 fold hinges plunge to the west-northwest or east-southeast indicate north-northeast-south-southwest shortening during D3. The fourth deformational event D4 is characterized by NE plunging open concentric folding overprint the pre-existing fold generations and formed under flexural slip mechanism reflecting coaxial deformation and indicating change in the stress regime as a result of the change in shortening from NE-SW to NW-SE. This phase is probably accompanied with the final assembly of east and west Gondwana. The dextral NW-SE shear zone that bounded the southwestern portion of the metamorphic belt is

Timing and Nature of Events Leading to the Formation of the Albion-Raft River-Grouse Creek (ARG) Metamorphic Core complex, Northern Great Basin, W. U.S.

NASA Astrophysics Data System (ADS)

Miller, E. L.; Konstantinou, A.; Sheu, D.; Strickland, A.; Grove, M.

2016-12-01

Interpretations of the geodynamic significance of metamorphic core complexes in the northern Basin and Range are intimately tied to a combination of P-T data, geochronology and mica thermochronology used to infer episodes of deformation and uplift related to syn-shortening gravitational collapse of the crust in the latest Cretaceous-early Cenozoic. The ARG is no exception and we bring new geologic mapping, microstructural analysis, geochronology and 40Ar/39Ar thermochronology to bear on these questions. The petrogenesis of Eocene-Miocene magmas, the structural fabrics and metamorphism developed in wall rocks of plutons and the history of flanking basins outline a three-part Cenozoic story of this complex: Part 1: Mantle-derived heat input into the crust in the Eocene (42-36 Ma), related to Farallon slab removal, produced volcanism, plutonism, but little regional extension. Part 2: Heat input led to increased crustal melting as surface volcanism ceased. Diapiric rise of granite-cored gneiss domes sheathed by high grade, high strain metamorphic fabrics and mylonites took place over a protracted time, 32-25 Ma, stalling at depths > 10 km. Transitions upward from penetrative stretching fabrics to brittle crust were complex damage zones of multiply deformed and faulted Paleozoic strata overlain by a more intact 7-8 km thick section of Late Paleozoic and Triassic. Extension was localized and no sedimentary basins formed during this time. Part 3: Metamorphic and igneous rocks were brought to near surface conditions during Miocene extension, between 14-8 Ma ago. Structures accommodating E-W extension are high-angle, rotational normal faults that currently bound both sides of the ARG complex with linked sedimentary basins in their hanging wall. New 40Ar/39Ar data show that country rocks near the Oligocene Almo pluton share the pluton's cooling history. Further from the pluton, where pre-Oligocene fabrics are variably preserved, white mica total gas and plateau ages increase

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.

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?

Tectono-metamorphic evolution and magmatic processes in the thermo-metamorphic aureole of the Monte Capanne pluton (Elba Island, Northern Tyrrhenian Sea, Italy).

NASA Astrophysics Data System (ADS)

Morelli, M.; Pandeli, E.; Principi, G.

2003-04-01

Introduction In this work we present new structural and petrographic data collected in the thermo-metamorphic aureole of Monte Capanne (western Elba Island) and its metamorphic evolution. In the western Elba Island the Monte Capanne monzogranitic body (ca. 7 Ma) and its thermo-metamorphic aureole crop out. At least two different tectonic units can be distinguished: the Punta Le Tombe Unit, weak re-crystallized, and the Punta Nera Unit. In the latter one the re-crystallization is strong and a pre-intrusion tectono-metamorphic framework is evident (Morelli et al., 2002). The latter is mainly constituted by thermo-metamorphosed meta-ophiolites and meta-sedimentary successions previously correlated by Barberi et al. (1969) with the un-metamorphic ones (Complex IV and V of Trevisan, 1950) cropping out in the central-eastern Elba. According to Perrin (1975) and Reutter &Spohn (1982) a pre-intrusion tectono-metamorphic framework was recognized into such rocks. As suggested by Daniel &Jolivet (1995) complex relationships between metamorphic evolution and magmatic events are also recognizable. Geological Data The Punta Nera Unit crops out all around the Monte Capanne magmatic body and the primary contact with the underlying granitoid is somewhere preserved. This unit, strongly re-crystallized and locally crosscut by aplitic and porphyritic dikes, is represented by (Coli &Pandeli, 1997; Morelli, 2000) tectonized meta-serpentinites, meta-gabbros with rodingitic dikes, rare meta-basalts and meta-ophicalcites, meta-cherts, marbles, cherty meta-limestones, phyllites and meta-limestones with rare meta-arenites intercalations. A "pre-magmatic" tectono-metamorphic framework of this unit is well evident only in its meta-sedimentary portion. The meta-sediments are deformed by syn-metamorphic isoclinal folds caractherized by N-S trending axes, west dipping axial planes and easternward vergence. A later folding and flattening event clearly post-dated the above said folds and associated

The onset of metamorphism in ordinary and carbonaceous chondrites

USGS Publications Warehouse

Grossman, J.N.; Brearley, A.J.

2005-01-01

Ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by X-ray mapping techniques. A variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and cathodoluminescence (CL) methods. The distribution of Cr in FeO-rich olivine systematically changes as metamorphism increases between type 3.0 and type 3.2. Igneous zoning patterns are replaced by complex ones and Cr-rich coatings develop on all grains. Cr distributions in olivine are controlled by the exsolution of a Cr-rich phase, probably chromite. Cr in olivine may have been partly present as tetrahedrally coordinated Cr3+. Separation of chromite is nearly complete by petrologic type 3.2. The abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type. TEM shows this to be the result of crystallization of albite. Residual glass compositions systematically change during metamorphism, becoming increasingly rich in K. Glass in type I chondrules also gains alkalis during metamorphism. Both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules. The matrix in the least metamorphosed chondrites is rich in S and Na. The S is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains. Progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules. Alkalis initially leave the matrix and enter chondrules during early metamorphism. Feldspar subsequently nucleates in the matrix and Na re-enters from chondrules. These metamorphic trends can be used to refine classification schemes for chondrites. Cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to

Metamorphic Epitaxy for Multijunction Solar Cells

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

France, Ryan M.; Dimroth, Frank; Grassman, Tyler J.

Multijunction solar cells have proven to be capable of extremely high efficiencies by combining multiple semiconductor materials with bandgaps tuned to the solar spectrum. Reaching the optimum set of semiconductors often requires combining high-quality materials with different lattice constants into a single device, a challenge particularly suited for metamorphic epitaxy. In this article, we describe different approaches to metamorphic multijunction solar cells, including traditional upright metamorphic, state-of-the-art inverted metamorphic, and forward-looking multijunction designs on silicon. We also describe the underlying materials science of graded buffers that enables metamorphic subcells with low dislocation densities. Following nearly two decades of research, recentmore » efforts have demonstrated high-quality lattice-mismatched multijunction solar cells with very little performance loss related to the mismatch, enabling solar-to-electric conversion efficiencies over 45%.« less

Isotope and chemical age of the Greater Caucasus basement metamorphic rocks

NASA Astrophysics Data System (ADS)

Konilov, A. N.; Somin, M. L.; Mukhanova, A. A.

2009-04-01

It is widely accepted that metamorphic basement of the Greater Caucasus is essentially Proterozoic [i.e. Gamkrelidze & Shengelia, 2005 ]. New results of geochronological study, mainly on magmatic zircon, contradict this opinion [Somin, 2007; Somin et al., 2007a, b, c and references therein]. To precise age of metamorphism we tried to apply CHIME method on monazite [Suzuki, Adachi, 1991]. The facility consists of Tescan SEM VEGA II xmu equipped with EDS Energy 400 and WDS Wave 500 from Oxford Instruments. This system and analytical protocol for monazite analysis are close to described by Slagstad [2006]. Samples of three metamorphic units were used with purpose to investigate their PT conditions and chemical composition of accessory monazite, xenotime and zircon. In the Blyb Complex Ky-bearing St-Grt-Bt schist was studied. Temperature calculated using Grt-St and Grt-Bt thermometers are 550-600 oC at 10 kb. Because xenotime absence and very low Y2O3 content in monazite, temperature determination on Mnz thermometer was impossible. Isochron chemical age of monazite is 288±24 Ma. In the Gondary Complex the Sil-bearing Grt-Bt gneiss was studied. Temperature calculated using Grt-Bt thermometer and Grt-Pl-Sil-Qtz geobarometer correspond to 610 oC at 4 kb. Monazite thermometer [Pyle et al., 2001] indicates temperature range 533-640 oC for three samples. Monazite chemical age is 303±31 Ma, zircon of leucosome yields SHRIMP age 321-288 Ma. In the Makera Complex the And-Bt-Ms and Grt-Bt-Ms metapelites were examinated. Temperature calculated using Grt-Bt thermometer and Grt-Pl-And-Qtz geobarometer correspond to 500 oC at 2,5 kb. Monazite thermometer indicates average temperatures 293-433-447 oC. Two isochrones correspond to 239±28 Ma and 282±19 Ma. Our results of monazite dating are close to the U-Pb zircon data although not similar being some younger. Therefore conclusion on Precambrian metamorphic events in the studied complexes of the Greater Caucasus is erroneous. These

Evidence for multiple metamorphic events in the Adirondack Mountains, N. Y

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

McLelland, J.; Lochhead, A.; Vyhnal, C.

1988-05-01

Field evidence consisting of: (1) rotated, foliated xenoliths, (2) country rock foliation truncated by isoclinally folded igneous intrusions bearing granulite facies assemblages document one, or more, early dynamothermal event(s) of regional scale and high grade. Early metamorphism resulted in pronounced linear and planar fabric throughout the Adirondacks and preceded the emplacement of the anorthosite-mangerite-charnockite-granite-alaskite (AMCA) suite which contains xenoliths of the metamorphosed rocks. Olivine metagabbros, believed to be approximately contemporaneous with the AMCA-suite, also crosscut and contain xenoliths of, strongly foliated metasediments. These intrusive rocks caused contact metamorphism in the metasediments which locally exhibit both anatectite and restite assemblages. Subsequently,more » this already complex framework underwent three phases of folding, including an early recumbent isoclinical event, and was metamorphosed to granulite facies P,T conditions. The age of the early metamorphism cannot yet be narrowly constrained, but isotopic results suggest that it may be as young as approx. 1200 Ma or older than approx. 1420 Ma. U-Pb zircon ages indicate emplacement of the AMCA-(metagabbro)-suite in the interval 1160-1130 Ma and place the peak of granulite facies metamorphism between 1070-1025 Ma. The anorogenic character of the AMCA-suite, and the occurrence of metadiabase dike swarms within it, are further evidence of the separate nature of the metamorphic events that precede and postdate AMCA emplacement.« less

Deformation sequences of the Day Nui Con Voi metamorphic belt, northern Vietnam

NASA Astrophysics Data System (ADS)

Yeh, M. W.; Lee, T. Y.; Lo, C. H.; Chung, S. L.; Lan, C. Y.; Lee, J. C.; Lin, T. S.; Lin, Y. J.

2003-04-01

The correlation of structure, microstructure and metamorphic assemblages is of fundamental importance to the understanding of the complex tectonic history and kinematics of the Day Nui Con Voi (DNCV) metamorphic belt in Vietnam along the Ailao Shan-Red River (ASRR) shear zone as it provides constraints on the relative timing of the deformation, kinematics and metamorphism. High-grade metamorphic rocks of amphibolite faces showed consistent deformation sequences of three folding events followed by one brittle deformation through all four cross sections from Lao Cai to Viet Tri indicated the DNCV belt experienced similar deformation condition throughout its length. The first deformation event, D1, produced up-right folds (locally preserved) with sub-vertical, NE-SW striking axial planes with dextral sense of shear probably formed during the early phase of the lowermost Triassic Indosinian orogeny. Followed by this compressional event is a gravitational collapsing event, D2, which is the major deformation and metamorphic event characterized by kyanite grade metamorphism and large scale horizontal folds with NW-SE (320) striking sub-horizontal axial pane showing sinsistral sense of shear most likely formed during the Oligocene-Miocene SE extrusion of Indochina peninsula. The 3rd folding event, D3, is a post-metamorphism doming event with NW-SE (310) striking sub-vertical axial plane that folded/tilted the once sub-horizontal D2 axial planes into shallowly (<30 degrees) NE dipping on the NE limb, and SW dipping on the SW limb possibly due to left-lateral movement of the N-S trending Xian Shui He fault system in Mid-Miocene. The outward decreasing of the metamorphic grade from kyanite to garnet then biotite indicated the D3 occurred post metamorphism. Reactivation of the sub-horizontal D2 fold axial planes showed dextral sense of shear possibly due to Late Miocene-Pliocene right-lateral movement of the ASRR shear zone. This right lateral movement continuously deformed

Fluid-absent metamorphism in the Adirondacks

NASA Technical Reports Server (NTRS)

Valley, J. W.

1986-01-01

Results on late Proterozoic metamorphism of granulite in the Adirondacks are presented. There more than 20,000 sq km of rock are at granulite facies. Low water fugacites are implied by orthopyroxene bearing assemblages and by stability of k'spar-plag-quartz assemblages. After mentioning the popular concept of infiltration of carbon dioxide into Precambrian rocks and attendent generation of granulite facies assemblages, several features of Adirondack rocks pertinent to carbon dioxide and water during their metamorphism are summarized: wollastonite occurs in the western lowlands; contact metamorphism by anorthosite preceeding granulite metamorphism is indicated by oxygen isotopes. Oxygen fugacity lies below that of the QFM buffer; total P sub water + P sub carbon dioxide determined from monticellite bearing assemblages are much less than P sub total (7 to 7.6 kb). These and other features indicate close spatial association of high- and low-P sub carbon dioxide assemblages and that a vapor phase was not present during metamorphism. Thus Adirondack rocks were not infiltrated by carbon dioxide vapor. Their metamorphism, at 625 to 775 C, occurred either when the protoliths were relatively dry or after dessication occurred by removal of a partial melt phase.

A Geothermochronologic Investigation of the Coyote Mountains Metamorphic Core Complex (AZ)

NASA Astrophysics Data System (ADS)

Borel, M.; Gottardi, R.; Casale, G.

2017-12-01

The Coyote Mountains metamorphic core complex (CM-MCC) makes up the northern end of the Baboquivari Mountain complex, which is composed of Mesozoic rocks, Tertiary granites, pegmatites, and metasediments. The CM-MCC expose the Pan Tak granite, a 58 Ma intrusive muscovite-biotite-garnet peraluminous granite. The Pan Tak and other intrusions within the Baboquivari Mountains have been interpreted as anatectic melts representing the culmination of a Laramide crustal shortening orogenic event started in the Late Cretaceous ( 70 Ma). Evidence of this magmatic episode includes polysynthetic twinning in plagioclase, myrmekitic texture in alkali feldspars, and garnet, mica and feldspar assemblages. The magmatic fabric is overprinted by a Tertiary tectonic fabric, associated with the exhumation of the CM-MCC along the Ajo road décollement and associated shear zone. In the shear zone, the Pan Tak mylonite display N-dipping foliation defined by gneissic layering and aligned muscovite, and N-trending mineral stretching lineation. Various shear sense indicators are all consistent with a top-to the-N shear sense. Preliminary argon geochronology results suggest that the shear zone was exhumed 29 Ma ago, an age similar to the onset of detachment faulting in other nearby MCCs (Catalina, Rincon, Pinaleño). In the Pan Tak mylonite, quartz grains display regime 2 to 3 microstructures and shows extensive recrystallization by subgrain rotation and grain boundary migration. The recrystallized grain size ranges between 20 and 50 µm in all samples. Quartz crystallographic preferred orientation measured using electron backscatter diffraction (EBSD) shows that recrystallization was accommodated by dominant prism and minor rhomb slip, suggesting deformation temperature ranging from 450°C to 550°C. These preliminary results constrain the timing of uplift and exhumation, and thermomechanical evolution of the CM-MCC, and improve our understanding of recycling of the continental crust in

Lunar anorthosite 15415: Texture, mineralogy, and metamorphic history

USGS Publications Warehouse

James, O.B.

1972-01-01

Lunar anorthosite 15415 consists almost entirely of anorthite (homogeneous anorthite 96.6 molecule percent), with accessory diopsidic augite and traces of hypersthene, ilmenite, and a silica mineral. The rock has had a complex metamorphic history. The texture reflects at least two episodes of shearing (followed by intense and partial recrystallization, respectively), one episode of cataclastic deformation, and one or more episodes of shattering and fragmentation.

Post-metamorphic brecciation in type 3 ordinary chondrites

NASA Technical Reports Server (NTRS)

Scott, E. R. D.; Mccoy, T. J.; Keil, K.

1993-01-01

Type 3.1-3.9 ordinary chondrites can be divided into two kinds: those in which the compositions of chondrule silicates are entirely consistent with metamorphism of type 3.0 material, and those in which the computational heterogeneity appears to be too extreme for in situ metamorphism. We present petrologic data for three LL3 chondrites of the second kind--Ngawi, ALH A77278 (both type 3.6), and Hamlet (type 3.9)--and compare these data with results for the first kind of LL3-4 chondrites. Given that chondrules form in the nebula and that metamorphic equilibration occurs in asteroids, our new data imply that Ngawi, A77278, Hamlet, and many other type 3 ordinary chondrites are post-metamorphic breccias containing materials with diverse metamorphic histories; they are not metamorphic rocks or special kinds of 'primitive breccias.' We infer also that metamorphism to type 3.1-3.9 levels produces very friable material that is easily remixed into breccias and lithified by mild shock. Thus, petrologic types and subtypes of chondrites indicate the mean metamorphic history of the ingredients, not the thermal history of the rock. The metamorphic history of individual type 1 or 2 porphyritic chondrules in type 3 breccias is best derived from olivine and pyroxene analyses and the data of McCoy et al. for unbrecciated chondrites. The new chondrule classification schemes of Sears, DeHart et al., appears to provide less information about the original state and metamorphic history of individual porphyritic chondrules and should not replace existing classification schemes.

Post-metamorphic brecciation in type 3 ordinary chondrites

NASA Astrophysics Data System (ADS)

Scott, E. R. D.; McCoy, T. J.; Keil, K.

1993-03-01

Type 3.1-3.9 ordinary chondrites can be divided into two kinds: those in which the compositions of chondrule silicates are entirely consistent with metamorphism of type 3.0 material, and those in which the computational heterogeneity appears to be too extreme for in situ metamorphism. We present petrologic data for three LL3 chondrites of the second kind--Ngawi, ALH A77278 (both type 3.6), and Hamlet (type 3.9)--and compare these data with results for the first kind of LL3-4 chondrites. Given that chondrules form in the nebula and that metamorphic equilibration occurs in asteroids, our new data imply that Ngawi, A77278, Hamlet, and many other type 3 ordinary chondrites are post-metamorphic breccias containing materials with diverse metamorphic histories; they are not metamorphic rocks or special kinds of 'primitive breccias.' We infer also that metamorphism to type 3.1-3.9 levels produces very friable material that is easily remixed into breccias and lithified by mild shock. Thus, petrologic types and subtypes of chondrites indicate the mean metamorphic history of the ingredients, not the thermal history of the rock. The metamorphic history of individual type 1 or 2 porphyritic chondrules in type 3 breccias is best derived from olivine and pyroxene analyses and the data of McCoy et al. for unbrecciated chondrites. The new chondrule classification schemes of Sears, DeHart et al., appears to provide less information about the original state and metamorphic history of individual porphyritic chondrules and should not replace existing classification schemes.

Metamorphic InAsSb-based Barrier Photodetectors for the Long Wave Infrared Region

DTIC Science & Technology

2013-08-02

The character of the I–V for structures with AlInSb layer grown undoped reflects the complex nature of the potential profile in the valence band ...Al0.75In0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga1?xInxSb buffer layers and GaSb substrates by...ABSTRACT InAs0.6Sb0.4/Al0.75In0.25Sb-based barrier photodetectors were grown metamorphically on compositionally graded Ga1?xInxSb buffer layers and GaSb

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

Cadomian magmatism and metamorphism at the Ossa Morena/Central Iberian zone boundary, Iberian Massif, Central Portugal: Geochemistry and P-T constraints of the Sardoal Complex

NASA Astrophysics Data System (ADS)

Henriques, S. B. A.; Neiva, A. M. R.; Tajčmanová, L.; Dunning, G. R.

2017-01-01

A well preserved Cadomian basement is exposed in the Iberian Massif, Central Portugal, at the Ossa Morena/Central Iberian zone boundary, which allows the determination of reliable geochemical data. A sequence of Cadomian and Variscan magmatic and tectonometamorphic events has been already described for this area and are documented in other areas of the Avalonian-Cadomian orogen. However, the geochemical information concerning the Cadomian basement for this area is still limited. We present whole rock geochemical and oxygen isotopic information to characterize the igneous protoliths of the Sardoal Complex, located within the Tomar-Badajoz-Córdoba Shear Zone, and identify their tectonic setting. We use detailed petrography, mineral chemistry and P-T data to characterize the final Cadomian tectonometamorphic event. The Sardoal Complex contains orthogneiss and amphibolite units. The protoliths of the orthogneiss are calc-alkaline magmas of acid composition and peraluminous character that were generated in an active continental margin in three different stages (ca. 692 Ma, ca. 569 Ma and ca. 548 Ma). The most significant processes in their petrogenesis are the partial melting of old metasedimentary and meta-igneous crust at different crustal levels and the crystal fractionation of plagioclase, alkali feldspars, apatite, zircon and Fe-Ti oxides. The protoliths of the amphibolite, older than ca. 540 Ma, are tholeiitic and calc-alkaline magmas of basic composition that display N-, T- and E-MORB affinities. They were generated in an active continental margin. Crustal contamination and fractional crystallization of hornblende and diopside were involved in their petrogenesis. However, the fractional crystallization was not significant. The magmatic activity recorded in the Sardoal Complex indicates the existence of a long-lived continental arc (ca. 692-540 Ma) with coeval felsic and mafic magmatism. The final stage of the Cadomian metamorphism is usually represented in other

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.

Timing and heat sources for the Barrovian metamorphism, Scotland

NASA Astrophysics Data System (ADS)

Viete, Daniel R.; Oliver, Grahame J. H.; Fraser, Geoff L.; Forster, Marnie A.; Lister, Gordon S.

2013-09-01

New SHRIMP U/Pb zircon ages of 472.2 ± 5.8 Ma and 471.2 ± 5.9 Ma are presented for the age of peak metamorphism of Barrovian migmatites. 40Ar/39Ar ages for white mica from the Barrovian metamorphic series are presented, and are recalculated using recently-proposed revisions to the 40K decay constants to allow more precise and accurate comparison with U/Pb ages. The 40Ar/39Ar ages are found to vary systematically with increasing metamorphic grade, between c. 465 Ma for the biotite zone and c. 461 Ma for the sillimanite zone. There is no evidence for any significant metamorphic heating during the first 15 Myr of the Grampian Orogeny (before c. 473 Ma) or the final 4 Myr (after c. 465 Ma). The Barrovian metamorphism occurred over a period of ~ 8 Myr within the ~ 27-Myr Grampian Orogeny. The Barrovian metamorphism records punctuated heating, was temporally and spatially associated with large-scale bimodal magmatism, and developed within crust that was not overthickened. The temporally distinct nature of the Barrovian metamorphic episode within the Grampian Orogeny, and its heating pattern and tectonic context, are not consistent with significant heat contribution from thermal equilibration of overthickened crust. Rather, the Barrovian metamorphism records a transient phase of crustal thermal disequilibrium during the Grampian Orogeny. Temporal and spatial association with Grampian bimodal magmatism is consistent with production of the Barrovian metamorphic series within the middle crust as the result of advection of heat from the lower crust and/or mantle. The Barrovian metamorphic series - the classic example of ‘orogenic regional metamorphism’ - did not form in response to crustal thickening and thermal relaxation, but appears to record large-scale contact metamorphism.

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

Metamorphic density controls on early-stage subduction dynamics

NASA Astrophysics Data System (ADS)

Duesterhoeft, Erik; Oberhänsli, Roland; Bousquet, Romain

2013-04-01

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

First description of a metamorphic sole related to ophiolite obduction in the northern Caribbean: Geochemistry and petrology of the Güira de Jauco Amphibolite complex (eastern Cuba) and tectonic implications

NASA Astrophysics Data System (ADS)

Lázaro, C.; Blanco-Quintero, I. F.; Rojas-Agramonte, Y.; Proenza, J. A.; Núñez-Cambra, K.; García-Casco, A.

2013-10-01

The Güira de Jauco Amphibolite Complex underlies the Mayarí-Baracoa Ophiolitic Belt (eastern Cuba) and is composed of highly foliated amphibolite, locally with blocks of sheared serpentinitie that enclose concordant layers of amphibolite. These amphibolites are interpreted as remnants of a sub-ophiolitic metamorphic sole likely formed during late Cretaceous times before the initiation of the collision between the Caribbean and the North American plates. The complex includes common amphibolites (Hbl + Pl ± Ep ± Ttn ± Rt ± Qtz ± Ap), garnet amphibolites (Hbl + Grt + Pl + Ep ± Ttn ± Qtz ± Ap) and clinopyroxene amphibolites (Hbl + Pl + Cpx ± Ep ± Ttn ± Qtz ± Ap). Geochemical data indicates that the protoliths are igneous mafic rocks of basaltic composition that likely formed part of the upper and lower(?)crust of an oceanic lithosphere. Rare Earth element contents suggest a Mid-Ocean Ridge Basalt (MORB) origin. However, the enrichment in Large-Ion Lithophile elements and the depletion in NbTaTi as compared to Normal-MORB, suggests a suprasubduction scenario, either a back-arc or a fore-arc setting. The pressure-temperature estimates of metamorphism indicate that the entire amphibolite body underwent similar peak metamorphic conditions at 650-665 °C and 8.5-8.7 kbar (ca. 30 km depth), corresponding to a relatively high apparent geothermal gradient of 23 °C/km.

Geophysical evidence for the evolution of the California Inner Continental Borderland as a metamorphic core complex

USGS Publications Warehouse

ten Brink, Uri S.; Zhang, Jie; Brocher, Thomas M.; Okaya, David A.; Klitgord, Kim D.; Fuis, Gary S.

2000-01-01

We use new seismic and gravity data collected during the 1994 Los Angeles Region Seismic Experiment (LARSE) to discuss the origin of the California Inner Continental Borderland (ICB) as an extended terrain possibly in a metamorphic core complex mode. The data provide detailed crustal structure of the Borderland and its transition to mainland southern California. Using tomographic inversion as well as traditional forward ray tracing to model the wide-angle seismic data, we find little or no sediments, low (≤6.6 km/s) P wave velocity extending down to the crust-mantle boundary, and a thin crust (19 to 23 km thick). Coincident multichannel seismic reflection data show a reflective lower crust under Catalina Ridge. Contrary to other parts of coastal California, we do not find evidence for an underplated fossil oceanic layer at the base of the crust. Coincident gravity data suggest an abrupt increase in crustal thickness under the shelf edge, which represents the transition to the western Transverse Ranges. On the shelf the Palos Verdes Fault merges downward into a landward dipping surface which separates "basement" from low-velocity sediments, but interpretation of this surface as a detachment fault is inconclusive. The seismic velocity structure is interpreted to represent Catalina Schist rocks extending from top to bottom of the crust. This interpretation is compatible with a model for the origin of the ICB as an autochthonous formerly hot highly extended region that was filled with the exhumed metamorphic rocks. The basin and ridge topography and the protracted volcanism probably represent continued extension as a wide rift until ∼13 m.y. ago. Subduction of the young and hot Monterey and Arguello microplates under the Continental Borderland, followed by rotation and translation of the western Transverse Ranges, may have provided the necessary thermomechanical conditions for this extension and crustal inflow.

An enigmatic source of hematitic carbonate beds containing vast amounts of iron oxidizers in a paleozoic metamorphic complex, South Hungary, Geresd-Hills, Ófalu.

NASA Astrophysics Data System (ADS)

Jáger, Viktor; Dabi, Gergely; Menyhárt, Adrienn

2013-04-01

Near the village of Ófalu, in the Geresd Hills, South Hungary, within the "Mecsekalja tectonic belt", low and intermediate grade paleozoic metamorphic complex (phyllite, gneiss) contains vein-like hematitic carbonate beds, up to 30 cm in thickness. The carbonate mineral is calcite. These hematitic carbonate beds cross-cut the foliation of the phyllite, and show no signs of any metamorphic alteration. In the studied section the red carbonate beds are associated with a vein system filled with multiple generations of vein carbonates(Dabi et al., 2011). The red carbonate beds contain a vaste number of twisted stalks of the iron oxidizing taxon of Gallionella. Rarely in some siliceous parts, Leptothrix-like microbial fossils can be found and these beds also contain numerous unidentifiable, hematitic foraminifers. According to ICP-AES measurements, the hematitic carbonate beds contains 8 % Fe, 0.86 % Mn and 0.12 % Ba. XRD and Raman measurements proved that the iron phase is hematite. The SEM observations revealed that the bacterial microfossils and foraminifers are built up of micron-submicron sized pseudohexagonal platy hematite. The bacterial microfossils of the Gallionella iron oxidizer are very well preserved and reaches about 80 µm length and about 2-3 µm width. The above observations raise the following issues: 1. how did these non metamorphic hematitic-carbonatic beds get inside into the metamorphic complex?, 2. what is the age of the formation of these beds?, and 3. what was the source of the iron? If we consider that the hematitic beds contain foraminifers and iron oxidizing bacteria, and no signs of metamorphic alteration nor foliations can be observed in these beds, the only answer for the first question is that the formations are fractures filled with lime-mud, i.e. neptunian dykes, which penetrated into the cracks of the phyllite. The presence of foraminifers and the geotectonic situation of the unit imply marine origin. Considering that these beds are

Thermal durations and heating behaviour for the Barrovian metamorphism, Scotland

NASA Astrophysics Data System (ADS)

Viete, D. R.; Lister, G. S.; Hermann, J.; Forster, M. A.; Oliver, G. J.

2008-12-01

Published U/Pb ages for the syn-metamorphic gabbros and granites of the Grampian Terrane, Scotland, that provided heat for the classical Barrovian metamorphism, suggests that they were emplaced between 473.5 and 470 Ma. New SHRIMP U/Pb ages of 472.2 ± 5.8 Ma and 470.4 ± 6.1 Ma for peak metamorphism in the highest-grade units of the Barrovian metamorphic series are consistent with a 473.5 to 470 Ma heating episode in the highest-grade units. U/Pb-calibrated 40Ar/39Ar ages for white mica from the Barrovian metamorphic series vary from c. 465 Ma for the biotite zone to c. 461 Ma for the sillimanite zone and suggest that the Barrovian thermal episode lasted less than 8.5 million years in the biotite zone and less than 12.5 million years in the sillimanite zone. The lowest-grade units of the Barrovian metamorphic series retain detrital ages in white mica 40Ar/39Ar step-heating spectra, while units metamorphosed to temperatures of 475°C or more yield Grampian 40Ar/39Ar plateau ages. Forward modelling of Ar diffusion from white mica grains was carried out for different grain sizes and thermal histories to match the position of the across-metamorphic-grade transition from detrital 40Ar/39Ar patterns to Grampian 40Ar/39Ar plateau ages. The results of Ar diffusion modelling are consistent with thermal durations of between one and 4.5 million years for the Barrovian metamorphism of the biotite zone. Microstructural observations suggest that peak metamorphism and cooling occurred earliest in the lowest-grade units of the Barrovian metamorphic series and metamorphism in the higher-grade units continued for longer. We propose metamorphic durations of between 3.5 and eight million years for the Barrovian metamorphism of the sillimanite zone. Geochemical textures preserved within high-grade garnets from the Barrovian metamorphic series record evidence of Mn diffusion over c. 1000 μm lengthscales during the Barrovian metamorphism. In addition, sillimanite-grade garnets from the

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

Color Me Metamorphic.

ERIC Educational Resources Information Center

Birdd, Donald L.

1990-01-01

Described are five activities using crayons to demonstrate the rock cycle including weathering, erosion and sedimentation, and sedimentary, metamorphic, and igneous rock formation. Discussed are materials, procedures, and probable results. (CW)

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.

New U-Pb zircon age data on polyphase plutono-metamorphic complex in western Enderby Land (East Antarctica) and its implications for Neoproterozoic amalgamation of the Gondwanaland

NASA Astrophysics Data System (ADS)

Mikhalskii, Evgenii; Krylov, Dmitriy; Rodionov, Nikolay

2017-04-01

Western Enderby Land occupies a key position on Gondwanaland reconstructions near India - Sri Lanka - Antarctica junction and eastwards the Lützow-Holm Bay metamorphic complex commonly identified as a Cambrian suture zone. We present U-Pb zircon isotopic age determinations with SHRIMP II obtained on tonalite- to granite-gneiss samples from the Thala Hills and the Polkanova Hills. In the Thala Hills three high-temperature tectonomagmatic episodes may be distinguished at ca 980-970 Ma, ca 780-720 Ma, and ca 545-530 Ma. All of them included sin-kinematic granitic orthogneiss protolith emplacements and high-grade metamorphism. In the Polkanova Hills tonalitic to granodioritic orthogneisses, intercalated with prevailing amphibolites, were emplaced during ca 980-950 Ma episode (or at both of these ages) and subsequently metamorphosed under amphibolite facies accompanied by migmatization at ca 600-530 Ma. The ca 980-950 Ma event corresponds to the Rayner Structural Episode which affected much of East Antarctica, including Sør Rondane Mountains to the west and Kemp Land to the east of study area. The Polkanova Hills area is underlain by basic amphibolites and tonalitic to granodioritic orthogneisses characterized by LILE enrichment and Nb-Ta troughs in a primitive mantle normalized spiderdiagram suggestive of derivation in arc-related convergent palaeotectonic environments. Co-eval orthogneisses in the Thala Hills are characterized by granitic compositions and occur in intercalation with paragneisses, which points out to more in-land palaeotectonic environments. The ca 780-720 Ma episode included two events at ca 780 Ma (high-grade anatexis) and 720 Ma (sin-tectonic granitoid emplacement) and was roughly co-eval with magmatic and/or metamorphic events in Dronning Maud Land of East Antarctica as well as in other Gondwanaland regions, like Madagascar, Sri Lanka and eastern Africa. The ca 780-720 Ma episode (Thala Episode) may be correlated with the East African Orogeny

Two Tertiary metamorphic events recognized in metapelites of the Nevado-Filabride Complex (Betic Cordillera, S Spain)

NASA Astrophysics Data System (ADS)

Li, Botao; Massonne, Hans-Joachim

2017-04-01

The orogenic belt of the Betic Cordillera in southern Spain resulted from the collision of the African plate with the southwestern edge of the Eurasian plate in Alpine times. This belt can be considered as a large nappe stack with the Nevado-Filabride Complex in the eastern Betic Cordillera representing the lowest nappe, in which high-pressure (HP > 10 kbar) rocks such as eclogites occur. We have studied two metapelites from the Ragua (former Veleta) unit, which is the lowest unit of the Nevado-Filabride Complex. These rocks were sampled at Cerro de los Machos (sample 23085) and c. 3 km east of this locality at the Laguna de la Caldera (sample 23098) and contain quartz, potassic white-mica, paragonite, chlorite, garnet, biotite, tourmaline, epidote, rutile, ilmenite, apatite, zircon and monazite and titanite (23085) or calcite and albite (23098). Garnet in both rocks is similarly zoned. An inclusion-rich core shows a prograde metamorphic zonation with high and low Mn contents in the center (e.g. for 23085: Alm64.5Grs27Py2.5Sps6) and at the rim (Alm84Grs8Py6Sps2), respectively, of the core domain. After corrosion of this domain a garnet mantle formed with an inner zone being again relatively rich in Mn and an outermost rim being poor in Mn. This mantle is significantly richer in Mg and poorer in Ca compared to the core domain. Potassic white-mica in the samples also shows a considerable compositional spread (Si = 3.05-3.20 in 23085 and 3.13-3.33 in 23098) with the highest Si contents in the core of potassic white-mica grains. To elucidate the metamorphic evolution of the rocks we calculated various P-T pseudosections for different H2O-CO2 contents and Fe3+/Fe2+ ratios with PERPLE_X. On the basis of the compositions of the garnet inner core and the highest Si content in potassic white mica contrasting peak pressures at c. 535˚ C resulted for the rocks (23085: 12.8 kbar, 23098: 18.3 kbar). A subsequent pressure release to about 8 (23085) or 5 kbar (23098) at slightly

Mesoproterozoic syntectonic garnet within Belt Supergroup metamorphic tectonites: Evidence of Grenville-age metamorphism and deformation along northwest Laurentia

USGS Publications Warehouse

Nesheim, T.O.; Vervoort, J.D.; McClelland, W.C.; Gilotti, J.A.; Lang, H.M.

2012-01-01

Northern Idaho contains Belt-Purcell Supergroup equivalent metamorphic tectonites that underwent two regional deformational and metamorphic events during the Mesoproterozoic. Garnet-bearing pelitic schists from the Snow Peak area of northern Idaho yield Lu-Hf garnet-whole rock ages of 1085??2. Ma, 1198??79. Ma, 1207??8. Ma, 1255??28. Ma, and 1314??2. Ma. Garnet from one sample, collected from the Clarkia area, was micro-drilled to obtain separate core and rim material that produced ages of 1347??10. Ma and 1102??47. Ma. The core versus rim ages from the micro-drilled sample along with the textural and spatial evidence of the other Lu-Hf garnet ages indicate two metamorphic garnet growth events at ~. 1330. Ma (M1) and ~. 1080. Ma (M2) with the intermediate ages representing mixed ages. Some garnet likely nucleated and grew M1 garnet cores that were later overgrown by younger M2 garnet rims. Most garnet throughout the Clarkia and Snow Peak areas are syntectonic with a regional penetrative deformational fabric, preserved as a strong preferred orientation of metamorphic matrix minerals (e.g., muscovite and biotite). The syntectonic garnets are interpreted to represent one regional, coeval metamorphic and deformation event at ~. 1080. Ma, which overlaps in time with the Grenville Orogeny. The older ~. 1330. Ma ages may represent an extension of the East Kootenay Orogeny described in western Canada. These deformational and metamorphic events indicate that western Laurentia (North America) was tectonically active in the Mesoproterozoic and during the assembly of the supercontinent Rodinia. ?? 2011 Elsevier B.V.

High-temperature metamorphism and its relation with magmatism (Svecofennian Belt, the Ladoga region, Russia)

NASA Astrophysics Data System (ADS)

Baltybaev, Shauket

2010-05-01

surrounding rocks. Baltybaev Sh. K., Levchenkov O. A., Levsky L. K., Eklund O., Kilpeläinen T. 2006. Two metamorphic stages in the Svecofennian Domain: evidence from the isotopic geochronological study of the Ladoga and Sulkava metamorphic complexes. Petrology, 14(3), 247-261.

Kinematics of Faulting and Structural Evolution of Neogene Supra-detachment Basins on the Menderes Metamorphic Core Complex, Western Anatolia

NASA Astrophysics Data System (ADS)

Dilek, Y.; Oner, Z.; Davis, E. A.

2007-12-01

The Menderes metamorphic massif (MM) in western Anatolia is a classic core complex with exhumed high-grade crustal rocks intruded by granodioritic plutons and overlain by syn-extensional sedimentary rocks. Timing and the mechanism(s) of the initial exhumation of the MM are controversial, and different hypotheses exist in the literature. Major structural grabens (i.e. Alasehir, Buyuk Menderes) within the MM that are bounded by high-angle and seismically active faults are late-stage brittle structures, which characterize the block-faulting phase in the extensional history of the core complex and are filled with Quaternary sediments. On the southern shoulder of the Alasehir graben high-grade metamorphic rocks of the MM are overlain by the Miocene and younger sedimentary rocks above a N-dipping detachment surface. The nearly 100-m-thick cataclastic shear zone beneath this surface contain S-C fabrics, microfaults, Riedel shears, mica-fish structures and shear bands, all consistently indicating top-to-the North shearing. Granodioritic plutons crosscutting the MM and the detachment surface are exposed within this cataclastic zone, displaying extensional ductile and brittle structures. The oldest sedimentary rocks onlapping the cataclastic shear zone of the MM here are the Middle Miocene lacustrine shale and limestone units, unconformably overlain by the Upper Miocene fluvial and alluvial fan deposits. Extensive development of these alluvial fan deposits by the Late Miocene indicates the onset of range-front faulting in the MM by this time, causing a surge of coarse clastic deposition along the northern edge of the core complex. The continued exhumation and uplift of the MM provided the necessary relief and detrital material for the Plio-Pleistocene fluvial systems in the Alasehir supradetachment basin (ASDB). A combination of rotational normal faulting and scissor faulting in the extending ASDB affected the depositional patterns and drainage systems, and produced local

Possible giant metamorphic core complex at the center of Artemis Corona, Venus

USGS Publications Warehouse

Spencer, J.E.

2001-01-01

Hundreds of circular features on Venus known as coronae are characterized by annular fractures and commonly associated radial fractures and lava flows. Coronae are thought to have been produced by buoyant mantle diapirs that flatten and spread at the base of the lithosphere and cause fracturing, uplift, and magmatism. The interior of Artemis Corona, by far the largest corona at 2100 km diameter, is divided in half by a northeast-trending deformation belt that contains numerous rounded ridges resembling antiforms. The largest of these ridges, located at the center of Artemis Corona, is ???5 km high on its steep northwest flank where it is adjacent to a flat-bottomed, 10-km-wide trough interpreted as a rift valley. The 280-km-long antiformal ridge is marked by perpendicular grooves that cross the ???50-km-wide ridge and extend southeastward as far as 120 km across adjacent plains. The grooves abruptly terminate northwestward at the rift trough. The large antiformal ridge terminates southwestward at a transform shear zone that parallels the grooves. These features-rift valley, antiformal uplift, grooves, and transform shear zone-are morphologically and geometrically similar to grooved, elevated, submarine metamorphic core complexes on the inside corners of ridge-transform intersections of slow-spreading ridges on Earth. As with submarine core complexes, the grooved surface on Venus is interpreted as the footwall of a large-displacement normal fault, and the grooves are inferred to be the product of plastic molding of the footwall to irregularities on the underside of the hanging wall followed by tectonic exhumation of the molded grooves and conveyer-belt-like transport up and over the large antiform and across the southeastern plains. According to this interpretation, the trend of the grooves records the direction of extension, which is perpendicular to the thrusts at the leading edge of the annular thrust belt 1000 km to the southeast. Both may have formed at the

Geochemistry and metamorphism of the Mouriscas Complex, Ossa-Morena/Central Iberian zone boundary, Iberian Massif, Central Portugal: Implications for the Cadomian and Variscan orogenies

NASA Astrophysics Data System (ADS)

Henriques, S. B. A.; Neiva, A. M. R.; Tajčmanová, L.; Dunning, G. R.

2018-01-01

The Mouriscas Complex is a deformed and metamorphosed predominantly mafic igneous complex of Ediacaran and Ordovician age and crops out at the Ossa-Morena/Central Iberian zone boundary in the Iberian Massif, Central Portugal. It comprises amphibolite with Neoproterozoic protoliths (ca. 544 Ma), protomylonitic felsic dykes derived from younger trondhjemitic protoliths (ca. 483 Ma) and garnet amphibolite derived of even younger dioritic protoliths (ca. 477 Ma). The protoliths of the Neoproterozoic amphibolites are calc-alkaline magmas of basic to intermediate compositions with intraplate and active continental margin affinities and are considered to represent the final phase of the Cadomian arc magmatism. They are interpreted to have originated as coarse-grained intrusions, likely gabbro or diorite and generated from the partial melting of meta-igneous lower crust and mantle. Their emplacement occurred near the Cadomian metamorphic event dated at ca. 540 Ma (P = 7-8 kbar and T = 640-660 °C) which is interpreted to represent a continental collision. During the Late Cambrian-Early Ordovician an extensional episode occurred in the central-southern Iberian Massif and was also observed in other areas of the Variscan Orogen. It led to mantle upwelling and to the development of an aborted intracratonic rift located at the Ossa-Morena/Central Iberian zone boundary and to the opening of the Rheic Ocean to the south of the area studied in present coordinates (i.e., between the Ossa-Morena and South Portuguese Zones). This event has been dated at ca. 477 Ma and was responsible for the melting of deep ancient mafic crust and mantle with formation of bimodal magmatism in an intra-plate setting, as indicated by the protoliths of the protomylonitic felsic dykes with trondhjemitic composition and of the garnet amphibolite. Subsequent Variscan metamorphism took place under amphibolite facies conditions (P = 4-5.5 kbar; T = 600-625 °C) at lower P-T conditions than the Cadomian

The co-genetic evolution of metamorphic core complexes and drainage systems

NASA Astrophysics Data System (ADS)

Trost, Georg; Neubauer, Franz; Robl, Jörg

2016-04-01

Metamorphic core complexes (MCCs) are large scale geological features that globally occur in high strain zones where rocks from lower crustal levels are rapidly exhumed along discrete fault zones, basically ductile-low-angle normal faults recognizable by a metamorphic break between the cool upper plate and hot lower plate. Standard methods, structural analysis and geochronology, are applied to reveal the geodynamic setting of MCCs and to constrain timing and rates of their exhumation. Exhumation is abundantly accompanied by spatially and temporally variable vertical (uplift) and horizontal motions (lateral advection) representing the tectonic driver of topography formation that forces drainage systems and related hillslopes to adjust. The drainage pattern commonly develops in the final stage of exhumation and contributes to the decay of the forming topography. Astonishingly, drainage systems and their characteristic metrics (e.g. normalized steepness index) in regions coined by MCCs have only been sparsely investigated to determine distinctions between different MCC-types (A- and B-type MCCs according to Le Pourhiet et al., 2012). They however, should significantly differ in their topographic expression that evolves by the interplay of tectonic forcing and erosional surface processes. A-type MCCs develop in an overall extensional regime and are bounded partly by strike-slip faults showing transtensional or transpressional components. B-type MCCs are influenced by extensional dynamics only. Here, we introduce C-type MCCs that are updoming along oversteps of crustal-scale, often orogen-parallel strike-slip shear zones. In this study, we analyze drainage systems of several prominent MCCs, and compare their drainage patterns and channel metrics to constrain their geodynamic setting. The Naxos MCC represents an A-type MCC. The Dayman Dome located in Papua New Guinea a B-type MCC, whereas MCCs of the Red River Shear Zone, the Diancang, Ailao-Shan and Day Nui Con Voi

Organic matter and metamorphic history of CO chondrites

NASA Astrophysics Data System (ADS)

Bonal, Lydie; Bourot-Denise, Michèle; Quirico, Eric; Montagnac, Gilles; Lewin, Eric

2007-03-01

The metamorphic grades of a series of eight CO3 chondrites (ALHA77307, Colony, Kainsaz, Felix, Lancé, Ornans, Warrenton and Isna) have been quantified. The method used was based on the structural grade of the organic matter trapped in the matrix, which is irreversibly transformed by thermal metamorphism. The maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration. This metamorphic tracer is thus valid whatever the chemical class of chondrites. Moreover, it is sensitive to the peak metamorphic temperature. The structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals, Fa and Fs silicate composition in type I chondrules, presolar grains and noble gas (P3 component) abundance. The deduced metamorphic hierarchy and the attributed petrographic types are the following: ALHA77307 (3.03) < Colony (3.1) < Kainsaz (3.6) < Felix (3.6 (1)) < Ornans (3.6 (2)) < Lancé (3.6 (3)) < Warrenton (3.7 (1)) < Isna (3.7 (2)). For most metamorphosed objects, the peak metamorphic temperature can be estimated using a geothermometer calibrated with terrestrial metasediments [Beyssac O., Goffe B., Chopin C., and Rouzaud J. N. (2002) Raman spectrum of carbonaceous material in metasediments: a new geothermometer. J. Metamorph. Geol., 20, 859-871]. A value of 330 °C was obtained for Allende (CV chondrite), Warrenton and Isna, consistent with temperatures estimated from Fe diffusion [Weinbruch S., Armstrong J., and Palme H. (1994). Constraints on the thermal history of the Allende parent body as derive from olivine-spinel thermometry and Fe/Mg interdiffusion in olivine. Geochim. Cosmochim. Acta58(2), 1019-1030.], from the Ni content in sulfide-metal assemblages [Zanda B., Bourot-Denise M., and Hewins R. (1995) Condensate sulfide and its metamorphic transformations in primitive chondrites. Meteorit. Planet. Sci.30, A605.] and from the d002 interlayer spacing in poorly

Timing of mid-crustal ductile extension in the northern Snake Range metamorphic core complex, Nevada: Evidence from U/Pb zircon ages

NASA Astrophysics Data System (ADS)

Lee, J.; Blackburn, T.; Johnston, S. M.

2016-12-01

Metamorphic core complexes (Mccs) within the western U.S. record a history of Cenozoic ductile and brittle extensional deformation, metamorphism, and magmatism, and exhumation within the footwall of high-angle Basin and Range normal faults. Documenting these histories within Mccs have been topics of research for over 40 years, yet there remains disagreement about: 1) whether the detachment fault formed and moved at low angles or initiated at high angles and rotated to a low angle; 2) whether brittle and ductile extensional deformation were linked in space and time; and 3) the temporal relationship of both modes of extension to the development of the detachment fault. The northern Snake Range metamorphic core complex (NSR), Nevada has been central to this debate. To address these issues, we report new U/Pb dates from zircon in deformed and undeformed rhyolite dikes emplaced into ductilely thinned and horizontally stretched lower plate rocks that provide tight bounds on the timing of ductile extension at between 38.2 ± 0.3 Ma and 22.50 ± 0.36 Ma. The maximum age constraint is from the Northern dike swarm (NDS), which was emplaced in the northwest part of the range pre- to syn-tectonic with ductile extension. The minimum age constraint is from the Silver Creek dike swarm (SDS) that was emplaced in the southern part of the range post ductile extensional deformation. Our field observations, petrography, and U/Pb zircon ages on the dikes combined with published data on the geology and kinematics of extension, moderate and low temperature thermochronology on lower plate rocks, and age and faulting histories of Cenozoic sedimentary basins adjacent to the NSR are interpreted as recording an episode of localized upper crustal brittle extension during the Eocene that drove upward ductile extensional flow of hot middle crustal rocks from beneath the NSR detachment soon after, or simultaneous with, emplacement of the NDS. Exhumation of the lower plate continued in a rolling

Metamorphic quantum dots: Quite different nanostructures

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

Seravalli, L.; Frigeri, P.; Nasi, L.

In this work, we present a study of InAs quantum dots deposited on InGaAs metamorphic buffers by molecular beam epitaxy. By comparing morphological, structural, and optical properties of such nanostructures with those of InAs/GaAs quantum dot ones, we were able to evidence characteristics that are typical of metamorphic InAs/InGaAs structures. The more relevant are: the cross-hatched InGaAs surface overgrown by dots, the change in critical coverages for island nucleation and ripening, the nucleation of new defects in the capping layers, and the redshift in the emission energy. The discussion on experimental results allowed us to conclude that metamorphic InAs/InGaAs quantummore » dots are rather different nanostructures, where attention must be put to some issues not present in InAs/GaAs structures, namely, buffer-related defects, surface morphology, different dislocation mobility, and stacking fault energies. On the other hand, we show that metamorphic quantum dot nanostructures can provide new possibilities of tailoring various properties, such as dot positioning and emission energy, that could be very useful for innovative dot-based devices.« less

Archean metamorphic sequence and surfaces, Kangerdlugssuaq Fjord, East Greenland

NASA Technical Reports Server (NTRS)

Kays, M. A.

1986-01-01

The characteristics of Archean metamorphic surfaces and fabrics of a mapped sequence of rocks older than about 3000 Ma provide information basic to an understanding of the structural evolution and metamorphic history in Kangerdlugssuaq Fjord, east Greenland. This information and the additional results of petrologic and geochemical studies have culminated in an extended chronology of Archean plutonic, metamorphic, and tectonic events. The basis for the chronology is considered, especially the nature of the metamorphic fabrics and surfaces in the Archean sequence. The surfaces, which are planar mineral parageneses, may prove to be mappable outside Kangerdlugssuaq Fjord, and if so, will be helpful in extending the events that they represent to other Archean sequences in east Greenland. The surfaces will become especially important reference planes if the absolute ages of their metamorphic assemblages can be determined in at least one location where strain was low subsequent to their recrystallization. Once an isochron is obtained, the dynamothermal age of the regionally identifiable metamorphic surface is determined everywhere it can be mapped.

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.

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

The brittle stage of the exhumation of a metamorphic core complex: Naxos, Cyclades, Greece and some general rules

NASA Astrophysics Data System (ADS)

Neubauer, F.; Cao, S.

2012-04-01

Structures of hangingwall units of major detachment systems in extensional settings leading to metamorphic core complexes are equally important to the generally well-studied footwall rocks. Here, we describe hanging-wall structures of the North-Cycladic Detachment System on Naxos Island of the Aegean Sea and found that they well monitor the structural evolution of hanging blocks complementary to the footwall structures, vertical fluid flow as well as late-stage inversion of the whole extensional system. On Naxos, Upper Oligocene-Miocene and Pliocene sedimentary successions are deposited on the hangingwall unit, which is largely an ophiolite. The Upper Oligocene-Miocene and Pliocene sedimentary successions are separated by a hiatus arguing for a two-step evolution. Whereas the first step, Miocene, indicate moderate subsidence and relief, and only denudation of the hangingwall unit, the Pliocene conglomerates indicate a sharply increasing relief and an over-steepened topography. Hydrothermal systems developed in hangingwall rock succession (e.g. Miocene at Steladia) play an important role and resulted in large-scale silica precipitation and associated alteration similar as these found in subvolcanic epithermal systems. This constrains a close link between footwall granodiorite intrusion and near-surface processes. The Pliocene coarse boulder conglomerate with its abundant first appearance of granite/granodiorite, and subsequent marble-rich debris on distant places like Palatia indicate a sudden erosion and high-gradient relief leading to erosion of the mantle of the migmatite dome during Pliocene. On Naxos, we recognize, therefore, a three-stage tectonic evolution in the hangingwall unit: (i) moderate subsidence of an Upper Oligocene-Miocene basin, in part below sea level; (2) a second stage with deposition of Pliocene coarse conglomerates, and (iii) post-Pliocene faulting affecting the conglomerates. During the second stage, surface exposure of the metamorphic core

Alpine extensional detachment tectonics in the Grande Kabylie metamorphic core complex of the Maghrebides (northern Algeria)

NASA Astrophysics Data System (ADS)

Saadallah, A.; Caby, R.

1996-12-01

The Maghrebides are part of the peri-Mediterranean Alpine orogen. They expose in their inner zone inliers of high-grade crystalline rocks surrounded by Oligo-Miocene and younger Miocene cover. Detailed mapping coupled with structural and petrological investigations in the Grande Kabylie massif, and the reinterpretation of the available geochronological data, allow us to refute the traditional concept of rigid behaviour of this massif during Alpine events. We show that the dome geometry, the kinematic and metamorphic evolutions and the age pattern are typical of metamorphic core complexes exhumed by extension. A major low-angle detachment fault defined by mylonites and by younger cataclasites has been traced in the massif. The upper unit encompasses pre-Permian phyllites with Variscan {40Ar }/{39Ar } cooling ages, capped by unconformable Mesozoic to Tertiary cover of the Calcareous Range, both mainly affected by extensive Tertiary brittle deformation and normal faulting. The lower unit exposes in two half-domes a continuous tectonic pile, 6-8 km thick, of amphibolite facies rocks and orthogneisses affected by syndashmetamorphic ductile deformation, devoid of retrogression. The regular increase of paleotemperature downward and the {40Ar }/{39Ar } plateau ages around 80 Ma suggest that the high-temperature foliation and associated WNW-directed shear under a high geothermal gradient relate to extensional tectonics developed during Mesozoic lithospheric thinning of the Variscan south European margin. To the north, the Sidi Alli Bou Nab massif exposes another crustal section affected throughout by WNW-directed extensional shear during {HP }/{HT } syndashmetamorphic thinning and with overall {40Ar }/{39Ar } plateau ages of 25 Ma. The Eocene oblique collisional event responsible for crustal thickening was totally overprinted by this new extensional regime, synchronous with the beginning of the opening of the Western Mediterranean oceanic basin. This was also coeval with

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

Calculation of metamorphic two-dimensional quantum energy system: Application to wetting layer states in InAs/InGaAs metamorphic quantum dot nanostructures

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

Seravalli, L.; Trevisi, G.; Frigeri, P.

In this work, we calculate the two-dimensional quantum energy system of the In(Ga)As wetting layer that arises in InAs/InGaAs/GaAs metamorphic quantum dot structures. Model calculations were carried on the basis of realistic material parameters taking in consideration their dependence on the strain relaxation of the metamorphic buffer; results of the calculations were validated against available literature data. Model results confirmed previous hypothesis on the extrinsic nature of the disappearance of wetting layer emission in metamorphic structures with high In composition. We also show how, by adjusting InGaAs metamorphic buffer parameters, it could be possible: (i) to spatially separate carriers confinedmore » in quantum dots from wetting layer carriers, (ii) to create an hybrid 0D-2D system, by tuning quantum dot and wetting layer levels. These results are interesting not only for the engineering of quantum dot structures but also for other applications of metamorphic structures, as the two design parameters of the metamorphic InGaAs buffer (thickness and composition) provide additional degrees of freedom to control properties of interest.« less

Metamorphic III–V Solar Cells: Recent Progress and Potential

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

Garcia, Ivan; France, Ryan M.; Geisz, John F.

Inverted metamorphic multijunction solar cells have been demonstrated to be a pathway to achieve the highest photovoltaic (PV) conversion efficiencies. Attaining high-quality lattice-mismatched (metamorphic) semiconductor devices is challenging. However, recent improvements to compositionally graded buffer epitaxy and junction structures have led to the achievement of high-quality metamorphic solar cells exhibiting internal luminescence efficiencies over 90%. For this high material quality, photon recycling is significant, and therefore, the optical environment of the solar cell becomes important. In this paper, we first present recent progress and performance results for 1- and 0.7-eV GaInAs solar cells grown on GaAs substrates. Then, an electroopticalmore » model is used to assess the potential performance improvements in current metamorphic solar cells under different realizable design scenarios. The results show that the quality of 1-eV subcells is such that further improving its electronic quality does not produce significant Voc increases in the four-junction inverted metamorphic subcells, unless a back reflector is used to enhance photon recycling, which would significantly complicate the structure. Conversely, improving the electronic quality of the 0.7-eV subcell would lead to significant Voc boosts, driving the progress of four-junction inverted metamorphic solar cells.« less

The Taili-Yiwulüshan metamorphic core complex corridor: Diachronous exhumation and relationships to the adjacent basins based on new 40Ar/39Ar and (U-Th-Sm)/He mineral ages

NASA Astrophysics Data System (ADS)

Liang, Chenyue; Neubauer, Franz; Liu, Yongjiang; Genser, Johann; Dunkl, István; Heberer, Bianca; Jin, Wei; Zeng, Zuoxun; Li, Weimin; Wen, Quanbo; Li, Jing

2015-04-01

The Xingcheng-Taili ductile shear zone (western Liaoning Province in China) formed during latest Jurassic to Early Cretaceous crustal extension of the eastern North China craton, and exhumed low to medium metamorphic grade Archean, Upper Triassic and Upper Jurassic granitic rocks. The Mesozoic Yiwulüshan metamorphic core complex (Yiwulüshan MCC) is dominated by a NNE-SSW elongated dome with a left-lateral shear zone, which is located in the northeastern part of Xingcheng-Taili ductile shear zone, and combine as Taili-Yiwulüshan metamorphic core complex corridor. To the east, it is bounded by the NNE-trending Cretaceous to Eocene Liaohe basin (the northern extension of the Bohai Bay basin), and to the west by the Cretaceous-aged Fuxin-Yixian basin, which could potentially interpreted as supra-detachment basins. Here, we present results from a multi-method thermochronological study and coupled with structural investigations and sections of adjacent supra-detachment basins, which constrain the timing of regional deformation as well as the cooling history and exhumation processes of the low- to middle-grade metamorphic complex in the Taili-Yiwulüshan MCC corridor, in order to understand the mode of lithospheric scale reactivation, extension and thinning of the North China craton. The new40Ar/39Ar muscovite, biotite, K-feldspar and (U-Th)/He apatite ages from granitic rocks help constrain the thermal evolution during its exhumation. The thermochronologic studies have shown at least three stages of exhumation and cooling from late Jurassic to Eocene in Xingcheng-Taili shear zone should be distinguished, e.g., ~ 150-130 Ma, 130-115 Ma and 115-52 Ma, respectively. Diachronous onset and subsequent parallel cooling and exhumation characterize the early thermal history. The Yiwulüshan MCC has a similar exhumation history from 135 to 97 Ma with a similar cooling history. The development of Taili-Yiwulüshan MCC corridor is associated with synkinematic emplacement

CHRONOLOGY OF MAJOR METAMORPHIC EVENTS IN THE SOUTHEASTERN UNITED STATES

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

Long, L.E.; Kulp, J.L.; Eckelmann, F.D.

1959-10-01

Potassium-argon and rubidium-strontium age measurements have been made on a variety of granites, pegmatites, gneiases and schists which comprise the plutonicmetamorphic complex of the Piedmont and Blue Ridge of the southeastern United States. Large portions of the area appear to have been metamorphosed initially approximately at the same time as the Grenville Province, i.e., about 900 to 1100 m.y. ago. Superimposed on this older metamorphic province was a major orogenic event culminating at about 350 m.y. with widespread recrystallization of existing rocks and intrusion of pegmatites in the Spruce Pine, Franklin-Sylva and Bryson City Districts, and granites in the Virginiamore » and North Carolina Piedmont. There is strong evidence of an additional metamorphic epoch between 350 and 1000 m.y., but its effects have been largely obliterated by the 350 m.y. event. In western North Carolina a transition of apparent ages from 355 to 890 m.y. occurs in the same rock unit. (Cranberry gneiss) over a distance of about 10 miles across the strike of the border- of the 350 m.y. event. In the southeastern Piedmont of Georgia and South Carolina a younger metamorphic event or events can be detected producing rocks of apparent age ranging from 230 to 310 m.y. The time of these orogenies is compared with those in the Central and Northern Appalachians. Evidence is accumulating that the Holmes' time scale will have to be considerably lengthened. (auth)« less

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

Extensional unroofing of the metamorphic core of the southern Appalachian orogen prior to the breakup of Pangea: Insights from 40Ar/39Ar thermochronology

NASA Astrophysics Data System (ADS)

Ma, C.; Foster, D. A.; Hames, W. E.; Mueller, P. A.

2017-12-01

Orogenic collapse commonly occurs following the collisional phase of an orogeny and often leads to exhumation of deep crustal metamorphic rocks. The Alleghanian orogeny in the southern Appalachian orogen (SAO) occurred during final assembly of Pangea. 40Ar/39Ar data of hornblende, muscovite, and biotite from Alleghanian granitic plutons in Georgia, Alabama, and Florida of the SAO give cooling ages that progressively young toward the south-southeast prior to ca. 280 Ma and young locally toward the north-northwest after ca. 280 Ma. These cooling-age gradients, along with geometry of the Suwannee suture zone and timing/structures of the South Georgia basin, suggest that metamorphic rocks north of the Suwannee suture in the study area formed the lower plate of a metamorphic core complex. The faults of the Suwannee suture zone were reactivated to form a master extensional detachment fault with the Suwannee terrane comprising the upper plate. Thermochronologic data show that rapid extension of the metamorphic core complex footwall started at ca. 300-295 Ma and the extension continued to at least ca. 240 Ma. The maximum average extension rate is estimated to be 10.3 km/m.y. during ca. 300-280 Ma along the master detachment fault and 2.4 km/m.y. during ca. 280-240 Ma along a secondary detachment fault, reflecting differential extension over time. Main cooling rates of 10‒85˚C/m.y. and exhumation rates of 0.3‒2.8 km/m.y. are calculated for the Alleghanian granitic plutons studied. This work shows that, in the southernmost Appalachians, orogenic collapse resulted in metamorphic core complex-style extension between about 300 and 240 Ma. The horst-and-graben systems of the South Georgia basin formed within the upper plate in this tectonic setting. Metamorphic core complex-style extension, therefore, played a critical role in initial rifting that led to the eventual breakup of Pangea and formation of the Atlantic Ocean and the Gulf of Mexico.

Single quantum dot emission at telecom wavelengths from metamorphic InAs/InGaAs nanostructures grown on GaAs substrates

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

Seravalli, L.; Trevisi, G.; Frigeri, P.

We report on the growth by molecular beam epitaxy and the study by atomic force microscopy and photoluminescence of low density metamorphic InAs/InGaAs quantum dots. subcritical InAs coverages allow to obtain 10{sup 8} cm{sup -2} dot density and metamorphic In{sub x}Ga{sub 1-x}As (x=0.15,0.30) confining layers result in emission wavelengths at 1.3 {mu}m. We discuss optimal growth parameters and demonstrate single quantum dot emission up to 1350 nm at low temperatures, by distinguishing the main exciton complexes in these nanostructures. Reported results indicate that metamorphic quantum dots could be valuable candidates as single photon sources for long wavelength telecom windows.

Regional metamorphism at extreme conditions: Implications for orogeny at convergent plate margins

NASA Astrophysics Data System (ADS)

Zheng, Yong-Fei; Chen, Ren-Xu

2017-09-01

Regional metamorphism at extreme conditions refers either to Alpine-type metamorphism at low geothermal gradients of <10 °C/km, or to Buchan-type metamorphism at high geothermal gradients of >30 °C/km. Extreme pressures refer to those above the polymorphic transition of quartz to coesite, so that ultrahigh-pressure (UHP) eclogite-facies metamorphism occurs at mantle depths of >80 km. Extreme temperatures refer to those higher than 900 °C at crustal depths of ≤80 km, so that ultrahigh-temperature (UHT) granulite-facies metamorphism occurs at medium to high pressures. While crustal subduction at the low geothermal gradients results in blueschist-eclogite facies series without arc volcanism, heating of the thinned orogenic lithosphere brings about the high geothermal gradients for amphibolite-granulite facies series with abundant magmatism. Therefore, UHP metamorphic rocks result from cold lithospheric subduction to the mantle depths, whereas UHT metamorphic rocks are produced by hot underplating of the asthenospheric mantle at the crustal depths. Active continental rifting is developed on the thinned lithosphere in response to asthenospheric upwelling, and this tectonism is suggested as a feasible mechanism for regional granulite-facies metamorphism, with the maximum temperature depending on the extent to which the mantle lithosphere is thinned prior to the rifting. While lithospheric compression is associated with subduction metamorphism in accretionary and collisional orogens, the thinned orogenic lithosphere undergoes extension due to the asthenospheric upwelling to result in orogen-parallel rifting metamorphism and magmatism. Thus, the rifting metamorphism provides a complement to the subduction metamorphism and its operation marks the asthenospheric heating of the orogenic lithosphere. Because of the partial melting and melt extraction of the lower continental crust, contemporaneous granite-migmatite-granulite associations may serve as a petrological

Recycling argon through metamorphic reactions: The record in symplectites

NASA Astrophysics Data System (ADS)

McDonald, Christopher S.; Regis, Daniele; Warren, Clare J.; Kelley, Simon P.; Sherlock, Sarah C.

2018-02-01

The 40Ar/39Ar ages of metamorphic micas that crystallized at high temperatures are commonly interpreted as cooling ages, with grains considered to have lost 40Ar via thermally-driven diffusion into the grain boundary network. Recently reported laser-ablation data suggest that the spatial distribution of Ar in metamorphic micas does not always conform to the patterns predicted by diffusion theory and that despite high metamorphic temperatures, argon was not removed efficiently from the local system during metamorphic evolution. In the Western Gneiss Region (WGR), Norway, felsic gneisses preserve microtextural evidence for the breakdown of phengite to biotite and plagioclase symplectites during near isothermal decompression from c. 20-25 to c. 8-12 kbar at 700 °C. These samples provide an ideal natural laboratory to assess whether the complete replacement of one K-bearing mineral by another at high temperatures completely 'resets' the Ar clock, or whether there is some inheritance of 40Ar in the neocrystallized phase. The timing of the high-temperature portion of the WGR metamorphic cycle has been well constrained in previous studies. However, the timing of cooling following the overprint is still much debated. In-situ laser ablation spot dating in phengite, biotite-plagioclase symplectites and coarser, texturally later biotite yielded 40Ar/39Ar ages that span much of the metamorphic cycle. Together these data show that despite residence at temperatures of 700 °C, Ar is not completely removed by diffusive loss or during metamorphic recrystallization. Instead, Ar released during phengite breakdown appears to be partially reincorporated into the newly crystallizing biotite and plagioclase (or is trapped in fluid inclusions in those phases) within a close system. Our data show that the microtextural and petrographic evolution of the sample being dated provides a critical framework in which local 40Ar recycling can be tracked, thus potentially allowing 40Ar/39Ar dates

Organic nitrogen chemistry during low-grade metamorphism

USGS Publications Warehouse

Boudou, J.-P.; Schimmelmann, A.; Ader, M.; Mastalerz, Maria; Sebilo, M.; Gengembre, L.

2008-01-01

Most of the organic nitrogen (Norg) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil Norg within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of Norg and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of Norg a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of Norg speciation, transformation and elimination before and during metamorphism and advocates the use of X-ray photoelectron spectroscopy (XPS) to monitor changes in Norg speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset Norg is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much Norg is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for Norg elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate Norg along a progressing reaction front, without causing nitrogen

Another dimension to metamorphic phase equilibria: the power of interactive movies for understanding complex phase diagram sections

NASA Astrophysics Data System (ADS)

Moulas, E.; Caddick, M. J.; Tisato, N.; Burg, J.-P.

2012-04-01

The investigation of metamorphic phase equilibria, using software packages that perform thermodynamic calculations, involves a series of important assumptions whose validity can often be questioned but are difficult to test. For example, potential influences of deformation on phase relations, and modification of effective reactant composition (X) at successive stages of equilibrium may both introduce significant uncertainty into phase diagram calculations. This is generally difficult to model with currently available techniques, and is typically not well quantified. We present here a method to investigate such phenomena along pre-defined Pressure-Temperature (P-T) paths, calculating local equilibrium via Gibbs energy minimization. An automated strategy to investigate complex changes in the effective equilibration composition has been developed. This demonstrates the consequences of specified X modification and, more importantly, permits automated calculation of X changes that are likely along the requested path if considering several specified processes. Here we describe calculations considering two such processes and show an additional example of a metamorphic texture that is difficult to model with current techniques. Firstly, we explore the assumption that although water saturation and bulk-rock equilibrium are generally considered to be valid assumptions in the calculation of phase equilibria, the saturation of thermodynamic components ignores mechanical effects that the fluid/melt phase can impose on the rock, which in turn can modify the effective equilibrium composition. Secondly, we examine how mass fractionation caused by porphyroblast growth at low temperatures or progressive melt extraction at high temperatures successively modifies X out of the plane of the initial diagram, complicating the process of determining best-fit P-T paths for natural samples. In particular, retrograde processes are poorly modeled without careful consideration of prograde

A Simulated Research Problem for Undergraduate Metamorphic Petrology.

ERIC Educational Resources Information Center

Amenta, Roddy V.

1984-01-01

Presents a laboratory problem in metamorphic petrology designed to simulate a research experience. The problem deals with data on scales ranging from a geologic map to hand specimens to thin sections. Student analysis includes identifying metamorphic index minerals, locating their isograds on the map, and determining the folding sequence. (BC)

Extension Within The Australia-Eurasia Collision: The Metamorphic Rocks Of Central Sulawesi, Indonesia

NASA Astrophysics Data System (ADS)

Watkinson, I. M.; Hall, R.; Hennig, J.; Forster, M.

2012-12-01

Low-angle mylonitic fabrics from the metamorphic basement of central Sulawesi reveal a complex history of extension from the late Miocene to the present-day. Sulawesi is situated in the convergent triple junction between the Australian, Eurasian and Philippine Sea plates. The island is cut by the Palu-Koro and Matano faults, major active strike-slip zones that were initiated no earlier than about 5 Ma and have previously been attributed to collision-related processes. Within, and to the north and east of the strike-slip faults, are a suite of metamorphic complexes that include mica schists, schistose amphibolites, gneisses, migmatites, granulites, eclogites, marbles and ultramafic rocks including garnet peridotites. Mylonitic fabrics are widespread throughout the metamorphic rocks. The orientation of the mylonitic foliation is highly variable but typically dips less than 30°. Kinematic indicators record transport directions dominantly between top-to-the-NW and top-to-the-NE. Medium to high-grade mylonites, particularly in the south and west, are associated with ductile boudinage of eclogite and kyanite-bearing layers, 'snowball' garnet porphyroclasts, dynamic recrystallisation of feldspar and amphibole, and mylonitic deformation was locally synchronous with partial melting. Medium to high-grade mylonites are commonly overprinted by isoclinal asymmetric similar folds. Low grade mylonites are characterised by quartz recrystallisation only. Mica growth during mylonitic deformation is recorded by young 40Ar-39Ar plateaux between 5.05 ± 0.01 Ma and 2.07 ± 0.03 Ma in the west and 11.33 ± 0.02 Ma in the east. Undeformed aplitic dykes of similar composition to the migmatite leucosomes locally cross-cut the migmatitic mylonites and have yielded a biotite 40Ar-39Ar plateau of 3.62 ± 0.02 Ma. In the east the mylonitic fabric is cut by a low-angle detachment surface expressed as anomalously corrugated topography. On the basis of lithologic variation, shear

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

Different origins of garnet in high pressure to ultrahigh pressure metamorphic rocks

NASA Astrophysics Data System (ADS)

Xia, Qiong-Xia; Zhou, Li-Gang

2017-09-01

Garnet in high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic rocks in subduction zone commonly shows considerable zonation in major and trace elements as well as mineral inclusions, which bears information on its growth mechanism via metamorphic or peritectic reactions in coexistence with relic minerals and metamorphic fluids or anatectic melts at subduction-zone conditions. It provides an important target to retrieve physicochemical changes in subduction-zone processes, including those not only in pressure and temperature but also in the durations of metamorphism and anatexis. Garnet from different compositions of HP to UHP metamorphic rocks may show different types of major and trace element zonation, as well as mineral inclusions. Discrimination between the different origins of garnet provides important constraints on pressure and temperature and the evolution history for the HP to UHP metamorphic rocks. Magmatic garnet may occur as relics in granitic gneisses despite metamorphic modification at subduction-zone conditions, with spessartine-increasing or flat major element profiles from inner to outer core and exceptionally higher contents of trace elements than metamorphic mantle and rim. Metamorphic garnet can grow at different metamorphic stages during prograde subduction and retrograde exhumation, with spessartine-decreasing from core to rim if the intracrystalline diffusion is not too fast. The compositional profiles of metamorphic garnet in the abundances of grossular, almandine and pyrope are variable depending on the composition of host rocks and co-existing minerals. Peritectic garnet grows through peritectic reactions during partial melting of HP to UHP rocks, with the composition of major elements to be controlled by anatectic P-T conditions and the compositions of parental rocks and anatectic melts. Trace element profiles in garnet with different origins are also variable depending on the coexisting mineral assemblages, the garnet

P- T- t constraints on the development of the Doi Inthanon metamorphic core complex domain and implications for the evolution of the western gneiss belt, northern Thailand

NASA Astrophysics Data System (ADS)

Macdonald, A. S.; Barr, S. M.; Miller, B. V.; Reynolds, P. H.; Rhodes, B. P.; Yokart, B.

2010-01-01

The western gneiss belt in northern Thailand is exposed within two overlapping Cenozoic structural domains: the extensional Doi Inthanon metamorphic core complex domain located west of the Chiang Mai basin, and the Mae Ping strike-slip fault domain located west of the Tak batholith. New P- T estimates and U-Pb and 40Ar/ 39Ar age determinations from the Doi Inthanon domain show that the gneiss there records a complex multi-stage history that can be represented by a clockwise P- T- t path. U-Pb zircon and titanite dating of mylonitic calc-silicate gneiss from the Mae Wang area of the complex indicates that the paragneissic sequence experienced high-grade, medium-pressure metamorphism (M1) in the Late Triassic - Early Jurassic (ca. 210 Ma), in good agreement with previously determined zircon ages from the underlying core orthogneiss exposed on Doi Inthanon. Late Cretaceous monazite ages of 84 and 72 Ma reported previously from the core orthogneiss are attributed to a thermal overprint (M2) to upper-amphibolite facies in the sillimanite field. U-Pb zircon and monazite dating of granitic mylonite from the Doi Suthep area of the complex provides an upper age limit of 40 Ma (Late Eocene) for the early stage(s) of development of the actual core complex, by initially ductile, low-angle extensional shearing under lower amphibolite-facies conditions (M3), accompanied by near-isothermal diapiric rise and decompression melting. 40Ar/ 39Ar laserprobe dating of muscovite from both Doi Suthep and Doi Inthanon provided Miocene ages of ca. 26-15 Ma, representing cooling through the ca. 350 °C isotherm and marking late-stage development of the core complex by detachment faulting of the cover rocks and isostatic uplift of the sheared core zone and mantling gneisses in the footwall. Similarities in the thermochronology of high-grade gneisses exposed in the core complex and shear zone domains in the western gneiss belt of northern Thailand (and also in northern Vietnam, Laos, Yunnan

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

Very low-grade metamorphic rocks in some representative districts in Tibet

NASA Astrophysics Data System (ADS)

Bi, X.; Mo, X.

2011-12-01

*Response author: Bi,Xianmei,bixm10@sina.com Very low grade metamorphic rocks are widely distributed in Tibet, providing an insight into deformation and metamorphism during the evolution of the Tibetan Plateau. Eighty five Samples of clay mineral-bearing rocks has been collected from various strata including D, P1, T1, T2, T3, J1, J3, K1, K2 and N strata in the Qiangtang terrane, the Gangdese, the Yarlung Zangbo suture and the Tethyan Himalaya. Analyses and refining of clay minerals in samples have been conducted in the Laboratory of X-ray Diffraction, Institute of Petroleum Exploration. Index of illite crystallinity (Ic) along with average thickness of crystal layers of illite, reflectivity of vitrinite and of clay mineral association have been employed as indicators of degree of very low-grade metamorphism. The scheme of classification[1,2] of very-low grade metamorphism based on clay mineral indexes ( mainly index of illite crystallinity) has been used in the present work, that is, low metamorphism (Ic<0.25), higher very-low grade metamorphism (Ic = 0.25-0.30), lower very-low grade metamorphism (Ic = 0.30-0.42) and diagenesis (Ic>0.42). The analytical results show interesting information. In the Qiangtang terrane, clay minerals in the Jurassic strata have indexes of illite crystalinity (Ic) 0.47-0.70, indicating higher diagenesis and in favor of petroleum-generation. However, index of illite crystalinity (Ic) for the Devonian is 0.23, indicating low metamorphism. Indexes of illite crystalinity (Ic) for the J-K strata in middle Gangdese are mostly 0.37-0.25 (very-low grade metamorphism) and a few 0.78-0.48 (diagenesis). Indexes of illite crystalinity (Ic) for the C-P strata in eastern Gangdese are mostly 0.25-0.42 (very-low grade metamorphism) and a few 0.20-0.25 (low metamorphism). The Mesozoic and Cenozoic magmatism and related mineralization are very strong in the Gangdese, which may affect in some extent on indexes of illite crystalinity. In Tethyan Himalaya

Geology of the Biwabik Iron Formation and Duluth Complex.

PubMed

Jirsa, Mark A; Miller, James D; Morey, G B

2008-10-01

The Biwabik Iron Formation is a approximately 1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by approximately 1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact.

Geology of the Biwabik Iron Formation and Duluth Complex

USGS Publications Warehouse

Jirsa, M.A.; Miller, J.D.; Morey, G.B.

2008-01-01

The Biwabik Iron Formation is a ???1.9 billion year-old sequence of iron-rich sedimentary rocks that was metamorphosed at its eastern-most extent by ???1.1 billion year-old intrusions of the Duluth Complex. The metamorphic recrystallization of iron-formation locally produced iron-rich amphiboles and other fibrous iron-silicate minerals. The presence of these minerals in iron-formation along the eastern part of what is known as the Mesabi Iron Range, and their potential liberation by iron mining has raised environmental health concerns. We describe here the geologic setting and mineralogic composition of the Biwabik Iron Formation in and adjacent to the contact metamorphic aureole of the Duluth Complex. The effects of metamorphism are most pronounced within a few kilometers of the contact, and decrease progressively away from it. The contact aureole has been divided into four metamorphic zones-each characterized by the composition and crystal structure of the metamorphic minerals it contains. The recrystallization of iron-formation to iron-rich amphibole minerals (grunerite and cummingtonite) and iron-pyroxene minerals (hedenbergite and ferrohypersthene) is best developed in zones that are most proximal to the Duluth Complex contact. ?? 2007 Elsevier Inc. All rights reserved.

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

Temporal and spatial distribution of Paleozoic metamorphism in the southern Appalachian Blue Ridge and Inner Piedmont delimited by ion microprobe U-Pb ages of metamorphic zircon

USGS Publications Warehouse

Merschat, Arthur J.; Bream, Brendan R.; Huebner, Matthew T.; Hatcher, Robert D.; Miller, Calvin F.

2017-01-01

Ion microprobe U-Pb zircon rim ages from 39 samples from across the accreted terranes of the central Blue Ridge, eastward across the Inner Piedmont, delimit the timing and spatial extent of superposed metamorphism in the southern Appalachian orogen. Metamorphic zircon rims are 10–40 µm wide, mostly unzoned, and dark gray to black or bright white in cathodoluminescence, and truncate and/or embay interior oscillatory zoning. Black unzoned and rounded or ovoid-shaped metamorphic zircon morphologies also occur. Th/U values range from 0.01 to 1.4, with the majority of ratios less than 0.1. Results of 206Pb/238U ages, ±2% discordant, range from 481 to 305 Ma. Clustering within these data reveals that the Blue Ridge and Inner Piedmont terranes were affected by three tectonothermal events: (1) 462–448 Ma (Taconic); (2) 395–340 Ma (Acadian and Neoacadian); and (3) 335–322 Ma, related to the early phase of the Alleghanian orogeny. By combining zircon rim ages with metamorphic isograds and other published isotopic ages, we identify the thermal architecture of the southern Appalachian orogen: juxtaposed and superposed metamorphic domains have younger ages to the east related to the marginward addition of terranes, and these domains can serve as a proxy to delimit terrane accretion. Most 462–448 Ma ages occur in the western and central Blue Ridge and define a continuous progression from greenschist to granulite facies that identifies the intact Taconic core. The extent of 462–448 Ma metamorphism indicates that the central Blue Ridge and Tugaloo terranes were accreted to the western Blue Ridge during the Taconic orogeny. Zircon rim ages in the Inner Piedmont span almost 100 m.y., with peaks at 395–385, 376–340, and 335–322 Ma, and delimit the Acadian-Neoacadian and Alleghanian metamorphic core. The timing and distribution of metamorphism in the Inner Piedmont are consistent with the Devonian to Mississippian oblique collision of the Carolina superterrane

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

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

Geospeedometry in the inverted metamorphic gradient of the Nestos Thrust Zone in central Rhodope (Northern Greece)

NASA Astrophysics Data System (ADS)

Cioldi, Stefania; Moulas, Evangelos; Burg, Jean-Pierre

2015-04-01

Thrust tectonics and inverted metamorphic gradients are major consequences of large and likely fast movements of crustal segments in compressional environments. The purpose of this study is to investigate the tectonic setting and the timescale of inverted metamorphic zonations related to crustal-scale thrusting. The aim is to contribute understanding the link between mechanical and thermal evolution of major thrust zones and to clarify the nature and the origin of orogenic heat. The Rhodope metamorphic complex (Northern Greece) is interpreted as a part of the Alpine-Himalaya orogenic belt and represents a collisional system with an association of both large-scale thrusting and pervasive exhumation tectonics. The Nestos Shear Zone overprints the suture boundary with a NNE-dipping pile of schists displaying inverted isograds. The inverted metamorphic zones start from chlorite-muscovite grade at the bottom and reach kyanite-sillimanite grades with migmatites in the upper structural levels. In order to reconstruct the thermo-tectonic evolution of inverted metamorphic zonation, reliable geochronological data are essential. 40Ar/39Ar geochronology with step-heating technique on white mica from micaschists provided a temporal resolution with the potential to characterize shearing. 40Ar/39Ar dating across the Nestos Shear Zone yields Late Eocene-Early Oligocene (40-30 Ma) cooling (~400-350° C) ages, which correspond to local thermo-deformation episodes linked to late and post-orogenic intrusions. U-Pb Sensitive High Resolution Ion Microprobe (SHRIMP) zircon geochronology on leucosomes from migmatitic orthogneisses were considered to estimate the age of peak metamorphic conditions, contemporaneous with anatexis. U-Pb ages of zircon rims specify regional partial melting during the Early Cretaceous (160-120 Ma). This is in disagreement with previous assertions, which argued that the formation of leucosomes in this region is Late Eocene (42-35 Ma) and implied multiple

The lateral boundary of a metamorphic core complex: The Moutsounas shear zone on Naxos, Cyclades, Greece☆

PubMed Central

Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai

2013-01-01

We describe the structure, microstructures, texture and paleopiezometry of quartz-rich phyllites and marbles along N-trending Moutsounas shear zone at the eastern margin of the Naxos metamorphic core complex (MCC). Fabrics consistently indicate a top-to-the-NNE non-coaxial shear and formed during the main stage of updoming and exhumation between ca. 14 and 11 Ma of the Naxos MCC. The main stage of exhumation postdates the deposition of overlying Miocene sedimentary successions and predates the overlying Upper Miocene/Pliocene conglomerates. Detailed microstructural and textural analysis reveals that the movement along the Moutsounas shear zone is associated with a retrograde greenschist to subgreenschist facies overprint of the early higher-temperature rocks. Paleopiezometry on recrystallized quartz and calcite yields differential stresses of 20–77 MPa and a strain rate of 10−15–10−13 s−1 at 350 °C for quartz and ca. 300 °C for calcite. Chlorite geothermometry of the shear zone yields two temperature regimes, 300–360 °C, and 200–250 °C. The lower temperature group is interpreted to result from late-stage hydrothermal overprint. PMID:26523079

Histamine is a modulator of metamorphic competence in Strongylocentrotus purpuratus (Echinodermata: Echinoidea)

PubMed Central

2012-01-01

Background A metamorphic life-history is present in the majority of animal phyla. This developmental mode is particularly prominent among marine invertebrates with a bentho-planktonic life cycle, where a pelagic larval form transforms into a benthic adult. Metamorphic competence (the stage at which a larva is capable to undergo the metamorphic transformation and settlement) is an important adaptation both ecologically and physiologically. The competence period maintains the larval state until suitable settlement sites are encountered, at which point the larvae settle in response to settlement cues. The mechanistic basis for metamorphosis (the morphogenetic transition from a larva to a juvenile including settlement), i.e. the molecular and cellular processes underlying metamorphosis in marine invertebrate species, is poorly understood. Histamine (HA), a neurotransmitter used for various physiological and developmental functions among animals, has a critical role in sea urchin fertilization and in the induction of metamorphosis. Here we test the premise that HA functions as a developmental modulator of metamorphic competence in the sea urchin Strongylocentrotus purpuratus. Results Our results provide strong evidence that HA leads to the acquisition of metamorphic competence in S. purpuratus larvae. Pharmacological analysis of several HA receptor antagonists and an inhibitor of HA synthesis indicates a function of HA in metamorphic competence as well as programmed cell death (PCD) during arm retraction. Furthermore we identified an extensive network of histaminergic neurons in pre-metamorphic and metamorphically competent larvae. Analysis of this network throughout larval development indicates that the maturation of specific neuronal clusters correlates with the acquisition of metamorphic competence. Moreover, histamine receptor antagonist treatment leads to the induction of caspase mediated apoptosis in competent larvae. Conclusions We conclude that HA is a modulator

Detrital zircon and igneous protolith ages of high-grade metamorphic rocks in the Highland and Wanni Complexes, Sri Lanka: Their geochronological correlation with southern India and East Antarctica

NASA Astrophysics Data System (ADS)

Kitano, Ippei; Osanai, Yasuhito; Nakano, Nobuhiko; Adachi, Tatsuro; Fitzsimons, Ian C. W.

2018-05-01

The high-grade metamorphic rocks of Sri Lanka place valuable constraints on the assembly of central parts of the Gondwana supercontinent. They are subdivided into the Wanni Complex (WC), Highland Complex (HC) and Vijayan Complex (VC), but their correlation with neighbouring Gondwana terranes is hindered by a poor understanding of the contact between the HC and WC. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of remnant zircon cores from 45 high-grade metamorphic rocks in Sri Lanka reveals two domains with different age characteristics that correlate with the HC and WC and which help constrain the location of the boundary between them. The HC is dominated by detrital zircon ages of ca. 3500-1500 Ma from garnet-biotite gneiss, garnet-cordierite-biotite gneiss, some samples of garnet-orthopyroxene-biotite gneiss and siliceous gneiss (interpreted as paragneisses) and igneous protolith ages of ca. 2000-1800 Ma from garnet-hornblende-biotite gneiss, other samples of garnet-orthopyroxene-biotite gneiss, garnet-two-pyroxene granulite, two-pyroxene granulite and charnockite (interpreted as orthogneisses). In contrast, the WC is dominated by detrital zircon ages of ca. 1100-700 Ma from paragneisses and igneous protolith ages of ca. 1100-800 Ma from orthogneisses. This clearly suggests the HC and WC have different origins, but some of our results and previous data indicate their spatial distribution does not correspond exactly to the unit boundary proposed in earlier studies using Nd model ages. Detrital zircon and igneous protolith ages in the HC suggest that sedimentary protoliths were eroded from local 2000-1800 Ma igneous rocks and an older Paleoproterozoic to Archean craton. In contrast, the WC sedimentary protoliths were mainly eroded from local late Mesoproterozoic to Neoproterozoic igneous rocks with very minor components from an older 2500-1500 Ma craton, and in the case of the WC precursor sediments there was possibly

The "granite pump": LP/HT metamorphism and exhumation in the Montagne Nore (S-France)

NASA Astrophysics Data System (ADS)

Franke, W.; Doublier, M. P.; Doerr, W.; Stein, E.

2003-04-01

The Montagne Noire at the southern margin of the French Massif Central represents an exceptional case of a hot metamorphic core complex evolved from a thrust stack in a foreland position. The core of the structure (Zone Axiale) exposes granites and LP/HT gneisses up to anatectic grade. The hot core is encased by ENE-trending shear zones, which define a dextral pull-apart structure. Ductile extension is documented by top WSW shearing in the W, and ENE shearing in the E part of the Zone Axiale (eg, MATTE et al., 1998). Extension in ENE and reduction of the metamorphic profile are accompanied by NNW-directed contraction ("pinched pull-apart"). Palaeozoic sediments on the southern flank of the Zone Axiale exhibit only greenschist to diagenetic grades of metamorphism. Conodont alteration index (WIEDERER et al., 2002) and illite crystallinity (Doublier, this meeting) reveal a decrease of metamorphic temperature away from the hot core. Metamorphic isograds cut across the axial planes of D1 nappes. These features suggest that metamorphism was imposed by the rising hot core. Accordingly, the palaeozoic sediments show a tectonic evolution which closely resembles that of the gneissic core (extension top ENE, contraction in NNW). Structures relating to stacking (D1) have survived at the southern margin of the Montagne Noire. U-Pb studies (TIMS on single zircon and monazite) reveal peak metamorphism and magmatism already at c. 315 Ma (KLAMA et al., 2001), i.e., only <10 Ma after the end of flysch deposition in latest Visean/Early Namurian time (<= 323 Ma). The coincidence, within error, of the U-Pb ages and earlier Ar/Ar ages (MALUSKI et al., 1991) suggest rapid cooling. Synchronous granite emplacement and metamorphism is best explained by advective heating. Since granites are not generated in foreland settings, we propose derivation of the melts from areas of thickened crust adjacent to the N. Transport and emplacement of granites was essentially driven by the hydraulic

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

Nature and origin of fluids in granulite facies metamorphism

NASA Technical Reports Server (NTRS)

Newton, R. C.

1988-01-01

The various models for the nature and origin of fluids in granulite facies metamorphism were summarized. Field and petrologic evidence exists for both fluid-absent and fluid-present deep crustal metamorphism. The South Indian granulite province is often cited as a fluid-rich example. The fluids must have been low in H2O and thus high in CO2. Deep crustal and subcrustal sources of CO2 are as yet unproven possibilities. There is much recent discussion of the possible ways in which deep crustal melts and fluids could have interacted in granulite metamorphism. Possible explanations for the characteristically low activity of H2O associated with granulite terranes were discussed. Granulites of the Adirondacks, New York, show evidence for vapor-absent conditions, and thus appear different from those of South India, for which CO2 streaming was proposed. Several features, such as the presence of high-density CO2 fluid inclusions, that may be misleading as evidence for CO2-saturated conditions during metamorphism, were discussed.

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.

Evolution Process and Structural Analysis of Precambrian Jirisan Metamorphic and Sancheong Anorthosite Complexes in the Jirisan Province, Yeongnam Massif, Korea

NASA Astrophysics Data System (ADS)

Kang, J. H.; Lee, D. S.

2016-12-01

The Jirisan metamorphic complex consists mainly of schist, blastoporphyritic granite gneiss, granitic gneiss, leucocratic gneiss, biotite gneiss, banded gneiss, migmatitic gneiss and granite gneiss. The Paleoproterozoic (1.87 1.79 Ga) Sancheong anorthosite complex, which intrude it, is classified into massive-type and foliation-type Sancheong anorthosite, Fe-Ti ore body, and mafic granulite which were formed from the multiple fractionation and polybaric crystallization of the coeval and cogenetic magma. These complexes went at least through three times of ductile deformation during Early Proterozoic Late Paleozoic. The D1 deformation formed sheath or "A" type folds and its characteristic orientation was uncertain due to the intensive multi-deformation superimposed after that. The D2 deformation occurred under the EW- or WNW-directed tectonic compression, and formed a regional NS or NNE trend of isoclinal and intrafolial folds and an extensive ductile shear zone accompanied by mylonitization. The D3 deformation occurred under the NS- or NNW-directed tectonic compression environment, and formed an EW or ENE trend of open and tight folds and a partial semibrittle shear zone accompanied by mylonitization, and rearranged the NS-trend pre-D3 structural elements into (E)NE or (W)NW direction. The D2 deformation generally increases from the center toward the margin of Sancheong anorthosite complex but is more intensive in the eastern than western parts of Sancheong anorthosite complex. While the D3 deformation is inversely more intensive in the its western than eastern parts. The D2 and D3 deformations are closely related to the distribution features of Sancheong anorthosite complex. These three tectonic events are expected to give important information in understanding and reconstructing the tectonic movement after the formation of Columbia Supercontinent as well as the present NS-trend tectonic frame of the Jirisan province of the Yeongnam massif, the Korean Peninsula.

Stable isotope evidence for hydrologic conditions during regional metamorphism in the Panamint Mountains, California

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

Bergfeld, D.; Nabelek, P.I.; Labotka, T.C.

1992-01-01

The Kingston Peak Formation forms part of the Panamint Mountains, California, metamorphic core-complex. Peak tremolite-grade metamorphism as exhibited in Wildrose Canyon occurred in the Jurassic; a retrograde thermal event may have occurred in the Cretaceous. The formation consists dominantly of interbedded siliceous limestones and graphitic calcareous schists. Stable isotopic analysis shows two distinct groups of data. delta O-18 values of calcite from the limestones range between 15.3 and 17.3[per thousand], probably reflecting their original Proterozoic depositional values. Likewise the delta C-13 values are also unshifted, ranging from +1% to +3.8%o. In contrast, delta O-18 values of calcite from the schistsmore » are for the most part > 20[per thousand]. These high values could reflect the original depostional conditions; however, they may be due to equilibration with silicate minerals which range from 14.9 to 17.9[per thousand]. Overall, the combined oxygen and carbon isotopic data indicate that most isotopic changes can be explained by closed-system equilibration. Only a limited amount of interaction with externally-derived fluids during metamorphism is evident in the isotopic data. The interaction may have been confined to vicinities of faults and fractures which are common in Wildrose Canyon.« less

Metamorphism and aqueous alteration in low petrographic type ordinary chondrites

NASA Technical Reports Server (NTRS)

Xie, T.; Lipschutz, M. E.; Sears, D. W. G.; Guimon, R. K.; Jie, Lu; Benoit, P. H.; O'D. Alexander, C. M.; Wright, Ian; Pillinger, C.; Morse, A. D.;

Post-Metamorphic Thermal Anomaly across the Nacimiento Block, Central California: a Hydrothermal Overprint?

NASA Astrophysics Data System (ADS)

Lacroix, B.; Hughes, J.; Lahfid, A.; Delchini, S.

2017-12-01

The thermal history of the Nacimiento block located within the Franciscan Complex (California, USA) has been previously proposed based on both vitrinite reflectance (Rm) and illite cristallinity methods (Underwood et al., 1995). These authors suggest that the Nacimiento block is locally perturbed by a thermal anomaly (up to 300ºC), probably caused by post-metamorphic hydrothermal activity linked to the emplacement of an Au-deposit: the Los Burros Gold deposit. Although both thermal anomaly and deposit seem spatially correlated, their relationship is still poorly constrained. Detailed geological and structural mapping within the Los Burros Mining District (LBMD) coupled with a thermal study was conducted to better understand processes responsible for the anomalous temperatures recorded near the deposit. The regional maximum temperature reached by metasediments from the Nacimiento block have been first investigated using the Raman Spectroscopy of Carbonaceous Materials (RSCM) method. In addition, through careful fluid-inclusion and stable isotopes (O and C) studies on the deposit, the temperature and the potential source of the fluid responsible for the Los Burros Au-deposit emplacement were investigated. RSCM technique confirms the presence of a thermal anomaly in the range 260-320ºC near LBMD. However, our structural and petrographic results suggest that the thermal anomaly is not correlated to a post-metamorphic hydrothermal overprint but rather to a late, transpressive deformation uplifting buried metamorphic rocks.

Zircon and monazite response to prograde metamorphism in the Reynolds Range, central Australia

NASA Astrophysics Data System (ADS)

Rubatto, Daniela; Williams, Ian S.; Buick, Ian S.

2001-01-01

We report an extensive field-based study of zircon and monazite in the metamorphic sequence of the Reynolds Range (central Australia), where greenschist- to granulite-facies metamorphism is recorded over a continuous crustal section. Detailed cathodoluminescence and back-scattered electron imaging, supported by SHRIMP U-Pb dating, has revealed the different behaviours of zircon and monazite during metamorphism. Monazite first recorded regional metamorphic ages (1576 ± 5 Ma), at amphibolite-facies grade, at ˜600 °C. Abundant monazite yielding similar ages (1557 ± 2 to 1585 ± 3 Ma) is found at granulite-facies conditions in both partial melt segregations and restites. New zircon growth occurred between 1562 ± 4 and 1587 ± 4 Ma, but, in contrast to monazite, is only recorded in granulite-facies rocks where melt was present (≥700 °C). New zircon appears to form at the expense of pre-existing detrital and inherited cores, which are partly resorbed. The amount of metamorphic growth in both accessory minerals increases with temperature and metamorphic grade. However, new zircon growth is influenced by rock composition and driven by partial melting, factors that appear to have little effect on the formation of metamorphic monazite. The growth of these accessory phases in response to metamorphism extends over the 30 Ma period of melt crystallisation (1557-1587 Ma) in a stable high geothermal regime. Rare earth element patterns of zircon overgrowths in leucosome and restite indicate that, during the protracted metamorphism, melt-restite equilibrium was reached. Even in the extreme conditions of long-lasting high temperature (750-800 °C) metamorphism, Pb inheritance is widely preserved in the detrital zircon cores. A trace of inheritance is found in monazite, indicating that the closure temperature of the U-Pb system in relatively large monazite crystals can exceed 750-800 °C.

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

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

The Mt. Ochi melange (South Evvia Island, Greece): a case study for HP metamorphism and syn-convergent exhumation.

NASA Astrophysics Data System (ADS)

Moustaka, Eleni; Soukis, Konstantinos; Huet, Benjamin; Lozios, Stylianos; Magganas, Andreas

2014-05-01

The Attic-Cycladic complex (central Aegean Sea, Greece) experienced profound extension since at least the Oligo-Miocene boundary during which the previously thickened crust was reworked by a series of detachments forming the NE directed North Cycladic Detachment System (NCDS) and the SSW directed West Cycladic Detachment System (WCDS). South Evvia Island is located at the northwestern part of the Attic Cycladic complex linking the highly thinned and polymetamorphosed central part of the complex with mainland Greece. Furthermore, greenschists-facies retrograde metamorphism has only partially overprinted the HP mineral assemblages. Consequently, it is an ideal area to study tectonic processes associated with subduction, HP metamorphism and subsequent exhumation from eclogitic depths to the surface. Geological mapping in 1:2:000 scale revealed that the tectonostratigraphy of Mt. Ochi includes three distinct units all metamorphosed in HP conditions followed by greenschist facies overprint. These units are from top to bottom a) the Ochi Unit, a thick metavolcanosedimentary sequence with some intensely folded cipoline marble intercalations and isolated occurrences of metabasic rocks b) the ophiolitic mélange (metagabbros, metawherlites, peridotites, metabasites within a metasedimentary+serpentinite matrix) and c) the lowermost Styra Unit, a cipoline marble-dominated unit with thin mica schists and rare quartzitic layers often boudinaged. The thrust fault that was responsible for the juxtaposition of these three units acted in an early stage during HP metamorphism and it was isoclinally folded and sheared by the following syn-metamorphic deformation events. Detailed structural study in meso- and microscopic scale combined with petrological and geochemical analyses of the Mt Ochi rocks led to the distinction of at least three syn-metamorphic and two post-metamorphic deformation episodes that affected all units. The oldest structure identified is a relic foliation formed

Volatile transfer and recycling at convergent margins: Mass-balance and insights from high-P/T metamorphic rocks

NASA Astrophysics Data System (ADS)

Bebout, Gray E.

The efficiency with which volatiles are deeply subducted is governed by devolatilization histories and the geometries and mechanisms of fluid transport deep in subduction zones. Metamorphism along the forearc slab-mantle interface may prevent the deep subduction of many volatile components (e.g., H2O, Cs, B, N, perhaps As, Sb, and U) and result in their transport in fluids toward shallower reservoirs. The release, by devolatilization, and transport of such components toward the seafloor or into the forearc mantle wedge, could in part explain the imbalances between the estimated amounts of subducted volatiles and the amounts returned to Earth's surface. The proportion of the initially subducted volatile component that is retained in rocks subducted to depths greater than those beneath magmatic arcs (>100 km) is largely unknown, complicating assessments of deep mantle volatile budgets. Isotopic and trace element data and volatile contents for the Catalina Schist, the Franciscan Complex, and eclogite-facies complexes in the Alps (and elsewhere) provide insight into the nature and magnitude of fluid production and transport deep in subduction zones and into the possible effects of metamorphism on the compositions of subducting rocks. Compatibilities of the compositions of the subduction-related rocks and fluids with the isotopic and trace element compositions of various mantle-derived materials (igneous rocks, xenoliths, serpentinite seamounts) indicate the potential to trace the recycling of rock and fluid reservoirs chemically and isotopically fractionated during subduction-zone metamorphism.

Raman spectral characteristics of magmatic-contact metamorphic coals from Huainan Coalfield, China

NASA Astrophysics Data System (ADS)

Chen, Shancheng; Wu, Dun; Liu, Guijian; Sun, Ruoyu

2017-01-01

Normal burial metamorphism of coal superimposed by magmatic-contact metamorphism makes the characteristics of the Raman spectrum of coal changed. Nine coal samples were chosen at a coal transect perpendicular to the intrusive dike, at the No. 3 coal seam, Zhuji Coal Mine, Huainan Coalfield, China, with different distances from dike-coal boundary (DCB). Geochemical (proximate and ultimate) analysis and mean random vitrinite reflectance (R0, %) indicate that there is a significant relationship between the values of volatile matter and R0 in metamorphosed coals. Raman spectra show that the graphite band (G band) becomes the major band but the disordered band (D band) disappears progressively, with the increase of metamorphic temperature in coals, showing that the structural organization in high-rank contact-metamorphosed coals is close to that of well-crystallized graphite. Evident relationships are observed between the calculated Raman spectral parameters and the peak metamorphic temperature, suggesting some spectral parameters have the potentials to be used as geothermometers for contact-metamorphic coals.

Timing and conditions of regional metamorphism and crustal shearing in the granulite facies basement of south Namibia: Implications for the crustal evolution of the Namaqualand metamorphic basement in the Mesoproterozoic

NASA Astrophysics Data System (ADS)

Bial, Julia; Büttner, Steffen; Appel, Peter

2016-11-01

Granulite facies basement gneisses from the Grünau area in the Kakamas Domain of the Namaqua-Natal Metamorphic Province in south Namibia show high-grade mineral assemblages, most commonly consisting of garnet, cordierite, sillimanite, alkali feldspar and quartz. Cordierite + hercynitic spinel, and in some places quartz + hercynitic spinel, indicate granulite facies P-T conditions. The peak assemblage equilibrated at 800-850 °C at 4.0-4.5 kbar. Sillimanite pseudomorphs after kyanite1 and late-stage staurolite and kyanite2 indicate that the metamorphic record started and ended within the stability field of kyanite. Monazite in the metamorphic basement gneisses shows a single-phase growth history dated as 1210-1180 Ma, which we interpret as the most likely age of the regional metamorphic peak. This time coincides with the emplacement of granitic plutons in the Grünau region. The ∼10 km wide, NW-SE striking Grünau shear zone crosscuts the metamorphic basement and overprints high-temperature fabrics. In sheared metapelites, the regional metamorphic peak assemblage is largely obliterated, and is replaced by synkinematic biotite2, quartz, alkali feldspar, sillimanite and cordierite or muscovite. In places, gedrite, staurolite, sillimanite and green biotite3 may have formed late- or post-kinematically. The mylonitic mineral assemblage equilibrated at 590-650 °C at 3.5-5.0 kbar, which is similar to a retrograde metamorphic stage in the basement away from the shear zone. Monazite cores in two mylonite samples are similar in texture and age (∼1200 Ma) to monazite in metapelites away from the shear zone. Chemically distinct monazite rims indicate a second growth episode at ∼1130-1120 Ma. This age is interpreted to date the main deformation episode along the Grünau shear zone and the retrograde metamorphic stage seen in the basement. The main episode of ductile shearing along the Grünau shear zone took place 70-80 million years after the thermal peak metamorphism

The Age and Geodynamic Evolution of the Metamorphic sole rocks from Izmir-Ankara-Erzıncan suture zone (Northern-Turkey)

NASA Astrophysics Data System (ADS)

Melih Çörtük, Rahmi; Faruk Çelik, Ömer; Özkan, Mutlu; Sherlock, Sarah C.; Marzoli, Andrea; Altıntaş, İsmail Emir; Topuz, Gültekin

2016-04-01

The İzmir-Ankara-Erzincan suture zone in northern Turkey is one of the major tectonic zones separating the Pontides to the North from the Anatolide-Tauride block and Kı rşehir Massif to the South. The accretionary complex of the İzmir-Ankara-Erzincan suture zone, near Artova, is composed mainly of peridotites with varying degree serpentinization, metamorphic rocks, basalt, sandstones, pelagic and neritic limestones. The metamorphic rocks are represented by amphibolite, garnet micaschit, calc-schist and marble. The metamorphic rocks were interpreted as the metamorphic sole rocks. Because; (i) They are tectonically located beneath the serpentinized peridotites. (ii) Foliation planes of both the amphibolites and mantle tectonites are parallel to each other. (iii) The metamorphic rocks are crosscut by non-metamorphic dolerite dikes which exhibite Nb and Ta depletion relative to Th enrichment on the N-MORB normalized multi-element spider diagram. The dolerite dikes display flat REE patterns (LaN/YbN=0.85-1.24). These geochemical signatures of the dolerite dikes are indicative of subduction component during their occurrences. Geochemical observations of the amphibolites suggest E-MORB- and OIB-like signatures (LaN/SmN= 1.39-3.14) and their protoliths are represented by basalt and alkali basaltic rocks. Amphiboles from the amphibolites are represented by calcic amphiboles (magnesio-hornblende, tchermakite and tremolite) and they yielded 40Ar-39Ar ages between 157.8 ± 3.6 Ma and 139 ± 11 Ma. These cooling ages were interpreted to be the intra-oceanic subduction/thrusting time of the İzmir-Ankara-Erzincan oceanic domain. This study was funded by TÜBİTAK (Project no: 112Y123).

Microprobe monazite geochronology: new techniques for dating deformation and metamorphism

NASA Astrophysics Data System (ADS)

Williams, M.; Jercinovic, M.; Goncalves, P.; Mahan, K.

2003-04-01

High-resolution compositional mapping, age mapping, and precise dating of monazite on the electron microprobe are powerful additions to microstructural and petrologic analysis and important tools for tectonic studies. The in-situ nature and high spatial resolution of the technique offer an entirely new level of structurally and texturally specific geochronologic data that can be used to put absolute time constraints on P-T-D paths, constrain the rates of sedimentary, metamorphic, and deformational processes, and provide new links between metamorphism and deformation. New analytical techniques (including background modeling, sample preparation, and interference analysis) have significantly improved the precision and accuracy of the technique and new mapping and image analysis techniques have increased the efficiency and strengthened the correlation with fabrics and textures. Microprobe geochronology is particularly applicable to three persistent microstructural-microtextural problem areas: (1) constraining the chronology of metamorphic assemblages; (2) constraining the timing of deformational fabrics; and (3) interpreting other geochronological results. In addition, authigenic monazite can be used to date sedimentary basins, and detrital monazite can fingerprint sedimentary source areas, both critical for tectonic analysis. Although some monazite generations can be directly tied to metamorphism or deformation, at present, the most common constraints rely on monazite inclusion relations in porphyroblasts that, in turn, can be tied to the deformation and/or metamorphic history. Examples will be presented from deep-crustal rocks of northern Saskatchewan and from mid-crustal rocks from the southwestern USA. Microprobe monazite geochronology has been used in both regions to deconvolute overprinting deformation and metamorphic events and to clarify the interpretation of other geochronologic data. Microprobe mapping and dating are powerful companions to mass spectroscopic

Garnet zoning and metamorphism of the Barrovian type area, Scotland

NASA Astrophysics Data System (ADS)

Dempster, T. J.

1985-03-01

A microprobe investigation of the high grade metamorphic zones from the Barrovian type area in Angus, Scotland, shows the importance of local zones of retrograde cation exchange between garnet, staurolite and biotite. The interpretation of this zoning, established during a slow cooling history, is critical to any study of metamorphic reactions or conditions. The extent and intensity of these diffusion effects are dependent on a number of parameters including grainsize, fabric orientation, heating and cooling history, and the modal abundance of the phases. Increasing diffusion within garnets with metamorphic grade, and the subsequent retrograde effects are modelled using Temperature-Time-Transformation diagrams and provide information on the activation energy for Fe-Mg diffusion in garnet.

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.

Chemical and mineralogical data and processing methods management system prototype with application to study of the North Caucasus Blybsky Metamorphic Complexes metamorphism PT-condition

NASA Astrophysics Data System (ADS)

Ivanov, Stanislav; Kamzolkin, Vladimir; Konilov, Aleksandr; Aleshin, Igor

2014-05-01

There are many various methods of assessing the conditions of rocks formation based on determining the composition of the constituent minerals. Our objective was to create a universal tool for processing mineral's chemical analysis results and solving geothermobarometry problems by creating a database of existing sensors and providing a user-friendly standard interface. Similar computer assisted tools are based upon large collection of sensors (geothermometers and geobarometers) are known, for example, the project TPF (Konilov A.N., 1999) - text-based sensor collection tool written in PASCAL. The application contained more than 350 different sensors and has been used widely in petrochemical studies (see A.N. Konilov , A.A. Grafchikov, V.I. Fonarev 2010 for review). Our prototype uses the TPF project concept and is designed with modern application development techniques, which allows better flexibility. Main components of the designed system are 3 connected datasets: sensors collection (geothermometers, geobarometers, oxygen geobarometers, etc.), petrochemical data and modeling results. All data is maintained by special management and visualization tools and resides in sql database. System utilities allow user to import and export data in various file formats, edit records and plot graphs. Sensors database contains up to date collections of known methods. New sensors may be added by user. Measured database should be filled in by researcher. User friendly interface allows access to all available data and sensors, automates routine work, reduces the risk of common user mistakes and simplifies information exchange between research groups. We use prototype to evaluate peak pressure during the formation of garnet-amphibolite apoeclogites, gneisses and schists Blybsky metamorphic complex of the Front Range of the Northern Caucasus. In particular, our estimation of formation pressure range (18 ± 4 kbar) agrees on independent research results. The reported study was

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

Late Cretaceous Localized Crustal Thickening as a Primary Control on the 3-D Architecture and Exhumation Histories of Cordilleran Metamorphic Core Complexes

NASA Astrophysics Data System (ADS)

Gans, P. B.; Wong, M.

2014-12-01

The juxtaposition of mylonitic mid-crustal rocks and faulted supracrustal rocks in metamorphic core complexes (MMCs) is usually portrayed in 2 dimensions and attributed to a single event of large-scale slip ± isostatic doming along a low-angle "detachment fault"/ shear zone. This paradigm does not explain dramatic along strike (3-D) variations in slip magnitude, footwall architecture, and burial / exhumation histories of most MMCs. A fundamental question posed by MMCs is how did their earlier thickening and exhumation histories influence the geometric evolution and 3-D slip distribution on the subsequent detachment faults? New geologic mapping and 40Ar/39Ar thermochronology from the Snake Range-Kern Mts-Deep Creek Mts (SKDC) complex in eastern Nevada offer important insights into this question. Crustal shortening and thickening by large-scale non-cylindrical recumbent folds and associated thrust faults during the late Cretaceous (90-80 Ma) resulted in deep burial (650°C, 20-25 km) of the central part of the footwall, but metamorphic grade decreases dramatically to the N and S in concert with decreasing amplitude on the shortening structures. Subsequent Paleogene extensional exhumation by normal faulting and ESE-directed mylonitic shearing is greatest in areas of maximum earlier thickening and brought highest grade rocks back to depths of~10-12 km. After ≥15 Ma of quiescence, rapid E-directed slip initiated along the brittle Miocene Snake Range detachment at 20 Ma and reactivated the Eocene shear zone. The ≥200°C gradient across the footwall at this time implies that the Miocene slip surface originated as a moderately E-dipping normal fault. This Miocene slip surface can be tracked for more than 100 km along strike, but the greatest amount of Miocene slip also coincides with parts of the footwall that were most deeply buried in the Cretaceous. These relations indicate that not only is the SKDC MMC a composite feature, but that the crustal welt created by

Magnetic properties of Apollo 14 breccias and their correlation with metamorphism.

NASA Technical Reports Server (NTRS)

Gose, W. A.; Pearce, G. W.; Strangway, D. W.; Larson, E. E.

1972-01-01

The magnetic properties of Apollo 14 breccias can be explained in terms of the grain size distribution of the interstitial iron which is directly related to the metamorphic grade of the sample. In samples 14049 and 14313 iron grains less than 500 A in diameter are dominant as evidenced by a Richter-type magnetic aftereffect and hysteresis measurements. Both samples are of lowest metamorphic grade. The medium metamorphic-grade sample 14321 and the high-grade sample 14312 both show a logarithmic time-dependence of the magnetization indicative of a wide range of relaxation times and thus grain sizes, but sample 14321 contains a stable remanent magnetization whereas sample 14312 does not. This suggests that small multidomain particles (less than 1 micron) are most abundant in sample 14321 while sample 14312 is magnetically controlled by grains greater than 1 micron. The higher the metamorphic grade, the larger the grain size of the iron controlling the magnetic properties.

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

Pathway to 50% efficient inverted metamorphic concentrator solar cells

NASA Astrophysics Data System (ADS)

Geisz, John F.; Steiner, Myles A.; Jain, Nikhil; Schulte, Kevin L.; France, Ryan M.; McMahon, William E.; Perl, Emmett E.; Horowitz, Kelsey A. W.; Friedman, Daniel J.

2017-09-01

Series-connected five (5J) and six junction (6J) concentrator solar cell strategies have the realistic potential to exceed 50% efficiency to enable low-cost CPV systems. We propose three strategies for developing a practical 6J device. We have overcome many of the challenges required to build such concentrator solar cell devices: We have developed 2.1 eV AlGaInP, 1.7 eV AlGaAs, and 1.7 eV GaInAsP junctions with external radiative efficiency greater than 0.1%. We have developed a transparent tunnel junction that absorbs minimal light intended for the second junction yet resists degradation under thermal load. We have developed metamorphic grades from the GaAs to the InP lattice constant that are transparent to sub-GaAs bandgap light. We have grown and compared low bandgap junctions (0.7eV - 1.2 eV) using metamorphic GaInAs, metamorphic GaInAsP, and GaInAsP lattice-matched to InP. And finally, we have demonstrated excellent performance in a high voltage, low current 4 junction inverted metamorphic device using 2.1, 1.7, 1.4, and 1.1 eV junctions with over 8.7 mA/cm2 one-sun current density that operates up to 1000 suns without tunnel junction failure.

Pathway to 50% Efficient Inverted Metamorphic Concentrator Solar Cells

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

Geisz, John F; Steiner, Myles A; Jain, Nikhil

Series-connected five (5J) and six junction (6J) concentrator solar cell strategies have the realistic potential to exceed 50% efficiency to enable low-cost CPV systems. We propose three strategies for developing a practical 6J device. We have overcome many of the challenges required to build such concentrator solar cell devices: We have developed 2.1 eV AlGaInP, 1.7 eV AlGaAs, and 1.7 eV GaInAsP junctions with external radiative efficiency greater than 0.1%. We have developed a transparent tunnel junction that absorbs minimal light intended for the second junction yet resists degradation under thermal load. We have developed metamorphic grades from the GaAsmore » to the InP lattice constant that are transparent to sub-GaAs bandgap light. We have grown and compared low bandgap junctions (0.7eV - 1.2 eV) using metamorphic GaInAs, metamorphic GaInAsP, and GaInAsP lattice-matched to InP. And finally, we have demonstrated excellent performance in a high voltage, low current 4 junction inverted metamorphic device using 2.1, 1.7, 1.4, and 1.1 eV junctions with over 8.7 mA/cm2 one-sun current density that operates up to 1000 suns without tunnel junction failure.« less

Clumped isotope thermometry of calcite and dolomite in a contact metamorphic environment

NASA Astrophysics Data System (ADS)

Lloyd, Max K.; Eiler, John M.; Nabelek, Peter I.

2017-01-01

Clumped isotope compositions of slowly-cooled calcite and dolomite marbles record apparent equilibrium temperatures of roughly 150-200 °C and 300-350 °C, respectively. Because clumped isotope compositions are sensitive to the details of T-t path within these intervals, measurements of the Δ47 values of coexisting calcite and dolomite can place new constraints on thermal history of low-grade metamorphic rocks over a large portion of the upper crust (from ∼5 to ∼15 km depth). We studied the clumped isotope geochemistry of coexisting calcite and dolomite in marbles from the Notch Peak contact metamorphic aureole, Utah. Here, flat-lying limestones were intruded by a pluton, producing a regular, zoned metamorphic aureole. Calcite Δ47 temperatures are uniform, 156 ± 12 °C (2σ s.e.), across rocks varying from high-grade marbles that exceeded 500 °C to nominally unmetamorphosed limestones >5 km from the intrusion. This result appears to require that the temperature far from the pluton was close to this value; an ambient temperature just 20 °C lower would not have permitted substantial re-equilibration, and should have preserved depositional or early diagenetic Δ47 values several km from the pluton. Combining this result with depth constraints from overlying strata suggests the country rock here had an average regional geotherm of 22.3-27.4 °C/km from the late Jurassic Period until at least the middle Paleogene Period. Dolomite Δ47 in all samples above the talc + tremolite-in isograd record apparent equilibrium temperatures of 328-12+13 °C (1σ s.e.), consistent with the apparent equilibrium blocking temperature we expect for cooling from peak metamorphic conditions. At greater distances, dolomite Δ47 records temperatures of peak (anchi)metamorphism or pre-metamorphic diagenetic conditions. The interface between these domains is the location of the 330 °C isotherm associated with intrusion. Multiple-phase clumped isotope measurements are complemented by

Age of metamorphic events : petrochronology and hygrochronology

NASA Astrophysics Data System (ADS)

Bosse, Valerie; Villa, Igor M.

2017-04-01

Geodynamic models of the lithosphere require quantitative data from natural samples. Time is a key parameter: it allows to calculate rates and duration of geological processes and provides informations about the involved physical processes (Vance et al. 2003). Large-scale orogenic models require linking geochronological data with other parameters: structures, kinematics, magmatic and metamorphic petrology (P-T-A-X conditions), thermobarometric evolution of the lithosphere, chemical dynamics (Muller, 2003). This requires geochronometers that are both powerful chemical and petrological tracers. In-situ techniques allow dating a mineral in its petrological-microstructural environment. Getting a "date" has become quite easy... But what do we date in the end ? What is the link between the numbers obtained from the mass spectrometer and the age of the metamorphic event we are trying to date ? How can we transform the date into a geological meaningful age ? What do we learn about the behavior of the geochronometer minerals? Now that we can perform precise dating on very small samples directly in the studied rock, it is important to improve the way we interpret the ages to give them more pertinence in the geodynamic context. We propose to discuss the Th/U/Pb system isotopic closure in various metamorphic contexts using our published examples of in situ dating on monazite and zircon (Bosse et al. 2009; Didier et al. 2014, 2015). The studied examples show that (i) fluid assisted dissolution-precipitation processes rather than temperature-dependent solid diffusion predominantly govern the closure of the Th/U/Pb system (ii) monazite and zircon are sensitive to the interaction with fluids of specific composition (F, CO2, K ...), even at low temperature (iii) in the absence of fluids, monazite is able to record HT events and to retain this information in poly-orogenic contexts or during partial melting events (iv) complex chemical and isotopic zonations, well known in monazite

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.

The "Key" Method of Identifying Igneous and Metamorphic Rocks in Introductory Laboratory.

ERIC Educational Resources Information Center

Eves, Robert Leo; Davis, Larry Eugene

1987-01-01

Proposes that identification keys provide an orderly strategy for the identification of igneous and metamorphic rocks in an introductory geology course. Explains the format employed in the system and includes the actual key guides for both igneous and metamorphic rocks. (ML)

Age and tectonic implications of some low-grade metamorphic rocks from the Yucatan Channel

USGS Publications Warehouse

Vedder, J.G.; MacLeod, N.S.; Lanphere, M.A.; Dillon, William P.

1973-01-01

Phyllite and marble dredged from the lower part of the continental slope between Cuba and the Yucatan Peninsula seem to support the contention that a pre-early Tertiary metamorphic belt extends from the western Greater Antilles into northern Central America. The minimum K-Ar ages derived from the samples suggest that the metamorphic event was pre-Late Cretaceous, and evaluation of the K-Ar data implies that this metamorphic event is not older than Late Jurassic. Greater antiquity, however, is inferred from structural and stratigraphic relations in British Honduras, where the latest regional metamorphic event was post-Early Permian and pre-Middle Jurassic.  Rifting and extension related to plate motions along the British Honduras Quintana Roo margin through Mesozoic and earliest Cenozoic time presumably would preclude extensive regional metamorphism, permitting only limited development of schistose rocks there during that interval. The timing of metamorphic events in western Cuba is uncertain, but a pre-Middle Jurassic episode possibly is reflected in the phyllite and marble terranes of Isla de Pinos and Sierra de Trinidad. Local incipient metamorphism of Early and Middle Jurassic strata in the Sierra de los Organos may have resulted from severe tectonism that began in Late Cretaceous time and diminished in the Eocene.

Evidence for pre-Taconic metamorphism in the Potomac terrane, Maryland and Virginia: Hornblende and Muscovite [sup 40]Ar/[sup 39]Ar results

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

Becker, J.L.; Wintsch, R.P.; Kunk, M.J.

1993-03-01

New [sup 40]Ar/[sup 39]Ar age spectra of hornblende and white mica from the Great Falls area of the Potomac terrane of Maryland and Virginia indicate pre-Taconic metamorphism. Age spectra of hornblende samples are interpreted to represent cooling from peak metamorphic conditions through their closure temperatures for argon diffusion ([approximately]500C) at about 490 Ma. These older Ordovician postmetamorphic cooling ages strongly contrast with younger post-Ordovician metamorphic cooling ages now being reported in the Blue Ridge and Goochland terranes to the west and east respectively. A late phyllitic sheen observed on rocks in the field and petrographic observations of undulose plagioclase andmore » amphibole, and older muscovite, and kinked primary muscovite in the Bear Island Granodiorite reflect a younger retrogressive metamorphism involving the growth of secondary muscovite (Fisher's S4 ). [sup 40]Ar/[sup 39]Ar Age spectra of white micas from the Bear Island Granodiorite are complex and probably indicate both primary and secondary white mica, the latter apparently growing below the closure temperature for retention of argon in muscovite ([approximately]350C). The age spectra permit an estimate of a minimum age of 420 Ma for cooling through closure of the older generation of white mica. The above ages of hornblende and muscovite closure imply a minimum cooling rate of [approximately]2C/m.y., and exhumation rate of about 1 mm/yr. The projected time of peak metamorphism at upper amphibolite facies for the Great Falls area clearly predates the Ordovician Taconic orogeny and suggests that these rocks escaped this event and largely escaped younger Paleozoic metamorphic events, which are well documented in adjacent terranes.« less

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

A conceptual model for the development of pristine drainage systems during exhumation of metamorphic core complexes

NASA Astrophysics Data System (ADS)

Trost, Georg; Neubauer, Franz; Robl, Jörg

2017-04-01

Metamorphic core complexes (MCCs) are defined as large scale geological features of domal shape. The essential characteristic comprises metamorphic rocks, which have been exhumed from lower crustal levels and now are exposed to the surface. The updoming process occurs at different tectonic settings of high strain zones initially exposing pristine gently dipping fault planes to Earth's surface. Consequently, the dome shape highly influences the type of adaption of the drainage systems to the active landforms. However, drainage systems and their characteristic metrics in regions shaped by MCCs have only been sparsely investigated and were not examined regarding the distinction between different MCC-types (A-type, B-type, C-type). In this study we investigate the drainage patterns of MCCs formed by different tectonic settings and build up a conceptual model for the development of the drainage systems under these conditions. We apply the χ-method to detect variations in uplift, as well as spatial unconformities in the drainage patterns. The χ-method is a mathematical approach to transform stream longitudinal profiles to the χ space where the slope of steady state profiles is solely dependent on uplift rate and bedrock erodibility. From this transformation we calculate color-coded χ-maps and χ-profiles of the main streams draining the MCCs. The applied method allows the interpretation of channel metrics in terms of (a) spatial gradients in uplift rate and (b) the time dependent evolution of drainage divides including drainage divide migration. Our results show a high variation in the shape and greatest elevation of the χ-profiles. This indicates the migration of active uplift zones along the dome axes. Even though only MCCs younger than Miocene age are investigated, the shape of the χ-profiles clearly points to different development stages of these areas. K-profiles plotted over the detachment underlying an active updoming process show concave shaped �

P-T-t conditions, Nd and Pb isotopic compositions and detrital zircon geochronology of the Massabesic Gneiss Complex, New Hampshire: isotopic and metamorphic evidence for the identification of Gander basement, central New England

USGS Publications Warehouse

Dorais, Michael J.; Wintsch, Robert P.; Kunk, Michael J.; Aleinikoff, John; Burton, William; Underdown, Christine; Kerwin, Charles M.

2012-01-01

We present new evidence for the assignment of the Neoproterozoic Massabesic Gneiss Complex of New Hampshire to the Gander terrane rather than the Avalon terrane. The majority of Avalonian (sensu stricto) igneous and meta-igneous rocks as defined in Maritime Canada have positive whole-rock ɛNd compared to more negative values for Gander rocks, although there is a region of overlap in ɛNd between the two terranes. Our samples from areas in Connecticut previously thought to be Avalonian and samples from the Willimantic dome have the same isotopic signatures as Maritime Canada Avalon. In contrast, samples from the Clinton dome of southern Connecticut plots exclusively in the Gander field. The majority of the orthogneiss samples from Lyme dome (coastal Connecticut), Pelham dome (central Massachusetts) and Massabesic Gneiss Complex also plot in the Gander field, with a few samples plotting in the overlap zone between Gander and Avalon. U-Pb age distributions of detrital zircon populations from quartzites from the Massabesic Gneiss Complex more closely approximate the data from the Lyme Dome rather than Avalon. Additionally, the similarity of the P-T-t path for the rocks of the Massabesic Gneiss Complex (established by thermobarometry and 40Ar/39Ar dating of amphibole, muscovite, biotite and K-feldspar) with that established in the Ganderian Lyme dome of southern Connecticut strengthens the assignment of these rocks to a single Gander block that docked to Laurentia during the Salinic Orogeny. The identification of Ganderian isotopic signatures for these rocks all of which show evidence for Alleghanian metamorphism, supports the hypothesis that Neoproterozoic Gander lower crustal rocks underlie southern New Hampshire, Massachusetts, and Connecticut, and that all rocks of the overlying Central Maine trough that largely escaped high-grade Alleghanian metamorphism are allochthonous. We suggest that during the Alleghanian, the docking of Gondwana caused Avalon to wedge into

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.

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.

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

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

First evidence of the Ellesmerian metamorphism on Svalbard

NASA Astrophysics Data System (ADS)

Kośmińska, Karolina; Majka, Jarosław; Manecki, Maciej; Schneider, David A.

2016-04-01

The Ellesmerian fold-and-thrust belt is exposed in the High Arctic from Ellesmere Island in the east, through North Greenland, to Svalbard in the west (e.g. Piepjohn et al., 2015). It developed during Late Devonian - Early Carboniferous, and overprinted older (mainly Caledonian) structures. It is thought that this fold-and-thrust belt was formed due to collision of the Pearya Terrane and Svalbard with the Franklinian Basin of Laurentia. Traditionally, the Ellesmerian fold-and-thrust belt comprises a passive continental margin affected by foreland deformation processes, but the exact larger scale tectonic context of this belt is disputable. It is partly because the Eocene Eurekan deformation superimposed significantly the Ellesmerian structures, thus making the reconstruction of the pre-Eurekan history very difficult. Here we present for the first time evidence for Ellesmerian metamorphism within the crystalline basement of Svalbard. These rocks are exposed in the Pinkie unit on Prins Karls Forland (W-Svalbard), which exhibits tectonic contacts with the overlying sequences. The Pinkie unit is mainly composed of strongly deformed lithologies such as laminated quartzites, siliciclastic rocks and garnet-bearing mica schists. Detrital zircon dating yielded ages as young as Neoproterozoic (0.95-1.05 Ga), thus the Pinkie unit is considered to be Neoproterozoic (Kośmińska et al., 2015a). The M1 assemblages and D1 structures are affected by D2 mylonitization (cf. Faehnrich et al., 2016, this meeting). Petrological characterization and Th-U-total Pb chemical monazite dating have been performed on the Pinkie metapelites. These rocks exhibit an apparent inverted Barrovian metamorphic sequence, within which three metamorphic zones have been distinguished: garnet+staurolite+muscovite+biotite, garnet+staurolite+kyanite+muscovite+biotite, garnet+kyanite+muscovite+biotite. The P-T estimates using the QuiG barometry coupled with thermodynamic modelling revealed that the

Late-Paleozoic-Mesozoic deformational and deformation related metamorphic structures of Kuznetsk-Altai region

NASA Astrophysics Data System (ADS)

Zinoviev, Sergei

2014-05-01

deformation systems. 2) folded (folded-thrust) deformation systems combine deformation zones with relic lenses of Paleozoid substratum, and predominantly conform systems of the main faults. Despite a high degree of regional deformation the sedimentary-stratified and intrusive-contact relations of geological bodies are stored within the deformation systems, and this differs in the main the collision systems from zones of dynamic metamorphism. 3) regional zones of dynamic metamorphism of Kuznetsk-Altai region are the concentration belts of multiple mechanic deformations and contrast dynamometamorphism of complexes. The formational basis of dynamic metamorphism zones is tectonites of the collision stage. Zones of dynamic metamorphism attract special attention in the structural model of Kuznetsk-Altai region. They not only form the typical tectonic framework of collision sutures, but also contain the main part of ore deposits of this region. Pulse mode of structure formation of Kuznetsk-Altai region is detected. Major collision events in Kuznetsk-Altai region were in the late-Carboniferous-Triassic time (307-310, 295-285, 260-250 and 240-220 Ma). This study was supported by a grant of the Russian Foundation for Basic Research (project nos. 14-05-00117).

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

Late Neoproterozoic metamorphic assemblages along the Pan-African Hamisana Shear Zone, southeastern Egypt: Metamorphism, geochemistry and petrogenesis

NASA Astrophysics Data System (ADS)

Ali-Bik, Mohamed W.; Sadek, Mohamed F.; Ghabrial, Doris Sadek

2014-11-01

A variety of Late Neoproterozoic gneisses and amphibolites are distributed along the N-S trending Hamisana Shear Zone (HSZ), in southeastern Egypt. The HSZ originated after the accretion of the Arabian-Nubian Shield (ANS) and covers an area of about 1500 km2 in southeastern Egypt and northeastern Sudan. The architecture of the northern part of the HSZ is best explained as a tectono-stratigraphic column, in which allochthonous ophiolitic mélange was thrusted onto metamorphosed island-arc assemblages (gneisses and amphibolites). The latter rock units were generally subjected to two successive phases of amphibolite facies metamorphism, followed by a thermal phase and retrograde overprint. The early penetrative, low- to medium-pressure metamorphism (M1) was synchronous with D1-gneissosity and N-S trending lineation, demarcating the high strain HSZ. The mineral assemblages formed during the M1 phase include quartz + andesine + hornblende (I) + biotite (I) in hornblende-biotite gneiss, quartz + andesine + pargasitic hornblende (I) + ferroan pargasitic hornblende (I) + edenitic hornblende (I) in hornblende-schist, quartz + plagioclase + biotite + muscovite in psammopelitic gneiss, and diopside + tremolite + calcite + sphene ± garnet in calc-silicates, being characteristic for amphibolite facies with metamorphic conditions of 600 ± 50 °C and 5-6.5 kbar. The second metamorphic phase (M2) is related to the crystallization of biotite and/or hornblende in S2 foliation demarcating the NE-SW trending dextral shear deformation (D2). The calculated temperature for this M2 phase is about 592 °C. Subsequent thermal events are documented by growth of spinel and scapolite in calc-silicate rocks and of cordierite in psammopelitic gneiss in response to uplift, decomposition and heat provided by the nearby late-formed igneous intrusions. Finally, the rocks reached a temperature of about 530 °C during the cooling retrogressive stage. Based on geological, petrological and geochemical

Characterization of magmatism and deformation in "Foz do Douro Metamorphic Complex" (N Portugal): insights from AMS studies

NASA Astrophysics Data System (ADS)

Sousa, Mónica; Sant'Ovaia, Helena; Noronha, Fernando

2013-04-01

The "Foz do Douro Metamorphic Complex" (FDMC) is situated on the shoreline of Porto extending along ~3km series of small beaches. The geology of this zone is marked by magnificent outcrops of a thin band of Precambrian metamorphic rocks intruded by Variscan granites and by the effects of Porto-Tomar-Ferreira do Alentejo, N330° a N340°, dextral, shear zone [1,2]. The metamorphic band is represented by outcrops of metasedimentary rocks, spatially associated to different types of orthogneisses and amphibolites that constitute the FDMC [3]. The granites belong to a late-Variscan granite group (298±11Ma) [4]. Studies of Anisotropy of Magnetic Susceptibility (AMS) were carried out on several types of orthogneisses and amphibolites from the FDMC, as well as on the Variscan granites and tonalites. The results presented here are related to 218 samples collected on 21 sampling sites: 6 sites (n=67) on leucocratic orthogneisses (Group 1), 10 sites (n=99) on biotite orthogneisses (Group 2), 1 site (n=11) on amphibolite (Group 3), 1 site (n=11) on biotite granite (Group 4), 2 sites (n=20) on biotite porphyritic granites (Group 5) and 1 site (n=10) on tonalite (Group 6). Magnetic anisotropy, expressed by the ratio Kmax/Kmin, ranges from 1.045 to 1.144 in Groups 1, 3, 4 and 5 and from 1.139 to 1.297 in Groups 2 and 6. The magnetic fabric is characterized by subvertical magnetic foliations in all lithologies with directions varying from N41° to N86° in Groups 1 and 2, N0° to N10° in Group 3, N80° to N90° in Group 6 and N130° to N140° in Groups 4 and 5, and mainly subvertical magnetic lineations dipping 50° to 86° in Groups 1 and 2, 77 to 80° in Group 3, 75° to 80° in Group 5 and 65° to 70° in Group 6, with the exception of 3 orthogneisses (one belonging to Group 1 and two from Group 2) and two granites (one belonging to Group 4 and one to Group 5) which reveal subhorizontal (04° to 36°) magnetic lineations. Magnetic susceptibility (K) ranges between 20.0 and 74

Metamorphic reactions in mesosiderites - Origin of abundant phosphate and silica

NASA Technical Reports Server (NTRS)

Harlow, G. E.; Delaney, J. S.; Prinz, M.; Nehru, C. E.

1982-01-01

In light of a study of the Emery mesosiderite, it is determined that the high modal abundances of merrillite and tridymite in most mesosiderites are attributable to redox reactions between silicates and P-bearing Fe-Ni metal within a limited T-fO2 range at low pressure. The recalculated amounts of dissolved P and S in the metallic portion of Emery reduce the metal liquidus temperature to less than 1350 C, and the solidus to less than 800 C, so that the mixing of liquid metal with cold silicates would have resulted in silicate metamorphism rather than melting. This redox reaction and redistribution of components between metal and silicates illuminates the complexities of mesosiderite processing, with a view to the recalculation of their original components.

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

Mobility of gold during metamorphism of the Dalradian in Scotland

NASA Astrophysics Data System (ADS)

Pitcairn, I. K.; Skelton, A. D. L.; Wohlgemuth-Ueberwasser, C. C.

2015-09-01

Mobility of Au and related metals during metamorphism has been suggested to be the source of metals enriched in orogenic Au deposits. This study investigates the mobility of Au, As, and Sb during metamorphism of the Dalradian metasedimentary rocks of Scotland. The metamorphic processes in the Dalradian of Scotland are extremely well studied, and the terrane is an ideal area to investigate mobility of these metals. Our results show that of the 25 major and trace elements analysed, only Au, As, Sb, S and volatile contents as shown by loss on ignition (LOI) values show systematic variation with the metamorphic grade of the samples. Average Au concentrations decrease from 1.1 ± 0.55 ppb and 0.72 ± 0.34 ppb in chlorite and biotite zone rocks down to 0.4 ± 0.22 ppb and 0.34 ± 0.13 ppb in kyanite and sillimanite zone rocks. Average As concentrations decrease from 4.8 ppm (range 0.5 to 17.8 ppm) and 1.96 ± 1.9 ppm in chlorite and biotite zone rocks down to 0.24 ± 0.15 ppm and 0.2 ± 0.12 ppm in kyanite and sillimanite zone rocks. Average Sb concentrations decrease from 0.18 ± 0.15 ppm and 0.11 ± 0.10 ppm in chlorite and biotite zone rocks down to 0.04 ± 0.02 ppm in both kyanite and sillimanite zone rocks. Sulphur and LOI concentrations also show significant decreases. Mass balance calculations indicate that compared to chlorite and biotite zone samples, sillimanite zone samples have an average mass loss of 62 ± 14%, 94 ± 4% and 74 ± 14% for Au, As, and Sb respectively. Every 1 km3 of chlorite-biotite zone mixed psammitic-pelitic protolith rock that is metamorphosed to sillimanite zone conditions would release 1.5 t Au, 8613 t As, 270 t Sb, and 1.02 Mt S. The mobility of these elements is strongly controlled by the paragenesis of sulphide minerals. Pyrite, sphalerite, galena and cobaltite (as well as gersdorffite) decrease in abundance with increasing metamorphic grade in the Dalradian metasedimentary rocks. A critical aspect of the sulphide paragenesis is the

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.

Evolutionary genetics of metamorphic failure using wild-caught vs. laboratory axolotls (Ambystoma mexicanum).

PubMed

Voss, S R; Shaffer, H B

2000-09-01

In many organisms metamorphosis allows for an ecologically important habitat-shift from water to land. However, in some salamanders an adaptive life cycle mode has evolved that is characterized by metamorphic failure (paedomorphosis); these species remain in the aquatic habitat throughout the life cycle. Perhaps the most famous example of metamorphic failure is the Mexican axolotl (Ambystoma mexicanum), which has become a focal species for developmental biology since it was introduced into laboratory culture in the 1800s. Our previous genetic linkage mapping analysis, using an interspecific crossing design, demonstrated that a major gene effect underlies the expression of metamorphic failure in laboratory stocks of the Mexican axolotl. Here, we repeated this experiment using A. mexicanum that were sampled directly from their natural habitat at Lake Xochimilco, Mexico. We found no significant association between the major gene and metamorphic failure when wild-caught axolotls were used in the experimental design, although there is evidence of a smaller genetic effect. Thus, there appears to be genetic variation among Mexican axolotls (and possibly A. tigrinum tigrinum) at loci that contribute to metamorphic failure. This result suggests a role for more than one mutation and possibly artificial selection in the evolution of the major gene effect in the laboratory Mexican axolotl.

Structural evolution of the Semail Ophiolite metamorphic sole, Wadi Hawasina and Northern Jebel Nakhl Culmination, Oman

NASA Astrophysics Data System (ADS)

Hurtado, C.; Bailey, C.; Visokay, L.; Scharf, A.

2017-12-01

The Semail ophiolite is the world's largest and best-exposed ophiolite sequence, however the processes associated with both oceanic detachment and later emplacement onto the Arabian continental margin remain enigmatic. This study examines the upper mantle section of the ophiolite, its associated metamorphic sole, and the autochthonous strata beneath the ophiolite at two locations in northern Oman. Our purpose is to understand the structural history of ophiolite emplacement and evaluate the deformation kinematics of faulted and sheared rocks in the metamorphic sole. At Wadi Hawasina, the base of the ophiolite is defined by a 5- to 15-m thick zone of penetratively-serpentinized mylonitic peridotite. Kinematic indicators record top-to-the SW (reverse) sense-of-shear with a triclinic deformation asymmetry. An inverted metamorphic grade is preserved in the 300- to 500-m thick metamorphic sole that is thrust over deep-water sedimentary rocks of the Hawasina Group. The study site near Buwah, in the northern Jebel Nakhl culmination, contains a N-to-S progression of mantle peridotite, metamorphic sole, and underlying Jurassic carbonates. Liswanite crops out in NW-SE trending linear ridges in the peridotite. The metamorphic sole includes well-foliated quartzite, metachert, and amphibolite. Kinematic evidence indicates that the liswanite and a serpentinized mélange experienced top to-the north (normal) sense-of-shear. Two generations of E-W striking, N-dipping normal faults separate the autochthonous sequence from the metamorphic sole, and also cut out significant sections of the metamorphic sole. Fabric analysis reveals that the metamorphic sole experienced flattening strain (K<0.2) that accumulated during pure shear-dominated general shear (Wk<0.4). Normal faulting and extension at the Buwah site indicates that post-ophiolite deformation is significant in the Jebel Akhdar and Jebel Nakhl culminations.

Effect of food on metamorphic competence in the model system Crepidula fornicata.

PubMed

Padilla, Dianna K; McCann, Michael J; Glenn, Mica McCarty; Hooks, Alexandra P; Shumway, Sandra E

2014-12-01

Food quality and quantity, as well as temperature, are all factors that are expected to affect rates of development, and are likely to be affected by expected climatic change. We tested the effect of a mixed diet versus a single-food diet on metamorphic competence in the emerging model species Crepidula fornicata. We then compared our results with other published studies on this species that examined time to metamorphic competence across a range of food concentrations and rearing temperatures. Ours was the only study to test the effects of single food versus a mixed diet on metamorphic competence for this species. Diet composition did not affect metamorphic competence or survivorship. Comparing results across studies, we found that the shortest time to metamorphic competence was typically found when the food availability per larva was the greatest, independent of rearing temperature. Unfortunately, some published studies did not include important metadata needed for comparison with other studies; these data included larval rearing density, food density, frequency of feeding, and rearing temperature. Mortality rates were not always reported and when reported were often measured in different ways, preventing comparison. Such metadata are essential for comparisons among studies as well as among taxa, and for the determination of generalizable patterns and evolutionary trends. Increased reporting of all such metadata is essential if we are to use scientific studies performed to their fullest potential. © 2014 Marine Biological Laboratory.

Fluid heterogeneity during granulite facies metamorphism in the Adirondacks: stable isotope evidence

USGS Publications Warehouse

Valley, J.W.; O'Neil, J.R.

1984-01-01

The preservation of premetamorphic, whole-rock oxygen isotope ratios in Adirondack metasediments shows that neither these rocks nor adjacent anorthosites and gneisses have been penetrated by large amounts of externally derived, hot CO2-H2O fluids during granulite facies metamorphism. This conclusion is supported by calculations of the effect of fluid volatilization and exchange and is also independently supported by petrologic and phase equilibria considerations. The data suggest that these rocks were not an open system during metamorphism; that fluid/rock ratios were in many instances between 0.0 and 0.1; that externally derived fluids, as well as fluids derived by metamorphic volatilization, rose along localized channels and were not pervasive; and thus that no single generalization can be applied to metamorphic fluid conditions in the Adirondacks. Analyses of 3 to 4 coexisting minerals from Adirondack marbles show that isotopic equilibrium was attained at the peak of granulite and upper amphibolite facies metamorphism. Thus the isotopic compositions of metamorphic fluids can be inferred from analyses of carbonates and fluid budgets can be constructed. Carbonates from the granulite facies are on average, isotopically similar to those from lower grade or unmetamorphosed limestones of the same age showing that no large isotopic shifts accompanied high grade metamorphism. Equilibrium calculations indicate that small decreases in ??18O, averaging 1 permil, result from volatilization reactions for Adirondack rock compositions. Additional small differences between amphibolite and granulite facies marbles are due to systematic lithologie differences. The range of Adirondack carbonate ??18O values (12.3 to 27.2) can be explained by the highly variable isotopic compositions of unmetamorphosed limestones in conjunction with minor 18O and 13C depletions caused by metamorphic volatilization suggesting that many (and possibly most) marbles have closely preserved their

40Ar/39Ar and K-Ar data bearing on the metamorphic and tectonic history of western New England.

USGS Publications Warehouse

Sutter, J.F.; Ratcliffe, N.M.; Mukasa, S.B.

1985-01-01

40Ar/39Ar ages of coexisting biotite and hornblende from Proterozoic Y gneisses of the Berkshire and Green Mt massifs, as well as 40Ar/39Ar and K/Ar mineral and whole-rock ages from Palaeozoic metamorphic rocks, suggest that the thermal peaks for the dominant metamorphic recrystallization in western New England occurred 465 + or - 5 m.y. (Taconian). 40Ar/39Ar age data from a poorly-defined terrain along the eastern strip of the area suggests that the area has been retrograded during a metamorphism that peaked at least 376 + or - 5 m.y. (Acadian). Available age and petrological data from western New England indicate the presence of at least three separate metamorphic-structure domains of Taconic age: 1) a small area of relict high-P and low-T metamorphism, 2) a broad area of normal Barrovian metamorphism from chlorite to garnet grade characterized by a gentle metamorphic gradient and, 3) a rather narrow belt of steep-gradient, Barrovian series metamorphic rocks. Areas of maximum metamorphic intensity within the last domain coincide with areas of maximum crustal thickening in the later stage of Taconic orogeny. -L.di H

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.

Metamorphism of the Oddanchatram anorthosite, Tamil Nadu, South India

NASA Technical Reports Server (NTRS)

Wiebe, R. A.; Janardhan, A. S.

1988-01-01

The Oddanchatram anorthosite is located in the Madurai District of Tamil Nadu, near the town of Palni. It is emplaced into a granulite facies terrain commonly presumed to have undergone its last regional metamorphism in the late Archean about 2600 m.y. The surrounding country rock consists of basic granulites, charnockites and metasedimentary rocks including quartzites, pelites and calc-silicates. The anorthosite is clearly intrusive into the country rock and contains many large inclusions of previously deformed basic granulite and quartzite within 100 meters of its contact. Both this intrusion and the nearby Kaduvar anorthosite show evidence of having been affected by later metamorphism and deformation.

On the timing of high-pressure metamorphism in Alpine Corsica: the first Lu-Hf garnet and lawsonite ages

NASA Astrophysics Data System (ADS)

Vitale Brovarone, A.; Herwartz, D.; Castelli, D.; Malavieille, J.

2012-04-01

Timing of HP metamorphism in Alpine Corsica is highly debated. Controversial biostratigraphic and radiometric constraints results in a poor understanding of the evolution of Alpine Corsica and its meaning in the Western Mediterranean dynamics. Age estimates provided by means of several techniques (e.g. Ar-Ar, Sa-Nd, U-Pb) vary form Late Cretaceous to Late Eocene. Some authors favor a Late Cretaceous peak metamorphism under HP conditions followed by Late Eocene and Early Oligocene blueschist and greenschist retrogression, respectively. Others favor a Late Eocene peak metamorphism and consider the older estimates as affected by analytical inaccuracy. In order to unravel this debate, we provide new Lu-Hf constraints on garnet and lawsonite from the lawsonite-eclogite and lawsonite-blueschist units of Alpine Corsica, which represent a part of the so-called Schistes Lustrés complex. The two investigated units are interpreted to represent remnants of the former Corsican ocean-continent transition zone [2]. As Lu concentrates in the cores of the selected minerals during the early stages of growth and blocking temperatures are high, this method provides robust insight on the timing of prograde/peak metamorphism [1]. Garnet and lawsonite separated form three lawsonite-eclogite samples yield systematic Late Eocene ages at ~ 34 Ma, while lawsonite from the lawsonite-blueschist unit yields a slightly older age at ~ 37 Ma. These data are in agreement with U-Pb data on zircon from the lawsonite-eclogite unit (~ 34 Ma) [3], but are in contrast with a recent U-Pb estimate on the Corsican continental margin unit metamorphosed under blueschist condition, yielding an age of ~ 55 Ma [4]. These discrepancies indicate a complex paleogeographic setting and a diachronous metamorphic evolution along the Corsican ocean-continent transition zone. The Late Eocene HP metamorphism in the Schistes Lustrés of Alpine Corsica also provides important constraints in the evolution of the Alps

Metamorphism of CO3 Chondrites: A Carbon and Nitrogen Isotope Study

NASA Astrophysics Data System (ADS)

Newton, J.; Arden, J. W.; Pillinger, C. T.

1992-07-01

Our previous work involving carbon and nitrogen abundance and isotopic composition of Ornans group chondrites (1) has shown that these measurements have the potential for investigating parent body metamorphism, and we now expand this study. The HF/HCl residues of Colony, Kainsaz, Ornans, Lance and Acfer 094 show unimodal carbon yield profiles. The peak yields are seen to increase as a function of temperature according to known petrologic subtype (2), revealing a concordant increase in the crystallinity of the amorphous carbon with progressive metamorphism. Only the least metamorphosed Colony and Acfer 094 residues display any evidence of presolar silicon carbide. The inference here is that silicon carbide is destroyed during only mild metamorphism. Chromic and perchloric acid residues have revealed that CO3 diamonds are characterized by delta^13C minima of between -34.3o/oo and -40.3o/oo and delta^15N minima of -342+-9.2o/oo, consistent with similar work on other chondrites (3). C/N ratios of diamonds have been used as indicators of relative metamorphic grade (3,4), as nitrogen-rich diamonds are presumed to be lost progressively during metamorphism (5). On this basis, Colony has undergone a much lesser degree of metamorphism than Kainsaz or Lance which are less distinguishable on a C/N plot. An experiment on Ornans which provided only incomplete data suggests that its C/N plateau lies slightly above that of Colony, in agreement with its subtype. The diamond contents of these meteorites are 135 ppm (Colony), 61 ppm (Kainsaz) and 59 ppm (Lance), showing that diamond is present to moderate grades of metamorphism. Carbon data for silicon carbide has been acquired for Colony, Kainsaz and Lance from high temperature experiments on the diamond residues. The amount of SiC in Colony is now established as about 1 ppm of the whole-rock. Neither Kainsaz nor Lance show evidence of silicon carbide, although both show a heavy carbon component combusting around 800 degrees C

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

. 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.

Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures

NASA Technical Reports Server (NTRS)

French, Bevan M.

1998-01-01

This handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures emphasizes terrestrial impact structures, field geology, and particularly the recognition and petrographic study of shock-metamorphic effects in terrestrial rocks. Individual chapters include: 1) Landscapes with Craters: Meteorite Impacts, Earth, and the Solar System; 2) Target Earth: Present, Past and Future; 3) Formation of Impact Craters; 4) Shock-Metamorphic Effects in Rocks and Minerals; 5) Shock-Metamorphosed Rocks (Impactities) in Impact Structures; 6) Impact Melts; 7) How to Find Impact Structures; and 8) What Next? Current Problems and Future Investigations.

Fiskenaesset Anorthosite Complex: Stable isotope evidence for shallow emplacement into Archean ocean crust

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

Peck, W.H.; Valley, J.W.

1996-06-01

Oxygen and hydrogen isotope ratios indicate that unusual rocks at the upper contact of the Archean Fiskenaesset Anorthosite Complex at Fiskenaesset Harbor (southwest Greenland) are the products of hydrothermal alteration by seawater at the time of anorthosite intrusion. Subsequent granulite-facies metamorphism of these Ca-poor and Al- and Mg-rich rocks produced sapphirine- and kornerupine-bearing assemblages. Because large amounts of surface waters cannot penetrate to depths of 30 km during granulite-facies metamorphism, the isotopic signature of the contact rocks must have been obtained prior to regional metamorphism. The stable isotope and geochemical characteristics of the contact rocks support a model of shallowmore » emplacement into Archean ocean crust for the Fiskenaesset Anorthosite Complex. 45 refs., 3 figs., 2 tabs.« less

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

Geochemical, Metamorphic and Geodynamic Evolution implications from subduction-related serpentinites and metarodingites at East Thessaly (Central Greece)

NASA Astrophysics Data System (ADS)

Koutsovitis, Petros

2017-04-01

retrograde metamorphic processes (P<8 kbar and T<350 ˚ C) [1]. Retrograde metamorphism also resulted in the occurrence of late-stage rodingitization and derodingitization processes upon the rodingite intrusions hosted within the serpentinites. Late-stage derodingitization processes (T=250-300 oC) account for the formation of metarodingites (vesuvianite and/or chlorite bearing). Chlorite-serpentinite schists represent a reaction zone between the serpentinites and the hosted metarodingites [1]. Exhumation of the high-pressure serpentinite- and metabasic-bearing metaophiolitic occurrences may have occurred from either one or even from both of the bilateral oceanic basins (Pindos and Vardar) that coexisted besides the elongated Pelagonian zone. The Middle-Late Jurassic Pindos oceanic SSZ model appears to successfully interpret not only the geochemical and structural data recorded in the western Hellenic-Dinaric ophiolitic complexes, but additionally seems to explain the formation and emplacement for many of the East Thessaly metaophiolite occurrences. In this context, the exhumed metaophiolites represent parts either of a serpentinized subduction channel or of the serpentinized wedge, located on the hanging wall side close to the slab in the forearc system of the Pindos Ocean. The Hellenic-Dinaric ophiolitic units, as well as the metaophiolitic occurrences, were likely remobilized during thrusting of the flyschic nappe at the main Alpine orogenetic phase of the Upper Cretaceous-Paleogene period. References. [1] Koutsovitis 2016: Lithos, Special Issue, in Press. DOI: 10.1016/j.lithos.2016.11.008

Geochronology of high-grade metamorphic rocks from the Anjul area, Lut block, eastern Iran

NASA Astrophysics Data System (ADS)

Bröcker, Michael; Fotoohi Rad, Gholamreza; Abbaslu, Fateme; Rodionov, Nikolay

2014-03-01

U-Pb and Rb-Sr geochronology has been used to constrain robust ages for leucosomes and high-grade gneisses from the Anjul area in the eastern part of the Lut block, Iran. The new results do not support the previously suggested Proterozoic age for this occurrence, but instead reveal the importance of Jurassic and Cretaceous magmatic and/or metamorphic processes. Ionprobe U-Pb zircon dating yielded four age groups (>200, ˜168, ˜120 and ˜110 Ma). Textural observations suggest that ages >200 Ma represent inherited zircons. The majority of zircons yielded Jurassic (168 ± 2 and 169 ± 2 Ma) and Cretaceous (120 ± 3, 108 ± 2, 111 ± 3 Ma) intercept ages. Explanations for the two dominant age groups (˜168 and ˜110 Ma) include the following alternatives: (a) the Jurassic ages constrain the protolith age of magmatic precursors that experienced metamorphic overprinting at ˜110 Ma; and (b) both the ˜168 Ma and ˜110 Ma ages indicate the time of metamorphic episodes, e.g. zircon-formation during different anatectic events or migmatization followed by a lower temperature overprint associated with new zircon growth. Multi-point Rb-Sr mineral isochrons of three additional gneisses indicated ages of 102 ± 3 Ma, 102 ± 1 Ma and 97 ± 2 Ma. These ages further document the importance of Cretaceous metamorphism in the Anjul area. The difference compared to the U-Pb ages of zircon overgrowths is interpreted to indicate cooling after a thermal event with or without partial melting. The two major occurrences of metamorphic rocks in the eastern Lut block are exposed in the Deh-Salm and the Anjul region. These occurrences may represent two different segments of a single metamorphic belt that can broadly be related to accretionary and/or collisional processes induced by convergence between the Afro-Arabian and Eurasian plates. Our geochronological study provides a conclusive evidence for Cretaceous metamorphism. We speculate that zircon overgrowths with Cretaceous ages reflect

Lu/Hf dating of garnet constrains timing of metamorphism and deformation, Prince Rupert Area, British Columbia

NASA Astrophysics Data System (ADS)

Wolf, D. E.; Andronicos, C. L.; Vervoort, J. D.; Mansfield, M.

2008-12-01

contains sigmoidal inclusion trails that suggest rotation during left lateral shear, consistent with shear bands and C-S fabrics developed in the matrix of the sample. Grt in the sample produced a twelve-point isochron of 107.3±2.6 Ma (2σ, MSWD=1.6), indicating deformation and metamorphism at this time. Sample 06B-57, a garnet amphibolite migmatite from the inner aureole of the Ecstall pluton, contains grt up to 4 cm in diameter concentrated in leucosome layers. Qtz inclusion trails are consistent with rotation during reverse shear (pluton-side up), in addition to meso-scale folds, shear bands and dike arrays in adjacent rocks. This sample had complex systematics that record an older age of ~105 Ma with a younger overprinting of 90- 94 Ma during pluton emplacement. Pegmatite dikes contained within the Ecstall occur at high angles to the magmatic foliation, normal to the pluton margins, and indicate that the pluton was not folded after the pegmatite dikes were intruded. These new ages directly date garnet growth during metamorphism and deformation in the Prince Rupert area, and show that development of the inverted metamorphic sequence predated emplacement of the Ecstall pluton by 10 to 15 Ma. The data further indicate that left lateral strike slip shearing occurred between 107 and 102 Ma, at the same time much of the North American Cordillera was undergoing major contractional deformation.

Eclogite-facies metamorphism in impure marble from north Qaidam orogenic belt: Geodynamic implications for early Paleozoic continental-arc collision

NASA Astrophysics Data System (ADS)

Chen, Xin; Xu, Rongke; Schertl, Hans-Peter; Zheng, Youye

2018-06-01

In the North Qaidam ultrahigh-pressure (UHP) metamorphic belt, impure marble and interbedded eclogite represent a particular sedimentary provenance and tectonic setting, which have important implications for a controversial problem - the dynamic evolution of early Paleozoic subduction-collision complexes. In this contribution, detailed field work, mineral chemistry, and whole-rock geochemistry are presented for impure marble to provide the first direct evidence for the recycling of carbonate sediments under ultrahigh-pressures during subduction and collision in the Yuka terrane, in the North Qaidam UHP metamorphic belt. According to conventional geothermobarometry, pre-peak subduction to 0.8-1.3 GPa/485-569 °C was followed by peak UHP metamorphism at 2.5-3.3 GPa/567-754 °C and cooling to amphibolite facies conditions at 0.6-0.7 GPa/571-589 °C. U-Pb dating of zircons from impure marble reveals a large group with ages ranging from 441 to 458 Ma (peak at 450 Ma), a smaller group ranging from 770 to 1000 Ma (peak at 780 Ma), and minor >1.8 Ga zircon aged ca. 430 Ma UHP metamorphism. The youngest detrital zircons suggest a maximum depositional age of ca. 442 Ma and a burial rate of ca. 1.0-1.1 cm/yr when combined with P-T conditions and UHP metamorphic age. The REE and trace element patterns of impure marble with positive Sr and U anomalies, negative high field strength elements (Nb, Ta, Zr, Hf, and Ti), and Ce anomalies imply that the marble had a marine limestone precursor. Impure marble intercalated with micaschist and eclogite was similar to limestone and siltstone protoliths deposited in continental fore-arc or arc setting with basic volcanic activity. Therefore, the Yuka terrane most likely evolved in a continental island arc setting during the Paleozoic. These data suggest that metasediments were derived from a mixture of Proterozoic continental crust and juvenile early Paleozoic oceanic and/or island arc crust. In addition, their protoliths were likely

Metamorphic reactions in ruby corundum amphibolite from the Chunky Gal Mountain mafic-ultramafic complex, Clay County, North Carolina

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

Ranson, W.A.; Garihan, J.M.; Ulmer, K.E.

1992-01-01

Amphibolite outcrops of unusual mineralogy within the Chunky Gal Mountain mafic-ultramafic complex display cm-scale rhythmic layers with moderate-steep dips. Layers are troctolitic, gabbroic, and anorthositic in composition, locally in contact with dunite of the Buck Creek ultramafic body. Meta-gabbroic layers contain striking bladed, emerald green amphibole as the chief mafic phase and relict bronzite with reacted margins. An additional major phase is plagioclase, [approximately]An 95 based on microprobe analysis. Ruby corundum is a minor (> 5%) constituent, which in some of the gabbroic rocks is mantled by a reaction rim of fibrolite. The clinoamphibole has optical properties resembling magnesio-cummingtonite: colorlessmore » to pale green in plane light with (+) sign and 2V = 60--70[degree]. However, microprobe analysis of the clinoamphibole indicates alumino-magnesio-hornblende. Although the texture of the bronzite shows that it is breaking down, it is clear that the clinoamphibole and corundum could not be the reaction products without the addition of Al, Ca, and Si in an aqueous fluid. Associated meta-troctolitic layers contain plagioclase and coarse, anhedral olivines displaying an inner corona of bladed orthopyroxene, rimmed by symplectite. The granulite facies reactions is: plagioclase + olivine = clinopyroxene + garnet. The mesoscopic-scale proximity of troctolitic and gabbroic rhythmic layers indicates both underwent granulite facies metamorphism. Retrogression to amphibolite grade is apparent only in the gabbroic layers, resulting in assemblages distinguished locally by abundant emerald green clinoamphibole and corundum porphyroblasts rimmed by fibrolite.« less

Metamorphic Testing for Cybersecurity.

PubMed

Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey; Zhou, Zhi Quan

2016-06-01

Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity.

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.

Decompressional metamorphic P-T paths from kyanite-sillimanite-andalusite bearing rocks in north-central New Mexico

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

Daniel, C.G.; Thompson, A.G.; Grambling, J.A.

1992-01-01

Proterozoic rocks in six uplifts in northern and central New mexico display decompressional metamorphic P-T paths, apparently, related to crustal extension at a time near 1,440 Ma. Metamorphic P-T paths from the Picuris, Rincon, Truchas, Rio Mora, Sandia and southern Manzano Mountains are constrained by three independent techniques: (1) Al[sub 2]SiO[sub 5] and other mineral parageneses; (2) the Gibbs method applied to compositional zoning in garnet and plagioclase; and (3) a new technique based upon Fe[sup 3+] and Mn[sup 3+] zoning in andalusite. Aluminum silicate textures suggest that kyanite and subsequent sillimanite (commonly aligned parallel to the regional foliation andmore » lineation) are earlier than andalusite, which overprints foliation. The decompressional P-T paths are interpreted to reflect crustal extension. Contact metamorphic aureoles associated with the Priest pluton in the southern Manzano and the Sandia Granite in the Sandia Mountains place constraints upon the timing of the Ky-Sil-And metamorphism. In the southern Manzano Mountains metamorphic isograds marking the first appearance of staurolite and (closer to the pluton) sillimanite are parallel to the margin of the 1,440 Ma Priest quartz monzonite pluton. Similarly, isograds also surround the NW margin of the 1,420 Ma Sandia pluton. The regional metamorphism appears to have coincided with and to have been enhanced by the emplacement of the plutons. Because plutonism and regional metamorphism appear to have been synchronous, pluton emplacement occurred during decompression.« less

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

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.

Over 400 m.y. metamorphic history of the Fennoscandian lithospheric segment in the Proterozoic (the East European Craton)

NASA Astrophysics Data System (ADS)

Skridlaite, G.; Bogdanova, S.; Taran, L.; Baginski, B.; Krzeminska, E.; Wiszniewska, J.; Whitehouse, M.

2009-04-01

Several Palaeoproterozoic terranes in the Fennoscandian lithospheric segment of the East European Craton (EEC) evolved differently prior to their final amalgamation at c. 1.8 Ga. South-westward younging of the major tectono-thermal events characterizes the Baltic -Belarus region between the Baltic and Ukrainian Shields of the EEC. While at c.1.89-1.87 Ga and 1.85-1.84 Ga rocks of some northern and eastern terranes (Estonia, Belarus and eastern Lithuania) experienced syncollisional, moderate P metamorphism, subduction-related volcanic island arc magmatism still dominated southwestern terranes in Lithuania and Poland. The available age determinations of metamorphic zircon (SIMS/NORDSIM and TIMS methods, Stockholm, SHRIMP method, RSES, ANU, Canberra) and metamorphic monazite (TIMS, Stockholm and EPMA method, Warsaw University) allow to distinguish several metamorphic events related to major orogenic processes: - 1.90-1.87 Ga amphibolite-facies H/MP metamorphism occurred along with emplacements of juvenile TTG-type granitoids in the North Estonian and Lithuanian-Belarus terranes. They are coeval with the main accretionary growth of the crust in the Svecofennian Domain in the Baltic Shield (e.g. Lahtinen et al., 2005). - 1.84-1.79 Ga high-grade metamorphism affected sedimentary and igneous rocks in almost all the terranes and is assumed to have been related to the major aggregation of the EEC (Bogdanova et al, 2006, 2008). In the metasedimentary granulites of western Lithuania, a prograde metamorphism commenced with monazite growth prior garnet at 1.84-1.83 Ga. The sediments and mafic igneous rocks in Lithuania, felsic igneous rocks in NE Poland underwent peak metamorphism and deformation at 1.81-1.79 Ga (zircon and monazite ages). The 1.83-1.79 Ga metamorphism has the same age as a metamorphic imprint and strong shearing of the crust in central Sweden (Andersson et al., 2004). The postcollisional granulite metamorphism of mafic intrusions at 1.80-1.79 Ga in Belarus

Constraining metamorphic rates through allanite and monazite petrochronology: a case study from the Miyar Valley (High Himalayan Crystalline of Zanskar, NW India)

NASA Astrophysics Data System (ADS)

Robyr, Martin; Goswami-Banerjee, Sriparna

2014-05-01

Dating metamorphic rocks raises specific issues because metamorphism comprises a complex sequence of structural changes and chemical reactions that can be extended over millions or tens of millions of years so that metamorphic rocks cannot in general be said to have "an age". Therefore, an accurate interpretation of radiometric age data from metamorphic rocks requires first to establish the behavior of the isotopic system used for dating relative to the pressure and temperature (P-T) conditions that a metamorphic rock experienced. As the U-Th-Pb system in LREE-accessory phases like monazite and allanite is not easily reset during subsequent temperature increase, allanite and monazite U-Th-Pb ages are collectively interpreted as reflecting crystallization ages. As a consequence, to correctly interpret allanite and monazite crystallization ages, it is essential to accurately determine the physical conditions of their crystallization. A meticulous account of the chemical and textural evolution of monazite and allanite along a well constrained prograde pelitic sequence of the High Himalayan Crystalline of Zanskar (Miyar Valley; e.g. Robyr et al., 2002; 2006; 2014) reveals that: (1) the occurrence of the first metamorphic allanite coincides with the biotite-in isograd and (2) the formation of the first metamorphic monazite occurs at the staurolite-in isograd. The finding of both monazite and allanite as inclusion in staurolite porphyroblasts indicates that the breakdown of allanite and the formation of monazite occurred during staurolite crystallization. Thermobarometry results show that the metamorphic allanites are appeared in the 400-420 °C, while the signature of the first metamorphic monazite is found at ~ 600 °C with staurolite-in isograd. Allanite and monazite U-Th-Pb ages thus constrain the timing when the rocks reached the ~ 420 °C and ~ 600 °C isotherms respectively. In situ LA-ICPMS dating of coexisting allanite and monazite inclusions in garnet

Possible polyphase metamorphic evolution of high grade metabasic rocks from the Songshugou ophiolite, Qinling orogen, China

NASA Astrophysics Data System (ADS)

Belic, Maximilian; Hauzenberger, Christoph; Dong, Yunpeng; Chen, Danling

2014-05-01

cycle or developed during a separate event. The financial support by Eurasia-Pacific Uninet is gratefully acknowledged. Dong, Y.P., Zhou, M.F., Zhang, G.W., Zhou, D.W., Liu, L., Zhang, Q., 2008. The Grenvillian Songshugou ophiolite in the Qinling Mountains, Central China: implications for the tectonic evolution of the Qinling orogenic belt. Journal of Asian Earth Science 32 (5-6), 325-335. Zhang, Z.J., 1999. Metamorphic evolution of garnet-clinopyroxene-amphibole rocks from the Proterozoic Songshugou mafic-ultramafic complex, Qinling Mountains, central China. The Island Arc, 8, 259-280.

The effects of metamorphism on iron mineralogy and the iron speciation redox proxy

NASA Astrophysics Data System (ADS)

Slotznick, Sarah P.; Eiler, John M.; Fischer, Woodward W.

2018-03-01

As the most abundant transition metal in the Earth's crust, iron is a key player in the planetary redox budget. Observations of iron minerals in the sedimentary record have been used to describe atmospheric and aqueous redox environments over the evolution of our planet; the most common method applied is iron speciation, a geochemical sequential extraction method in which proportions of different iron minerals are compared to calibrations from modern sediments to determine water-column redox state. Less is known about how this proxy records information through post-depositional processes, including diagenesis and metamorphism. To get insight into this, we examined how the iron mineral groups/pools (silicates, oxides, sulfides, etc.) and paleoredox proxy interpretations can be affected by known metamorphic processes. Well-known metamorphic reactions occurring in sub-chlorite to kyanite rocks are able to move iron between different iron pools along a range of proxy vectors, potentially affecting paleoredox results. To quantify the effect strength of these reactions, we examined mineralogical and geochemical data from two classic localities where Silurian-Devonian shales, sandstones, and carbonates deposited in a marine sedimentary basin with oxygenated seawater (based on global and local biological constraints) have been regionally metamorphosed from lower-greenschist facies to granulite facies: Waits River and Gile Mountain Formations, Vermont, USA and the Waterville and Sangerville-Vassalboro Formations, Maine, USA. Plotting iron speciation ratios determined for samples from these localities revealed apparent paleoredox conditions of the depositional water column spanning the entire range from oxic to ferruginous (anoxic) to euxinic (anoxic and sulfidic). Pyrrhotite formation in samples highlighted problems within the proxy as iron pool assignment required assumptions about metamorphic reactions and pyrrhotite's identification depended on the extraction techniques

Conodont color and textural alteration: an index to regional metamorphism, contact metamorphism, and hydrothermal alteration.

USGS Publications Warehouse

Rejebian, V.A.; Harris, A.G.; Huebner, J.S.

1987-01-01

Experimental and field data are used to extend the utility of conodonts as semi-quantitative thermal indices into the regimes of regional and contact metamorphism, as well as hydrothermal alteration. These experiments approximate the type of Colour Alteration Indices mixture characteristically found in conodonts recovered from hydrothermally altered rocks. These data indicate that CAI values of 6 to 8 cannot be used to assess precise temperatures of hydrothermally altered rocks but may serve as useful indicators of potential mineralization. - from Authors

Near infrared spectra of muscovite, Tschermak substitution, and metamorphic reaction progress: Implications for remote sensing

NASA Astrophysics Data System (ADS)

Duke, Edward F.

1994-07-01

Near infrared (NIR) spectra of Precambrian metagraywacke in the Black Hills, South Dakota, demonstrate that reflectance spectroscopy can be used to monitor progressive changes in mineral chemistry as a function of metamorphic grade. The wavelength of a combination Al-O-H absorption band in muscovite, measured using both laboratory and field-portable NIR spectrometers, shifts from 2217 nm in the biotite zone to 2199 nm in the sillimanite + K-feldspar zone. The band shift corresponds to an increase in the Alvi content of muscovite, determined by electron microprobe, and is thus a monitor of Al2Si-1(Fe,Mg)-1 (Tschermak) exchange. Spectroscopic measurements such as these are useful in the case of aluminum-deficient rocks, which lack metamorphic index minerals or appropriate assemblages for thermobarometric studies, and in low-grade rocks (subgarnet zone), which lack quantitative indicators of metamorphic grade and are too fine grained for petrographic or microprobe studies. More important, spectroscopic detection of mineral-chemical variations in metamorphic rocks provides petrologists with a tool to recover information on metamorphic reaction histories from high-spectral-resolution aircraft or satellite remote sensing data.

Composition and formations conditions of andalusite-kyanite-sillimanite pegmatoid segregstions in metamorphic rocks of the Tseel block (Mongolian Altai)

NASA Astrophysics Data System (ADS)

Sukhorukov, Vasiliy

2010-05-01

Quartz veins and pegmatoid segregations containing polymorphous Al2SiO5 modifications often occur in metamorphic complexes. Metapelites abound in various combinations of two Al2SiO5 polymorphs, e.g., andalusite + sillimanite and sillimanite + kyanite (Kerrick, 1990). Rocks with three polymorphs are much scarcer; they result from subsequent crystallization during progressive metamorphism or combined regional and contact metamorphism or from metastable crystallization (Kerrick, 1990). Study of veins containing various Al2SiO5 modifications can give insight into the PT-conditions of metamorphism and their temporal changes. The Tsel block is localized in the basins of the Tseliyn, Hudjertiyn, Sharin, and Deresetuin Rivers and is part of the Hercynides structure on the southern flank of Mongolian Altay. Pegmatoid segregations containing polymorphous Al2SiO5 modifications were discovered in the vicinity of the western contact of one of the largest basic-rock massifs, Buren-Hairhan.They are hosted by schists bearing paragenesis Bt + Ms + St + Grt + Ky + Sill + And + Fibr + Pl + Qtz. Visual examination of the pegmatoid segregations showed the presence of large (up to 4-5 cm) mineral aggregates —kyanite pseudomorphs developed after andalusite. They are prismatic, with rhombic sections, and are composed of chaotically arranged kyanite crystals with irregular-shaped andalusite relics between them. The samples also contain large (1 cm) muscovite plates localized between the pseudomorphs as well as quartz grains. The pegmatoid segregations bear the following mineral assemblage: And + Ky + Sil + Fibr + Ms + Qtz + Pl + St +Grt + Bt. Predominant minerals are Al2SiO5 polymorphs (30-50 vol.%), muscovite (30-60 vol.%), and quartz (up to 20 vol.%). Biotite and plagioclase are present in small amounts; staurolite and garnet are occasional. Based on the observed mineral correlations, the following sequence of formation of Al2SiO5 polymorphs has been established: First, andalusite was

Regional metamorphism in the Condrey Mountain Quadrangle, north-central Klamath Mountains, California

USGS Publications Warehouse

Hotz, Preston Enslow

1979-01-01

A subcircular area of about 650 km 2 in northern California and southwestern Oregon is occupied by rocks of the greenschist metamorphic facies called the Condrey Mountain Schist. This greenschist terrane is bordered on the east and west by rocks belonging to the amphibolite metamorphic facies that structurally overlie and are thrust over the Condrey Mountain Schist. The amphibolite facies is succeeded upward by metavolcanic and metasedimentary rocks belonging to the greenschist metamorphic facies. The Condrey Mountain Schist is composed predominantly of quartz-muscovite schist and lesser amounts of actinolite-chlorite schist formed by the metamorphism of graywacke and spilitic volcanic rocks that may have belonged to the Galice Formation of Late Jurassic age. Potassium-argon age determinations of 141?4 m.y. and 155?5 m.y. obtained on these metamorphic rocks seem to be incompatible with the Late Jurassic age usually assigned the Galice. The rocks that border the amphibolite facies are part of an extensive terrane of metavolcanic and metasedimentary rocks belonging to the western Paleozoic and Triassic belt. The metavolcanic rocks include some unmetamorphosed spilite but are mostly of the greenschist metamorphic facies composed of oligoclase (An15-20) and actinolite with subordinate amounts of chlorite and clinozoisiteepidote. The interbedded sedimentary rocks are predominantly argillite and slaty argillite, less commonly siliceous argillite and chert, and a few lenticular beds of marble. On the south, high-angle faults and a tabular granitic pluton separate the greenschist metavolcanic terrane from the amphibolite facies rocks; on the east, nonfoliated amphibolite is succeeded upward, apparently conformably, by metasedimentary rocks belonging to the greenschist metavolcanic terrane. In the southern part of Condrey Mountain quadrangle, an outlier of a thrust plate composed of the Stuart Fork Formation overlies the metavolcanic and metasedimentary rocks. The Stuart

Ediacaran ( 620 Ma) high grade regional metamorphism in the northern Arabian Nubian Shield: U/Th-Pb monazite ages of the Elat schist

NASA Astrophysics Data System (ADS)

Elisha, Bar; Katzir, Yaron; Kylander-Clark, Andrew

2017-04-01

Ediacaran times witnessed a hemisphere-scale orogenesis forming the extensive Pan-African mountain ranges and resulting in the final assembly of Gondwana supercontinent. The Elat metamorphic basement (S Israel) located at the northernmost tip of a major Pan-African orogenic suture, the Arabian Nubian Shield (ANS), comprises amphibolite facies schists and gneisses and was most likely shaped by this major continental collision. However the timing, number and duration of metamorphic events in Elat and elsewhere in the ANS are non-conclusive and a major emphasis was given to pre-Ediacaran island-arc related tectonics. This is mostly because U-Pb dating of zircon, widely used in Elat and elsewhere, is very successful in constraining the ages of the igneous and sedimentary protoliths, but is 'blind' to metamorphism at grades lower than granulite. Here U/Th-Pb dating of monazite, a precise chronometer of metamorphic mineral growth, is systematically applied to the Elat schist and unveils the tectono-metamorphic evolution of the Elat basement. Previous U-Pb dating of detrital zircon has shown that the sedimentary protoliths of the Elat schist are the oldest basement components (≥800 Ma), and detailed structural observations of the schists portrayed a complex deformation history including four successive phases (Shimron, 1972). The earliest three phases were defined as ductile and penetrative, but some of the available geochronological data apparently contradict field relations. In-situ analysis of metamorphic monazites by LASS (Laser Ablation Split Stream) involves simultaneous measurement of U/Th-Pb isotope ratios and REE contents in a single 10 μm sized grain or domain, thus allowing determining the age of specific texture and metamorphic assemblage. Monazite dating of the Elat schist yielded two concordant age clusters at 712±6 and 613±5 Ma. The corresponding REE patterns of the dated monazite grains indicate that porphyroblast growth, either garnet or staurolite

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

On the Role of Subduction Dynamics on Emplacement of Metamorphic Core Complexes and Geothermal Systems

NASA Astrophysics Data System (ADS)

Roche, V. M.; Sternai, P.; Guillou-Frottier, L.; Menant, A.; Jolivet, L.; Bouchot, V.; Gerya, T.

2017-12-01

Subduction-induced extensional tectonics in back-arc domains results in the development of metamorphic core complexes (MCCs) and low-angle normal faults (detachments) that also control magma ascent and fluid circulation. However, possible links with the genesis of high-enthalpy geothermal resources (HEGRs) remain barely explored, and no unifying mechanism responsible for both the generation of MCCs and emplacement of HEGRs has yet been recognized. Although discussions on the possible role of magmatic intrusions beneath these systems are still active, another source of heat is required when one considers the scale of a geothermal Province. An additional source of heat, for instance, could arise from the deep dynamics implied by large-scale tectonic processes such as subduction. Firstly, we investigate subduction dynamics through 3D numerical geodynamic models involving slab rollback and tearing constrained primarily by, geothermal anomaly measurements from western Turkey. Our results show that subduction-induced extensional tectonics controls the genesis and distribution of crustal-scale thermal domes, analogous to crustal and lithospheric boudinage. The thermal domes weaken the crust, localize deformation and enhance development of crustal-scale detachments. Thus, these thermo-mechanical instabilities primarily trigger and control the distribution of MCCs. In addition, subduction-related asthenospheric return flow and shear heating in the mantle increase the temperature of the Moho by up to 250°C. Such forcing is observed in natural settings such as the Menderes (western Anatolia) and the Basin and Range (Western United States). Secondly, the numerically-obtained subduction-induced thermal signature at the base of the continental crust is then imposed as basal thermal condition for 2D high-resolution crustal models dedicated to the understanding of fluid flow around detachments. Our results show that permeable detachments control the bulk of the heat transport and

Links between fluid circulation, temperature, and metamorphism in subducting slabs

USGS Publications Warehouse

Spinelli, G.A.; Wang, K.

2009-01-01

The location and timing of metamorphic reactions in subducting lithosph??re are influenced by thermal effects of fluid circulation in the ocean crust aquifer. Fluid circulation in subducting crust extracts heat from the Nankai subduction zone, causing the crust to pass through cooler metamorphic faci??s than if no fluid circulation occurs. This fluid circulation shifts the basalt-to-eclogite transition and the associated slab dehydration 14 km deeper (35 km farther landward) than would be predicted with no fluid flow. For most subduction zones, hydrothermal cooling of the subducting slab will delay eclogitization relative to estimates made without considering fluid circulation. Copyright 2009 by the American Geophysical Union.

Metamorphic Testing for Cybersecurity

PubMed Central

Chen, Tsong Yueh; Kuo, Fei-Ching; Ma, Wenjuan; Susilo, Willy; Towey, Dave; Voas, Jeffrey

2016-01-01

Testing is a major approach for the detection of software defects, including vulnerabilities in security features. This article introduces metamorphic testing (MT), a relatively new testing method, and discusses how the new perspective of MT can help to conduct negative testing as well as to alleviate the oracle problem in the testing of security-related functionality and behavior. As demonstrated by the effectiveness of MT in detecting previously unknown bugs in real-world critical applications such as compilers and code obfuscators, we conclude that software testing of security-related features should be conducted from diverse perspectives in order to achieve greater cybersecurity. PMID:27559196

Ion microprobe survey of the grain-scale oxygen isotope geochemistry of minerals in metamorphic rocks

NASA Astrophysics Data System (ADS)

Ferry, John M.; Kitajima, Kouki; Strickland, Ariel; Valley, John W.

2014-11-01

The oxygen isotope compositions of calcite, diopside, dolomite, forsterite, garnet, K-feldspar, kyanite, plagioclase, quartz, and wollastonite were analyzed in suites of contact and regional metamorphic rocks using an ion microprobe. Spatial resolution was ∼10 μm. Precision, measured as the standard deviation of working standards averaged over the entire project, was 0.13-0.18‰ for three carbonate standards and 0.11-0.12‰ for two silicate standards. A total of 1176 analyses (excluding standards) were made of 73 minerals in 23 samples. Both intercrystalline and intracrystalline variability in δ18O is greater in contact than in regional metamorphic rocks. Of 27 minerals analyzed in contact metamorphosed rocks, 70% exhibit statistically significant grain-to-grain variability in δ18O over areas ⩽1.41 cm2 with the largest range in silicates and carbonates in a single sample of 7.4‰ (forsterite) and 10.6‰ (dolomite). Of 88 grains analyzed in two or more places in contact metamorphosed rocks, 32% exhibit statistically significant intracrystalline variability in δ18O with the largest range in a single silicate and carbonate grain of 3.1‰ (forsterite) and 10.1‰ (dolomite). In contrast, 44% of 45 minerals in regional metamorphic rocks exhibit significant grain-to-grain variability in δ18O over areas ⩽1.17 cm2 with the largest range in silicates and carbonates in a single sample of only 1.1‰ (plagioclase) and 0.9‰ (calcite). Only 6% of 144 grains analyzed in two or more places in regional metamorphic rocks exhibit significant intracrystalline variability in δ18O with the largest range in a single silicate and carbonate grain of only 1.5‰ (diopside) and 0.7‰ (calcite). The difference in intercrystalline and intracrystalline variability in δ18O between contact and region metamorphic rocks is explained by the longer duration and slower reaction rates of regional metamorphism rather than to differences in temperature. There is no significant

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

Permeability of the continental crust: Implications of geothermal data and metamorphic systems

USGS Publications Warehouse

Manning, C.E.; Ingebritsen, S.E.

1999-01-01

In the upper crust, where hydraulic gradients are typically 10 MPa km-1, the mean permeabilities required to accommodate the estimated metamorphic fluid fluxes decrease from ~10-16 m2 to ~10-18 m2 between 5- and 12-km depth. Below ~12 km, which broadly corresponds to the brittle-plastic transition, mean k is effectively independent of depth at ~10(-18.5??1) m2. Consideration of the permeability values inferred from thermal modeling and metamorphic fluxes suggests a quasi-exponential decay of permeability with depth of log k ~ -3.2 log z - 14, where k is in meters squared and z is in kilometers. At mid to lower crustal depths this curve lies just below the threshold value for significant advection of heat. Such conditions may represent an optimum for metamorphism, allowing the maximum transport of fluid and solute mass that is possible without advective cooling.

Structural development of the Red Hill portion of the Feather River ultramafic complex, Pulmas County, California

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

Weisenberg, C.W.

1979-01-01

The Feather River Ultramafic Complex is a partially serpentinized body of metamorphosed alpine peridotite and gabbro that lies along the northern part of the Melones fault zone, a NNW trending belt in the Northern Sierra Nevada. The complex was studied in the area of Red Hill, near the canyon of the North Fork, Feather River. The complex is separated from the Calaveras Terrain and Arlington Formation country rocks by steep faults; the Melones Fault on the east and the Rich Bar Fault on the west. Units recognized within the complex include Rich Bar metamorphic rocks, peridotite, metaperidotite, tremolite-olivine schist, hornblendemore » schist, and layered metagabbro. The Rich Bar metamorphic rocks are tectonic slices of amphibolite grade hornblende schist, mica schist, and quartzite found along the Rich Bar Fault. The complex shows evidence of 4 major events. E-1 (Pennsylvania-Permian) was formation of the peridotite-gabbro complex. E-2 (Permo-Triassic) consisted of pervasive shearing parallel to the Rich Bar Fault associated with initial emplacement within the Sierra Nevada. E-3 is believed to be compression and metamorphism (serpentinization) associated with the Nevadan orogeny. E-4 was associated with intrusion of nearby plutons. The regional association of the complex with late paleozoic arc volcanics of the Taylorsville area suggest formation near or under an island arc. Metamorphism during emplacement indicates association with the arc at that time. Left-lateral shear during emplacement along the Rich Bar Fault indicates NW directed thrusting when the layering in metagabbro is rotated to horizontal.« less

Revealing the significance and polyphase tectonothermal evolution of a major metamorphic unit in an orogen: the central Sanandaj-Sirjan zone, Zagros Mts., Iran

NASA Astrophysics Data System (ADS)

Shakerardakani, Farzaneh; Neubauer, Franz; Genser, Johann; Liu, Xiaoming; Dong, Yunpeng; Monfaredi, Behzad; Benroider, Manfred; Finger, Fritz; Waitzinger, Michael

2016-04-01

The Dorud-Azna region in the central Sanandaj-Sirjan metamorphic belt plays a key role in promoting the tectonic evolution of Zagros orogen, within the frame of the Arabia-Eurasia collision zone. From footwall to hangingwall, structural data combined with the U-Pb zircon and extensive 40Ar-39Ar mineral dating survey demonstrate three metamorphosed tectonic units, which include: (1) The Triassic June complex is metamorphosed within greenschist facies conditions, overlain by (2) the amphibolite-grade metamorphic Galeh-Doz orthogneiss, which is intruded by mafic dykes, and (3) the Amphibolite-Metagabbro unit. To the east, these units were intruded by the Jurassic Darijune gabbro. We present U-Pb detrital zircon ages of a garnet-micaschist from the Amphibolite-Metagabbro unit, which yield six distinctive age groups, including a previously unrecognized Late Grenvillian age population at ~0.93 to 0.99 Ga. We speculate that this unique Late Grenvillian group coupled with biogeographic evidence suggests either relationship with the South China craton or to the "Gondwana superfan". The laser ablation ICP-MS U-Pb zircon ages of 608 ± 18 Ma and 588 ± 41 Ma of the granitic Galeh-Doz orthogneiss reveals a Panafrican basement same as known from the Yazd block of Central Iran. Geochemistry and Sr-Nd isotopes of alkaline and subalkaline mafic dykes within the Galeh-Doz orthogneiss show OIB-type to MORB-type and indicate involvement of both depleted and enriched sources for its genesis. The new 40Ar-39Ar amphibole age of ca. 322.2 ± 3.9 Ma from the alkaline mafic dyke implies Carboniferous cooling age after intrusion. The metagabbros (including the Dare-Hedavand metagabbro with a 206Pb/238U age of 314.6 ± 3.7 Ma) and amphibolites with E-MORB geochemical signature of the Amphibolite-Metagabbro unit represent an Upper Paleozoic rift. The geochemical composition of the Triassic greenschist facies metamorphosed June complex, implying formation in a same, but younger tectonic

3D-Reconstructions and Virtual 4D-Visualization to Study Metamorphic Brain Development in the Sphinx Moth Manduca Sexta.

PubMed

Huetteroth, Wolf; El Jundi, Basil; El Jundi, Sirri; Schachtner, Joachim

2010-01-01

DURING METAMORPHOSIS, THE TRANSITION FROM THE LARVA TO THE ADULT, THE INSECT BRAIN UNDERGOES CONSIDERABLE REMODELING: new neurons are integrated while larval neurons are remodeled or eliminated. One well acknowledged model to study metamorphic brain development is the sphinx moth Manduca sexta. To further understand mechanisms involved in the metamorphic transition of the brain we generated a 3D standard brain based on selected brain areas of adult females and 3D reconstructed the same areas during defined stages of pupal development. Selected brain areas include for example mushroom bodies, central complex, antennal- and optic lobes. With this approach we eventually want to quantify developmental changes in neuropilar architecture, but also quantify changes in the neuronal complement and monitor the development of selected neuronal populations. Furthermore, we used a modeling software (Cinema 4D) to create a virtual 4D brain, morphing through its developmental stages. Thus the didactical advantages of 3D visualization are expanded to better comprehend complex processes of neuropil formation and remodeling during development. To obtain datasets of the M. sexta brain areas, we stained whole brains with an antiserum against the synaptic vesicle protein synapsin. Such labeled brains were then scanned with a confocal laser scanning microscope and selected neuropils were reconstructed with the 3D software AMIRA 4.1.

Age and duration of eclogite-facies metamorphism, 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, at the southeast end of the North Qaidam terrane, enclose minor eclogite and peridotite which record ultra-high pressure (UHP) metamorphism associated with the Early Paleozoic continental collision of the Qilian and Qaidam microplates. 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. SHRIMP-RG U-Pb and REE analyses of zircons from four eclogites yield weighted mean ages of 449 to 422 Ma, and REE patterns (flat HREE, no Eu anomaly) and inclusions of garnet, omphacite, and rutile indicate these ages record eclogite-facies metamorphism. The coherent field relations of these samples, and the similar range of individual ages in each sample suggests that the ???25 m.y. age range reflects the duration of eclogite-facies conditions in the studied samples. Analyses from zircon cores in one sample yield scattered 433 to 474 Ma ages, reflecting partial overlap on rims, and constrain the minimum age of eclogite protolith crystallization. Inclusions of Th + REE-rich epidote, and zircon REE patterns are consistent with prograde metamorphic growth. In the Lu??liang Shan, approximately 350 km northwest in the North Qaidam terrane, ages interpreted to record eclogite-facies metamorphism of eclogite and garnet peridotite are as old as 495 Ma and as young as 414 Ma, which suggests that processes responsible for extended high-pressure residence are not restricted to the Dulan region. Evidence of prolonged eclogite-facies metamorphism in HP/UHP localities in the Northeast Greenland eclogite province, the Western Gneiss Region of Norway, and the western Alps suggests that long eclogite-facies residence may be globally significant in continental subduction/collision zones.

Signature of Cenozoic orogenic movements in combustion metamorphic rocks: mineralogy and geochronology (example of the Salair-Kuznetsk Basin transition)

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

Novikov, I.S.; Sokol, E.V.; Travin, A.V.

Cenozoic combustion metamorphic (CM) complexes produced by fossil natural coal fires are widespread at range-basin junctions worldwide. Large-scale fires accompany the initial orogenic phases as fresh coal-bearing strata become drawn into the aeration zone as a result of crustal deformation. In combustion metamorphism, the protolith melts to different degrees either into ferrous basic paralava or in glassy clinker. The melt rocks have a phase composition favorable for Ar-40/Ar-39 dating of ignition coeval with the onset of each episode in Late Cenozoic orogenic events. We suggest an algorithm providing correct Ar-40/Ar-39 age determination of CM rocks followed by well-grounded geological interpretationmore » and test the new approach on melt rocks from the Kuznetsk Coal Basin. Paralava samples were dated by Ar-40/Ar-39 incremental heating and the isotope ratios were corrected for Ca-, Cl-, and K-derived Ar isotopic interferences. The interpretation of age-spectrum results was checked against internal and external criteria. The former were plateau and isochrone ages and the latter included the so-called 'couple criterion' and conventional relative ages inferred from geological and stratigraphic evidence. As a result, we distinguished two groups of dates for combustion metamorphic events bracketed between 1.2 {+-} 0.4 and 0.2 {+-} 0.3 Ma. The older ages represent rocks in the western edge of the Prokopievsk-Kiselevsk block of the Salair zone and the younger dates correspond to those in its eastern edge. The reported dates record the time when the fault boundaries of the blocks were rejuvenated during recent activity and the block accreted to the Salair orogenic area as a submontane step. The suggested approach to the choice of objects, classification of rocks, and interpretation of Ar-40/Ar-39 spectra is universal and can be practiced in any area of combustion metamorphism.« less

Paleoproterozoic multistage metamorphic events in Jining metapelitic rocks from the Khondalite Belt in the North China Craton: Evidence from petrology, phase equilibria modelling and U-Pb geochronology

NASA Astrophysics Data System (ADS)

Cai, Jia; Liu, Fulai; Liu, Pinghua

2017-05-01

Metapelitic rocks of the Jining Complex (sillimanite-cordierite-garnet (Sil-Crd-Grt) gneisses, sillimanite-garnet (Sil-Grt) gneisses and quartzofeldspathic rocks) are exposed in the eastern segment of the Khondalite Belt (KB) in the North China Craton (NCC). The Sil-Crd-Grt gneisses have preserved polyphase mineral assemblages and microstructural evidence of anatexis, resulting from biotite dehydration melting. Petrological observations revealed that the Sil-Crd-Grt gneisses contain three metamorphic assemblages: a peak assemblage of garnet porphyroblast and matrix biotite + sillimanite + K-feldspar + plagioclase + quartz + ilmenite + magnetite, a post-peak near-isothermal decompressional assemblage of garnet + cordierite + biotite + sillimanite + K-feldspar + plagioclase + quartz + ilmenite + magnetite, and a decompressional cooling assemblage of garnet + biotite + cordierite + K-feldspar + plagioclase + quartz + ilmenite + magnetite. A clockwise P-T path was defined involving the inferred peak stage followed by post-peak near-isothermal decompression and decompressional cooling stages, with P-T conditions of 790-825 °C and 9-10 kbar, 810-890 °C and 6.0-6.5 kbar, and 780-810 °C and 4.0-5.5 kbar, respectively. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb analyses of the Sil-Crd-Grt gneisses and Sil-Grt gneisses for the detrital and metamorphic zircons yielded a protolith age of ∼2.0 Ga and the late Paleoproterozoic metamorphic age of 1895-1885 Ma. The results reveal that the metapelitic rocks of the Jining Complex underwent continent-continent subduction or collision in the peak metamorphic stage, followed by a post-collisional exhumation event in the post-peak decompressional stage, and a subsequent decompressional cooling stage between the Yinshan and Ordos blocks to form the Paleoproterozoic KB.

U-Pb age of the Diana Complex and Adirondack granulite petrogenesis

USGS Publications Warehouse

Basu, A.R.; Premo, W.R.

2001-01-01

U-Pb isotopic analyses of eight single and multi-grain zircon fractions separated from a syenite of the Diana Complex of the Adirondack Mountains do not define a single linear array, but a scatter along a chord that intersects the Concordia curve at 1145 ?? 29 and 285 ?? 204 Ma. For the most concordant analyses, the 207Pb/206Pb ages range between 1115 and 1150 Ma. Detailed petrographic studies revealed that most grains contained at least two phases of zircon growth, either primary magmatic cores enclosed by variable thickness of metamorphic overgrowths or magmatic portions enclosing presumably older xenocrystic zircon cores. The magmatic portions are characterized by typical dipyramidal prismatic zoning and numerous black inclusions that make them quite distinct from adjacent overgrowths or cores when observed in polarizing light microscopy and in back-scattered electron micrographs. Careful handpicking and analysis of the "best" magmatic grains, devoid of visible overgrowth of core material, produced two nearly concordant points that along with two of the multi-grain analyses yielded an upper-intercept age of 1118 ?? 2.8 Ma and a lower-intercept age of 251 ?? 13 Ma. The older age is interpreted as the crystallization age of the syenite and the younger one is consistent with late stage uplift of the Appalachian region. The 1118 Ma age for the Diana Complex, some 35 Ma younger than previously believed, is now approximately synchronous with the main Adirondack anorthosite intrusion, implying a cogenetic relationship among the various meta-igneous rocks of the Adirondacks. The retention of a high-temperature contact metamorphic aureole around Diana convincingly places the timing of Adirondack regional metamorphism as early as 1118 Ma. This result also implies that the sources of anomalous high-temperature during granulite metamorphism are the syn-metamorphic intrusions, such as the Diana Complex.

Towards an integrated magmatic, structural and metamorphic model for the 1.1-0.9 Ga Sveconorwegian orogeny

NASA Astrophysics Data System (ADS)

Slagstad, Trond; Roberts, Nick M. W.; Røhr, Torkil S.; Marker, Mogens K.

2013-04-01

Orogeny involves magmatic, metamorphic, deformational and erosional processes that are caused by or lead to crustal thickening and the development of high topography. In general, these processes operate along the margins of continental plates, either as a result of subduction of oceanic crust (accretionary) or collision between two or more continental plates (collisional). Many of these processes are common to accretionary and collisional orogeny, and do not uniquely discriminate between the two. With only a fragmented geological record, unravelling the style of orogenesis in ancient orogens may, therefore, be far from straightforward. Adding to the complexity, modern continental margins, e.g., the southern Asian margin, display significant variation in orogenic style along strike, rendering along-strike comparisons and correlations unreliable. The late Mesoproterozoic Sveconorwegian province in SW Baltica is traditionally interpreted as the eastward continuation of the Grenville province in Canada, resulting from collision with Amazonia and forming a central part in the assembly of the Rodinia supercontinent. We recently proposed that the Sveconorwegian segment of this orogen formed as a result of accretionary processes rather than collision. This hypothesis was based mainly on considerations of the Sveconorwegian magmatic evolution. Here, we show how the metamorphic/structural record supports (or at least may be integrated in) our model as well. The key elements in our accretionary model are: 1) formation of the Sirdal Magmatic Belt (SMB) between 1070 and 1020 Ma, most likely representing a continental arc batholith. Coeval deformation and high-grade metamorphism farther east in the orogen could represent deformation in the retroarc. 2) cessation of SMB magmatism at 1020 Ma followed by UHT conditions at 1010-1005 Ma, with temperatures in excess of 1000°C at 7.5 kbar. Subduction of a spreading ridge at ca. 1020 Ma would result in an end to arc magmatism and

Geochronology of multi-stage metamorphic events: Constraints on episodic zircon growth from the UHP eclogite in the South Altyn, NW China

NASA Astrophysics Data System (ADS)

Liu, Liang; Wang, Chao; Cao, Yu-Ting; Chen, Dan-Ling; Kang, Lei; Yang, Wen-Qiang; Zhu, Xiao-Hui

2012-04-01

Petrography, mineral chemistry and pressure-temperature (P-T) estimates were carried out for the eclogite from the South Altyn in NW China. The results suggest three stages of metamorphism: an ultra-high pressure (UHP) eclogite-facies metamorphism at 717-871 °C and ≥ 2.8 GPa, a high pressure (HP) granulite-facies metamorphism at 624-789 °C and 1.42-1.52 GPa, and an amphibolite-facies metamorphism at 597-728 °C and 0.99-1.17 GPa. Cathodoluminescence investigation revealed that zircons from the retrograde eclogite display a distinct core-rim structure. Cores are grey-white luminescent and contain mineral inclusions of Garnet + Omphacite + Rutile + Quartz, suggesting eclogite-facies metamorphic origin. The rims are dark grey luminescent and contain Garnet + Clinopyroxene + Pagioclase inclusions, forming at HP granulite-facies conditions. A few residual zircon grains with mottled internal structure also occur as the metamorphic cores. LA-ICPMS zircon U-Pb dating yielded three discrete age groups: (1) a Neoproterozoic protolith age of 752 ± 7 Ma for the residual grains, (2) an eclogite-facies metamorphic age of 500 ± 7 Ma for the metamorphic cores, and (3) a HP granulite-facies retrograde age of 455 ± 2 Ma for the rims. These ages indicate that the protolith of the Altyn eclogite probably formed in response to breakup of the Rodinia supercontinent during the Neoproterozoic; it was subjected to continental deep subduction and UHP metamorphism during early Paleozoic (~ 500 Ma) and subsequently underwent two stages of retrograde metamorphism during exhumation. The petrological and geochronological data suggest a clockwise P-T-t path for the UHP eclogite. According to pressures and ages for the peak UHP eclogite-facies and the retrograde HP granulite-facies metamorphism, an exhumation rate of 1.2 mm/yr was estimated for the eclogite, which is considerably slower than that of some UHP rocks from other UHP terranes (> 5 mm/yr). While the peak metamorphic age of 500 Ma

Removing the effects of metamorphism from the Neoproterozoic carbon isotope record: a case study on Islay, western Scotland

NASA Astrophysics Data System (ADS)

Skelton, Alasdair

2016-04-01

The Port Askaig Formation on Islay, western Scotland is the first discovered tillite (glacial sediment) of Neoproterozoic age. This formation is sandwiched between carbonate rocks which preserve an extreme negative carbon isotope excursion. This so called "Islay anomaly" has been correlated with other such anomalies worldwide and together with the tillites has been cited as evidence of major (worldwide) glaciation events. During subsequent mountain building, this carbonate-tillite- carbonate sequence has been folded, producing a major en-echelon anticlinal fold system. Folding was accompanied by metamorphism at greenschist facies conditions which was, in turn, accompanied by metamorphic fluid flow. Mapping of the δ18O and δ13C values of these carbonate rocks reveals that metamorphic fluids were channelled through the axial region of the anticlinal fold. The metamorphic fluid was found to have a highly negative δ13C value, which was found to be in equilibrium with metamorphosed graphitic mudstones beneath the carbonate-tillite-carbonate sequence. Devolatilisation of these mudstones is therefore a likely source of this metamorphic fluid. Removal of the effects of metamorphic fluid flow on δ13C values recorded by metamorphosed carbonate rocks on Islay allows us to re-evaluate the isotopic evidence used to reconstruct Neoproterozoic climate. We are able to show that extreme negative δ13C values can partly be attributed to metamorphic fluid flow.

Improved GaSb-based quantum well laser performance through metamorphic growth on GaAs substrates

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

Richardson, Christopher J. K., E-mail: richardson@lps.umd.edu; He, Lei; Apiratikul, Paveen

The promise of the metamorphic growth paradigm is to enable design freedom of the substrate selection criteria beyond current choices that are limited by lattice matching requirements. A demonstration of this emerging degree of freedom is reported here by directly comparing identical laser structures grown both pseudomorphically on a GaSb substrate and metamorphically on a GaAs substrate. Improved thermal performance of the metamorphic laser material enables a higher output power before thermal roll-over begins. These performance gains are demonstrated in minimally processed gain-guided broad-area type-I lasers emitting close to 2-μm wavelengths and mounted p-side up. Continuous wave measurements at roommore » temperature yield a T{sub 0} of 145 K and peak output power of 192 mW from metamorphic lasers, compared to a T{sub 0} of 96 K and peak output power of 164 mW from identical lasers grown pseudomorphically on GaSb.« less

Structure, metamorphism, and geochronology of the Cosmos Hills and Ruby Ridge, Brooks Range schist belt, Alaska

USGS Publications Warehouse

Christiansen, Peter B.; Snee, Lawrence W.

1994-01-01

The boundary of the internal zones of the Brooks Range orogenic belt (the schist belt) is a fault contact that dips toward the hinterland (the Yukon-Koyukuk province). This fault, here referred to as the Cosmos Hills fault zone, juxtaposes oceanic rocks and unmetamorphosed sedimentary rocks structurally above blueschist-to-greenschist facies metamorphic rocks of the schist belt. Near the fault contact, schist belt rocks are increasingly affected by a prominent, subhorizontal transposition foliation that is locally mylonitic in the fault zone. Structural and petrologic observations combined with 40Ar/39Ar incremental-release geochronology give evidence for a polyphase metamorphic and deformational history beginning in the Middle Jurassic and continuing until the Late Cretaceous. Our 40Ar/39Ar cooling age for Jurassic metamorphism is consistent with stratigraphic and other evidence for the onset of Brooks Range orogenesis. Jurassic metamorphism is nearly everywhere overprinted by a regional greenschist-facies event dated at 130–125 Ma. Near the contact with the Cosmos Hills fault zone, the schist belt is increasingly affected by a younger greenschist metamorphism that is texturally related to a prominent foliation that folds and transposes an older fabric. The 40Ar/39Ar results on phengite and fuchsite that define this younger fabric give recrystallization ages ranging from 103 to less than 90 Ma. We conclude that metamorphism that formed the transposition fabric peaked around 100 Ma and may have continued until well after 90 Ma. This age for greenschist metamorphism is broadly synchronous with the depositional age of locally derived, shallow-marine clastic sedimentary strata in the hanging wall of the fault zone and thus substantiates the interpretation that the fault zone accommodated extension in the Late Cretaceous. This extension unroofed and exhumed the schist belt during relative subsidence of the Yukon-Koyukuk province.

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.

Dynamic coupling among channel flow, plateau growth, foreland shortening, and the formation of metamorphic core complexes: Application to the Tibetan plateau

NASA Astrophysics Data System (ADS)

Rey, P. F.; Teyssier, C.; Whitney, D. L.

2009-04-01

Gravitational potential energy stored in an orogenic plateau can be sufficiently strong to deform the surrounding region (foreland), hence contributing to both plateau growth and collapse. Gravity-driven channel flow from the plateau lower crust into the foreland lower crust, or channel extrusion, has been proposed as a main contributor to the eastward growth of the Tibetan plateau, possibly driving the lower crust channel as far as 1000 km beneath the foreland (eg. Royden et al., 2008). On the basis of numerical modeling using temperature-dependent viscosities and densities, we show that four processes impose severe limitations to channel extrusion: (1) cooling of the extruded channel, (2) convective motion in the plateau channel, (3) surface extension of the plateau, and (4) erosion of the plateau edge. Model results show that peak velocities in the extrusion channel drop rapidly (in less than a few My) from ca. 5 cm/year to less than 1 cm/year, owing to the rapid cooling in the channel from 750-850°C to 650-550°C as it travels into the foreland region. Channel flow extrusion is further slowed when convective flow initiates in the plateau channel as a result of only a few percent drop in density. This convection inhibits laminar flow in the channel, reduces the peak horizontal velocity in the channel to a few mm, and even drives a counter flow at the base of the channel, preventing its propagation toward the foreland. If the foreland is actively pulled away from the plateau (extending boundaries), the plateau upper crust undergoes extension and the lower crust moves up efficiently into a metamorphic core complex, which inhibits flow of the channel away from the plateau and even generates a counter flow from the foreland to the metamorphic core complex. If the foreland is fixed, the same phenomenon occurs as long as the foreland upper crust undergoes shortening (likely weakened by high pore fluid pressure), which enhances extension of the plateau and upward flow

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

Structure and thermochronology of the metamorphic core of the Brooks Range, Alaska

NASA Astrophysics Data System (ADS)

Toro, Jaime

1999-11-01

Detailed field studies were undertaken in two key areas of the Central Belt of the Brooks Range: (1) the north flank of Mt. Igikpak in the Survey Pass Quadrangle and (2) in the Shishakshinovik Pass area in the eastern Ambler River Quadrangle. In both areas structural, stratigraphic, petrologic, 40Ar/39Ar, apatite fission-track and U-Pb data were used to constrain the kinematic and thermal history of metamorphic rocks of those areas. North of the Mt. Igikpak massif a crustal section ˜15 km thick is exposed. There are upper greenschist facies rocks in the deeper portions, and very low grade metamorphic rocks at higher structural levels. Two foliations are found: a higher grade relict S1 fabric and a lower grade S 2 fabric that controls the metamorphic layering. 40Ar/ 39Ar analyses from S1 white mica in the low-grade rocks at the northern end of the transect indicate that peak M1 metamorphism occurred before ˜112 Ma. We ascribe M1 to shortening that occurred during collision of an island arc against the Arctic Alaska margin. S 2 involved the retrogression of earlier assemblages. Kinematic indicators on S2 are top-to-the-north. A rapid cooling event from 500 +/- 50°C to 300 +/- 50°C took place between ˜98 and ˜90 Ma. The driving mechanism for ductile deformation during S2, and for rapid cooling documented by our thermochronologic data, was probably the gravitational collapse of the core of the orogen, over-thickened during the preceding collision. At Shishakshinovik Pass there are Mississippian Lisburne Group strata surrounded by metamorphic rocks typical of the Central Belt of the Brooks Range. All the rocks at Shishakshinovik Pass are intensely deformed, so that one cannot distinguish between an autochthonous and an allochthonous sequence. Furthermore the Mississippian rocks, instead of being attached to the underlying basement, are in the hanging wall of a northwest dipping shear zone. Based on the variations in metamorphic grade and the 40Ar/ 39Ar

Genomics of a Metamorphic Timing QTL: met1 Maps to a Unique Genomic Position and Regulates Morph and Species-Specific Patterns of Brain Transcription

PubMed Central

Page, Robert B.; Boley, Meredith A.; Kump, David K.; Voss, Stephen R.

2013-01-01

Very little is known about genetic factors that regulate life history transitions during ontogeny. Closely related tiger salamanders (Ambystoma species complex) show extreme variation in metamorphic timing, with some species foregoing metamorphosis altogether, an adaptive trait called paedomorphosis. Previous studies identified a major effect quantitative trait locus (met1) for metamorphic timing and expression of paedomorphosis in hybrid crosses between the biphasic Eastern tiger salamander (Ambystoma tigrinum tigrinum) and the paedomorphic Mexican axolotl (Ambystoma mexicanum). We used existing hybrid mapping panels and a newly created hybrid cross to map the met1 genomic region and determine the effect of met1 on larval growth, metamorphic timing, and gene expression in the brain. We show that met1 maps to the position of a urodele-specific chromosome rearrangement on linkage group 2 that uniquely brought functionally associated genes into linkage. Furthermore, we found that more than 200 genes were differentially expressed during larval development as a function of met1 genotype. This list of differentially expressed genes is enriched for proteins that function in the mitochondria, providing evidence of a link between met1, thyroid hormone signaling, and mitochondrial energetics associated with metamorphosis. Finally, we found that met1 significantly affected metamorphic timing in hybrids, but not early larval growth rate. Collectively, our results show that met1 regulates species and morph-specific patterns of brain transcription and life history variation. PMID:23946331

Tertiary plate tectonics and high-pressure metamorphism in New Caledonia

USGS Publications Warehouse

Brothers, R.N.; Blake, M.C.

1973-01-01

The sialic basement of New Caledonia is a Permian-Jurassic greywacke sequence which was folded and metamorphosed to prehnite-pumpellyite or low-grade greenschist facies by the Late Jurassic. Succeeding Cretaceous-Eocene sediments unconformably overlie this basement and extend outwards onto oceanic crust. Tertiary tectonism occurred in three distinct phases. 1. (1) During the Late Eocene a nappe of peridotite was obducted onto southern New Caledonia from northeast to southwest, but without causing significant metamorphism in the underlying sialic rocks. 2. (2) Oligocene compressive thrust tectonics in the northern part of the island accompanied a major east-west subduction zone, at least 30 km wide, which is identified by an imbricate system of tectonically intruded melanges and by development of lawsonite-bearing assemblages in adjacent country rocks; this high-pressure mineralogy constituted a primary metamorphism for the Cretaceous-Eocene sedimentary pile, but was overprinted on the Mesozoic prehnite-pumpellyite metagreywackes. 3. (3) Post-Oligocene transcurrent faulting along a northwest-southeast line (the sillon) parallel to the west coast caused at least 150 km of dextral offset of the southwest frontal margin of the Eocene ultramafic nappe. At the present time, the tectonics of the southwest Pacific are related to a series of opposite facing subduction (Benioff) zones connected by transform faults extending from New Britain-Solomon Islands south through the New Hebrides to New Zealand and marking the boundary between the Australian and Pacific plates. Available geologic data from this region suggest that a similar geometry existed during the Tertiary and that the microcontinents of New Guinea, New Caledonia and New Zealand all lay along the former plate boundary which has since migrated north and east by a complex process of sea-floor spreading behind the active island arcs. ?? 1973.

Metamorphic P-T path and zircon U-Pb dating of HP mafic granulites in the Yushugou granulite-peridotite complex, Chinese South Tianshan, NW China

NASA Astrophysics Data System (ADS)

Zhang, Lu; Zhang, Lifei; Xia, Bin; Lü, Zeng

2018-03-01

Co-existing granulite and peridotite may represent relics of the paleo-suture zone and provides an optimal opportunity for better understanding of orogeny between two blocks. In this study, we carried out petrological and U-Pb zircon dating investigation on the HP mafic granulites associated with peridotite complex at Yushugou in Chinese South Tianshan. The studied samples include garnet-bearing high-pressure mafic granulites which can be subdivided into two types: Type I orthopyroxene-free and Type II orthopyroxene-bearing granulites and amphibolite. Type I granulite (Y21-2) has a mineral assemblage of garnet (33 vol.%), clinopyroxene (32 vol.%) and plagioclase (30 vol.%); and Type II granulite (Y18-8) has a mineral assemblage of garnet (22 vol.%), clinopyroxene (10 vol.%), orthopyroxene (14 vol.%), plagioclase (45 vol.%) and quartz. Garnet in both granulites exhibits core-rim structure characterized by increasing grossular and decreasing pyrope from core to rim. Petrographic observations and phase equilibrium modeling using THERMOCALC in the NCFMASHTO system for the mafic granulites (Y21-2 and Y18-8) show three stages of metamorphism: Stage I (granulite facies) was recognized by the large porphyroblastic garnet core, with P-T conditions of 9.8-10.4 Kbar and 860-900 °C (Y21-2) and 9.9-10.6 Kbar and 875-890 °C (Y18-8), respectively; Stage II (HP granulite facies) has peak P-T conditions of 12.1 Kbar at 755 °C (Y21-2) and 13.8 Kbar at 815 °C (Y18-8) using mineral assemblages combining with garnet rim compositions with maximum grossular and minimum pyrope contents; Stage III (amphibolite facies) was characterized by the development of calcic amphibole in granulites with temperature of 446-563 °C. Therefore, an anticlockwise P-T path characterized by simultaneous temperature-decreasing and pressure-increasing was inferred for the Yushugou HP mafic granulite. Studies of zircon morphology and inclusions, combined with zircon U-Pb dating and REE geochemistry

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.

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

Teaching Igneous and Metamorphic Petrology Through Guided Inquiry Projects

NASA Astrophysics Data System (ADS)

McMillan, N. J.

2003-12-01

Undergraduate Petrology at New Mexico State University (GEOL 399) has been taught using three, 5-6 week long projects in place of lectures, lab, and exams for the last six years. Reasons for changing from the traditional format include: 1) to move the focus from identification and memorization to petrologic thinking; 2) the need for undergraduate students to apply basic chemical, structural, and field concepts to igneous and metamorphic rocks; 3) student boredom in the traditional mode by the topic that has captivated my professional life, in spite of my best efforts to offer thrilling lectures, problems, and labs. The course has three guided inquiry projects: volcanic, plutonic, and pelitic dynamothermal. Two of the rock suites are investigated during field trips. Each project provides hand samples and thin sections; the igneous projects also include whole-rock major and trace element data. Students write a scientific paper that classifies and describes the rocks, describes the data (mineralogical and geochemical), and uses data to interpret parameters such as tectonic setting, igneous processes, relationship to phase diagrams, geologic history, metamorphic grade, metamorphic facies, and polymetamorphic history. Students use the text as a major resource for self-learning; mini-lectures on pertinent topics are presented when needed by the majority of students. Project scores include evaluation of small parts of the paper due each Friday and participation in peer review as well as the final report. I have found that petrology is much more fun, although more difficult, to teach using this method. It is challenging to be totally prepared for class because students are working at different speeds on different levels on different aspects of the project. Students enjoy the course, especially the opportunity to engage in scientific investigation and debate. A significant flaw in this course is that students see fewer rocks and have less experience in rock classification

A versatile digitally-graded buffer structure for metamorphic device applications

NASA Astrophysics Data System (ADS)

Ma, Yingjie; Zhang, Yonggang; Chen, Xingyou; Gu, Yi; Shi, Yanhui; Ji, Wanyan; Du, Ben

2018-04-01

Exploring more effective buffer schemes for mitigating dislocation deficiencies is the key technology towards higher performance metamorphic devices. Here we demonstrate a versatile metamorphic grading structure consisting of 38-period alternated multilayers of In0.52Al0.48As and In0.82Al0.18As on InP substrate, thicknesses of which in each period were gradually varied in opposite directions from 48.7 and 1.3 nm to 1.3 and 48.7 nm, respectively, akin to a digital alloy. Both preferentially dislocation nucleation and blocking of threading dislocation transmission are observed near the In0.82Al0.18As/In0.52Al0.48As interfaces, which help relax the strain and lower the residual defect density. A 2.6 μm In0.83Ga0.17As pin photodetector is fabricated on this pseudo-substrate, attaining a low dark current density of 2.9  ×  10‑6 A cm‑2 and a high detectivity of 1.8  ×  1010 cmHz1/2W‑1 at room temperature, comparable with the states of the art that on linearly-graded buffer layers. These results indicate such digitally-graded buffer structures are promising for enhancing performances of metamorphic devices, and can be easily generalized to other lattice-mismatched material systems.

3D-Reconstructions and Virtual 4D-Visualization to Study Metamorphic Brain Development in the Sphinx Moth Manduca Sexta

PubMed Central

Huetteroth, Wolf; el Jundi, Basil; el Jundi, Sirri; Schachtner, Joachim

2009-01-01

During metamorphosis, the transition from the larva to the adult, the insect brain undergoes considerable remodeling: new neurons are integrated while larval neurons are remodeled or eliminated. One well acknowledged model to study metamorphic brain development is the sphinx moth Manduca sexta. To further understand mechanisms involved in the metamorphic transition of the brain we generated a 3D standard brain based on selected brain areas of adult females and 3D reconstructed the same areas during defined stages of pupal development. Selected brain areas include for example mushroom bodies, central complex, antennal- and optic lobes. With this approach we eventually want to quantify developmental changes in neuropilar architecture, but also quantify changes in the neuronal complement and monitor the development of selected neuronal populations. Furthermore, we used a modeling software (Cinema 4D) to create a virtual 4D brain, morphing through its developmental stages. Thus the didactical advantages of 3D visualization are expanded to better comprehend complex processes of neuropil formation and remodeling during development. To obtain datasets of the M. sexta brain areas, we stained whole brains with an antiserum against the synaptic vesicle protein synapsin. Such labeled brains were then scanned with a confocal laser scanning microscope and selected neuropils were reconstructed with the 3D software AMIRA 4.1. PMID:20339481

Evolution of the Specific Surface Area of Snow in a High Temperature Gradient Metamorphism

NASA Astrophysics Data System (ADS)

Wang, X.; Baker, I.

2014-12-01

The structural evolution of low-density snow under a high temperature gradient over a short period usually takes place in the surface layers during diurnal recrystallization or on a clear, cold night. To relate snow microstructures with their thermal properties, we combined X-ray computed microtomography (micro-CT) observations with numerical simulations. Different types of snow were tested over a large range of TGs (100 K m-1- 500 K m-1). The Specific Surface Area (SSA) was used to characterize the temperature gradient metamorphism (TGM). The magnitude of the temperature gradient and the initial snow type both influence the evolution of SSA. The SSA evolution under TGM was dominated by grain growth and the formation of complex surfaces. Fresh snow experienced a logarithmic decrease of SSA with time, a feature been observed previously by others [Calonne et al., 2014; Schneebeli and Sokratov, 2004; Taillandier et al., 2007]. However, for initial rounded and connected snow structures, the SSA will increase during TGM. Understanding the SSA increase is important in order to predict the enhanced uptake of chemical species by snow or increase in snow albedo. Calonne, N., F. Flin, C. Geindreau, B. Lesaffre, and S. Rolland du Roscoat (2014), Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy, The Cryosphere Discussions, 8, 1407-1451, doi:10.5194/tcd-8-1407-2014. Schneebeli, M., and S. A. Sokratov (2004), Tomography of temperature gradient metamorphism of snow and associated changes in heat conductivity, Hydrological Processes, 18(18), 3655-3665, doi:10.1002/hyp.5800. Taillandier, A. S., F. Domine, W. R. Simpson, M. Sturm, and T. A. Douglas (2007), Rate of decrease of the specific surface area of dry snow: Isothermal and temperature gradient conditions, Journal of Geophysical Research: Earth Surface (2003-2012), 112(F3), doi: 10.1029/2006JF000514.

Metamorphism, graphite crystallinity, and sulfide anatexis of the Rampura-Agucha massive sulfide deposit, northwestern India

NASA Astrophysics Data System (ADS)

Mishra, Biswajit; Bernhardt, Heinz-Jurgen

2009-02-01

Located adjacent to the Banded Gneissic Complex, Rampura-Agucha is the only sulfide ore deposit discovered to date within the Precambrian basement gneisses of Rajasthan. The massive Zn-(Pb) sulfide orebody occurs within graphite-biotite-sillimanite schist along with garnet-biotite-sillimanite gneiss, calc-silicate gneisses, amphibolites, and garnet-bearing leucosomes. Plagioclase-hornblende thermometry in amphibolites yielded a peak metamorphic temperature of 720-780°C, whereas temperatures obtained from Fe-Mg exchange between garnet and biotite (580-610°C) in the pelites correspond to postpeak resetting. Thermodynamic considerations of pertinent silicate equilibria, coupled with sphalerite geobarometry, furnished part of a clockwise P- T- t path with peak P- T of ˜6.2 kbar and 780°C, attained during granulite grade metamorphism of the major Zn-rich stratiform sedimentary exhalative deposits orebody and its host rocks. Arsenopyrite composition in the metamorphosed ore yielded a temperature [and log f( S 2)] range of 352°C (-8.2) to 490°C (-4.64), thus indicating its retrograde nature. Contrary to earlier research on the retrogressed nature of graphite, Raman spectroscopic studies on graphite in the metamorphosed ore reveal variable degree of preservation of prograde graphite crystals (490 ± 43°C with a maximum at 593°C). The main orebody is mineralogically simple (sphalerite, pyrite, pyrrhotite, arsenopyrite, galena), deformed and metamorphosed while the Pb-Ag-rich sulfosalt-bearing veins and pods that are irregularly distributed within the hanging wall calc-silicate gneisses show no evidence of deformation and metamorphism. The sulfosalt minerals identified include freibergite, boulangerite, pyrargyrite, stephanite, diaphorite, Mn-jamesonite, Cu-free meneghinite, and semseyite; the last three are reported from Agucha for the first time. Stability relations of Cu-free meneghinite and semseyite in the Pb-Ag-rich ores constrain temperatures at >550°C and

Fitness consequences of larval traits persist across the metamorphic boundary.

PubMed

Crean, Angela J; Monro, Keyne; Marshall, Dustin J

2011-11-01

Metamorphosis is thought to provide an adaptive decoupling between traits specialized for each life-history stage in species with complex life cycles. However, an increasing number of studies are finding that larval traits can carry-over to influence postmetamorphic performance, suggesting that these life-history stages may not be free to evolve independently of each other. We used a phenotypic selection framework to compare the relative and interactive effects of larval size, time to hatching, and time to settlement on postmetamorphic survival and growth in a marine invertebrate, Styela plicata. Time to hatching was the only larval trait found to be under directional selection, individuals that took more time to hatch into larvae survived better after metamorphosis but grew more slowly. Nonlinear selection was found to act on multivariate trait combinations, once again acting in opposite directions for selection acting via survival and growth. Individuals with above average values of larval traits were most likely to survive, but surviving individuals with intermediate larval traits grew to the largest size. These results demonstrate that larval traits can have multiple, complex fitness consequences that persist across the metamorphic boundary; and thus postmetamorphic selection pressures may constrain the evolution of larval traits. © 2011 The Author(s). Evolution© 2011 The Society for the Study of Evolution.

Roles of insulin-like growth factors in metamorphic development of turbot (Scophthalmus maximus).

PubMed

Jia, Yudong

2018-01-31

Larval turbot (Scophthalmus maximus) undergo metamorphosis, a late post-embryonic developmental event that precedes juvenile transition. Insulin-like growth factors (IGFs) are important endocrine/autocrine/paracrine factors that provide essential signals to control of the embryonic and postnatal development of vertebrate species, including fish. Accumulating evidence suggests that IGFs are involved in regulating the metamorphic development of flatfish. This mini review focus on the functions of all known IGFs (IGF-I and IGF-II) during the metamorphic development of turbot. Information about IGFs and insulin-like growth factors binding proteins (IGFBPs) from other teleosts is also included in this review to provide an overview of IGFs functions in the metamorphic development of turbot. These findings may enhance our understanding of the potential roles of the IGFs system in controlling of flatfish metamorphosis and contributing to the improvement of broodstock management strategies for larval turbot. Copyright © 2018 Elsevier Inc. All rights reserved.

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.

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

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.

Semantically Enabling Knowledge Representation of Metamorphic Petrology Data

NASA Astrophysics Data System (ADS)

West, P.; Fox, P. A.; Spear, F. S.; Adali, S.; Nguyen, C.; Hallett, B. W.; Horkley, L. K.

2012-12-01

More and more metamorphic petrology data is being collected around the world, and is now being organized together into different virtual data portals by means of virtual organizations. For example, there is the virtual data portal Petrological Database (PetDB, http://www.petdb.org) of the Ocean Floor that is organizing scientific information about geochemical data of ocean floor igneous and metamorphic rocks; and also The Metamorphic Petrology Database (MetPetDB, http://metpetdb.rpi.edu) that is being created by a global community of metamorphic petrologists in collaboration with software engineers and data managers at Rensselaer Polytechnic Institute. The current focus is to provide the ability for scientists and researchers to register their data and search the databases for information regarding sample collections. What we present here is the next step in evolution of the MetPetDB portal, utilizing semantically enabled features such as discovery, data casting, faceted search, knowledge representation, and linked data as well as organizing information about the community and collaboration within the virtual community itself. We take the information that is currently represented in a relational database and make it available through web services, SPARQL endpoints, semantic and triple-stores where inferencing is enabled. We will be leveraging research that has taken place in virtual observatories, such as the Virtual Solar Terrestrial Observatory (VSTO) and the Biological and Chemical Oceanography Data Management Office (BCO-DMO); vocabulary work done in various communities such as Observations and Measurements (ISO 19156), FOAF (Friend of a Friend), Bibo (Bibliography Ontology), and domain specific ontologies; enabling provenance traces of samples and subsamples using the different provenance ontologies; and providing the much needed linking of data from the various research organizations into a common, collaborative virtual observatory. In addition to better

The ammonium content in the Malayer igneous and metamorphic rocks (Sanandaj-Sirjan Zone, Western Iran)

NASA Astrophysics Data System (ADS)

Ahadnejad, Vahid; Hirt, Ann Marie; Valizadeh, Mohammad-Vali; Bokani, Saeed Jabbari

2011-04-01

The ammonium (NH4+) contents of the Malayer area (Western Iran) have been determined by using the colorimetric method on 26 samples from igneous and metamorphic rocks. This is the first analysis of the ammonium contents of Iranian metamorphic and igneous rocks. The average ammonium content of metamorphic rocks decreases from low-grade to high-grade metamorphic rocks (in ppm): slate 580, phyllite 515, andalusite schist 242. In the case of igneous rocks, it decreases from felsic to mafic igneous types (in ppm): granites 39, monzonite 20, diorite 17, gabbro 10. Altered granitic rocks show enrichment in NH4+ (mean 61 ppm). The high concentration of ammonium in Malayer granites may indicate metasedimentary rocks as protoliths rather than meta-igneous rocks. These granitic rocks (S-types) have high K-bearing rock-forming minerals such as biotite, muscovite and K-feldspar which their potassium could substitute with ammonium. In addition, the high ammonium content of metasediments is probably due to inheritance of nitrogen from organic matter in the original sediments. The hydrothermally altered samples of granitic rocks show highly enrichment of ammonium suggesting external sources which intruded additional content by either interaction with metasedimentary country rocks or meteoritic solutions.

Neodymium and strontium isotopic dating of diagenesis and low-grade metamorphism of argillaceous sediments

NASA Astrophysics Data System (ADS)

Schaltegger, Urs; Stille, Peter; Rais, Naoual; Piqué, Alain; Clauer, Norbert

1994-03-01

The behaviour of the Rb-Sr and Sm-Nd isotopic systems with increasing degree of Hercynian metamorphic overprint was studied along a transect in Cambrian shales of northwestern Morocco. Clay fractions of < 0.2 to 2-6 μm size from five samples were investigated, representing a range from nonmetamorphic to epizonal metamorphic conditions. The samples were washed in cold l N HC1 prior to digestion to separate soluble/exchangeable Rb, Sr, Sm, and Nd from amounts of these elements fixed in the crystallographic sites of the minerals and to analyze both components separately. The results reveal that the Rb-Sr isotopic system is dominated by Sr hosted by clay mineral phases (both detrital and authigenic illite and chlorite) and carbonate-hosted soluble Sr. Isotopic homogenization of Sr occurred during Hercynian metamorphism, yielding ages between 309 and 349 Ma. The Sm-Nd isotopic system, on the other hand, is dominated by cogenetic apatite and Fe oxide/ hydroxide, both having high contents of leachable REEs. The leachates yield a Sm-Nd isochron age of 523 ± 72 Ma, indicating diagenetic equilibrium between apatite and Fe-oxide/hydroxide. Fine-grained clay fractions of < 0.2 μm size plot onto this reference line, suggesting isotopic equilibrium with the leachates. Size fractions > 0.2 μm show inheritance of a detrital Nd component. The study demonstrates that the diagenesis of the investigated argillaceous sediments can be dated by the Sm-Nd chronometer in authigenic cement phases. The isotopic system of these minerals (apatite, Fe hydroxide/oxide) was homogenized during authigenic mineral growth in a sediment that was flushed by diagenetic fluids and had abundant primary or secondary interconnected pore space. The Hercynian metamorphic overprint caused partial isotopic rehomogenization of the adsorbed and clay-hosted portion of the Sr as well as of the carbonate-hosted Sr. The Sm-Nd system in the cement phases survived this metamorphism. This results in decoupling of

Syn-metamorphic interconnected porosity during blueschist facies reactive fluid fluxes at the slab-mantle interface

NASA Astrophysics Data System (ADS)

Konrad-Schmolke, Matthias; Klitscher, Nicolai; Halama, Ralf; Wirth, Richard; Morales, Luiz

2017-04-01

At the slab-mantle interface in subdution zones fluids released from the downgoing plate infiltrate into a mechanical mixture of rocks with different chemical compositions, different hydration states and different rheological behaviour resulting in a highly reactive mélange within a steep temperature gradient. Fluid pathways, reaction mechanisms and reaction rates of such fluxes, however, are poorly known, although these parameters are thought to be crucial for several seismic phenomena, such as those commonly referred to as slow earthquakes (e.g., episodic tremor and slip (ETS)). We discovered syn-metamorphic fluid-pathways in the form of interconnected metamorphic porosity in eclogite and blueschist facies mélange rocks from the Franciscan Complex near Jenner, CA. The sampled rocks occur as rigid mafic blocks of different sizes (cm to decametre) in a weak chlorite-serpentine matrix interpreted to be an exhumed slab-mantle interface. Some of these mafic blocks record reactive fluid infiltration that transforms dry eclogite into hydrous blueschist with a sharp reaction front clearly preserved and visible from outcrop- down to µm-scale. We can show that a number of interconnected fluid pathways, such as interconnected metamorphic porosity between reacting omphacite and newly formed sodic amphibole enabled fluid infiltration and interface coupled solution-reprecipitation reactions at blueschist facies conditions. We investigated the different types of fluid pathways with TEM and visualized their interconnectivity with 3D focused ion beam (FIB) sections. The eclogitic parts of the samples preserve porous primary omphacite as a product of amphibole and epidote breakdown during subduction. This primary porosity in omphacite I results from a negative volume change in the solids during amphibole and epidote dehydration. The resulting pores appear as (fluid filled) elongated inclusions the orientations of which are controlled by the omphacite lattice. During

Phase equilibria of HP mica schists from the Kamieniec Metamorphic Belt (Sudetes, NE Bohemian Massif)

NASA Astrophysics Data System (ADS)

Szczepanski, Jacek; Golen, Marcin; Anczkiewicz, Robert

2017-04-01

, S., Muszynski, A., Schliestedt, M., 1997. The northeasternmost eclogite occurrence in the Saxothuringian Zone, West Sudetes (Poland). Chem. ERDE-Geochem. 57, 51-61. Józefiak, D., 2000. Geothermobarometry in staurolilte-grade mica schists from the southern part of the Niemcza-Kamieniec Metamorphic Complex (Fore-Sudetic Block, SW Poland). Neues Jahrb. Für Mineral. - Abh. 175, 223-248. Konopásek, J., 2001. Eclogitic micaschists in the central part of the Krušné hory Mountains (Bohemian Massif). Eur. J. Mineral. 13, 87-100. Mazur, S., Turniak, K., Szczepański, J., McNaughton, N.J., 2015. Vestiges of Saxothuringian crust in the Central Sudetes, Bohemian Massif: Zircon evidence of a recycled subducted slab provenance. Gondwana Res. Nowak, I., 1998. Polyphase exhumation of eclogite-bearing high-pressure mica schists from the Fore-Sudetic Block, SW Poland. Geol. Sudet. 31, 3-31.

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.

Prolonged episodic Paleoproterozoic metamorphism in the Thelon Tectonic Zone, Canada: an in-situ SHRIMP/EPMA monazite geochronology study

NASA Astrophysics Data System (ADS)

Mitchell, Rhea; William, Davis; Robert, Berman; Sharon, Carr; Michael, Jercinovic

2017-04-01

The Thelon Tectonic zone (TTZ), Nunavut, Canada, is a >500km long geophysically, lithologically and structurally distinct N-NNE striking Paleoproterozoic boundary zone between the Slave and Rae Archean provinces. The TTZ has been interpreted as a ca. 2.0 Ga continental arc on the western edge of the Rae craton, that was deformed during collision with the Slave craton ca. 1.97 Ga. Alternatively, the Slave-Rae collision is interpreted as occurring during the 2.35 Ga Arrowsmith orogeny while the 1.9-2.0 Ga TTZ represents an intra-continental orogenic belt formed in previously thinned continental crust, postdating the Slave-Rae collision. The central part of the TTZ comprises three >100 km long, 10-20 km wide belts of ca. 2.0 Ga, mainly charnockitic plutonic rocks, and a ca. 1910 Ma garnet-leucogranite belt. Metamorphism throughout these domains is upper-amphibolite to granulite-facies, with metasedimentary rocks occurring as volumetrically minor enclaves and strands of migmatites. The Ellice River domain occurs between the western and central plutonic belts. It contains ca. 1950 Ma ultramafic to dacitic volcanic rocks and foliated Paleoproterozoic psammitic metasedimentary rocks at relatively lower grade with lower to middle amphibolite-facies metamorphic assemblages. In-situ U-Pb analyses of monazite using a combination of Sensitive High-Resolution Ion Microprobe (SHRIMP) and Electron Probe Microanalyzer (EPMA) were carried out on high-grade metasedimentary rocks from seventeen samples representing the eastern margin of the Slave Province and all major lithological domains of the TTZ. 207Pb/206Pb monazite ages from SHRIMP analysis form the foundation of this dataset, while EPMA ages are supplementary. The smaller <6µm spot size of EPMA allowed for further constraint on ages of micro-scale intra-crystalline domains in some samples. Monazite ages define four distinct Paleoproterozoic metamorphic events and one Archean metamorphic event at ca. 2580 Ma. The latter is

Contrasting accessory mineral behavior in minimum-temperature melts: Empirical constraints from the Himalayan metamorphic core

NASA Astrophysics Data System (ADS)

Cottle, John M.; Larson, Kyle P.; Yakymchuk, Chris

2018-07-01

Medium-grained leucogranite in the Tama Kosi region of the Nepalese Himalayan Metamorphic Core yields a relatively narrow range of monazite 208Pb/232Th dates with a dominant population at 21.0 Ma inferred to represent crystallization of an early plutonic phase. In contrast, the pegmatitic portion of the same intrusive complex, that cross-cuts the medium-grained leucogranite, contains zircon, monazite and xenotime that each display near-identical age spectra, recording semi-continuous (re-)crystallization from 27.5 Ma to 21.0 Ma, followed by a 2 m.y. hiatus then further (re-)crystallization between 19.4 and 18.6 Ma. The "gap" in pegmatite dates corresponds well to the crystallization age of the older leucogranite, whereas the end of accessory phase growth in the pegmatite coincides with the onset of regional-scale cooling. Detailed textural, trace element and thermochronologic data indicate that the range of zircon, monazite and xenotime dates recorded in the pegmatite reflect inherited components that underwent semi-continuous (re-)crystallization during metamorphism and/or anatexis in the source region(s), whereas dates younger than the hiatus indicate accessory phase recrystallization, related to both fluid influx and a concomitant increase in temperature. In contrast, the lack of an inherited component(s) in the medium-grained leucogranite phase is inferred to be a result of complete dissolution during partial melting. A model is proposed in which influx of heat and H2O-rich fluids associated with early leucogranite emplacement temporarily delayed zircon and monazite and xenotime crystallization, respectively. These data highlight the importance of measuring spatially resolved dates, trace elements and textural patterns from multiple accessory minerals combined with model constraints to better understand the often-complex crystallization history of anatectic melts in collisional orogens.

The metamorphic fate of supernumerary caudal vertebrae in South Asian litter frogs (Anura: Megophryidae)

PubMed Central

Handrigan, Gregory R; Wassersug, Richard J

2007-01-01

Tadpoles of the Megophryidae, a South Asian family of litter frogs, are unique among anurans by virtue of their expanded caudal skeletons, which include supernumerary vertebral centra. The number of these vertebrae varies widely within the family, with tadpoles of Leptobrachella having as many as 30 and Leptolalax only five. Vertebral morphology is also quite variable, ranging from complete, perichordal centra to fragmentary ossifications. This variation in the caudal osteology of larval megophryids, however, is not manifested in the adult morphology. Post-metamorphic litter frogs have a typical anuran axial skeleton, invariably comprising eight presacral vertebrae, a single sacral vertebra and, postsacrally, the urostyle. To resolve this incongruity between life phases and to determine the precise metamorphic fate of supernumerary caudal vertebrae in megophryids, we examined metamorphic specimens from the genera Leptobrachella, Leptolalax, Ophryophryne and Megophrys. In all four, the caudal larval skeleton undergoes massive reduction, leaving only the coccyx and hypochord untouched. Caudal centra are apparently degraded by osteoclasts, which have not previously been implicated in vertebral remodelling during anuran metamorphosis. In Megophrys and Ophryophryne metamorphs, presacral centra also undergo resorption, consistent with an epichordal mode of centrum formation. The conservation of megophryid adult axial osteology in the face of extensive larval skeletal diversity reveals the role of metamorphosis in constraining anuran morphology. PMID:17559539

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.

Tectonic and metamorphic discontinuities in the Greater Himalayan Sequence in Central Himalaya: in-sequence shearing by accretion from the Indian plate

NASA Astrophysics Data System (ADS)

Carosi, Rodolfo

2016-04-01

The Greater Himalayan Sequence (GHS) is the main metamorphic unit of the Himalayas, stretching for over 2400 km, bounded to the South by the Main Central Thrust (MCT) and to the North by the South Tibetan Detachment (STD) whose contemporanous activity controlled its exhumation between 23 and 17 Ma (Godin et al., 2006). Several shear zones and/or faults have been recognized within the GHS, usually regarded as out of sequence thrusts. Recent investigations, using a multitechnique approach, allowed to recognize a tectonic and metamorphic discontinuity, localized in the mid GHS, with a top-to-the SW sense of shear (Higher Himalayan Discontinuity: HHD) (Carosi et al., 2010; Montomoli et al., 2013). U-(Th)-Pb in situ monazite ages provide temporal constraint of the acitivity of the HHD from ~ 27-25 Ma to 18-17 Ma. Data on the P and T evolution testify that this shear zone affected the tectono-metamorphic evolution of the belt and different P and T conditions have been recorded in the hanging-wall and footwall of the HHD. The HHD is a regional tectonic feature running for more than 700 km, dividing the GHS in two different portions (Iaccarino et al., 2015; Montomoli et al., 2015). The occurrence of even more structurally higher contractional shear zone in the GHS (above the HHD): the Kalopani shear zone (Kali Gandaki valley, Central Nepal), active from ~ 41 to 30 Ma (U-Th-Pb on monazite) points out to a more complex deformation pattern in the GHS characterized by in sequence shearing. The actual proposed models of exhumation of the GHS, based exclusively on the MCT and STD activities, are not able to explain the occurrence of the HHD and other in-sequence shear zones. Any model of the tectonic and metamorphic evolution of the GHS should account for the occurrence of the tectonic and metamorphic discontinuities within the GHS and its consequences on the metamorphic paths and on the assembly of Himalayan belt. References Godin L., Grujic D., Law, R. D. & Searle, M. P. 2006

Metamorphic waters from the pacific tectonic belt of the west coast of the United States

USGS Publications Warehouse

Barnes, I.

1970-01-01

Waters unusually rich in ammonia, boron, carbon dioxide, hydrogen sulfide, and hydrocarbons are found in more than 100 localities along the Pacific coast of the United States. The waters are believed to be products of low-grade metamorphism of marine sediments. The marine sedimentary rocks would have to be tectonically emplaced below crystalline rocks in many places. Mercury are deposits are probably also products of the low-grade metamorphism.

[sup 40]Ar/[sup 39]Ar mineral ages from southwestern Penobscot Bay, Maine: Evidence for Silurian metamorphism

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

West, D.P. Jr.; Guidotti, C.V.; Lux, D.R.

1992-01-01

The nature and timing of metamorphic events in the Coastal Lithotectonic Block of Maine remain poorly understood. Immediately west and southwest of Penobscot Bay the rocks are polymetamorphic showing evidence for at least two episodes of amphibolite facies metamorphism and later, perhaps regionally extensive, retrograde events. Hornblende mineral separates from two amphibolites din the Port Clyde area have identical Ar-40/Ar-39 plateau ages of 414.0 [+-] 3.3 and 414.0 [+-] 3.9 Ma. These ages are interpreted to reflect the time of cooling following the last significant thermal event in this area. Biotite from an amphibolite in the Port Clyde area givesmore » a total gas age of 346.5 [+-] 3.2 Ma. Hornblende from an amphibolite 7 km to the west near Friendship gives a nearly concordant release spectrum with a plateau age of 369.0 [+-] 3.7 Ma. Coexisting biotite from this amphibolite gives a total gas age of 289.2 [+-] 2.7 Ma. Muscovite from the Waldoboro pluton has a nearly concordant release spectrum with a plateau age of 306.3 [+-] 2.2 Ma. Biotite from this sample gives a total gas age of 288.9 [+-] 2.2 Ma. The 414.0 Ma hornblende cooling ages from the Port Clyde area reflect cooling following a significant high grade Silurian thermal event. This Silurian metamorphism is the same age as tectonothermal events in the Nashoba Terrane in eastern Massachusetts, the Kingston Complex in southern New Brunswick, the Aspy Terrane in Cape Breton island, Nova Scotia, and the Hermitage Flexure in southern Newfoundland.d Thus a distinctive Silurian tectonothermal province located along the western edge of the Avalon Zone appears to extend discontinuously from Massachusetts to Newfoundland.« less

Response of zircon to melting and metamorphism in deep arc crust, Fiordland (New Zealand): implications for zircon inheritance in cordilleran granites

NASA Astrophysics Data System (ADS)

Bhattacharya, Shrema; Kemp, A. I. S.; Collins, W. J.

2018-04-01

The Cretaceous Mount Daniel Complex (MDC) in northern Fiordland, New Zealand was emplaced as a 50 m-thick dyke and sheet complex into an active shear zone at the base of a Cordilleran magmatic arc. It was emplaced below the 20-25 km-thick, 125.3 ± 1.3 Ma old Western Fiordland Orthogneiss (WFO) and is characterized by metre-scale sheets of sodic, low and high Sr/Y diorites and granites. 119.3 ± 1.2 Ma old, pre-MDC lattice dykes and 117.4 ± 3.1 Ma late-MDC lattice dykes constrain the age of the MDC itself. Most dykes were isoclinally folded as they intruded, but crystallised within this deep-crustal, magma-transfer zone as the terrain cooled and was buried from 25 to 50 km (9-14 kbar), based on published P-T estimated from the surrounding country rocks. Zircon grains formed under these magmatic/granulite facies metamorphic conditions were initially characterized by conservatively assigning zircons with oscillatory zoning as igneous and featureless rims as metamorphic, representing 54% of the analysed grains. Further petrological assignment involved additional parameters such as age, morphology, Th/U ratios, REE patterns and Ti-in-zircon temperature estimates. Using this integrative approach, assignment of analysed grains to metamorphic or igneous groupings improved to 98%. A striking feature of the MDC is that only 2% of all igneous zircon grains reflect emplacement, so that the zircon cargo was almost entirely inherited, even in dioritic magmas. Metamorphic zircons of MDC show a cooler temperature range of 740-640 °C, reflects the moderate ambient temperature of the lower crust during MDC emplacement. The MDC also provides a cautionary tale: in the absence of robust field and microstructural relations, the igneous-zoned zircon population at 122.1 ± 1.3 Ma, derived mostly from inherited zircons of the WFO, would be meaningless in terms of actual magmatic emplacement age of MDC, where the latter is further obscured by younger (ca. 114 Ma) metamorphic overgrowths

Evaluating the importance of metamorphism in the foundering of continental crust.

PubMed

Chapman, Timothy; Clarke, Geoffrey L; Piazolo, Sandra; Daczko, Nathan R

2017-10-12

The metamorphic conditions and mechanisms required to induce foundering in deep arc crust are assessed using an example of representative lower crust in SW New Zealand. Composite plutons of Cretaceous monzodiorite and gabbro were emplaced at ~1.2 and 1.8 GPa are parts of the Western Fiordland Orthogneiss (WFO); examples of the plutons are tectonically juxtaposed along a structure that excised ~25 km of crust. The 1.8 GPa Breaksea Orthogneiss includes suitably dense minor components (e.g. eclogite) capable of foundering at peak conditions. As the eclogite facies boundary has a positive dP/dT, cooling from supra-solidus conditions (T > 950 ºC) at high-P should be accompanied by omphacite and garnet growth. However, a high monzodioritic proportion and inefficient metamorphism in the Breaksea Orthogneiss resulted in its positive buoyancy and preservation. Metamorphic inefficiency and compositional relationships in the 1.2 GPa Malaspina Pluton meant it was never likely to have developed densities sufficiently high to founder. These relationships suggest that the deep arc crust must have primarily involved significant igneous accumulation of garnet-clinopyroxene (in proportions >75%). Crustal dismemberment with or without the development of extensional shear zones is proposed to have induced foundering of excised cumulate material at P > 1.2 GPa.

Structural, metamorphic and geochronological insights on the Variscan evolution of the Alpine basement in the Belledonne Massif (France)

NASA Astrophysics Data System (ADS)

Fréville, Kévin; Trap, Pierre; Faure, Michel; Melleton, Jérémie; Li, Xian-Hua; Lin, Wei; Blein, Olivier; Bruguier, Olivier; Poujol, Marc

2018-02-01

A structural and petrochronological study was carried out in the southern part of the Belledonne crystalline massif. A first tectonometamorphic event, Dx, corresponds to the eastward thrusting of the Chamrousse ophiolitic complex characterized by a low-temperature-moderate-pressure metamorphism reaching 0.535 ± 0.045 GPa and 427.5 ± 17.5 °C. A subsequent D1 deformation is defined by a penetrative S1 foliation that mostly dips toward the west and displays an E-W- to NE-SW-trending mineral and stretching lineation L1. D1 is associated with a top-to-the east shearing and is responsible for the crustal thickening accommodated by the eastward nappe stacking and the emplacement of the Chamrousse ophiolitic complex upon the Rioupéroux-Livet unit. This event is characterized by an amphibolite facies metamorphism (0.58 GPa ± 0.06; 608 ± 14 °C) that attains partial melting at the base of the nappe pile (0.78 ± 0.07 GPa; 680.5 ± 11.5 °C). LA-ICP-MS U-Pb dating of monazite grains from the mica schists of the Rioupéroux-Livet unit constrain the age of D1 to 337 ± 7 Ma. The D2 tectono-metamorphic event is characterized by NE-SW trending, upright to NE-verging synfolial folding. Folding associated with D2 is pervasively developed in all lithotectonic units with the development of a steeply-dipping S2 foliation. In particular, D2 involves the uppermost weakly metamorphosed Taillefer unit. LA-ICP-MS U-Pb dating performed on detrital zircon grains shows that the Taillefer conglomerates was deposited during the Visean. A zircon SIMS U-Pb age of 352 ± 1 Ma from a plagioglase-rich leucocratic sill of the Rioupéroux-Livet unit is interpreted as the age of magmatic emplacement. Our results suggest that the D2 event took place between 330 Ma and 310 Ma. We propose a new interpretation of the tectonometamorphic evolution of the southern part of the Belledonne massif, focusing on the Middle Carboniferous stages of the Variscan orogeny.

Distributed consensus for metamorphic systems using a gossip algorithm for CAT(0) metric spaces

NASA Astrophysics Data System (ADS)

Bellachehab, Anass; Jakubowicz, Jérémie

2015-01-01

We present an application of distributed consensus algorithms to metamorphic systems. A metamorphic system is a set of identical units that can self-assemble to form a rigid structure. For instance, one can think of a robotic arm composed of multiple links connected by joints. The system can change its shape in order to adapt to different environments via reconfiguration of its constituting units. We assume in this work that several metamorphic systems form a network: two systems are connected whenever they are able to communicate with each other. The aim of this paper is to propose a distributed algorithm that synchronizes all the systems in the network. Synchronizing means that all the systems should end up having the same configuration. This aim is achieved in two steps: (i) we cast the problem as a consensus problem on a metric space and (ii) we use a recent distributed consensus algorithm that only make use of metrical notions.

Onset of the Sveconorwegian orogeny: 1220-1130 Ma bimodal magmatism, sedimentation and granulite-facies metamorphism

NASA Astrophysics Data System (ADS)

Bingen, Bernard; Viola, Giulio; Engvik, Ane K.; Solli, Arne

2013-04-01

indicates that Kongsberg was linked to Telemarkia, before 1147 Ma and before their final tectonic juxtaposition. A similar pattern is known between the Bamble and Telemarkia terranes, indicating similar relations. (4) The classical medium pressure granulite-facies metamorphism in Tromøy-Arendal, Bamble, was redated. Three granulite samples show metamorphic zircon at 1147 +/-18 and 1132 +/-7 Ma. Protolith ages between c. 1553 and 1544 Ma demonstrate a Gothian low-K calc-alkaline orthogneiss protolith and question recent interpretations representing the Tromøy complex as an early Sveconorwegian oceanic volcanic arc accreted to the Bamble terrane. (5) A granulite-facies domain was discovered north of Kragerø in Bamble, in an area generally assigned to amphibolites-facies metamorphism. Geothermobarometry and pseudosection calculation using the Grt +Opx +/-Cpx +Pl +Qtz assemblage yield an estimate of about 1.15 GPa and 800°C for peak granulite facies metamorphism. Late clinopyroxene and garnet zoning are consistent with an anticklockwise P-T path and suggest magma loading and heating of the crust. Soccer ball zircon dates this metamorphism at 1144 ±6 Ma. (6) C. 1193-1183 Ma A-type granite plutonism is reported in the Caledonian Middle-Allochthon Risberget Nappe and c. 1221-1204 Ma syenite plutons are known along the Sveconorwegian Frontal Deformation Zone. C. 1220-1130 Ma magmatism is however entirely lacking in the Idefjorden terrane. Using these constraints, we envisage the 1220-1130 Ma pre- to early-Sveconorwegian event in a trans(?)-tensional continental setting at the margin of Baltica, before final continental collision. The Telemarkia terrane was possibly located in a back arc position above an east dipping subduction system. Abundant magmatism is possibly a consequence of subduction of an oceanic ridge. Inversion took place after 1130 Ma leading to westwards thrusting of the Bamble and Kongsberg terranes.

Ar-Ar and Rb-Sr dating of very low-/low-grade metamorphism along the main Iapetus suture, Newfoundland

NASA Astrophysics Data System (ADS)

Willner, Arne P.; Glodny, Johannes; Massonne, Hans-Joachim; Romer, Rolf L.; Sudo, Masafumi; Van Staal, Cees R.; Zagorevski, Alexandre

2013-04-01

The Late Ordovician closure of the main tract of Iapetus resulted in juxtaposition of the leading edge of the peri-Gondwanan microplate Ganderia and the composite Laurentian margin. The suture is the Red Indian Line, which separates the Iapetan realm into peri-Gondwanan and peri-Laurentian arc-backarc complexes. The discrete Red Indian Line forms part of a wider collision zone that has a protracted and complicated tectonic history starting with underplating of oceanic terranes beneath the composite margin of Laurentia at ca. 471 Ma during the early stages of the Taconic orogeny. Final collision along the Red Indian Line and closure of the Iapetus ocean occurred at 455 Ma with the underthrusting of the peri-Gondwanan Victoria arc and its Ganderian basement beneath the composite Laurentian margin. The accreted Iapetan realm terranes were progressively deformed during the closure of a remaining Iapetan marginal basin, resulting locally in significant overprint and reactivation during the Silurian (Salinic orogeny). Metamorphic overprint in the deformed Laurentia margin (Notre Dame Zone) above the Red Indian Line is mainly of very low grade to low grade and very heterogeneous. PT-conditions cluster at 3-5 kbar, 300-400°C and 6-7 kbar, 270-330°C. Medium grade conditions are related to local contact metamorphism. Ages of the local peak metamorphism in the peri-Laurentian Iapetan realm were determined by dating white mica with the Ar-Ar system and white mica-bearing assemblages with the Rb-Sr mineral isochron method. Both methods yielded ages that postdate the closure of the main tract of Iapetus. These generally belong to two age ranges: 418-430 Ma (Salinic events) and 350-390 Ma Neoacadian events). Partly two overprints can be detected in one and the same sample. Metamorphism is related to (1) reactivation of deformation in shear zones which partly cause further crustal thickening or strike slip-related deformation, (2) to external fluid influx, (3) to advective

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

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.

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 model for the origin of Himalayan anatexis and inverted metamorphism

NASA Astrophysics Data System (ADS)

Harrison, T. Mark; Grove, Marty; Lovera, Oscar M.; Catlos, E. J.

1998-11-01

The origin of the paired granite belts and inverted metamorphic sequences of the Himalaya has generally been ascribed to development of the Main Central Thrust (MCT). Although a variety of models have been proposed that link early Miocene anatexis with inverted metamorphism, recent dating studies indicate that recrystallization of elements of the MCT footwall occurred in the central Himalaya as recently as ˜6 Ma. The recognition that hanging wall magmatism and footwall metamorphism are not spatially and temporally related renders unnecessary the need for exceptional physical conditions to explain generation of the High Himalayan leucogranites and North Himalayan granites, which differ in age, petrogenesis, and emplacement style. We suggest that their origin is linked to shear heating on a continuously active thrust that cuts through Indian supracrustal rocks that had previously experienced low degrees of partial melting. Numerical simulations assuming a shear stress of 30 MPa indicate that continuous slip on the Himalayan decollement beginning at 25 Ma could trigger partial melting reactions leading to formation of the High Himalayan granite chain between 25 and 20 Ma and the North Himalayan belt between 17 and 8 Ma. The ramp-flat geometry we apply to model the Himalayan thrust system requires that the presently exposed rocks of the hanging wall resided at middle crustal levels above the decollement throughout the early and middle Miocene. Late Miocene, out-of-sequence thrusting within the broad shear zone beneath the MCT provides a mechanism to bring these rocks to the surface in their present location (i.e., well to the north of the present tectonic front) and has the additional benefit of explaining how the inverted metamorphic sequences formed beneath the MCT. We envision that formation of the MCT Zone involved successive accretion of tectonic slivers of the Lesser Himalayan Formations to the hanging wall and incorporate these effects into the model. The model

Dating an actively exhuming metamorphic core complex, the Suckling Dayman Massif in SE Papua New Guinea

NASA Astrophysics Data System (ADS)

Oesterle, J.; Seward, D.; Little, T.; Stockli, D. F.; Mizera, M.

2016-12-01

Low-temperature thermochronology is a powerful tool for revealing the thermal and kinematic evolution of metamorphic core complexes (MCCs). Most globally studied MCCs are ancient, partially eroded, and have been modified by deformation events that postdate their origin. The Mai'iu Fault is a rapidly slipping active low-angle normal fault (LANF) in the Woodlark Rift in Papua New Guinea that has exhumed a >25 km-wide (in the slip direction), and over 3 km-high domal fault surface in its footwall called the Suckling-Dayman massif. Some knowledge of the present-day thermal structure in the adjacent Woodlark Rift, and the pristine nature of this active MCC make it an ideal candidate for thermochronological study of a high finite-slip LANF. To constrain the thermal and kinematic evolution of this MCC we apply the U/Pb, fission-track (FT) and (U-Th)/He methods. Zircon U/Pb analyses from the syn-extensional Suckling Granite that intrudes the footwall of the MCC yield an intrusion age of 3.3 Ma. Preliminary zircon FT ages from the same body indicate cooling below 300 °C at 2.7 Ma. Ages decrease to 2.0 Ma with increasing proximity to the Mai'iu Fault and imply cooling controlled by tectonic exhumation. Almost coincident zircon U/Pb and FT ages from the nearby syn-extensional Mai'iu Monzonite, on the other hand, record extremely rapid cooling from magmatic temperatures to 300 °C at 2 Ma. As apparent from the preliminary He extraction stage, these syn-extensional plutons have young zircon and apatite (U-Th)/He ages. These initial results suggest that the Mai'iu Fault was initiated as an extensional structure by 3.3 Ma. We infer that it reactivated an older ophiolitic suture that had emplaced the Papuan Ultramafic body in the Paleogene. Rapid cooling of the Mai'iu Monzonite indicates that it was intruded into a part of the MCC's footwall that was already shallow in the crust by 2 Ma. This inference is further supported by the mineral andalusite occurring in the contact

Plate tectonics. Seismological detection of slab metamorphism.

PubMed

Julian, Bruce

2002-05-31

The occurrence of more or less continuous ground vibrations ("volcanic tremor") is an important indicator of volcanic activity. But results from the "Hi-net" seismic network in Japan reported by Obara show that continuous ground vibrations can occur far away from any volcanic activity. In his Perspective, Julian discusses the idea that this tremor is excited by flow of metamorphic fluids. He also identifies other possible locations where such a tremor may be detected and explains what may be learnt from measuring it.

Analysis of magnetotelluric profile data from the Ruby Mountains metamorphic core complex and southern Carlin Trend region, Nevada

USGS Publications Warehouse

Wannamaker, Philip E.; Doerner, William M.; Stodt, John A.; Sodergen, Timothy L.; Rodriguez, Brian D.

2002-01-01

We have collected about 150 magnetotelluric (MT) soundings in northeastern Nevada in the region of the Ruby Mountains metamorphic core complex uplift and southern Carlin mineral trend, in an effort to illuminate controls on core complex evolution and deposition of world-class gold deposits. The region has experienced a broad range of tectonic events including several periods of compressional and extensional deformation, which have contributed to the total expression of electrical resistivity. Most of the soundings are in three east-west profiles across increasing degrees of core uplift to the north (Bald Mountain, Harrison Pass and Secret Pass latitudes). Two shorter lines cross a prominent east-west structure to the north of the northern profile. MT impedance tensor and vertical magnetic field rotations imply a N-NNE average regional geoelectric strike, similar to surface geologic trends. Model resistivity cross sections were derived using a 2-D inversion algorithm, which damps departures of model parameters from an a priori structure, emphasizing the transverse magnetic (TM) mode and vertical magnetic field data. Geological interpretation of the resistivity combines previous seismic, potential field and isotope models, structural and petrological models for regional compression and extension, and detailed structural/stratigraphic interpretations incorporating drilling for petroleum and mineral exploration. To first order, the resistivity structure is one of a moderately conductive, Phanerozoic sedimentary section fundamentally disrupted by intrusion and uplift of resistive crystalline rocks. Late Devonian and early Mississippian shales of the Pilot and Chainman Formations together form an important conductive marker sequence in the stratigraphy and show pronounced increases in conductance (conductivity-thickness product) from east to west. These increases in conductance are attributed to graphitization caused by Elko-Sevier era compressional shear deformation and

Malleability and optimization of tetrahedral metamorphic element for deployable truss antenna reflector

NASA Astrophysics Data System (ADS)

Hu, Fei; Song, Yanping; Huang, Zhirong; Liu, Wenlan; Li, Wan

2018-05-01

The tetrahedral elements that make up the large deployable reflector (LDR) are a kind of metamorphic element, which belongs to the multi-loop coupling mechanism. Firstly, the method of combining topology with screw theory is put forward. The parametric model and the constrained matrix are established to analyze the malleability of 3RR-3RRR tetrahedral element. Secondly, the kinematics expression of each motion pair is deduced by the relationship between the velocity and the motion spinor. Finally, the configuration of the metamorphic element is optimized to make the parabolic antenna fully folded, so that the antenna can meet the maximum folding ratio. The results show that the 3RR-3RRR element is a single-degree of freedom (DOF) mechanism. What's more, three new configurations 3RS-3RRR, 3SR-3RRR and 3UU-3RRR are obtained on the basis of optimization. In particular, it proves to be that the LDR which consists of the 3RS-3RRR metamorphic element can achieve the maximum folding ratio. This paper provides a theoretical basis for the computer-aided design of the truss antennas, which has an excellent applicability in the field of aerospace and other multi-loop coupling mechanism.

Petrology, geochemistry and zirconology of impure calcite marbles from the Precambrian metamorphic basement at the southeastern margin of the North China Craton

NASA Astrophysics Data System (ADS)

Liu, Yi-Can; Zhang, Pin-Gang; Wang, Cheng-Cheng; Groppo, Chiara; Rolfo, Franco; Yang, Yang; Li, Yuan; Deng, Liang-Peng; Song, Biao

2017-10-01

Impure calcite marbles from the Precambrian metamorphic basement of the Wuhe Complex, southeastern margin of the North China Craton, provide an exceptional opportunity to understand the depositional processes during the Late Archean and the subsequent Palaeoproterozoic metamorphic evolution of one of the oldest cratons in the world. The studied marbles are characterized by the assemblage calcite + clinopyroxene + plagioclase + K-feldspar + quartz + rutile ± biotite ± white mica. Based on petrography and geochemistry, the marbles can be broadly divided into two main types. The first type (type 1) is rich in REE with a negative Eu anomaly, whereas the second type (type 2) is relatively poor in REE with a positive Eu anomaly. Notably, all marbles exhibit remarkably uniform REE patterns with moderate LREE/HREE fractionation, suggesting a close genetic relationship. Cathodoluminescence imaging, trace elements and mineral inclusions reveal that most zircons from two dated samples display distinct core-rim structures. Zircon cores show typical igneous features with oscillatory growth zoning and high Th/U ratios (mostly in the range 0.3-0.7) and give ages of 2.53 - 2.48 Ga, thus dating the maximum age of deposition of the protolith. Zircon rims overgrew during granulite-facies metamorphism, as evidenced by calcite + clinopyroxene + rutile + plagioclase + quartz inclusions, by Ti-in-zircon temperatures in the range 660-743 °C and by the low Th/U (mostly < 0.1) and Lu/Hf (< 0.001) ratios. Zircon rims from two dated samples yield ages of 1839 ± 7 Ma and 1848 ± 23 Ma, respectively, suggesting a Palaeoproterozoic age for the granulite-facies metamorphic event. These ages are consistent with those found in other Precambrian basement rocks and lower-crustal xenoliths in the region, and are critical for the understanding of the tectonic history of the Wuhe Complex. Positive Eu anomalies and high Sr and Ba contents in type 2 marbles are ascribed to syn-depositional felsic

U-Pb Dating of Unabraded Detrital Zircon Metamorphic Rims in the Nanaimo Basin, British Columbia

NASA Astrophysics Data System (ADS)

Boivin, M. P.; Guest, B.; Matthews, W.

2016-12-01

Thin metamorphic rims on detrital zircons from the Nanaimo Basin in SW British Columbia offer a unique opportunity to further constrain the source of these zircons, helping to resolve the long standing Baja BC controversy. Here we present an analytical approach for dating thin zircon rims and use it to show that zircons from the Nanaimo Basin are most likely derived from metamorphic rocks in southern California. Conventional in-situ laser ablation sample preparation typically requires mounting and polishing zircon grains to expose their core. However, in order to date these thin metamorphic zircon rims a depth-profiling approach on unabraded grains was employed. Zircon grains from the Upper Cretaceous Geoffrey, Spray, and Gabriola formations of the Nanaimo Group exposed on Denman and Hornby Islands (British Columbia) were sorted into five groups based on morphology. The zircons were then mounted on tape along with several grains of a well-characterised zircon reference material to validate the uncertainty of the method. The zircons were then imaged using a Zygo Zescope optical profilometer in order to correct for grain-to-grain variations in elevation relative to mounting medium and ensure consistent laser focus. Backscatter electron images (BSE) were used to further characterised the grains and optimize the location of laser ablation targets. Zircons were ablated using a Resonetics 193 nm excimer laser and uranium and lead isotopic ratios were measured using an Agilent 7700 quadrupole mass spectrometer. A low frequency laser repetition rate extended the data collection period on relatively thin zircon rims. Our results show that metamorphic zircon growth occurred in two main phases at 100 Ma and 77 Ma suggesting two sources of detrital zircons with differing metamorphic histories were present in the catchment area. The timing of metamorphism of the source area for the Nanaimo basin is inconsistent with derivation from sources in the Rocky Mountains (Lemhi sub

Silicate-Oxide Equilibria in the Wilson Lake Terrane, Labrador - Evidence for a Pre- Metamorphic Oxidizing Event

NASA Astrophysics Data System (ADS)

Korhonen, F. J.; Stout, J. H.

2006-05-01

The presence of Fe3+ and Ti in silicates and their presumed equilibration with Fe2+-Fe3+-Ti oxide minerals has long been recognized as an important factor in metamorphic phase equilibria. The Red Wine Mountains massif is a granulite facies unit in the Wilson Lake terrane of central Labrador, where this equilibration is especially important for estimating both temperature and fO2 during peak metamorphism. Peak assemblages are sapphirine + quartz, and orthopyroxene + sillimanite + quartz. The coexisting oxides, which are largely responsible for the pronounced aeromagnetic high of the massif, consist of nearly pure magnetite and an exsolved titanohematite. Estimates of fO2 based on magnetite + integrated titanohematite compositions are slightly below that defined by the pure magnetite-hematite buffer. This assemblage is also responsible for the magnetic signature of metagabbro and metanorite dikes, a fact which challenges the conventional wisdom that the high Fe3+ content of the host paragneisses was inherited from a highly oxidized ferruginous shale. We suggest here that prior to granulite facies metamorphism, an oxidizing hydrothermal event either coeval or following the emplacement of mafic dikes into the paragneiss host was responsible for the highly oxidized nature of the massif as a whole. Subsequent metamorphism then produced the observed assemblages. This scenario is supported by recent U-Pb zircon and monazite ages of ca. 1626 ± 10 Ma, which indicate that both metagabbro dikes and host paragneiss were metamorphosed at the same time. Dike emplacement and the oxidizing event must have preceded 1626 Ma. The implications of this pre-metamorphic oxidizing event is that Fe3+ becomes an inherent and fixed component in the chemical system during metamorphism. Phase relationships, preliminary thermodynamic modeling, and geothermobarometric constraints indicate that peak temperatures are lower than those previously determined for Fe3+-absent systems. More appropriate

Paleoproterozoic high-pressure metamorphism in the northern North China Craton and implications for the Nuna supercontinent

PubMed Central

Wan, Bo; Windley, Brian F.; Xiao, Wenjiao; Feng, Jianyun; Zhang, Ji'en

2015-01-01

The connection between the North China Craton (NCC) and contiguous cratons is important for the configuration of the Nuna supercontinent. Here we document a new Paleoproterozoic high-pressure (HP) complex dominated by garnet websterite on the northern margin of the NCC. The peak metamorphism of the garnet websterite was after ∼1.90 Ga when it was subducted to eclogite facies at ∼2.4 GPa, then exhumed back to granulite facies at ∼0.9 GPa before ∼1.82 Ga. The rock associations with their structural relationships and geochemical affinities are comparable to those of supra-subduction zone ophiolites, and supported by subduction-related signatures of gabbros and basalts. We propose that a ∼1.90 Ga oceanic fragment was subducted and exhumed into an accretionary complex along the northern margin of the NCC. Presence of the coeval Sharyzhalgai complex with comparable HP garnet websterites in the southern Siberian active margin favours juxtaposition against the NCC in the Paleoproterozoic. PMID:26388458

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

Morphological preservation of carbonaceous plant fossils in blueschist metamorphic rocks from New Zealand.

PubMed

Galvez, M E; Beyssac, O; Benzerara, K; Bernard, S; Menguy, N; Cox, S C; Martinez, I; Johnston, M R; Brown, G E

2012-03-01

Morphological and chemical evidence of ancient life is widespread in sedimentary rocks retrieved from shallow depths in the Earth's crust. Metamorphism is highly detrimental to the preservation of biological information in rocks, thus limiting the geological record in which traces of life might be found. Deformation and increasing pressure/temperature during deep burial may alter the morphology as well as the composition and structure of both the organic and mineral constituents of fossils. However, microspore fossils have been previously observed in intensely metamorphosed rocks. It has been suggested that their small size, and/or the nature of the polymer composing their wall, and/or the mineralogy of their surrounding matrix were key parameters explaining their exceptional preservation. Here, we describe the remarkable morphological preservation of plant macrofossils in blueschist metamorphic rocks from New Zealand containing lawsonite. Leaves and stems can be easily identified at the macroscale. At the microscale, polygonal structures with walls mineralized by micas within the leaf midribs and blades may derive from the original cellular ultrastructure or, alternatively, from the shrinkage during burial of the gelified remnants of the leaves in an abiotic process. Processes and important parameters involved in the remarkable preservation of these fossils during metamorphism are discussed. Despite the excellent morphological preservation, the initial biological polymers have been completely transformed to graphitic carbonaceous matter down to the nanometer scale. This occurrence demonstrates that plant macrofossils may experience major geodynamic processes such as metamorphism and exhumation involving deep changes and homogenization of their carbon chemistry and structure but still retain their morphology with remarkable integrity even if they are not shielded by any hard-mineralized concretion. © 2012 Blackwell Publishing Ltd.

Ostwald ripening of clays and metamorphic minerals

USGS Publications Warehouse

Eberl, D.D.; Srodon, J.; Kralik, M.; Taylor, B.E.; Peterman, Z.E.

1990-01-01

Analyses of particle size distributions indicate that clay minerals and other diagenetic and metamorphic minerals commonly undergo recrystallization by Ostwald ripening. The shapes of their particle size distributions can yield the rate law for this process. One consequence of Ostwald ripening is that a record of the recrystallization process is preserved in the various particle sizes. Therefore, one can determine the detailed geologic history of clays and other recrystallized minerals by separating, from a single sample, the various particle sizes for independent chemical, structural, and isotopic analyses.

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.

Crustal structure in the Elko-Carlin Region, Nevada, during Eocene gold mineralization: Ruby-East Humboldt metamorphic core complex as a guide to the deep crust

USGS Publications Warehouse

Howard, K.A.

2003-01-01

The deep crustal rocks exposed in the Ruby-East Humboldt metamorphic core complex, northeastern Nevada, provide a guide for reconstructing Eocene crustal structure ~50 km to the west near the Carlin trend of gold deposits. The deep crustal rocks, in the footwall of a west-dipping normal-sense shear system, may have underlain the Pinon and Adobe Ranges about 50 km to the west before Tertiary extension, close to or under part of the Carlin trend. Eocene lakes formed on the hanging wall of the fault system during an early phase of extension and may have been linked to a fluid reservoir for hydrothermal circulation. The magnitude and timing of Paleogene extension remain indistinct, but dikes and tilt axes in the upper crust indicate that spreading was east-west to northwest-southeast, perpendicular to a Paleozoic and Mesozoic orogen that the spreading overprinted. High geothermal gradients associated with Eocene or older crustal thinning may have contributed to hydrothermal circulation in the upper crust. Late Eocene eruptions, upper crustal dike intrusion, and gold mineralization approximately coincided temporally with deep intrusion of Eocene sills of granite and quartz diorite and shallower intrusion of the Harrison Pass pluton into the core-complex rocks. Stacked Mesozoic nappes of metamorphosed Paleozoic and Precambrian rocks in the core complex lay at least 13 to 20 km deep in Eocene time, on the basis of geobarometry studies. In the northern part of the complex, the presently exposed rocks had been even deeper in the late Mesozoic, to >30 km depths, before losing part of their cover by Eocene time. Nappes in the core plunge northward beneath the originally thicker Mesozoic tectonic cover in the north part of the core complex. Mesozoic nappes and tectonic wedging likely occupied the thickened midlevel crustal section between the deep crustal core-complex intrusions and nappes and the overlying upper crust. These structures, as well as the subsequent large

Microdeformation in Vredefort rocks; evidence for shock metamorphism

NASA Technical Reports Server (NTRS)

Reimold, W. U.; Andreoli, M. A. G.; Hart, R. J.

1988-01-01

Planar microdeformations in quartz from basement or collar rocks of the Vredefort Dome have been cited for years as the main microtextural evidence for shock metamorphism in this structure. In addition, Schreyer describes feldspar recrystallization in rocks from the center of the Dome as the result of transformation of diaplectic glass, and Lilly reported the sighting of mosaicism in quartz. These textural observations are widely believed to indicate either an impact or an internally produced shock origin for the Vredefort Dome. Two types of (mostly sub) planar microdeformations are displayed in quartz grains from Vredefort rocks: (1) fluid inclusion trails, and (2) straight optical discontinuities that sometimes resemble lamellae. Both types occur as single features or as single or multiple sets in quartz grains. Besides qualitative descriptions of cleavage and recrystallization in feldspar and kinkbands in mica, no further microtextural evidence for shock metamorphism at Vredefort has been reported to date. Some 150 thin sections of Vredefort basement rocks were re-examined for potential shock and other deformation effects in all rock-forming minerals. This included petrographic study of two drill cores from the immediate vicinity of the center of the Dome. Observations recorded throughout the granitic core are given along with conclusions.

Gold deposits in metamorphic belts: Overview of current understanding, outstanding problems, future research, and exploration significance

USGS Publications Warehouse

Groves, D.I.; Goldfarb, R.J.; Robert, F.; Hart, C.J.R.

2003-01-01

Metamorphic belts are complex regions where accretion or collision has added to, or thickened, continental crust. Gold-rich deposits can be formed at all stages of orogen evolution, so that evolving metamorphic belts contain diverse gold deposit types that may be juxtaposed or overprint each other. This partly explains the high level of controversy on the origin of some deposit types, particularly those formed or overprinted/remobilized during the major compressional orogeny that shaped the final geometry of the hosting metamorphic belts. These include gold-dominated orogenic and intrusion-related deposits, but also particularly controversial gold deposits with atypical metal associations. There are a number of outstanding problems for all types of gold deposits in metamorphc belts. These include the following: (1) definitive classifications, (2) unequivocal recognition of fluid and metal sources, (3) understanding of fluid migration and focusing at all scales, (4) resolution of the precise role of granitoid magmatism, (5) precise gold-depositional mechanisms, particularly those producing high gold grades, and (6) understanding of the release of CO2-rich fluids from subducting slabs and subcreted oceanic crust and granitoid magmas at different crustal levels. Research needs to be better coordinated and more integrated, such that detailed fluid-inclusion, trace-element, and isotopic studies of both gold deposits and potential source rocks, using cutting-edge technology, are embedded in a firm geological framework at terrane to deposit scales. Ultimately, four-dimensional models need to be developed, involving high-quality, three-dimensional geological data combined with integrated chemical and fluid-flow modeling, to understand the total history of the hydrothermal systems involved. Such research, particularly that which can predict superior targets visible in data sets available to exploration companies before discovery, has obvious spin-offs for global- to deposit

Ammonium loss and nitrogen isotopic fractionation in biotite as a function of metamorphic grade in metapelites from western Maine, USA

NASA Astrophysics Data System (ADS)

Plessen, Birgit; Harlov, Daniel E.; Henry, Darrell; Guidotti, Charles V.

2010-08-01

Ammonium fixed in micas of metamorphic rocks is a sensitive indicator both of organic-inorganic interactions during diagenesis as well as of the devolatilization history and fluid/rock interaction during metamorphism. In this study, a collection of geochemically well-characterized biotite separates from a series of graphite-bearing Paleozoic greenschist- to upper amphibolite-facies metapelites, western Maine, USA, were analyzed for ammonium nitrogen ( NH4+-N) contents and isotopic composition (δ 15N NH4) using the HF-digestion distillation technique followed by the EA-IRMS technique. Biotite separates, sampled from 9 individual metamorphic zones, contain 3000 to 100 ppm NH4+-N with a wide range in δ 15N from +1.6‰ to +9.1‰. Average NH4+-N contents in biotite show a distinct decrease from about 2750 ppm for the lowest metamorphic grade (˜500 °C) down to 218 ppm for the highest metamorphic grade (˜685 °C). Decreasing abundances in NH4+ are inversely correlated in a linear fashion with increasing K + in biotite as a function of metamorphic grade and are interpreted as a devolatilization effect. Despite expected increasing δ 15N NH4 values in biotite with nitrogen loss, a significant decrease from the Garnet Zones to the Staurolite Zones was found, followed by an increase to the Sillimanite Zones. This pattern for δ 15N NH4 values in biotite inversely correlates with Mg/(Mg + Fe) ratios in biotite and is discussed in the framework of isotopic fractionation due to different exchange processes between NH4+-NH or NH4+-N, reflecting devolatilization history and redox conditions during metamorphism.

A- and I-type metagranites from the North Shahrekord Metamorphic Complex, Iran: Evidence for Early Paleozoic post-collisional magmatism

NASA Astrophysics Data System (ADS)

Badr, Afsaneh; Davoudian, Ali Reza; Shabanian, Nahid; Azizi, Hossein; Asahara, Yoshihiro; Neubauer, Franz; Dong, Yunpeng; Yamamoto, Koshi

2018-02-01

The North Shahrekord Metamorphic Complex (NSMC) of the central Sanandaj-Sirjan Zone (SaSZ) consists of metagranitoid bodies, which were metamorphosed within high pressure-low temperature conditions. Whole rock chemistry shows relatively high amounts of SiO2 (65-77 wt%) and Al2O3 (12-15 wt%), low amounts of Nb, P, Sr, Ti, a high ratio of Ga/Al (4-9) and a negative Eu anomaly. The chemical compositions of metagranites are reasonably similar to A- and I-type granites. U-Pb zircon ages of three samples of metagranites indicate that crystallization of the granites occurred at 521.6 ± 9.1 to 513.5 ± 8.5 Ma, Middle Cambrian. The initial 87Sr/86Sr and 143Nd/144Nd ratios of samples vary from 0.7057-0.7239 and 0.511801-0.511890, respectively. High initial 87Sr/86Sr ratios and low εNd(t) values (- 3.39 to - 1.07) associated with high ratios of 206Pb/204Pb(t) = 17.8557-18.8045, 207Pb/204Pb(t) = 15.6721-15.7220, and 208Pb/204Pb(t) = 37.7490-38.4468 infer a significant contribution of continental crust in generating the source magma of the metagranite bodies. The results reveal that the metagranites were mainly produced through mixing of basaltic melts with components similar to metasedimentary sources. The new results show that crystallization of the metagranites occurred in Early Paleozoic times and much earlier than break-up and drifting of the SaSZ from the Arabian plate, suggesting that the metagranites were mainly produced in the western Iran after the closure of the Proto-Tethys Ocean. This model is consistent with the previously suggested models for formation of an Early Paleozoic granitoid belt along the northern rim of Gondwana.

Revised nomenclature and stratigraphic relationships of the Fredericksburg Complex and Quantico Formation of the Virginia Piedmont

USGS Publications Warehouse

Pavlides, Louis

1980-01-01

The Fredericksburg Complex, in part a migmatitic terrane in northeast Virginia, is subdivided on the basis of lithology, as well as aeromagnetic and aeroradiometric data, into two metamorphic suites. These suites are separated by the northeast-trending Spotsylvania lineament, a rectilinear geophysical feature that is probably the trace of an old fault zone. East of the lineament, the Po River Metamorphic Suite, of Proterozoic Z and (or) early Paleozoic age, consists dominantly of biotite gneiss, generally augen gneiss, and lesser amounts of hornblende gneiss and mica schist. West of the Spotsylvania lineament is the Ta River Metamorphic Suite, composed mostly of amphibolite and amphibole gneiss. However, to the southwest, along its strike belt, the Ta River contains abundant biotite gneiss and mica schist. Both the Ta River and Po River contain abundant foliated granitoid and pegmatoid bodies as concordant tabular masses and as crosscutting dikes; these rocks are considered part of the Ta River and Po River Metamorphic Suites. The amphibolitic Holly Corner Gneiss is interpreted to be a western allochthonous equivalent of the Ta River. Both the Ta River and Holly Corner are considered to be coeval, eastern, distal facies of the Lower Cambrian(?) Chopawamsic Formation. The Paleozoic Falls Run Granite Gneiss intrudes the Ta River Metamorphic Suite and the Holly Corner Gneiss; locally the Falls Run is interpreted to have been transported westward with the Holly Corner after intrusion. The Quantico Formation, in the core of the Quantico-Columbia synclinorium, rests with angular unconformity along its northwest and southeast limbs, respectively, on the Chopawamsic Formation and the Ta River Metamorphic Suite. The Quantico Formation is assigned the same Late Ordovician age and similar stratigraphic position as the Arvonia Slate of the Arvonia syncline. The youngest rocks of the area are the granitoid and pegmatoid bodies of the Falmouth Intrusive Suite. They consist of

Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

NASA Astrophysics Data System (ADS)

Zheng, Nan; Ahrenkiel, S. Phillip

2017-07-01

Metamorphic growth presents routes to novel nanomaterials with unique properties that may be suitable for a range of applications. We discuss self-assembled, epitaxial nanowires formed during metalorganic chemical vapor deposition of metamorphic GaAs/GaPAs short-period superlattices. The heterostructures incorporate strain-engineered GaPAs compositional grades on 6°-<111>B miscut GaAs substrates. Lateral diffusion within the SPS into vertically aligned, three-dimensional columns results in nanowires extending along <110>A directions with a lateral period of 70-90 nm. The microstructure is probed by transmission electron microscopy to confirm the presence of coherent GaAs nanowires within GaPAs barriers. The compositional profile is inferred from analysis of {200} dark-field image contrast and <210> lattice images.

Retrogressive hydration of calc-silicate xenoliths in the eastern Bushveld complex: evidence for late magmatic fluid movement

NASA Astrophysics Data System (ADS)

Wallmach, T.; Hatton, C. J.; De Waal, S. A.; Gibson, R. L.

1995-11-01

Two calc-silicate xenoliths in the Upper Zone of the Bushveld complex contain mineral assemblages which permit delineation of the metamorphic path followed after incorporation of the xenoliths into the magma. Peak metamorphism in these xenoliths occurred at T=1100-1200°C and P <1.5 kbar. Retrograde metamorphism, probably coinciding with the late magmatic stage, is characterized by the breakdown of akermanite to monticellite and wollastonite at 700°C and the growth of vesuvianite from melilite. The latter implies that water-rich fluids (X CO 2 <0.2) were present and probably circulating through the cooling magmatic pile. In contrast, calc-silicate xenoliths within the lower zones of the Bushveld complex, namely in the Marginal and Critical Zones, also contain melilite, monticellite and additional periclase with only rare development of vesuvianite. This suggests that the Upper Zone cumulate pile was much 'wetter' in the late-magmatic stage than the earlier-formed Critical and Marginal Zone cumulate piles.

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

Proterozoic metamorphism and uplift history of the north-central Laramie Mountains, Wyoming, USA

USGS Publications Warehouse

Patel, S.C.; Frost, B.R.; Chamberlain, K.R.; Snyder, G.L.

1999-01-01

The Laramie Mountains of south-eastern Wyoming contain two metamorphic domains that are separated by the 1.76 Ga. Laramie Peak shear zone (LPSZ). South of the LPSZ lies the Palmer Canyon block, where apatite U-Pb ages are c. 1745 Ma and the rocks have undergone Proterozoic kyanite-grade Barrovian metamorphism. In contrast, in the Laramie Peak block, north of the shear zone, the U-Pb apatite ages are 2.4-2.1 Ga, the granitic rocks are unmetamorphosed and supracrustal rocks record only low-T amphibolite facies metamorphism that is Archean in age. Peak mineral assemblages in the Palmer Canyon block include (a) quartz-biotite-plagioclase-garnet-staurolite-kyanite in the pelitic schists; (b) quartz-biotite-plagioclase-low-Ca amphiboles-kyanite in Mg-Al-rich schists, and locally (c) hornblende-plagioclase-garnet in amphibolites. All rock types show abundant textural evidence of decompression and retrograde re-equilibration. Notable among the texturally late minerals are cordierite and sapphirine, which occur in coronas around kyanite in Mg-Al-rich schists. Thermobarometry from texturally early and late assemblages for samples from different areas within the Palmer Canyon block define decompression from > 7 kbar to < 3 kbar. The high-pressure regional metamorphism is interpreted to be a response to thrusting associated with the Medicine Bow orogeny at c. 1.78-1.76 Ga. At this time, the north-central Laramie Range was tectonically thickened by as much as 12 km. This crustal thickening extended for more than 60 km north of the Cheyenne belt in southern Wyoming. Late in the orogenic cycle, rocks of the Palmer Canyon block were uplifted and unroofed as the result of transpression along the Laramie Peak shear zone to produce the widespread decompression textures. The Proterozoic tectonic history of the central Laramie Range is similar to exhumation that accompanied late-orogenic oblique convergence in many Phanerozoic orogenic belts.

Testing and Validating Machine Learning Classifiers by Metamorphic Testing☆

PubMed Central

Xie, Xiaoyuan; Ho, Joshua W. K.; Murphy, Christian; Kaiser, Gail; Xu, Baowen; Chen, Tsong Yueh

2011-01-01

Machine Learning algorithms have provided core functionality to many application domains - such as bioinformatics, computational linguistics, etc. However, it is difficult to detect faults in such applications because often there is no “test oracle” to verify the correctness of the computed outputs. To help address the software quality, in this paper we present a technique for testing the implementations of machine learning classification algorithms which support such applications. Our approach is based on the technique “metamorphic testing”, which has been shown to be effective to alleviate the oracle problem. Also presented include a case study on a real-world machine learning application framework, and a discussion of how programmers implementing machine learning algorithms can avoid the common pitfalls discovered in our study. We also conduct mutation analysis and cross-validation, which reveal that our method has high effectiveness in killing mutants, and that observing expected cross-validation result alone is not sufficiently effective to detect faults in a supervised classification program. The effectiveness of metamorphic testing is further confirmed by the detection of real faults in a popular open-source classification program. PMID:21532969

Building a Six-Junction Inverted Metamorphic Concentrator Solar Cell

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

Geisz, John F.; Steiner, Myles A.; Jain, Nikhil

We propose practical six-junction (6J) inverted metamorphic multijunction (IMM) concentrator solar cell designs with the potential to exceed 50% efficiency using moderately high quality junction materials. We demonstrate the top three junctions and their monolithic integration lattice matched to GaAs using 2.1-eV AlGaInP, 1.7-eV AlGaAs or GaInAsP, and 1.4-eV GaAs with external radiative efficiencies >0.1%. We demonstrate tunnel junctions with peak tunneling current >400 A/cm 2 that are transparent to <2.1-eV light. We compare the bottom three GaInAs(p) junctions with bandgaps of 1.2, 1.0, and 0.7 eV grown on InP and transparent metamorphic grades with low dislocation densities. The solutionmore » to an integration challenge resulting from Zn diffusion in the GaAs junction is illustrated in a five-junction IMM. Excellent 1-sun performance is demonstrated in a complete 6J IMM device with VOC = 5.15 V, and a promising pathway toward >50% efficiency at high concentrations is presented.« less

Building a Six-Junction Inverted Metamorphic Concentrator Solar Cell

DOE PAGES

Geisz, John F.; Steiner, Myles A.; Jain, Nikhil; ...

2017-12-20

We propose practical six-junction (6J) inverted metamorphic multijunction (IMM) concentrator solar cell designs with the potential to exceed 50% efficiency using moderately high quality junction materials. We demonstrate the top three junctions and their monolithic integration lattice matched to GaAs using 2.1-eV AlGaInP, 1.7-eV AlGaAs or GaInAsP, and 1.4-eV GaAs with external radiative efficiencies >0.1%. We demonstrate tunnel junctions with peak tunneling current >400 A/cm 2 that are transparent to <2.1-eV light. We compare the bottom three GaInAs(p) junctions with bandgaps of 1.2, 1.0, and 0.7 eV grown on InP and transparent metamorphic grades with low dislocation densities. The solutionmore » to an integration challenge resulting from Zn diffusion in the GaAs junction is illustrated in a five-junction IMM. Excellent 1-sun performance is demonstrated in a complete 6J IMM device with VOC = 5.15 V, and a promising pathway toward >50% efficiency at high concentrations is presented.« less

The Later Paleozoic granites of the Greater Caucasus Fore Range zone: geochemistry, magnetic properties and the structural and metamorphic evolution.

NASA Astrophysics Data System (ADS)

Kamzolkin, Vladimir; Latyshev, Anton; Ivanov, Stanislav; Vidjapin, Jury

2017-04-01

Clarification of the position of the granitic intrusions associated with the Blyb Metamorphic Complex is the important problem of the reconstruction of the structural evolution of the Greater Caucasus Fore Range zone. Based of the rock geochemistry we found out that the quartz diorites, granodiorites and syeno-granites of the BMC formed in suprasubduction conditions and refer to I-type granites. However, their emplacement was multistage coinciding with the various stages of the BMC evolution. We detected the mineral associations typical for the epidote-amphibolite facies in the Balkan massif, but these metamorphic features are absent in the granodiorite intrusions in the southern part of the Fore Range zone. Thus, quartz diorites of the Balkan intrusion intruded after the high-pressure metamorphism of the host rocks, but before the epidote-amphibolite stage, and the Southern granodiorite intrusions are younger. The measurements of the anisotropy of the magnetic susceptibility (AMS) in the Balkan intrusion indicated the shallow orientation of the minimal (north-eastern strike) and maximal (north-western strike) axes of the AMS ellipsoid. This result is compatible with the idea of the north-east compression fixed in the fold deformation structures of the BMC host rocks (Vidyapin, Kamzolkin, 2015). However, the macroscopic foliation in the granites dips to the east steeply. The discrepancy of the texture orientation of the granites, the host rock structure and the magnetic fabric can be explained as a result of the repeated changes of the stress field during the evolution of the Fore Range nappe structures. The reported study was partially supported by RFBR, research projects No. 16-35-00571mol_a; 16-05-01012a.

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

Geochemical investigation of Archaean Bimodal and Dwalile metamorphic suites, Ancient Gneiss Complex, Swaziland

USGS Publications Warehouse

Hunter, D.R.; Barker, F.; Millard, H.T.

1984-01-01

The bimodal suite (BMS) comprises leucotonalitic and trondhjemitic gneisses interlayered with amphibolites. Based on geochemical parameters three main groups of siliceous gneiss are recognized: (i) SiO2 14%, and fractionated light rare-earth element (REE) and flat heavy REE patterns; (ii) SiO2 and Al2O3 contents similar to (i) but with strongly fractionated REE patterns with steep heavy REE slopes; (iii) SiO2 > 73%, Al2O3 < 14%, Zr ??? 500 ppm and high contents of total REE having fractionated light REE and flat heavy REE patterns with large negative Eu anomalies. The interlayered amphibolites have major element abundances similar to those of basaltic komatiites, Mg-tholeiites and Fe-rich tholeiites. The former have gently sloping REE patterns, whereas the Mg-tholeiites have non-uniform REE patterns ranging from flat (??? 10 times chondrite) to strongly light REE-enriched. The Fe-rich amphibolites have flat REE patterns at 20-30 times chondrite. The Dwalile metamorphic suite, which is preserved in the keels of synforms within the BMS, includes peridotitic komatiites that have depleted light REE patterns similar to those of compositionally similar volcanics in the Onverwacht Group, Barberton, basaltic komatiites and tholeiites. The basaltic komatiites have REE patterns parallel to those of the BMS basaltic komatiites but with lower total REE contents. The Dwalile tholeiites have flat REE patterns. The basic and ultrabasic liquids were derived by partial melting of a mantle source which may have been heterogeneous or the heterogeneity may have resulted from sequential melting of the mantle source. The Fe-rich amphibolites were derived either from liquids generated at shallow levels or from liquids generated at depth which subsequently underwent extensive fractionation. ?? 1984.

Mapping contact metamorphic aureoles in Extremadura, Spain, using Landsat thematic mapper images

USGS Publications Warehouse

Rowan, L.C.; Anton-Pacheco, C.; Brickey, D.W.; Kingston, M.J.; Payas, A.

1987-01-01

In the Extremadura region of western Spain, Ag, Pb, Zn, and Sn deposits occur in the pieces of late Hercynian granitic plutons and near the pluton contacts in late Proterozoic slate and metagraywacke that have been regionally metamorphosed to the green schist facies. The plutons generally are well exposed and have distinctive geomorphological expression and vegetation; poor exposures of the metasedimentary host rocks and extensive cultivation, however, make delineation of the contact aureoles difficult. Landsat Thematic Mapper (TM) images have been used to distinguish soil developed on the contact metamorphic rocks from soil formed on the stratigraphically equivalent slate-metagraywacke sequence. The mineral constituents of these soils are similar, except that muscovite is more common in the contact metamorphic soil; carbonaceous material is common in both soils. Contact metamorphic soil have lower reflectance, especially in the 1.6-micrometers wavelength region (TM 5), and weaker Al-OH, Mg-OH, and Fe3+ absorption features than do spectra of the slate-metagraywacke soil. The low-reflectance and subdued absorption features exhibited by the contact metamorphic soil spectra are attributed to the high absorption coefficient f the carbonaceous material caused by heating during emplacement of the granitic plutons. These spectral differences are evident in a TM 4/3, 4/5, 3/1 color-composite image. Initially, this image was used to outline the contact aureoles, but digital classification of the TM data was necessary for generating internally consistent maps of the distribution of the exposed contact metamorphic soil. In an August 1984, TM scene of the Caceras area, the plowed, vegetation-free fields were identified by their low TM 4/3 values. Then, ranges of TM 4/5 and 3/1 values were determine for selected plower fields within and outside the contact aureoles; TM 5 produced results similar to TM 4/5. Field evaluation, supported by X-ray diffraction and petrographic

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.

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

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.

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.

HP LT Variscan metamorphism in the Cubito-Moura schists (Ossa-Morena Zone, southern Iberia)

NASA Astrophysics Data System (ADS)

Booth-Rea, Guillermo; Simancas, José Fernando; Azor, Antonio; Azañón, José Miguel; González-Lodeiro, Francisco; Fonseca, Paulo

2006-12-01

Multi-equilibrium thermobarometry shows that low-grade metapelites (Cubito-Moura schists) from the Ossa-Morena Zone underwent HP-LT metamorphism from 340-370 °C at 1.0-0.9 GPa to 400-450 °C at 0.8-0.7 GPa. These HP-LT equilibriums were reached by parageneses including white K mica, chlorite and chloritoid, which define the earliest schistosity (S 1) in these rocks. The main foliation in the schists is a crenulation cleavage (S 2), which developed during decompression from 0.8-0.7 to 0.4-0.3 GPa at increasing temperatures from 400-450 °C to 440-465 °C. Fe 3+ in chlorite decreased greatly during prograde metamorphism from molar fractions of 0.4 determined in syn-S 1 chlorites down to 0.1 in syn-S 2 chlorites. These new data add to previous findings of eclogites in the Moura schists indicating that a pile of allochtonous rocks situated next to the Beja-Acebuches oceanic amphibolites underwent HP-LT metamorphism during the Variscan orogeny. To cite this article: G. Booth-Rea et al., C. R. Geoscience 338 (2006).

Impact-shocked zircons: discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

USGS Publications Warehouse

Bohor, B.F.; Betterton, W.J.; Krogh, T.E.

1993-01-01

Textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously. However, planar deformation features (PDF) due to shock metamorphism are well documented in quartz and other mineral grains from these same environments. An etching technique was developed that allows SEM visualization of PDF and other probable shock-induced textural features, such as granular (polycrystalline) texture, in zircons from a variety of impact shock environments. These textural features in shocked zircons from K/T boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the UPb isotopic system. ?? 1993.

Impact-shocked zircons: Discovery of shock-induced textures reflecting increasing degrees of shock metamorphism

NASA Technical Reports Server (NTRS)

Bohor, B. F.; Betterton, W. J.; Krogh, T. E.

1993-01-01

Textural effects specifically characteristic of shock metamorphism in zircons from impact environments have not been reported previously. However, planar deformation features (PDF) due to shock metamorphism are well documented in quartz and other mineral grains from these same environments. An etching technique was developed that allows scanning electron microscope (SEM) visualization of PDF and other probable shock-induced textural features, such as granular (polycrystalline) texture, in zircons from a variety of impact shock environments. These textural features in shocked zircons from K/T boundary distal ejecta form a series related to increasing degrees of shock that should correlate with proportionate resetting of the U-Pb isotopic system.

Time-Lapse Micro-Tomography Measurements and Determination of Effective Transport Properties of Snow Metamorphism Under Advective Conditions

NASA Astrophysics Data System (ADS)

Ebner, P. P.; Grimm, S.; Steen-Larsen, H. C.; Schneebeli, M.; Steinfeld, A.

2014-12-01

The metamorphism of snow under advective air flow, with and without temperature gradient, was never experimentally investigated. We developed a new sample holder where metamorphism under advective conditions can be observed and measured using time-lapse micro-tomography [1]. Long-term experiments were performed and direct pore-level simulation (DPLS) [2,3] was directly applied on the extracted 3D digital geometry of the snow to calculate the effective transport properties by solving the governing fluid flow equations. The results showed no effect of isothermal advection, compared to rates typical for isothermal metamorphism. Appling a temperature gradient, the results showed increased snow metamorphism compared to rates typical for temperature gradient metamorphism. However, for both cases a change in the isotopic composition in the air as well as in the snow sample could be observed. These measurements could be influential to better understand snow-air exchange processes relevant for atmospheric chemistry and isotopic composition. REFERENCES[1] Ebner P. P., Grimm S., Schneebeli M., and Steinfeld A.: An instrumented sample holder for time-lapse micro-tomography measurements of snow under advective airflow. Geoscientific Instrumentation, Methods and Data Systems 4(2014), 353-373. [2] Zermatten E., Haussener S., Schneebeli M., and Steinfeld A.: Tomography-based determination of permeability and Dupuit-Forchheimer coefficient of characteristic snow samples. Journal of Glaciology 57(2011), 811-816. [3] Zermatten E., Schneebeli M., Arakawa H., and Steinfeld A.: Tomography-based determination of porosity, specific area and permeability of snow and comparison with measurements. Cold Regions Science and Technology 97 (2014), 33-40. Fig. 1: 3-D surface rendering of a refrozen wet snow sample with fluid flow streamline.

Metamorphism, argon depletion, heat flow and stress on the Alpine fault

NASA Technical Reports Server (NTRS)

Scholz, C. H.; Beavan, J.; Hanks, T. C.

1978-01-01

The Alpine fault of New Zealand is a major continental transform fault which was uplifted on its southeast side 4 to 11 km within the last 5 m.y. This uplift has exposed the Haast schists, which were metamorphosed from the adjacent Torlesse graywackes. The Haast schists increase in metamorphic grade from prehnite-pumpellyite facies 9-12 km from the fault through the chlorite and biotite zones of the greenschist facies to the garnet-oligoclase zone amphibolite facies within 4 km of the fault. These metamorphic zone boundaries are subparallel to the fault for 350 km along the strike. The K-Ar and Rb-Sr ages of the schists increase with distance from the fault: from 4 m.y. within 3 km of the fault to approximately 110 m.y. 20 km from the fault. Field relations show that the source of heat that produced the argon depletion aureole was the fault itself.

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

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.

Igneous and metamorphic petrology in the field: a problem-based, writing-intensive alternative to traditional classroom petrology

NASA Astrophysics Data System (ADS)

DeBari, S. M.

2011-12-01

The Geology Department at Western Washington University (~100 geology majors) offers field and classroom versions of its undergraduate petrology course. This is a one-quarter course (igneous and metamorphic petrology) with mineralogy as a prerequisite. The field version of the course is offered during the three weeks prior to fall quarter and the classroom version is offered in spring quarter. We take 15-20 students around the state of Washington, camping at different outcrop sites where students integrate observational skills, petrologic knowledge, and writing. Petrogenetic associations in various tectonic settings provide the theme of the course. We compare ophiolites vs. arc sequences (volcanic, plutonic, and metamorphic rocks), S- vs. I-type granitoids (plutonic rocks and associated metamorphic rocks), Barrovian vs. Buchan vs. subduction zone metamorphism of different protoliths, and flood-basalt vs. active-arc volcanism. Some basics are covered in the first day at WWU, followed by 17 days of field instruction. Lecture is integrated with outcrop study in the field. For example, students will listen to a lecture about magma differentiation processes as they examine cumulate rocks in the Mt. Stuart batholith, and a lecture about metamorphic facies as they study blueschist facies rocks in the San Juan Islands. Students study multiple outcrops around a site for 1-4 days. They then use their observations (sketches and written descriptions of mineral assemblages, rock types, rock textures, etc.) and analysis techniques (e.g. geochemical data plotting, metamorphic protolith analysis) to write papers in which the data are interpreted in terms of a larger tectonic problem. In advance of the writing process, students use group discussion techniques such as whiteboarding to share their observational evidence and explore interpretations. Student evaluations indicate that despite the intense pace of the course, they enjoy it more. Students also feel that they retain more

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.

Review of metamorphic and kinematic data from Internal Crystalline Massifs (Western Alps): PTt paths and exhumation history

NASA Astrophysics Data System (ADS)

Gasco, Ivano; Gattiglio, Marco; Borghi, Alessandro

2013-01-01

Detailed geological mapping combined with micro-structural and petrological investigation allowed to clarify the tectono-metamorphic relationships between continental and oceanic units transition in the Penninic domain of the Western Alps. The three study areas (Gressoney, Orco and Susa sections) take into consideration the same structural level across the axial metamorphic belt of the Western Italian Alps, i.e., a geological section across the Internal Crystalline Massifs vs Piedmont Zone boundary. The units outcropping in these areas can be grouped into two Tectonic Elements according to their tectono-metamorphic evolution. The Lower Tectonic Element (LTE) consists of the Internal Crystalline Massifs and the Lower Piedmont Zone (Zermatt-Saas like units), both showing well preserved eclogite facies relics. Instead, the Upper Tectonic Element (UTE) consists of the Upper Piedmont Zone (Combin like units) lacking evidence of eclogite facies relics. In the Lower Tectonic Element two main Alpine tectono-metamorphic stages were identified: M1/D1 developed under eclogite facies conditions and M2/D2 is related to the development of the regional foliation under greenschist to epidote-albite amphibolite facies conditions. In the Upper Tectonic Element the metamorphic stage M1/D1 developed under bluschist to greenschist facies conditions and M2/D2 stage under greenschist facies conditions. These two Tectonic Elements are separated by a tectonic contact of regional importance generally developed along the boundary between the Lower and the Upper Piedmont zone under greenschist facies conditions. PT data compared to geochronology indicate that the first exhumation of ICM can be explained by buoyancy forces acting along the subduction channel that occurred during the tectonic coupling between the continental and oceanic eclogite units. These buoyancy forces vanished at the base of the crust where the density difference between the subducted crustal units and the surroundings

Metamorphism and plutonism around the middle and south forks of the Feather River, California

USGS Publications Warehouse

Hietanen, Anna Martta

1976-01-01

The area around the Middle and South Forks of the Feather River provides information on metamorphic and igneous processes that bear on the origin of andesitic and granitic magmas in general and on the variation of their potassium content in particular. In the north, the area joins the Pulga and Bucks Lake quadrangles studied previously. Tectonically, this area is situated in the southern part of an arcuate segment of the Nevadan orogenic belt in the northwestern Sierra Nevada. The oldest rocks are metamorphosed calcalkaline island-arc-type andesite, dacite, and sodarhyolite with interbedded tuff layers (the Franklin Canyon Formation), all probably correlative with Devonian rocks in the Klamath Mountains. Younger rocks form a sequence of volcanic, volcaniclastic, and sedimentary rocks including some limestone (The Horseshoe Bend Formation), probably Permian in age. All the volcanic and sedimentary rocks were folded and recrystallized to the greenschist facies during the Nevadan (Jurassic) orogeny and were invaded by monzotonalitic magmas shortly thereafter. A second lineation and metamorphism to the epidote-amphibolite facies developed in a narrow zone around the plutons. In light of the concept of plate tectonics, it is suggested that the early (Devonian?) island-arc-type andesite, dacite, and sodarhyolite (the Franklin Canyon Formation) were derived from the mantle above a Benioff zone by partial melting of peridotite in hydrous conditions. The water was probably derived from an oceanic plate descending to the mantle. Later (Permian?) magmas were mainly basaltic; some discontinuous layers of potassium-rich rhyolite indicate a change into anhydrous conditions and a deeper level of magma generation. The plutonic magmas that invaded the metamorphic rocks at the end of the Jurassic may contain material from the mantle, the subducted oceanic lithosphere, and the downfolded metamorphic rocks. The ratio of partial melts from these three sources may have changed with time

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

Metamorphic sole genesis at the base of ophiolite nappes: Insights from numerical models

NASA Astrophysics Data System (ADS)

Yamato, Philippe; Agard, Philippe; Duretz, Thibault

2015-04-01

Obduction emplaces oceanic lithosphere on top of continental lithosphere. Although a number of studies have focused on this enigmatic process, the initial stages of obduction remain poorly understood. Field, petrological, and geochronological data reveal that during the first stages of the obduction (i.e., during the first 1-2 Myrs) a HT-LP metamorphic sole (~700-800 ° C and ~1 GPa) is systematically welded at the base of ophiolite nappes. However, the reason why such welding of the ophiolite soles occurs at these particular P-T conditions, and only at the onset of obduction, is still an open issue. The aim of this study is to explore the conditions required to explain the genesis of metamorphic soles. For this, we employ two-dimensional numerical modelling, constrained by the wealth of available data from the Oman ophiolite. We first present a thermo-kinematic model in which the velocity field is prescribed in order to simulate obduction initiation. The heat advection-diffusion equation is solved at each time step. The model is intentionally kept simple in order to control each parameter (e.g., convergence rate, dip angle, thermal age) and to test its influence on the resulting P-T conditions obtained through time along the obduction interface. Results show that the key factor allowing the formation of metamorphic soles is the age of the oceanic lithosphere involved. Moreover, we speculate that the reason why metamorphic soles are always welded at the same P-T conditions is due to the fact that, at these particular conditions, strength jumps occur within the oceanic lithosphere. These jumps lead to changes in strain localisation and allow the spalling of oceanic crust and its juxtaposition to the ophiolite nappe. This hypothesis is further tested using thermo-mechanical models in which the obduction initiates dynamically (only initial and boundary conditions are prescribed). The interplay between the temperature evolution and the mechanical behaviour is then

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.

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

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.

The case for metamorphic base metal mineralization: pyrite chemical, Cu and S isotope data from the Cu-Zn deposit at Kupferberg in Bavaria, Germany

NASA Astrophysics Data System (ADS)

Höhn, S.; Frimmel, H. E.; Debaille, V.; Pašava, J.; Kuulmann, L.; Debouge, W.

2017-12-01

The stratiform Cu-Zn sulfide deposit at Kupferberg in Germany represents Bavaria's largest historic base metal producer. The deposit is hosted by Early Paleozoic volcano-sedimentary strata at the margin of a high-grade allochthonous metamorphic complex. The present paper reports on the first Cu and S isotope data as well as trace element analyses of pyrite from this unusual deposit. The new data point to syn-orogenic mineralization that was driven by metamorphic fluids during nappe emplacement. Primary Cu ore occurs as texturally late chalcopyrite within stratiform laminated pyrite in black shale in two different tectonostratigraphic units of very low and low metamorphic grade, respectively, that were juxtaposed during the Variscan orogeny. Trace element contents of different pyrite types suggest the presence of at least one hydrothermal pyrite generation (mean Co/Ni = 35), with the other pyrite types being syn-sedimentary/early diagenetic (mean Co/Ni = 3.7). Copper isotope analyses yielded a narrow δ65Cu range of -0.26 to 0.36‰ for all ore types suggesting a hypogene origin for the principal chalcopyrite mineralization. The ore lenses in the two different tectonostratigraphic units differ with regard to their δ34S values, but little difference exists between poorly and strongly mineralized domains within a given locality. A genetic model is proposed in which syn-sedimentary/early diagenetic pyrite with subordinate chalcopyrite and sphalerite formed in black shale beds in the two different stratigraphic units, followed by late-tectonic strata-internal, hydrothermal mobilization of Fe, Cu, and Zn during syn-orogenic thrusting, which concentrated especially Cu to ore grade. In agreement with this model, Cu distribution in stream sediments in this region shows distinct enrichments bound to the margin of the allochthonous complex. Thus, Kupferberg can be considered a rare example of a syn-orogenic Cu deposit with the Cu probably being derived from syn

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.

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

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

Fault block kinematics at a releasing stepover of the Eastern California shear zone: Partitioning of rotation style in and around the Coso geothermal area and nascent metamorphic core complex

NASA Astrophysics Data System (ADS)

Pluhar, Christopher J.; Coe, Robert S.; Lewis, Jonathan C.; Monastero, Francis C.; Glen, Jonathan M. G.

2006-10-01

, K. Richards-Dinger, The Coso geothermal field: a nascent metamorphic core complex, Geol. Soc. Amer. Bull. 117 (2005) 1534-1553.] characterize as a nascent metamorphic core complex. Consistent with upper plate disruption above a detachment, surface rocks (i.e. the upper plate of the detachment system) at the Coso geothermal area are tilted westward. However they appear to exhibit no detectable rotation. Thus, the style of block rotation may be partitioned: with clockwise vertical-axis rotation dominating in the Wild Horse Mesa and horizontal axis rotation (tilting) in the geothermal area.

Models for coupled fluid flow, mineral reaction, and isotopic alteration during contact metamorphism: The Notch Peak aureole, Utah

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

Ferry, J.M.; Dipple, G.M.

Three different models were developed to simulate the effect of contact metamorphism and fluid-rock interaction on the prograde mineralogical and O isotopic evolution of calcareous argillites from the Notch Peak aureole, Utah. All models assume local mineral-fluid equilibrium, a steady-state temperature profile corresponding to peak metamorphic values, and the thermodynamic data for minerals and fluid of Berman (1988). The preferred model, metamorphism with flow of a time-integrated fluid flux of 2 {plus minus} 0.5 {center dot} 10{sup 4} mol/cm{sup 2} in the direction of increasing temperature, successfully reproduces the principal petrologic and isotopic features of the aureole: (1) occurrence andmore » positions (in map view) of diopside-in, tremolite-out, grossular-in, wollastonite-in, and quartz-out isograds; (2) stable coexistence of tremolite + calcite + quartz + diopside over an {approx}1 km distance between the diopside-in and tremolite-out isograds; (3) variable whole-rock {sup 18}O depletions of {approx}6-9{per thousand} adjacent to the contact; and (4) a gradual and irregular increase in {delta}{sup 18}O with increasing distance from the pluton. Results demonstrate how isotopic and petrologic data for contact aureoles can be integrated to provide quantitative constraints on the magnitude and geometry of metamorphic fluid flow.« less

Breccia pipes in the Karoo Basin, South Africa, as conduits for metamorphic gases to the Early Jurassic atmosphere

NASA Astrophysics Data System (ADS)

Silkoset, Petter; Svensen, Henrik; Planke, Sverre

2014-05-01

The Toarcian (Early Jurassic) event was manifested by globally elevated temperatures and anoxic ocean conditions that particularly affected shallow marine taxa. The event coincided with the emplacement of the vast Karoo-Ferrar Large Igneous Province. Among the suggestions for trigger mechanisms for the climatic perturbation is metamorphic methane generation from black shale around the sills in the Karoo Basin, South Africa. The sill emplacement provides a mechanism for voluminous in-situ production and emission of greenhouse gases, and establishes a distinct link between basin-trapped and atmospheric carbon. In the lower stratigraphic levels of the Karoo Basin, black shales are metamorphosed around sills and the sediments are cut by a large number of pipe structures with metamorphic haloes. The pipes are vertical, cylindrical structures that contain brecciated and baked sediments with variable input of magmatic material. Here, we present borehole, petrographic, geochemical and field data from breccia pipes and contact aureoles based on field campaigns over a number of years (2004-2014). The metamorphism around the pipes show equivalent metamorphic grade as the sediments around nearby sills, suggesting a more prominent phreatomagmatic component than previously thought. The stratigraphic position of pipes and the breccia characteristics strengthens the hypothesis of a key role in the Toarcian carbon isotope excursion.

Unusual Cathodoluminescence in Diamonds: Evidence for Metamorphism or a Source Characteristic

NASA Astrophysics Data System (ADS)

Bruce, L. F.; Longo, M.; Kopylova, M.; Ryder, J.

2009-05-01

Cathodoluminescence (CL) is a useful means of diamond "fingerprinting". CL-active cratonic macrodiamonds usually cathodoluminesce blue or yellow, and always exhibit prominent wide CL emittance peaks at 430-450 nm and 480-490 nm. Exceptions to this norm are diamond suites recently discovered in the Archean rocks metamorphosed in the greenschist facies. These macrodiamonds cathodoluminesce red, orange and yellow, and invariably exhibit the most prominent CL peak at 520 nm. The diamond suites with the unusual CL are derived from two different locations within the Michipicoten Greenstone Belt (Southern Superior craton), near the town of Wawa (Ontario). One suite is extracted from the 2.68-2.74 Ga polymict volcanic breccias and lamprophyres and the other suite - from the 2.68 Ga sedimentary conglomerates grading into overlying sandstones of the Dore assemblage. The diamondiferous conglomerates are found in an area 8 km south of the breccias and 12 km northeast of Wawa. CL emittance of macrodiamonds (> 0.5 mm) extracted from the breccias consists of a broad band at 520 nm, a sharp peak at 575.5 nm, and several lines at 550-670 nm. The conglomerate macrodiamonds mostly show a dominant peak at 520 nm, whereas corresponding microdiamonds exhibit two peaks at about 576 and 600 nm. None of the diamonds show a maximum peak at 420 nm. Polycrystalline stones from conglomerates show distinct CL spectra and colours for all intergrown crystals in the same diamond. The relative abundances of the CL colors of the conglomerate diamonds are orange-red (46%), yellow (28%), orange-green (10%), green (6%), and non-uniform colors (10%). These colours are more diverse than mostly orange CL colours in the breccia diamonds; this results from a larger variety of positions and intensity of CL peaks in the conglomerate diamonds. We propose two models for explaining the presence of the 520 nm CL peak in the breccia and conglomerate diamonds in Wawa. The first model suggests metamorphism as the

LA-ICP-MS trace element mapping: insights into the crystallisation history of a metamorphic garnet population

NASA Astrophysics Data System (ADS)

George, Freya; Gaidies, Fred

2017-04-01

In comparison to our understanding of major element zoning, relatively little is known about the incorporation of trace elements into metamorphic garnet. Given their extremely slow diffusivities and sensitivity to changing mineral assemblages, the analysis of the distribution of trace elements in garnet has the potential to yield a wealth of information pertaining to interfacial attachment mechanisms during garnet crystallisation, the mobility of trace elements in both garnet and the matrix, and trace element geochronology. Due to advances in the spatial resolution and analytical precision of modern microbeam techniques, small-scale trace element variations can increasingly be documented and used to inform models of metamorphic crystallisation. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) in particular, can be used to rapidly quantify a wide range of elemental masses as a series of laser rasters, producing large volumes of spatially constrained trace element data. In this study, we present LA-ICP-MS maps of trace element concentrations from numerous centrally-sectioned garnets representative of the crystal size-distribution of a single sample's population. The study sample originates from the garnet-grade Barrovian zone of the Lesser Himalayan Sequence in Sikkim, northeast India, and has been shown to have crystallised garnet within a single assemblage between 515 ˚C and 565˚C, with no evidence for accessory phase reaction over the duration of garnet growth. Previous models have indicated that the duration of garnet crystallisation was extremely rapid (<1 Myr), with negligible diffusional homogenisation of major divalent cations. Consequently, the trace element record likely documents the primary zonation generated during garnet growth. In spite of straightforward (i.e. concentrically-zoned) major element garnet zonation, trace elements maps are characterised by significant complexity and variability. Y and the heavy rare earth elements

Uraniferous bitumen nodules in the Talvivaara Ni-Zn-Cu-Co deposit (Finland): influence of metamorphism on uranium mineralization in black shales

NASA Astrophysics Data System (ADS)

Lecomte, Andreï; Cathelineau, Michel; Deloule, Etienne; Brouand, Marc; Peiffert, Chantal; Loukola-Ruskeeniemi, Kirsti; Pohjolainen, Esa; Lahtinen, Hannu

2014-04-01

In the central part of the Fennoscandian Shield, the Talvivaara Ni-Zn-Cu-Co deposit, hosted by Palaeoproterozoic metamorphosed black schists, contains low uranium concentrations ranging from 10 to 30 ppm. The Talvivaara black schists were deposited 2.0-1.9 Ga ago and underwent subsequent metamorphism during the 1.9-1.79 Ga Svecofennian orogeny. Anhedral uraninite crystals rimmed by bitumen constitute the main host of uranium. U-Pb secondary ion mass spectrometry dating indicates that uraninite crystals were formed between 1,878 ± 17 and 1,871 ± 43 Ma, during peak metamorphism. Rare earth element patterns and high Th content (average 6.38 wt%) in disseminated uraninite crystals indicate that U was concentrated during high temperature metamorphism (>400 °C). The formation of bitumen rims around uraninite may be explained by two distinct scenarios: (a) a transport of U coincident with the migration of hydrocarbons or (b) post-metamorphic formation of bitumen rims, through radiolytic polymerization of gaseous hydrocarbons at the contact with uraninite.

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

CL-imaging and ion microprobe dating of single zircons from a high-grade rock from the Central Zone, Limpopo Belt, South Africa: Evidence for a single metamorphic event at ˜2.0 Ga

NASA Astrophysics Data System (ADS)

Mouri, H.; Brandl, G.; Whitehouse, M.; de Waal, S.; Guiraud, M.

2008-02-01

The combination of ion microprobe dating and cathodoluminescence (CL) imaging of zircons from a high-grade rock from the Central Zone of the Limpopo Belt were used to constrain the age of metamorphic events in the area. Zircon grains extracted from an orthopyroxene-gedrite-bearing granulite were prepared for single crystal CL-imaging and ion microprobe dating. The grains display complex zoning when using SEM-based CL-imaging. A common feature in most grains is the presence of a distinct core with a broken oscillatory zoned structure, which clearly appears to be the remnant of an original grain of igneous origin. This core is overgrown by an unzoned thin rim measuring about 10-30 μm in diameter, which is considered as new zircon growth during a single metamorphic event. Selected domains of the zircon grains were analysed for U, Pb and Th isotopic composition using a CAMECA IMS 1270 ion microprobe (Nordsim facility). Most of the grains define a near-concordant cluster with some evidence of Pb loss. The most concordant ages of the cores yielded a weighted mean 207Pb/ 206Pb age of 2689 ± 15 (2 σ) Ma, interpreted as the age of the protolith of an igneous origin. The unzoned overgrowths of the zircon grains yielded a considerably younger weighted mean 207Pb/ 206Pb age of ˜2006.5 ± 8.0 Ma (2 σ), and these data are interpreted to reflect closely the age of the ubiquitous high-grade metamorphic event in the Central Zone. This study shows clearly, based on both the internal structure of the zircons and the data obtained by ion microprobe dating, that only a single metamorphic event is recorded by the studied 2.69 Ga old rocks, and we found no evidence of an earlier metamorphic event at ˜2.5 Ga as postulated earlier by some workers.

Modelling metamorphism in the Hoosac Schist, Western Massachusetts: new approaches to a New England problem

NASA Astrophysics Data System (ADS)

Bidgood, Anna; Waters, Dave; Gardiner, Nick

2015-04-01

Along the western margin of the metamorphic Appalachians in New England, Taconic (Ordovician) tectonism and metamorphism are overprinted towards the east by Acadian (Devonian) structures and metamorphism. The Hoosac Schist, a probable correlate of the well-known Gassetts Schist of Vermont, lies in the region of overprinting. It forms a narrow N-S-trending tectonically-bound zone crossing several Barrovian mineral-assemblage zones from garnet to kyanite grade. Highly aluminous units containing cm-sized garnets (Cheney & Brady, 1992) are noted for the occurrence of textural unconformities within the garnets, separating inclusion-rich cores from inclusion-poor rims. Matrix domains contain both paragonite and muscovite. Muscovite is present in at least two compositionally distinct generations, with broad later laths cutting across a microfolded earlier fabric. Rutile is restricted to inclusions in garnet, whereas the matrix Ti- phase is ilmenite. These features suggest a polymetamorphic history, potentially recording the superimposition of Acadian metamorphism on Taconic, but it has not yet proved possible to demonstrate the presence of two metamorphic cycles. This study aims to test and employ the new and revised activity models recently developed for metapelites in the full system MnNCKFMASHTO (White et al, 2014), for use with the Holland & Powell data-set 6. Features that can now be more explicitly modelled include garnet zonation in relation to its inclusion suites and microstructural features, the occurrence, texture and distribution of Ti-bearing accessory minerals, and the assemblages and compositional trends in white micas. Preliminary modelling, correlated with microstructural observation, indicates (1) some confirmation of the concern expressed by White et al (2014) that the stability of margarite-bearing assemblages may be somewhat overestimated, (2) that apart from this, the early growth history of garnet is consistent with its suite of trapped inclusions

Metamorphic P-T paths and Precambrian crustal growth in East Antarctica

NASA Technical Reports Server (NTRS)

Harley, S. L.

1988-01-01

The metamorphic constraints on crustal thicknesses in Archean and post-Archean terranes are summarized along with possible implications for tectonic processes. It is important to recognize that P-T estimates represent perturbed conditions and should not be used to estimate steady state geothermal gradients or crustal thicknesses. The example is cited of the Dora Maira complex in the French Alps, where crustal rocks record conditions of 35 kbar and 800 C, implying their subduction to depths of 100 km or more, followed by subsequent uplift to the surface. Therefore such P-T estimates tell more about processes than crustal thicknesses. More importantly, according to the author, are determinations of P-T paths, particularly coupled with age measurements, because these may provide constraints on how and when perturbed conditions relax back to steady state conditions. P-T paths are illustrated that should be expected from specific tectonic processes, including Tibetan style collision, with and without subsequent extension, rifting of thin or thickened crust, and magmatic accretion. Growth of new crust, associated with magmatic accretion, for example, could possibly be monitored with these P-T paths.

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

The metamorphic basement of the southern Sierra de Aconquija, Eastern Sierras Pampeanas: Provenance and tectonic setting of a Neoproterozoic back-arc basin

NASA Astrophysics Data System (ADS)

Cisterna, Clara Eugenia; Altenberger, Uwe; Mon, Ricardo; Günter, Christina; Gutiérrez, Antonio

2018-03-01

The Eastern Sierras Pampeanas are mainly composed of Neoproterozoic-early Palaeozoic metamorphic complexes whose protoliths were sedimentary sequences deposited along the western margin of Gondwana. South of the Sierra de Aconquija, Eastern Sierras Pampeanas, a voluminous metamorphic complex crops out. It is mainly composed of schists, gneisses, marbles, calk-silicate schists, thin layers of amphibolites intercalated with the marbles and granitic veins. The new data correlate the Sierra de Aconquija with others metamorphic units that crop out to the south, at the middle portion of the Sierra de Ancasti. Bulk rock composition reflects originally shales, iron rich shales, wackes, minor litharenites and impure limestones as its protoliths. Moreover, comparisons with the northern Sierra de Aconquija and from La Majada (Sierra de Ancasti) show similar composition. Amphibolites have a basaltic precursor, like those from the La Majada (Sierra de Ancasti) ones. The analyzed metamorphic sequence reflects low to moderate weathering conditions in the sediments source environment and their chemical composition would be mainly controlled by the tectonic setting of the sedimentary basin rather than by the secondary sorting and reworking of older deposits. The sediments composition reveal relatively low maturity, nevertheless the Fe - shale and the litharenite show a tendency of minor maturity among them. The source is related to an acid one for the litharenite protolith and a more basic to intermediate for the other rocks, suggesting a main derivation from intermediate to felsic orogen. The source of the Fe-shales may be related to and admixture of the sediments with basic components. Overall the composition point to an upper continental crust as the dominant sediment source for most of the metasedimentary rocks. The protolith of the amphibolites have basic precursors, related to an evolving back-arc basin. The chemical data in combination with the specific sediment association

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.

Evidence for low-grade metamorphism, hydrothermal alteration, and diagenesis on Mars from phyllosilicate mineral assemblages

USGS Publications Warehouse

Ehlmann, Bethany L.; Mustard, John F; Clark, Roger N.; Swayze, Gregg A.; Murchie, Scott L.

2011-01-01

The enhanced spatial and spectral resolution provided by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO) has led to the discovery of numerous hydrated silicate minerals on Mars, particularly in the ancient, cratered crust comprising the southern highlands. Phases recently identified using visible/near-infrared spectra include: smectite, chlorite, prehnite, high-charge phyllosilicates (illite or muscovite), the zeolite analcime, opaline silica, and serpentine. Some mineral assemblages represent the products of aqueous alteration at elevated temperatures. Geologic occurrences of these mineral assemblages are described using examples from west of the Isidis basin near the Nili Fossae and with reference to differences in implied temperature, fluid composition, and starting materials during alteration. The alteration minerals are not distributed homogeneously. Rather, certain craters host distinctive alteration assemblages: (1) prehnite-chlorite-silica, (2) analcime-silica-Fe,Mg-smectite-chlorite, (3) chlorite-illite (muscovite), and (4) serpentine, which furthermore has been found in bedrock units. These assemblages contrast with the prevalence of solely Fe,Mg-smectites in most phyllosilicate-bearing terrains on Mars, and they represent materials altered at depth then exposed by cratering. Of the minerals found to date, prehnite provides the clearest evidence for subsurface, hydrothermal/metamorphic alteration, as it forms only under highly restricted conditions (T = 200–400ºC). Multiple mechanisms exist for forming the other individual minerals; however, the most likely formation mechanisms for the characteristic mineralogic assemblages observed are, for (1) and (2), low-grade metamorphism or hydrothermal (<400ºC) circulation of fluids in basalt; for (3), transformation of trioctahedral smectites to chlorite and dioctahedral smectites to illite during diagenesis; and for (4), low-grade metamorphism or

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

2.8 {mu}m emission from type-I quantum wells grown on InAs{sub x}P{sub 1-x}/InP metamorphic graded buffers

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

Jung, Daehwan; Song, Yuncheng; Larry Lee, Minjoo

We report 2.8 {mu}m emission from compressively strained type-I quantum wells (QWs) grown on InP-based metamorphic InAs{sub x}P{sub 1-x} step-graded buffers. High quality metamorphic graded buffers showed smooth surface morphology and low threading dislocation densities of approximately 2.5 Multiplication-Sign 10{sup 6} cm{sup -2}. High-resolution x-ray diffraction scans showed strong satellites from multiple quantum wells grown on metamorphic buffers, and cross-sectional transmission electron microscopy revealed smooth and coherent quantum well interfaces. Room-temperature photoluminescence emission at 2.8 {mu}m with a narrow linewidth ({approx}50 meV) shows the promise of metamorphic growth for mid-infrared laser diodes on InP.

Age of zircons from the xenolith of metapelite in granitoids of the Verkhisetsk massif (Middle Urals): Evidence for granite-related stages of metamorphism

NASA Astrophysics Data System (ADS)

Zinkova, E. A.; Pribavkin, S. V.

2016-02-01

Two age stages in the formation of high-aluminous gneisses related to the major stages of granite formation of the Uralian mobile belt were revealed in this study. The first stage (372 ± 2 Ma) corresponds to the age of metamorphism of the amphibolite facies and is controlled by intrusion of the tonalite-trondhjemite series under the environment of the continental margin. At the second stage (307 ± 3 Ma), gneiss underwent contact metamorphism under the influence of plutons of the adamellite-granite composition formed during the early episodes of collisional metamorphism.

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.

Photoelectric properties of the metamorphic InAs/InGaAs quantum dot structure at room temperature

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

Golovynskyi, S. L., E-mail: golovynskyi@isp.kiev.ua; Seravalli, L.; Trevisi, G.

We present the study of optical and photoelectric properties of InAs quantum dots (QDs) grown on a metamorphic In{sub 0.15}Ga{sub 0.85}As buffer layer: such nanostructures show efficient light emission in the telecom window at 1.3 μm (0.95 eV) at room temperature. We prepared a sample with vertical geometry of contacts isolated from the GaAs substrate. The structure is found to be photosensitive in the spectral range above 0.9 eV at room temperature, showing distinctive features in the photovoltage and photocurrent spectra attributed to QDs, InAs wetting layer, and In{sub 0.15}Ga{sub 0.85}As metamorphic buffer, while a drop in the photoelectric signal above 1.36 eV ismore » related to the GaAs layer. No effect of defect centers on the photoelectrical properties is found, although they are observed in the absorption spectrum. We conclude that metamorphic QDs have a low amount of interface-related defects close to the optically active region and charge carriers can be effectively collected into InAs QDs.« less

Rubidium-strontium geochronology of the Oaxaca and Acatlan metamorphic areas of southern Mexico

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

Ruiz Castellanos, M.

1979-01-01

A Rb-Sr study was carried out on crystalline basement rocks from two small separate areas of southern Mexico: Oaxaca area and the Acatlan area. The Oaxaca area consists mainly of orthogneisses and paragneisses of amphibolite to granulite grade metamorphism as well as granitic intrusives. In the present study the following dates and initial /sup 87/Sr//sup 86/Sr rates (Sr/sub 0/) were obtained from rocks of this area: El Cortijo gneisses 341 +/- 61 my, Sr/sub 0/ 0.7226 +/- 0.0027; Ojo de Agua pegmatite 975 +/- 25 my, assumed Sr/sub 0/ 0.710; El Catrin gneisses 1500 +/- 230 my, Sr/sub 0/ 0.7026more » +/- 0.0005; Suchilquitongo granite 272 +/- 8 my, Sr/sup 0/ 0.7047 +/- 0.0005; Laachila marble 901 +/- 24 my, Sr/sub 0/ 0.7062 +/- 0.0007; Laachila granitic dike 236 +/- 5 my, Sr/sub 0/ 0.8477 +/- 0.0009. The Acatlan area consists typically of greenschist facies metasedimentary rocks with similar structural and metamorphic characteristics through the area. In the present study, muscovite, biotite and whole rock data points from the typical Acatlan schists collected at different locations within the Acatlan Complex define two different linear arrays from which an age of 481 +/- 9 my, and two Sr/sub 0/ intercepts of 0.7075 +/- 0.0008 and 0.7112 +/- 0.0006 (95% confidence level) are obtained. The same date is obtained for 18 samples of the Piaxtla augen schist 480 +/- 84 my. Other dates obtained are: Caltepec granitic rocks 269 +/- 21 my, Sr/sub 0/ 0.7056 +/- 0.0004; Tepejillo intrusive bodies 207 +/- 10 my, Sr/sub 0/ 0.7037 +/- 0.0003 and Tepejillo pegmatite 173 +/- 0.3 my, Sr/sub 0/ 0.7044 +/- 0.0002. The tectonic histories of the Oaxaca and Acatlan areas are substantially different and have been unrelated at least until Late Paleozoic times.« less

Early Metamorphic Insertion Technology for Insect Flight Behavior Monitoring

PubMed Central

Bozkurt, Alper

2014-01-01

Early Metamorphosis Insertion Technology (EMIT) is a novel methodology for integrating microfabricated neuromuscular recording and actuation platforms on insects during their metamorphic development. Here, the implants are fused within the structure and function of the neuromuscular system as a result of metamorphic tissue remaking. The implants emerge with the insect where the development of tissue around the electronics during pupal development results in a bioelectrically and biomechanically enhanced tissue interface. This relatively more reliable and stable interface would be beneficial for many researchers exploring the neural basis of the insect locomotion with alleviated traumatic effects caused during adult stage insertions. In this article, we implant our electrodes into the indirect flight muscles of Manduca sexta. Located in the dorsal-thorax, these main flight powering dorsoventral and dorsolongitudinal muscles actuate the wings and supply the mechanical power for up and down strokes. Relative contraction of these two muscle groups has been under investigation to explore how the yaw maneuver is neurophysiologically coordinated. To characterize the flight dynamics, insects are often tethered with wires and their flight is recorded with digital cameras. We also developed a novel way to tether Manduca sexta on a magnetically levitating frame where the insect is connected to a commercially available wireless neural amplifier. This set up can be used to limit the degree of freedom to yawing “only” while transmitting the related electromyography signals from dorsoventral and dorsolongitudinal muscle groups. PMID:25079130

High-pressure metamorphism and uplift of the Olympic subduction complex

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

Brandon, M.T.; Calderwood, A.R.

1990-12-01

The discovery of the critical assemblage lawsonite + quartz + calcite indicates that a significant part of the Cenozoic Olympic subduction complex of northwestern Washington State formed by underplating at a depth of about 11 km. The deep structural level exposed in this area is attributed to the presence of a 10-km-high arch in the underlying Juan de Fuca plate. The authors postulate that this arch was formed when the southern Cordilleran coastline swung westward as a result of middle Miocene to recent extension in the Basin and Range province.

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

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

Effect of Metamorphic Foliation on Regolith Thickness, Catalina Critical Zone Observatory, Arizona

NASA Astrophysics Data System (ADS)

Leone, J. D.; Holbrook, W. S.; Chorover, J.; Carr, B.

2016-12-01

Terrestrial life is sustained by nutrients and water held in soil and weathered rock, which are components of the Earth's critical zone, referred to as regolith. The thickness of regolith in the near-surface is thought to be influenced by factors such as climate, topographic stress, erosion and lithology. Our study has two aims: to determine the effect of metamorphic foliation on regolith thickness and to test an environmental model, Effective Energy Mass Transfer (EEMT), within a zero-order basin (ZOB) in the Santa Catalina Mountains. Seismic refraction and electrical resistivity data show a stark contrast in physical properties, and inferred regolith thickness, on north- versus south-facing slopes: north-facing slopes are characterized by higher seismic velocities and higher resistivities, consistent with thin regolith, while south-facing slopes show lower resistivities and velocities, indicative of deeper and more extensive weathering. This contrast is exactly the opposite of that expected from most climatic models, including the EEMT model, which predicts deeper regolith on north-facing slopes. Instead, regolith thickness appears to be controlled by metamorphic foliation: we observed a general, positive correlation between interpreted regolith thickness and foliation dip within heavily foliated lithologies and no correlation in weakly foliated lithologies. We hypothesize that hydraulic conductivity controls weathering here: where foliation is parallel to the surface topography, regolith is thin, but where foliation pierces the surface topography at a substantial angle, regolith is thick. The effect of foliation is much larger than that expected from environmental models: regolith thickness varies by a factor of 4 (2.5 m vs. 10 m). These results suggest that metamorphic foliation, and perhaps by extension sedimentary layering, plays a key role in determining regolith thickness and must be accounted for in models of critical zone development.

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.

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.

Shock metamorphism of ordinary chondrites

NASA Technical Reports Server (NTRS)

Stoeffler, Dieter; Keil, Klaus; Scott, Edward R. D.

1991-01-01

This study proposes a revised petrographic classification of progressive stages of shock metamorphism of 26 ordinary chondrites. Six stages of shock (S1 to S6) are defined on the basis of shock effects in olivine and plagioclase as recognized by thin section microscopy, and the characteristic shock effects of each shock stage are described. It is concluded that shock effects and the sequence of progressively increasing degrees of shock metamorphosis are very similar in H, L, and LL groups. Differences in the frequency distribution of shock stages are relatively minor. It is suggested that the collisional histories of the H, L, and LL parent bodies were similar. Petrologic type-3 chondrites are deficient in stages S4 and S6 and, with increasing petrologic type, the frequency of stages S4 to S6 increases. It is suggested that the more porous and volatile-rich Type-3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type. Stage S3 is the most abundant in nearly all petrologic types.

Chemical and physical studies of type 3 chondrites 12: The metamorphic history of CV chondrites and their components

NASA Technical Reports Server (NTRS)

Guimon, R. Kyle; Symes, Steven J. K.; Sears, Derek W. G.

1995-01-01

The induced thermoluminescence (TL) properties of 16 CV and CV-related chondrites, four CK chondrites and Renazzo (CR2) have been measured in order to investigate their metamorphic history. The petrographic, mineralogical and bulk compositional differences among the CV chondrites indicate that the TL sensitivity of the approximately 130 C TL peak is reflecting the abundance of ordered feldspar, especially in chondrule mesostasis, which in turn reflects parent-body metamorphism. The TL properties of 18 samples of homogenized Allende powder heated at a variety of times and temperatures, and cathodoluminescence mosaics of Axtell and Coolidge, showed results consistent with this conclusion. Five refractory inclusions from Allende, and separates from those inclusions, were also examined and yielded trends reflecting variations in mineralogy indicative of high peak temperatures (either metamorphic or igneous) and fairly rapid cooling. The CK chondrites are unique among metamorphosed chondrites in showing no detectable induced TL, which is consistent with literature data that suggests very unusual feldspar in these meteorites. Using TL sensitivity and several mineral systems and allowing for the differences in the oxidized and reduced subgroups, the CV and CV-related meteorites can be divided into petrologic types analogous to those of the ordinary and CO type 3 chondrites. Axtell, Kaba, Leoville, Bali, Arch and ALHA81003 are type 3.0-3.1, while ALH84018, Efremovka, Grosnaja, Allende and Vigarano are type 3.2-3.3 and Coolidge and Loongana 001 are type 3.8. Mokoia is probably a breccia with regions ranging in petrologic type from 3.0 to 3.2. Renazzo often plots at the end of the reduced and oxidized CV chondrite trends, even when those trends diverge, suggesting that in many respects it resembles the unmetamorphosed precursors of the CV chondrites. The low-petrographic types and low-TL peak temperatures of all samples, including the CV3.8 chondrites, indicates metamorphism

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

Microtectonic-assisted P-T determination on low-grade Alpine metamorphic rocks from the "Tisia Mega-Unit" of the Slavonian Mountains in Croatia

NASA Astrophysics Data System (ADS)

Balen, Dražen; Lihter, Iva; Massonne, Hans-Joachim

2016-04-01

The internal structure of the Tisia (Tisza) Mega-Unit in the Alpine-Carpathian-Dinaridic orogenic system encompasses large Alpine nappe systems brought to its present-day position by complex regional-scale movements. The Slavonian Mountains are part of the Bihor nappe system which is below the Codru and above the Mecsek nappe systems. The low-grade metamorphic schist unit of the Slavonian Mountains includes numerous rocks which were previously related to Precambrian and/or Lower Paleozoic orogeneses. However, recent studies (e.g. Balen, 2014, European Geosciences Union General Assembly, EGU 2014-6122) show that the metapelites of this unit should be attributed to the Alpine orogeny and the poorly known P-T conditions, which they experienced, should be refined. Although metapelites can be sensitive to changes of metamorphic conditions and, therefore, be suitable for the P-T estimation of metamorphic event(s), the extraction of mineral assemblages, being in equilibrium, and associated microtectonic data for particular low-grade metamorphic rocks is not straightforward. On the contrary, due to lack of suitable minerals and complex mictotectonic features, one can be faced with a severe problem concerning (dis)equilibrium. To avoid this, the observation scale in the research was set to the sub-mm level taking into account microtectonic positions of minerals. The investigated samples from the Slavonian Mountains are fine-grained schists consisting of chlorite (15-30 vol. %), white mica (15-25 vol. %), quartz (10-25 vol. %), feldspars (albite 10-15 vol. %; some K-feldspar), biotite (<5 vol. %), opaques (<5 vol. %), and accessory minerals (zircon, monazite, xenotime, apatite, chalcopyrite, pyrite, barite, parisite-(Ce), rutile). The schists show complex microtectonic fabric including well-developed foliations, pervasive folding, crenulation and cleavage. Foliations are defined by the preferred orientation of phyllosilicates and thin quartz and feldspar ribbons. Chlorite

Metabolism of thyroxine in Rana catesbeiana tadpoles during metamorphic climax

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

Galton, V.A.; Munck, K.

1981-01-01

Previous studies have indicated that premetamorphic tadpoles do not convert T4 to T3 to a measurable extent (1). The present study was performed to determine whether a T4 5'-monodeiodinating system is acquired at later stages of development. (/sup 125/I)T4 metabolism in vivo was determined in tadpoles at most stages of prometamorphosis and metamorphic climax and, for comparison, in premetamorphic tadpoles. The conversion of (/sup 125/I)T4 to (/sup 125/I)T3, as indicated by the presence of an /sup 125/I-labeled product in serum and liver preparations that cochromatographed with carrier T3, was sometimes observed in tadpoles near the end of prometamorphosis and wasmore » always evident in tadpoles that were either undergoing or had completed metamorphic climax. However, during this phase, no correlation could be drawn between the extent of T3 production and morphological development. The formation of T3 from T4 in vivo was significantly decreased in tadpoles pretreated with propylthiouracil. The T45'-monodeiodinating system could be induced in premetamorphic tadpoles by injecting them with either T4 or T3. This finding together with the observation that normal acquisition of this system occurs at the time when endogenous T4 and T3 levels are rising rapidly suggest that its development is under the control of the thyroid hormones.« less

U-Pb zircon and CHIME monazite dating of granitoids and high-grade metamorphic rocks from the Eastern and Peninsular Thailand - A new report of Early Paleozoic granite

NASA Astrophysics Data System (ADS)

Kawakami, T.; Nakano, N.; Higashino, F.; Hokada, T.; Osanai, Y.; Yuhara, M.; Charusiri, P.; Kamikubo, H.; Yonemura, K.; Hirata, T.

2014-07-01

In order to understand the age and tectonic framework of Eastern to Peninsular Thailand from the viewpoint of basement (metamorphic and plutonic) geology, the LA-ICP-MS U-Pb zircon dating and the chemical Th-U-total Pb isochron method (CHIME) monazite dating were performed in the Khao Chao, Hub-Kapong to Pran Buri, and Khanom areas in Eastern to Peninsular Thailand. The LA-ICP-MS U-Pb zircon dating of the garnet-hornblende gneiss from the Khao Chao area gave 229 ± 3 Ma representing the crystallization age of the gabbro, and that of the garnet-biotite gneisses gave 193 ± 4 Ma representing the timing of an upper amphibolite facies metamorphism. The CHIME monazite dating of pelitic gneiss from the Khao Chao gneiss gave scattered result of 68 ± 22 Ma, due to low PbO content and rejuvenation of older monazite grains during another metamorphism in the Late Cretaceous to Tertiary time. The U-Pb ages of zircon from the Hua Hin gneissic granite in the Hub-Kapong to Pran Buri area scatter from 250 Ma to 170 Ma on the concordia. Granite crystallization was at 219 ± 2 Ma, followed by the sillimanite-grade regional metamorphism at 185 ± 2 Ma. Monazite in the pelitic gneiss from this area also preserves Early to Middle Jurassic metamorphism and rejuvenation by later contact metamorphism by non-foliated granite or by another fluid infiltration event in the Late Cretaceous to Tertiary time. The Khao Dat Fa granite from the Khanom area of Peninsular Thailand gave a U-Pb zircon age of 477 ± 7 Ma. This is the second oldest granite pluton ever reported from Thailand, and is a clear evidence for the Sibumasu block having a crystalline basement that was formed during the Pan-African Orogeny. The Khao Pret granite gives U-Pb zircon concordia age of 67.5 ± 1.3 Ma, which represents the timing of zircon crystallization from the granitic melt and accompanied sillimanite-grade contact metamorphism against surrounding metapelites and gneisses. Metamorphic rocks in the Doi Inthanon area

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

Metaultramafic schists and dismembered ophiolites of the Ashe Metamorphic Suite of northwestern North Carolina, USA

USGS Publications Warehouse

Raymond, Loren A.; Merschat, Arthur J.; Vance, R. Kelly

2016-01-01

Metaultramafic rocks (MUR) in the Ashe Metamorphic Suite (AMS) of northwestern North Carolina include quartz ± feldspar-bearing QF-amphibolites and quartz-deficient, locally talc-, chlorite-, and/or Mg-amphibole-bearing TC-amphibolites. Some workers divide TC-amphibolites into Todd and Edmonds types, based on mineral and geochemical differences, and we provisionally add a third type – olivine ± pyroxene-rich, Rich Mountain-type rocks. Regionally, MUR bodies range from equant, Rich Mountain- to highly elongate, Todd-TC-amphibolite-type bodies. The MURs exhibit three to five mineral associations containing assemblages with olivine, anthophyllitic amphibole, Mg-hornblende, Mg-actinolite, cummingtonite, and serpentine representing decreasing eclogite to greenschist facies grades of metamorphism over time. MUR protoliths are difficult to determine. Southwestern MUR bodies have remnant olivine ± pyroxene-rich assemblages representing ultrabasic-basic, dunite-peridotite-pyroxenite protoliths. Northeastern TC-amphibolite MURs contain hornblende and actinolitic amphiboles plus chlorites – aluminous and calcic assemblages suggesting to some that metasomatism of basic, QF-amphibolites yields all TC-amphibolites. Yet MgO-CaO-Al2O3 and trace element chemistries of many TC-amphibolites resemble compositions of plagioclase peridotites. We show that a few AMS TC-amphibolites had basaltic/gabbroic protoliths, while presenting arguments opposing application of the metasomatic hypothesis to all TC-amphibolites. We establish that MUR bodies are petrologically heterolithic and that TC-amphibolites are in contact with many rock types; that those with high Cr, Ni, and Mg have olivine- or pyroxene-dominated protoliths; that most exhibit three or more metamorphic mineral associations; and that contacts thought to be metasomatic are structural. Clearly, different MUR bodies have different chemistries representing various protoliths, and have different mineral assemblages, reflecting

Tourmaline's record of Alpine metamorphism and segregation formation in the Pfitsch Formation, Western Tauern Window

NASA Astrophysics Data System (ADS)

Berryman, E. J.; Kutzschbach, M.; Trumbull, R. B.; Meixner, A.; van Hinsberg, V.; Kasemann, S.; Franz, G.

2017-12-01

Tourmaline, a common accessory mineral in the metasedimentary units of the Pfitsch Formation in the Western Tauern Window, Eastern Alps, records the variation in fluid composition and B mobilization during Alpine metamorphism. These post-Variscan metasediments are part of the Subpenninic nappes, the former European distal margin, and experienced peak metamorphic conditions of 550°C, 1.0 GPa. In all investigated units, tourmaline is predominantly dravitic, with high Fe contents. Charge balance calculations combined with Fe-Mg and Fe-Al variation suggest a significant proportion of ferric iron. Tourmaline's composition reflects its host rock assemblage, with the relative predominance of Fe-Mg or Fe-Al exchange in tourmaline from different units corresponding to the presence of biotite/chlorite or muscovite, respectively. Boron content and correspondingly tourmaline abundance is highest in a 25 m thick unit of feldspathic gneiss ( 20-200 ppm B). The abundance and size of the tourmaline crystals increases near coarse-grained quartzofeldspathic segregations ( 1200 ppm B), reflecting the mobilization and concentration of B by the metamorphic fluid. Tourmaline crystals near segregations have up to three growth zones, recording pro- ( 350-500°C, 0.7-1.0 GPa) and retrograde (400°C, 0.2 GPa) growth. They show the largest amount of compositional variation, covering the range of compositional space represented by tourmaline occurring away from segregations. Tourmaline near segregations has the highest inferred ferric iron content, which decreases across growth zones, potentially reflecting the gradual reduction of the fluid during metamorphism. Whole rock δ11B values (-15 to -34‰) vary with the heaviest values found near B-rich segregations, and the lightest values in B-depleted samples. This correlation reflects the preferential mobilization of 11B towards the segregations. Isotopic zonation of individual tourmaline crystals with -11‰ in their cores and -20‰ in

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

Fe-Ni metal in primitive chondrites: Indicators of classification and metamorphic conditions for ordinary and CO chondrites

USGS Publications Warehouse

Kimura, M.; Grossman, J.N.; Weisberg, M.K.

2008-01-01

We report the results of our petrological and mineralogical study of Fe-Ni metal in type 3 ordinary and CO chondrites, and the ungrouped carbonaceous chondrite Acfer 094. Fe-Ni metal in ordinary and CO chondrites occurs in chondrule interiors, on chondrule surfaces, and as isolated grains in the matrix. Isolated Ni-rich metal in chondrites of petrologic type lower than type 3.10 is enriched in Co relative to the kamacite in chondrules. However, Ni-rich metal in type 3.15-3.9 chondrites always contains less Co than does kamacite. Fe-Ni metal grains in chondrules in Semarkona typically show plessitic intergrowths consisting of submicrometer kamacite and Ni-rich regions. Metal in other type 3 chondrites is composed of fine- to coarse-grained aggregates of kamacite and Ni-rich metal, resulting from metamorphism in the parent body. We found that the number density of Ni-rich grains in metal (number of Ni-rich grains per unit area of metal) in chondrules systematically decreases with increasing petrologic type. Thus, Fe-Ni metal is a highly sensitive recorder of metamorphism in ordinary and carbonaceous chondrites, and can be used to distinguish petrologic type and identify the least thermally metamorphosed chondrites. Among the known ordinary and CO chondrites, Semarkona is the most primitive. The range of metamorphic temperatures were similar for type 3 ordinary and CO chondrites, despite them having different parent bodies. Most Fe-Ni metal in Acfer 094 is martensite, and it preserves primary features. The degree of metamorphism is lower in Acfer 094, a true type 3.00 chondrite, than in Semarkona, which should be reclassified as type 3.01. ?? The Meteoritical Society, 2008.

Post-metamorphic fluid infiltration into granulites from the Adirondack Mountains, USA

NASA Technical Reports Server (NTRS)

Morrison, J.; Valley, John W.

1988-01-01

Post-metamorphic effects in the anorthosites of the Adirondacks, New York were described. Calcite-chlorite-sericite assemblages occur as veins, in disseminated form and as clots, and document retrograde fluid infiltration. These features are associated with late-state CO2-rich fluid inclusions. Stable isotope analyses of calcites indicates that the retrograde fluids interacted with meta-igneous and supracrustal lithologies, but the precise timing of the retrogression is as yet unknown.

Neoarchean metamorphism recorded in high-precision Sm-Nd isotope systematics of garnets from the Jack Hills (Western Australia)

NASA Astrophysics Data System (ADS)

Eccles, K. A.; Baxter, E. F.; Mojzsis, S. J.; Marschall, H.; Williams, M. L.; Jercinovic, M. J.

2013-12-01

Studies of metasedimentary rocks from the Jack Hills, which host Earth's oldest known detrital minerals, have focused on zircon and occasionally monazite or xenotime, but no attention has been directed toward one of the most common mineral markers of metamorphism: garnet. Garnet can provide a record of the post-depositional, prograde metamorphic history of Archean metasedimentary rocks. Additionally, the use of a newly developed detrital garnet dating technique [1,2] may reveal information about pre-depositional metamorphism that could address lingering questions about the nature and timing of Earth's earliest tectonometamorphic events. Here we investigate garnet from the Jack Hills metasedimentary rocks to test whether they record in situ metamorphism or are a detrital relict of even older metamorphic events. We identified garnet in two bulk quartz-pebble conglomerate samples collected from the 'discovery' outcrop at Eranondoo Hill in the Jack Hills of Western Australia. Electron microprobe analyses of polished grains and SEM measurements of unpolished grain surfaces are consistent, revealing garnet composition indicative of a single generation/population of predominantly almandine-spessartine solid solution (~10-35% mole fraction spessartine). Compositional maps of garnet grains reveal little zoning and no discontinuities, most consistent with a single growth event. Dating Jack Hills' garnet via the Sm-Nd system is possible due to continued development of small sample analysis techniques, including running NdO+ TIMS analyses with Ta2O5 activator [3] permitting <50 ppm 2 sigma analytical precision on a 400pg in-house standard and continued improvement in blanks (<15pg full procedural blanks). Additionally, employing a nondestructive chemical prescreening technique (tabletop SEM) allows for grouping of multiple grains based on chemical similarity. Final Nd loads in the 450-750pg range routinely yield dates with precisions <×10Ma for two point isochrons between

Penecontemporaneous metamorphism, fragmentation, and reassembly of ordinary chondrite parent bodies

NASA Technical Reports Server (NTRS)

Grimm, R. E.

1985-01-01

The thermal histories of ordinary chondrites and the canonical internal heating or onion shell models, which predict an inverse relation between the petrologic type of chondrites and the metallographic cooling rate, are reviewed. The thermal and accretional requirements of the 'metamorphosed planetesimal' model proposed by Scott and Rajan (1981) are analyzed, and an alternative model consistent with the metallographic cooling rate constraints is suggested in which ordinary chondrite parent bodies are collisionally fragmented and then rapidly reassembled before metamorphic heat has been dissipated.

Heterostructures of metamorphic GaInAs photovoltaic converters fabricated by MOCVD on GaAs substrates

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

Mintairov, S. A., E-mail: mintairov@scell.ioffe.ru; Emelyanov, V. M.; Rybalchenko, D. V.

Heterostructures of metamorphic GaInAs photovoltaic converters (PVCs) are on GaAs substrates by the metal-organic chemical vapor deposition (MOCVD) method. It is shown that using a multilayer metamorphic buffer with a step of 2.5% in indium content and layer thicknesses of 120 nm provides the high quality of bulk layers subsequently grown on the buffer up to an indium content of 24%. PVCs with a long-wavelength photosensitivity edge up to 1300 nm and a quantum efficiency of ~80% in the spectral range 1050–1100 nm are fabricated. Analysis of the open-circuit voltage of the PVCs and diffusion lengths of minority carriers inmore » the layers demonstrates that the density of misfit dislocations penetrating into the bulk layers increases at an indium content exceeding 10%.« less

FeO and MgO in plagioclase of lunar anorthosites: Igneous or metamorphic?

NASA Technical Reports Server (NTRS)

Phinney, W. C.

1994-01-01

The combined evidence from terrestrial anorthosites and experimental laboratory studies strongly implies that lunar anorthosites have been subjected to high-grade metamorphic events that have erased the igneous signatures of FeO and MgO in their plagioclases. Arguments to the contrary have, to this point, been more hopeful than rigorous.

The metamorphic sole of New Caledonia ophiolite: 40Ar/39Ar, U-Pb, and geochemical evidence for subduction inception at a spreading ridge

NASA Astrophysics Data System (ADS)

Cluzel, Dominique; Jourdan, Fred; Meffre, SéBastien; Maurizot, Pierre; Lesimple, StéPhane

2012-06-01

Amphibolite lenses that locally crop out below the serpentinite sole at the base of the ophiolite of New Caledonia (termed Peridotite Nappe) recrystallized in the high-temperature amphibolite facies and thus sharply contrast with blueschists and eclogites of the Eocene metamorphic complex. Amphibolites mostly display the geochemical features of MORB with a slight Nb depletion and thus are similar to the youngest (Late Paleocene-Eocene) BABB components of the allochthonous Poya Terrane. Thermochronological data from hornblende (40Ar/39Ar), zircon, and sphene (U-Pb) suggest that these mafic rocks recrystallized at ˜56 Ma. Using various geothermobarometers provides a rough estimate of peak recrystallization conditions of ˜0.5 GPa at ˜800-950°C. The thermal gradient inferred from the metamorphic assemblage (˜60°C km-1), geometrical relationships, and geochemical similarity suggest that these mafic rocks belong to the oceanic crust of the lower plate of the subduction/obduction system and recrystallized when they subducted below young and hot oceanic lithosphere. They were detached from the down-going plate and finally thrust onto unmetamorphosed Poya Terrane basalts. This and the occurrence of slab melts at ˜53 Ma suggest that subduction inception occurred at or near to the spreading ridge of the South Loyalty Basin at ˜56 Ma.

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

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

Anatexis and metamorphism in tectonically thickened continental crust exemplified by the Sevier hinterland, western North America

NASA Technical Reports Server (NTRS)

Patino Douce, Alberto E.; Humphreys, Eugene D.; Johnston, A. Dana

1990-01-01

This paper presents a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening exemplified by the Sevier hinterland in western North America, and uses the model to examine the geological and physical processes leading to crustally derived magmatism. The results of numerical experiments show that anatexis was an inevitable end-product of Barrovian metamorphism in the thickened crust of the late Mesozoic Sevier orogenic belt and that the advection of heat across the lithosphere, in the form of mantle-derived mafic magmas, was not required for melting of metasedimentary rocks. It is suggested that, in the Sevier belt, as in other intracontinental orogenic belts, anatexis occurred in the midcrust and not at the base of the crust.

Geometric description and analysis of metamorphic tectonites (Pelagonian Zone, Internal Hellenides, Northern Greece)

NASA Astrophysics Data System (ADS)

Diamantopoulos, A.

2009-04-01

An assortment of alpine and pre-Permian metamorphic tectonites, belonging to the Pelagonian Zone of the Internal Hellenides, are analyzed from Askion, Vernon and Vorras mountains. They in fact compose the Upper plate of the Western Macedonia core complex, overlying Late Tertiary high-P rocks through large-scale detachment fautls (Diamantopoulos et al. 2007). This work wants to determine the architecture and the kinematic path of rocks in a 3D assumption. Field analysis concludes: a) Meta-sedimentary lithologies and amphibolites, meta-igneous lithologies, granitoid mylonites composed of augen fieldspar gneisses, Permo-Triassic fossiliferous rocks, meta-carbonates of Triassic-Jurassic age, a Jurassic mélange including meta-sedimentary lithologies, serpentinites and carbonate tectonic blocks, Mesozoic Ophiolites, Cretaceous limestones and conglomerates as well as flysch sediments compose the architecture of the study area, b) Multiple high and low-angle cataclastic zones of intense non-coaxial strain separate distinct pre-Permian lithologies, alpine from pre-alpine rocks, Triassic-Jurassic rocks from Permo-Triassic rocks, Jurassic mélange from flysch sediments, Jurassic mélange from Triassic-Jurassic rocks, Cretaceous rocks from the Jurassic mélange, Cretaceous limestones from flysch lithologies and Cretaceous rocks from serpentinites, c) Geometric analysis and description of asymmetric structures found in fault cores, damage zones and in the footwall-related rocks showed a prominent kinematic direction towards WSW in low-T conditions affected all the rock lithologies, d) Multiple S- and L- shape fabric elements in the pre-Permian and Permo-Triassic rocks appear an intricate orientation, produced by intense non-coaxial syn-metamorphic deformation, e) Sheath and isoclinal folds oriented parallel to the L-shape fabric elements as well as a major S-shape fabric element, producing macroscopic fold-like structures compose the main syn-metamorphic fabric elements in the

Differentiating Metamorphic Events in a Polymetamorphic Terrane using Zr-in-Ttn thermometry and Titanite U-Pb Geochronology

NASA Astrophysics Data System (ADS)

Kenney, M.; Roeske, S.; Mulcahy, S. R.; Cottle, J. M.; Coble, M. A.

2016-12-01

In polymetamorphic terranes, it is problematic to link ages from geochronometers to metamorphic fabrics and, therefore, to a specific deformation event(s). It is necessary to analyze a mineral which may preserve multiple age domains. Titanite has been shown to retain multiple age and elemental domains in single grains through high-grade metamorphism. In this study, titanite U-Pb geochronology is used to examine whether ages are thermally reset along a sample transect towards a mylonitic shear zone in NW Argentina. This work also seeks to understand the conditions under which titanite resists resetting. A combination of petrographic and electron microprobe analyses reveal the textures and compositional domains in titanite, garnet, and hornblende. Titanite are elongate, wrapped by the mylonitic fabric, and have patchy elemental zoning. Garnet has distinct cores with prograde zoning and thin rims, which appear to be in equilibrium with the fabric defining minerals. Hornblende has inclusion rich cores and thin overgrowth rims in equilibrium with the fabric defining minerals. In-situ U-Pb and trace element data was collected in titanite from four samples, which all preserve lower-intercept ages between 900Ma and 1.0Ga. We observed no correlation between age and elemental domains; these domains correlate with Al and Nb variations. Zr-in-titanite temperatures preserve upper amphibolite facies conditions, 660ºC-710ºC. Given these results, we conclude that titanite U-Pb ages and temperatures reflect original Grenville metamorphism. 40Ar/39Ar hornblende cooling ages, of 515 Ma, suggested titanite may be reset near the shear zone but overprinting P-T of 560ºC and 0.8 GPa, fluid infiltration, and deformation did not cause significant Pb loss. Overprinting conditions and cooling ages suggest that rims of garnet and hornblende correlate to Paleozoic metamorphism, while textural evidence and titanite ages suggest garnet and hornblende cores grew during the Proterozoic.

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.

Chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks

Treesearch

Jason R. Price; Michael A. Velbel

2003-01-01

Chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample. Generally, on homogeneous parent rocks, weathering indices change systematically with depth. However, the weathering of heterogeneous metamorphic rocks confounds the relationship between...

Petrography and zircon U-Pb isotopic study of the Bayanwulashan Complex: Constrains on the Paleoproterozoic evolution of the Alxa Block, westernmost North China Craton

NASA Astrophysics Data System (ADS)

Wu, Sujuan; Hu, Jianmin; Ren, Minghua; Gong, Wangbin; Liu, Yang; Yan, Jiyuan

2014-11-01

The Bayanwulashan Metamorphic Complex (BMC) exposes along the eastern margin of the Alxa Block, the westernmost part of the North China Craton (NCC). BMC is principally composed of metamorphic rocks with amphibole plagiogneiss, biotite plagioclase gneiss and granitic gneiss. Our research has been focused on the petrography and zircon U-Pb geochronology of the BMC to better understand the evolution of the Alxa Block and its relationship with the NCC. Evidences from field geology, petrography, and mineral chemistry indicate that two distinct metamorphic assemblages, the amphibolite and greenschist facies, had overprinted the preexisting granitic gneiss and suggest that the BMC experienced retrograde metamorphic episodes. The LA-ICP-MS zircon U-Pb ages reveal that the primary magmatic activities of BMC were at ca. 2.30-2.24 Ga and the two metamorphic events were at ca. 1.95-1.91 Ga and ca. 1.88-1.85 Ga respectively. These ages indicate that BMC initially intruded during Paleoproterozoic, not as previously suggested at Archean period. The Early Paleoproterozoic metamorphic records and the magmatic thermochronological data in BMC exhibit different evolution paths between the Alxa Block and the NCC. The Alxa Block was most likely an independent Early Paleoproterozoic terrain. Following different amalgamation processes, The Alxa Block combined with Western Block at ca. 1.95 Ga and then united with NCC at ca. 1.85 Ga.

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).

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.

Optimization of structural and growth parameters of metamorphic InGaAs photovoltaic converters grown by MOCVD

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

Rybalchenko, D. V.; Mintairov, S. A.; Salii, R. A.

Metamorphic Ga{sub 0.76}In{sub 0.24}As heterostructures for photovoltaic converters are grown by the MOCVD (metal–organic chemical vapor deposition) technique. It is found that, due to the valence-band offset at the p-In{sub 0.24}Al{sub 0.76}As/p-In{sub 0.24}Ga{sub 0.76}As (wide-gap window/emitter) heterointerface, a potential barrier for holes arises as a result of a low carrier concentration in the wide-gap material. The use of an InAlGaAs solid solution with an Al content lower than 40% makes it possible to raise the hole concentration in the widegap window up ~9 × 10{sup 18} cm{sup –3} and completely remove the potential barrier, thereby reducing the series resistance ofmore » the device. The parameters of an GaInAs metamorphic buffer layer with a stepwise In content profile are calculated and its epitaxial growth conditions are optimized, which improves carrier collection from the n-GaInAs base region and provides a quantum efficiency of 83% at a wavelength of 1064 nm. Optimization of the metamorphic heterostructure of the photovoltaic converter results in that its conversion efficiency for laser light with a wavelength of 1064 nm is 38.5%.« less

Investigation of InP/In0.65Ga0.35As metamorphic p-channel doped-channel field-effect transistor

NASA Astrophysics Data System (ADS)

Tsai, Jung-Hui

2016-07-01

In this article, the device mechanism and characteristics of InP/InGaAs metamorphic p-channel field-effect transistor (FET), which has a high indium mole fraction of InGaAs channel, grown on the GaAs substrate is demonstrated. The device was fabricated on the top of the InxGa1-xP graded metamorphic buffer layer, and the In0.65Ga0.35As pseudomorphic channel was employed to elevate the transistor performance. For the p-type FET, due to the considerably large valence band discontinuity at InP/In0.65Ga0.35As heterojunction and a relatively thin as well as heavily doped pseudomorphic In0.65Ga0.35As channel between two undoped InP layers, a maximum extrinsic transconductance of 27.3 mS/mm and a maximum saturation current density of -54.3 mA/mm are obtained. Consequently, the studied metamorphic FET is suitable for the development in signal amplification, integrated circuits, and low supply-voltage complementary logic inverters.

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.

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.

High-pressure granulite-facies metamorphism in central Dronning Maud Land (East Antarctica): Implications for Gondwana assembly

NASA Astrophysics Data System (ADS)

Palmeri, Rosaria; Godard, Gaston; Di Vincenzo, Gianfranco; Sandroni, Sonia; Talarico, Franco M.

2018-02-01

Central Dronning Maud Land (DML; East Antarctica) is located in a key region of the Gondwana supercontinent. The Conradgebirge area (central DML) consists of orthogneisses, derived from both volcanic and plutonic protoliths, and minor metasedimentary rocks, intruded by Cambrian syn- to post-metamorphic plutons and dykes. Mafic-ultramafic boudins in the metavolcanic and metaplutonic gneisses from Conradgebirge consist of amphibolites and high-grade garnet-bearing pyroxene- and amphibole-rich granofels. They occur either as discontinuous levels or as pods boudinaged within highly-strained and strongly-migmatized gneisses. Bulk-rock major and trace-element compositions, together with geochemical discriminant diagrams (e.g., Th/Yb versus Ta/Yb and V versus Ti), suggest derivation from enriched mantle source for the mafic rocks boudinaged in metaplutonic gneisses, whereas a calc-alkaline signature is common for the mafic boudins in metavolcanic rocks. The microstructural study and P-T modelling of an ultramafic metagabbroic rock reveal a prograde metamorphic evolution from amphibolite-facies (ca. 0.5 GPa; 500 °C) up to high-P granulite-facies conditions (ca. 1.5-1.7 GPa; 960-970 °C). Partial melting is testified by "nanogranitoid" inclusions enclosed in garnet. An almost isothermal decompression down to ca. 0.4 GPa and 750-850 °C produced well-developed An + Opx-bearing symplectites around garnet. A final isobaric cooling at nearly 0.4 GPa is testified by Grt coronas around high-T symplectites. The above reconstruction traces a clockwise loading-heating P-T evolution with a peak metamorphism at high-P granulite-facies conditions suggesting crustal thickening at nearly 570 Ma, followed by a tectonically assisted rapid exhumation, and then, by an isobaric cooling. 40Ar-39Ar dating of amphibole and biotite at 505-480 Ma testify mineral re-equilibration at upper crustal level (T < 650 °C) during the isobaric cooling. This tectono-metamorphic scenario seems

Structural Maturation of HIV-1 Reverse Transcriptase—A Metamorphic Solution to Genomic Instability

PubMed Central

London, Robert E.

2016-01-01

Human immunodeficiency virus 1 (HIV-1) reverse transcriptase (RT)—a critical enzyme of the viral life cycle—undergoes a complex maturation process, required so that a pair of p66 precursor proteins can develop conformationally along different pathways, one evolving to form active polymerase and ribonuclease H (RH) domains, while the second forms a non-functional polymerase and a proteolyzed RH domain. These parallel maturation pathways rely on the structural ambiguity of a metamorphic polymerase domain, for which the sequence–structure relationship is not unique. Recent nuclear magnetic resonance (NMR) studies utilizing selective labeling techniques, and structural characterization of the p66 monomer precursor have provided important insights into the details of this maturation pathway, revealing many aspects of the three major steps involved: (1) domain rearrangement; (2) dimerization; and (3) subunit-selective RH domain proteolysis. This review summarizes the major structural changes that occur during the maturation process. We also highlight how mutations, often viewed within the context of the mature RT heterodimer, can exert a major influence on maturation and dimerization. It is further suggested that several steps in the RT maturation pathway may provide attractive targets for drug development. PMID:27690082

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

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.

Design concepts of monolithic metamorphic vertical-cavity surface-emitting lasers for the 1300–1550 nm spectral range

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

Egorov, A. Yu., E-mail: anton@beam.ioffe.ru; Karachinsky, L. Ya.; Novikov, I. I.

Possible design concepts for long-wavelength vertical-cavity surface-emitting lasers for the 1300–1550 nm spectral range on GaAs substrates are suggested. It is shown that a metamorphic GaAs–InGaAs heterostructure with a thin buffer layer providing rapid transition from the lattice constant of GaAs to that of In{sub x}Ga{sub 1–x}As with an indium fraction of x < 0.3 can be formed by molecular-beam epitaxy. Analysis by transmission electron microscopy demonstrated the effective localization of mismatch dislocations in the thin buffer layer and full suppression of their penetration into the overlying InGaAs metamorphic layer.

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

Metamorphism and gold mineralization in the Blue Ridge, Southernmost Appalachians

USGS Publications Warehouse

Stowell, H.H.; Lesher, C.M.; Green, N.L.; Sha, P.; Guthrie, G.M.; Sinha, A.K.

1996-01-01

Lode gold mineralization in the Blue Ridge of the southernmost Appalachians is hosted by metavolcanic rocks (e.g., Anna Howe mine, AL; Royal Vindicator mine, GA), metaplutonic rocks (e.g., Hog Mountain mine, AL), and metasedimentary rocks (e.g., Lowe, Tallapoosa, and Jones Vein mines, AL). Most gold occurs in synkinematic quartz ?? plagioclase ?? pyrite ?? pyrrhotite ?? chlorite veins localized along polydeformational faults that juxtapose rocks with significantly different peak metamorphic mineral assemblages. Mineralogy, chemistry, and O and H isotope studies suggest that the three types of host rocks have undergone differing amounts and types of alteration during mineralization. Limited wall-rock alteration in metavolcanic- and metasediment-hosted deposits, and relatively extensive wall-rock alteration in granitoid-hosted deposits, suggests that most deposits formed from fluids that were close to equilibrium with metavolcanic and metasedimentary rocks. Stable isotope compositions of the fluids calculated from vein minerals and vein selvages are consistent with a predominantly metasedimentary fluid source, but vary from deposit to deposit (-22 to -47??? ??D, 4-5??? ??18O, and 5-7??? ??34S at Anna Howe and Royal Vindicator; -48 to -50??? ??D, 9-13??? ??18O, and ca. 19??? ??34S at Lowe and Jones Vein; and -22 to -23??? ??D, 8-11??? ??18O, 9-10??? ??34S, and -6 ??13C at Hog Mountain). Silicate mineral thermobarometry of vein, vein selvage, and wall-rock mineral assemblages indicate that mineralization and regional metamorphism occured at greenschist to amphibolite facies (480?? ?? 75??C at Anna Howe, 535?? ?? 50??C at 6.4 ?? 1 kbars at Lowe, 530?? ?? 50??C at 6.9 ?? 1 kbars at Tallapoosa, and 460?? ?? 50??C at 5.5 ?? 1 kbars at Hog Mountain). Oxygen isotope fractionation between vein minerals and selvage minerals consistently records equilibration temperatures that are similar to or slightly lower than those estimated from silicate thermometry. Auriferous veins

Protracted tectono-metamorphic history of the SE Superior Province : contribution of 40Ar/39Ar thermochronology in the Abitibi-Opatica contact zone, Québec, Canada

NASA Astrophysics Data System (ADS)

Daoudene, Yannick; Tremblay, Alain; Ruffet, Gilles; Leclerc, François; Goutier, Jean

2015-04-01

Archean orogens mainly consist of greenstone belts juxtaposing deeper crustal domains of TTG-type plutonic rocks. The greenstone belts show regional folds, penetrative steeply-dipping fabrics, and localised shear zones, whereas the plutonic belts predominantly display dome structures. Concurrently, rocks in Archean orogens undergone MT/HT-LP/MP metamorphic conditions that vary, from upper to lower crustal domains, between greenschist- and granulite-facies, respectively. These structural and metamorphic variations are well-documented, but modes of deformation related to such orogens is still debated. Some studies suggest that the Archean tectonic processes were comparable to present-day plate tectonics and the Archean greenstone belts were interpreted as tectonic collages commonly documented in Phanerozoic subduction/collision zones. Alternative models propose that the Archean tectonics were different from those predicted by the plate tectonics paradigm, mainly due to the existence of a hotter mantle and a mechanically weak crust. In such models, the burying and exhumation of crustal rocks are attributed to the vertical transfer of material, resulting in the development of pop-down and domes structures. As a contribution of the study of mechanisms that might have operated during the Archean, we present a structural and metamorphic study of the contact zone between the Abitibi subprovince (ASP), which contains greenstone belts, and the Opatica subprovince (OSP), which is dominated by plutonic rocks, of the Superior Province. The 40Ar/39Ar dating of amphiboles and micas is used to constrain the age and duration of regional metamorphism and associated deformations. On the basis of seismic profiling, showing a north-dipping lithospheric-scale reflector, the ASP-OSP contact has been interpreted as the surficial trace of an Archean subduction zone. However, our structural analysis suggest that the ASP overlies the OSP and that the ASP-OSP contact does not show evidences

Microstructures of the Kirsehir Complex, Central Turkey

NASA Astrophysics Data System (ADS)

ISIK, V.; Caglayan, A.; Uysal, T.; Bolhar, R.

2011-12-01

Turkey is positioned on the boundary between the Eurasian and African/Arabian plates, providing an ideal natural laboratory for learning passive and active earth processes such as deformation, metamorphism, earthquakes and volcanism. Central Turkey historically has played an important role in evolution of the Alpine orogeny. The Kirsehir Complex is one of three Mesozoic-Early Tertiary metamorphic and plutonic mid-crustal basement units exposed in central Turkey. The most common lithology of the metamorphites are the banded gneisses, which are intercalated with layers of schists, amphibolites and quartzite, and marbles representing the structurally the highest metamorphites of the study area. The metamorphites are characterized by multiple folding episodes and overprinting faults (thrust, normal and strike-slip). These metamorphites reached peak metamorphic conditions of upper amphibolite facies, as indicated by local presence of clinopyroxene, sillimanite, hornblende, andalusite and garnet. Later, retrograde greenschist facies conditions were attained characterized by the alteration of feldspar and mafic minerals to muscovite and chlorite/actinolite, respectively. The microstructures of selected minerals can be used to bracket the metamorphic grade during which microstructure formed. Quartz displays undulose extinction, deformation bands, subgrains and deformation lamellae, and recrystallisation. The presence of lobate grain boundaries of quartz indicates that GBM recrystallisation occurred. Undulose extinction and recrystallisation are common in micas. Recrystallisation, core-mantle structures in feldspar, myrmekites in K-feldspars within the gneisses suggest that deformation occurred within the amphibolite facies. Garnet occurs as slightly elliptical porphroclats. Sillimanite is present as fibrolite growing near biotite and microboudinaged. Andalusite porphyroblast/porphroclats are elongate and microboudinaged. Kinematic indicators (asymmetric mantled grains, S

Chemical zoning and homogenization of Pasamonte-type pyroxene and their bearing on thermal metamorphism of a howardite parent body

NASA Technical Reports Server (NTRS)

Miyamoto, M.; Duke, M. B.; Mckay, D. S.

1985-01-01

The Mg-Fe zoning of pyroxenes in Pasamonte and Juvinas eucrites is examined in order to gain a better understanding of the metamorphism in the surface layer of a eucrite/howardite parent body. Three distinct types of Ca-Mg-Fe zoning of Pasamonte pyroxenes are identified. The wide compositional range of the zoned pyroxenes suggests that Pasamonte is less metamorphosed than previously believed. It is also found that a Pasamonte-type pyroxene may yield a Juvinas-type pyroxene by thermal metamorphism. Calculations imply that the homogenization of Juvinas pyroxenes may have occurred during later reheating events rather than during initial cooling.

Implications of contact metamorphism of Mancos Shale for critical zone processes

NASA Astrophysics Data System (ADS)

Navarre-Sitchler, A.

2016-12-01

Bedrock lithology imparts control on some critical zone processes, for example rates and extent of chemical weathering, solute release though mineral dissolution, and water flow. Bedrock can be very heterogeneous resulting in spatial variability of these processes throughout a catchment. In the East River watershed outside of Crested Butte, Colorado, bedrock is dominantly comprised of the Mancos Shale; a Cretaceous aged, organic carbon rich marine shale. However, in some areas the Mancos Shale appears contact metamorphosed by nearby igneous intrusions resulting in a potential gradient in lithologic change in part of the watershed where impacts of lithology on critical zone processes can be evaluated. Samples were collected in the East River valley along a transect from the contact between the Tertiary Gothic Mountain laccolith of the Mount Carbon igneous system and the underlying Manocs shale. Porosity of these samples was analyzed by small-angle and ultra small-angle neutron scattering. Results indicate contact metamorphism decreases porosity of the shale and changes the pore shape from slightly anisotropic pores aligned with bedding in the unmetamorphosed shale to isotropic pores with no bedding alignment in the metamorphosed shales. The porosity analysis combined with clay mineralogy, surface area, carbon content and oxidation state, and solute release rates determined from column experiments will be used to develop a full understanding of the impact of contact metamorphism on critical zone processes in the East River.

A transect of metamorphic rocks along the Copper River, Cordova and Valdez Quadrangles, Alaska: A section in The United States Geological Survey in Alaska: Accomplishments during 1982

USGS Publications Warehouse

Miller, Marti L.; Dumoulin, Julie A.; Nelson, S.W.

1984-01-01

The lower Tertiary Orca Group is juxtaposed against the Upper Cretaceous Valdez Group along the Contact fault system (Winkler and Plafker, 1974, 198; Plafker and others, 1977)(fig. 33). In both groups, turbidites are the dominant rock type, with lesser mafic volcanic rocks (table 10). The Valdez Group, on the north, has traditionally been considered to be of higher metamorphic grade than the Orca Group (Moffit, 1954; Tysdal and Case, 1979; Winkler and Plafker, 198; Winkler and others, 1981). In 1982, we made a transect across the regional strike of the rocks and the contact between the two groups. The transect area follows the Copper River for 85 km from the Cordova quadrangle north into the Valdez quadrangle and extends for about 25 km on either side of the river (fig. 33). We planned, by systematic sampling of the area, to examine the metamorphic differences between the Orca and Valdez Groups. We found, however, that a strong thermal metamorphic event has overprinted and obscured regional metamorphic relations. We believe intrusion of Tertiary granite (fig. 33) to be responsible for this metamorphism. (Figures 33 and 34 and tables follow this article.)

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.

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

Petrology and metamorphic evolution of ultramafic rocks and dolerite dykes of the Betic Ophiolitic Association (Mulhacén Complex, SE Spain): evidence of eo-Alpine subduction following an ocean-floor metasomatic process

NASA Astrophysics Data System (ADS)

Puga, E.; Nieto, J. M.; Díaz de Federico, A.; Bodinier, J. L.; Morten, L.

1999-10-01

The Betic Ophiolitic Association, cropping out within the Mulhacén Complex (Betic Cordilleras), is made up of numerous metre- to kilometre-sized lenses of mafic and/or ultramafic and meta-sedimentary rocks. Pre-Alpine oceanic metasomatism and metamorphism caused the first stage of serpentinization in the ultramafic sequence of this association, which is characterized by local clinopyroxene (Cpx) breakdown and Ca-depletion, and complementary rodingitization of the basic dykes intruded in them. Subsequent eo-Alpine orogenic metamorphism developed eclogite facies assemblages in ultramafic and basic lithotypes, which were partly retrograded in Ab-Ep-amphibolite facies conditions during a meso-Alpine event. The heterogeneous development of the oceanic metasomatism in the ultramafic rock-types led to the patchy development of highly serpentinized Ca-depleted domains, without gradual transition to the host, and less serpentinized, Cpx-bearing ultramafites, mainly lherzolitic in composition. The high-pressure eo-Alpine recrystallization of these ultramafites in subduction conditions originated secondary harzburgites in the Ca-depleted domains, consisting of a spinifex-like textured olivine+orthopyroxene paragenesis, and a diopside+Ti-clinohumite paragenesis in the enclosing lherzolitic rocks. During the meso-Alpine event, secondary harzburgites were partly transformed into talc+antigorite serpentinites, whereas the diopside and clinohumite-bearing residual meta-lherzolites were mainly transformed into Cpx-bearing serpentinites. Relics of mantle-derived colourless olivine may be present in the more or less serpentinized secondary harzburgites. These relics are overgrown by the eo-Alpine brown pseudo-spinifex olivine, which contains submicroscopic inclusions of chromite, ilmenite and occasional halite and sylvite, inherited from its parental oceanic serpentine. The same type of mantle-derived olivine relics is also preserved within the Cpx-bearing serpentinites, although it

The fate of carbon and CO2 - fluid-rock interaction during subduction metamorphism of serpentinites

NASA Astrophysics Data System (ADS)

Menzel, Manuel D.; Garrido, Carlos J.; López Sánchez-Vizcaíno, Vicente; Marchesi, Claudio; Hidas, Károly

2016-04-01

Given to its large relevance for present and past climate studies, the deep carbon cycle received increasing attention recently. However, there are still many open questions concerning total mass fluxes and transport processes between the different carbon reservoirs in the Earth's interior. One key issue is the carbon transfer from the subducting slab into fluids and rocks in the slab and mantle wedge. This transfer is controlled by the amount and speciation of stable carbon-bearing phases, which have a strong impact on the pH, redox conditions and trace-element budget of slab fluids. As recent experiments and thermodynamic modeling have shown, water released from dehydrating serpentinites has a great potential to produce CO2-enriched slab fluids by dissolution of carbonate minerals. To constrain the fate of carbon and CO2-fluid-rock interactions during subduction metamorphism of serpentinites, we have studied carbonate-bearing serpentinites recording different prograde evolutions from antigorite schists to Chl-harzburgites in high-P massifs of the Nevado-Filabride Complex (Betic Cordillera, S. Spain). Our results indicate that dissolution of dolomite in marbles in contact with dehydrating serpentinites is spatially limited during prograde metamorphism of carbonate-bearing serpentinites, but it can lead to the formation of silicate-rich zones in marbles close to the contacts. In lower grade serpentinite massifs (1.0-1.5 GPa / 550 °C), the presence of marble lenses in contact with antigorite schists appears to promote local dehydration of serpentinite coupled with carbonation of antigorite, forming Cpx-Tr-Chl-bearing high grade ophicarbonate zones. At the Cerro del Almirez ultramafic massif, where a dehydration front from antigorite-serpentinite to prograde Chl-harzburgite is preserved (1.9 GPa / 680 °C), a significant amount of carbon is retained in prograde Chl-harzburgites and Tr-Dol-marble lenses. This observation is at odds with thermodynamic models that

U-Pb dating and isotopic signature of the alkaline ring complexes of Bou Naga (Mauritania): its bearing on late proterozoic plate tectonics around the West African craton

NASA Astrophysics Data System (ADS)

Blanc, A.; Bernard-Griffiths, J.; Caby, R.; Caruba, C.; Caruba, R.; Dars, R.; Fourcade, S.; Peucat, J. J.

1992-04-01

In the West African fold belt of Mauritania, high-grade metamorphic series, similar to those of Amsaga (Reguibat shield-West African Craton), are exposed in a window. At Bou Naga-Mauritania (19° N, 13° 15' W) in the South of this window, an alkaline ring complex has intruded the metamorphic country rocks. This complex consists of two geological formations: the Eastern formation is mainly composed of red rhyolite sills, whereas the Western formation is made up of several kinds of alkaline rocks both saturated and under-saturated which cross cut the earlier saturated units. Three U-Pb zircon age measurements have been made on the alkaline complex, and one on an orthogneiss from the metamorphic country rocks. The syenite and the alkaline granite of the Western block are 676 ± 8 and 687 ± 5 Ma old. The orthogneiss is Archaean with an age of 2709 ± 136 Ma, but the lower intercept of discordia on concordia, shows an age of 756 ± 25 Ma linked with the genesis of the alkaline complex. A major crustal contribution is recorded by Nd and O isotopes in the SiO 2-saturated rocks. These results provide evidence for the correlation of the metamorphic country rocks with the Reguibat Archaean basement and for an early Pan-African continental rifting phase in this area before the tectonometamorphic events in the Mauritanide belt. Furthermore, with regards with previous geodynamic works of the West African Craton, our results leads us to suggest a significant diachronism between late Proterozoic crustal evolution to the West and to the East of the West African Craton. This is a further evidence for modern-type plate tectonics at this time.

The role of evaporites in the formation of gems during metamorphism of carbonate platforms: a review

NASA Astrophysics Data System (ADS)

Giuliani, Gaston; Dubessy, Jean; Ohnenstetter, Daniel; Banks, David; Branquet, Yannick; Feneyrol, Julien; Fallick, Anthony E.; Martelat, Jean-Emmanuel

2018-01-01

The mineral and fluid inclusions trapped by gemstones during the metamorphism of carbonate platform successions are precious markers for the understanding of gem genesis. The nature and chemical composition of inclusions highlight the major contribution of evaporites through dissolution or fusion, depending on the temperature of formation from greenschist to granulite facies. The fluids are highly saline NaCl-brines circulating either in an open system in the greenschist facies (Colombian and Afghan emeralds) and with huge fluid-rock metasomatic interactions, or sulphurous fluids (ruby, garnet tsavorite, zoisite tanzanite and lapis-lazuli) or molten salts formed in a closed system with a low fluid mobility (ruby in marble) in the conditions of the amphibolite to granulite facies. These chloride-fluoride-sulphate ± carbonate-rich fluids scavenged the metals essential for gem formation. At high temperature, the anions SO4 2-, NO3 -, BO3 - and F- are powerful fluxes which lower the temperature of chloride- and fluoride-rich ionic liquids. They provided transport over a very short distance of aluminium and/or silica and transition metals which are necessary for gem growth. In summary, the genetic models proposed for these high-value and ornamental gems underline the importance of the metamorphism of evaporites formed on continental carbonate shelves and emphasise the chemical power accompanying metamorphism at moderate to high temperatures of evaporite-rich and organic matter-rich protoliths to form gem minerals.

Study of the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and the atomic structure of InAlAs/InGaAs MHEMT heterostructures

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

Galiev, G. B.; Pushkarev, S. S., E-mail: s_s_e_r_p@mail.ru; Vasil'evskii, I. S.

The results of studying the influence of strained superlattices introduced into a metamorphic buffer on the electrophysical properties and atomic crystal structure of In{sub 0.70}Al{sub 0.30}As/In{sub 0.76}Ga{sub 0.24}As/In{sub 0.70}Al{sub 0.30}As metamorphic high-electron-mobility transistor (MHEMT) nanoheterostructures on GaAs substrates are presented. Two types of MHEMT structures are grown by molecular beam epitaxy, namely, one with a linear increase in x in the In{sub x}Al{sub 1-x}As metamorphic buffer, and the second with two mismatched superlattices introduced inside the metamorphic buffer. The electrophysical and structural parameters of the grown samples are studied by the van der Pauw method, transmission electron microscopy (including scanningmore » and high-resolution microscopy), atomic-force microscopy, and energy dispersive X-ray analysis. It is revealed that the introduction of superlattices into a metamorphic buffer substantially improves the electrophysical and structural characteristics of MHEMT structures.« less

Dehydration reactions, mass transfer and rock deformation relationships during subduction of Alpine metabauxites: insights from LIBS compositional profiles between metamorphic veins

NASA Astrophysics Data System (ADS)

Verlaguet, A.; Brunet, F.; Goffe, B.; Menut, D.; Findling, N.; Poinssot, C.

2011-12-01

In subduction zones, the significant amounts of aqueous fluid released in the course of the successive dehydration reactions occurring during prograde metamorphism are expected to strongly influence the rock rheology, as well as kinetics of metamorphic reactions and mass transfer efficiency. Mineralized veins, ubiquitous in metamorphic rocks, can be seen as preserved witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation). However, the driving forces and mechanisms of mass transfer towards fluid-filled open spaces remain somewhat unclear. The aim of this study is to investigate the modalities of mass transfer during local fluid-rock interactions, and their links with fluid production and rock deformation. This study focuses on karstic pockets (metre scale) of Triassic metabauxites embedded in thick carbonate units, that have been isolated from large-scale fluid flow during HP-LT Alpine metamorphism (W. Vanoise, French Alps). These rocks display several generations of metamorphic veins containing various Al-bearing minerals, which give particular insights into mass transfer processes. It is proposed that the internally-derived fluid (~13 vol% produced by successive dehydration reactions) has promoted the opening of fluid-filled open spaces (euhedral habits of vein minerals) and served as medium for diffusive mass transfer from rock to vein. Based on mineralogical and textural features, two vein types can be distinguished: (1) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (2) the second vein type is filled with cookeite (Li-Al-rich chlorite) or pyrophyllite, that were present in the host rock prior to the vein formation. In this closed chemical system, mass transfer from rock to vein was achieved through the fluid, in a dissolution

Sr and Nd isotope composition of the metamorphic, sedimentary and ultramafic xenoliths of Lanzarote (Canary Islands): Implications for magma sources

NASA Astrophysics Data System (ADS)

Aparicio, Alfredo; Tassinari, Colombo C. G.; García, Roberto; Araña, Vicente

2010-01-01

The lavas produced by the Timanfaya eruption of 1730-1736 (Lanzarote, Canary Islands) contain a great many sedimentary and metamorphic (metasedimentary), and mafic and ultramafic plutonic xenoliths. Among the metamorphosed carbonate rocks (calc-silicate rocks [CSRs]) are monomineral rocks with forsterite or wollastonite, as well as rocks containing olivine ± orthopyroxene ± clinopyroxene ± plagioclase; their mineralogical compositions are identical to those of the mafic (gabbros) and ultramafic (dunite, wherlite and lherzolite) xenoliths. The 87Sr/ 86Sr (around 0.703) and 143Nd/ 144Nd (around 0.512) isotope ratios of the ultramafic and metasedimentary xenoliths are similar, while the 147Sm/ 144Nd ratios show crustal values (0.13-0.16) in the ultramafic xenoliths and mantle values (0.18-0.25) in some CSRs. The apparent isotopic anomaly of the metamorphic xenoliths can be explained in terms of the heat source (basaltic intrusion) inducing strong isotopic exchange ( 87Sr/ 86Sr and 143Nd/ 144Nd) between metasedimentary and basaltic rocks. Petrofabric analysis also showed a possible relationship between the ultramafic and metamorphic xenoliths.

Titanite-bearing calc-silicate rocks constrain timing, duration and magnitude of metamorphic CO2 degassing in the Himalayan belt

NASA Astrophysics Data System (ADS)

Rapa, Giulia; Groppo, Chiara; Rolfo, Franco; Petrelli, Maurizio; Mosca, Pietro; Perugini, Diego

2017-11-01

The pressure, temperature, and timing (P-T-t) conditions at which CO2 was produced during the Himalayan prograde metamorphism have been constrained, focusing on the most abundant calc-silicate rock type in the Himalaya. A detailed petrological modeling of a clinopyroxene + scapolite + K-feldspar + plagioclase + quartz ± calcite calc-silicate rock allowed the identification and full characterization - for the first time - of different metamorphic reactions leading to the simultaneous growth of titanite and CO2 production. The results of thermometric determinations (Zr-in-Ttn thermometry) and U-Pb geochronological analyses suggest that, in the studied lithology, most titanite grains grew during two nearly consecutive episodes of titanite formation: a near-peak event at 730-740 °C, 10 kbar, 30-26 Ma, and a peak event at 740-765 °C, 10.5 kbar, 25-20 Ma. Both episodes of titanite growth are correlated with specific CO2-producing reactions and constrain the timing, duration and P-T conditions of the main CO2-producing events, as well as the amounts of CO2 produced (1.4-1.8 wt% of CO2). A first-order extrapolation of such CO2 amounts to the orogen scale provides metamorphic CO2 fluxes ranging between 1.4 and 19.4 Mt/yr; these values are of the same order of magnitude as the present-day CO2 fluxes degassed from spring waters located along the Main Central Thrust. We suggest that these metamorphic CO2 fluxes should be considered in any future attempts of estimating the global budget of non-volcanic carbon fluxes from the lithosphere.

Broadband light sources based on InAs/InGaAs metamorphic quantum dots

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

Seravalli, L.; Trevisi, G.; Frigeri, P.

We propose a design for a semiconductor structure emitting broadband light in the infrared, based on InAs quantum dots (QDs) embedded into a metamorphic step-graded In{sub x}Ga{sub 1−x}As buffer. We developed a model to calculate the metamorphic QD energy levels based on the realistic QD parameters and on the strain-dependent material properties; we validated the results of simulations by comparison with the experimental values. On this basis, we designed a p-i-n heterostructure with a graded index profile toward the realization of an electrically pumped guided wave device. This has been done by adding layers where QDs are embedded in In{submore » x}Al{sub y}Ga{sub 1−x−y}As layers, to obtain a symmetric structure from a band profile point of view. To assess the room temperature electro-luminescence emission spectrum under realistic electrical injection conditions, we performed device-level simulations based on a coupled drift-diffusion and QD rate equation model. On the basis of the device simulation results, we conclude that the present proposal is a viable option to realize broadband light-emitting devices.« less

Effect of salinity on locomotor performance and thermal extremes of metamorphic Andean Toads (Rhinella spinulosa) from Monte Desert, Argentina.

PubMed

Sanabria, Eduardo; Quiroga, Lorena; Vergara, Cristina; Banchig, Mariana; Rodriguez, Cesar; Ontivero, Emanuel

2018-05-01

Rhinella spinulosa is distributed from Peru to Argentina (from 1200 to 5000 m elevation), inhabiting arid mountain valleys of the Andes, characterized by salty soils. The variations in soil salinity, caused by high evapotranspiration of water, can create an osmotic constraint and high thermal oscillations for metamorphsed Andean toad (R. spinulosa), affecting their thermoregulation and extreme thermal tolerances. We investigated the changes in thermal tolerance parameters (critical thermal maximum and crystallization temperature) of a population of metamorphosed R. spinulosa from the Monte Desert of San Juan, Argentina, under different substrate salinity conditions. Our results suggest that the locomotor performance of metamorphs of R. spinulosa is affected by increasing salinity concentrations in the environment where they develop. On the other hand, the thermal extremes of metamorphs of R. spinulosa also showed changes associated with different salinity conditions. According to other studies on different organisms, the increase of the osmolarity of the internal medium may increase the thermal tolerance of this species. More studies are needed to understand the thermo-osmolar adjustments of the metamorphs of toads to environmental variability. Copyright © 2018 Elsevier Ltd. All rights reserved.

Structural and Optical Characteristics of Metamorphic Bulk InAsSb

DTIC Science & Technology

2014-01-01

0.815 0.820 0.825 InAsSb 5 /a ⊥ ( Å ) 3√2/a|| (Å) 0.25 0.40 0.75 1.3 1.5 1.8 2.2 hkl = 335 GaSb Structural and Optical Characteristics of Metamorphic...Conduction- and Valence- Band Energies in Bulk InAs1−xSbx and Type II InAs1−xSbx/InAs Strained-Layer Superlattices”, J. of Electron. Mater., 42, 918...0188 3. DATES COVERED (From - To) - UU UU UU UU Approved for public release; distribution is unlimited. Structural and Optical Characteristics of

Selection of diet by metamorphic and juvenile western toads (Bufo boreas) in northeastern Oregon

Treesearch

Evelyn L Bull; Jane L. Hayes

2009-01-01

The decline of Bufo boreas, the Western Toad, in portions of its range has accentuated the need for more complete information on all life stages of this species. Our objectives were to describe the diet of recently metamorphosed and juvenile (one-year old) B. boreas and then compare it to the available arthropods. Metamorphs (n...

Anisotropic strain relaxation of Si-doped metamorphic InAlAs graded buffers on InP

NASA Astrophysics Data System (ADS)

Gu, Yi; Zhang, Yonggang; Chen, Xingyou; Ma, Yingjie; Zheng, Yuanliao; Du, Ben; Zhang, Jian

2017-09-01

The effects of Si doping on the strain relaxation of InP-based metamorphic In x Al1-x As graded buffers have been investigated. The highly Si-doped sample shows an increased ridge period along the [1 1 0] direction in the cross-hatch morphology measured by atomic force microscope. X-ray diffraction reciprocal space mapping measurements reveal that the high Si-doping induced incomplete relaxation as well as inhomogeneous residual strain along the [1 -1 0] direction, which was also observed in micro-Raman measurements. The anisotropic strain relaxation is attributed to the Si-doping enhanced anisotropy of misfit dislocations along the orthogonal directions. The α-misfit dislocations along the [1 -1 0] direction are further delayed to generate in highly Si-doped InAlAs buffer, while the β-misfit dislocations along the [1 1 0] direction are not. These results supply useful suggestions on the design and demonstration of semiconductor metamorphic devices.

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.

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

Metamorphic distributed Bragg reflectors for the 1440–1600 nm spectral range: Epitaxy, formation, and regrowth of mesa structures

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

Egorov, A. Yu., E-mail: anton@beam.ioffe.ru; Karachinsky, L. Ya.; Novikov, I. I.

It is shown that metamorphic In{sub 0.3}Ga{sub 0.7}As/In{sub 0.3}Al{sub 0.7}As distributed Bragg reflectors (DBRs) with a reflection band at 1440–1600 nm and a reflectance of no less than 0.999 can be fabricated by molecular beam epitaxy (MBE) on a GaAs substrate. It is demonstrated that mesa structures formed from metamorphic DBRs on a GaAs substrate can be regrown by MBE and microcavities can be locally formed in two separate epitaxial processes. The results obtained can find wide application in the fabrication of vertical-cavity surface-emitting lasers (VCSELs) with a buried tunnel junction.

Metamorphic evolution and geochronology of the Dunhuang orogenic belt in the Hongliuxia area, northwestern China

NASA Astrophysics Data System (ADS)

Wang, Hao Y. C.; Wang, Juan; Wang, Guo-Dong; Lu, Jun-Sheng; Chen, Hong-Xu; Peng, Tao; Zhang, Hui C. G.; Zhang, Qian W. L.; Xiao, Wen-Jiao; Hou, Quan-Lin; Yan, Quan-Ren; Zhang, Qing; Wu, Chun-Ming

2017-03-01

Garnet-bearing mafic granulites and amphibolites from the Hongliuxia area of the southern Dunhuang orogenic belt, northwestern China, commonly occur as lenses or boudinages enclosed within metapelite or marble, which represent the block-in-matrix feature typical of orogenic mélange. Three to four generations of metamorphic mineral assemblages are preserved in these rocks. In the high-pressure amphibolites, prograde mineral assemblages (M1) occur as inclusions (hornblende + plagioclase + quartz ± chlorite ± epidote ± ilmenite) preserved within garnet porphyroblasts, and formed at 550-590 °C and 7.7-9.2 kbar based on geothermobarometry. The metamorphic peak mineral assemblages (M2) are composed of garnet + hornblende + plagioclase + quartz + clinopyroxene, as well as titanite + zircon + rutile + apatite as accessory minerals in the matrix, and are estimated to have formed at 640-720 °C and 14.1-16.0 kbar. The first retrograde assemblages (M3) are characterized by "white-eye socket" symplectites (hornblende + plagioclase + quartz ± biotite ± epidote ± magnetite) rimming garnet porphyroblasts, which formed at the expense of the garnet rims and adjacent matrix minerals during the decompression stage under P-T conditions of 610-630 °C and 5.6-11.8 kbar. The second retrograde assemblages (M4) are intergrowths of actinolite and worm-like quartz produced by the breakdown of the matrix hornblendes, and formed under P-T conditions of ∼490 °C and ∼2.8 kbar. For the high-pressure mafic granulites, the prograde assemblages (M1) are represented by plagioclase + quartz preserved within the garnet porphyroblasts. The metamorphic peak assemblages (M2) are garnet + matrix minerals (clinopyroxene + plagioclase + quartz + hornblende + rutile + zircon) and were estimated to have formed at ∼680 °C and ∼15.4 kbar. The retrograde assemblages (M3) are characterized by fine-grained patches of hornblende + plagioclase + quartz rimming the garnet porphyroblasts, as well as

Aqueous Alteration and Shock Metamorphism of Antarctic CR Chondrites

NASA Technical Reports Server (NTRS)

Komatsu, M.; Fagan, T. J.; Yamaguchi, A.; Mikouchi, T.; Yasutake, M.; Zolensky, M. E.

2018-01-01

CR chondrites are the group of carbonaceous chondrites that best preserve records of formation of their components in the solar nebula. Although they are affected by aqueous alteration, many chondrules and CAIs are well-preserved, suggesting they have experienced little thermal metamorphism. We have been investigating the petrologic variations among the CR chondrites in the NIPR Antarctic meteorite collection. We focused particular attention on the petrology of amoeboid olivine aggregates (AOAs) in order to understand secondary alteration on the CR chondrite parent body. AOAs are composed of fine-grained forsteritic olivine and refractory minerals formed by condensation in the solar nebula, and can be used as sensitive indicators of secondary alteration processes.

Effects of Oxygen Element and Oxygen-Containing Functional Groups on Surface Wettability of Coal Dust with Various Metamorphic Degrees Based on XPS Experiment

PubMed Central

Zhou, Gang; Xu, Cuicui; Cheng, Weimin; Zhang, Qi; Nie, Wen

2015-01-01

To investigate the difference of surface oxygen element and oxygen-containing functional groups among coal dusts with different metamorphic degrees and their influence on surface wettability, a series of X-ray photoelectron spectroscopy experiments on 6 coal samples are carried out. The result demonstrates that the O/C ratio of coal surface shows an overall increasing trend compared with the result of its elements analysis. As the metamorphic degree increases, the O/C ratio on the surface gradually declines and the hydrophilic groups tend to fall off from coal surface. It could be found that different coals show different surface distributions of carboxyl and hydroxyl which are considered as the greatest promoter to the wettability of coal surface. With the change of metamorphic degree, the distribution of ether group is irregular while the carbonyl distribution keeps stable. In general, as the metamorphic degree goes higher, the content of oxygen-containing polar group tends to reduce. According to the measurement results, the contact angle is negatively related to the content of oxygen element, surface oxygen, and polar groups. In addition, compared with surface oxygen content, the content of oxygen-containing polar group serves as a more reasonable indicator of coal dust wettability. PMID:26257980

Single and multiphase inclusions in metapelitic garnets of the Rhodope Metamorphic Province, NE Greece.

PubMed

Mposkos, Evripidis; Perraki, Maria; Palikari, Sarra

2009-08-01

Single and multiphase inclusions in garnet porphyroblasts from the diamond-bearing pelitic gneisses were studied by means of combined Raman Spectroscopy and Electron Scanning Microscopy (SEM/EDX). They are either randomly distributed or with preferred orientation within the garnet host and their dimensions vary from less than 5 up to 60 microm. In the single-phase inclusions quartz, rutile, kyanite and graphite dominate. Biotite, zircon, apatite, monazite and allanite are also common. Two types of multiphase inclusions were recognized, hydrous silicate (Type I) and silicate-carbonate (Type II) ones. The carbon-bearing multiphase inclusions predominantly consist of Mg-siderite+graphite+CO(2)+muscovite+quartz formed by a high density carboniferous fluid rich in Fe, Mg, Si and less Ca, Mn, Al and K trapped in the growing garnet in a prograde stage of metamorphism at high-pressure (HP) conditions. The carbon-free multiphase inclusions predominantly consist of biotite+quartz+rutile+/-kyanite+muscovite formed through decompression-dehydration/melting reactions of pre-existing phengite. Single and multiphase inclusions are characterized by polygonal to negative crystal shape formed by dissolution-reprecipitation mechanism between the garnet host and the inclusions during the long lasting cooling period (>100 Ma) of the Kimi Complex.

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

U-Th-PbT Monazite Gechronology in the South Carpathian Basement: Variscan Syn-Metamorphic Tectonic Stacking and Long-Lasting Post-Peak Decompressional Overprints

NASA Astrophysics Data System (ADS)

Săbău, G.; Negulescu, E.

2012-12-01

Dating metamorphic events appears to be unsatisfactorily addressed by most of the widely-employed and otherwise accurate and productive isotopic techniques, because the phases and systems investigated do not directly relate to the metamorphic events themselves. An adequate answer to this challenge is instead provided by microprobe-assisted chemical U-Th-PbT monazite geochronology, by its spatial resolution, truly in situ character and the possibility to reference analyses against well-defined textural environments and features, as well as a qualitative timeframe derived therefrom. Though chemical U-Th-PbT monazite geochronology is increasingly applied to seek answers ranging form a general characterization to fine details of the thermotectonic evolution of magmatic and metamorphic rocks, there are so far, unlike in the case of isotopic geochronological methods, no clearly defined standard analytical and data processing protocols. Two main reasons for this have to be mentioned, namely that chemical U-Th-PbT chronology is actually a proxy for isotopic geochronology, and the quantification of the errors and their propagation cannot be directly assessed because apparent ages are related to the measured element concentrations by an implicit function, the law of radioactive decay. Current approaches rely on treating calculated individual age values as primary data, a priori grouping of analyses supposed (and subsequently tested) to be coeval, and their statistical processing in order to obtain age values. An alternative approach we applied in basement units of the South Carpathians consists in an explicit approximation of the age formula and associated errors propagated from element concentrations to age values, and individual treatment of each age datum. The separation of the age clusters from the overall age spectrum of each sample was operated by tracing the variations of the normalized age gradient on the age spectrum sorted by increasing age values, and fine

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

Radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico with annotated bibliography. [Over 600 citations

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

McLemore, V. T.

1982-01-01

From an extensive literature search and field examination of 96 nonsandstone radioactive occurrences, the author compiled an annotated bibliography of over 600 citations and a list of 327 radioactive occurrences in veins and igneous and metamorphic rocks of New Mexico. The citations are indexed by individual radioactive occurrence, geographic area, county, fluorspar deposits and occurrences, geochemical analyses, and geologic maps. In addition, the geology, mineralization, and uranium and thorium potential of 41 geographic areas in New Mexico containing known radioactive occurrences in veins and igneous and metamorphic rocks or that contain host rocks considered favorable for uranium or thorium mineralizationmore » are summarized. A list of aerial-radiometric, magnetic, hydrogeochemical, and stream-sediment survey reports is included.« less

U-Pb SHRIMP II age and origin of zircon from lhertzolite of the bug Paleoarchean complex, Ukrainian Shield

NASA Astrophysics Data System (ADS)

Lobach-Zhuchenko, S. B.; Baltybaev, Sh. K.; Glebovitsky, V. A.; Sergeev, S. A.; Lokhov, K. O.; Egorova, Yu. S.; Balagansky, V. V.; Skublov, S. G.; Galankina, O. L.; Stepanyuk, L. M.

2017-12-01

Complex study of the U-Pb and Lu-Hf systems of zircon from a lhertzolite lens of Archean gneiss enderbites of the Bug complex, Ukrainian Shield, showed that ultramafic magma was contaminated by the material of the country gneiss enderbites. The age of the zircons of 2.81 ± 0.05 Ga corresponds to the period of ultramafic magmatism within the Bug complex. Previously, this peak of endogenic activity was considered the stage of manifestation of metamorphism and magmatism of mafic composition.

Ductile deformation history in Laibid metamorphic rocks, Sanandaj-Sirjan Zone, Iran

NASA Astrophysics Data System (ADS)

Aflaki, Mahtab; Mohajjel, Mohammad

2010-05-01

Sanandaj-Sirjan zone, in northeast of Zagros suture zone, is the metamorphic belt of the Zagros orogen which is metamorphosed during Late Mesozoic, as the active margin of the Neotethys subduction system. Since Late Cretaceous, oblique collision between Afro-Arabian continent and Central Iran micro continent resulted in dextral transpression and Poly-phase deformations of this zone. Laibid area, northwest of Esfahan province, is situated in complexly deformed sub zone of the Sanandaj-Sirjan zone in which structurally exposed Permian metamorphosed rocks are separated from the younger Triassic-Jurassic metamorphic rocks by faulted boundaries. Cretaceous unites do not exist in the study area, but in southern most parts un-metamorphosed Early Cretaceous rocks rest on Jurassic metamorphic units over an angular unconformity. Field observations reveal the existence of 3 folding patterns, folded dikes, semi-ductile to ductile shear zones and also sin-tectonic granite intrusion. Hassan-Robat Alkali-porphyritic-granite is exposed in the eastern part of the area with the possible ages between post-Early Cretaceous to pre-Eocene. In this research, the focus is on ductile structures and their deformation history in the Laibid area. Structural analysis of the folds reveals three deformation stages of a progressive deformation in this area. These folding patterns observed in all pre-Cretaceous metamorphosed unites, but not in Cretaceous rocks. The first stage includes tight to isoclinal folds, S0 || S1, with the aspect ratio changes respectively from tall and short. Although their axial plane and fold axis orientations change due to other two folding stages, but they mostly have moderately dipping to the NE axial plane and moderately plunging fold axis to NW or SE. In the eastern part of the area the trend of F1 foliation changes around the Hassan-Robat granite. The second folding stage includes open to close asymmetric folds which have broad aspect ratio. This folding stage

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.

Dehydration reactions, mass transfer and rock deformation relationships during subduction of Alpine metabauxites: insights from LIBS compositional profiles between metamorphic veins

NASA Astrophysics Data System (ADS)

Verlaguet, Anne; Brunet, Fabrice; Goffé, Bruno; Menut, Denis; Findling, Nathaniel; Poinssot, Christophe

2013-04-01

In subduction zones, the significant amounts of aqueous fluid released in the course of the successive dehydration reactions occurring during prograde metamorphism are expected to strongly influence the rock rheology, as well as kinetics of metamorphic reactions and mass transfer efficiency. Mineralized veins, ubiquitous in metamorphic rocks, can be seen as preserved witnesses of fluid and mass redistribution that partly accommodate the rock deformation (lateral segregation). However, the driving forces and mechanisms of mass transfer towards fluid-filled open spaces remain somewhat unclear. The aim of this study is to investigate the vein-forming processes and the modalities of mass transfer during local fluid-rock interactions, and their links with fluid production and rock deformation, with new insights from Laser Induced Breakdown Spectroscopy (LIBS) profiles. This study focuses on karstic pockets (metre scale) of Triassic metabauxites embedded in thick carbonate units, that have been isolated from large-scale fluid flow during HP-LT Alpine metamorphism (W. Vanoise, French Alps). These rocks display several generations of metamorphic veins containing various Al-bearing minerals, which give particular insights into mass transfer processes. It is proposed that the internally-derived fluid (~13 vol% produced by successive dehydration reactions) has promoted the opening of fluid-filled open spaces (euhedral habits of vein minerals) and served as medium for diffusive mass transfer from rock to vein. Based on mineralogical and textural features, two vein types can be distinguished: (1) some veins are filled with newly formed products of either prograde (chloritoid) or retrograde (chlorite) metamorphic reactions; in this case, fluid-filled open spaces seem to offer energetically favourable nucleation/growth sites; (2) the second vein type is filled with cookeite (Li-Al-rich chlorite) or pyrophyllite, that were present in the host rock prior to the vein formation. In

Timing of metamorphism of the Lansang gneiss and implications for left-lateral motion along the Mae Ping (Wang Chao) strike-slip fault, Thailand

NASA Astrophysics Data System (ADS)

Palin, R. M.; Searle, M. P.; Morley, C. K.; Charusiri, P.; Horstwood, M. S. A.; Roberts, N. M. W.

2013-10-01

The Mae Ping fault (MPF), western Thailand, exhibits dominantly left-lateral strike-slip motion and stretches for >600 km, reportedly branching off the right-lateral Sagaing fault in Myanmar and extending southeast towards Cambodia. Previous studies have suggested that the fault assisted the large-scale extrusion of Sundaland that occurred during the Late Eocene-Early Oligocene, with a geological offset of ˜120-150 km estimated from displaced high-grade gneisses and granites of the Chiang Mai-Lincang belt. Exposures of high-grade orthogneiss in the Lansang National Park, part of this belt, locally contain strong mylonitic textures and are bounded by strike-slip ductile shear zones and brittle faults. Geochronological analysis of monazite from a sample of sheared biotite-K-feldspar orthogneiss suggests two episodes of crystallization, with core regions documenting Th-Pb ages between c. 123 and c. 114 Ma and rim regions documenting a significantly younger age range between c. 45-37 Ma. These data are interpreted to represent possible magmatic protolith emplacement for the Lansang orthogneiss during the Early Cretaceous, with a later episode of metamorphism occurring during the Eocene. Textural relationships provided by in situ analysis suggest that ductile shearing along the MPF occurred during the latter stages of, or after, this metamorphic event. In addition, monazite analyzed from an undeformed garnet-two-mica granite dyke intruding metamorphic units at Bhumipol Lake outside of the Mae Ping shear zone produced a Th-Pb age of 66.2 ± 1.6 Ma. This age is interpreted to date the timing of dyke emplacement, implying that the MPF cuts through earlier formed magmatic and high-grade metamorphic rocks. These new data, when combined with regional mapping and earlier geochronological work, show that neither metamorphism, nor regional cooling, was directly related to strike-slip motion.

U-Pb SHRIMP geochronology of zircon in garnet peridotite from the Sulu UHP terrane, China: Implications for mantle metasomatism and subduction-zone UHP metamorphism

USGS Publications Warehouse

Zhang, R.Y.; Yang, J.S.; Wooden, J.L.; Liou, J.G.; Li, T.F.

2005-01-01

We studied the Zhimafang ultrahigh-pressure metamorphic (UHP) peridotite from pre-pilot drill hole PP-1 of Chinese Continental Scientific Drilling project in the Sulu UHP terrane, eastern China. The peridotite occurs as lens within quartofeldspathic gneiss, and has an assemblage of Ol + Opx + Cpx + Phl + Ti-clinohumite (Ti-Chu) + Grt (or chromite) ?? magnesite (Mgs). Zircons were separated from cores at depths of 152 m (C24, garnet lhezolite), 160 m (C27, strongly retrograded phlogopite-rich peridotite) and 225 m (C50, banded peridotite), and were dated by SHRIMP mass spectrometer. Isometric zircons without inherited cores contain inclusions of olivine (Fo91-92), enstatite (En91-92), Ti-clinohumite, diopside, phlogopite and apatite. The enstatite inclusions have low Al2O3 contents of only 0.04-0.13 wt.%, indicating a UHP metamorphic origin. The weighted mean 206Pb/238U zircon age for garnet lherzolite (C24) is 221 ?? 3 Ma, and a discordia lower intercept age for peridotite (C50) is 220 ?? 2 Ma. These ages are within error and represent the time of subduction-zone UHP metamorphism. A younger lower intercept age of 212 ?? 3 Ma for a foliated wehrlite (C27) was probably caused by Pb loss during retrograde metamorphism. The source of zirconium may be partially attributed to melt/fluid metasomatism within the mantle wedge. Geochronological and geochemical data confirm that the mantle-derived Zhimafang garnet peridotites (probably the most representative type of Sulu garnet peridotites) were tectonically inserted into a subducting crustal slab and subjected to in situ Triassic subduction-zone UHP metamorphism. ?? 2005 Elsevier B.V. All rights reserved.

The Hardwood Gneiss: Evidence for high P-T Archean metamorphism in the southern province of the Lake Superior region

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

Peterson, J.W.; Geiger, C.A.

1990-03-01

The Hardwood Gneiss is an areally small unit of Precambrian granulite-grade rocks exposed in the Archean gneiss terrane of the southern Lake Superior region. The rocks are located in the southwestern portion of the Upper Peninsula of Michigan and consist of a structurally conformable package of quartzitic, metapelitic, amphibolitic, and metabasic units. Three texturally distinct garnet types are present in the metabasites and are interpreted to represent two metamorphic events. Geothermobarometry indicates conditions of {approximately}8.2-11.6 kbar and {approximately}770C for M1, and conditions of {approximately}6.0-10.1 kbar and {approximately}610-740C for M2. It is proposed that M1 was Archean and contemporaneous with amore » high-grade metamorphic event recorded in the Minnesota River Valley. The M2 event was probably Early Proterozoic and pre-Penokean, with metamorphic conditions more intense than those generally ascribed to the Penokean Orogeny in Michigan, but similar to the conditions reported for the Kapuskasing zone of Ontario. The high paleopressures and temperatures of the M1 event make the Hardwood Gneiss distinct from any rocks previously described in the southern Lake Superior region, and suggest intense tectonic activity during the Archean.« less

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

Variation of illite/muscovite 40Ar/39Ar age spectra during progressive low-grade metamorphism: an example from the US Cordillera

NASA Astrophysics Data System (ADS)

Verdel, Charles; van der Pluijm, Ben A.; Niemi, Nathan

2012-09-01

40Ar/39Ar step-heating data were collected from micron to submicron grain-sizes of correlative illite- and muscovite-rich Cambrian pelitic rocks from the western United States that range in metamorphic grade from the shallow diagenetic zone (zeolite facies) to the epizone (greenschist facies). With increasing metamorphic grade, maximum ages from 40Ar/39Ar release spectra decrease, as do total gas ages and retention ages. Previous studies have explained similar results as arising dominantly or entirely from the dissolution of detrital muscovite and precipitation/recrystallization of neo-formed illite. While recognizing the importance of these processes in evaluating our results, we suggest that the inverse correlation between apparent age and metamorphic grade is controlled, primarily, by thermally activated volume diffusion, analogous to the decrease in apparent ages with depth observed for many thermochronometers in borehole experiments. Our results suggest that complete resetting of the illite/muscovite Ar thermochronometer occurs between the high anchizone and epizone, or at roughly 300 °C. This empirical result is in agreement with previous calculations based on muscovite diffusion parameters, which indicate that muscovite grains with radii of 0.05-2 μm should have closure temperatures between 250 and 350 °C. At high anchizone conditions, we observe a reversal in the age/grain-size relationship (the finest grain-size produces the oldest apparent age), which may mark the stage in prograde subgreenschist facies metamorphism of pelitic rocks at which neo-formed illite/muscovite crystallites typically surpass the size of detrital muscovite grains. It is also approximately the stage at which neo-formed illite/muscovite crystallites develop sufficient Ar retentivity to produce geologically meaningful 40Ar/39Ar ages. Results from our sampling transect of Cambrian strata establish a framework for interpreting illite/muscovite 40Ar/39Ar age spectra at different

Co-axial superposed folding and inverted regional metamorphism in the Tonga Formation: Cretaceous accretionary thrust tectonics in the Cascades crystalline core

NASA Astrophysics Data System (ADS)

Luke, Jensen; Lebit, Hermann; Paterson, Scott; Miller, Robert; Vernon, Ron

2017-04-01

The Cascades crystalline core forms part of the Cretaceous magmatic belt of western North America and exposes a crustal section composed of primarily tonalitic plutons that intruded siliciclastic metasediments of an arc-derived accretional system, and local meta-basalt/chert sequences. This study is the first attempt to correlate the well understood intrusive and P-T-t history of the metasedimentary and plutonic terrane with the kinematics and tectonic boundary conditions by rigorous analysis of structures documented in the Tonga Formation exposed at the western edge of the core. The Tonga Formation comprises pelite-psammite metasediments, which increase from greenschist ( 300-350° C) to amphibolite grade ( 500-600° C) from south to north. This metamorphic gradient is inverted relative to a major westward verging and downward facing fold system that dominates the internal architecture of the formation and implies that the initial regional metamorphic signature was established prior to the early fold generation. Subsequent co-axial fold superposition is seen as a consequence of the persistent accretional west-vergent thrusting in the foreland of the magmatic arc. The central section of the Cascades Range, exposed in western Washington, forms part of the Cretaceous accretional/magmatic arc extending over 4,000 km along western North America from Baja California to British Columbia (Fig. 1a) (e.g. Misch, 1966; Brown, 1987; Tabor et al., 1989). Two models exist for the evolution of the Cascades crystalline core with one invoking magmatic loading (e.g. Brown and Walker, 1993) as the major cause for rapid loading, consequent regional metamorphism and vertical uplift (Evans and Berti, 1986). Conversely, other workers favor a model that suggests loading as a consequence of tectonic, thrust-related thickening, followed by rapid exhumation of the exposed crustal section of 10 to 40 km paleodepth (e.g. Matzel, 2004; Patterson et al., 2004; Stowell et al., 2007). In this

Granite intrusion in a metamorphic core complex: the example of the Mykonos laccolith (Cyclades, Greece)

NASA Astrophysics Data System (ADS)

Denèle, Yoann; Lecomte, Emmanuel; Jolivet, Laurent; Huet, Benjamin; Labrousse, Loïc.; Le Pourhiet, Laetitia; Lacombe, Olivier

2010-05-01

Numerical and analogical modelling underlined the importance of a pre-existing anomaly of viscosity-density such as a granite or migmatitic body below the brittle-ductile transition as a primary cause of metamorphic core complex (MCC) developpement. While field studies of MCC show a spatial and temporal link between MCC formation and plutonic activity, thermochronological studies show that there is no link between the intrusion of granites and the velocity of slip on the detachement plane. The Aegean domain is a good natural laboratory for studying the formation of MCC and syn-tectonic granites. In the northern Cyclades, the Mykonos-Delos-Rhenia MCC is characterised by the intrusion of a plurikilometric Late Miocene pluton of I-type granite within a migmatitic gneiss dome. AMS (Anisotropy of magnetic susceptibility) and microstructural studies in the Mykonos granites combined with recent cooling rate data allow us to use the granites as strain marker. The Mykonos granitoïds form a plurikilometric laccolith slightly deeping to the east and presenting an elliptical shape with a N170°E long axis. The laccolith is strongly asymmetrical with an outlying root zone in the SW cropping out on Delos and Rhenia islands and a major body mainly developed to the NE and cropping out on Mykonos Island. The laccolith consists of various petrographic facies presenting straight contacts that demonstrate emplacement by successive pulses of more or less differentiated magmas. The laccolith was developed at the interface between the Cycladic Basement and the Blueschists Unit and within the Blueschist Unit. Two events of deformation have been recorded in the granites. The first event is characterized by submagmatic and high to middle temperature protomylonite microstructures developped during or just after the intrusion. The second event of deformation characterized by low temperature mylonites and cataclasites close to the major detachment fault corresponds to the localization of

Model for threading dislocations in metamorphic tandem solar cells on GaAs (001) substrates

NASA Astrophysics Data System (ADS)

Song, Yifei; Kujofsa, Tedi; Ayers, John E.

2018-02-01

We present an approximate model for the threading dislocations in III-V heterostructures and have applied this model to study the defect behavior in metamorphic triple-junction solar cells. This model represents a new approach in which the coefficient for second-order threading dislocation annihilation and coalescence reactions is considered to be determined by the length of misfit dislocations, LMD, in the structure, and we therefore refer to it as the LMD model. On the basis of this model we have compared the average threading dislocation densities in the active layers of triple junction solar cells using linearly-graded buffers of varying thicknesses as well as S-graded (complementary error function) buffers with varying thicknesses and standard deviation parameters. We have shown that the threading dislocation densities in the active regions of metamorphic tandem solar cells depend not only on the thicknesses of the buffer layers but on their compositional grading profiles. The use of S-graded buffer layers instead of linear buffers resulted in lower threading dislocation densities. Moreover, the threading dislocation densities depended strongly on the standard deviation parameters used in the S-graded buffers, with smaller values providing lower threading dislocation densities.

Contact metamorphism, partial melting and fluid flow in the granitic footwall of the South Kawishiwi Intrusion, Duluth Complex, USA

NASA Astrophysics Data System (ADS)

Benko, Z.; Mogessie, A.; Molnar, F.; Severson, M.; Hauck, S.; Lechler, P.; Arehart, G.

2012-04-01

The footwall of the South Kawishiwi Intrusion (SKI) a part of the Mesoproterozoic (1.1 Ga) Duluth Complex consists of Archean granite-gneiss, diorite, granodiorite (Giant Range Batholith), thin condensed sequences of Paleoproterozoic shale (Virginia Fm.), as well as banded iron formation (Biwabik Iron Fm). Detailed (re)logging and petrographic analysis of granitic footwall rocks in the NM-57 drillhole from the Dunka Pit area has been performed to understand metamorphic processes, partial melting, deformation and geochemical characteristics of de-volatilization or influx of fluids. In the studied drillhole the footwall consists of foliated metagranite that is intersected by mafic (dioritic) dykes of older age than the SKI. In the proximal contact zones, in the mafic dykes, the orthopyroxene+clinopyroxene+plagioclase+quartz+Fe-Ti-oxide+hornblende±biotite porphyroblasts embedded in a plagioclase+K-feldspar+orthopyroxene+apatite matrix indicate pyroxene-hornfels facies conditions. Migmatitization is revealed by the euhedral crystal faces of plagioclase and pyroxene against anhedral quartz crystals in the in-situ leucosome and by the presence of abundant in-source plagioclase±biotite leucosome veinlets. Amphibole in the melanosome of mafic dykes was formed with breakdown of biotite and implies addition of H2O to the system during partial melting. Towards the deeper zones, the partially melted metatexite-granite can be characterized by K-feldspar+plagioclase+quartz+ortho/clinopyroxene+biotite+Fe-Ti-oxide+apatite mineral assemblage. The felsic veins with either pegmatitic or aplititic textures display sharp contact both to the granite and the mafic veins. They are characterized by K-feldspar+quartz±plagioclase±muscovite mineral assemblage. Sporadic occurrence of muscovite suggest local fluid saturated conditions. Emplacement of gabbroic rocks of the SKI generated intense shear in some zones of the granitic footwall resulting in formation of biotite-rich mylonites with

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

At what conditions does zircon grow/dissolve during high-T metamorphism? Relating zircon textures to PT-conditions

NASA Astrophysics Data System (ADS)

Kunz, Barbara E.; Regis, Daniele; Manzotti, Paola; Engi, Martin

2015-04-01

A key question in ziconology is when and how zircon grows during metamorphism. To shed light on zircon forming processes and the corresponding PT-conditions during high-T metamorphism a case study was undertaken. The Ivrea Zone (N-Italy) exposes a lower continental crustal section in which a continuous metamorphic field gradient from amphibolite to granulite facies is documented. This field gradient is thought to reflect protracted heating during late Paleozoic times, with a probable high-T peak in the Permian. We present first results from a primarily textural study supported by U-Pb ages, Th/U ratios and Ti-in-Zrn thermometry. Four types of zircon were identified based on their overgrowth proportions and the preservation of detrital cores. Zircon grains were thus classified as Type1 - detrital grains with no overgrowth or very narrow rims (300 Ma) and appears to reflect an early dehydration phase. Rim2b has Permian ages (median 275 Ma), is by far the most common overgrowth type, found in a wide PT-range. Its development appears related to biotite breakdown. Rim3 is texturally indicative of magmatic zircon, occurs only in diatexites. Rim4 is the latest overgrowth and is locally found at all metamorphic grades. Textural features suggest late fluid-related recrystallization of existing zircon. At lowest grade (675±35°C, 6±2 kbar) zircons show type1 only, overgrowths are too thin to clearly identify the rim type. Further upgrade (~700°C, 7 kbar) type1 and type2 dominate. Type2 zircons show rim1, rim2a and occasionally rim4. At the Mu-out isograd (750±50°C, 8.2±1.4 kbar) most zircons are of type2, now with rim2b instead of 2a, in addition to rim1 and rim4. Near and in granulite facies (to 800°C, 8±2 kbar) mostly zircon type2 and type4 are present. While rim1 gets more narrow with increasing metamorphic grade, rim2b grows significantly thicker. Occasionally rim2a and rim4 occur. Close to the Bt-out isograd (~860°C, 9.2±1.7 kbar), mostly type3 and type4 are

Dissecting the dynamic conformations of the metamorphic protein lymphotactin.

PubMed

Harvey, Sophie R; Porrini, Massimiliano; Konijnenberg, Albert; Clarke, David J; Tyler, Robert C; Langridge-Smith, Patrick R R; MacPhee, Cait E; Volkman, Brian F; Barran, Perdita E

2014-10-30

A mass spectrometer provides an ideal laboratory to probe the structure and stability of isolated protein ions. Interrogation of each discrete mass/charge-separated species enables the determination of the intrinsic stability of a protein fold, gaining snapshots of unfolding pathways. In solution, the metamorphic protein lymphotactin (Ltn) exists in equilibrium between two distinct conformations, a monomeric (Ltn10) and a dimeric (Ltn40) fold. Here, we use electron capture dissociation (ECD) and drift tube ion mobility-mass spectrometry (DT IM-MS) to analyze both forms and use molecular dynamics (MD) to consider how the solution fold alters in a solvent-free environment. DT IM-MS reveals significant conformational flexibility for the monomer, while the dimer appears more conformationally restricted. These findings are supported by MD calculations, which reveal how salt bridges stabilize the conformers in vacuo. Following ECD experiments, a distinctive fragmentation pattern is obtained for both the monomer and dimer. Monomer fragmentation becomes more pronounced with increasing charge state especially in the disordered regions and C-terminal α-helix in the solution fold. Lower levels of fragmentation are seen in the β-sheet regions and in regions that contain salt bridges, identified by MD simulations. The lowest charge state of the dimer for which we obtain ECD data ([D+9H](9+)) exhibits extensive fragmentation with no relationship to the solution fold and has a smaller collision cross section (CCS) than charge states 10-13+, suggesting a "collapsed" encounter complex. Other charge states of the dimer, as for the monomer, are resistant to fragmentation in regions of β-sheets in the solution fold. This study provides evidence for preservation and loss of global fold and secondary structural elements, providing a tantalizing glimpse into the power of the emerging field of native top-down mass spectrometry.

Metamorphic reactions, grain size reduction and deformation of mafic lower crustal rocks

NASA Astrophysics Data System (ADS)