Science.gov

Sample records for granulite body bohemian

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

    NASA Astrophysics Data System (ADS)

    Jedlicka, Radim; Faryad, Shah Wali

    2017-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Schantl, Philip; Hauzenberger, Christoph; Linner, Manfred

    2016-04-01

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

  3. Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

    NASA Astrophysics Data System (ADS)

    Maierova, Petra; Lexa, Ondrej; Jeřábek, Petr; Franěk, Jan; Schulmann, Karel

    2015-04-01

    A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 μm) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 μm grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 μm grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most

  4. Metamorphic evolution of granulite facies rocks from the Drosendorf nappe (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Sorger, Dominik; Hauzenberger, Christoph; Linner, Manfred

    2017-04-01

    Conspicuous variable rocks assemble the Drosendorf nappe, which was therefore called "Variegated Unit". At its base is the granodioritic Dobra gneiss, overlain by paragneiss, quartzite, amphibolite, marble, calc-silicate rock and graphite bearing schist. A grt-bt-sil-paragneiss from the southernmost part of the Drosendorf nappe exhibits the mineral assemblage garnet + biotite + sillimanite + K-feldspar + plagioclase + quartz + ilmenite. Inclusion rich garnet porphyroblasts (8-10mm) occur in a matrix composed of (2mm) K-feldspar and smaller (<1mm) plagioclase and quartz. Large garnet grains show a conspicuous zoning pattern, particularly apparent is a sharp increase of grossular component from garnet core (Xgrs=0.06-0.07) to rim (Xgrs=0.09-0.10), followed by subsequent decrease to the outermost garnet rim (Xgrs=0.04-0.05). Cores of garnet grains are rich in inclusions such as biotite, K-feldspar, plagioclase, muscovite, kyanite, quartz, ilmenite and rutile. Obtained P-T conditions of 750 - 800°C and 0.7-0.8 GPa for the matrix assemblage are similar to former petrological work in southern part of the Drosendorf nappe (Petrakakis, 1997). The mineral assemblage ms + qz + kfs + ky in garnet cores implies that the muscovite breakdown reaction was overstepped within the stability field of kyanite and the conspicuous high Si content (3.20 apfu) of muscovite inclusions suggest high pressure conditions for garnet core growth. Resorbed garnets with typical opx + pl symplectites are preserved in grt-opx-pl gneiss from the Kremstal in the western part of the Drosendorf nappe. These textures usually appear in granulite facies rocks following a near isothermal decompression path at high temperatures (ITD). Garnet bearing, partly migmatic paragneiss and amphibolite occur in the northern part of the Drosendorf nappe and in the adjacent Gföhl nappe system. However, no petrological data are available whether these units share a similar high grade metamorphic evolution or not. The

  5. Evidence of unadulterated mantle-depth, granitic melt inclusions: kumdykolite and kokchetavite crystallized from melt in Bohemian Massif granulites.

    NASA Astrophysics Data System (ADS)

    O´Brien, Patrick J.; Ferrero, Silvio; Ziemann, Martin A.; Walczak, Katarzyna; Wunder, Bernd; Hecht, Lutz; Wälle, Markus

    2016-04-01

    Partial melting under near-UHP conditions of metagranitoids (now HP felsic granulites) at mantle depth in the Orlica-Śnieżnik Dome (Bohemian Massif, Poland) is recorded in small volumes of hydrous melt trapped as primary melt inclusions (MI) in peritectic garnets. When free of cracks connecting the inclusion with the leucocratic matrix, these "nanogranites" (≤ 50μm inclusion diameter) contain a unique assemblage including kumdykolite, kokchetavite and cristobalite - polymorphs of albite, K-feldspar and quartz, respectively. These usually metastable phases crystallized from the melt (glass?) during rapid exhumation (cm/a) at high T but the crack-free state strongly suggests over-pressuring of the inclusion with respect to the pressure-time path followed by the matrix. Reports of both kumdykolite and kokchetavite have been mainly from natural rocks equilibrated in the diamond stability field. The precise calculation of the PT path of the MI on cooling and the comparison with previous studies suggests, however, that pressure is not influential to their formation, ruling out the possible interpretation of kumdykolite and kokchetavite as indicators of ultra-high pressure conditions. Experimental re-homogenization of these crack-free nanogranites was achieved using a piston cylinder apparatus at 2.7 GPa and 875°C. These conditions are consistent with the results of geothermobarometric calculations on the host rock, suggesting that no H2O loss occurred during exhumation as this would have caused a shift of the inclusion melting T toward higher values. Coupled with the absence of H2O-loss microstructural evidence, e.g. decrepitation cracks and/or vesciculation in re-homogenized nanogranites, this evidence suggests that the nanogranites still preserve the original H2O content of the melt. Both experimental and microstructural evidence support the hypothesis that the presence of these polymorphs should be regarded as direct mineralogical criterion to identify former

  6. Coincidence of gabbro and granulite formation and their implication for Variscan HT metamorphism in the Moldanubian Zone (Bohemian Massif), example from the Kutná Hora Complex

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Kachlík, Václav; Sláma, Jiří; Jedlicka, Radim

    2016-11-01

    Leucocratic metagabbro and amphibolite from a mafic-ultramafic body within migmatite and granulite in the Kutná Hora Complex were investigated. The mafic-ultramafic rocks show amphibolite facies metamorphism, but in the central part of the body some metagabbro preserves cumulus and intercumulus plagioclase, clinopyroxene and spinel. Spinel forms inclusions in both clinopyroxene and plagioclase and shows various degree of embayment structure, that was probably a result of reaction with melt during magmatic crystallization. In the metagabbro, garnet forms coronae around clinopyroxene at the contacts with plagioclase. Amphibolite contains garnet with prograde zoning and plagioclase. Phase relations of igneous and metamorphic minerals indicate that magmatic crystallization and subsequent metamorphism occurred as a result of isobaric cooling at a depth of 30-35 km. U-Pb dating on zircon from leucogabbro yielded a Variscan age (337.7 ± 2 Ma) that is similar or close to the age of granulite facies metamorphism (ca 340 Ma) in the Moldanubian Zone. Based on the calculated PT conditions and age data, both the mafic-ultramafic body and surrounding granulite shared the same exhumation path from their middle-lower crustal position at the end of Variscan orogeny. The coincidence of mafic-ultramafic intrusives and granulite-amphibolite facies metamorphism is explained by lithospheric upwelling beneath the Moldanubian Zone that occurred due to slab break-off during the final stages of subduction of the Moldanubian plate beneath the Teplá Barrandian Block. The model also addresses questions about the preservation of minerals and/or their compositions from the early metamorphic history of the rocks subjected to ultradeep subduction and subsequent granulite facies metamorphism.

  7. Kumdykolite, kokchetavite, and cristobalite crystallized in nanogranites from felsic granulites, Orlica-Snieznik Dome (Bohemian Massif): not an evidence for ultrahigh-pressure conditions

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; Ziemann, Martin A.; Angel, Ross J.; O'Brien, Patrick J.; Wunder, Bernd

    2016-01-01

    A unique assemblage including kumdykolite and kokchetavite, polymorphs of albite and K-feldspar, respectively, together with cristobalite, micas, and calcite has been identified in high-pressure granulites of the Orlica-Snieznik dome (Bohemian Massif) as the product of partial melt crystallization in preserved nanogranites. Previous reports of both kumdykolite and kokchetavite in natural rocks are mainly from samples that passed through the diamond stability field. However, because the maximum pressure recorded in these host rocks is <3 GPa, our observations indicate that high pressure is not required for the formation of kumdykolite and kokchetavite, and their presence is not therefore an indicator of ultrahigh-pressure conditions. Detailed microstructural and microchemical investigation of these inclusions indicates that such phases should instead be regarded as (1) a direct mineralogical criteria to identify former melt inclusions with preserved original compositions, including H2O and CO2 contents and (2) indicators of rapid cooling of the host rocks. Thus, the present study provides novel criteria for the interpretation of melt inclusions in natural rocks and allows a more rigorous characterization of partial melts during deep subduction to mantle depth as well as their behavior on exhumation.

  8. High-pressure granulites of the Podolsko complex, Bohemian Massif: An example of crustal rocks that were subducted to mantle depths and survived a pervasive mid-crustal high-temperature overprint

    NASA Astrophysics Data System (ADS)

    Faryad, Shah Wali; Žák, Jiří

    2016-03-01

    The Podolsko complex, Bohemian Massif, is a mid-crustal migmatite-granite dome exposed along a tectonic boundary separating the upper crust from the deeply eroded interior of the Variscan orogen, referred to as the Moldanubian Zone. This study examines metamorphic history of mafic and felsic granulites that occur in this complex as minor lenses or layers hosted in pervasively anatectic rocks. The mafic granulite contains garnet with preserved high-Ca cores, which based on pseudosection modelling indicates pressure conditions near the coesite stability field at temperatures of ca. 550-600 °C. The relicts of an earlier eclogite-facies stage have been overprinted by a later granulite-facies assemblage consisting of ternary feldspar, orthopyroxene, and spinel in the mafic granulite and sillimanite and spinel in the felsic granulite. Composition of younger garnet (in rims and as smaller grains) in both granulites suggests that a near isothermal decompression of these rocks was followed by heating that reached temperature of ca. 900 °C at pressure of ca. 0.5 GPa. It is thus concluded that the granulites underwent at least two temporally separate tectonometamorphic events: they were first subducted to mantle depths and exhumed rapidly at relatively low temperatures and then near isobarically heated at mid-crustal levels. The preservation of earlier eclogite-facies garnet in the mafic granulite indicates that the latter event was short-lived and was followed by near isobaric cooling. The geologically brief granulite-facies metamorphism was previously explained as a result of slab break-off and mantle upwelling after the main phase of microplate convergence in the Bohemian Massif. To put the Podolsko complex into a broader tectonic context, we synthesize the available petrologic and structural data from the correlative (U)HP assemblages of the Moldanubian Zone to suggest that they typically do not preserve structural record of the subduction stage, only rarely preserve an

  9. Partial melting of granitoids under eclogite-facies conditions: nanogranites from felsic granulites from Orlica-Śnieżnik Dome (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; O'Brien, Patrick; Walczak, Katarzyna; Wunder, Bernd; Hecht, Lutz

    2014-05-01

    Melt inclusions (MI) study in migmatites is a powerful tool to retrieve the original composition of the anatectic melt, both as major elements (Ferrero et al., 2012) and fluid contents (Bartoli et al., 2013). Crystallized MI, or "nanogranites" (Cesare et al., 2009), were identified within HP felsic granulites from Orlica-Śnieżnik Dome, NE Bohemian Massif (Walczak, 2011). The investigated samples are Grt+Ky leucogranulites originated from a granitic protolith, with assemblage Qtz+Pl+Kfs+Grt+Ky+Ttn+Rt+Ilm. Nanogranites occur in garnet as primary inclusions, and consist of Qtz+Ab+Bt+Kfs±Ep±Ap. Such assemblage results from the crystallization of a melt generated during a partial melting reaction; the same reaction is also responsible for the production of the host garnet, interpreted therefore as a peritectic phase. Besides nanogranites, former presence of melt is supported by the occurrence of tiny pseudomorphs of melt-filled pores (Holness & Sawyer, 2008) and euhedral faces in garnet. Garnet composition, with Grs =0.28-0.31, phase assemblage (kyanite, ternary feldspar) and classic thermobarometry suggest that partial melting took place at T≥875°C and P~2.2-2.6 GPa, under eclogite-facies conditions. Although other authors reported palisade quartz after coesite in this area (see e.g. Bakun-Czubarow, 1992), no clear evidence of UHP conditions have been identified during this study. Piston cylinder re-homogenization experiments were performed on MI-bearing garnet chips to obtain the composition of the pristine anatectic melt. The first data from experiments in the range 850-950°C and 2-2.2 GPa show that nanogranites can be re-melted at T≥875°. However, homogenization has not been reached yet since new Grt, with lower CaO and higher MgO, crystallizes on the walls of the inclusion. As P increases, the modal amount of new phase decreases, while its composition evolves closer to those of the host garnet. Further experiments at higher pressure are in underway, with

  10. Timing of Variscan HP-HT metamorphism in the Moldanubian Zone of the Bohemian Massif: U-Pb SHRIMP dating on multiply zoned zircons from a granulite from the Dunkelsteiner Wald Massif, Lower Austria

    NASA Astrophysics Data System (ADS)

    Friedl, Gertrude; Cooke, Rob A.; Finger, Friedrich; McNaughton, Neal J.; Fletcher, Ian R.

    2011-10-01

    In an attempt to better constrain the timing of Variscan HP-HT metamorphism in the SE Bohemian Massif we have dated zoned zircons from a garnet-kyanite granulite of granitic composition from the Dunkelsteiner Wald Massif, Lower Austria, by means of sensitive high-resolution ion microprobe (SHRIMP) technique. In order to combine isotopic information with crystal growth textures, CL and BSE images were systematically taken from the dated zircons. A characteristic threefold concentric zoning was found in many zircons. This involves pre-Variscan protolithic cores followed by two distinct metamorphic/anatectic overgrowth shells of Variscan age. The inner overgrowth shell is characterized by a weak CL but bright BSE signal, and yields high contents of uranium (0.1 to 0.2 wt.%). A pooled U-Pb Concordia age for this zone is 342.0 ± 3.0 Ma ( n = 11, MSWD = 0.12). The second, outer, overgrowth shell is always bright in the CL image, dark in the BSE image, and has generally low uranium contents (mostly <500 ppm). A pooled U-Pb Concordia age for this zone is 337.1 ± 2.7 Ma ( n = 11, MSWD = 0.22). These results imply that the Variscan HT crystallisation history of the Moldanubian granulites took place over a period of a few million years and was not an extremely rapid subduction-exhumation process. SHRIMP measurements in the protolithic cores yield a cluster of (sub)concordant ages between ˜390 and 460 Ma and a few outliers at higher ages mostly represented by cores in cores. Core domains, which are large, homogeneous and with undisturbed igneous oscillatory zoning, yielded preferentially ages between 430 and 460 Ma. We therefore consider that granitic protolith formation took place at that time. The still older inner cores are interpreted as inherited into the granitic melt.

  11. Formation of a Granite Bodies in Depleted Granulite Terranes: the Wuluma Granite, Central Australia

    NASA Astrophysics Data System (ADS)

    Lavaure, S.; Sawyer, E. W.

    2009-05-01

    replaced by biotite (or chlorite), although, small crystals of garnet within the matrix persist locally. Virtually all of the granite contains a magmatic foliation, and this together with the presence of small dykes of granite in shears and in fold hinges indicates that the granite body formed during regional deformation (the local D3 event). Thus, the Wuluma granite did not form by in situ partial melting. Rather, it formed at a site where small increments of anatectic melt extracted from the surrounding granulite terrane during regional deformation were able to accumulate.

  12. Nanogranitoids in garnet clinopyroxenites of the Granulitgebirge (Bohemian Massif): evidence for metasomatism and partial melting?

    NASA Astrophysics Data System (ADS)

    Borghini, Alessia; Ferrero, Silvio; Wunder, Bernd; O'Brien, Patrick J.; Ziemann, Martin A.

    2017-04-01

    Primary nanogranitoids occur in garnet from the garnet clinopyroxenites of the Granulitgebirge, Bohemian Massif. They form clusters in the inner part of the garnet, and may occur both as polycrystalline and glassy inclusions with size from 5 to 20 µm. Because of their random distribution in garnet these inclusions are interpreted as primary inclusions, thus formed during the growth of the garnet. Garnet does not show any major element zoning. Nanogranitoids were identified in garnet clinopyroxenites from two different locations and show slightly different mineral assemblages. Kumdykolite or albite, phlogopite, osumilite, kokchetavite and a variable amount of quartz occur in both locations. However, osumilite is more abundant in one locality and kokchetavite in the other. All these phases are identified using Raman Spectroscopy. Both assemblages are consistent with the origin of these inclusions as former droplets of melt. Nanogranitoids from one locality have been re-homogenized at 1000°C and 22 kbar to a hydrous glass of granodioritic/quartz-monzonitic composition in a piston cylinder apparatus. The chosen experimental conditions correspond to the formation of the host garnet (O'Brien & Rötzler, 2003) and thus of melt entrapment. Nanogranitoid-bearing garnet clinopyroxenites occur in bodies of serpentinized peridotites, hosted in turn in felsic granulites. The garnet clinopyroxenites show granoblastic texture dominated by garnet and clinopyroxene porphyroblasts with a variable amount of interstitial plagioclase, biotite, two generations of amphiboles (brown and green) and rutile and opaque minerals as accessories. The bulk rock composition is basic to intermediate, and the garnet chemistry varies from 24% Alm, 65% Prp and 11% Grs to 38% Alm, 36% Prp and 26 % Grs between one outcrop and the other. The origin of the investigated inclusions could be due to different processes: localized melting of metasomatized mafic rocks with simultaneous production of garnet or

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    The Orlica-Śnieżnik Dome (OSD), located on the NE margin of the Bohemian Massif, is predominantly composed of amphibolite-facies orthogneiss that contain bodies of HP and UHP eclogites and granulites. Numerous geochronological studies have been undertaken to constrain the timing of the ultra-high grade metamorphic event. Despite this, the exact timing of UHP-(U)HT conditions remain dubious (e.g. Brueckner et al., 1991; Anczkiewicz et al., 2007; Bröcker et al., 2009 & 2010). We have utilized garnet and zircon geochronology to provide time constraints on the evolution of the UHT-(U)HP rocks of the OSD. We have combined the ages with trace element analyses in garnet and zircon to better understand the significance of the obtained ages in petrological context. Lu-Hf grt-wr dating of peritectic garnet from two felsic granulites constrained the time of its initial growth at 346.9 ± 1.2 and 348.3 ± 2.0 Ma, recording peak conditions of 2.7 GPa and 950°C (e.g. Ferrero et al., 2015). In situ U-Pb SHRIMP dating of zircon from the same granulite gave a younger age of 342.2 ± 3.4 Ma. HREE partitioning between garnet rim and metamorphic zircon indicate their growth in equilibrium, hence, the U-Pb zircon date constrains the terminal phase of garnet crystallization. Similar ages were obtained from two eclogite bodies from Międzygórze and Nowa Wieś localities; Lu-Hf (grt-cpx-wr) dating provided ages of 346.5 ± 2.4 and 348.1 ± 9.1 Ma for samples from Międzygórze and Nowa Wieś, respectively. The same age (within error) of 346.3 ± 5.2 Ma was reported by Bröcker et al. (2010) for zircon from the Międzygórze eclogite. Comparison of REE concentrations in garnet (this study) and in metamorphic zircon (reported in Bröcker et al., 2010) indicate that garnet and zircon crystallized in equilibrium. Furthermore, M-HREE patterns observed in both garnet and zircon strongly suggest their growth at eclogite facies conditions. Sm-Nd garnet ages obtained for both felsic and mafic

  14. NATO granulite conference

    NASA Astrophysics Data System (ADS)

    Vielzeuf, D.; Vidal, Ph.

    On September 5-9, 1988, 83 participants from 20 different countries gathered in Clermont- Ferrand, France, for the workshop Petrology and Geochemistry of Granulites a nd Related Rocks. All geoscience disciplines were represented. The workshop was cosponsored by Universite Blaise Pascal, UFR Scientifique et Technique, Centre National de la Recherche Scientifique, International Lithosphere Program (working Group 2c), IGCP Project 235, Societe Francaise d e Mineralogie, Ministere de l'Education Nationale (DAGIC), Ministere des Affaires Etrangeres (DGSTD), Conseil Regional d Auvergne , Conseil General du Puy de Dome, Mairie de Clermont-Ferrand.

  15. Metamorphic evolution of the Río Santa Rosa Granulites, northern Sierra de Comechingones, Argentina

    NASA Astrophysics Data System (ADS)

    Otamendi, J. E.; Tibaldi, A. M.; Demichelis, A. H.; Rabbia, O. M.

    2005-01-01

    Highly anhydrous granulites from Río Santa Rosa in the eastern Sierras Pampeanas of Argentina occur as a thick lens surrounded by melt-depleted migmatites. Grt-Crd granulite composed of Qtz+Pl+Grt+Crd+Ilm±Spl±Ath±Phl is the dominant rock, whereas Opx-Grt granulite appears as discontinuous lenses in the center of the granulite body. Grt-Crd granulite includes blocks of metabasite that are relics of refractory lithologic beds interlayered in the supracrustal sequence. A distinct assemblage composed of Qtz, Pl, Grt, Crd, Opx, Spl, Crn, Sil, Bt, Phl, Ath, and Fe-Ti oxides in different combinations was generated in a reaction zone between Grt-Crd granulites and metabasites at peak metamorphism (850-900 °C and 7.6±0.5 kbar). The P- T trajectory of Grt-Crd granulites suggests an early prograde garnet-forming stage followed by nearly isothermal decompression that caused garnet breakdown. Melting and melt draining accompanying garnet growth was active during heating (to 900 °C) at intermediate pressures (˜7.6 kbar). Peak P- T estimates for Opx-Grt granulites are similar to those obtained with Grt-Crd granulites, which indicates that both granulites passed through the highest thermal stage. These results constrain the late evolution of Opx-Grt granulite to a garnet-consuming stage. Furthermore, they imply that garnet formation in Opx-Grt granulite happened at an early prograde P- T trajectory. Garnet growth in Opx-Grt granulite cannot result from heating at high pressure, which would lead to an apparent contradiction in the prograde P- T paths of the two granulites. This discrepancy may be solved by demonstrating that Opx-Grt granulite is the product of synmetamorphic mafic magmatism that was contaminated while cooling. The Río Santa Rosa granulites are inferred to have formed in a thickened crust in which mafic magmatic activity providing a local heat input.

  16. Superposition of replacements in the mafic granulites of the Jijal complex of the Kohistan arc, northern Pakistan: dehydration and rehydration within deep arc crust

    NASA Astrophysics Data System (ADS)

    Yamamoto, Hiroshi; Yoshino, Takashi

    1998-09-01

    A deep-level crustal section of the Cretaceous Kohistan arc is exposed in the northern part of the Jijal complex. The occurrence of mafic to ultramafic granulite-facies rocks exhibits the nature and metamorphic evolution of the lower crust. Mafic granulites are divided into two rock types: two-pyroxene granulite (orthopyroxene+clinopyroxene+plagioclase±quartz [1]); and garnet-clinopyroxene granulite (garnet+clinopyroxene+plagioclase+quartz [2]). Two-pyroxene granulite occurs in the northeastern part of the Jijal complex as a relict host rock of garnet-clinopyroxene granulite, where the orthopyroxene-rich host is transected by elongated patches and bands of garnet-clinopyroxene granulite. Garnet-clinopyroxene granulite, together with two-pyroxene granulite, has been partly replaced by amphibolite (hornblende±garnet+plagioclase+quartz [3]). The garnet-bearing assemblage [2] is expressed by a compression-dehydration reaction: hornblende+orthopyroxene+plagioclase=garnet+clinopyroxene+quartz+H 2O↑. Subsequent amphibolitization to form the assemblage [3] is expressed by two hydration reactions: garnet+clinopyroxene+plagioclase+H 2O=hornblende+quartz and plagioclase+hornblende+H 2O=zoisite+chlorite+quartz. The mafic granulites include pod- and lens-shaped bodies of ultramafic granulites which consist of garnet hornblendite (garnet+hornblende+clinopyroxene [4]) associated with garnet clinopyroxenite, garnetite, and hornblendite. Field relation and comparisons in modal-chemical compositions between the mafic and ultramafic granulites indicate that the ultramafic granulites were originally intrusive rocks which dissected the protoliths of the mafic granulites and then have been metamorphosed simultaneously with the formation of garnet-clinopyroxene granulite. The results combined with isotopic ages reported elsewhere give the following tectonic constraints: (1) crustal thickening through the development of the Kohistan arc and the subsequent Kohistan-Asia collision

  17. A geophysical model of the Variscan orogenic root (Bohemian Massif): Implications for modern collisional orogens

    NASA Astrophysics Data System (ADS)

    Guy, Alexandra; Edel, Jean-Bernard; Schulmann, Karel; Tomek, Čestmir; Lexa, Ondrej

    2011-05-01

    A new model of the structure and composition of the Variscan crust in the Bohemian Massif is proposed based on 3D gravity modelling, geological data, seismic refraction (CEL09) and reflection (9HR) sections. The Bohemian Massif crust is characterized by a succession of positive and negative anomalies of about 60-80 km wavelength for nearly constant Moho depths. The south-western part of the Bohemian Massif displays a large negative Bouguer anomaly corresponding to high grade rocks (granulites and migmatites) of the Palaeozoic crustal root represented by the Moldanubian domain. The adjacent Neo-Proterozoic Bruno-Vistulian microcontinent displays an important gravity high reflecting mafic and intermediate medium grade metamorphic and magmatic rocks. The deep crustal boundary between the root domain and the Bruno-Vistulian microcontinent is represented by a strong gradient located 50 to 70 km westwards from the surface boundary between these units indicating that the high density basement rocks are covered by a thin sheet of low density granulites and migmatites. North-west from the Moldanubian domain occurs an important gravity high corresponding to the Neo-Proterozoic basement of the Teplá-Barrandian Unit limited in the north by southeast dipping reflectors of the Teplá suture which is characterized by high density eclogites and ultramafics. The footwall of the suture corresponds to low density felsic crust of the Saxothuringian basement. The reflection and refraction seismics and gravity modelling suggest a complex lithological structure of the Moldanubian domain marked by a low density 5-10 km thick lower crustal layer located above the Moho, a 5-10 km thick heavy mafic layer, a 10 km thick mid-crustal layer of intermediate density and a locally developed 2-5 km thick low density layer at the surface. The low density lower crust correlates well with low P-wave velocities in the range 6.0-6.4 km s- 1 in the CEL09 section. This complex geophysical structure and

  18. On the formation of granulites

    USGS Publications Warehouse

    Bohlen, S.R.

    1991-01-01

    The tectonic settings for the formation and evolution of regional granulite terranes and the lowermost continental crust can be deduced from pressure-temperature-time (P-T-time) paths and constrained by petrological and geophysical considerations. P-T conditions deduced for regional granulites require transient, average geothermal gradients of greater than 35??C km-1, implying minimum heat flow in excess of 100 mW m-2. Such high heat flow is probably caused by magmatic heating. Tectonic settings wherein such conditions are found include convergent plate margins, continental rifts, hot spots and at the margins of large, deep-seated batholiths. Cooling paths can be constrained by solid-solid and devolatilization equilibria and geophysical modelling. -from Author

  19. Computational study of deformation mechanisms and grain size evolution in granulites - Implications for the rheology of the lower crust

    NASA Astrophysics Data System (ADS)

    Maierová, Petra; Lexa, Ondrej; Jeřábek, Petr; Schulmann, Karel; Franěk, Jan

    2017-05-01

    Most of granulite terrains worldwide are characterized by large mean grain sizes of 1 mm or more. An important exception are the high-pressure felsic granulites in the Bohemian Massif, the European Variscan belt. There, recrystallization of original coarse-grained ternary feldspar led to formation of a fine-grained (∼100 μm) mixed matrix dominated by plagioclase and K-feldspar. This change occurred at temperatures of ∼850 °C and was probably caused by chemically induced decomposition related to slight cooling and enhanced by deformation during continental collision. The resulting microstructure shows indications of diffusion creep assisted by melt-enhanced grain-boundary sliding. Further on, minor coarsening occurred associated with deformation by dislocation creep and aggregation of mineral phases. Using a thermodynamics-based model of grain size evolution we show that stability of the fine-grained microstructure crucially depends on Zener pinning in the two-phase mineral matrix. Pinning efficiently hinders grain growth, and the small grain size that resulted from the ternary feldspar decomposition can be stable even at high temperatures. The late switch from the grain-size-sensitive creep to dislocation creep is rather difficult to explain by temperature and strain rate (or stress) changes only. However, a simple incorporation of melt solidification can successfully simulate this behavior. Alternatively, the switch and the associated grain size growth can be related to mineral phase aggregation at lower pressure-temperature conditions resulting into a decrease of pinning efficiency. This study suggests that the fine grain size of the Bohemian granulites, in contrast to the common coarse-grained type, stems from abrupt recrystallization during the high-pressure high-temperature conditions, and pinning in the fine-grained matrix. Such a process may in some cases significantly and suddenly reduce the strength of the lower continental crust and allow for its

  20. Continental crust subducted deeply into lithospheric mantle: the driving force of Early Carboniferous magmatism in the Variscan collisional orogen (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Janoušek, Vojtěch; Schulmann, Karel; Lexa, Ondrej; Holub, František; Franěk, Jan; Vrána, Stanislav

    2014-05-01

    The vigorous Late Devonian-Early Carboniferous plutonic activity in the core of the Bohemian Massif was marked by a transition from normal-K calc-alkaline, arc-related (~375-355 Ma), through high-K calc-alkaline (~346 Ma) to (ultra-)potassic (343-335 Ma) suites, the latter associated with mainly felsic HP granulites enclosing Grt/Spl mantle peridotite bodies. The changing chemistry, especially an increase in K2O/Na2O and 87Sr/86Sri with decrease in 143Nd/144Ndi in the basic end-members, cannot be reconciled by contamination during ascent. Instead it has to reflect the character of the mantle sources, changing over time. The tectonic model invokes an oceanic subduction passing to subduction of the attenuated Saxothuringian crust under the rifted Gondwana margin (Teplá-Barrandian and Moldanubian domains). The deep burial of this mostly refractory felsic metaigneous material is evidenced by the presence of coesite/diamond (Massonne 2001; Kotková et al. 2011) in the detached UHP slices exhumed through the subduction channel and thrusted over the Saxothuringian basement, and by the abundance of felsic HP granulites (> 2.3 GPa), some bearing evidence for small-scale HP melt separation, in the orogen's core (Vrána et al. 2013). The subduction channel was most likely formed by 'dirty' serpentinites contaminated by the melts/fluids derived from the underlying continental-crust slab (Zheng 2012). Upon the passage through the orogenic mantle, the continental crust-slab derived material not only contaminated the adjacent mantle forming small bodies/veins of pyroxenites (Becker 1996), glimmerites (Becker et al. 1999) or even phlogopite- and apatite-bearing peridotites (Naemura et al. 2009) but the felsic HP-HT granulites also sampled the individual peridotite types at various levels. Eventually the subducted felsic material would form an (U)HP continental wedge under the forearc/arc region, to be later redistributed under the Moldanubian crust by channel flow and crustal

  1. Relative strength of lithospheric mantle compared to granulite lower crust in orogenic roots: insight from field laboratory.

    NASA Astrophysics Data System (ADS)

    Kusbach, V.; Ulrich, S.; Schulmann, K.

    2009-04-01

    The continental lithosphere is composed by strong lithospheric mantle and weak lower crust for average and hot geotherms. However, some experiments and seismic studies show that the strength contrast between mantle and crust can vary in order of several magnitudes. The internal zone of the European Variscan orogen (Bohemian Massif, Czech Republic) contains large complexes of Ky - K-feldspar granulites with incorporated spinel and garnet peridotites that can respond to question of mantle-lower crust strength contrast from the field perspective. The studied spinel-garnet harzburgite body (the Mohelno peridotite) represents probably a fragment of strongly depleted oceanic lithosphere showing peak conditions of 22,4-27,6 kbar and 1120-1275°C. The peridotite forms large folded sheet with steep hinge and vertical axial plane. It exhibits presence of spinel along the outer arc and the internal part of the fold and garnet along inner arc, both related to coarse-grained orthopyroxene - olivine microstructure. This coarse microstructure is dynamically recrystallized forming fine-grained matrix (~10 - 20 microns) and the EBSD measurements show presence of axial [100] LPO olivine pattern dominantly along the outer arc of the fold and in spinel harzburgite, while the inner arc of the fold and partly also garnet harzburgite reveals presence of axial [010] LPO pattern. Steep foliation and sub-horizontal to moderately plunging lineation determined from olivine EBSD data defines the shape of the megafold. Host rocks exhibit transposed mylonitic fabric S1-2 revealing peak conditions of 18 kbar, 800°C and heterogeneous D3 retrogression at about 10 - 7 kbar, 650°C. The foliation S2-3 is fully concordant with limbs of peridotite megafold, but close to the outer arc it is affected by asymmetrical folds with axial planar leucosomes coherent with the shape of the megafold hinge zone. In contrast, the S2 in the internal part of the megafold is affected by sinistral and dextral melt

  2. Granulites by name but eclogite facies by formation conditions: extreme metamorphism recorded by Saxony-type granulites

    NASA Astrophysics Data System (ADS)

    O Brien, P. J.

    2003-04-01

    overwhelmingly felsic bulk compositions of the granulites, suggests a deep subduction of upper crust to mantle depths which, on geochronological grounds, must have been closely followed by a rapid, buoyancy-driven exhumation. A comparable present-day situation is represented by the rapidly ascending Nanga Parbat or Namche Barwa gneissic bodies as part of the continuing Himalayan collision. In both cases hot rocks have forced their way to shallow depths in a very short time and, in the case of the felsic kyanite-K-feldspar-bearing Namche Barwa granulites, are represented by rocks extremely similar to those found in the older European orogeny.

  3. Mineralogy, petrology, and chronology of the lunar granulitic breccias

    NASA Astrophysics Data System (ADS)

    Hudgins, Jillian Amy

    Before the return of the Apollo and Luna samples, many basic geological questions about the Moon remained unanswered. The study of returned samples, in addition to remote sensing data and the growing collection of meteorites has revealed that the Moon is a geologically complex body with a history dominated by impact events. Lunar meteorites provide samples of the crust far removed from the Apollo landing sites and are probably more representative of the average lunar crust. SaU 300 was previously misclassified as an anorthositic regolith breccia. Here, I reclassify it as a polymict crystalline impact-melt breccia with an anorthositic norite bulk composition. SaU 300 is a new meteorite that is unpaired with any of the currently known lunar meteorite samples. The main objective of this study was to gain a better understanding of the early evolution of the Moon by studying some of the oldest samples available: the granulitic breccias. The following samples were studied: Apollo samples 60035, 77017, 78155, and 79215 and paired meteorites NWA 3163/4881/4483. Granulitic breccias exhibit poikiloblastic to granoblastic matrix textures and occur as individual rocks and as fragments in impact-melt rocks, the regolith, and in lunar meteorites. These rocks contain 70 -- 80% anorthite, low concentrations of incompatible trace elements, and moderately high concentrations of siderophile elements. Their history was dominated by impact events and thermal metamorphism. Matrix pyroxenes in the granulitic breccias last equilibrated at ˜1050+/-50°C. 40Ar/39Ar data reveal that 60035, 77017, and 78155 have peak metamorphic ages of 4.1 Ga, while 79215 has a peak metamorphic age of 3.9 Ga. NWA 3163 has a peak metamorphic age of 3.3 Ga. Samples 60035, 77017, and NWA 4881 were partially reset by low temperature heating events following metamorphism. Granulitic breccias have been described as "homogeneous on a millimetre scale" throughout the literature. Although they appear to be

  4. Monazite Geochronology of Al-Fe Granulites Of Amesmessa Area from In-Ouzzal Terrane (Western Hoggar, Algeria)

    NASA Astrophysics Data System (ADS)

    Ahmed, Benbatta; Abderrahmane, Bendaoud; Bénédicte, Cenki-Tok; Zohir, Adjerid; Olivier, Bruguier; Jesus, Garrido Marin Carlos; Safouane, Djemai; Khadija, Ouzegane

    2017-04-01

    ABSTRACT: The In Ouzzal terrane in western Hoggar (South Algeria) preserves evidence of ultrahigh-temperature (UHT) crustal metamorphism. It consists in Archean crustal units, composed of orthogneissic domes and green stone belts, strongly remobilized during the Paleoproterozoic orogeny (2000 Ma, Peucat et al., 1996). Ouzegane et al. (2003) summarize this UHT metamorphic history as two granulitic stages of high temperature : a prograde evolution with peak conditions around 9-11 kbar and 950-1050°C, leading to the appearance of exceptional paragenèses with corundum-quartz, sapphirine-quartz and sapphirine-spinel-quartz in Al-Mg granulites, Al-Fe granulites and quartzites; followed by retrograde event characterized by a pressure drop to 5-7 kbar. This retrograde event is marked by intrusive carbonatite bodies and the occurrence of leptynites veins. The present study is interested in Al-Fe granulites which outcrop in a still little known region situated in southeastern part of In-Ouzzal terrane. These granulites are mainly composed by quartz, spinel, garnet, sillimanite, cordierite, biotite, perthitic feldspar, ilmenite, ± corundum. The study consist to dating these Al-Fe granulites by monazites (U-Pb - ICP-MS method) combined with their internal structures revealed by BSE imaging. The primary results suggest two major facts: 1- for the first time, the existence of at least one metamorphism older than 2.5 Ga; 2- a long live paleoproterozoic high temperature metamorphism. These geochronological results completed and combined with a detailed phases relationship study of these Al-Fe granulites will are of major importance as for future discussion on the geodynamic context responsible for this regional UHT metamorphism as well as indicating a record the time of the different stages of granulitic metamorphism. Keywords: UHT metamorphism, Granulites, Paleoproterozoïc, Archaean; Southeastern In Ouzzal terrane; Monazite geochronology; Hoggar

  5. Three-dimensional S-wave velocity model of the Bohemian Massif from Bayesian ambient noise tomography

    NASA Astrophysics Data System (ADS)

    Valentová, Lubica; Gallovič, František; Maierová, Petra

    2017-10-01

    We perform two-step surface wave tomography of phase-velocity dispersion curves obtained by ambient noise cross-correlations in the Bohemian Massif. In the first step, the inter-station dispersion curves were inverted for each period (ranging between 4 and 20 s) separately into phase-velocity maps using 2D adjoint method. In the second step, we perform Bayesian inversion of the set of the phase-velocity maps into an S-wave velocity model. To sample the posterior probability density function, the parallel tempering algorithm is employed providing over 1 million models. From the model samples, not only mean model but also its uncertainty is determined to appraise the reliable features. The model is correlated with known main geologic structures of the Bohemian Massif. The uppermost low-velocity anomalies are in agreement with thick sedimentary basins. In deeper parts (4-20 km), the S-wave velocity anomalies correspond, in general, to main tectonic domains of the Bohemian Massif. The exception is a stable low-velocity body in the middle of the high-velocity Moldanubian domain and high-velocity body resembling a promontory of the Moldanubian into the Teplá-Barrandian domain. The most pronounced (high-velocity) anomaly is located beneath the Eger Rift that is a part of a Tertiary rift system across Europe.

  6. Heat transfer by fluids in granulite metamorphism

    NASA Technical Reports Server (NTRS)

    Morgan, Paul; Ashwal, Lewis D.

    1988-01-01

    The thermal role of fluids in granulite metamorphism was presented. It was shown that for granulites to be formed in the middle crust, heat must be advected by either magma or by volatile fluids, such as water or CO2. Models of channelized fluid flow indicate that there is little thermal difference between channelized and pervasive fluid flow, for the same total fluid flux, unless the channel spacing is of the same order or greater than the thickness of the layer through which the fluids flow. The volumes of volatile fluids required are very large and are only likely to be found associated with dehydration of a subducting slab, if volatile fluids are the sole heat source for granulite metamorphism.

  7. A geophysical model of lower crustal structure of the Palaezoic crustal root (Bohemian Massif): implications for modern collisional orogens

    NASA Astrophysics Data System (ADS)

    Guy, Alexandra; Edel, Jean Bernard; Schulmann, Karel; Tomek, Cestmir; Lexa, Ondrej

    2010-05-01

    A new model of the structure and composition of Variscan crust is proposed based on 3D gravity modelling, geological data, seismic refraction (CEL09) and reflection (9HR) sections. The Bohemian Massif crust is characterized by succession of positive and negative anomalies of about 60 - 80 km wavelength for nearly constant Moho depths. The southwestern part of the Bohemian Massif displays a large negative Bouguer anomaly corresponding to high grade rocks (granulites, migmatites) of the Palaeozoic crustal root represented by the Moldanubian domain. Adjacent Neo-Proterozoic Brunia microcontinent displays important gravity high corresponding to mafic and intermediate medium grade metamorphic and magmatic rocks. However, the strong gradient marking deep crustal boundary between the root domain and the Brunia microcontinent is located 50 to 70 km westwards from the surface boundary between these units suggesting that in this area the high density basement rocks are covered by thin sheet of low density granulites and migmatites. NW from the Moldanubain domain occurs an important gravity high corresponding to the Neo-Proterozoic basement of the Teplá-Barrandian Unit limited in the north by southeast dipping reflectors of the Teplá suture which is characterized by high density eclogites and ultramafics. The footwall of the suture corresponds to low density felsic crust of the Saxothuringian basement. The reflection and refraction seismics and gravity modelling suggest a complex lithological structure of the Moldanubian domain marked by low density 5 - 10 km thick lower crustal layer located above MOHO, 5 - 10 km thick heavy mafic layer, 10 km thick mid-crustal layer of intermediate density and locally developed 2 - 5 km thick low density layer at the surface. The low density lower crust correlates well with low P velocities in the range 6.0-6.4 km-sec in the CEL09 section. This complex geophysical structure and surface geology are interpreted as a result of partial

  8. Possibilities of Using Transport Terminals in South Bohemian Region

    NASA Astrophysics Data System (ADS)

    Čejka, Jiří; Bartuška, Ladislav; Turinská, Libuše

    2017-03-01

    Currently, when there is a need for transport services adapted to the customer requirements and create a workable operational system, there is increasing talk about transport terminals. Since the South Bohemian region is one of those where this issue will be increasingly dealt with, this paper suggests ways to use transport terminals as important support systems for freight and passenger transport.

  9. Granulites from Northwest Indian Shield: Their differences and similarities with Southern Indian granulite terrain

    NASA Technical Reports Server (NTRS)

    Sharma, R. S.

    1988-01-01

    Granulite facies suite in the NW Indian Shield is exposed at Sand Mata, Udaipur district, Rajasthan, as an oval-shaped massif within amphibolite facies rocks of the Banded Gneissic Complex (3.5 to 2.6 b.y. old) - a possible analogue of the Peninsular gneiss of Dharwar craton. On the basis of quantitative P-T estimates, combined with the textural evidence for the crystallization sequence of the Al-silicate polymorphs (kyanite to sillimanite to kyanite) in the pelitic granulite, the deduced P-T path for the Sand Mata granulites is the reverse of that characterizing the Plate tectonic collision zone. It, however, agrees with the P-T path inferred in the case of the southern Indian granulitic rocks.

  10. Petrology and geochemistry of the high-pressure Nilgiri Granulite Terrane, Southern India

    NASA Technical Reports Server (NTRS)

    Srikantappa, C.; Ashamanjari, K. G.; Raith, M.

    1988-01-01

    The Nilgiri granulite terrane in Southern India is predominantly composed of late Archaean medium- to coarse-grained enderbitic to charnockitic rocks. The dominant regional foliation strikes N60 to 70E with generally steep dips. Tight minor isoclinal folds have been observed in places. Granoblastic polygonal micro-structures are common and indicate thorough post-kinematic textural and chemical equilibration at conditions of the granulite facies (2.5 Ga ago). Late compressional deformation in connection with the formation of the Moyar and Bhavani shear zones to the north and south of the Nilgiri block, resulted in wide-spread development of weakly to strongly strained fabrics and was accompanied by minor rehydration. Enderbites and charnockites range from tonalitic to granodioritic in composition. A magmatogenic origin of the protoliths is inferred from their chemical characteristics which resemble those of the andesitic to dacitic members of Cordillera-type calc-alkaline igneous suites. A significant lithological feature of the Nilgiri granulite terrane are numerous extended bodies, lenses and pods of gabbroic and pyroxenitic rocks which are aligned conformable to the foliation of the enderbite-charnockite complex and which have also been deformed and metamorphosed at granulite facies conditions.

  11. Mineralogy and cooling history of magnesian lunar granulite 67415

    NASA Technical Reports Server (NTRS)

    Takeda, Hiroshi; Miyamoto, Masamichi

    1993-01-01

    Apollo granulite 67415 was investigated by mineralogical techniques to gain better understanding of cooling histories of lunar granulities. Cooling rates were estimated from chemical zoning of olivines in magnesian granulitic clasts by computer simulation of diffusion processes. The cooling rate of 10 deg C/yr obtained is compatible with a model of the granulite formation, in which the impact deposit was cooled from high temperature or annealed, at the depth of about 25 m beneath the surface.

  12. Mineralogy and cooling history of magnesian lunar granulite 67415

    NASA Technical Reports Server (NTRS)

    Takeda, Hiroshi; Miyamoto, Masamichi

    1993-01-01

    Apollo granulite 67415 was investigated by mineralogical techniques to gain better understanding of cooling histories of lunar granulities. Cooling rates were estimated from chemical zoning of olivines in magnesian granulitic clasts by computer simulation of diffusion processes. The cooling rate of 10 deg C/yr obtained is compatible with a model of the granulite formation, in which the impact deposit was cooled from high temperature or annealed, at the depth of about 25 m beneath the surface.

  13. Numerical simulation of the 2008 West-Bohemian earthquake swarm

    NASA Astrophysics Data System (ADS)

    Heinze, Thomas; Hamidi, Sahar; Galvan, Boris; Miller, Stephen A.

    2017-01-01

    CO2 has long been suspected of driving the Bohemian earthquake swarms because of the migrating nature of the swarms and expressions of CO2 degassing at the surface. Modeling to date primarily employed linear diffusion models, but more sophisticated modeling that includes a coupled fluid - and rock mechanical model has been lacking. In this work, we apply a model that couples mechanics to heat and flow of a super-critical CO2 through a fracture network. We present a continuum mechanical approach to derive the seismic moment magnitude using the deviatoric strain as an indicator of rupturing processes during individual events. We use a peak-detection algorithm to identify rapid changes in deviatoric strain, indicative of slip events. This method has been shown to work very well in dry and fluid-induced fracturing experiments at the laboratory scale, and in this work we extend the method to the scale of the West Bohemia/Vogtland earthquake swarms. We show very good agreement between model results and observations of the 2008 swarm, further supporting the hypothesis that the Bohemian earthquake swarms are predominately fluid-driven.

  14. CO2-rich fluid inclusions in greenschists, migmatites, granulites, and hydrated granulites

    NASA Technical Reports Server (NTRS)

    Hollister, L. S.

    1988-01-01

    Data was discussed from several different terrains in which CO2-rich fluid inclusions occur despite parageneses that predict the presence of H2O-rich fluids. CO2-rich fluid inclusions, some having densities appropriate for peak-metamorphic conditions, were found in greenschists, amphibolites, migmatites, and hydrated granulites. The author suggested that there may be a common process that leads to CO2-rich secondary inclusions in metamorphic rocks.

  15. Project Bohema: Bohemian Massif Heterogeneity And Anisotropy

    NASA Astrophysics Data System (ADS)

    Korn, M.; Bohema Working Group

    of the major results of the experiment. We want to concentrate on distinguishing between thermal anomalies and anisotropic structures, both being major causes of variations of seismic velocities in the crust and upper man- tle. We want either to confirm, or deny the existenc of a hypothetical mantle plume, or a shallower magmatic body which is the most probable source of CO2 and He gas emanations.

  16. Carbonic metamorphism, granulites and crustal growth

    NASA Technical Reports Server (NTRS)

    Newton, R. C.; Smith, J. V.; Windley, B. F.

    1980-01-01

    Stabilization of early crust against melting by high radioactivity and against resorption into the mantle by fast convective overturn requires that water and heat producers were flushed upwards within 50 Myr of accretion. Creation of a refractory base of granulite by metamorphism associated with CO2 vapour explains CO2-rich fluid inclusions in ancient high-grade rocks, minor-element depletions and local phenomena of arrested development of charnockite in Precambrian terrains. The hot-spot and plate-tectonic models of Precambrian crustal evolution lead to different schemes for CO2 delivery to continental roots. New tectonic concepts may be needed to explain carbonic metamorphism and other features of early crustal evolution.

  17. Hot granulite nappes — Tectonic styles and thermal evolution of the Proterozoic granulite belts in East Africa

    NASA Astrophysics Data System (ADS)

    Fritz, Harald; Tenczer, Veronika; Hauzenberger, Christoph; Wallbrecher, Eckart; Muhongo, Sospeter

    2009-11-01

    A section through the Neoproterozoic Mozambique Belt of Tanzania exposes western foreland (Archaean Tanzania Craton and Palaeoproterozoic Usagaran Belt), marginal (Western Granulites) and eastern, internal (Eastern Granulites) portions of the orogen. The assembly of granulite nappes at ca. 620 Ma displays westward emplacement along an eastward deepening basal decollement and forward propagation of thrusts, climbing from the deep crust to the surface. This goes along with eastward increase of syntectonic temperatures, derived from prevalent deformation mechanisms, and eastward decrease of the kinematic vorticity number. Distinctly different pressure - temperature paths with a branch of isothermal decompression (ITD) in Western Granulites and isobaric cooling (IBC) in Eastern Granulites reflect residence times of rocks within lower crustal levels. Western Granulites, exhumed rapidly at the orogen margin, display ITD and non-coaxial fabrics. Eastern Granulites in the internal orogen portions escaped from rapid exhumation and show IBC and co-axial flow fabrics. The vertical variation of structural elements, i.e. basement — cover relations within the Eastern Granulites, shows decoupling between lower and middle crust with horizontal west — east stretching in the basement and horizontal west — east shortening in the cover. A model of hot fold nappes [Beaumont, C., Nguyen, M.H., Jamieson, R.A., Ellis, S., 2006. Crustal flow modes in large hot orogens. In: Law, R.D., Searle, M.P., Godin, L., (eds). Channel Flow, Ductile Extrusion and Exhumation in Continental Collision Zones. Geological Society, London, Special Publications. vol. 268, 91-145] is adopted to explain flow diversity in the deep crust. The lower crust represented by Eastern Granulite basement flowed coaxially outwards (westward) in response to thickened crust and elevated gravitational forces, supported by a melt-weakened, viscous channel at the crustal base. Horizontal flow with rates faster than thermal

  18. P-wave Receiver Functions reveal the Bohemian Massif crust

    NASA Astrophysics Data System (ADS)

    Kampfova Exnerova, Hana; Plomerova, Jaroslava; Vecsey, Ludek

    2015-04-01

    In this study we present initial results of P-wave Receiver Functions (RF) calculated from broad-band waveforms of teleseismic events recorded by temporary and permanent stations in the Bohemian Massif (BM, Central Europe). Temporary arrays BOHEMA I (2001-2003), BOHEMA II (2004-2005) and BOHEMA III (2005-2006) operated during passive seismic experiments oriented towards studying velocity structure of the lithosphere and the upper mantle. Receiver Functions show relative response of the Earth structure under a seismic station and nowadays represent frequently-used method to retrieve structure of the crust, whose knowledge is needed in various studies of the upper mantle. The recorded waveforms are composites of direct P and P-to-S converted waves that reverberate in the structure beneath the receiver (Ammon, 1997). The RFs are sensitive to seismic velocity contrast and are thus suited to identifying velocity discontinuities in the crust, including the Mohorovičić discontinuity (Moho). Relative travel-time delays of the converted phases detected in the RFs are transformed into estimates of discontinuity depths assuming external information on the vp/vs and P velocity. To evaluate RFs we use the Multiple-taper spectral correlation (MTC) method (Park and Levin, 2000) and process signals from teleseismic events at epicentral distances of 30 - 100° with magnitude Mw > 5.5. Recordings are filtered with Butterworth band-pass filter of 2 - 8 s. To select automatically signals which are strong enough, we calculate signal-to-noise ratios (SNR) in two steps. In the first step we calculate SNR for signals from intervals (-1s, 3s)/(-10s, -2s), where P-arrival time represent time zero. In the second step we broaden the intervals and calculate SNR for (-1s, 9s)/(-60s, -2s). We also employ forward modelling of the RFs using Interactive Receiver Functions Forward Modeller (IRFFM) (Tkalčić et al., 2010) to produce, in the first step, one-dimensional velocity models under

  19. 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.

  20. Nature and origin of fluids in granulite facies metamorphism

    NASA Astrophysics Data System (ADS)

    Newton, R. C.

    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.

  1. Granulites: Melts and fluids in the deep crust

    NASA Technical Reports Server (NTRS)

    Valley, John W.

    1988-01-01

    Known examples of granulite facies metamorphism span at least 3.5 by. of Earth history. Mineralogic geobarometry indicates that such metamorphism has occurred in the deep crust, typically at 20 to 30 km (6 to 9 kbar). Geothermometry indicates that peak T = 700 to 900 C and therefore that T was elevated by at least 200 C over an anorgenic geotherm of 15 to 20 C/km. Commonly invoked sources of heat include rising magmas, radioactive decay insulated by continent/continent collision, mantle volatiles, or crustal thinning. Present day crustal thicknesses are normal beneath exposed granulite terranes and the common absence of evidence for post-metamorphic underplating suggests synmetamorphic thicknesses of 60 to 80 km. Thus granulites form in tectonically active regions of thickened crust and elevated geotherm. Xenolith suites suggest that granulite facies mineralogy persists in the deepest crust after tectonism in spite of declining temperature to greenschist/amphibolite facies conditions. The relative proportions of granulite terranes that are formed by Adirondack-type metamorphism dominantly magmatic/fluid-absent), India-type metamorphism (CO2 saturated), or some combination of 1 and 2 remains an important tectonic question.

  2. Documentation and evaluation of slope instabilities and other geological phenomena in the Geopark Bohemian Paradise (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Krejčí, Oldřich; Krejčí, Vladimíra; Švábenická, Lilian; Hartvich, Filip

    2016-04-01

    Geographically, the area is part of the Bohemian Cretaceous Basin, the unit Jičín Hilly land. Since October 2005, the area belongs to the European Geopark UNESCO Bohemian Paradise. The reason of the protection is a major complex of rocks, natural forest communities and geomorphological valuable territory. The territory has been newly geologically mapped in a scale of 1 : 25,000. Sediments of the Czech Cretaceous Basin covers an area of 181 km2 and were deposited transgressively on the Permian - Carboniferous and crystalline basement of the Bohemian Massif. Except for locally developed basal sediments of fluvial origin they are mostly shallow marine sediments. Middle Turonian to Lower Coniacian rocks of the Jizera lithofacies are dominant by calcareous sandstones deposited under extremely dynamic conditions. Scattered alkaline volcanics penetrate the older formations as small intrusions and form locally preserved bodies at the surface. Area is strongly predisposed to the development of various types of landforms by structural segmentation of the Cretaceous sandstones and claystones and by Plio-Pleistocene inverse erosion. Numerous archival manuscripts are available from this area together with published geological, engineering-geological, geomorphological and historical papers. This is due to the fact that in 1926 a large landslide destroyed a substantial part of the village Dneboh, situated on the slope below a rock castle Drabske Svetnicky. Drabske Svetnicky is a ruin of a 13th century castle. It is located on the ragged edge of a sandstone cliff high above surrounding landscape. The castle covers a group of seven sandstone rocks, connected with wooden bridges. In the 50ies of the 20th century, an increased attention was paid to Drabske Svetnicky by experts on medieval architecture and a restoration of the original state of the castle rock was accomplished. Remnants of pottery and other findings suggest that the plateau region of the castle was first inhabited

  3. Bohemian circular structure, Czechoslovakia: Search for the impact evidence

    NASA Technical Reports Server (NTRS)

    Rajlich, Petr

    1992-01-01

    Test of the impact hypothesis for the origin of the circular, 260-km-diameter structure of the Bohemian Massif led to the discovery of glasses and breccias in the Upper Proterozoic sequence that can be compared to autogeneous breccias of larger craters. The black recrystallized glass contains small exsolution crystals of albite-oligoclase and biotite, regularly dispersed in the matrix recrystallized to quartz. The occurrence of these rocks is limited to a 1-sq-km area. It is directly underlain by the breccia of the pelitic and silty rocks cemented by the melted matrix, found on several tens of square kilometers. The melt has the same chemistry as rock fragments in major and in trace elements. It is slightly impoverished in water. The proportion of melted rocks to fragments varies from 1:5 to 10:1. The mineralogy of melt viens is the function of later, mostly contact metamorphism. On the contact of granitic plutons it abounds on sillimanite, cordierite, and small bullets of ilmenite. Immediately on the contact with syenodiorites it contains garnets. The metamorphism of the impact rock melt seems the most probable explanation of the mineralogy and the dry total fusion of rocks accompanied by the strong fragmentation. Other aspects of this investigation are discussed.

  4. Passive seismic experiment BOHEMA - BOhemian Massif Anisotropy and HEterogeneity

    NASA Astrophysics Data System (ADS)

    Babuska, V.; Bohema Working, Group

    2003-04-01

    A dense network of stations, consisting of 61 permanent and 84 temporary stations, has been deployed to operate during most of 2002 and the beginning of 2003. The array is centered in the geodynamically active part of the western Bohemian Massif (BM) around the crossing of the Eger Graben (EG) with the Marianske Lazne Fault (MLF). A joint inversion of the shear-wave splitting parameters and P-residual spheres aims at finding a general 3D orientation of anisotropic structures. A three-dimensional anisotropic tomographic model will be one of major results of the experiment. Special attention will be paid to spatial variations of the vP/vS ratio with the aim to map concentrations of fluids which probably play an important role in triggering the earthquake swarms. The BOHEMA research team, formed by scientists from 10 institutions of the Czech republic, Germany and France, will concentrate on distinguishing between thermal anomalies and anisotropic structures and try to answer the question about a possible existence of a thermal plume beneath the western EG. The resulting geodynamic model of the lithosphere-asthenosphere system, based on all available geophysical, geological and petrological data, will shed light on possible causes of earthquake swarms, which periodically occur in the region, as well as on a deep-seated source of the numerous CO2 and He gas emanations. Among preliminary results we present lateral variations of the shear-wave splitting across and along the EG in comparison with the near- surface tectonics.

  5. The timing and mechanism of depletion in Lewisian granulites

    NASA Technical Reports Server (NTRS)

    Cohen, A. S.; Onions, R. K.; Ohara, M. J.

    1988-01-01

    Large Ion Lithophile (LIL) depletion in Lewisian granulites is discussed. Severe depletions in U, Th, and other LIL have been well documented in Lewisan mafic and felsic gneisses, but new Pb isotopic analyses show little or no depletion in lithologies with high solidus temperatures, such as peridotite. This suggests that LIL transport in this terrane took place by removal of partial melts rather than by pervasive flooding with externally derived CO2. The Pb and Nd isotopic data gathered on these rocks show that the depletion and granulite metamorphism are distinct events about 250 Ma apart. Both fluid inclusions and cation exchange geothermometers date from the later metamorphic event and therefore have little bearing on the depletion event, suggesting a note of caution for interpretations of other granulite terranes.

  6. Survey of lunar plutonic and granulitic lithic fragments

    NASA Technical Reports Server (NTRS)

    Bickel, C. E.; Warner, J. L.

    1978-01-01

    A catalog of lunar plutonic rocks and granulitic impactites belonging to the ANT suite has been compiled. The coarser-grained, plutonic rocks in the compilation are probably pristine; they belong to two groups, Mg-rich plutonic rocks and anorthosites, with a preponderance of the latter type. The granulitic impactites, however, have bulk and mineral compositions that fall between the two groups defined by the pristine nonmare samples of Warren and Wasson (1977). Thus the granulitic impactites may have originated by metamorphism of mixed impactites in early breccia sheets. The catalog, representative of the lunar crust before the end of heavy bombardment, suggests a crust with over 78 vol. % plagioclase and about equal proportions of material with noritic and troctolitic affinity.

  7. Nature and interpretation of fluid inclusions in granulites

    NASA Technical Reports Server (NTRS)

    Touret, Jacques L. R.

    1988-01-01

    Many granulites contain CO2 rich high density fluid inclusions (carbonic fluids). This observation has led to the concept of carbonic metamorphism, the dry character of granulites being less explained by the absence of water (vapor absent metamorphism) than by the presence of a CO2-rich fluid phase which dilutes the water and lowers considerably its partial pressure. Recent observations have indicated that the situation is much more complicated than initially assumed and that any interpretation must be carefully evaluated and discussed against other, independent evidence. The nature of fluid inclusions and the interpretation of fluid inclusion densities are discussed.

  8. A Treasure Chest of Nanogranites: the Bohemian Massif (Central Europe)

    NASA Astrophysics Data System (ADS)

    Ferrero, S.; O'Brien, P. J.; Walczak, K.; Wunder, B.; Ziemann, M. A.; Hecht, L.

    2014-12-01

    Despite 150 years of investigation of the Bohemian Massif (Central Europe), it is only recently that the investigation of old and new samples displayed the occurrence of tiny portions of crystallized anatectic melt in regional migmatites. These vestiges of magma, called "nanogranites", are natural probes of the partial melting processes in the crust. Original melt composition and water content can be directly analyzed after piston cylinder re-homogenization. When compared to classic re-melting experiments, nanogranites are ideal "natural" experimental charges of anatectic melt. They are encapsulated in peritectic garnet immediately after production - both phases are products of the same partial melting reaction. Sheltered inside garnet, they remain unaffected by the physico-chemical changes which affected the host migmatites during their slow cooling, unlike leucosomes and anatexis-related plutons. Five different case studies of nanogranite-bearing high-grade rocks have been identified so far: three in metapelites from the Moldanubian Zone, and two in metagranitoids from the Granulitgebirge and Orlica-Śnieżnik Dome. Their characterization provides insights into how the continental crust melts at different depths, from shallow levels to mantle depths, during different moments of its metamorphic history (prograde vs. decompressional melting). For example, the investigation and experimental re-melting of nanogranites from Grt+Ky leucogranulites (Orlica-Śnieżnik Dome) recently provided evidence of prograde melting of metagranitoids under eclogite-facies conditions (T≥875°C and P~2.7 GPa), close to the stability field of coesite. The melt generated is granitic, hydrous (6 wt% H2O) and metaluminous (ASI=1.03), and is at the moment the "deepest" glass obtained through re-homogenization of primary polycrystalline inclusions in natural rocks. This work confirms that nanogranites in migmatites 1) are a powerful tool to constrain anatexis in natural rocks, and 2) can

  9. The Curious Case of the Lunar Magnesian Granulitic Breccias

    NASA Technical Reports Server (NTRS)

    Korotev, R. L.; Jolliff, B. L.

    2001-01-01

    Magnesian granulitic breccias have high Th/Sm ratios, they are not related to Mg-suite plutonic rocks in any straightforward manner, and they may have an igneous rock precursor that is not yet recognized among our samples of the Moon. Additional information is contained in the original extended abstract.

  10. Cl-rich minerals in Archean granulite facies ironstones from the Beartooth Mountains, Montana, USA: Implications for fluids involved in granulite metamorphism

    NASA Technical Reports Server (NTRS)

    Henry, D. J.

    1988-01-01

    The implications of Cl-rich minerals in granulite facies rocks are discussed. Results from ironstones of the Beartooth Mountains, Montana are discussed. It is suggested that CO2-brine immiscibility might be applicable to granulite facies conditions, and if so, then aqueous brines might be preferentially adsorbed onto mineral surfaces relative to CO2.

  11. Crustal structure of the Bohemian Massif in the light of seismic refraction data

    NASA Astrophysics Data System (ADS)

    Hrubcova, Pavla

    2010-05-01

    The Bohemian Massif is one of the largest stable outcrops of pre-Permian rocks in Central and Western Europe. It forms the easternmost part of the Variscan Belt, which developed approximately between 500 and 250 Ma during a stage of large-scale crustal convergence, collision of continental plates and microplates, and possibly also subduction. It consists mainly of low- to high-grade metamorphic and plutonic Palaeozoic rocks. The area of the Bohemian Massif can be subdivided into various tectonostratigraphic units separated by faults, shear zones or thrusts trending roughly in a SW-NE direction, and reflecting varying influence of the Cadomian and Variscan orogenies: the Saxothuringian, Teplá-Barrandian, Moldanubian and Moravo-Silesian. Geographically, it comprises the area of the Czech Republic, partly Austria, Germany and Poland. While the post-collisional history of the Variscan Bohemian Massif is relatively clear, the kinematics of plate movements before and during collision is still subject of debates. To investigate such a complex structure, the Bohemian Massif has been covered by a network of seismic experiments as a result of a massive international cooperative effort in central Europe. Detailed analyses of the data from the main profiles of the CELEBRATION 2000, ALP 2002, and SUDETES 2003 refraction and wide-angle reflection seismic experiments show crustal and uppermost mantle structure of the massif and delimit the continuation of various tectonic units in depth. The differences in seismic velocities reflect, to some extent, the structural variances and give some indications for tracing of crust-forming processes during individual tectonic events. Lower crust in the Saxothuringian exhibits complicated structure, ranging from a highly reflective lower crustal layer above Moho with a strong velocity contrast at the top of this layer. Another possible explanation can be a double Moho or the Moho with some lateral topography. This complicated lower crust

  12. Post-granulite facies fluid infiltration in the Adirondack Mountains

    SciTech Connect

    Morrison, J.; Valley, J.W.

    1988-06-01

    Granulite facies lithologies from the Adirondack Mountains of New York contain alteration assemblages composed dominantly of calcite +/- chlorite +/- sericite. These assemblages document fluid infiltration at middle to upper crustal levels. Cathodoluminescence of samples from the Marcy anorthosite massif indicates that the late fluid infiltration is more widespread than initially indicated by transmitted-light petrography alone. Samples that appear unaltered in transmitted light show extensive anastomosing veins of calcite (< 0.05 mm wide) along grain boundaries, in crosscutting fractures, and along mineral cleavages. The presence of the retrograde calcite documents paleopermeability in crystalline rocks and is related to the formation of high-density CO/sub 2/-rich fluid inclusions. Recognition of this process has important implications for studies of granulite genesis and the geophysical properties of the crust.

  13. Origin of granulite terranes and the formation of the lowermost continental crust.

    PubMed

    Bohlen, S R; Mezger, K

    1989-04-21

    Differences in composition and pressures of equilibration between exposed, regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust, as had been thought, but rather middle and lower-middle crustal levels. Application of well-calibrated barometers indicate that exposed granulites record equilibration pressures of 0.6 to 0.8 gigapascal (20 to 30 kilometers depth of burial), whereas granulite xenoliths, which also tend to be more mafic, record pressures of at least 1.0 to 1.5 gigapascals (35 to 50 kilometers depth of burial). Thickening of the crust by the crystallization of mafic magmas at the crust-mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep-seated mafic crust represented by many xenolith suites.

  14. Origin of granulite terranes and the formation of the lowermost continental crust

    USGS Publications Warehouse

    Bohlen, S.R.; Mezger, K.

    1989-01-01

    Differences in composition and pressures of equilibration between exposed, regional granulite terranes and suites of granulite xenoliths of crustal origin indicate that granulite terranes do not represent exhumed lowermost crust, as had been thought, but rather middle and lower-middle crustal levels. Application of well-calibrated barometers indicate that exposed granulites record equilibration pressures of 0.6 to 0.8 gigapascal (20 to 30 kilometers depth of burial), whereas granulite xenoliths, which also tend to be more mafic, record pressures of at least 1.0 to 1.5 gigapascals (35 to 50 kilometers depth of burial). Thickening of the crust by the crystalliztion of mafic magmas at the crust-mantle boundary may account for both the formation of regional granulite terranes at shallower depths and the formation of deep-seated mafic crust represented by many xenolith suites.

  15. August, 2002 - floods events, affected areas revitalisation and prevention for the future in the central Bohemian region, Czech Republic

    NASA Astrophysics Data System (ADS)

    Bina, L.; Vacha, F.; Vodova, J.

    2003-04-01

    Central Bohemian Region is located in a shape of a ring surrounding the capitol of Prague. Its total territorial area is 11.014 sq.km and population of 1 130.000 inhabitants. According to EU nomenclature of regional statistical units, the Central Bohemian Region is classified as an independent NUTS II. Bohemia's biggest rivers, Vltava and Labe form the region's backbone dividing it along a north-south line, besides that there are Sazava and Berounka, the two big headwaters of Vltava, which flow through the region and there also are some cascade man made lakes and 2 important big dams - Orlik and Slapy on the Vltava River in the area of the region. Overflowing of these rivers and their feeders including cracking of high-water dams during the floods in August 2002 caused total or partial destruction or damage of more than 200 towns and villages and total losses to the extend of 450 mil. EUR. The worst impact was on damaged or destroyed human dwellings, social infrastructure (schools, kindergartens, humanitarian facilities) and technical infrastructure (roads, waterworks, power distribution). Also businesses were considerably damaged including transport terminals in the area of river ports. Flowage of Spolana Neratovice chemical works caused critical environmental havoc. Regional crisis staff with regional Governor in the lead worked continuously during the floods and a regional integrated rescue system was subordinated to it. Due to the huge extent of the floods the crisis staff coordinated its work with central bodies of state including the Government and single "power" resorts (army, interior, transport). Immediately after floods a regional - controlled management was set up including an executive body for regional revitalisation which is connected to state coordinating resort - Ministry for Local Development, EU sources and humanitarian aid. In addition to a program of regional revitalisation additional preventive flood control programs are being developed

  16. Magnetism of the Lower Crust: Observations from the Athabasca Granulite Terrain, Northern Canada

    NASA Astrophysics Data System (ADS)

    Brown, L. L.; Williams, M. L.; Seaman, S. J.; Regan, S.; Webber, J.; Orlandini, O. F.

    2012-12-01

    granulites rich with oxide (magnetite) layers. NRM values also show considerable variability, from 1 mA/m to 10 A/m, with the weakest magnetization found in many of the Chipman mafic dikes, intruding across the AGT at ~1.9 Ga, and in granite bodies both in the east and west. The magnetite layers in the mafic granulites are readily identified on ground magnetic traverses. Q values (Koenigsberger ratios) indicate that nearly 30% of the samples measured (N=66) have remanent magnetization greater than induced magnetization. Hysteresis and low temperature measurements identify PSD (pseudo-single domain) magnetite as the predominant oxide; pyrrhotite is also present in a number of samples. In this section of lower crust the high anomalies are directly related to zones of mafic granulite riddled with magnetite layers; the lower anomalies reflect rocks very low in, or even devoid of, magnetic material.

  17. High-pressure mafic granulites of the South Muya Block (Central Asian Orogenic Belt)

    NASA Astrophysics Data System (ADS)

    Skuzovatov, S. Yu.; Shatsky, V. S.; Dril, S. I.

    2017-04-01

    Mineralogical, petrographic, and geochemical studies of mafic granulites of the South Muya Block (Central Asian Orogenic Belt) have been carried out. The granulite protoliths were olivine- and plagioclase- rich cumulates of ultramafic-mafic magmas with geochemical affinities of suprasubduction rocks. The isotope-geochemical characteristics of the granulites indicate the enriched nature of their source, associated with recycling into the mantle of either ancient crust or oceanic sediments, or intracrustal contamination of melts at the basement of the ensialic arc. Formation of garnet-bearing parageneses has occurred during high-pressure granulite metamorphism associated with accretion in the eastern part of the Baikal-Muya composite terrane.

  18. Grampian high-pressure-granulite-facies metamorphism of the Slishwood Division, NW Ireland and its enigmatic eclogite-facies precursor

    NASA Astrophysics Data System (ADS)

    Daly, J. S.; Flowerdew, M. J.; Whitehouse, M. J.

    2012-04-01

    The Slishwood Division of NW Ireland is located along the SW margin of the Grampian belt, whose metamorphism and deformation is generally attributed to the collision of outboard magmatic arcs with the Laurentian continental margin during the c. 470 Ma Grampian Orogeny. The unusual metamorphic history of the Slishwood Division (with eclogite-facies and later high-pressure-granulite-facies assemblages) is a unique feature of the Grampian belt and has long been regarded as evidence for pre-Caledonian tectonism, possibly of Grenvillian age. Detrital zircon U-Pb dating of Slishwood Division metasediments shows that they were deposited after c. 926 Ma, ruling out a Grenville event. A maximum age for the eclogite-facies event is provided by a U-Pb zircon age of 596 ± 6 Ma for a suite of metabasite intrusives, which exhibit varying degrees of decompression from eclogite- to high pressure granulite-facies or amphibolite-facies assemblages accompanied by the development of migmatitic leucosomes. Zircons in these leucosomes yield U-Pb zircon ages of c. 470 Ma identical to metamorphic zircons in a relatively dry partially decompressed eclogite. Following polyphase deformation, migmatitic leucosomes in metasediments crystallized under high pressure granulite-facies conditions during sinistral transtension. Dating these leucosomes has been challenging because the majority of zircons within them are inherited and generally only thin (< 15 μm) euhedral magmatic zircon overgrowths are present. Careful targeting with the ion microprobe yields U-Pb ages of c. 470 Ma, consistent with a U-Pb zircon age of c. 470 Ma from a cross-cutting granite pegmatite. In addition the high pressure granulite facies mineral fabrics are cut by tonalite bodies also dated at 470 Ma (ref. 1). Based on these results, we interpret the Slishwood Division as a Neoproterozoic metasedimentary sequence deposited after c. 926 Ma on what became a microcontinental fragment that detached from Laurentia during the

  19. Tephroite-hausmannite-galaxite from a granulite-facies manganese rock of the United Arab Emirates

    NASA Astrophysics Data System (ADS)

    Gnos, Edwin; Peters, Tjerk

    1995-07-01

    The assemblage tephroite-hausmanniteSS-galaxiteSS has been found in a granulite-facies manganese ore body associated with metabasites and quartz-rich lithologies. The metamorphic rocks are located in the Khawr Fakkan massif near the northern end of the Semail Ophiolite, United Arab Emirates (U.A.E.), metamorphosed at 800 850° C and 6.5 9 kbar. The galaxite shows approximately 35% solid solution of hausmannite, similar to that reported for jacobsite and franklinite whereas the solid solution of galaxite in hausmannite is maximally 7%. The assemblage of tephroite-hausmannite and hausmannite-galaxite indicates a restricted log f O2 of -9 to -11 which is outside the stability of braunite under similar physico-chemical conditions. The modal abundance of the minerals and bulk rock chemistry indicate that the present assemblage was formed from the breakdown of Fe-poor braunitess+hausmannitess.

  20. Campylobacteriosis in the South Bohemian Region - a Recurrent Problem.

    PubMed

    Hamplová, L; Kotrbová, K; Príkazská, M

    Campylobacteriosis is among the most frequently reported foodborne diseases in both the Czech Republic (CR) and South Bohemian Region (SBR). Campylobacteriosis has been a notifiable disease in the CR since 1984. The objective of this study is the analysis of the data reported to the surveillance system between 2005 and 2014 to describe the seasonal variation, age specific incidence, and route of transmission of campylobacteriosis in the South Bohemian Region. The data reported to the surveillance system EPIDAT from 2005 to 2014 were analysed in order to determine the incidence trends and seasonality, age distribution, and route of transmission of campylobacteriosis in the South Bohemian Region. Campylobacteriosis incidence in the South Bohemian Region follows the same annual pattern as in the Czech Republic. There is a very slight declining trend in the incidence over the study period. A strong seasonal variation was observed, with a late summer peak and a winter low. An exception to the regularity of the incidence pattern was an outbreak notified in 2010. The most affected age groups are children 1 to 5 years and newborns (0 age group). In the other age groups, the incidence has a declining tendency. The most common vehicles for the transmission of campylobacteriosis are chicken and meat products while other vehicles and routes of transmission have been reported exceptionally. Only one third of cases have been notified along with the suspected route of transmission. The most common route of transmission is through the consumption of contaminated chicken and meat, including smoked meat products. Therefore, the measures targeting consumers and also producers of poultry, meat, and unpasteurized milk products may contribute to the reduction of campylobacteriosis incidence.

  1. Significance of Geological Units of the Bohemian Massif, Czech Republic, as Seen by Ambient Noise Interferometry

    NASA Astrophysics Data System (ADS)

    Růžek, Bohuslav; Valentová, Lubica; Gallovič, František

    2016-05-01

    Broadband recordings of 88 seismic stations distributed in the Bohemian Massif, Czech Republic, and covering the time period of up to 12 years were processed by a cross-correlation technique. All correlograms were analyzed by a novel approach to get both group and phase dispersion of Rayleigh and Love waves. Individual dispersion curves were averaged in five distinct geological units which constitute the Bohemian Massif (Saxothuringian, Teplá-Barrandean, Sudetes, Moravo-Silesian, and Moldanubian). Estimated error of the averaged dispersion curves are by an order smaller than the inherent variability due to the 3D distribution of seismic velocities within the units. The averaged dispersion data were inverted for 1D layered velocity models including their uncertainty, which are characteristic for each of the geological unit. We found that, overall, the differences between the inverted velocity models are of similar order as the variability inside the geological units, suggesting that the geological specification of the units is not fully reflected into the S-wave propagation velocities on a regional scale. Nevertheless, careful treatment of the dispersion data allowed us to identify some robust characteristics of the area. The vp to vs ratio is anomalously low (~1.6) for all the units. The Moldanubian is the most rigid and most homogeneous part of the Bohemian Massif. Middle crust in the depth range of ~3-15 km is relatively homogeneous across the investigated region, while both uppermost horizon (0-3 km) and lower crust (>15 km) exhibit lower degree of homogeneity.

  2. Southeastern slope of the Bohemian Massif: Paleogene submarine fill of the Nesvacilka depression and its importance for petroleum exploration

    SciTech Connect

    Benada, S.; Berka, J.; Brzobohaty, J.; Rehanek, J. )

    1993-09-01

    The Nesvacilka depression is a trough-like paleovalley, about 2000 m deep, that was cut at the transition from the Cretaceous to the Paleocene by fluvial erosion into Jurassic and Carboniferous strata. This morphological feature, which is superimposed on an ancient tectonic zone, trends to the present southeast boundary of the Bohemian massif and is, from a hydrocarbon exploration point of view, the most important structure in the Czech Republic. During the Paleogene, marine transgressions gradually flooded this paleovalley. In the resulting relatively closed water body, more than 1500 m of thick deeper water clastics accumulated. These clastics display features similar to those described from submarine fan lobes in other hydrocarbon-producing basins. Following the discovery of two oil and gas accumulations contained in Jurassic and Paleogene clastic rocks, exploration was focused on the central parts of the Nesvacilka depression. The depositional pattern of its Paleogene fill was worked out on the basis of well data and the results of two-dimensional and three-dimensional seismic surveys. From this, it was concluded that accumulation of the Paleogene clastic series was significantly influenced by sea level changes. The depositional concepts developed may be applied to the deeper parts of the Nesvacilka Canyon, where exploration for hydrocarbons is still at an early stage. Results obtained so far indicate that the Nesvacilka depression can be ranked as the most prospective oil play in the Czech Republic. Play concepts developed may be extrapolated to similar morphological features occurring elsewhere in the Carpathian foreland.

  3. Comparison of Archean and Phanerozoic granulites: Southern India and North American Appalachians

    NASA Technical Reports Server (NTRS)

    Mcsween, Harry Y., Jr.; Kittleson, Roger C.

    1988-01-01

    Archean granulites at the southern end of the Dharwar craton of India and Phanerozoic granulites in the southern Appalachians of North America share an important characteristic: both show continuous transitions from amphibolite facies rocks to higher grade. This property is highly unusual for granulite terranes, which commonly are bounded by major shears or thrusts. These two terranes thus offer an ideal opportunity to compare petrogenetic models for deep crustal rocks formed in different time periods, which conventional wisdom suggests may have had different thermal profiles. The salient features of the Archean amphibolite-to-granulite transition in southern India have been recently summarized. The observed metamorphic progression reflects increasing temperature and pressure. Conditions for the Phanerozoic amphibolite-to-granulite transition in the southern Appalachians were documented. The following sequence of prograde reactions was observed: kyanite = sillimanite, muscovite = sillimanite + K-feldspar, partial melting of pelites, and hornblende = orthopyroxene + clinopyroxene + garnet. The mineral compositions of low-variance assemblages in mafic and intermediate rocks are almost identical for the two granulite facies assemblages. In light of their different fluid regimes and possible mechanisms for heat flow augmentation, it seems surprising that these Archean and Phanerozoic granulite terranes were apparently metamorphosed under such similar conditions of pressure and temperature. Comparison with other terrains containing continuous amphibolite-to-granulite facies transitions will be necessary before this problem can be addressed.

  4. Precursor lithologies and metamorphic history of granulitic breccias from North Ray crater, Station 11, Apollo 16

    NASA Astrophysics Data System (ADS)

    Ostertag, R.; Stoffler, D.; Borchardt, R.; Palme, H.; Spettel, B.; Wanke, H.

    1987-01-01

    Two distinctly different types of granulitic breccias in the ejecta of North Ray crater, Station 11, Apollo 16 have been analyzed for their modal and chemical composition. Samples 67485, 67488, 67615, 67749, 67947, and 67566 are characterized by a fine-grained granoblastic to poikiloblastic matrix and abundant lithic and mineral clasts predominantly derived from ferroan anorthosites. The mineral clasts in sample 67566 were derived from ferroan anorthosites and Mg-rich lithologies. The fine-grained granulitic breccias are compositionally almost identical to the feldspathic microporphyritic melt breccias (fmmbs) of Station 11, Apollo 16 which are older than, and therefore are possible precursors of, the fine-grained granulitic breccias. The second type of granulitic lithology (67746) is medium-grained, anorthositic-noritic in composition, and contains well equilibrated minerals derived from Mg-rich rocks. The precursors of both granulitic lithologies were KREEP-free and according to their Ir/Au ratio were old lunar highland rocks. A comparison of major, minor, and trace element contents shows that the two types of granulites are unrelated. The different recrystallization textures of the two types of granulitic lithologies imply different metamorphic histories. Metamorphism of the fine-grained granulitic breccias occurred near the lunar surface and the heat source was probably a superheated impact melt. The texture and degree of equilibration in the minerals of 67746 require a much more intense metamorphism with slow cooling. Metamorphism of lunar rocks and breccias was a wide-spread process that occurred several times in lunar history.

  5. Retrograde fluids in granulites: Stable isotope evidence of fluid migration

    SciTech Connect

    Morrison, J. ); Valley, J.W. )

    1991-07-01

    Widespread retrograde alteration assemblages document the migration of mixed H{sub 2}O-CO{sub 2} fluids into granulite facies rocks in the Adirondack Mountains. Fluid migration is manifest by (1) veins and patchy intergrowths of chlorite {plus minus} sericite {plus minus} calcite, (2) small veins of calcite, many only identifiable by cathodoluminescence, and (3) high-density, CO{sub 2}-rich or mixed H{sub 2}O-CO{sub 2} fluid inclusions. The distinct and varied textural occurrences of the alteration minerals indicate that fluid-rock ratios were low and variable on a local scale. Stable isotope ratios of C, O, and S have been determined in retrograde minerals from samples of the Marcy anorthosite massif and adjacent granitic gneisses (charnockites). Retrograde calcite in the anorthosite has a relatively small range in both {delta}{sup 18}O{sub SMOW} and {delta}{sup 13}C{sub PDB} (8.6 to 14.9% and {minus}4.1 to 0.4%, respectively), probably indicating that the hydrothermal fluids that precipitated the calcite had exchanged with a variety of crustal lithologies including marbles and orthogneisses, and that calcite was precipitated over a relatively narrow temperature interval. Values of {delta}{sup 34}S{sub CDT} that range from 2.8 to 8.3% within the anorthosite can also be interpreted to reflect exchange between orthogneisses and metasediments. The recognition of retrograde fluid migration is particularly significant in granulite facies terranes because the controversy surrounding the origin of granulites arises in part from differing interpretations of fluid inclusion data, specifically, the timing of entrapment of high-density, CO{sub 2}-rich inclusions. Results indicate that retrograde fluid migration, which in some samples may leave only cryptic petrographic evidence, is a process capable of producing high-density, CO{sub 2}-rich fluid inclusions.

  6. Comparative oxygen barometry in granulites, Bamble sector, SE Norway

    SciTech Connect

    Harlov, D.E. )

    1992-07-01

    Oxygen fugacities have been estimated for the high-grade portion of the Bamble granulite facies terrane, SE Norway, using both titaniferous magnetite-ilmenite and orthopyroxene-titaniferous magnetite-quartz oxygen barometers. The two oxygen barometers show good agreement, for samples indicating high titaniferous magnetite-ilmenite temperatures whereas agreement is poor for low-temperature samples. Oxygen fugacities estimated from titaniferous magnetite-ilmenite are considerably lower than those estimated from orthopyroxene-titaniferous magnetite-quartz. This discrepancy increases with a decrease in temperature, which appears to reflect preferential resetting of the hematite content in the ilmenite grains, without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains. The mean temperature for non-reset samples, 795 {plus minus} 60C (1{sigma}), agrees well with temperatures obtained from garnet-orthopyroxene K{sub D} exchange thermometry in the same region, 785 {plus minus} 60C (1{sigma}). The non-reset oxygen fugacities also agree well with an independent study of the Bamble granulites by Cameron. The QUIlP equilibrium (Quartz-Ulvospinel-Ilmenite-Pyroxene) is used to project self-consistent equilibrium temperatures and oxygen fugacities for samples reset due to hematite loss from the ilmenite grains. These projected temperatures and oxygen fugacities agree reasonably well with non-reset samples. The mean projected temperature is 830 {plus minus} 40C (1{sigma}). This agreement strongly supports the conclusion that low titaniferous magnetite-ilmenite temperatures (down to 485C) and accompanying low-oxygen fugacities are the result of hematite loss from the ilmenite grains at some time after granulite-facies metamorphism.

  7. Reactivity of North Bohemian coals in coprocessing of coal/oil mixtures

    SciTech Connect

    Sebor, G.; Cerny, J.; Maxa, D.; Blazek, J.; Sykorova, I.

    1995-12-01

    Autoclave experiments with North Bohemian coal were done in order to evaluate their reactivity in coprocessing with petroleum vacuum residue, Selected coals were comprehensively characterized by using a number of analytical methods. While the coals were of similar geological origin, some of their characteristics differed largely from one coal to another. Despite the differences in physical and chemical structure, the coals provided very similar yields of desired reaction products. The yields of a heavy non- distillable fraction and/or an insoluble solid residue were, under experimental conditions, largely affected by retrogressive reactions (coking). The insoluble solid fractions were examined microscopically under polarized light.

  8. Neutron activation and X-ray fluorescence analyses of Early Roman Age Bohemian artifacts

    NASA Astrophysics Data System (ADS)

    Fikrle, M.; Frána, J.; Droberjar, E.

    2006-05-01

    Composition of more than 500 metallic artifacts was studied by means of INAA and XRF, including 404 objects of copper alloys. Analyses proved not only use of specialized bronze alloys in the imported Roman vessels, but also use of very pure brass with average content of 20% zinc in the production of decorative brooches, especially in the 1st century A.D. These artifacts were evidently made on the Bohemian territory, but raw brass was probably imported from the Roman provinces. Common products are mostly made of mixed materials possibly recycling old objects and using local raw materials.

  9. Anomalous induction zone near the eastern margin of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Petr, V.; Pěčová, J.; Praus, O.; Pěč, K.

    1987-03-01

    Wiese vectors, induction vectors, field separation and a physical-statistical approach were used to identify a zone of geoelectrical inhomogeneity near the eastern margin of the Bohemian Massif. This zone seems to mark an important geological and tectonic boundary separating two different tectogenes. The spatial distribution of the induction characteristics along five profiles traversing the boundary suggests a general 3-D model of internal geoelectrical-geological structure for the region. Common reference transfer functions and corresponding in- and out-of-phase vectors calculated by relating the data at a particular station and a common reference station were also derived as a tool for mapping internal geoelectrical structure.

  10. UHP-UHT peak conditions and near-adiabatic exhumation path of diamond-bearing garnet-clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Haifler, Jakub; Kotková, Jana

    2016-04-01

    Intermediate garnet-clinopyroxene rocks from the Eger Crystalline Complex, North Bohemian Massif, contain microdiamonds enclosed in garnet and zircon. The variable mineral assemblage of these rocks allows for an evaluation of the P-T evolution using numerous univariant equilibria and thermodynamic modelling, in addition to the ternary feldspar solvus, Ti-in-garnet, Zr-in-rutile and Ti-in-zircon thermometry. Zircon mantle domains with diamond inclusions contain 111-189 ppm Ti, reflecting temperatures of 1037-1117 °C. The peak pressure consistent with diamond stability corresponds to c. 4.5-5.0 GPa. Ti-in-garnet thermometry using the Ti content of diamond-bearing garnet core yielded temperatures of 993-1039 °C at c. 5.0 GPa. An omphacite inclusion in garnet (reflecting c. 2.3-2.4 GPa at c. 1050 °C) and metastably preserved kyanite represent relics of eclogite-facies conditions. The dominant high-pressure granulite-facies mineral assemblage of low-Ca garnet, diopsidic clinopyroxene, antiperthitic feldspar and quartz equilibrated at 1.8-2.1 GPa and c. 1050 °C, based on the XGrs isopleth of the garnet mantle, garnet-feldspar-kyanite-quartz univariant equilibria and ternary feldspar solvus. Our thermodynamic modelling shows that a steep decrease of XGrs from a maximum core value of 0.32 to 0.17 at the rim as well as a rimward XMg increase (from 0.42 to 0.50) are consistent with significant decompression without heating. The latter is related to omphacite and kyanite breakdown reactions producing garnet and plagioclase. The Ti content in the rim zone of zircon (13-42 ppm), exsolved plagioclase and K-feldspar associated with matrix diopside and garnet rim, and late biotite reflect temperatures of c. 830-900 °C at c. 1.4 GPa. A similar temperature is recorded by matrix rutile grains, containing 2028-4390 ppm Zr and representing a relatively homogeneous population in contrast to rutile enclosed in garnet with variable Zr content. Our results show that the garnet

  11. Early Triassic change in the erosional level in the eastern part of the Bohemian Massif revealed by detrital garnet assemblages from the Buntsandstein siliciclastics of southern Poland

    NASA Astrophysics Data System (ADS)

    Kowal-Linka, Monika; Walczak, Klaudia

    2017-04-01

    Garnets, as constituents of various magmatic and metamorphic rocks, show different chemical compositions depending on the type of magma or primary rock, the temperature, and the pressure. This diversity of chemical compositions makes detrital garnets a very useful tool for provenance analysis and deciphering changes in erosional levels of source areas. Preliminary works reveal that the Lower and Middle Buntsandstein terrigenous and marine sandstones cropping out in southern Poland (50˚ 28'20"N, 18˚ 04'33"E and 50˚ 27'35"N, 18˚ 07'23"E) are characterized by very different heavy mineral assemblages (HMA) and types of detrital garnets. The aim of the research is to recognize the source areas and causes of these distinct variations using petrographic analysis, heavy mineral analysis, and electron probe microanalysis. During the Early Triassic, the area under study was located between two landmasses: the eastern margin of the Bohemian Massif (BM) to the west and Pre-Carpathian Land (PCL) to the east. Presently, the sampled area is situated ˜50 km from the NE margin of the BM, which consists of many garnet-bearing rocks and is a presumable source area for the examined grains. The PCL was hidden under the Carpathians during the Alpine orogeny and knowledge of its composition is very limited. Petrographic analysis shows that the older sandstones are red to rusty quartz arenites with a hematite-rich matrix and well-rounded grains (aeolian deposits). The younger sandstones are bicolored quartz wackes (dirty pink with grey patches) with a calcite matrix and angular to rounded grains (shallow marine deposits). The arenites contain zircon, tourmaline, and rutile grains accompanied by garnet, staurolite, apatite, and topaz. The opaque heavy minerals include ilmenite, ilmenite-rutile aggregates, magnetite and rarely chromian spinel. In contrast, the HMA from the wackes consist mostly of garnets, while the minerals listed above occur in subordinate amounts. The garnets from

  12. The main features of the interaction of mantle magmas with granulite complexes of the lower crust and their relationship with granitic melts (exemplified by the Early Caledonides of the West Baikal Region, Russia)

    NASA Astrophysics Data System (ADS)

    Vladimirov, Alexandr; Khromykh, Sergei; Mekhonoshin, Alexei; Volkova, Nina; Travin, Alexei; Mikheev, Evgeny; Vladimirova, Anna

    2016-04-01

    Granulite complexes occurring in the Early Caledonian southern folded framing of the Siberian Craton are deeply eroded fragments of the Vendian-Early Paleozoic accretionary prism, which is an indicator of the early stages of the Paleo-Asian Ocean (Gladkochub et al., 2010). The main feature of the granulite complexes is a wide development of gabbro-pyroxenites composing tectonic plates, synmetamorphic intrusive bodies, and numerous disintegrated fragments (boudins and enclaves), immersed in a metamorphic matrix. The volume of basites reaches 5-10 %, which allows us to consider mantle magmatism as a heat source for the granulite metamorphism. The most studied polygon is Chernorud granulite zone, which is a part of the Olkhon metamorphic terrane, West Baikal Region. Just this polygon was used for considering the problems of interaction of mantle magmas with lower crust granulite complexes and their relationship with granitic melts. The Chernorud Zone is a typical example of the accretionary prism with a predominance of metabasalts (70-80 %), subordinate amounts of marbles, quartzites and metapelites that have been subjected to granulite facies metamorphism and viscoelastic flow of rock masses. Study of two-pyroxene granulites (metabasalts) and garnet-sillimanite gneisses (metapelites) allows us to estimate P-T metamorphic conditions (P = 7.7-8.6 kbar, T = 770-820°C) and their U-Pb metamorphic age (530-500 Ma). Metabasalts correspond in their geochemistry to the island-arc tholeiitic series (Volkova et al., 2010; Gladkochub et al., 2010). Sin-metamorphic gabbro-pyroxenites formed in two stages: 1) Chernorud complex - tectonic slices and body's exhumed from deep earth crust levels (10-12 kb) and composed of arc tholeiitic series rocks (age T ≥ 500 Ma); 2) Ulan-Khargana complex - supply magmatic canals and fragmented tabular intrusions. This rocks composition corresponds to subalkaline petrochemical series (OIB) and U/Pb age is equal to 485±10 Ma (Travin et al., 2009

  13. Significance of the late Archaean granulite facies terrain boundaries, Southern West Greenland

    NASA Technical Reports Server (NTRS)

    Friend, C. R. L.; Nutman, A. P.; Mcgregor, V. R.

    1988-01-01

    Three distinct episodes and occurrences of granulite metamorphism in West Greenland are described: (1) the oldest fragmentary granulites occur within the 3.6-Ga Amitsoq gneisses and appear to have formed 200 Ma after the continental crust in which they lie (Spatially associated rapakivi granites have zircon cores as old as 3.8 Ga, but Rb-Sr, whole-rock Pb-Pb, and all other systems give 3.6 Ga, so these granulites apparently represent a later metamorphic event); (2) 3.0-Ga granulites of the Nordlandet Peninsula NW of Godthaab, developed immediately after crustal formation in hot, dry conditions, are carbonate-free, associated with voluminous tonalite, and formed at peak metamorphic conditions of 800 C and 7 to 8 kbar (Synmetamorphic trondhjemite abounds and the activity of H2O has been indicated by Pilar to have varied greatly); and (3) 2.8-Ga granulites south of Godthaab, lie to the south of retrogressed amphibolite terranes. Prograde amphibolite-granulite transitions are clearly preserved only locally at the southern end of this block, near Bjornesund, south of Fiskenaesset. Progressively deeper parts of the crust are exposed from south to north as a major thrust fault is approached. Characteristic big hornblende pegmatites, which outcrop close to the thrust in the east, have been formed by replacement of orthopyroxene. Comparable features were not seen in South Indian granulites. It was concluded that no one mechanism accounts for the origin of all granulites in West Greenland. Various processes have interacted in different ways, and what happened in individual areas must be worked out by considering all possible processes.

  14. Metamorphic evolution of pelitic-semipelitic granulites in the Kon Tum massif (south-central Vietnam)

    NASA Astrophysics Data System (ADS)

    Tích, Vu Van; Leyreloup, Andrey; Maluski, Henry; Lepvrier, Claude; Lo, Chinh-hua; Vượng, Nguyễn V.

    2013-09-01

    Pelitic and semipelitic anatectic granulites form one of the major lithological units in Kan Nack complex of the Kon Tum massif (in south-central Vietnam), which comprises HT metamorphic and magmatic rocks including granulites and charnockites is classically regarded as the older part of the Gondwana-derived Indosinia terrain. Metamorphic evolution study of pelitic granulite, the most abundant among granulites exposed in this massif, facilitates to understand that tectonic setting take place during the Indosinian time. The paragenetic assemblages, mineral chemistry, thermobarometry and P-T evolution path of pelitic-semipelitic granulites from Kon Tum massif has been studied in detail. Petrographic feature demonstrates that the pelitic granulite experienced prograde history, from pregranulitic conditions in the amphibolite facies up to the peak granulitic assemblages. Successive prograde reactions led to the temperature-climax giving rise to assemblages with cordierite-hercynite and cordierite-hercynite-K-feldspar. Then, as attested by the mineralogic association occurring in cordieritic coronas, these rocks have been affected by retrograde conditions coeval with a decrease of the pressure. Thermobarometic results show that the highest temperature obtained by ksp/pl thermometry is 850 °C and the highest pressure obtained by GASP (Garnet Alumino-Silicate Plagioclase) is 7.8 kbar. The obtained clockwise P-T evolution path involving heating decompression, then nearly isothermal decompression and nearly isobar cooling conditions shows that high temperature-low pressure metamorphism of the studied pelitic anatectic granulites of Kan Nack complex occurred possibly in extensional setting during the Indosinian orogeny of 260-240 Ma in age.

  15. Sulphur and nitrogen fluxes and budgets in the Bohemian Forest and Tatra Mountains during the Industrial Revolution (1850-2000)

    NASA Astrophysics Data System (ADS)

    Kopcek, J.; Vesel, J.; Stuchlk, E.

    Major fluxes of sulphur and dissolved inorganic nitrogen were estimated in Central European mountain ecosystems of the Bohemian Forest (forest lakes) and Tatra Mountains (alpine lakes) over the industrial period. Sulphur outputs from these ecosystems were comparable to inputs during a period of relatively stable atmospheric deposition (10-35 mmol m-2 yr-1) around the 1930s. Atmospheric inputs of sulphur increased by three- to four-fold between the 1950s and 1980s to ~140 and ~60 mmol mm-2 yr-1 in the Bohemian Forest and Tatra Mountains, respectively. Sulphur outputs were lower than inputs due to accumulation in soils, which was higher in forest soils than in the sparser alpine soils and represented 0.8-1.6 and 0.2-0.3 mol m-2, respectively, for the whole 1930-2000 period. In the 1990s, atmospheric inputs of sulphur decreased 80% and 50% in the Bohemian Forest and Tatra Mountains, respectively, and sulphur outputs exceeded inputs. Catchment soils became pronounced sources of sulphur with output fluxes averaging between 15 and 31 mmol m-2 yr-1. Higher sulphur accumulation in the forest soils has delayed (by several decades) recovery of forest lakes from acidification compared to alpine lakes. Estimated deposition of dissolved inorganic nitrogen was 53-75 mmol m-2 yr-1 in the Bohemian Forest and 35-45 mmol m-2 yr-1 in the Tatra Mountains in the 1880- 1950 period, i.e. below the empirically derived threshold of ~70 mmol m-2 yr-1, above which nitrogen leaching often occurs. Dissolved inorganic nitrogen was efficiently retained in the ecosystems and nitrate export was negligible (0-7 mmol m-2 yr-1). By the 1980s, nitrogen deposition increased to ~160 and ~80 mmol m-2 yr-1 in the Bohemian Forest and Tatra Mountains, respectively, and nitrogen output increased to 120 and 60 mmol m-2 yr-1. Moreover, assimilation of nitrogen in soils declined from ~40 to 10-20 mmol m-2 yr-1 in the alpine soils and even more in the Bohemian Forest, where one of the catchments has even become

  16. P T and fluid evolution of barren and lithium pegmatites from Vlastějovice, Bohemian Massif, Czech Republic

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Zachariáš, Jiří; Pudilová, Marta

    2007-08-01

    Fluid inclusions, mineral thermometry and stable isotope data from two types of mineralogically and texturally contrasting pegmatites, barren ones and lithium ones, from the Moldanubian Zone of the Bohemian Massif were studied in order to constrain P T conditions of their emplacement, subsolidus hydrothermal evolution and to estimate composition of the early exsolved fluid and that of the parental melt. Despite the fact that the lithium pegmatites are abundant throughout the crystalline units of the Bohemian Massif, data similar to this paper have not been published yet. The studied pegmatites are hosted by iron-rich calcic skarn bodies. This specific setting allowed scavenging of calcium, fluorine and some other elements from the host rocks into the pegmatitic melts and post-magmatic fluids. Such contamination process was important namely in the case of barren pegmatites, as can be deduced from the variation in anorthite contents in plagioclase and from the presence of fluorite, hornblende (with F content) or garnet in the contact zones of pegmatite dykes. Fluid inclusions were studied mostly in quartz, but also in fluorite, titanite and apatite. Early aqueous carbonic and late aqueous fluids were identified in both pegmatite types. The P T conditions of crystallization as well as the detailed composition of exsolved magmatic fluid, however, particularly differ. The magmatic fluids associated with barren pegmatites correspond to H2O CO2 low salinity fluids, composition of which evolved from 20 to 23 to <5 mol% CO2, and from 2 to 4 6 mol% NaCl eq. Sudden decrease in the CO2 content of the post-magmatic fluids (<5 mol% CO2) seems to coincide with the enrichment of the fluid in calcium (from the contamination process) and resulted in precipitation of calcites (frequently found as trapped solid phases in fluid inclusions). The fluids associated with lithium pegmatites are more complex (H2O CO2/N2 H3BO3 NaCl). The CO2 content of early exsolved fluid is 26 20 mol% CO2

  17. Latest Cambrian-Early Ordovician rift-related magmatic activity in the Kouřim Unit, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Soejono, Igor; Machek, Matej; Sláma, Jiří; Janoušek, Vojtěch

    2017-04-01

    Pre-collisional history of high-grade Variscan complexes is mostly difficult to reveal, due to intense reworking during the development of the orogenic belt. An ancient magmatism could provide a unique possibility to study it. The Kouřim Unit represents an extensive pre-Variscan plutonic body involved into the tectonic collage of the Kutná Hora Crystalline Complex, at the northern margin of the Moldanubian Domain in the Bohemian Massif. The LA-ICP-MS zircon ages and geochemical characteristics of (meta-)igneous rocks from the Kouřim Unit allow us to determine the timing and nature of magmatic activity within this part of the Bohemian Massif and thus to decipher its pre-Variscan evolution. The Kouřim Unit is composed of strongly metamorphosed and deformed sequence of magmatic rocks, dominated mainly by various types of migmatites, coarse-grained orthogneisses and minor metadiorites. The newly obtained LA-ICP-MS U-Pb zircon ages of four orthogneisses ranging between 486 ± 2 Ma and 484 ± 2 Ma are interpreted as timing the magma crystallization. The single metadiorite gave concordia age of 337 ± 2 Ma interpreted as the age of migmatitization. Few discordant older ages from metadiorite are considered as older xenocrysts more or less reset during the Variscan metamorphism. The orthogneisses are acid (SiO2 = 68.6-76.4 wt. %), exclusively subaluminous and seem to form a single calc-alkaline trend, whereas the metadiorite is intermediate (SiO2 = 54.3 wt. %; mg# = 61), distinctly metaluminous and displays tholeiitic character. The chondrite-normalized REE patterns for the orthogneisses show LREE enrichment (LaN/YbN = 1.5-8.9) and deep negative Eu anomalies (Eu/Eu* = 0.42-0.32); the NMORB-normalized spiderplots feature LILE/HFSE enrichment with deep negative Nb- Ta-Ti anomalies. In contrast, both patterns of metadiorite resemble those of NMORB (LaN/YbN = 0.5, Eu/Eu* = 0.96). The apparent magmatic arc-like geochemical signature of the orthogneisses is interpreted as

  18. Archean granulite gneisses from eastern Hebei Province, China: rare earth geochemistry and tectonic implications

    NASA Astrophysics Data System (ADS)

    Jahn, Bor-Ming; Zhang, Zong-Qing

    1984-03-01

    The granulite gneisses and their retrograded products of the Qianxi Group from eastern Hebei Province, China, have been investigated for their isotope and trace element geochemistry. A consistent age of about 2.5 AE has been obtained by the Rb-Sr and Sm-Nd whole-rock isochron methods, in agreement with the zircon U-Pb data (Pidgeon 1980; D.Y. Liu, unpubl.). Geochemical arguments from initial isotopic ratios (ISr and INd) and elemental distribution patterns have led us to conclude that this age of about 2.5 AE represents the time of granulite facies metamorphism, which must have followed closely the primary emplacement of their protoliths. Previous claims for early Archean ages (>3.5 AE) of these granulites are not substantiated. The mineral isotope systematics register an important thermal event at about 1.7 AE, roughly corresponding to the time of the widespread Luliang Orogeny (Ma and Wu 1981) or Chungtiao Movement (Huang 1978). The granulites of the Qianxi Group have diverse compositions ranging from ultrabasic through basic-intermediate to acid. Discriminant function calculations suggest that most analyzed samples have igneous parentage. Only a few show characteristics of metasedimentary rocks. The igneous protoliths apparently belong to two series — tholeiitic and calc-alkaline, with the latter dominating in abundance. The majority of the acid granulites have compositions corresponding to tonalite-granodiorite. Except for ultrabasic and metasedimentary rocks, all REE patterns are significantly fractionated with LREE enrichment. The degree of fractionation, as measured by the (La/Yb)N ratios, is most important in the acid granulites. These rocks often show positive Eu anomalies and HREE depletions that are typical of Archean TTG rocks (tonalitetrondhjemite-granodiorite). The existence of komatiites has been previously reported in this region. Although a few rocks have a major element chemistry similar to that for peridotitic komatiites, the lack of associated

  19. Paleomagnetic results from Cenozoic volcanics of Lusatia, NW Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Schnabl, P.; Cajz, V.; Tietz, O.; Buechner, J.; Suhr, P.; Pecskay, Z.; Cizkova, K.

    2013-05-01

    Lusatia is situated in the NE continuation of the Ohre Rift (OR) behind Lusatian Overtrust. Compared to the neighbouring volcanic complex of the České stredohorí Mts. (CS) inside the OR. The scattered occurrences of basaltic bodies in Lusatia are spread on wider area. This can be caused by different tectonic development of the regions and from derived erosional conditions. The Lusatian Overtrust, high-order tectonic structure running across the course of the OR, separates Lusatian region into two different geological areas where Cretaceous sediments or granodiorites of Lusatian Massif represent the country rock of the Cenozoic volcanism, respectively. The age of volcanic activity ranges from 19 to 33 Ma, it's proved by newly obtained Ar-Ar data from Freiberg and K-Ar data from Debrecen. Forty two scattered remnants of Cenozoic volcanic products were sampled to get paleomagnetic data. The superficial volcanics with detectable geological position and volcanology were chosen preferentially, several dykes and separate vents were sampled as well. Paleomagnetic research was processed on more than 500 samples which were demagnetized using alternate field in the range 0-80 mT. Q-ratio was counted to prevent the lightning influence - solitary volcanic occurrences build positive morphology and thus, they are prone to be targeted by lightnings. The values of Q-ratio predominantly span from 0.1 to 7.0; those samples having the value over 10, were excluded for evaluation. The mean paleomagnetic direction (MPD) was acquired from several samples on each sampling site. Declination and Inclination show values of 11.8 deg and 62.7 deg (α95 = 9.3 deg) for normal polarity, or 182.1 deg and -59.2 deg (α95 = 6.1 deg) for reverse polarity, respectively,The corresponding paleolatitude of 41.9 deg was counted from the Inclination. This is 1000 km to the South, compared to recent position. The dispersions of the MPD are relatively wide. This coincides well with the idea of long

  20. Discrimination of iron ore deposits of granulite terrain of Southern Peninsular India using ASTER data

    NASA Astrophysics Data System (ADS)

    Rajendran, Sankaran; Thirunavukkarasu, A.; Balamurugan, G.; Shankar, K.

    2011-04-01

    This work describes a new image processing technique for discriminating iron ores (magnetite quartzite deposits) and associated lithology in high-grade granulite region of Salem, Southern Peninsular India using visible, near-infrared and short wave infrared reflectance data of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Image spectra show that the magnetite quartzite and associated lithology of garnetiferrous pyroxene granulite, hornblende biotite gneiss, amphibolite, dunite, and pegmatite have absorption features around spectral bands 1, 3, 5, and 7. ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in RGB are constructed by summing the bands representing the shoulders of absorption features as a numerator, and the band located nearest the absorption feature as a denominator to map iron ores and band ratios ((2 + 4)/3, (5 + 7)/6, (7 + 9)/8) in RGB for associated lithology. The results show that ASTER band ratios ((1 + 3)/2, (3 + 5)/4, (5 + 7)/6) in a Red-Green-Blue (RGB) color combination identifies the iron ores much better than previously published ASTER band ratios analysis. A Principal Component Analysis (PCA) is applied to reduce redundant information in highly correlated bands. PCA (3, 2, and 1 for iron ores and 5, 4, 2 for granulite rock) in RGB enabled the discrimination between the iron ores and garnetiferrous pyroxene granulite rock. Thus, this image processing technique is very much suitable for discriminating the different types of rocks of granulite region. As outcome of the present work, the geology map of Salem region is provided based on the interpretation of ASTER image results and field verification work. It is recommended that the proposed methods have great potential for mapping of iron ores and associated lithology of granulite region with similar rock units of granulite regions of Southern Peninsular India. This work also demonstrates the ability of ASTER's to provide information on iron ores, which is valuable

  1. Formation of Garnet Granulite in the Lower Crust of a paleo-Island Arc

    NASA Astrophysics Data System (ADS)

    Garrido, Carlos J.; Padrón-Navarta, José Alberto; López Sánchez-Vizcaíno, Vicente; Bodinier, Jean-Louis; Bosch, Delphine; Marchesi, Claudio; Hidas, Károly

    2016-04-01

    The Jijal complex (Kohistan paleo-island arc complex, NW Pakistan) is a unique occurrence of high-pressure (HP), mafic, opx-free, garnet granulite formed in the lower crust of an island arc. The upper part of the Jijal Granulitic Gabbro Unit (GGU) records the arrested transformation of hornblende gabbronorite to garnet granulite, involving the coeval breakdown of amphibole and orthopyroxene, and the formation of garnet and quartz. Close to the transformation front (2-3 cm), clinopyroxene from the granulite displays a strong Ca-tschermak zoning with lower Al-contents at rims. REE zoning of clinopyroxene and pseudosection diagrams indicate that only clinopyroxene rims reflect chemical equilibrium with garnet in the reaction front (P = 1.1 ± 0.1 GPa, T = 800 ± 50 °C), whereas the cores retained high-Al contents inherited from precursor gabbronorite clinopyroxene and remained in chemical disequilibrium within a few centimeters of the garnet granulite assemblage. Clinopyroxene of garnet granulites from the Jijal lower GGU are completely re-equilibrated with garnet (P = 1.5 ± 0.1 GPa, T = 800 ± 50 °C). If ferric iron corrections are disregarded, equilibration pressure and temperature are highly overestimated yielding exceedingly high pressures for an island arc setting. The pressure difference between the upper and lower Jijal GGU granulites (~0.4 GPa) and its current thickness (<5 km) implies delamination of the denser parts of Jijal crust. Thermodynamically computed phase diagram sections for upper GGU bulk compositions show that, at the equilibration conditions of Jijal garnet granulite, the equilibrium assemblage is orthopyroxene-free and amphibole-free garnet granulite coexisting with melt or a fluid phase, depending on the water activity at the onset of amphibole breakdown. Pseudosections indicate that hornblende gabbronorite assemblages are highly metastable at lower arc crust depths. The transformation to garnet granulite was therefore substantially

  2. Petrology, geochemistry and geodynamics of basic granulite from the Altay area, North Xinjiang, China.

    PubMed

    Li, Zi-Long; Chen, Han-Lin; Yang, Shu-Feng; Dong, Chuan-Wan; Xiao, Wen-Jiao

    2004-08-01

    The basic granulite of the Altay orogenic belt occurs as tectonic lens in the Devonian medium- to lower-grade metamorphic beds through fault contact. The Altay granulite (AG) is an amphibole plagioclase two-pyroxene granulite and is mainly composed of two pyroxenes, plagioclase, amphibole and biotite. Its melano-minerals are rich in Mg/(Mg+Fe2+), and its amphibole and biotite are rich in TiO2. The AG is rich in Mg/(Mg+Fe2+), Al2O3 and depletion of U, Th and Rb contents. The AG has moderate SigmaREE and LREE-enriched with weak positive Eu anomaly. The AG shows island-arc pattern with negative Nb, P and Ti anomalies, reflecting that formation of the AG may be associated with subduction. Geochemical and mineral composition data reflect that the protolith of the AG is calc-alkaline basalt and formed by granulite facies metamorphism having peak P-T conditions of 750 degrees C-780 degrees C and 0.6-0.7 Gpa. The AG formation underwent two stages was suggested. In the early stage of oceanic crustal subduction, calc-alkaline basalt with island-arc environment underwent granulite facies metamorphism to form the AG in deep crust, and in the late stage, the AG was thrust into the upper crust.

  3. Thermal contraints on high-pressure granulite metamorphism of supracrustal rocks

    NASA Technical Reports Server (NTRS)

    Ashwal, L. D.; Morgan, P.; Leslie, W. W.

    1983-01-01

    The circumstances leading to the formation and exposure at the Earth's surface of supracrustal granulites are examined. These are defined as sediments, volcanics, and other rock units which originally formed at the surface of the Earth, were metamorphosed to high-pressure granulite facies (T = 700-900 C, P = 5-10 kbar), and reexposed at the Earth's surface, in many cases underlain by normal thicknesses of continental crust (30-40 km). Five possible heating mechanisms to account for granulite metamorphism of supracrustal rocks are discussed: magnetic heating, thermal relaxation of perturbed temperature profiles following underthrusting of the continental crust, thermal relaxation after underthrusting of thin slivers of supracrustal rocks below continental crust of normal thickness, major preheating of the upper plate, and shear heating caused by frictional stress along the thrust plane.

  4. Petrology and mineral equilibrium modeling of incipient charnockite from the Trivandrum Granulite Block, southern India: implications for granulite formation in a Gondwana fragment

    NASA Astrophysics Data System (ADS)

    Endo, T.; Tsunogae, T.; Santosh, M.

    2012-04-01

    The Southern Granulite Terrane (SGT) in India is known for its classic exposures of regionally metamorphosed granulite-facies rocks formed during the collisional orogeny related to the amalgamation of Gondwana supercontinent. The SGT is composed of a collage of Proterozoic crustal blocks dissected by large Late Neoproterozoic shear/suture zones. The Trivandrum Granulite Block (TGB) is comprises dominantly metasedimentary sequence with khondalites, leptynites and charnockites with subordinate quartzite, mafic granulite, calc-silicate rocks, and meta-ultramafic rocks. The TGB is known as one of the classic examples for the spectacular development of 'incipient charnockites' within orthopyroxene-free felsic gneisses as exposed in several quarry sections in the states of Kerala and Tamil Nadu. The charnockite-forming process in the TGB is considered to have been triggered by the infiltration of CO2-rich anhydrous fluids along structural pathways within upper amphibolite facies gneisses, resulting in the lowering of water activity and stabilization of orthopyroxene through the breakdown of biotite. However, no quantitative study on the stability of charnockitic mineral assemblage using mineral equilibrium modeling approach has been done so far. In this study, we report a new occurrence of incipient charnockite from Mavadi in the TGB and discuss the petrogenesis of granulite formation in an arrested stage on the basis of petrography, geothermobarometry, and mineral equilibrium modeling. In Mavadi, patches and lenses of charnockite (Kfs + Qtz + Pl + Bt + Grt + Opx + Ilm + Mag) of about 30 to 120 cm in length occur within Opx-free Grt-Bt gneiss (Kfs + Qtz + Pl + Bt + Grt + Ilm) host rocks. The application of mineral equilibrium modeling on charnockite assemblage in NCKFMASHTO system to constrain the conditions of charnockitization defines a P - T range of 800° C at 4.5 kbar to 850° C at 8.5 kbar, which is broadly consistent with the results from the conventional

  5. The granulitic impactite suite: Impact melts and metamorphic breccias of the early lunar crust

    NASA Astrophysics Data System (ADS)

    Cushing, Janet A.; Taylor, G. Jeffrey; Norman, Marc D.; Keil, Klaus

    1999-03-01

    An important and poorly understood group of rocks found in the ancient lunar highlands is called "feldspathic granulitic impactites." Rocks of the granulite suite occur at most of the Apollo highlands sites as hand samples, rake samples, clasts in breccias, and soil fragments. Most lunar granulites contain 70-80% modal plagioclase, but they can range from anorthosite to troctolite and norite. Previous studies have led to different interpretations for the thermal history of these rocks, including formation as igneous plutons, long-duration metamorphism at high temperatures, and short-duration metamorphism at low temperatures. This paper reports on a study of 24 polished thin sections of lunar granulites from the Apollo 15, 16, and 17 missions. We identify three different textural types of granulitic breccias: poikilitic, granoblastic, and poikilitic-granoblastic breccias. These breccias have similar equilibration temperatures (1100 +/- 50 deg C), as well as common compositions. Crystal size distributions in two granoblastic breccias reveal that Ostwald ripening took place during metamorphism. Solid-state grain growth and diffusion calculations indicate relatively rapid cooling during metamorphism, 0.5 to 50 deg C/year, and thermal modeling shows that they cooled at relatively shallow depths (<200 m). In contrast, we conclude that the poikilitic rocks formed by impact melting, whereas the poikilitic-granoblastic rocks were metamorphosed and may have partially melted. These results indicate formation of lunar granulites in relatively small craters (30-90 km in diameter), physically associated with the impact-melt breccia pile, and possibly from fine-grained fragmental precursor lithologies.

  6. Polymetamorphic evolution of the granulite-facies Paleoproterozoic basement of the Kabul Block, Afghanistan

    NASA Astrophysics Data System (ADS)

    Collett, Stephen; Faryad, Shah Wali; Mosazai, Amir Mohammad

    2015-08-01

    The Kabul Block is an elongate crustal fragment which cuts across the Afghan Central Blocks, adjoining the Indian and Eurasian continents. Bounded by major strike slip faults and ophiolitic material thrust onto either side, the block contains a strongly metamorphosed basement consisting of some of the only quantifiably Proterozoic rocks south of the Herat-Panjshir Suture Zone. The basement rocks crop-out extensively in the vicinity of Kabul City and consist predominantly of migmatites, gneisses, schists and small amounts of higher-grade granulite-facies rocks. Granulite-facies assemblages were identified in felsic and mafic siliceous rocks as well as impure carbonates. Granulite-facies conditions are recorded by the presence of orthopyroxene overgrowing biotite in felsic rocks; by orthopyroxene overgrowing amphibole in mafic rocks and by the presence of olivine and clinohumite in the marbles. The granulite-facies assemblages are overprinted by a younger amphibolite-facies event that is characterized by the growth of garnet at the expense of the granulite-facies phases. Pressure-temperature (P-T) conditions for the granulite-facies event of around 850 °C and up to 7 kbar were calculated through conventional thermobarometry and phase equilibria modeling. The younger, amphibolite-facies event shows moderately higher pressures of up to 8.5 kbar at around 600 °C. This metamorphism likely corresponds to the dominant metamorphic event within the basement of the Kabul Block. The results of this work are combined with the litho-stratigraphic relations and recent geochronological dating to analyze envisaged Paleoproterozoic and Neoproterozoic metamorphic events in the Kabul Block.

  7. Occurrence of wagnerite in Mg-Al granulites of Sonapahar, Meghalaya

    NASA Astrophysics Data System (ADS)

    Dwivedi, S. B.; Theunuo, K.

    2017-06-01

    We report for the first time the occurrence of rare phosphate wagnerite as a stable phase from the Mg-Al granulites of Sonapahar. The wagnerite bearing assemblages consist of the spinel, phlogopite, brucite and corundum. The wagnerite appears in the Mg-Al granulites due to the break-down of spinel and fluorapatite. The mineral chemistry of the phases has been discussed from the EPMA data, which reveals that the fluorine content of the wagnerite is relatively low due to the exchange of F to coexisting phases. The major oxide analysis of the rocks show the low content of Ca, which is the requisite for the occurrences of wagnerite.

  8. In Situ Chemical Characterization of Mineral Phases in Lunar Granulite Meteorite Northwest Africa 5744

    NASA Technical Reports Server (NTRS)

    Kent, J. J.; Brandon, A. D.; Lapen, T. J.; Peslier, A. H.; Irving, A. J.; Coleff, D. M.

    2012-01-01

    Northwest Africa (NWA) 5744 meteorite is a granulitic and troctolitic lunar breccia which may represent nearly pristine lunar crust (Fig. 1). NWA 5744 is unusually magnesian compared to other lunar breccias, with bulk [Mg/(Mg+Fe)] 0.79 [1, 2]. Inspection shows impactor content is likely to be very minor, with low Ni content and a lack of metal grains. Some terrestrial contamination is present, evidenced by calcite within cracks. NWA 5744 has notably low concentrations of incompatible trace elements (ITEs) [2]. The goal of this study is to attempt to classify this lunar granulite through analyses of in situ phases.

  9. Stable isotope studies on granulites from the high grade terrain of Southern India

    NASA Technical Reports Server (NTRS)

    Jackson, D. H.; Santosh, M.; Mattey, D. P.; Harris, N. B. W.

    1988-01-01

    Fluid inclusion and petrologic characteristics of South India granulites and their bearing on the sources of metamorphic fluids are discussed. This paper served as a review and an introduction to the next paper by D. Jackson. Jackson presented carbon isotope data from gases extracted from fluid inclusions in South Indian granulites. The uniformly low Delta C-13 values (minus 10 plus or minus 2 per mil) and the greater abundance of CO2 in the incipient charnockites are suggestive of fluid influx from an externally buffered reservoir.

  10. 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

    The Kamieniec Metamorphic Belt (KMB), situated in the north-eastern part of the Bohemian Massif, represents the easternmost part of the Variscan Belt of Europe and is interpreted as a fragment of Central Sudetic accretionary wedge containg vestiges of the Saxothuringian crust (Mazur et al., 2015). The KMB comprises a volcano-sedimentary succession dominated by mica schists with intercalations of quartzo-feldspatic schists and subordinate marbles, amphibolites and eclogites. These rocks bear an imprint of Variscan tectonometamorphic reworking. PT conditions of these events were previously estimated at ca. 550 - 590 oC and 7.5 up to 12 kbars (Nowak, 1998; Józefiak, 2000) for mica schists and at 15 kbar and 575 oC for eclogites (Achramowicz et al., 1997). The metamorphic evolution of micaschists comprise the early HP/LT assemblage M1 with Cld+Phe and also earlier reported pseudomorphs after lawsonite (Nowak, 1998) followed by MP/MT mineral assemblage M2 comprising Grt+Pl+Bt+Ms+Qtz±St. Minerals of the M1 and M2 metamorphic events were overprinted by the LP/MT assemblage M3 containing Pl+Chl+Bt+Ms+Qtz±And. Thermodynamic modelling suggests that mineral assemblages record peak-pressure conditions of 20-25 kbar at 520 oC (M1) followed by nearly isothermal decompression to 6-7 kbar, and subsequent metamorphism with record of temperature progression from 500 to 600 oC at 10 kbar (M2) and final retrogression to 3 kbar and 550 oC (M3). The calculated PT conditions indicate a surprisingly low geothermal gradient during the M1 event of 5.5-7.1 oC/km. However, similar eclogitic mica schists with recognised geothermal gradient of ca. 8 oC/km were documented elsewhere from the Saxothuringian domain (Konopásek, 2001). Presented data provides the first report on mica schists from the KMB metamorphosed under eclogite-facies conditions at such low geothermal gradient. Acknowledgements: The study was supported from NCN research grant UMO-2015/17/B/ST10/02212. References Achramowicz

  11. The granulite suite: Impact melts and metamorphic breccias of the early lunar crust

    NASA Technical Reports Server (NTRS)

    Cushing, J. A.; Taylor, G. J.; Norman, M. D.; Keil, K.

    1993-01-01

    The granulite suite consists of two major types of rocks. One is coarse-grained and poikilitic with many euhedral crystals of olivine and plagioclase. These characteristics indicate crystallization from a melt; the poikilitic granulites are impact melt breccias. The other group is finer-grained and granoblastic, with numerous triple junctions; the granoblastic granulites are metamorphic rocks. Compositional groups identified by Lindstrom and Lindstrom contain both textural types. Two pyroxene thermometry indicates that both groups equilibrated at 1000 to 1150 C. Calculations suggest that the granoblastic group, which has an average grain size of about 80 microns, was annealed for less than 6 x 10 exp 4 y at 1000 C, and for less than 2500 y at 1150 C. Similar equilibration temperatures suggest that both groups were physically associated after impact events produced the poikilitic melts. Granulitic impactites hold important information about the pre-Nectarian bombardment history of the Moon, and the composition and thermal evolution of the early lunar crust. Granulitic impactites are widely considered to be an important rock type in the lunar crust, but how they formed is poorly understood. Metal compositions and elevated concentrations of meteoritic siderophile elements suggest that most lunar granulites are impact breccias. Their occurrence as clasts in approximately 3.9 Ga breccias, and Ar-(40-39) ages greater than or = 4.2 Ga for some granulites show that they represent a component of the lunar crust which formed prior to the Nectarian cataclysm. Petrographic characteristics of lunar granulites indicate at least two endmember textural variants which apparently formed in fundamentally different ways. One type has granoblastic textures consisting of equant, polygonal to rounded grains, and abundant triple junctions with small dispersions around 120 degrees indicating a close approach to textural equilibrium. As suggested by many authors, granoblastic granulites

  12. Large plates and small blocks: The Variscan orogeny in the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Kroner, Uwe; Romer, Rolf L.

    2017-04-01

    The Bohemian Massif of the Central European Variscides consists of several late Proterozoic / early Paleozoic low-strain crustal units, namely the Bruno-Vistulian continental block of the Laurussian plate that is juxtaposed with the Tepla-Barrandian Unit and the Lausitz block of the Gondwana plate. These pre-Variscan low-strain units are separated by high-strain zones that contain the mid- and lower crustal record of the Variscan orogeny (400-300 Ma), with nappes reflecting successive subduction exhumation events, voluminous migmatites and a wide range of geochemically contrasting granites. Although the principal constraints are undisputed, there is no consensus regarding the general tectonics of this area. Here we present a plate tectonic model explaining the Bohemian Massif as an orogenic wedge with a Gondwana pro-wedge and a Laurussia retro-wedge area. The principal formation steps are as follows. Subduction of the oceanic crust of the Gondwana plate, i.e. the southern part of the Rheic Ocean eventually followed by continental subduction of the distal Peri-Gondwana shelf produced the early Devonian (U)HP complexes now exposed in the uppermost allochthonous units. The arrival of the Tepla-Barrandian Cadomian block initiates a flip of subduction polarity, leading to the complete closure of the Rheic Ocean in the late Devonian coeval with the exhumation of the early Variscan (U)HP units. Caused by the Lausitz block entering the plate boundary zone in the early Carboniferous, this early subduction accretion stage was followed by continent continent collision. The resulting orogenic wedge is characterized by an intra-continental subduction zone in the pro-wedge area superimposed by the crustal stack of early and mid-Variscan accreted units. Due to heating of the subducted slab in the mantle, the isothermal exhumation of this deeply buried continental crust caused HT-LP metamorphism during the final transpressional stage. Lateral extrusion tectonics coeval with the

  13. Mantle anisotropy of the Bohemian Massif as seen by SKS-wave splitting

    NASA Astrophysics Data System (ADS)

    Vecsey, Ludek; Plomerova, Jaroslava; Babuska, Vladislav

    2014-05-01

    The Bohemian Massif (BM) assembled during the collision of Laurasia (Laurentia-Baltica) and Gondwana as a part of the Armorican Terrane Assemblage. It represents the estern-most outcrop of the European Variscan belt. The detailed tomographic and seismic anisotropy research of the deep structure of the BM has proceeded in several passive seismic experiments: BOHEMA I (2001-2003), BOHEMA II (2004-2005), BOHEMA III (2005-2006), PASSEQ (2006-2008) and Eger Rift (2007-2011). During these periods, the whole massif was stepwise covered by networks of temporal short-period and broad-band stations that recorded large amount of data from teleseismic events. The inferences from seismic anisotropy image the Bohemian Massif as a mosaic of microplates with a rigid mantle lithosphere preserving a fossil olivine fabric. The mantle domains can be associated with the tectonic units recognized by geological studies: Saxothuringian (ST), Teplá-Barrandian (TB), Moldanubian (MB) and finally Moravian (M) and Silesian (S) parts of the MS Zone, overlying the Brunovistulian mantle lithosphere. In this contribution, we concetrate on the large-scale mantle anisotropy modelled from splitting of SKS waves and their particle motion (PM). An advantage of using PM analysis is its ability to employ even events with lower signal-to-noise ratio (SNR) that are otherwise not usable for splitting analysis. To improve results of splitting analysis of signals distorted by noise, we use stacking of individual splitting measurements from waves closely propagating through the mantle. Another way of improving our analysis is a stacking of individual splittings of a single event measured at nearby stations. On average, the fast shear waves are polarized in the E-W direction in the ST, MD, TB units, but exhibit different regional variations of the splitting parameters in dependence on back-azimuths. Thus, different lithosphere mantle fabrics in the ST, MD and TB units were modelled. Moreover, the ST unit can

  14. Petrology and geochemistry of lower crustal granulites from the Geronimo Volcanic Field, southeastern Arizona

    SciTech Connect

    Kempton, P.D.; Hawkesworth, C.J. ); Harmon, R.S. ); Moorbath, S. )

    1990-12-01

    Mafic to intermediate composition granulite xenoliths occur in Pliocene to Recent alkali basalts from the Geronimo Volcanic Field (GVF), southeastern Arizona, USA. The range of compositions and mineral assemblages observed suggests that the ultimate derivation of these rocks is from a variety of protoliths and that more than one mechanism has operated during the geologic evolution of the lower crust in this area. Two-pyroxene, two-feldspar granulites (meta-diorites) have major and trace element characteristics similar to estimates of post-Archaen lower crust. Low {sup 143}Nd/{sup 144}Nd values and Proterozoic Nd-depleted-mantle model ages (1.2-1.4 Ga) for these rocks require that Precambrian material exists in the lower crust of southeastern Arizona, either as the meta-diorites themselves or as older crust available for melting during production of the meta-diorite protoliths. K-feldspar-free granulites have more mafic compositions and their trace element characteristics are consistent with a cumulate origin. A negative correlation of {sup 208}Pb/{sup 204}Pb vs. {sup 206}Pb/{sup 204}Pb suggests that the meta-cumulate granulites represent mixing between Basin and Range age lavas with older meta-diorite crust and is, thus, evidence for Cenozoic underplating of the lower crust beneath the Basin and Range.

  15. Paleoarchean orthopyroxenites of the Bug granulite-gneiss domain at the Ukrainian shield

    NASA Astrophysics Data System (ADS)

    Lobach-Zhuchenko, S. B.; Balaganskii, V. V.; Koreshkova, M. Yu.; Lokhov, K. I.; Baltybaev, Sh. K.; Stepanyuk, L. M.; Egorova, Yu. S.; Sergeev, S. A.; Kapitonov, I. N.; Galankina, O. L.; Bogomolov, E. S.; Berezhnaya, N. G.; Sukach, V. V.

    2017-06-01

    This report presents data on the geological structure and location of the orthopyroxenite inclusion in gneissic enderbites of the Bug granulite-gneiss domain. Three stages of orthopyroxenite formation were identified on the basis of studies of the mineral composition along with the U-Pb and Lu-Hf isotope systems of zircons.

  16. Mass transfer and trace element redistribution during hydration of granulites in the Bergen Arcs, Norway

    NASA Astrophysics Data System (ADS)

    Centrella, Stephen; Austrheim, Håkon; Putnis, Andrew

    2016-10-01

    The Bergen Arcs, located on the western coast of Norway, are characterized by Precambrian granulite facies rocks partially hydrated at amphibolite and eclogite facies conditions. At Hilland Radöy, granulite displays sharp hydration fronts across which the granulite facies assemblage composed of garnet (55%) and clinopyroxene (45%) is replaced by an amphibolite facies mineralogy defined by chlorite, epidote, and amphibole. The replacement of both phases is pseudomorphic and the overall reaction is isovolumetric. In the present study, LA ICPMS has been used to determine the trace element redistribution during the hydration. Although the bulk concentrations of the trace elements do not change, the LILE, HFSE, and REE losses and gains in replacing the garnet are qualitatively balanced by the opposite gains and losses associated with the replacement of clinopyroxene. From the REE compositions of the parent granulite and the product amphibolite, measured in μg/cm3, we conclude that the mass of rock lost to the fluid phase during the hydration is approximately 20%. This suggests a mechanism for coupling between the local stress generated by hydration reactions and mass transfer, dependent on the spatial scale over which the system is open.

  17. Ultrahigh-Temperature Metamorphism in Madurai Granulites, Southern India: Evidence from Carbon Isotope Thermometry.

    PubMed

    Satish-Kumar

    2000-07-01

    Ultrahigh-temperature (UHT) metamorphism in the Madurai Block of the southern Indian granulite terrain has been verified using the calcite-graphite isotope exchange thermometer. Carbon isotope thermometry has been applied to marbles from a locality near the reported occurrence of sapphirine granulites that have yielded temperature estimates of around 1000 degrees C. The delta(13)C and delta(18)O values of calcite are homogenous, implying equilibration of the isotopes during metamorphism. However, the delta(13)C values of single graphite crystals show variations in the order of 1 per thousand within a hand specimen. Detailed isotopic zonation studies indicate that graphite preserves either the time-integrated crystal growth history or reequilibrium fractionation during its cooling history. The graphite cores preserve higher delta(13)C values than the rims. The fractionation between calcite and graphite cores gives the highest metamorphic temperature of about 1060 degrees C, which matches the petrologically inferred temperature estimates in the high-magnesian pelites. The fractionation between graphite rims and calcite suggests a temperature of around 750 degrees C, which is interpreted to reflect retrograde cooling. This event is also observed in the sapphirine granulites. Calcite-graphite thermometry thus provides a useful tool to define UHT metamorphism in granulite terrains.

  18. Adjusting stream-sediment geochemical maps in the Austrian Bohemian Massif by analysis of variance

    USGS Publications Warehouse

    Davis, J.C.; Hausberger, G.; Schermann, O.; Bohling, G.

    1995-01-01

    The Austrian portion of the Bohemian Massif is a Precambrian terrane composed mostly of highly metamorphosed rocks intruded by a series of granitoids that are petrographically similar. Rocks are exposed poorly and the subtle variations in rock type are difficult to map in the field. A detailed geochemical survey of stream sediments in this region has been conducted and included as part of the Geochemischer Atlas der Republik O??sterreich, and the variations in stream sediment composition may help refine the geological interpretation. In an earlier study, multivariate analysis of variance (MANOVA) was applied to the stream-sediment data in order to minimize unwanted sampling variation and emphasize relationships between stream sediments and rock types in sample catchment areas. The estimated coefficients were used successfully to correct for the sampling effects throughout most of the region, but also introduced an overcorrection in some areas that seems to result from consistent but subtle differences in composition of specific rock types. By expanding the model to include an additional factor reflecting the presence of a major tectonic unit, the Rohrbach block, the overcorrection is removed. This iterative process simultaneously refines both the geochemical map by removing extraneous variation and the geological map by suggesting a more detailed classification of rock types. ?? 1995 International Association for Mathematical Geology.

  19. On the occurrence of Ctenocheles (Decapoda, Axiidea, Ctenochelidae) in the Bohemian Cretaceous Basin

    PubMed Central

    HYŽNÝ, MATÚŠ; VESELSKÁ, MARTINA KOČOVÁ; DVOŘÁK, PAVEL

    2015-01-01

    Because of close morphological affinities, fossil cheliped fragments of the ghost shrimp Ctenocheles (Decapoda, Axiidea, Ctenochelidae) can be easily misidentified as remains of different decapod crustacean taxa. Re-examination of the Cretaceous decapods deposited in the National Museum in Prague revealed that all supposed specimens of the lobster genus Oncopareia found in the Middle Coniacian calcareous claystones of the Březno Formation, including one of the Fritsch’s original specimens of Stenocheles parvulus, actually belong to Ctenocheles. This material together with newly collected specimens from the same locality, allowed for erection of a new species, Ctenocheles fritschi. Its major chela possesses a serrated ischium and ovoid, unarmed merus; therefore, it is considered a close relative of the extant C. collini and C. maorianus. Ctenocheles fritschi sp. nov. represents the first report on the occurrence of the genus from the Bohemian Cretaceous Basin. It is one of the oldest records of Ctenocheles and simultaneously one of the best preserved fossils of the genus reported to date. Confusing taxonomy of S. parvulus is reviewed and shortly discussed. PMID:25983568

  20. The Auchenorrhyncha fauna of peat bogs in the Austrian part of the Bohemian Forest (Insecta, Hemiptera)

    PubMed Central

    Holzinger, Werner E.; Schlosser, Lydia

    2013-01-01

    Abstract The first overview on the Auchenorrhyncha fauna of peat bogs of the Austrian Bohemian Forest is presented. Seven oligotrophic peat bog sites were studied in 2011 by suction sampler (“G-Vac”) and 93 Auchenorrhyncha species (with 7465 adult specimens) were recorded. Eleven species (about 18 % of the individuals) are tyrphobiontic or tyrphophilous. The relative species abundance plot is not very steep; the six most abundant species represent 50 % of the individuals. The most common species is Conomelus anceps (17 % of the individuals). Compared to the whole Austrian Auchenorrhyncha fauna, the fauna of peat bogs comprises distinctly more univoltine species and more species hibernating in nymphal stage. Densities of adult Auchenorrhyncha in peat bogs are low in spring (about 10–60 individuals per m²) and high in July, with up to 180 (±50) individuals per m². Disturbed peat bogs have higher species numbers and higher Auchenorrhyncha densities in total, but lower numbers and densities in peat bog specialists. PMID:24039517

  1. Radioactivity in mushrooms from selected locations in the Bohemian Forest, Czech Republic.

    PubMed

    Čadová, Michaela; Havránková, Renata; Havránek, Jiří; Zölzer, Friedo

    2017-03-03

    (137)Cs is one of the most important radionuclides released in the course of atmospheric nuclear weapon tests and during accidents in nuclear power plants such as that in Chernobyl, Ukraine, or Fukushima, Japan. The aim of this study was to compare (137)Cs and (40)K concentrations in particular species of mushrooms from selected locations in the Bohemian Forest (Czech: Šumava), Czech Republic, where a considerable contamination from the Chernobyl accident had been measured in 1986. Samples were collected between June and October 2014. Activities of (137)Cs and (40)K per dry mass were measured by means of a semiconductor gamma spectrometer. The (137)Cs values measured range from below detection limit to 4300 ± 20 Bq kg(-1), in the case of (40)K from 910 ± 80 to 4300 ± 230 Bq kg(-1). Differences were found between individual locations, due to uneven precipitation in the course of the movement of the radioactive cloud after the Chernobyl accident. There are, however, also differences between individual species of mushrooms from identical locations, which inter alia result from different characteristics of the soil and depths of mycelia. The values measured are compared with established limits and exposures from other radiation sources present in the environment. In general, it can be stated that the values measured are relatively low and the effects on the health of the population are negligible compared to other sources of ionizing radiation.

  2. Eclogitization of dry granulite triggers deep crustal seismicity in Southern Tibet

    NASA Astrophysics Data System (ADS)

    Shi, Feng; Wang, Yanbin; Yu, Tony; Zhu, Lupei; Gasc, Julien; Zhang, Junfeng; Jin, Zhenmin

    2017-04-01

    Intermediate-depth earthquakes (IDEQs) occur at focal depths from about 50 km to 300 km. Their physical mechanism has been enigmatic, because as pressure and temperature increase with depth, brittle failure should be suppressed, and rocks tend to flow plastically. IDEQs have been recorded down to depths of 80 - 100 km in Southern Tibet, where the lower crust is considered hot and dry [1]. It is questionable whether such seismicity can be produced by unassisted brittle shear fracture or frictional sliding. Pseudotachylytes that formed under conditions corresponding to the eclogitic facies are ubiquitously observed in western Norway [2], demonstrating that faulting took place in granulite, which is the main constituent of lower continental crust at pressures approaching 3 GPa. These observations suggest strongly that eclogitization is potentially involved in the seismicity in the deep continental crust. Here we conduct deformation experiments on natural and nominally dry granulite in a deformation-DIA (DDIA) apparatus and Griggs apparatus within the thermal stability fields of both granulite and eclogite, to investigate the mechanism of intermediate earthquake. The D-DIA, installed at the synchrotron beamline of GSECARS, is interfaced with an acoustic emission (AE) monitoring system, allowing in-situ detection of mechanical instability along with the progress of eclogitization based on x-ray diffraction. We found that granulite deformed within its own stability field (< 2 GPa and 1000°C) behaved in a ductile fashion without any AE activity. Unstable fault slip, on the other hand, occurred during deformation of metastable granulite in the eclogite field above 2 GPa. Numerous AE events were observed. Microstructural observation on recovered samples shows conjugated macroscopic faults. Strain is highly localized along the fault, and microcracks observed along grain boundary likely involve with eclogitization products. The fault zones consist of fine- grained (<< 1

  3. Fluid evolution of the Hub Stock, Horní Slavkov-Krásno Sn-W ore district, Bohemian Massif, Czech Republic

    NASA Astrophysics Data System (ADS)

    Dolníček, Zdeněk; René, Miloš; Prochaska, Walter; Kovář, Michal

    2012-10-01

    The Horní Slavkov-Krásno Sn-W ore district is hosted by strongly altered Variscan topaz-albite granite (Krudum granite body) on the northwestern margin of the Bohemian Massif. We studied the fluid inclusions on greisens, ore pockets, and ore veins from the Hub Stock, an apical expression of the Krudum granite. Fluid inclusions record almost continuously the post-magmatic cooling history of the granite body from ˜500 to <50°C. Rarely observed highest-temperature (˜500°C) highest-salinity (˜30 wt.% NaCl eq.) fluid inclusions are probably the result of secondary boiling of fluids exsolved from the crystallizing magma during pressure release which followed hydraulic brecciation of the gneissic mantle above the granite cupola. The greisenization was related to near-critical low-salinity (0-7 wt.% NaCl eq.) aqueous fluids with low amount of CO2, CH4, and N2 (≤10 mol% in total) at temperatures of ˜350-400°C and pressures of 300-530 bar. Crush-leach data display highly variable and negatively correlated I/Cl and Br/Cl values which are incompatible with both orthomagmatic and/or metamorphic origin of the fluid phase, but can be explained by infiltration of surficial and/or sedimentary fluids. Low fluid salinity indicates a substantial portion of meteoric waters in the fluid mixture that is in accordance with previous stable isotope data. The post-greisenization fluid activity associated with vein formation and argillitization is characterized by decreasing temperature (<350 to <50°C), decreasing pressure (down to ˜50-100 bar), and mostly also decreasing salinity.

  4. Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Haluzová, Eva; Creaser, Robert A.; Pašava, Jan; Veselovský, František; Breiter, Karel; Erban, Vojtěch; Drábek, Milan

    2017-06-01

    Molybdenite is a common mineral accompanying Sn-W, Au, and base metal mineralizations located in different geotectonic units of the Bohemian Massif, but it is also widespread in granitoids and/or related quartz veins/pegmatites forming disseminated Mo mineralization. Thirty Re-Os ages were obtained for molybdenite samples from the Bohemian Massif to provide constraints on the timing and duration of mineralization event(s) within the framework of previously published geochronological data for the host and/or associated rocks. The obtained data for Sn-W-(Li) deposits in the Erzgebirge metallogenetic province indicate the predominance of one and/or multiple short-time mineralization events taking place between ˜319 and 323 Ma, with the exception of the Krupka deposit associated with the Altenberg-Teplice caldera where the data may suggest prolonged activity until ˜315 Ma. The ages of the Pb-Zn-(Au-Mo) Hůrky u Rakovníka and Fe-Cu-As Obří důl mineralizations from the exocontacts of the Čistá pluton and Krkonoše-Jizera Plutonic Complex, respectively, provide evidence for synchronous emplacement of the ore and the associated granitic rocks. In contrast, the Padrť Fe-As-Mo mineralization postdates the age of the associated Padrť granite. Disseminated Mo mineralization in Cadomian and Variscan granitoids and/or related to quartz veins/pegmatites provides Re-Os ages that overlap with the previously published geochronological data for the host rocks, suggesting coeval evolution. Molybdenite samples from the Sázava suite granites of the Central Bohemian Plutonic Complex (CBPC) have resolvable younger ages than their host granites, but similar to the age of spatially related Au mineralization which is associated with the latest evolution of the CBPC.

  5. Temporal evolution of mineralization events in the Bohemian Massif inferred from the Re-Os geochronology of molybdenite

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Haluzová, Eva; Creaser, Robert A.; Pašava, Jan; Veselovský, František; Breiter, Karel; Erban, Vojtěch; Drábek, Milan

    2016-10-01

    Molybdenite is a common mineral accompanying Sn-W, Au, and base metal mineralizations located in different geotectonic units of the Bohemian Massif, but it is also widespread in granitoids and/or related quartz veins/pegmatites forming disseminated Mo mineralization. Thirty Re-Os ages were obtained for molybdenite samples from the Bohemian Massif to provide constraints on the timing and duration of mineralization event(s) within the framework of previously published geochronological data for the host and/or associated rocks. The obtained data for Sn-W-(Li) deposits in the Erzgebirge metallogenetic province indicate the predominance of one and/or multiple short-time mineralization events taking place between ˜319 and 323 Ma, with the exception of the Krupka deposit associated with the Altenberg-Teplice caldera where the data may suggest prolonged activity until ˜315 Ma. The ages of the Pb-Zn-(Au-Mo) Hůrky u Rakovníka and Fe-Cu-As Obří důl mineralizations from the exocontacts of the Čistá pluton and Krkonoše-Jizera Plutonic Complex, respectively, provide evidence for synchronous emplacement of the ore and the associated granitic rocks. In contrast, the Padrť Fe-As-Mo mineralization postdates the age of the associated Padrť granite. Disseminated Mo mineralization in Cadomian and Variscan granitoids and/or related to quartz veins/pegmatites provides Re-Os ages that overlap with the previously published geochronological data for the host rocks, suggesting coeval evolution. Molybdenite samples from the Sázava suite granites of the Central Bohemian Plutonic Complex (CBPC) have resolvable younger ages than their host granites, but similar to the age of spatially related Au mineralization which is associated with the latest evolution of the CBPC.

  6. The Freyenstein Shear Zone - Implications for exhumation of the South Bohemian Batholith (Moldanubian Superunit, Strudengau, Austria)

    NASA Astrophysics Data System (ADS)

    Griesmeier, Gerit; Iglseder, Christoph; Konstantin, Petrakakis

    2016-04-01

    The Moldanubian superunit is part of the internal zone of the Variscan Orogen in Europe and borders on the Saxothuringian and Sudetes zones in the north. In the south, it is blanketed by the Alpine foreland molasse. Tectonically it is subdivided into the Moldanubian Nappes (MN), the South Bohemian Batholith (SBB) and the Bavarian Nappes. This work describes the ~ 500 m thick Freyenstein shear zone, which is located at the southern border of the Bohemian Massif north and south of the Danube near Freyenstein (Strudengau, Lower Austria). The area is built up by granites of Weinsberg-type, which are interlayered by numerous dikes and paragneisses of the Ostrong nappe system. These dikes include medium grained granites and finegrained granites (Mauthausen-type granites), which form huge intrusions. In addition, smaller intrusions of dark, finegrained diorites und aplitic dikes are observed. These rocks are affected by the Freyenstein shear zone und ductily deformed. Highly deformed pegmatoides containing white mica crystals up to one cm cut through the deformed rocks and form the last dike generation. The Freyenstein shear zone is a NE-SW striking shear zone at the eastern edge of the SBB. The mylonitic foliation is dipping to the SE with angles around 60°. Shear-sense criteria like clast geometries, SĆ structures as well as microstructures show normal faulting top to S/SW with steep (ca. 50°) angles. The Freyenstein shear zone records a polyphase history of deformation and crystallization: In a first phase, mylonitized mineral assemblages in deformed granitoides can be observed, which consist of pre- to syntectonic muscovite-porphyroclasts and biotite as well as dynamically recrystallized potassium feldspar, plagioclase and quartz. The muscovite porphyroclasts often form mica fishes and show top to S/SW directed shear-sense. The lack of syntectonic chlorite crystals points to metamorphic conditions of lower amphibolite-facies > than 450° C. In a later stage fluid

  7. 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

  8. Mass transfer and trace element redistribution during hydration of granulites in the Bergen Arcs, Norway.

    NASA Astrophysics Data System (ADS)

    Centrella, Stephen; Austrheim, Håkon; Putnis, Andrew

    2016-04-01

    The Bergen Arcs located on the Western coast of Norway are characterized by Precambrian granulite facies rocks partially hydrated at amphibolite and eclogite facies conditions. Over an area of ca. 1000 km², relict of granulite facies lenses make up only ca. 10% of the observed outcrops. At Hilland Radöy, granulite displays sharp hydration fronts across which the granulite facies assemblage composed of garnet (55%) and clinopyroxene (45%) is replaced by an amphibolite facies mineralogy defined by chlorite, epidote and amphibole. The major element bulk composition does not change significantly across the hydration front, apart from the volatile components (loss on ignition, LOI) that increases from 0.17 wt.% in the granulite to 2.43 wt.% in the amphibolite (Centrella et al., 2015). The replacements of garnet and clinopyroxene are pseudomorphic indicating a perfect preservation of the parent crystal shape. The textural evolution during the replacement is consistent with the coupled dissolution-precipitation mechanism where garnet is replaced by chlorite, epidote and pargasite and clinopyroxene by hornblende and quartz. Based on the observations of an isovolumetric replacement, the mass loss during hydration was estimated at 13%. This study is based on the trace element redistribution during the hydration using the same samples as Centrella et al. (2015). The local mass transfer during the replacement process determined from the major element is also confirmed by the trace element redistribution. The LILE, HFSE and REE losses and gains in replacing the garnet are approximately balanced by the opposite gains and losses associated with the replacement of clinopyroxene. Because the hydration involves reduction of rock density, the volume preservation (isovolumetric reaction), together with the mass balance calculations, requires a significant loss of the mass of the rock to the fluid phase: 13% based on the major element redistribution and around 20% based on the REE

  9. The rare earth element potential of kaolin deposits in the Bohemian Massif (Czech Republic, Austria)

    NASA Astrophysics Data System (ADS)

    Höhn, S.; Frimmel, H. E.; Pašava, J.

    2014-12-01

    Four kaolin deposits in the Bohemian Massif were studied in order to assess the potential for the recovery of rare earth elements (REE) as by-products from the residue after extraction and refining of the raw kaolin. The behaviour of REE + Y during kaolinitization was found to be largely a function of pre-alteration mineralogy. In the examples studied, i.e. granite-derived deposits of Kriechbaum (Austria) and Božičany, and arkose-derived deposits of Kaznějov and Podbořany (all Czech Republic), the REE + Y are predominantly hosted by monazite which has remained unaffected by kaolinitization. The overall REE + Y content of the variably kaolinitized rocks is strongly dependent on their genesis. While ion adsorption plays only a minor role in the concentration of REE + Y in the studied kaolinitized rocks, the processing and refining of the raw kaolin leads to residues that are enriched in REE + Y by a factor of up to 40. The use of a magnetic separator and a hydrocyclone in the processing of the raw material can yield REE + Y contents of as much as 0.77 wt%. Although this value compares well with the REE + Y concentration in some potentially economic REE + Y projects elsewhere, the overall tonnage of the (REE + Y)-enriched residue is by far not sufficient to consider economic extraction of REE + Y as by-product. Our results are most probably applicable also to other kaolin deposits derived from the weathering of Hercynian basement granites elsewhere (e.g. in Saxonia and Bavaria, Germany). Overall, the potential for REE + Y production as by-product from kaolin mining has to be regarded as minimal.

  10. Hydrochemical monitoring results in relation to the vogtland-nw bohemian earthquake swarm period 2000

    NASA Astrophysics Data System (ADS)

    Kämpf, H.; Bräuer, K.; Dulski, P.; Faber, E.; Koch, U.; Mrlina, J.; Strauch, G.; Weise, S. M.

    2003-04-01

    The Vogtland-NW Bohemian earthquake swarm area/Central Europe is characterised by carbon dioxide- rich mineral springs and mofetts. The August-December 2000 earthquake period was the strongest compared with the December 1985/86 swarms occurred in the area of Novy Kostel, Czech Republic. Here, we present first results of long-term hydrochemical monitoring studies before, during and after the 2000 swarm period. The swarm 2000 lasted from August 28 until December 26 and consisted of altogether nine sub-swarm episodes, each of them lasting for several days. At the mineral spring Wettinquelle, Bad Brambach/Germany the water chemistry and isotope (D, 18O) composition was monitored weekly and two-weekly, respectively, since May 2000. The mineral spring Wettinquelle is located in a distance of about 10 km from the epicentral area of Novy Kostel. The aim of our investigation was to look for seismic induced or seismic coupled changes of the chemical and isotope composition of the mineral water. We had to separate seismohydrological effects from seasonal and hydrological caused changes. The seasonal caused shifts were found for water temperature and alkaline elements (Li, Na, K, Rb and Cs) as well as for discharge, conductivity, hydrogenecarbonate- concentration, and the concentration of the alkaline earth's (Ca, Mg, Sr). Strain related anomalies which could influence the hydrogeochemistry of the mineral water seems to be visible in the iron- concentration of the spring water, in the methane- concentration of the free gas component and caused probably changes of the groundwater level of the well H3 located about 5 km SE of the Wettinquelle at Skalna.

  11. Flash flood in 1714 in the Bohemian-Moravian Highlands - Reconstructing a Catastrophe.

    NASA Astrophysics Data System (ADS)

    Elleder, Libor; Krejčí, Jakub; Šírová, Jolana

    2015-04-01

    Read against the backdrop of the past twenty years with their exceptional frequency of summer floods, records of historical flood events have become highly topical. Aside from the May flood of 1872, the flash flood that occurred at the turn of July and August 1714 in the Bohemian-Moravian Highlands is probably the most important case of its kind in the Czech lands, and may likely be ranked among the most notable occurrences of extreme weather even within the larger Central European context. Within the catchment basin of the Sázava River, the headwater level rose about three meters above the highest floods on the hydrological record and 1.5m above the highest historical flood-mark. Taking into account the time period - i.e., the beginning of the 18th century - some of the concurrent accounts of the flood are uncommonly detailed, containing not only a specification of the damage caused, but also high water mark figures and, at least in broad strokes, a record of the changing water levels over time. The flood caused tremendous material damage at the time, breaching e.g. about 70 fish ponds and destroying essentially all bridges; over 230 people were killed. It was revealed that the area of Žďárské vrchy (Žďár Hills) at the divide of the rivers Loučná, Chrudimka, Sázava, and Svratka which was impacted by the causative extreme precipitation may have measured 800 to 1000 square kilometers. Rough estimates of the headwater flow rate equal about four times current Q100 values. We therefore used the hydrological model Aqualog in order to determine whether an event of this scope was at all realistic. The goal was to assess whether it was realistically possible that precipitation may have been of such scope as to trigger a hydrological response of this intensity.

  12. Protolith age of Santa Maria Chico granulites dated on zircons from an associated amphibolite-facies granodiorite in southernmost Brazil.

    PubMed

    Hartmann, Léo A; Liu, Dunyi; Wang, Yenbin; Massonne, Hans-Joachim; Santos, João O S

    2008-09-01

    U-Pb dating of zircon was undertaken with the Beijing SHRIMP II (sensitive high resolution ion microprobe) on anamphibolite facies granodiorite and an almandine-albite granulite from the Santa Maria Chico Granulitic Complex, southern Brazilian Shield. This work was also done to unravel protolith ages which are often hidden in the array of partly reset data. The obtained metamorphic ages of the granodiorite gneiss and the granulite are 2035 +/- 9 Ma and 2006 +/- 3 Ma, respectively. These data are within the range of metamorphic ages determined in previous studies (2022 +/- 18 Ma and 2031 +/- 40 Ma). However, protolith ages for the granodiorite (2366 +/- 8 Ma) and the granulite (2489 +/- 6 Ma) were obtained which are outside the previously recognized range (> 2510-2555 Ma). The magmatic protolith age of the granodiorite refers to a previously little known magmatic event in the shield. Further investigations may demonstrate that amphibolite facies zircon crystals are useful as a window into geological events in associated granulites, because zircon ages are blurred in the studied granulites.

  13. Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications

    NASA Astrophysics Data System (ADS)

    Ishwar-Kumar, C.; Sajeev, K.; Windley, B. F.; Kusky, T. M.; Feng, P.; Ratheesh-Kumar, R. T.; Huang, Y.; Zhang, Y.; Jiang, X.; Razakamanana, T.; Yagi, K.; Itaya, T.

    2015-11-01

    The occurrence of high-pressure mafic-ultramafic bodies within major shear zones is one of the indicators of paleo-subduction. In mafic granulites of the Andriamena complex (north-eastern Madagascar) we document unusual textures including garnet-clinopyroxene-quartz coronas that formed after the breakdown of orthopyroxene-plagioclase-ilmenite. Textural evidence and isochemical phase diagram calculations in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2 system indicate a pressure-temperature (P-T) evolution from an isothermal (780 °C) pressure up to c. 24 kbar to decompression and cooling. Such a P-T trajectory is typically attained in a subduction zone setting where a gabbroic/ultramafic complex is subducted and later exhumed to the present crustal level during oceanic closure and final continental collision. The present results suggest that the presence of such deeply subducted rocks of the Andriamena complex is related to formation of the Betsimisaraka suture. LA-ICPMS U-Pb zircon dating of pelitic gneisses from the Betsimisaraka suture yields low Th/U ratios and protolith ages ranging from 2535 to 2625 Ma. A granitic gneiss from the Alaotra complex yields a zircon crystallization age of ca. 818 Ma and Th/U ratios vary from 1.08 to 2.09. K-Ar dating of muscovite and biotite from biotite-kyanite-sillimanite gneiss and garnet-biotite gneiss yields age of 486 ± 9 Ma and 459 ± 9 Ma respectively. We have estimated regional crustal thicknesses in NE Madagascar using a flexural inversion technique, which indicates the presence of an anomalously thick crust (c. 43 km) beneath the Antananarivo block. This result is consistent with the present concept that subduction beneath the Antananarivo block resulted in a more competent and thicker crust. The textural data, thermodynamic model, and geophysical evidence together provide a new insight to the subduction history, crustal thickening and evolution of the high-pressure Andriamena complex and its link to the terminal

  14. Finding of corundum-bearing rocks in the Lapland granulite belt

    NASA Astrophysics Data System (ADS)

    Terekhov, E. N.; Shcherbakova, T. F.; Konilov, A. N.

    2016-09-01

    Corundum-bearing rocks are described for the first time in the Kandalaksha structure of the Lapland granulite belt. Corundum is confined to rocks of two types: metagabbro‒anorthosites constituting lenses among metaanarthosites of the Kandalaksha massif and basic granulites. Corundum crystals (up to 200 μm long) occur in plagioclase and garnet and differ from each other depending on the host mineral, which serves as evidence against their xenogenic nature. Some corundum crystals exhibit an axial zone, which may indicate their crystallization from the gaseous phase. Corundum-bearing rocks are accompanied by piclogites (pyroxene‒garnet varieties with olivine). Piclogites and their minerals (clinopyroxene, garnet) are characterized by a positive Eu anomaly, which implies rock reworking by fluids during corundum formation, when deep-seated complexes were subjected to exhumation.

  15. Magnetism of the lower crust: Observations from the Chipman Domain, Athabasca Granulite Terrain, northern Canada

    NASA Astrophysics Data System (ADS)

    Brown, Laurie L.; Webber, Jeffery; Williams, Michael; Regan, Sean; Seaman, Sheila

    2014-06-01

    Magnetic properties of lower crustal rocks produce anomalies seen in satellite, aeromagnetic, and ground studies, and are assumed to be responsible for observed long wave-length anomalies (LWA) of +/- 20 nT. The soon to be launched SWARM satellites will provide extensive data on the magnetization of the lower to middle crust. In anticipation of this event we are investigating magnetic properties in a superbly exposed section of lower crust in northern Saskatchewan. The Athabasca Granulite Terrain (AGT) is a complex region of felsic and mafic lower crustal rocks, part of the Snowbird Tectonic zone, stretching NE-SW across the Canadian Shield. The AGT is composed of a sequence of rocks identified as lower crustal in origin by their high pressure (> 1.0 GPa) and high temperature (~ 800 °C) metamorphism, dated at 2.6 Ga and 1.9 Ga, with uplift and exhumation at 1.85-1.80 Ga. The AGT is characterized by low (negative) aeromagnetic anomalies with distinct large positive anomalies in the southern and central regions. The Chipman Domain, on the east side, consists of tonalites, mafic granulites, and granite, intruded by the Chipman dike swarm at ~ 1.9 Ga, where anomalies cut across mapped lithologic boundaries. Susceptibility measurements from both field and lab readings range over several orders of magnitude, from 1 × 10- 5 to 3 × 10- 1 SI, with higher values related to both mafic granulite and some tonalite samples. Remanence values also show considerable variability, from 0.1 mA/m to 90 A/m, with the weakest magnetization found in the Chipman dikes and the Fehr granite. Forty samples out of 89 have Koenigsberger ratios greater than 1, but low initial remanence limits its influence on anomalies. Hysteresis and low temperature measurements identify magnetite as the predominant iron oxide. This section of lower crustal rocks has paramagnetic granites and dikes, with ferromagnetic mafic granulites and bimodal tonalites, defined by geographic location.

  16. Granulite facies lower crustal xenoliths from the Eifel, West Germany: petrological and geochemical aspects

    NASA Astrophysics Data System (ADS)

    Loock, G.; Stosch, H.-G.; Seck, H. A.

    1990-06-01

    Petrographic, petrological and geochemical data for 16 mafic meta-igneous, granulite facies lower crustal xenoliths from the East Eifel were collected in order to develop a model for the lower crustal history for this region. The xenoliths consist of plagioclase±amphibole±clinopyroxene±garnet±orthopyroxene±scapolite + opaque minerals±apatite±rutile±zircon. Garnet has reacted to a variable extent with plagioclase and clinopyroxene to form a corona of plagioclaseII+ amphibole + orthopyroxeneII. Pyroxenes and plagioclases show complex zoning patterns with regard to Al and Ca which can be interpreted in terms of P, T history. Decreasing temperature and pressure conditions are recorded by decreasing Al in clinopyroxene rims coexisting with increasing anorthite contents in plagioclase rims and the breakdown of garnet. In addition, a young heating event that affected the granulites to different degrees is inferred from the complementary Ca-zoning patterns in clino- and orthopyroxenes. Rare earth element (REE) patterns of whole rocks together with the trends displayed and fractionated liquids. REE analyses of the mineral separates display equilibrium partitioning patterns for amphibole and clinopyroxene, although isotopic data show that amphibole contains externally-derived Sr and Nd components not recognized in other minerals. At least a 4-stage history for the granulites is recorded: (1) intrusion and crystal fractionation of basaltic magmas in the lower crust, probably accompanied by crustal assimilation, (2) granulite facies metamorphism, (3) a decrease in temperature and pressure, and (4) a later heating event. The complicated thermal history is reflected in Sm-Nd mineral isochron ages which range from about 170 Ma down to about 100 Ma and cannot be assigned to distinct geological events. These ages correlate with inferred temperatures; the low ages are measured for xenoliths with the highest temperatures. In some cases the young heating event is likely to be

  17. Crustal structure and tectonics of the northern part of the Southern Granulite Terrane, India

    USGS Publications Warehouse

    Rao, V.V.; Sain, K.; Reddy, P.R.; Mooney, W.D.

    2006-01-01

    Deep seismic reflection studies investigating the exposed Archean lower continental crust of the Southern Granulite Terrane, India, yield important constraints on the nature and evolution of the deep crust, including the formation and exhumation of granulites. Seismic reflection images along the Kuppam-Bhavani profile reveal a band of reflections that dip southward from 10.5 to 15.0??s two-way-time (TWT), across a distance of 50??km. The bottom of these reflections beneath the Dharwar craton is interpreted as the Moho. Further south, another reflection band dipping northward is observed. These bands of reflectivity constitute a divergent reflection fabric that converges at the Moho boundary observed at the Mettur shear zone. Reflection fabrics that intersect at a steep angle are interpreted as a collisional signature due to the convergence of crustal blocks, which we infer resulted in crustal thickening and the formation of granulites. Anomalous gravity and magnetic signatures are also observed across the Mettur shear zone. The gravity model derived from the Bouguer gravity data corroborates seismic results. The tectonic regime and seismic reflection profiles are combined in a 3-D representation that illustrates our evidence for paleo-subduction at a collision zone. The structural dissimilarities and geophysical anomalies suggest that the Mettur shear zone is a suture between the Dharwar craton in the north and another crustal block in the south. This study contributes significantly to our understanding of the operation of Archean plate tectonics, here inferred to involve collision and subduction. Furthermore, it provides an important link between the Gondwanaland and global granulite evolution occurring throughout the late Archean. ?? 2006 Elsevier B.V. All rights reserved.

  18. Upper Pleistocene Gulo gulo (Linne, 1758) remains from the Srbsko Chlum-Komin Hyena den cave in the Bohemian Karst, Czech Republic, with comparisons to contemporary wolverines

    Treesearch

    Cajus G. Diedrich; Jeffrey P. Copeland

    2010-01-01

    Wolverine bone material is described from the famous Upper Pleistocene cave Srbsko Chlum-Komin in the Bohemian Karst, Czech Republic, along with an overview of recently known Czech sites. The Gulo gulo Linne material was found in one of the largest Ice Age spotted-hyena dens in Europe. As a result of non-systematic excavations, the taphonomy is partly unclear. Lower-...

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  20. Decompressional P-T history in sapphirine-bearing granulites from Kodaikanal, southern India

    NASA Astrophysics Data System (ADS)

    Mohan, A.; Prakash, D.; Motoyoshi, Y.

    The sapphirine-bearing granulites exposed around the Kodaikanal region of the Madurai block, southern India, present a variety of mineral parageneses involving garnet, spinel, sillimanite, cordierite, orthopyroxene, phlogopite, potash feldspar and plagioclase. interpretation of multiphase reaction textures in conjunction with mineral chemical data and topology in the (FM)AS system is consistent with the main sapphirine-forming reactions: orthopyroxene + sillimanite = sapphirine + cordierite phlogopite + sillimanite = sapphirine + cordierite + K-feldspar + vapour Mg-tschermak = sapphirine + cordierite. The P-T evolution of these sapphirine granulites has been constrained through the use of conventional geothermobarometry, internally consistent TWEEQU programme and thermodynamically calibrated MAS equilibria. The P-T estimates define a retrograde trajectory with substantial decompression of c.4 kbar from P-Tmax of c.8 kbar at c.800°C. On the basis of the available evidence for a Pan-African granulite-facies event in the Madurai and Trivandrum blocks, the emerging concept of East Gondwana assembly is endorsed.

  1. Terrasar-X Insar Processing in Northern Bohemian Coal Basin Using Corner Reflectors (preliminary Results)

    NASA Astrophysics Data System (ADS)

    Hlaváčová, I.; Halounová, L.; Svobodová, K.

    2012-07-01

    The area of Northern Bohemian coal basin is rich in brown coal. Part of it is undermined, but large areas were mined using open-pit mines. There are numerous reclaimed waste dumps here, with a horse racetrack, roads and in some cases also houses. However, on most of the waste dumps, there are forests, meadows and fields. Above the coal basin, there are the Ore mountains which are suspected to be sliding down to the open mines below them. We installed 11 corner reflectors in the area and monitor them using the TerraSAR-X satellite. One of the reflectors is situated in the area of radar layover, therefore it cannot be processed. We present preliminary results of monitoring the remaining corner reflectors, with the use of 7 TerraSAR-X scenes acquired between June and December 2011. We process whole scene crops, as well as the artificial reflector information alone. Our scene set contains interferometric pairs with perpendicular baselines reaching from 0 to 150 m. Such a configuration allows us to distinguish deformations from DEM errors, which are usual when the SRTM (Shuttle Radar Topography Mission) DEM (X-band) is used for Stripmap data. Unfortunately, most of the area of interest is decorrelated due to vegetation that covers both the Ore mountains and the reclaimed waste dumps. We had to enlarge the scene crop in order to be able to distinguish deformations from the atmospheric delay. We are still not certain about the stability of some regions. For the installed artificial reflectors, the expected deformations are in the order of mm/year. Generally, deformations in the area of interest may reach up to about 5 cm/year for the Ervěnice corridor (a road and railway built on a waste dump). When processing artificial corner reflector information alone, we check triangular sums and perform the processing for all possible point combinations - and that allows us to correct for some unwrapping errors. However, the problem is highly ambiguous.

  2. Rehydration reactions and microstructure development in lower crustal granulites from the Bergen Arcs, Norway

    NASA Astrophysics Data System (ADS)

    Erickson, Timmons; Reddy, Steven; Clark, Chris; Hand, Martin; Bhowany, Kamini; Prent, Alex

    2017-04-01

    An investigation of the feedbacks generated between lower crust-derived fluids and deformation microstructures formed within retrogressed granulites from the Bergen Arcs on the west coast of Norway will be presented. We hope to assess the role of deformation microstructures in assisting fluid infiltration into nominally impermeable lower crustal rocks, the role of fluids in driving mineral reactions and thus weakening the rock strength, and the interplay between these mechanisms. Granulite wall-rock adjacent to an amphibolite facies shear zone near Isdal, Norway has been sectioned, texturally mapped using electron backscatter diffraction (EBSD) and chemically mapped using energy dispersive x-ray spectrometry (EDS). The granuilte protolith is made up of a Precambrian anorthosite - gabbro assemblage of plagioclase and coronas of garnet around clinopyroxene. Local alteration of the granulite to eclogite and amphibolite occurred during the Caledonian orogen and has been attributed to the infiltration of fluids during the high strain event (Mukai et al., 2014). In thin section a thin ( 75 µm) rim of pargasite amphibole can be seen between the garnet and plagioclase, while the rim of amphibole is thicker (600 µm) when between the clinopyroxene and plagioclase. Plagioclase is coarse grained (mms in diameter) and displays prominent growth twins within the undeformed regions of the granulite. However, within a sheared domain of the granulite the grain size has been significantly reduced (max diameter = 74 µm) as has the growth twinning. The plagioclase from the sheared domain also displays a crystallographic preferred orientation (CPO) which does not appear to be inherited from the 'parent' grains. Within the strained domain there is also an increase in the reaction of garnet to pargasite, which also displays a strong CPO. These textural relationships offer the opportunity to study the active mechanisms during hydration of the lower crust and evaluate the relationships

  3. UHT granulite-facies metamorphism in Rogaland, S Norway, is polyphase in nature

    NASA Astrophysics Data System (ADS)

    Laurent, Antonin; Duchene, Stéphanie; Bingen, Bernard; Seydoux-Guillaume, Anne-Magali; Bosse, Valérie

    2016-04-01

    Propensity of metamorphic assemblages to remain metastable after melt extraction complicates singularly the petrologist's task to discriminate between a single granulite-facies P-T path and a polyphase one. Using an integrated petrological and in-situ geochronological approach in key rock-samples, we reconstruct the pressure-temperature-time path of Sveconorwegian metamorphism across a 30 km-wide metamorphic gradient ranging from upper amphibolite facies to ultra-high temperature (UHT) granulite-facies in Rogaland, S. Norway. Thermodynamic modelling of phase equilibria in the Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-Ti2O-O2 chemical system (PerpleX code) are carried out with an emphasis on moderately oxidized, spinel-bearing assemblages resulting from either garnet or sapphirine breakdown. Geochronological U-(Th)-Pb data acquired on both monazite (LA-ICP-MS) and zircon (SIMS) are complemented by minor- and trace-elements signatures of both minerals, to monitor REE distribution through time and to evaluate garnet apparition or demise. Coupling field, petrological and geochronological data lead to a polyphase metamorphic history, lasting about 100 My. The onset of regional granulite facies metamorphism at 1035 Ma is associated with the emplacement of large volumes of granitic magmas in the amphibolite to granulite facies transition zone. In the deeper part of the crustal section, localized sapphirine-bearing restitic lithologies testify to UHT temperatures (900-920 °C). These conditions were reached at ca. 1010 Ma following a tight clockwise P-T path associated with minor exhumation (7 to 5.5 kbar) and subsequent cooling to 700 °C. A distinct thermal episode, initiated at ca. 950 Ma, reached UHT granulite-facies conditions with the intrusion of massif-type anorthosite plutons at ca. 930 Ma producing a 5-km wide aureole. The aureole is delimited by the presence of osumilite in high Fe-Al rocks yielding quantitative estimates of 900-950 °C at a maximum pressure of 5 kbar

  4. Amphibolite to granulite progressive metamorphism in the Niquelândia Complex, Central Brazil: regional tectonic implications

    NASA Astrophysics Data System (ADS)

    Filho, C. F. Ferreira; De Moraes, R.; Fawcett, J. J.; Naldrett, A. J.

    1998-01-01

    The Niquelândia Complex is a major Proterozoic mafic and ultramafic layered intrusion in central Brazil. Ductile deformation and associated metamorphic recrystallization are widespread along ductile shear zones. Bands of alumina and silica-rich rocks (less than few meters thick) occur in the central parts of these ductile shear zones. Metamorphic grade, ranging from amphibolite to granulite facies, increases progressively downward in the layered intrusion stratigraphy. The three mapped metamorphic zones: amphibolite zone, amphibolite-granulite transition zone and granulite zone, are parallel to the intrusion stratigraphy. Metabasites show progressive changes in mineral assemblages, texture, and Ca-amphibole composition in a traverse covering the three metamorphic zones. With increasing metamorphic grade, amphibolites (hbl+pl ± cpx ± grt ± ep) give way to hornblende granulites (hbl+pl+cpx+opx) and anhydrous mafic granulites (pl+cpx+opx). The Ti, A1 IV and Na+K content of amphiboles increase progressively with metamorphic grade. Quartz-rich rocks have kyanite as the Al 2SiO 5 polymorph in the amphibolite zone, whereas sillimanite occurs in the granulite zone. Geothermobarometry and mineral stability data indicate P-T conditions of peak metamorphism at about 700 °C and 6-8 kbars in the amphibolite zone and temperatures higher than 800 °C in the granulite zone. In quartz-rich rocks of the granulite zone, retrogressive processes are indicated by reaction coronas of sil+grt between peak metamorphic assemblages of hc+qtz and replacement of sillimanite by kyanite. These reactions have an appreciable temperature dependence and together they indicate a retrogressive path characterized by an initial period of nearly isobaric cooling. Previously reported U-Pb zircon dating demonstrates the coeval nature of the amphibolite and granulite facies metamorphism and supports the notion that the entire terrain represents a single continuous crustal section. The metamorphic age

  5. Pyroxenite and granulite xenoliths from beneath the Scottish Northern Highlands Terrane: evidence for lower-crust/upper-mantle relationships

    NASA Astrophysics Data System (ADS)

    Upton, B. G. J.; Aspen, P.; Hinton, R. W.

    2001-08-01

    Xenolith suites from Permian host rocks in Orkney and the extreme NE of the Scottish mainland (Duncansby Ness) are described and compared to those from elsewhere in the Northern Highlands Terrane. Those from the Tingwall dyke, Orkney, comprise roughly equal proportions of ultramafic rocks (wehrlites, clinopyroxenites, websterites, hornblendites) and mafic to felsic rocks (gabbroic, noritic and dioritic granulites, with subordinate tonalites and trondhjemites). Those from Duncansby (45 km to the south) are dominantly olivine-poor ultramafic rocks (clinopyroxenites, pargasite pyroxenites, biotite-pyroxenites), together with granulites grading from gabbroic through to tonalites and trondhjemites. Most of the granulites are meta-igneous, comprising plagioclase and one- or two-pyroxene species with equilibration temperatures of 810-710 °C, and are regarded as samples of the lower crust. Absence of garnet and olivine, together with the association of relatively sodic plagioclase and aluminous pyroxenes, is consistent with derivation from depths corresponding to 5-10 kbar. Positive Eu anomalies in the granulites imply that most originated as plagioclase-rich cumulates from basaltic magmas. Scarce peraluminous quartzo-feldspathic xenoliths, such as a garnet-sillimanite-bearing sample from Duncansby, are regarded as metasedimentary in origin. Pyroxenes (and biotites) in the ultramafic xenoliths tend to have higher mg numbers than those of the granulites, reflecting higher temperatures of formation. Whereas the pyroxene-rich ultramafic rocks may be partly interleaved with the granulites in the lower crust, it is concluded that they also constitute a zone of substantial thickness at or around Moho level, separating the granulites from underlying peridotites, and that they originated as cumulates cognate to the granulites. They have, however, been variably metasomatised with formation of amphibole. This zone may constitute a density trap at which melt fractions, rich in K, Fe

  6. Thermal evolution of the north-Pyrenean granulitic crust: a combined petrological, geochronological and thermal study of the Saint-Barthelemy Massif

    NASA Astrophysics Data System (ADS)

    Lemirre, Baptiste; Duchene, Stephanie; Gerbault, Muriel; de Saint Blanquat, Michel; Poujol, Marc

    2017-04-01

    The Variscan orogeny is the result of an oceanic subduction followed by a continental collision that ended with a late-collisional high temperature - low pressure event at the scale of the whole orogen. The singularity of the Pyrenean segment is the predominance of this late high temperature event which is characterized by an intense deformation synchronous with the high temperature metamorphism and an abundant and varied magmatism. The aim of this study is to determine pressure-temperature-time trajectories in the Saint Barthelemy Massif, and to discuss the origin of the geothermal gradients. The Saint Barthelemy Massif is one of the granulitic north-Pyrenean massifs constituting the deepest relics of the Variscan crust. It is composed of two main units separated by a low angle detachment. The upper unit is composed of Paleozoic metasediments, micaschists, migmatites and small plutonic bodies and represents the Variscan upper crust. The basal unit, made of granulitic to amphibolitic gneisses, corresponds to the intermediate to lower crust. Pressure-temperature-time data indicate a homogeneous temperature of 800 °C at a depth between 10 and 20 km around 300 Ma (U-Pb dating on zircons and monazites from granulites and migmatites). This temperature of 800 °C corresponds to the dehydration melting of biotite as constrained by thermodynamic modelling. In the upper part of the crust, we observe a maximal gradient higher than 80 °C/km above 10 km depth. This high temperature metamorphic event, characteristic of the north-Pyrenean massifs, followed a magmatic episode at ca. 305 Ma in the whole Variscan Pyrenees. The magmatic-metamorphic succession, as well as the absence of significant crustal thickening in the Pyrenean segment of the Variscan belt, suggests a mantellic origin for the late-Variscan thermal anomaly. A one-dimensional thermal model of the crust is used to investigate the effect of buffering by latent heat of fusion and the effect of advection of melts in

  7. Soil Collembola communities within Plešné Lake and Čertovo Lake catchments, the Bohemian Forest

    NASA Astrophysics Data System (ADS)

    Čuchta, Peter

    2016-04-01

    The soil Collembola communities were studied for three years in disturbed spruce forest stands in the catchments areas of Čertovo and Plešné Lakes in the Bohemian Forest, Czech Republic. The study was focused on the impact of the windthrow, bark beetle outbreak damage and consecutive changes in the forest stands including soil environment. Four different treatments were selected for the study on both study areas: undamaged (control) forest stands, "dead" forest stands damaged by bark beetle, slightly managed windthrown forest stands left for the natural succession, and freshly harvested windthrown stands. After two years of research a total of 7,294 Collembola specimens were recorded belonging to 93 species. We recorded the highest collembolan abundance and species richness in the reference stands within catchments of both lakes, while both given parameters were considerably lower in harmed forest stands. To summarize, the disturbance led to a general decrease of Collembola communities.

  8. Cross-border radon index map 1:100 000 Lausitz - Jizera - Karkonosze - Region (northern part of the Bohemian Massif).

    PubMed

    Barnet, Ivan; Pacherová, Petra; Preusse, Werner; Stec, Bartosz

    2010-10-01

    The first cross-border map describing the radon (Rn) risk from bedrock was assembled in the northern part of the Bohemian Massif at a scale 1:100 000. The map covers the area of Lausitz (Germany), Karkonosze (Czech Republic and Poland) and Jizera (Czech Republic). The map is based on 818 measurements of soil gas Rn in rock types of Precambrian to Mesozoic age with variable geology. Geographic information system (GIS) processing enabled a good coincidence of soil gas Rn concentrations between data from all three countries in lithologically adjacent rock types as well as the direct correlation to georeferenced indoor Rn values, which was tested using the Czech indoor Rn data. The method of data processing can contribute to assembling the European Geogenic Radon Map.

  9. Two species of Selaginella cones and their spores from the Bohemian Carboniferous continental basins of the Czech Republic.

    PubMed

    Bek, J; Oplustil, S; Drábková, J

    2001-03-01

    Two species of Selaginella cones from the Bohemian Upper Carboniferous continental basins of the Bolsovian and Westphalian D age are described, together with their in situ spores. Two specimens of Selaginella gutbierii yielded microspores closely comparable with the dispersed species Cirratriradites saturnii and megaspores closely comparable with the dispersed species Triangulatisporites vermiculatus. Microspores closely comparable with the dispersed species Cirratriradites annulatus and megaspores resemble the dispersed species Triangulatisporites tertius were isolated from cones of Selaginella cf. leptostachys. All the spores isolated from one cone are of the same type and would be referred to one dispersed micro- and megaspore species if found as Sporae dispersae. The paper contains a review of all palynologically studied Carboniferous Selaginella and Selaginella-like cones and reviews of all in situ and dispersed Cirratriradites and Triangulatisporites spores.

  10. [The occurrence of O-antigens of Escheria coli strains in calves suffering from diarrhea in the Eastern Bohemian Region].

    PubMed

    Svastová, A

    1980-06-01

    Coli infections in calves belong to the most serious diseases occurring in the early post-natal period and causing considerable losses to large cattle stocks. The calves affected by diarrhoea were studied as to the serological typification of E. coli. The total number of the calves examined was 1182. The examination yielded 2112 isolated strains. Twelve antisera made it possible to identify 569 strains, i. e. 26.94 %. O-antigens were found to occur with the following descending frequency: 015, 0139, 0117, 0141, 08, 0149, 09, 0101, 02, 0147, 078, and 0115. Although it is obvious that enteropathogenic strains of E. coli were not responsible for all cases of diarrhoea in the examined calves, the total set of animals was large enough to show which O-antigens could be involved in the diarrhoea in the calves kept on large cattle farms in the East Bohemian region.

  11. Evaluation of Water Use Efficiency of Short Rotation Poplar Coppice at Bohemian-Moravian Highlands

    NASA Astrophysics Data System (ADS)

    Hlaváčová, Marcela; Fischer, Milan; Mani Tripathi, Abhishek; Orság, Matěj; Trnka, Miroslav

    2015-04-01

    The water availability of the locality constitutes one of the main constraint for short rotation coppices grown on arable land. As a convenient characteristic assessing how the water use is coupled with the biomass yields, so called water use efficiency (WUE) is proposed. One method of water use efficiency determination is presented within this study. The study was carried out at short rotation poplar coppice (poplar clone J-105) at the Test Station Domanínek, Ltd. at Bohemian-Moravian Highlands during the growing season 2013. Diameters at breast height (DBH) were measured for 16 sample trees where sap flow measuring systems (Granier's Thermal Dissipation Probe, TDP) were installed. TDP outputs are expressed as temperature differences (ΔT) between the heated and non-heated probes. Estimation of sap flux density (Fd) by the Granier method relies on the measurement of temperature difference (ΔT). Determination of maximum temperature difference (ΔTmax) is fundamental for sap flux density (Fd) calculation. Although ΔTmax can be theoretically defined as ΔT at Fd = 0, many factors may prevent the occurrence of the zero flow state, such as night-time water movement for new growth (vegetative or reproductive) or water loss from the canopy due to high vapour pressure deficit (VPD). Therefore, the VPD condition was established for determination of ΔTmax. VPD condition was established as follows: VPD reaching values 0.2 at least 6 hours during night (from 21 p. m. to 3 a. m. and when the condition was fullfilled, the value at 3 a. m. was taken) because it is a supposed time after that the tree has no transpiration. The programmable part of Mini 32 software (www.emsbrno.cz) was used for application of the script establishing ΔTmax values under this VPD condition. Nevertheless, another script was applied on ΔT data set to determination of ΔTmax values for every night at 3 a. m. (as this is when ΔT should be at its daily maximum) without VPD condition restriction for

  12. Lunar highland meteorite Dhofar 026 and Apollo sample 15418: Two strongly shocked, partially melted, granulitic breccias

    USGS Publications Warehouse

    Cohen, B. A.; James, O.B.; Taylor, L.A.; Nazarov, M.A.; Barsukova, L.D.

    2004-01-01

    Studies of lunar meteorite Dhofar 026, and comparison to Apollo sample 15418, indicate that Dhofar 026 is a strongly shocked granulitic breccia (or a fragmental breccia consisting almost entirely of granulitic breccia clasts) that experienced considerable post-shock heating, probably as a result of diffusion of heat into the rock from an external, hotter source. The shock converted plagioclase to maskelynite, indicating that the shock pressure was between 30 and 45 GPa. The post-shock heating raised the rock's temperature to about 1200 ??C; as a result, the maskelynite devitrified, and extensive partial melting took place. The melting was concentrated in pyroxene-rich areas; all pyroxene melted. As the rock cooled, the partial melts crystallized with fine-grained, subophitic-poikilitic textures. Sample 15418 is a strongly shocked granulitic breccia that had a similar history, but evidence for this history is better preserved than in Dhofar 026. The fact that Dhofar 026 was previously interpreted as an impact melt breccia underscores the importance of detailed petrographic study in interpretation of lunar rocks that have complex textures. The name "impact melt" has, in past studies, been applied only to rocks in which the melt fraction formed by shock-induced total fusion. Recently, however, this name has also been applied to rocks containing melt formed by heating of the rocks by conductive heat transfer, assuming that impact is the ultimate source of the heat. We urge that the name "impact melt" be restricted to rocks in which the bulk of the melt formed by shock-induced fusion to avoid confusion engendered by applying the same name to rocks melted by different processes. ?? Meteoritical Society, 2004.

  13. Metamorphic history of LP/HT migmatites from the Bavarian Unit (Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Sorger, Dominik; Hauzenberger, Christoph; Linner, Manfred; Iglseder, Christoph

    2016-04-01

    Granulite facies migmatites are commonly observed in the Bavarian Unit which were formed during a late Variscan (post 330 Ma) LP-HT overprint. This event is related to a delamination of mantle lithosphere and subsequent asthenospheric upwelling. Most of these rocks underwent high degrees of melting forming meta- and diatexites. Former work in the Sauwald area, Upper Austria, by Tropper et al. (2006) determined metamorphic conditions of 700-800°C and 0.4-0.5 Gpa. In this study samples were taken along the (1) Danube valley (west of Linz), from the (2) Lichtenberg area (north of Linz), the (3) Bad Leonfelden area (west of the Rodl Fault) and the (4) Sauwald area (south of the river Danube). Biotite and plagioclase bearing migmatite is very common and occurs all over the investigated area. These rocks are the product of intensive melting (anatexite) and formed at conditions of ~650-700°C and 0.25-0.45 Gpa. Scarce outcrops of garnet bearing Al-rich migmatitic metapelites occur along the Danube valley. The formation of the migmatitc texture with well-developed leucosomes (K-feldspar, plagioclase, quartz) and melanosomes (garnet, cordierite, sillimanite, spinel, ilmenite, ± biotite) indicate high temperature metamorphism. Most of the garnet grains show a homogenous iron-rich composition and form generally an almandine-pyrope (Xalm=0.78-0.80, Xprp=0.16-0.18) solid solution with minor contents of grossular and spessartine (Xgrs=0.028-0.032, Xsps=0.020-0.024). Large garnet porphyroblasts (up to 1cm in size) display a distinct chemical zoning, especially in grossular component. Elevated homogeneous grossular content in the core is followed discontinously by low grossular content at the rim indicating a two stage growth. Garnet core and rim also display different mineral inclusions. Thermobarometric calculations using garnet core compositions with inclusions and garnet rim compositions with matrix phases as well as pseudosection calculations allow the reconstruction of a P

  14. 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

  15. The petrology and geochemistry of impact melts, granulites, and hornfelses from consortium breccia 61175

    NASA Technical Reports Server (NTRS)

    Winzer, S. R.; Meyerhoff, M.; Nava, D. F.; Schuhmann, S.; Philpotts, J. A.; Lindstrom, D. J.; Lum, R. K. L.; Lindstrom, M. M.; Schuhmann, P.

    1977-01-01

    The matrix and 58 clasts from breccia 61175 were analyzed for major, minor, and trace elements. The matrix is anorthositic and has lithophile trace element abundances 20 to 40 times chondrite. Clasts comprise impact melt rocks, xenocryst and xenolith-free very high aluminum (VHA) and anorthositic basalts, anorthosite, anorthosite-norite-troctolite granulites, and hornfelses. The VHA and anorthositic basalts are considered to be impact melts, and the hornfelses were probably formed by incorporation of breccias or preexisting melt rocks into a melt sheet prior to cooling. The range of melt-rock lithophile trace element abundances might indicate more than one melt sheet.

  16. An occurrence of metastable cristobalite in high-pressure garnet Granulite

    USGS Publications Warehouse

    Darling, R.S.; Chou, I.-Ming; Bodnar, R.J.

    1997-01-01

    High-pressure (0.8 gigapascals) granulite facies garnet from Gore Mountain, New York, hosts multiple solid inclusions containing the low- pressure silica polymorph cristobalite along with albite and minor ilmenite. Identification of cristobalite is based on Raman spectra, electron microprobe analysis, and microthermometric measurements on the ??/?? phase transformation. The cristobalite plus albite inclusions may have originated as small, trapped samples of hydrous sodium-aluminum-siliceous melt. Diffusive loss of water from these inclusions under isothermal, isochoric conditions may have resulted in a large enough internal pressure decrease to promote the metastable crystallization of cristobalite.

  17. Pan-African granulite facies rocks from SE-Kenya and Tanzania: a petrological overview

    NASA Astrophysics Data System (ADS)

    Hauzenberger, C. A.; Bauernhofer, A.; Sommer, H.; Tenczer, V.; Loizenbauer, J.; Hoinkes, G.; Wallbrecher, E.; Muhongo, S.

    2003-04-01

    The Mozambique belt (MB) in East Africa is a mainly NNW-SSE trending mountain range that consists predominantly of high-grade metamorphic rocks. To the west it is bordered by the Usagaran/Ubendian mountain belt and the Archaean Tanzania craton, to the east by Neogene sediments. Pan-African granulite facies rocks have been reported from the (1) Tsavo Nationalpark and Taita Hills (SE-Kenya); (2) the Usambara-Pare Mountains and the Wami River area (N-Tanzania); and (3) the Uluguru, Mahenge, Rubeho, Kiboriani, and Nguru Mountains (Central - Tanzania). (1) The most common mineral assemblage consists of migmatic Am-Bt-Fsp-Qtz+/-Grt+/-Cpx+/-Scp orthogneisses with intercalated bands of amphibolites, metasedimentary rocks (marbles, calcsilicates (Cpx-Grt-Am-Pl-Cc+/-Wo), and metapelites (Grt-Bt-Ky-Sil-Fsp-Qtz-Rt)), and ultramafic lenses. In the Tsavo Park, Sil is the only Al2SiO5 polymorph, whereas Ky, which is replaced subsequently by prismatic sillimanite and fibrolite, is observed in the Taita Hills. Peak PT estimates for the Tsavo Park area are 780°C-820°C and 0.8-0.9 GPa; in the Taita Hills 770-830°C and 1.0-1.2 GPa. (2) Orthogneisses and meta-tonalites/enderbites comprising the mineral assemblage Grt-Cpx-Opx-Am-Pl-Qtz are predominant in N-Tanzania. Some metapelitic intercalations show similar mineral assemblages and textures as observed in SE-Kenya. Small lenses of meta-anorthosites and ultramafic rocks are found in the Usambara-Pare Mountains. PT calculations yield 770-850°C and 1.0-1.2 GPa. (3) The Central-Tanzanian area consists of migmatic Bt-Fsp-Qtz+/-Grt bearing paragneisses with intercalations of metasediments (metapelites (Grt-Bt-Ky-Fsp-Qtz), calcsilicates, marbles), amphibolites, Grt-Cpx-Am-Pl-Qtz+/-Opx bearing meta-tonalites/enderbites, and meta-anorthosites. PT estimates vary from 770 to 830°C, pressures from 1.0-1.3 GPa. PT conditions of granulite facies rocks in SW-Kenya and Tanzania show surprisingly very uniform PT conditions of 770 to 850°C and 1

  18. The petrology and geochemistry of impact melts, granulites, and hornfelses from consortium breccia 61175

    NASA Technical Reports Server (NTRS)

    Winzer, S. R.; Meyerhoff, M.; Nava, D. F.; Schuhmann, S.; Philpotts, J. A.; Lindstrom, D. J.; Lum, R. K. L.; Lindstrom, M. M.; Schuhmann, P.

    1977-01-01

    The matrix and 58 clasts from breccia 61175 were analyzed for major, minor, and trace elements. The matrix is anorthositic and has lithophile trace element abundances 20 to 40 times chondrite. Clasts comprise impact melt rocks, xenocryst and xenolith-free very high aluminum (VHA) and anorthositic basalts, anorthosite, anorthosite-norite-troctolite granulites, and hornfelses. The VHA and anorthositic basalts are considered to be impact melts, and the hornfelses were probably formed by incorporation of breccias or preexisting melt rocks into a melt sheet prior to cooling. The range of melt-rock lithophile trace element abundances might indicate more than one melt sheet.

  19. Garnet granulite xenoliths from the Northern Baltic shield- The underplated lower crust of a palaeoproterozoic large igneous province

    USGS Publications Warehouse

    Kempton, P.D.; Downes, H.; Neymark, L.A.; Wartho, J.A.; Zartman, R.E.; Sharkov, E.V.

    2001-01-01

    Garnet granulite facies xenoliths hosted in Devonian lamprophyres from the Kola Peninsula are interpreted to represent the high-grade metamorphic equivalents of continental flood tholeiites, emplaced into the Baltic Shield Archaean lower crust in early Proterozoic time. Geochronological data and similarities in major and trace element geochemistry suggest that the xenoliths formed during the same plume-related magmatic event that created a widespread Palaeoproterozoic large igneous province (LIP) at 2.4-2.5 Ga. They are, thus, the first samples of the lower crust of a Palaeo-proterozoic LIP to be studied in petrological detail. The suite includes mafic granulites (gar + cpx + rutile ?? plag ?? opx ?? phlog ?? amph), felsic granulites (plag + gar + cpx + rutile ?? qtz ?? Kspar ?? phlog ?? amph) and pyroxenites (?? phlog ?? amph), but mafic garnet granulites predominate. Although some samples are restites, there is no evidence for a predominance of magmatic cumulates, as is common for Phanerozoic lower-crustal xenolith suites. Metasediments are also absent. Phlogopite and/or amphibole occur in xenoliths of all types and are interpreted to be metasomatic in origin. The K-rich metasomatic event occurred at ?????0 Ga, and led to substantial enrichment in Rb, K, LREE/HREE, Th/U, Th/Pb and, to a lesser extent, Nb and Ti. The fluids responsible for this metasomatism were probably derived from a second plume that arrived beneath the region at this time. Evidence for partial melting of mafic crust exists in the presence of migmatitic granulites. The timing of migmatization overlaps that of metasomatism, and it is suggested that migmatization was facilitated by the metasomatism. The metamorphism, metasomatism and migmatization recorded in the Kola granulite xenoliths may be representative of the processes responsible for converting Archaean LIP-generated proto-continents into continental crust.

  20. Inherent gravitational instability of thickened continental crust with regionally developed low- to medium-pressure granulite facies metamorphism

    NASA Astrophysics Data System (ADS)

    Gerya, Taras V.; Maresch, Walter V.; Willner, Arne P.; Van Reenen, Dirk D.; Smit, C. Andre

    2001-08-01

    Petrological arguments show that regionally developed low- to medium-pressure, high-temperature granulite facies metamorphism may critically enhance the lowering of crustal density with depth. This leads to gravitational instability of homogeneously thickened continental crust, mainly due to changes in mineral assemblages and the thermal expansion of minerals in conjunction with the exponential lowering of the effective viscosity of rocks with increasing temperature. It is argued that crustal processes of gravitational redistribution (crustal diapirism) contributing to the exhumation of granulite facies rocks may be activated in this way.

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

  2. From Gabbro to Granulite to Kyanite- and bimineralic Eclogite: A petrological, geochemical and mass balance approach to mantle eclogites

    NASA Astrophysics Data System (ADS)

    Sommer, H.; Jacob, D.

    2013-12-01

    In this study, we present the phase transition from gabbro into granulite and finally into kyanite- bearing and bimineralic eclogite. The investigated rock sample is a heterogeneous kyanite- bearing and bimineralic eclogite from the earth's mantle collected at the Roberts Victor Diamond mine in South Africa. Plagioclase of the former granulite reacted completely out under low H2O activity (fH2O) to form this kyanite- bearing and bimineralic eclogite. To quantify the phase transitions of the original gabbroic precursor, which was first metamorphosed under H-T granulite facies conditions followed by metamorphism under Earth's mantle conditions into both types of eclogite, a petrological, geochemical and a mass balance approach has been made. i) The results from our petrological approach show that Ca-rich garnet, which is coexistent with Ca-rich omphacite are the metastable phases from the original granulite in the kyanite-bearing relict while Mg-rich garnet, coexistent with Na-rich omphacite are the stable phases in the bimineralic eclogite part which shows equilibration conditions of ~5.5 Gpa and ~1200°C. ii) Our geochemical results show a positive Eu anomaly in garnet from the kyanite-bearing part, which indicates that the igneous precursor of the granulite was a gabbro, probably oceanic crust. Most of the rare earth elements show an excellent correlation with the major elements of the rock forming minerals during the plagioclase-out reaction of the former granulite. The LREE in garnet are removed during the formation of the bimineralic eclogite due to loss of the anorthite component in plagioclase of the former granulite. Contrary, the HREE are enriched in garnets in the bimineralic part of the eclogite compared to those in the kyanite zone, and correlate with the Mg-Ca exchange between both garnet generations. iii) The results from our mass balance approach indicate that garnet in bimineralic eclogite was formed by 0.925 mole of garnet and 0.075 mole of

  3. Lead isotopes and the origin of granulite and eclogite inclusions in deep-seated pipes

    USGS Publications Warehouse

    Lovering, J.F.; Tatsumoto, M.

    1968-01-01

    The isotopic composition of lead and the concentrations of lead, uranium, and thorium in Delegate basic pipes from Australia and in South African kimberlite pipes have been determined. The observed 238U/204Pb and observed 232Th/238U of eclogite inclusions in the pipes range from 2.9 to 18.7 and from 3.5 to 5.9, respectively. This result as well as the isotopic composition of lead suggests that the upper mantle is chemically heterogeneous with regard to the trace elements. Pyrochemically extracted leads from eclogite inclusions in the Delegate basic pipes and in a South African kimberlite pipe appear to be different in isotopic compositions from leads extracted from the host rock (matrix). These data are consistent with the hypothesis that the eclogitic inclusions in deep-seated pipes are of "accidental" origin and represent upper mantle materials caught up in the host materials during their intrusion. Lead extracted from a two-pyroxene granulite inclusion in one of the Delegate pipes has an isotopic composition indistinguishable from lead in the host rock. This observation is consistent either with a "cognate" origin for the granulite inclusion or with a modified "accidental" origin in which the isotopic composition of the original lead in the inclusion has been contaminated by lead from the host magma. Other evidence would indicate that an "accidental" origin be preferred. ?? 1968.

  4. Mantle heat flow and thermal structure of the northern block of Southern Granulite Terrain, India

    NASA Astrophysics Data System (ADS)

    Manglik, Ajay

    2006-07-01

    Continental shield regions are normally characterized by low-to-moderate mantle heat flow. Archaean Dharwar craton of the Indian continental shield also follows the similar global pattern. However, some recent studies have inferred significantly higher mantle heat flow for the Proterozoic northern block of Southern Granulite Terrain (SGT) in the immediate vicinity of the Dharwar craton by assuming that the radiogenic elements depleted exposed granulites constitute the 45-km-thick crust. In this study, we use four-layered model of the crustal structure revealed by integrated geophysical studies along a geo-transect in this region to estimate the mantle heat flow. The results indicate that: (i) the mantle heat flow of the northern block of SGT is 17 ± 2 mW/m 2, supporting the global pattern, and (ii) the lateral variability of 10-12 mW/m 2 in the surface heat flow within the block is of crustal origin. In terms of temperature, the Moho beneath the eastern Salem-Namakkal region appears to be at 80-100 °C higher temperature than that beneath the western Avinashi region.

  5. Pressure-temperature conditions in granulite facies rocks of the northern Canadian Shield, Arctic Canada

    SciTech Connect

    Frisch, T.

    1985-01-01

    The northernmost part of the Churchill Structural Province of the Canadian Shield, underlying 60,000 km/sup 2/ of southeastern Ellesmere Island, Coburg Island and eastern Devon Island, consists of granulite facies metasedimentary, meta-igneous and plutonic intrusive rocks 2400 to 1900 m.y. old. Garnet+pyroxene+plagioclase of quartzofeldspathic gneisses from Ellesmere and Coburg islands indicate pressures, at 750/sup 0/C, ranging from greater than or equal to 6 to approx. 4kb; the lower pressures are derived largely, but not solely, from rim compositions. Similar rocks from Devon Island consistently indicate higher pressures of 6 to 7 kb. Garnet and plagioclase cores in sillimanite+cordierite-rich pelitic gneisses give pressures between 5 and 6.5 kb at 750/sup 0/C, the highest pressures being found in Devon Island rocks. Orthopyroxene+cordierite symplectites around garnet in magnesian metapelites indicate pressures under 4 kb at 650/sup 0/C. All cordierite is clearly of retrograde origin, having formed as a result of decompression during uplift, but even the highest pressures determined fall below the stability limit of cordierite in metapelites. Circumstantial evidence exists for the former stable coexistence of orthopyroxene+sillimanite, which would attest to pressures well in excess of 7 kb, but existing geobarometric equilibria have been strongly influenced by retrograde processes. Retrograde pressure-temperature conditions may well predominate in many granulite terranes but are not always recognized due to a scarcity of suitable mineral assemblages.

  6. Crustal tomographic imaging and geodynamic implications toward south of Southern Granulite Terrain (SGT), India

    NASA Astrophysics Data System (ADS)

    Behera, Laxmidhar

    2011-09-01

    The crustal structure toward southern part of SGT is poorly defined leaving an opportunity to understand the tectonic and geodynamic evolution of this high-grade granulite terrain surrounded by major shear and tectonically disturbed zones like Achankovil Shear Zone (AKSZ) and Palghat Cauvery Shear Zone (PCSZ). To develop a geologically plausible crustal tectonic model depicting major structural elements, a comprehensive tomographic image was derived using deep-seismic-sounding data corroborated by Bouguer gravity modeling, coincident-reflection-seismic, heat-flow and available geological/geochronological informations along the N-S trending Vattalkundu-Kanyakumari geotransect. The final tectonic model represents large compositional changes of subsurface rocks accompanied by velocity heterogeneities with crustal thinning (44-36 km) and Moho upwarping from north to south. This study also reveals and successfully imaged anomalous zone of exhumation near AKSZ having transpression of exhumed rocks at mid-to-lower crustal level (20-30 km) with significant underplating and mantle upwelling forming a complex metamorphic province. The presence of shear zones with high-grade charnockite massifs in the upper-crust exposed in several places reveal large scale exhumation of granulites during the Pan-African rifting (~ 550 Ma) and provide important insights of plume-continental lithosphere interaction with reconstruction of the Gondwanaland.

  7. Cenozoic volcanism in the Bohemian Massif in the context of P- and S-velocity high-resolution teleseismic tomography of the upper mantle

    NASA Astrophysics Data System (ADS)

    Plomerová, Jaroslava; Munzarová, Helena; Vecsey, Luděk.; Kissling, Eduard; Achauer, Ulrich; Babuška, Vladislav

    2016-08-01

    New high-resolution tomographic models of P- and S-wave isotropic-velocity perturbations for the Bohemian upper mantle are estimated from carefully preprocessed travel-time residuals of teleseismic P, PKP and S waves recorded during the BOHEMA passive seismic experiment. The new data resolve anomalies with scale lengths 30-50 km. The models address whether a small mantle plume in the western Bohemian Massif is responsible for this geodynamically active region in central Europe, as expressed in recurrent earthquake swarms. Velocity-perturbations of the P- and S-wave models show similar features, though their resolutions are different. No model resolves a narrow subvertical low-velocity anomaly, which would validate the "baby-plume" concept. The new tomographic inferences complement previous studies of the upper mantle beneath the Bohemian Massif, in a broader context of the European Cenozoic Rift System (ECRIS) and of other Variscan Massifs in Europe. The low-velocity perturbations beneath the Eger Rift, observed in about 200km-broad zone, agree with shear-velocity models from full-waveform inversion, which also did not identify a mantle plume beneath the ECRIS. Boundaries between mantle domains of three tectonic units that comprise the region, determined from studies of seismic anisotropy, represent weak zones in the otherwise rigid continental mantle lithosphere. In the past, such zones could have channeled upwelling of hot mantle material, which on its way could have modified the mantle domain boundaries and locally thinned the lithosphere.

  8. Local stress distribution around garnet inclusions during hydration of granulite in the Bergen Arcs, Norway

    NASA Astrophysics Data System (ADS)

    Centrella, Stephen; Vrijmoed, Johannes C.; Putnis, Andrew; Austrheim, Håkon

    2017-04-01

    The importance of heterogeneous stress and pressure distribution within a rock has been established over the last decades (see review in Tajčmanová et al., 2015). During a hydration reaction, depending on whether the system is open to mass transfer, the volume changes of the reaction may be accommodated by removing material into the fluid phase that leaves the system (Centrella et al., 2015; Centrella et al., 2016). The magnitudes and the spatial distribution of stress and pressure that evolve during such processes is largely unknown. We present here a natural example where a granulite is hydrated at amphibolite facies conditions from the Bergen Arcs in Norway. Granulitic garnet is associated with kyanite and quartz on one side, and amphibole-biotite on the other side. The first couple replaces the plagioclase of the granulite matrix whereas the second replaces the garnet. We use electron probe microanalysis (EPMA) and X-ray mapping to investigate the spatial and possible temporal relationships between these two parageneses. Gresens' analysis has been used to determine the mass balance and the local volume changes associated with the two reactions. The reaction to kyanite+quartz induces a loss in volume compared to the original plagioclase whereas the second reaction amphibole+biotite gains volume compared to the original garnet. The specific mass evolution associated with both reactions suggests a local mass balance probably associated with a single hydration event. Using the methodology of Vrijmoed & Podladchikov (2015) we test whether the microstructure may be partly related to the local stress heterogeneity around the garnet inclusion. We evaluate the phase assemblage and distribution at chemical equilibrium under a given input pressure field that can be computed with the Thermolab software. By varying the input pressure field using the Finite Element Method and comparing the resulting equilibrium assemblage to the real data an estimate of the local stress

  9. Petrological Characterization of the Triassic Paleosurface in the Northern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Yao, Kouakou; Thiry, Medard; Szuszkiewicz, Adam; Turniak, Krzysztof

    2010-05-01

    ‘Albitization' is a widespread alteration process affecting sedimentary, igneous and metamorphic rocks. Albitized facies usually show a pinkish to red colour, depending on the degree of alteration. The main mineralogical process of this phenomenon is the pseudomorphic replacement of the primary Ca-Na plagioclases by secondary albite (Na). During this replacement biotite is often transformed to chlorite and inclusions of hematite, apatite, titanite, and calcite develop. So far, albitization has been systematically regarded as caused by magmatic derived hydrothermal brines, alkaline metasomatism reactions (Cathelineau, 1986; Petersson and Eliasson, 1997), or as a low grade metamorphic facies (Boles and Coombs, 1977). Recent studies in the Morvan Massif granites (Ricordel et al., 2007; Parcerisa et al., 2009) showed that the albitization there is related to the Triassic paleosurface. The decrease of this alteration with depth and its paleomagnetic age support the link of the albitization to the Triassic paleosurface. Furthermore, the petrographic data suggest the import of sodium by weathering solutions. The enrichement in Na+ of the fluids that triggered this alteration is probably linked to the Triassic salt deposits. Albitised pinkish facies have been recognized in the northern part of the Bohemian Massif (Polish Sudetes). Typical igneous and metamorphic rocks of the Klodzko area (southern Poland) are granites, granodiorites, schists, amphibolite, and gneisses, mostly of Paleozoic age. Three sites in the Klodzko area were sampled in detail from N to S: (1) Laski quarry, (2) Laski village, and (3) Chwalislaw. Here, the occurrence of the albitization is well developed and specific in its mineralogical paragenesis. Throughout the sample sites different albitization stages can be observed. The most albitized and therefore reddish facies can be found at the Laski village granite that consists of primary quartz and K-feldspar, biotite, and development of secondary

  10. Chemical Variation of Silicate Mineral Phases in Lunar Feldspathic Granulitic Impactites: Implications for Thermal Histories and Provenances

    NASA Technical Reports Server (NTRS)

    Fincke, E. M.; Ryder, G.

    2001-01-01

    We report on the internal variation and abundances of minor elements of silicate phases in lunar granulitic impactites to assess their thermal histories and the pre-metamorphic provenances of the minerals and the process that assembled the rocks. Additional information is contained in the original extended abstract.

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

    USGS Publications Warehouse

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

    2007-01-01

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

  12. Chemical Variation of Silicate Mineral Phases in Lunar Feldspathic Granulitic Impactites: Implications for Thermal Histories and Provenances

    NASA Technical Reports Server (NTRS)

    Fincke, E. M.; Ryder, G.

    2001-01-01

    We report on the internal variation and abundances of minor elements of silicate phases in lunar granulitic impactites to assess their thermal histories and the pre-metamorphic provenances of the minerals and the process that assembled the rocks. Additional information is contained in the original extended abstract.

  13. Open vs. closed-system behaviors in granitoid rocks during granulite-facies metamorphism: a case study from the Bulai Pluton (Central Limpopo Belt, South Africa)

    NASA Astrophysics Data System (ADS)

    Laurent, Oscar; Moyen, Jean-François; Martin, Hervé; Doucelance, Régis; Paquette, Jean-Louis

    2010-05-01

    close to the assumed age for this metamorphic overprint (~ 2000-2200 Ma), pointing to a partial resetting of the Sm-Nd system. On the other hand, there is no evidence for perturbation of bulk rock isotopic compositions, as a well-defined Sm-Nd external isochron established with 16 whole-rock data indicate an age of 2750 ± 200 Ma. Even imprecise, this age is consistent with new U-Pb LA-ICP-MS dating on separated zircons grains from 4 samples, which yielded concordant ages comprised between 2627 ± 18 Ma (granodiorite sample BUL-20 ; MSWD=0.7) and 2593 ± 17 Ma (monzodiorite dyke BUL-14 ; MSWD = 0.34), assumed to represent the timing of emplacement of the Bulai magmas. Moreover, zircons isotopic composition failed to prove any record of the ~ 2.0 Ga metamorphic event, indicating that they were affected by neither recrystallization, nor isotopic equilibration, and strongly supporting fluid-absent conditions. These results suggest that the main rock-forming minerals of the Bulai pluton underwent open-system equilibration associated with annealing during the granulite-facies overprint of the D3/M3 Paleoproterozoic event. Nevertheless, this thermal peak did not last long enough to generate large-scale and extensive chemical and isotopic equilibration, as evidenced by closed-system behavior for individual hand-samples and resistant minerals such as zircons. Consequently, the ~ 2.0 Ga regional granulitic event only led to discrete structural and chemical records within the Bulai pluton, which can be seen as a large refractory body compared with host rocks that accommodated most of the deformation and metamorphism. This conclusion has important implications for geochemical studies, since the whole-rock major-, trace-element and isotopic composition can be used to study the petrogenesis of such granitoids even if they underwent high-grade granulite-facies conditions.

  14. Palaeomagnetism and geochemistry of Early Palaeozoic rocks of the Barrandian (Teplé-Barrandian Unit, Bohemian Massif): palaeotectonic implications

    NASA Astrophysics Data System (ADS)

    Patočka, F.; Pruner, P.; Štorch, P.

    The Barrandian area (the Teplá-Barrandian unit, Bohemian Massif) provided palaeomagnetic results on Early Palaeozoic rocks and chemical data on siliciclastic sediments of both Middle Cambrian and Early Ordovician to Middle Devonian sedimentary sequences; an outcoming interpretation defined source areas of clastic material and palaeotectonic settings of the siliciclastic rock deposition. The siliciclastic rocks of the earliest Palaeozoic sedimentation cycle, deposited in the Cambrian Přı´bram-Jince Basin of the Barrandian, were derived from an early Cadomian volcanic island arc developed on Neoproterozoic oceanic lithosphere and accreted to a Cadomian active margin of northwestern Gondwana. Inversion of relief terminated the Cambrian sedimentation, and a successory Prague Basin subsided nearby since Tremadocian. Source area of the Ordovician and Early Silurian shallow-marine siliciclastic sediments corresponded to progressively dissected crust of continental arc/active continental margin type of Cadomian age. Since Late Ordovician onwards both synsedimentary within-plate basic volcanics and older sediments had been contributing in recognizable proportions to the siliciclastic rocks. The siliciclastic sedimentation was replaced by deposition of carbonate rocks throughout late Early Silurian to Early Devonian period of withdrawal of the Cadomian clastic material source. Above the carbonates an early Givetian flysch-like siliciclastic suite completed sedimentation in the Barrandian. In times between Middle Cambrian and Early/Middle Devonian boundary interval an extensional tectonic setting prevailed in the Teplá-Barrandian unit. The extensional regime was related to Early Palaeozoic large-scale fragmentation of the Cadomian belt of northwestern Gondwana and origin of Armorican microcontinent assemblage. The Teplá-Barrandian unit was also engaged in a peri-equatorially oriented drift of Armorican microcontinent assemblage throughout the Early Palaeozoic

  15. Late Cretaceous and Cenozoic dynamics of the Bohemian Massif inferred from the paleostress history of the Lusatian Fault Belt

    NASA Astrophysics Data System (ADS)

    Coubal, Miroslav; Málek, Jiří; Adamovič, Jiří; Štěpančíková, Petra

    2015-07-01

    An analysis of fault-slip data from the Lusatian Fault Belt, limiting the Lusatian Block of the Bohemian Massif in the SW, yielded parameters of eight successive paleostress patterns, Late Cretaceous to Plio-Pleistocene in age. These patterns were linked with specific stages in fault kinematics and fault-belt deformation. They include (1) α1, NE- to NNE-directed compression in a reverse fault regime (σ3 vertical) associated with major thrusting and drag zone formation in the latest Cretaceous, preceded by pre-drag origin of deformation bands α0; (2) αβ1-2, WNW-directed extension associated with emplacement of polzenite-group volcanics (≈80-61 Ma) and influx of hydrothermal fluids, overlapping in time with α1; (3) α2, N-directed compression in a reverse fault regime, probably Paleocene in age, associated with thrusting and intensive shear faulting in adjacent parts of blocks; (4) αβ3, Early Oligocene W- to WNW-directed extension in a regime of strike-slip faulting (σ2 vertical), probably connected with an emplacement of phonolitic magmas and influx of hydrothermal fluids; (5) α3, NNW-directed compression associated with activation of transverse/oblique faults of the fault belt, close in age to αβ3 with unclear mutual superposition; (6) β, Late Oligocene-Early Miocene multi-stage N- to NE-directed extension in a normal fault regime, specific to the Bohemian Massif, responsible for downfaulting of the hangingwall block; (7) γ, Mid to Late Miocene NE-directed compression in a reverse fault regime associated with thrusting; (8) δ, Pliocene (to Pleistocene?) NW- to NNW-directed compression in a strike-slip regime, associated with transverse faulting in the fault belt. The identified paleostress patterns show a good correlation with the hitherto identified paleostress fields transmitted to the Alpine foreland and refine the temporal sequence of paleostress states, especially in the post-Lower Miocene period.

  16. Granulite sulphides as tracers of lower crustal origin and evolution: An example from the Slave craton, Canada

    NASA Astrophysics Data System (ADS)

    Aulbach, Sonja; Krauss, Cristen; Creaser, Robert A.; Stachel, Thomas; Heaman, Larry M.; Matveev, Sergei; Chacko, Thomas

    2010-09-01

    We carried out a detailed study of sulphide minerals, a ubiquitous mineral group in lower crustal mafic to peraluminous granulite xenoliths from the Diavik kimberlites, to assess their use in constraining the origin and tectonothermal evolution of the deep crust, and to obtain additional data on the composition of lower crust beneath ancient continents. Sulphides are overwhelmingly pyrrhotite with minor Ni (0.7-3.9 at.%), Co (0.1-0.7 at.%), and Cu contents (0.4-3.9 at.%). Sulphide modes in mafic granulites range from 0.14 to 0.55 vol%, translating into bulk rock S contents from ˜600 to 2000 ppm, similar to S contents in other mafic igneous rocks and indicating preservation of primary igneous S contents. In mafic granulites, Re and Os abundances in sulphides range from 42.5 to 726 ppb and 3.2 to 180 ppb, respectively, whereas those in peraluminous granulites are distinctly lower (36.1-282 ppb and 1.8-7.2 ppb, respectively), suggestive of Re and Os loss to fractionating sulphides in the more evolved precursors of these rocks. The significant within-sample variability of 187Os/ 188Os and correlation with 187Re/ 188Os indicates the preservation of primary Re-Os isotope systematics and time-integrated decay of the measured 187Re. Within the large uncertainties inherent in the nature of the samples and technique, sulphides in some granulites may record major tectonothermal events in the central Slave craton spanning several billion years of evolution. Multiple generations of sulphide can occur in a single sample. These data attest to the heterogeneous composition and complex history of the Slave craton lower crust.

  17. Insights into the Crustal Structure and Geodynamic Evolution of the Southern Granulite Terrain, India, from Isostatic Considerations

    NASA Astrophysics Data System (ADS)

    Kumar, Niraj; Singh, A. P.; Singh, B.

    2011-10-01

    The Southern Granulite Terrain of India, formed through an ancient continental collision and uplift of the earth's surface, was accompanied by thickening of the crust. Once the active tectonism ceased, the buoyancy of these deep crustal roots must have supported the Nilgiri and Palani-Cardamom hills. Here, the gravity field has been utilized to provide new constraints on how the force of buoyancy maintains the state of isostasy in the Southern Granulite Terrain. Isostatic calculations show that the seismically derived crustal thickness of 43-44 km in the Southern Granulite Terrain is on average 7-8 km more than that required to isostatically balance the present-day topography. This difference cannot be solely explained applying a constant shift in the mean sea level crustal thickness of 32 km. The isostatic analysis thus indicates that the current topography of the Southern Granulite Terrain is overcompensated, and about 1.0 km of the topographic load must have been eroded from this region without any isostatic readjustment. The observed gravity anomaly, an order of magnitude lower than that expected (-125 mGal), however, shows that there is no such overcompensation. Thermal perturbations up to Pan-African, present-day high mantle heat flow and low Te together negate the possible resistance of the lithosphere to rebound in response to erosional unloading. To isostatically compensate the crustal root, compatible to seismic Moho, a band of high density (2,930 kg m-3) in the lower crust and low density (3,210 kg m-3) in the lithospheric mantle below the Southern Granulite Terrain is needed. A relatively denser crust due to two distinct episodes of metamorphic phase transitions at 2.5 Ga and 550 Ma and highly mobilized upper mantle during Pan-African thermal perturbation reduced significantly the root buoyancy that kept the crust pulled downward in response to the eroded topography.

  18. Dating High Temperature Mineral Fabrics in Lower Crustal Granulite Facies Rocks

    NASA Astrophysics Data System (ADS)

    Stowell, H. H.; Schwartz, J. J.; Tulloch, A. J.; Klepeis, K. A.; Odom Parker, K.; Palin, M.; Ramezani, J.

    2015-12-01

    Granulite facies rocks may record strain that provides a record of compressional and/or extensional crustal events in hot orogenic cores and the roots of magmatic arcs. Although the precise timing of these events is important for constructing tectonic histories, it is often difficult to determine due to uncertain relationships between isotopic signatures, mineral growth, and textural features that record strain. In addition, there may be large uncertainties in isotope data due to intracrystalline diffusion and multiple crystallization events. L-S tectonites in lower crustal rocks from Fiordland, NZ record the early stages of extensional collapse of thickened magmatic arc crust. The precise age of these fabrics is important for constraining the timing of extension that led to opening of the Tasman Sea. High temperature granulite facies L-S fabrics in garnet reaction zones (GRZ) border syn- to post-deformational leucosomes. U-Pb zircon, Lu-Hf garnet, and Sm-Nd garnet ages, and trace elements in these phases indicate the complexity of assigning precise and useful ages. Zircon have soccer ball morphology with patchy and sector zoned CL. Zircon dates for igneous host and adjacent GRZ range over ca. 17 Ma. 236U-208Pb LA-ICP-MS are 108-125 Ma, N=124 (host & GRZ); however, chemical abrasion (CA) shifts GRZ dates ca. 2 Ma older. 236U-208Pb SHRIMP-RG dates cluster in 2 groups: 118.5±0.8 Ma, N=23 and 111.0±0.8 Ma, N=6. CA single crystal TIMS dates also fall into 2 groups: 117.6±0.1 Ma, N=4 and 116.6±0.2 Ma N=4. Garnet isochron ages determined from coarse garnet selvages adjacent to leucosomes range from 112.8±2.2 (147Sm-143Nd, 10 pts.) to 114.8±3.5 (177Lu-176Hf, 6 pts.) Ma. Zircon dates from all methods show ranges (>10 Ma) and 2 distinct populations. Host and GRZ zircon cannot be readily distinguished by age, lack younger rims, but have distinct Th/U trends and Eu/Eu* vs. Hf ratios. Difference in zircon trace element composition indicates either early leucosome

  19. An experimental study on creep of partially molten granulite under high temperature and wet conditions

    NASA Astrophysics Data System (ADS)

    Zhou, Yongsheng; Zhang, Huiting; Yao, Wenming; Dang, Jiaxiang; He, Changrong

    2017-05-01

    Samples of natural granulite were deformed in a gas medium apparatus to evaluate the flow strength of the lower crust. The sample consists of ∼52 vol% plagioclase, ∼40 vol% pyroxene, ∼3 vol% quartz, ∼5 vol% magnetite and ilmenite. Water content was ∼0.17 ± 0.05 wt% in the deformed samples. 40 creep tests were performed on 13 samples at 300 MPa confining pressure, temperatures of 900-1200 °C, and strain rates between 3.13 × 10-6 and 5 × 10-5/s, resulting in axial stresses of 12-764 MPa and the total strain up to 7.8-20.5%. At low temperatures of 900-1000 °C, the microstructural observations show that the granulite samples were deformed in semi-brittle deformation regime, mainly by dislocation glide and intragranular microcracking. At medium temperatures (MT) of 1050-1100 °C, deformation was observed to be dominated by grain boundary migration recrystallization, corresponding to stress exponent nMT of 5.7 ± 0.1, activation energies QMT of 525 ± 34 kJ/mol, log AMT of 1.3. At high temperatures (HT) of 1125-1150 °C, the samples was deformed mainly by grain boundary migration recrystallization accommodated by partial melting and metamorphic reactions characterized by neo-crystallization of fine-grained olivine, with nHT of 4.8 ± 0.1, QHT of 1392 ± 63 kJ/mol, and log AHT of 37.5. Partial melting at high temperatures of 1125-1200 °C, which induces grain boundaries slip and enhances diffusion, has a significant weakening effect on the rheology of granulite, with an estimated strain rate enhancement by 5 times at melt fraction of ∼2 vol%. Reaction from pyroxene to olivine may affect the flow law parameters and deformation mechanism. Based on our data, a wet and cool continental lower crust may still be in brittle deformation regime, whereas a hot lower crust may likely have a weak layer with plastic deformation.

  20. Crustal evolution and the eclogite to granulite phase transition in xenoliths from the West African Craton

    NASA Technical Reports Server (NTRS)

    Haggerty, S. E.; Hills, D. V.; Toft, P. B.

    1988-01-01

    A suite of eclogite and granulite facies xenoliths from kimberlite pipes in the Archean Man Shield of West Africa is described. The xenoliths include lithologies ranging in composition from komatiite to anorthosite and appear to be geochemically, petrologically, and geophysically related. The suite may represent fractionation of felsic material separated from ancient mantle and added to early Archean crust. The samples can be used to define a xenolith geotherm, which may represent an ancient episode of high heat flow. The samples also imply that the crust-mantle boundary is a gradational and possibly interlayered geochemical, mineralogical, and seismic transition. It is speculated that the depleted subcontinental mantle required by diamond bearing coalescence of smaller depletion cells formed by extraction of ancient crustal components. These depleted zones are surrounded by fertile asthenospheric mantle, which may have given rise to later flood basalts such as the Karroo and Parana Provinces.

  1. Mid-Paleozoic age of granitoids in enclaves within early Cretaceous granulites, Fiordland, southwest New Zealand

    USGS Publications Warehouse

    Bradshaw, J.Y.; Kimbrough, D.L.

    1991-01-01

    Orthogneisses of granite, quartz monzonite, monzonite, and tonalite, occur locally as isolated enclaves within the Early Cretaceous granulite terrain (Western Fiordland Orthogneiss - WFO). Discordant U-Pb zircon isotopic data (seven fractions) from four granitoid samples from enclaves at George Sound, define an upper intecept age of 341??34 Ma that is interpreted as approximating the time of formation of the granitoid suite. The lower intercept age of 93??37 Ma is interpreted as approximating the time of zircon isotopic disturbance by major episodic Pb loss. The low 87Sr/ 86Sr initial ratio indicates that these mid-Paleozoic granitoids were derived from an isotopically primitive source. The granitoid enclaves within WFO show influences of several different sources. The granitoids provide evidence linking WFO to a mid-Palaeozoic country rock similar to the central Fiordland metasediments. -from Authors

  2. Pan-African granulite facies reworking along Moyar shear zone, south India: Implications for Gondwanaland assembly

    NASA Astrophysics Data System (ADS)

    Bhadra, Subhadip; Nasipuri, Pritam

    2014-05-01

    The present study documents metamorphic evolution of garnetiferrous quartzo-feldspathic gneiss from the Moyer shear zone (MSZ), southern granulite terrain (SGT). Quartz (Qtz), plagioclase feldspar (Pl) and biotite (Bt1) constitute the pre-metamorphic mineral assemblage in the rock, where as porphyroblastic garnet (Grt) and second generation biotite (Bt2) characterize the metamorphic mineral paragenesis. Mylonitic fabric in the rock is defined by biotite (Bt1) and poly-crystalline quartz ribbons that wraps garnet porphyroblast. Core compositions of the porphyroblastic garnets lie in almandine-pyrope-grossular ternary (Alm62Prp23Grs14Spss01). In the core to rim traverses within the garnet display variation in major element zoning patterns that depend on the neighboring mineral phase/phases. Along traverses where garnet rim shares contact with quartz, a flat Fe, rimwardly decreasing Mg, flat Mn and rimwardly increasing Ca (referred as Fe0Mg-Ca+Mn0) profile was observed. Embayed garnet sharing boundary with randomly oriented Bt2, displays rimwardly increasing Fe, rimwardly-decreasing Mg, rimwardly increasing Ca and flat Mn (referred as Fe+Mg-Ca+Mn0) profile. Bt2 shows complementary decrease of Fe and increase of Mg towards the interface with garnet. Garnet sharing contact with both Bt1 and plagioclase-feldspar displays rimwardly increasing Fe, rimwardly decreasing Mg, rimwardly increasing Ca and rimwardly increasing Mn (referred as Fe+Mg-Ca+Mn+) profile. Adjacent biotites show an increase of Fe and Mg towards the interface with garnet. Anorthite content of plagioclase decreases towards the interface. While Fe0Mg-Ca+Mn0profile can be interpreted with garnet growth (Bt1 + Pl → Grt) and compositional homogenization (flat Fe, Mn) during peak metamorphism, Fe+Mg-Ca+Mn+and Fe+Mg-Ca+Mn0 profiles can be linked with post-peak compositional modifications respectively via retrograde net-transfer (ReNTR: Grt + Ca-rich ± Qtz → BtII + Ca-poor Plag) and retrograde exchange (Re

  3. Evidence for fullerenes in solid bitumen from pillow lavas of Proterozoic age from Mítov (Bohemian Massif, Czech Republic)

    NASA Astrophysics Data System (ADS)

    Jehlička, Jan; Svatoš, Aleš; Frank, Ota; Uhlík, Filip

    2003-04-01

    Andesitic pillow lavas containing biogenic, solid bitumen (SB) are a constituent of a Neoproterozoic volcanosedimentary sequence (Teplá-Barrandian unit, Bohemian Massif) in the Mítov area of the Czech Republic. A black shale formation that is crosscut by these andesitic basalts is 565 Ma old. Carbon disulfide extracts of two powdered samples of SB contain 0.2 and 0.3 ppm of C 60, respectively, as determined by high-pressure liquid chromatography. The peak assignment based on retention time is fully supported by high-resolution electron ionization mass spectrometry (EI-MS). No C 70 was detected, nor was C 60 found in two other SB samples from this locality. Other investigated carbonaceous samples from Bohemia (coals and anthracites of Upper Paleozoic age and anthraxolite, graphitoids, and graphite of Upper Proterozoic age) did not contain fullerenes at concentrations above the detection limit of 0.01 ppm. The absence of C 60 in these samples was confirmed by EI-MS. The proposed mechanism of fullerene formation involves a primary algal phase, generation of a hydrocarbonaceous mixture in the course of thermal evolution of the sedimentary series, and their high-temperature transformation related to the extrusion of basalt. An important feature for fullerene conservation was the enclosure of fullerenes in SB with a structure similar to glasslike carbon, where the fullerene was protected against oxidation.

  4. Cross-borehole flow analysis to characterize fracture connections in the Melechov Granite, Bohemian-Moravian Highland, Czech Republic

    USGS Publications Warehouse

    Paillet, Frederick L.; Williams, John H.; Urik, Joseph; Lukes, Joseph; Kobr, Miroslav; Mares, Stanislav

    2012-01-01

    Application of the cross-borehole flow method, in which short pumping cycles in one borehole are used to induce time-transient flow in another borehole, demonstrated that a simple hydraulic model can characterize the fracture connections in the bedrock mass between the two boreholes. The analysis determines the properties of fracture connections rather than those of individual fractures intersecting a single borehole; the model contains a limited number of adjustable parameters so that any correlation between measured and simulated flow test data is significant. The test was conducted in two 200-m deep boreholes spaced 21 m apart in the Melechov Granite in the Bohemian-Moravian Highland, Czech Republic. Transient flow was measured at depth stations between the identified transmissive fractures in one of the boreholes during short-term pumping and recovery periods in the other borehole. Simulated flows, based on simple model geometries, closely matched the measured flows. The relative transmissivity and storage of the inferred fracture connections were corroborated by tracer testing. The results demonstrate that it is possible to assess the properties of a fracture flow network despite being restricted to making measurements in boreholes in which a local population of discrete fractures regulates the hydraulic communication with the larger-scale aquifer system.

  5. The evolution of a late-Variscan high-T/low-P region: the southeastern margin of the Bohemian massif

    NASA Astrophysics Data System (ADS)

    Büttner, S.; Kruhl, J. H.

    A characteristic feature of the Moldanubian part of the central European Variscides is late-orogenic high-T/low-P metamorphism. Its past history and the possible reasons for this metamorphism are highlighted by the tectonometamorphic development at the south- eastern margin of the Bohemian massif. During the Variscan orogeny, at ca. 340 Ma, two different crustal segments were juxtaposed by thrusting (the Drosendorf unit on top of the Monotonous unit). This probably marks a collisional event that is widespread in the southeastern Moldanubian zone. The collision was followed by crustal uplift accompanied by strong heating in the lowermost structural unit (Monotonous unit). During the subsequent orogenic collapse, the Moldanubian nappe pile was thrust over parts of the Moravo-Silesian terrane. A late stage of crustal extension under greenschist-facies conditions is linked with pluton emplacement. In general, magmatic underplating as well as delamination of the lithospheric mantle explains the high-T/low-P metamorphism and the large-scale plutonism in the southeastern Moldanubian zone.

  6. Long-term studies (1871-2000) on acidification and recovery of lakes in the Bohemian Forest (central Europe).

    PubMed

    Vrba, Jaroslav; Kopácek, Jirí; Fott, Jan; Kohout, Leos; Nedbalová, Linda; Prazáková, Miroslava; Soldán, Tomás; Schaumburg, Jochen

    2003-07-01

    This paper evaluates long-term changes in the atmospheric depositions of S and N compounds, lake water quality, and biodiversity at eight glacial lakes in the Bohemian Forest over the past 130 years. This time interval covers (i) the 'background' pre-acidification status of the lakes, (ii) a period of changes in the communities that can be partly explained by introduction of fish, (iii) a period of strong lake acidification with its adverse impacts on the communities, (iv) the lake reversal from acidity, which includes the recent status of the lakes. The lake water chemistry has followed-with a characteristic hysteresis-both the sharp increase and decline in the deposition trends of strong anions. Remarkable changes in biota have mirrored the changing water quality. Fish became extinct and most species of zooplankton (Crustacea) and benthos (Ephemeroptera and Plecoptera) retreated due to the lake water acidification. Independent of ongoing chemical reversal, microorganisms remain dominant in the recent plankton biomass as well as in controlling the pelagic food webs. The first signs of the forthcoming biological recovery have already been evidenced in some lakes, such as the population of Ceriodaphnia quadrangula (Cladocera) returning into the pelagial of one lake or the increase in both phytoplankton biomass and rotifer numbers in another lake.

  7. Granulite-facies rocks in the Whatley Mill gneiss, Pine Mountain basement massif, Eastern Alabama

    SciTech Connect

    Daniell, N.; Salpas, P.A. . Dept. of Geology)

    1993-03-01

    The Pine Mountain basement massif is a granulite terrane exposed in a tectonic window through the Inner Piedmont of western Georgia and eastern Alabama. Investigations of the westernmost extent of the massif, the Whatley Mill Gneiss, have revealed four distinct lithologies: (1) an augen gneiss, the type lithology; (2) mylonite that develops in the shear zones cutting the unit; (3) a phaneritic rock showing weak to no foliation; (4) enclaves of biotite gneiss within the weakly-foliated rock. Additionally, the weakly-foliated rock comprises two distinct phases which are in sharp contact along curved and undulating boundaries: phase 1 is a coarser-grained rock; phase 2 is a finer-grained rock of the same mineralogy as phase 1 except it contains rare hypersthene. This first recorded observation of hypersthene unequivocally confirms the granulite-facies origin of the unit. Major and trace element compositions of the phase 1 rock are identical to those of the augen gneiss. The phase 2 rock, has a distinct composition with higher SiO[sub 2] and lower incompatible trace elements than the phase 1 rock. The enclaves display a range in major elements but higher incompatible elements than the other lithologies. Geochemical and petrologic relationships leads one to interpret: (1) the weakly-foliated rock retains many of its primary igneous features including its two phases and enclaves; (2) the two phases of the weakly-foliated rock arose as a result of injection of one magma (phase 2) into a cooler, crystal mush solidifying from another magma (phase 1); (3) the enclaves represent either autoliths of xenoliths; (4) the augen gneiss arose by isochemical deformation of the phase 1 rock.

  8. Monazite behaviour during isothermal decompression in pelitic granulites: a case study from Dinggye, Tibetan Himalaya

    NASA Astrophysics Data System (ADS)

    Wang, Jia-Min; Wu, Fu-Yuan; Rubatto, Daniela; Liu, Shi-Ran; Zhang, Jin-Jiang; Liu, Xiao-Chi; Yang, Lei

    2017-10-01

    Monazite is a key accessory mineral for metamorphic geochronology, but interpretation of its complex chemical and age zoning acquired during high-temperature metamorphism and anatexis remains a challenge. We investigate the petrology, pressure-temperature and timing of metamorphism in pelitic and psammitic granulites that contain monazite from the Greater Himalayan Crystalline Complex (GHC) in Dinggye, southern Tibet. These rocks underwent isothermal decompression from pressure of >10 kbar to 5 kbar at temperatures of 750-830 °C, and recorded three metamorphic stages at kyanite (M1), sillimanite (M2) and cordierite-spinel grade (M3). Monazite and zircon crystals were dated by microbeam techniques either as grain separates or in thin sections. U-Th-Pb ages are linked to specific conditions of mineral growth on the basis of zoning patterns, trace element signatures, index mineral inclusions (melt inclusions, sillimanite and K-feldspar) in dated domains and textural relationships with co-existing minerals. The results show that inherited domains (500-400 Ma) are preserved in monazite even at granulite-facies conditions. Few monazites or zircon yield ages related to the M1-stage ( 30-29 Ma), possibly corresponding to prograde melting by muscovite dehydration. During the early stage of isothermal decompression, inherited or prograde monazites in most samples were dissolved in the melt produced by biotite dehydration-melting. Most monazite grains crystallized from melt toward the end of decompression (M3-stage, 21-19 Ma) and are chemically related to garnet breakdown reactions. Another peak of monazite growth occurred at final melt crystallization ( 15 Ma), and these monazite grains are unzoned and are homogeneous in composition. In a regional context, our pressure-temperature-time data constrains peak high-pressure metamorphism within the GHC to 30-29 Ma in Dinggye Himalaya. Our results are in line with a melt-assisted exhumation of the GHC rocks.

  9. Granulitic metamorphism in the Laouni terrane (Central Hoggar, Tuareg Shield, Algeria)

    NASA Astrophysics Data System (ADS)

    Bendaoud, Abderrahmane; Derridj, Amel; Ouzegane, Khadidja; Kienast, Jean-Robert

    2004-06-01

    In the Laouni terrane, which belongs to the polycyclic Central Hoggar domain, various areas contain outcrops of formations showing granulite-facies parageneses. This high-temperature metamorphism was accompanied by migmatization and the emplacement of two types of magmatic suite, one of continental affinity (garnet pyroxenites and granulites with orthoferrossilite-fayalite-quartz), and the other of arc affinity (layered metanorites). Paragenetic, thermobarometric and fluid-inclusion studies of the migmatitic metapelites and metabasites make it possible to reconstruct the P- T- aH 2O path undergone by these formations. This path is clockwise in the three studied areas, being characterized by a major decompression (Tamanrasset: 10.5 kbar at 825 °C to 6 kbar at 700 °C; Tidjenouine: 7.5 kbar at 875 °C; to 3.5 kbar at 700 °C; Tin Begane: 13.5 kbar at 850 °C; to 5 kbar at 720 °C), followed by amphibolitization that corresponds to a fall of temperature (from 700 to 600 °C) and an increase in water activity (from 0.2-0.4 to almost 1). The main observed features are in favour of petrogenesis and exhumation related to the Eburnean orogeny. However, the lacks of good-quality dating work and a comparison with juvenile Pan-African formations having undergone high-pressure metamorphism, in some cases reaching the eclogite facies, do not rule out the possibility that high-temperature parageneses are locally due to Pan-African events.

  10. Pressure-temperature and isotopic constraints on the progressive, fluid enhanced eclogitisation of granulites in the Bergen Arcs, western Norway.

    NASA Astrophysics Data System (ADS)

    Bhowany, Kamini; Hand, Martin; Clark, Chris; E Kelsey, David

    2017-04-01

    Exhumed eclogitic crust is rare and exposures that preserve both protoliths and altered domains are limited around the world. On Holsnøy Island, in the Bergen Arcs Norway, Neoproterozoic anorthositic granulites are exposed juxtaposing hydrous Ordovicio-Silurian eclogites which formed during well documented progressive fluid infiltration and deformation. Four stages of deformation for this progressive eclogitisation process can be identified based on structural overprinting relationships: 1) brittle deformation which formed pseudotachylite arrays in the granulite which are now recrystallised to K-feldpar-kyanite-plagioclase-clinopyroxene-garnet-quartz-rutile; 2) the development of discrete, small-scale shear zones associated with increased fluid-rock interaction, resulting in the formation of clinopyoxene-zoisite-kynaite-phengite-albitic plagioclase assemblages that partially to completely retrogressed garnets in the granulite protolith 3) the complete large-scale replacement of granulite by hydrous eclogite with interpreted peak metamorphic assemblage phengite-zoisite-omphacite-garnet-kyanite-rutile ; and 4) the retrogression of completely eclogitised domains resulting in coarse phengite dominated mineral assemblages (phengite-zoisite-omphacite-garnet-kyanite-amphibole-rutile-quartz), due to a significant availability of fluid. P-T constraints, determined by phase equilibria forward modelling, indicated that recrystallisation of the pseudotachylite occurred at around 15.5 kbar and 675 °C, peak eclogite assemblages formed at around 21.5 kbar and 680 °C and high-P retrogression at 16.5 kbar and 700 °C. As described by a number of workers, the transition from granulite to eclogite was catalysed by fluid. However limitations in fluid availability resulted in the recrystallised domains evolving to a fluid absent state, thereby freezing in the mineral assemblage and recording the P-T conditions associated with fluid ingress as the slab was subducted. Preliminary

  11. U-Pb zircon dating of the Gruf Complex: disclosing the late Variscan granulitic lower crust of Europe stranded in the Central Alps

    NASA Astrophysics Data System (ADS)

    Galli, A.; Le Bayon, B.; Schmidt, M. W.; Burg, J.-P.; Reusser, E.; Sergeev, S. A.; Larionov, A.

    2012-02-01

    Permian granulites associated with noritic intrusions and websterites are a common feature of the post-Variscan European crust. Such granulites are common in the Southern Alps (e.g. Ivrea Zone), but occur only in the Gruf Complex in the Central Alps. To understand the geotectonic significance of these granulites, in particular in the context of Alpine migmatisation, zircons from 15 high-grade samples have been U-Pb dated by SHRIMP II analysis. Oscillatory zoned zircons from charnockite sheets, interpreted as melts generated through granulite facies fluid-absent biotite melting at 920-940°C, yield ages of 282-260 Ma. Some of these zircons contain inclusions of opx, unequivocally attributable to the granulite facies, thus confirming a Permian age for the charnockites and associated granulites. Two samples from an enclave-rich orthogneiss sheet yield Cambrian and Ordovician zircon cores. Two deformed leucogranites and six ortho- and augengneisses, which compose two-thirds of the Gruf Complex, give zircon ages of 290-260 Ma. Most zircons have milky rims with ages of 34-29 Ma. These rims date the Alpine amphibolite facies migmatisation, an interpretation confirmed by directly dating a leucosome pocket from upper amphibolite facies metapelites. The Gruf charnockites associated with metre-scale schlieren and boudins of opx-sapphirine-garnet-granulites, websterites and gabbronorites can thus be identified as part of the post-Variscan European lower crust. A geotectonic reconstruction reveals that this piece of lower crust stranded in the (European) North upon rifting of the Neotethys, such contrasting the widespread granulite units in the Southern Alps. Emplacement of the Gruf lower crust into its present-day position occurred during migmatisation and formation of the Bergell Pluton in the aftermath of the breakoff of the European slab.

  12. Measurement of elastic wave velocities in granulite and amphibolite having identical H 2O-free bulk compositions up to 850°C at 1 GPa

    NASA Astrophysics Data System (ADS)

    Ito, Kazuhiko; Tatsumi, Yoshiyuki

    1995-07-01

    Simultaneous measurements of compressional and shear wave velocities ( VP and VS) in two rocks with identical chemistry but with different mineral assemblages were carried out from room temperature to 850°C at 1 GPa. One of the rocks is granulite and the other is amphibolite formed from the granulite by addition of H 2O. Both VP and VS in the granulite and amphibolite decreased linearly with increasing temperature, and there were obvious differences between the elastic wave velocities in the granulite and amphibolite. For example, the values of VP and VS at 700°C are, respectively, 7.75 km s -1 and 4.37 km s -1 for granulite and 7.40 km s -1 and 4.21 km s -1 for amphibolite. The low-velocity layer lies between the descending lithosphere and the overlying asthenosphere beneath the Japanese island arc, and the ratio of velocity drop for the low-velocity layer compared to the surroundings is approximately 5-6%. If the observed velocity drop were caused by a phase change (i.e., granulite + H 2O → amphibolite) the 5-6% velocity drop could indeed be explained by an appropriate phase change (e.g., anhydrous peridotite + H 2O → amphibole peridotite).

  13. Small scale heterogeneity of Phanerozoic lower crust: evidence from isotopic and geochemical systematics of mid-Cretaceous granulite gneisses, San Gabriel Mountains, southern California

    USGS Publications Warehouse

    Barth, A.P.; Wooden, J.L.; May, D.J.

    1992-01-01

    An elongate belt of mid-Cretaceous, compositionally banded gneisses and granulites is exposed in Cucamonga terrane, in the southeastern foothills of the San Gabriel Mountains of southern California. Banded gneisses include mafic granulites of two geochemical types: type 1 rocks are similar to high Al arc basalts and andesites but have higher HFSE (high-field-strength-element) abundances and extremely variable LILE (largeion-lithophile-element) abundances, while type 2 rocks are relatively low in Al and similar to alkali rich MOR (midocean-ridge) or intraplate basalts. Intercalated with mafic granulites are paragneisses which include felsic granulites, aluminous gneisses, marble, and calc-silicate gneisses. Type 1 mafic granulites and calcic trondhjemitic pegmatites also oceur as cross-cutting, synmetamorphic dikes or small plutons. Small-scale heterogeneity of deep continental crust is indicated by the lithologic and isotopic diversity of intercalated ortho-and paragneisses exposed in Cucamonga terrane. Geochemical and isotopic data indicate that K, Rb, and U depletion and Sm/Nd fractionation were associated with biotite +/- muscovite dehydration reactions in type 1 mafic granulites and aluminous gneisses during high-grade metamorphism. Field relations and model initial isotopic ratios imply a wide range of protolith ages, ranging from Early Proterozoic to Phanerozoic. ?? 1992 Springer-Verlag.

  14. Silvibacterium bohemicum gen. nov. sp. nov., an acidobacterium isolated from coniferous soil in the Bohemian Forest National Park.

    PubMed

    Lladó, Salvador; Benada, Oldrich; Cajthaml, Tomáš; Baldrian, Petr; García-Fraile, Paula

    2016-02-01

    During the course of a study assessing the bacterial diversity of a coniferous forest soil (pH 3.8) in the Bohemian Forest National Park (Czech Republic), we isolated strain S15(T) which corresponded to one of the most abundant soil OTUs. Strain S15(T) is represented by Gram-negative, motile, rod-like cells that are 0.3-0.5μm in diameter and 0.9-1.1μm in length. Its pH range for growth was 3-6, with optimal conditions found at approximately 4-5. It can grow at temperatures between 20°C and 28°C, with optimum growth at 22-24°C. Its respiratory quinone is MK-8, and its main fatty acid is iso-C15:0 (73.7%). The G+C DNA content was 58.2mol%. According to the 16S rRNA gene sequence analysis, strain S15(T) belongs to subdivision 1 of the phylum Acidobacteria, being affiliated to the cluster of Acidipila rosea AP8(T) and Acidobacterium capsulatum ATCC 51196(T). Analysis of the S15(T) genome revealed the presence of 404 genes that are involved in carbohydrate metabolism, which indicates the metabolic potential to degrade polysaccharides of plant and fungal origin. Based on genotypic and phenotypic characteristics, the strain S15(T) represents a new genus and species within the family Acidobacteriaceae, for which the name Silvibacterium bohemicum gen. nov., sp. nov. is proposed (type strain S15(T)=LMG 28607(T)=CECT 8790(T)). Copyright © 2015 Elsevier GmbH. All rights reserved.

  15. Country, cover or protection: what shapes the distribution of red deer and roe deer in the Bohemian Forest Ecosystem?

    PubMed

    Heurich, Marco; Brand, Tom T G; Kaandorp, Manon Y; Šustr, Pavel; Müller, Jörg; Reineking, Björn

    2015-01-01

    The Bohemian Forest Ecosystem encompasses various wildlife management systems. Two large, contiguous national parks (one in Germany and one in the Czech Republic) form the centre of the area, are surrounded by private hunting grounds, and hunting regulations in each country differ. Here we aimed at unravelling the influence of management-related and environmental factors on the distribution of red deer (Cervus elaphus) and roe deer (Capreolus capreolus) in this ecosystem. We used the standing crop method based on counts of pellet groups, with point counts every 100 m along 218 randomly distributed transects. Our analysis, which accounted for overdispersion as well as zero inflation and spatial autocorrelation, corroborated the view that both human management and the physical and biological environment drive ungulate distribution in mountainous areas in Central Europe. In contrast to our expectations, protection by national parks was the least important variable for red deer and the third important out of four variables for roe deer; protection negatively influenced roe deer distribution in both parks and positively influenced red deer distribution in Germany. Country was the most influential variable for both red and roe deer, with higher counts of pellet groups in the Czech Republic than in Germany. Elevation, which indicates increasing environmental harshness, was the second most important variable for both species. Forest cover was the least important variable for roe deer and the third important variable for red deer; the relationship for roe deer was positive and linear, and optimal forest cover for red deer was about 70% within a 500 m radius. Our results have direct implications for the future conservation management of deer in protected areas in Central Europe and show in particular that large non-intervention zones may not cause agglomerations of deer that could lead to conflicts along the border of protected, mountainous areas.

  16. Sedimentological downstream effects of dam failure and the role of sediment connectivity: a case study from the Bohemian Massif, Austria

    NASA Astrophysics Data System (ADS)

    Wurster, Maria-Theresia; Weigelhofer, Gabriele; Pichler-Scheder, Christian; Hein, Thomas; Pöppl, Ronald

    2017-04-01

    Sediment connectivity describes the potential for sediment transport through catchment systems, further defining locality and characteristics of sedimentation in river channels. Dams generally decrease sediment connectivity and act as temporary sediment sinks. When dams are removed these sediments are being reworked and released downstream. During dam restoration works along a small-sized stream in the Bohemian Massif of Austria in December 2015 a dam failure occurred which led to the entrainment of several tons of fine-grained reservoir sediments further entering and depositing in the downstream channel reaches, located in the Thayatal National Park. Aiming to remove these fine sediment deposits the National Park Authority decided to initiate a flushing event in April 2016. The main aim of the present study was to investigate the effects of dam failure-induced fine sediment release and reservoir flushing on downstream bed sediment characteristics by applying geomorphological mapping (incl. volumetric surveys) and sedimentological analyses (freeze-core sampling and granulometry), further discussing the role of in-channel sediment connectivity. The obtained results have shown that immediately after the dam failure event a total of ca. 18 m3 of fine-grained sediments have accumulated as in-channel sediment bars which were primarily formed in zones of low longitudinal connectivity (e.g. in the backwater areas of woody debris jams, or at slip-off bank locations). The flushing event has been shown to have caused remobilization and downstream translocation of these deposits, further reducing their total volume by approx. 60%. The results of the granulometric analyses of the freeze-core samples have revealed fine sediment accumulation and storage in the upper parts of the channel bed, having further increased after the flushing event. Additionally, effects on chemical conditions and invertebrate community have been observed. These observations clearly indicate a

  17. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    NASA Astrophysics Data System (ADS)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2017-04-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  18. Monazite and zircon as major carriers of Th, U, and Y in peraluminous granites: examples from the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Breiter, Karel

    2016-12-01

    The chemical compositions of zircon and monazite and the relationships between the contents of Th, U, Y, and REE in both minerals and in the bulk samples of their parental rocks were studied in three Variscan composite peraluminous granite plutons in the Bohemian Massif. It was established that granites of similar bulk composition contain zircon and monazite of significantly different chemistry. Monazite typically contains 5-13 wt% (rarely up to 28 wt%) ThO2, 0.4-2 wt% (up to 8.2 wt%) UO2, and 0.5-2 wt% (up to 5 wt%) Y2O3, whereas zircon typically contains less than 0.1 wt% (rarely up to 1.7 wt%) ThO2, less than 1 wt% UO2 (in the Plechý/Plockenstein granite, commonly, 1-2 wt% and scarcely up to 4.8 wt% UO2), and less than 1 wt% Y2O3 (in the Nejdek pluton often 2-5, maximally 7 wt% Y2O3). Monazite is an essential carrier of thorium, hosting more than 80 % of Th in all studied granites. Monazite also appears to be an important carrier of Y (typically 14-16 %, and in the Melechov pluton, up to 81 % of the total rock content) and U (typically 18-35 % and occasionally 6-60 % of the total rock budget). The importance of zircon for the rock budget of all the investigated elements in granites is lower: 4-26 % U, 5-17 % Y, and less than 5 % Th.

  19. Country, Cover or Protection: What Shapes the Distribution of Red Deer and Roe Deer in the Bohemian Forest Ecosystem?

    PubMed Central

    Heurich, Marco; Brand, Tom T. G.; Kaandorp, Manon Y.; Šustr, Pavel; Müller, Jörg; Reineking, Björn

    2015-01-01

    The Bohemian Forest Ecosystem encompasses various wildlife management systems. Two large, contiguous national parks (one in Germany and one in the Czech Republic) form the centre of the area, are surrounded by private hunting grounds, and hunting regulations in each country differ. Here we aimed at unravelling the influence of management-related and environmental factors on the distribution of red deer (Cervus elaphus) and roe deer (Capreolus capreolus) in this ecosystem. We used the standing crop method based on counts of pellet groups, with point counts every 100 m along 218 randomly distributed transects. Our analysis, which accounted for overdispersion as well as zero inflation and spatial autocorrelation, corroborated the view that both human management and the physical and biological environment drive ungulate distribution in mountainous areas in Central Europe. In contrast to our expectations, protection by national parks was the least important variable for red deer and the third important out of four variables for roe deer; protection negatively influenced roe deer distribution in both parks and positively influenced red deer distribution in Germany. Country was the most influential variable for both red and roe deer, with higher counts of pellet groups in the Czech Republic than in Germany. Elevation, which indicates increasing environmental harshness, was the second most important variable for both species. Forest cover was the least important variable for roe deer and the third important variable for red deer; the relationship for roe deer was positive and linear, and optimal forest cover for red deer was about 70% within a 500 m radius. Our results have direct implications for the future conservation management of deer in protected areas in Central Europe and show in particular that large non-intervention zones may not cause agglomerations of deer that could lead to conflicts along the border of protected, mountainous areas. PMID:25781942

  20. Isotopic composition of salt efflorescence from the sandstone castellated rocks of the Bohemian Cretaceous Basin (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Schweigstillová, Jana; Přikryl, Richard; Novotná, Miroslava

    2009-07-01

    The origin of sulphates in sulphate-rich efflorescences on quartz sandstones with a clay matrix, exposed in rural areas of the Czech Republic is interpreted, based upon an isotopic study of S and O. Sulphates such as gypsum and/or alums exhibit δ34S ranging from +1.3 to +6.1‰ and δ18O from +5.3 to +8.8‰. The low variability of S and O isotopes indicates a common source of the sulphur and a similar mode of sulphate formation. Atmospheric sulphates with a similar isotopic signature occur in the area, due to the combustion of sulphurous coal in power plants, located a few tens of kilometres from the sampling points. The sulphates crystallize from supersaturated pore waters that represent atmospheric precipitation, rich in sulphates, having percolated through the porous sandstone system. The previously proposed model of efflorescence growth (that it is due to the oxidation of pyrite) can be excluded, due to both the rare occurrence of pyrite and also to its different isotopic signature (δ34S about -22‰). Although gypsum prevails in the central and eastern part of the studied area, the north and north-west of the Bohemian Cretaceous Basin (the most polluted region) exhibits a significant presence of alums (NH4 + or K+-NH4 +-rich). Formation of alums can be explained by the partial dissolution of clay minerals or feldspars present in the sandstone matrix. Release of alumina from these phases is facilitated by the low pH of the precipitation (pH 4-4.5) and also locally by organic acids, traces of which were found in the studied efflorescences by the use of infrared spectroscopy.

  1. Petrography, geochemistry and geochronology of granite hosted rhyodacites associated with a disseminated pyrite mineralization (Arnolz, Southern Bohemian Massif, Austria)

    NASA Astrophysics Data System (ADS)

    Göd, Richard; Kurzweil, Johannes; Klötzli, Urs

    2016-09-01

    The study focuses on a subvolcanic rhyodacite dyke intruding a fine grained biotite granite and paragneisses of the South Bohemian Massif, part of the Variscan Orogenic Belt in Central Europe. The subvertical dyke strikes NNE, displays a thickness of about 30 m and has been traced by boulder mapping for approximately 7 km. The rhyodacites have been affected by two hydrothermal fluids. An older one of oxidizing condition giving rise to a reddish to brownish type of rock (Type I) and a younger fluid of reducing condition causing a greenish variety (Type II). The hydrothermal alteration is associated with the formation of the clay minerals chlorite, sericite, kaolinite and smectite and a disseminated pyrite mineralization. Bulk chemistries of the rhyodacites emphasize the hydrothermal alterations to be isochemical with the exception of sulphur enriched up to a maximum of 0.6 wt%. Trace element composition of the rhyodacites points to a barren geochemical environment in terms of base and precious elements. Sulphur isotope investigations of pyrites from the rhyodacites and the hosting granites respectively yield d34S data ranging from +0.07 to -2.22 ‰, emphasizing a magmatic origin of the sulphur. Geochronological investigations yield in situ U/Pb zircon ages of 312 ± 4 Ma for the biotite granite and of 292 ± 4 Ma for the rhyodacitic dykes indicating a time gap of ≈ 20 Ma between these two intrusive events. A contemporaneous but geochemically specialized granitic intrusion associated with NW striking "felsitic" dykes occurs about 10 to 20 km to the NW of Arnolz. However, the rhyodacites around Arnolz differ significantly from these felsitic dykes in their geochemistry and alteration phenomena which points to a different magmatic source. This coincides with a change in the orientation of the dykes from a NW direction controlling the geochemically specialized intrusions in the NW to a dominating NNE direction mirrored by the studied rhyodacites at Arnolz.

  2. The 3D crustal structure of Eastern Alps and Bohemian Massif revealed by ambient noise surface wave tomography

    NASA Astrophysics Data System (ADS)

    Molinari, Irene; Obermann, Anne; Kissling, Edi; Hetényi, György; AlpArray-EASI Working Group

    2017-04-01

    The Eastern Alps are the place of many unsolved questions regarding the tectonic evolution of the Alpine orogen: the nature of the Moho "gap" between the two plates, the anisotropic nature of the lower crust, the relationship between the Alpine orogen and the adjacent foreland basin to the north and the lithospheric blocks of the Bohemian Massif and to the Adria - northern Dinarides in the south. We exploit one year of continuous data recorded at 55 temporary broadband stations operated between 2014 and 2015 within the EASI AlpArray complementary experiment and 200 permanent broadband stations in the area ranging from 8°E to 19°E and from 45°N to 52°N to obtain a 3-D crustal model of this area. In particular, the EASI data allows us to image with high-resolution the shallower part of the crust (from the surface to ˜ 20 km depth). We first construct a database of ambient noise Rayleigh-wave group-velocity observations from 4s to 40s and we conduct a suite of linear least-squares inversions of the group-velocity data, resulting in 2-D maps of Rayleigh-wave group-velocity with a resolution of 20 km. The Rayleigh group-velocity maps are next jointly inverted via the Neighbourhood Algorithm to determine a set of one-dimensional shear-velocity models (one per group-velocity cell of 20km), resulting in a new 3-D model of shear-wave velocity (vS). We present here our firsts results and we compare them with other studies discussing geological/geodynamical implications that contribute to a better understanding of Eastern Alpine tectonics.

  3. Compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites: Examples from the Bohemian Massif, Czech Republic

    NASA Astrophysics Data System (ADS)

    Buriánek, David; Novák, Milan

    2007-04-01

    Two distinct textural types of tourmaline have been distinguished in leucocratic granites of the Bohemian Massif (Moldanubicum, Saxothuringicum): (i) commonly euhedral disseminated tourmaline (DT) crystallized during relatively early stage of the granite consolidation, and (ii) typically interstitial nodular tourmaline (NT) formed during the stage transitional from late solidus to early subsolidus crystallization. The following substitutions (exchange vectors) participated in tourmaline from the studied granites: (1) X□ YAl XNa - 1 YR 2+- 1 in the DT granites from the Moldanubicum; (2) X□ YAl 3WO 2XNa - 1 YR 2+- 3 W(OH) - 2 and (6) XNa YR 2+WF X□ - 1 YAl - 1 WOH - 1 in the DT and NT granites from the Saxothuringicum. Tourmaline in the NT granites from the Moldanubicum yielded a complicated pattern indicating participation of several substitutions such as (1), (2) and (3) X□ YAl 2WO XNa - 1 YR 2+- 2 W(OH) - 1 . Very similar chemical compositions and similar fractionation trends in both DT and NT tourmaline types indicate crystallization in a quasi-closed system from early solidus to early subsolidus stage of granite consolidation. Substitutions in tourmaline from NT granites in the Moldanubicum are more similar to substitutions in tourmaline from Li-poor granitic pegmatites in the same region relative to tourmaline from DT granites. Plotting up EMP analyses of tourmaline indicates that a combination of two ternary diagrams Al-Fe-Mg and Na-Ca- X-site vacancy, coupled with simple plots involving single cations (elements) such as Na/Al, F/Na, Fe/Mg, characterizes both their chemical composition as well as the probable substitution mechanisms. Complex diagrams such as R1 + R2 versus R3 do not enable a proper investigation of the compositional evolution in the X-site and W-site and oversimplify the real substitutions. As a consequence the use of specific diagrams for specific tourmaline compositions (e.g., Ca-rich, Li-rich) is recommended.

  4. K, Rb, Sr, Ba, U and Th geochemistry of the Lapland Granulites (Fennoscandia). LILE fractionation controlling factors

    NASA Astrophysics Data System (ADS)

    Barbey, P.; Cuney, M.

    1982-12-01

    The LILE geochemical patterns of the three main lithological units (graywacke-shale metasedimentary sequence, tholeiitic metaigneous rocks and migmatitic rocks) of the Lapland Granulite belt are described. K, Ba, Sr and Th concentrations in metasediments are nearly similar to average continental crust, whereas Rb and U are unevenly impoverished. In particular graphitic metashales and calcsilicate rocks are not significantly depleted in uranium. Tholeiitic metaigneous rocks comprises metavolcanics which present K/Rb ratios similar to metasediments, and metaplutonics with LILE abundances close to those of the low-K-tholeiites. Migmatites show wide range in LILE content. Metatexites and diatexites have higher K, Rb, Th and U concentrations and similar K/Rb ratios with respect to equivalent unmobilized rocks. Potassic pegmatoïds are strongly enriched K, Rb, Ba and Th but moderately in Sr and U. Plagioclasic pegmatoids and ferromagnesian restites are rich in Sr and poor in other LIL elements. A comparative review of the LILE geochemistry between Lapland granulites and equivalent lithological units taken from non metamorphosed to high grade terrains suggest that fractionation processes are not systematic but controlled by original lithology and mineralogy, mineral — fluid equilibria during progressive (or retrogressive) metamorphism and mineral-melt-fluid equilibria during anatexis. Moreover, statistical analysis on K-Rb distribution patterns in these various rock types shows that there is no metamorphic trend characteristic of granulite facies terrains as previously suggested.

  5. Regional granulite facies metamorphism in the Ivrea zone: Is the Mafic Complex the smoking gun or a red herring?

    NASA Astrophysics Data System (ADS)

    Barboza, Scott A.; Bergantz, George W.; Brown, Michael

    1999-05-01

    One widely accepted paradigm for the development of continental lower crust is that regional granulite facies metamorphism is caused by intrusion of mafic magma beneath or into the crust (magmatic accretion). The amphibolite to granulite facies supracrustal section exposed in the Ivrea zone (southern Alps, northern Italy) is commonly cited as a classic example establishing this postulated genetic relationship. Our interpretation of the pattern of metamorphic isograds, compositional trends in high-grade metasedimentary rocks, and textural evidence in metapelite, however, indicates that final emplacement of the mafic plutonic rocks (the Mafic Complex) occurred subsequent to the regional thermal maximum. Field and petrographic relations suggest that a spatially restricted contact-melting event in crustal rocks accompanied the emplacement of the Mafic Complex. This inference is consistent with leucosome compositions in migmatites and a low-pressure, high-temperature metamorphic overprint recorded by mineral assemblages in wall rocks proximal to the intrusion. Therefore, evidence of anatexis and metamorphism of crustal rocks associated unequivocally with emplacement of the Mafic Complex is found only within an ˜2-km-wide contact aureole overlying the intrusion. The narrow aureole associated with emplacement of the Mafic Complex demonstrates that, in some cases, emplacement of large volumes of mafic magma within the crust does not inexorably lead to regional-scale granulite facies metamorphism and large ion lithophile element depletion by melt loss.

  6. Deep resistivity sounding studies in detecting shear zones: A case study from the southern granulite terrain of India

    NASA Astrophysics Data System (ADS)

    Singh, S. B.; Stephen, Jimmy

    2006-10-01

    The resistivity signatures of the major crustal scale shear zones that dissect the southern granulite terrain (SGT) of South India into discrete geological fragments have been investigated. Resistivity structures deduced from deep resistivity sounding measurements acquired with a 10 km long Schlumberger spreads yield significant insights into the resistivity distribution within the E-W trending shear system comprising the Moyar-Bhavani-Salem-Attur shear zone (MBSASZ) and Palghat-Cauvery shear zone (PCSZ). Vertical and lateral extensions of low resistivity features indicate the possible existence of weak zones at different depths throughout the shear zones. The MBSASZ characterized by very low resistivity in its deeper parts (>2500 m), extends towards the south with slightly higher resistivities to encompass the PCSZ. A major resistivity transition between the northern and southern parts is evident in the two-dimensional resistivity images. The northern Archaean granulite terrain exhibits a higher resistivity than the southern Neoproterozoic granulite terrain. Though this resistivity transition is not clear at greater depths, the extension of low resistivity zones has been well manifested. It is speculated here that a network of crustal scale shear zones in the SGT may have influenced the strength of the lithosphere.

  7. The Pikwitonei granulite domain: A lower crustal level along the Churchill-Superior boundary in central Manitoba

    NASA Technical Reports Server (NTRS)

    Weber, W.

    1983-01-01

    The greenschist to amphibolite facies tonalite-greenstone terrain of the Gods Lake subprovince grades - in a northwesterly direction - into the granulite facies Pikwitonei domain at the western margins of the Superior Province. The transition is the result of prograde metamorphism and takes place over 50 - 100 km without any structural or lithological breaks. Locally the orthopyroxene isograd is oblique to the structural grain and transects greenstone belts, e.g., the Cross Lake belt. The greenstone belts in the granulite facies and adjacent lower grade domain consist mainly of mafic and (minor) ultramafic metavolcanics, and clastic and chemical metasedimentary rocks. Typical for the greenstone belts crossed by the orthopyroxene isograd are anorthositic gabbros and anorthosites, and plagiophyric mafic flows. The Pikwitonei granulite domain has been interpreted as to represent a lower crustal level which was uplifted to the present level of erosion. On the basis of gravimetric data this uplift has been modelled as an obduction onto the Churchill Province during the Hudsonian orogeny, similar to the Ivrea Zone. The fault between the Churchill and Superior Province is described.

  8. Single inclusion piezobarometry confirms high-temperature decompression path for Variscan granulites

    NASA Astrophysics Data System (ADS)

    Angel, Ross; Alvaro, Matteo; Mazzucchelli, Mattia; Nimis, Paolo; Nestola, Fabrizio

    2016-04-01

    The identification and chemistry of inclusions trapped in host minerals during growth of the host phase have long been used to infer P-T points on metamorphic paths. The determination of the remnant pressure on the inclusion, e.g., using data from X-ray diffractometry, birefringence analysis or Raman spectroscopy, provides an alternative method of barometry using elasticity theory. A remnant pressure in an inclusion is developed because the inclusion and the host have different thermal expansion and compressibilities, and the inclusion does not expand in response to P and T as would a free crystal. Instead it is restricted to expand only as much as the host mineral, and this constriction in volume can result in inclusions exhibiting over-pressures when the host is studied at room conditions. This concept has been known for a long time, but satisfactory quantitative modelling of inclusion-host systems based on non-linear elasticity theory and precise thermal-pressure euqations of state has only recently come available (Angel et al., 2014, 2015), even though it is still restricted to elastically isotropic minerals. No mineral is elastically isotropic, but garnets and diamond are almost so. Calculations show that diamonds trapped as inclusions in host silicates at P and T within the stability field of diamond should exhibit zero pressure when the samples are recovered to room conditions. However, some diamond inclusions in garnets in granulites are reported to exhibit significant residual overpressures (e.g., Kotková et al., 2011). This indicates that the inclusion was elastically re-equilibrated (e.g., by plastic flow in the garnet host) at high temperatures and lower pressures in the stability field of graphite, consistent also with the observed partial inversion of diamond to graphite. In this case, the elastic analysis of the diamond-in-garnet inclusions provides qualitative independent evidence that the Variscan granulites underwent pressure reduction at high

  9. Diffusion controlled corona growth in mafic dykes from Southern Granulite Terrain, India and their petrological implications

    NASA Astrophysics Data System (ADS)

    Banerjee, Ayoti; Banerjee, Meenakshi; Dutta, Upama; Sengupta, Pulak; Bhui, Uttam K.; Rajagopal, Anand; Mukhopadhyay, Dhruba

    2017-04-01

    Diffusion controlled corona growth in mafic dykes from Southern Granulite Terrain, India and their petrological implications Metamorphosed garnetiferous mafic dykes from Southern Granulite Terrain (SGT) are found intruding the high grade Archaean-Palaeoproterozoic felsic orthogneiss and their retrogressed equivalent. They contain phenocrysts of clinopyroxene (Cpx) and plagioclase (Pl) that preserve ophitic, subophitic and intergranular textures. The clinopyroxene contains closely spaced cleavage-parallel exsolution lamellae of orthopyroxene (Opx) and tiny rods of Fe-Ti oxides. Orthopyroxene is also found around clinopyroxene as granular exsolution. Large grains of Fe-Ti oxides occur within the interstitial space. Garnet (Grt) and quartz (Qtz) form at the contact of plagioclase and clinopyroxene. The product minerals are found as symplectite and/or corona rimming the reactants. In the corona, quartz always occurs near clinopyroxene whereas garnet forms close to the plagioclase. The proportions of garnet and quartz in symplectite are fairly constant and range from 75:25 to 70:30 (vol %). Similar coronitic texture is exhibited by amphibole (Amp) and quartz. Thin amphibole+quartz corona forms between plagioclase and clinopyroxene where amphibole occurs near plagioclase and quartz near clinopyroxene, though the rock is dominated by garnet over amphibole in the corona. Corona of garnet/amphibole is also found on Fe-Ti oxides at the contact of plagioclase and the products show TiO2 enrichement when they occur near Fe-Ti oxides. Formation of hydrous amphibole from anhydrous minerals necessitates the system to be open to H2O. Additionally, balanced chemical reactions for Pl+Cpx=Grt+Qtz and Pl+Cpx=Amp+Qtz require Fe+2 incorporation to explain the observed volume proportion of the product minerals. Formation of garnet/amphibole near plagioclase and quartz near clinopyroxene indicate restricted mobility of Al and Si within the reaction domain. Preferential enrichment of TiO2

  10. Modeling Peak T and Retrograde Evolution of Ultra-hot Granulites From Brazil

    NASA Astrophysics Data System (ADS)

    Baldwin, J. A.; Brown, M.; Moraes, R.; Fuck, R. A.; Piccoli, P. M.

    2003-12-01

    Granulite-facies rocks record extreme thermal perturbation of Earth's lithosphere. Characterizing these rocks yields information critical to our understanding of the P-T-X environment of formation and modification of continental crust. Ultrahigh-temperature (UHT) metamorphism was introduced for rocks that record extreme thermal conditions. Mineral associations characteristic of UHT conditions include Spr-Qtz and Sp-Qtz, and rare Opx-Sil-Qtz, which requires XMg >0.60-0.65, corresponding to minimum P and T of 8 kbar and 850° C. The migmatitic aspect of metapelites and metagreywackes suggests they were once melt-bearing, but survival of peak assemblages and depleted compositions suggest melt loss. Unless most melt is extracted, significant retrogression will occur during cooling as melt-consuming reactions are crossed. Where UHT assemblages are preserved, they occur within larger areas of common granulite. The restricted occurrence of UHT assemblages raises questions about the metamorphic processes involved. Did the extreme P-T conditions occur regionally? If so, did protolith composition restrict the record of these conditions or was retention of melt responsible for widespread retrogression? Given the clockwise P-T path inferred for many granulite terranes, how was the extreme thermal perturbation required by UHT assemblages achieved? We address these questions with new petrologic data from the An polis-Itau‡u Complex (AIC) of central Brazil, within the Neoproterozoic Bras¡lia Belt. The Bras¡lia Belt, including the Goi s arc, lies between the Sao Francisco and Amazon Cratons. Within the internal zone, the AIC comprises orthogranulite (metagabbro, charnockitic/enderbitic gneiss) and paragranulite (Grt-Sil/Opx-Sil gneiss, calc-silicate rock); magmatism and metamorphism occurred in the interval 650-630 Ma. Spr-Qtz occurs in Grt-Opx-Sil-Qtz assemblages at localities ~20 km apart, recording extreme T. At Fazenda Calif¢rnia, N of Goiƒnia, the post-peak evolution is

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    Polycrystalline inclusions occur in felsic granulites from northeastern Connecticut, US (Axler and Ague, 2015). They sit in the core of garnet porphyroblasts formed during peak metamorphism at T >1000°C and P >1 GPa. The investigated inclusions vary from needle-shaped, with length ≤50 microns and few microns across, to isometric with diameter ≤10 microns. They show a rather constant assemblage which includes quartz, phlogopite, biotite and very often a compositionally variable phase. Raman spectroscopy shows the occasional presence of glass and cristobalite (the latter only when quartz is absent). Crystallized phases and the presence of glass suggest that these inclusions formed originally as droplets of melt trapped during garnet growth, likely as result of partial melting of the original metasedimentary protolith. A prominent feature of the garnet is the presence of rutile needles and ilmenite oriented accordingly to the crystallographic planes of garnet. When elongated in shape, also the polycrystalline inclusions are generally oriented according to the same planes, and occasionally contain rutile and /or ilmenite occur as trapped phases. Re-heating experiments were performed on the polycrystalline inclusions using a piston cylinder apparatus and without adding water to the experimental capsules. Complete re-homogenization was achieved at T 1025-1050°C and P 1.7 GPa, confirming that these inclusions are nanogranites (Ferrero et al., 2015). Re-homogenized inclusions contain a peraluminous glass (ASI=1.36) with ≤6 wt% water, confirmed also via Raman spectroscopy. Its average composition is granitic, with K/Na= 4.37 and rather high FeO (3.70 wt%). Both K-rich character and FeO content are consistent with experimental melts generated at T of 900-1000°C and variable P via melting of metasediments. The investigation of the experimental products furthermore provides novel constraints for the peak conditions (and likely of anatexis) of these granulites. During

  12. Field and Microstructure Study of Transpressive Jogdadi shear zone near Ambaji, Aravalli- Delhi Mobile Belt, NW India and its tectonic implication on the exhumation of granulites.

    NASA Astrophysics Data System (ADS)

    Tiwari, Sudheer Kumar; Biswal, Tapas Kumar

    2016-04-01

    Aravalli- Delhi mobile belt is situated in the northwestern part of Indian shield. It comprises tectono- magmatic histories from Archean to Neoproterozoic age. It possesses three tectono- magmatic metamorphic belts namely Bhilwara Supergroup (3000 Ma), Aravalli Supergorup (1800 Ma) and Delhi Supergroup (1100 -750Ma). The Delhi Supergroup is divided in two parts North Delhi and South Delhi; North Delhi (1100 Ma to 850 Ma) is older than South Delhi (850 Ma to 750 Ma). The study area falls in the South Delhi terrane; BKSK granulites are the major unit in this terrane. BKSK granulites comprise gabbro- norite-basic granulite, pelitic granulite, calcareous granulite and occur within the surrounding of low grade rocks as meta- rhyolite, quartzite, mica schist and amphibolites. The high grade and low grade terranes share a sheared margin. Granulites have undergone three phases of folding, intruded by three phases of granites and traversed by many shear zones. One of the shear zones is Jogdadi shear zone which consists of granitic mylonites and other sheared rocks. Jogdadi shear zone carries the evidence of both ductile as well as brittle shearing. It strikes NW- SE; the mylonitic foliation dip moderately to SW or NE and stretching lineations are oblique towards SE. The shear zone is folded and gabbro- norite - basic granulite occurs at the core. One limb of fold passes over coarse grained granite while other limb occurs over gabbro- norite- basic granulite. Presence of mylonitic foliation, asymmetric folding, S-C fabrics, porphyroclasts, mica fishes and book shelf- gliding are indicative of ductile deformation. Most of the porphyroclasts are sigmoidal and delta types but there are also some theta and phi type porphyroclasts. Book shelf-gliding structures are at low angle to the C plane. The shear zone successively shows protomylonite, mylonite and ultramylonites from margin to the centre. As the mylonitization increases recrystallized quartz grains appear. Porphyroclasts

  13. Eclogite-facies metamorphic reactions under stress and faulting in granulites from the Bergen Arcs, Norway: an experimental investigation

    NASA Astrophysics Data System (ADS)

    Incel, Sarah; Hilairet, Nadège; Labrousse, Loïc; Andersen, Torgeir B.; Wang, Yanbin; Schubnel, Alexandre

    2017-04-01

    Field observations from the Bergen Arcs, Norway, demonstrate a network of pseudotachylites quenched under eclogite-facies conditions in mafic granulites. In these nominally anhydrous high-pressure high-temperature (HP/HT) rocks the formation of pseudotachylites, believed to represent fossilized earthquakes, cannot be explained by processes akin to dehydration embrittlement. On the contrary, the transition to eclogite is expected to involve hydration of the initial rock. To experimentally investigate the underlying mechanisms leading to brittle failure in HP/HT rocks, we performed deformation experiments on natural granulite samples from the Bergen Arcs. The experiments were conducted under eclogite-facies conditions (2-3 GPa, 990-1220 K) to trigger the breakdown of plagioclase - the main constituent of granulite. For these experiments, both a D-DIA and a Griggs apparatus were used. The D-DIA press is mounted on a synchrotron beamline, enabling us to monitor strain, stress, and phase changes in-situ while contemporaneously recording acoustic emissions. The Griggs experiments were performed on a new device installed at ENS Paris, in which only stress-strain were recorded, and post-mortem microstructures investigated. The initial material consisted of a fine grain size granulite powder (< 38 µm) composed of mainly plagioclase and minor amount of pyroxene. Hydrous phases are phlogopite and epidote group minerals that make up less than 1 vol. % of the total bulk rock powder plus the adhesion water on grain surfaces. Mechanical data together with XRD observations and the record of acoustic emissions demonstrate a correlation between stress drops, the growth of plagioclase breakdown products and the onset of acoustic emissions during deformation of our specimen within the eclogitic field. Microstructural analysis show remarkable similarities with that of the natural ecoligitic pseudotachylites of the Bergen arcs. The plagioclase decomposition products form narrow

  14. The Blaník Gneiss in the southern Bohemian Massif (Czech Republic): a rare rock composition among the early palaeozoic granites of Variscan Central Europe

    NASA Astrophysics Data System (ADS)

    René, Miloš; Finger, Fritz

    2016-08-01

    Metamorphosed and deformed tourmaline-bearing leucogranites with a Cambro-Ordovician formation age are widespread in the Monotonous Group of the Variscan southern Bohemian Massif, Czech Republic. The rocks, known locally as Blaník gneiss, are strongly peraluminous and classify as phosphorus-rich low-T, S-type granite. The magma formed from a metapelitic source, most likely through muscovite dehydration melting. With respect to its low-T origin and the abundance of tourmaline, the Blaník gneiss is exotic within the spectrum of Early Palaeozoic granites of the Variscan fold belt of Central Europe. Coeval granitic gneisses in the neighbouring Gföhl unit of the Bohemian Massif can be classified as higher T S-type granites and were probably generated through biotite dehydration melting. The geochemical differences between the Early Palaeozoic granitic magmatism in the Gföhl unit and the Monotonous Group support models claiming that these two geological units belonged to independent peri-Gondwana terranes before the Variscan collision. It is suggested here, that the Gföhl unit and the Monotonous Group represent zones of higher and lower heat flow within the Early Palaeozoic northern Gondwana margin, respectively. The geochemical data presented in this study could be helpful for terrane correlations and palaeogeographic reconstructions.

  15. The 3.5 Ga granulites of the Bug polymetamorphic complex, Ukraine (U-Pb SHRIMP-II zircon data)

    NASA Astrophysics Data System (ADS)

    Lobach-Zhuchenko, Svetlana; Kaulina, Tatiana; Baltybaev, Shauket; Yurchenko, Anastasija; Balagansky, Victor; Skublov, Sergei; Sukach, Vitaliji

    2014-05-01

    The Bug polymetamorphic complex composes the south-west of the Ukrainian Shield. It experienced multistage deformation and metamorphism of 3.6 to 1.95 Ga. The age of protolith of the gneiss enderbite is up to 3.7-3.6 Ga (Claesson et al., 2006: Lobach-Zhuchenko et al., 2010, 2013; Bibikova et al, 2013). The 3.5 old granulitic zircon (sample UR132) was found in a light grey massive medium grained with weak foliation granulite from the Odessa quarry located at the right riverside of the Bug (N 48° 13' 55.2''; E 29° 59' 75''). The rock is mafic in composition (SiO2 = 51.50 wt%, #mg=0.43, (La/Yb)n =7.5), and shows enrichment in Sr (333 ppm), Zr (244 ppm), and Nb (12 ppm) compared to MORB. This contains antiperthitic plagioclase (An30-35), hypersthene (En0.46 Fs0.53 Wo0.01 ), diopside (En0.33 Fs0.20Wo0.47), quartz, ilmenite, magnetite, apatite, and zircon. Three types of zircon are recognized. (1) Large (~300 μm) isometric and oval grains displaying bright colour and sector zoning in CL. Some crystals have fir-tree texture. Isometric shape together with fir-tree zoning is typical for zircons growing under conditions of granulite- facies metamorphism (Hoskin and Schaltegger, 2003). These zircons are low in U and Th, have high Th/U ratios (0.61-1.1), and display decreasing of element contents from the centre to margin (ppm): U - 68 to 44, Th - 58 to 19, total REE - 723 to 406, Y - 1049 to 553, and Li - 1.23 to 0.91 at the constant (Lu/La)n ratios (4200-4600). Zircon's crystallization temperature calculated from the Ti content is 705 °C and is consistent with those calculated on the base of the mineral composition. (2) Small sized (60-100 μm) zircons. Most of these occur within plagioclase and truncate antiperthite lamellae. They show euhedral zoned cores and bright rims in CL. (3) Zircons principally distinguished from those of groups 1 and 2. These are dark in CL, some grains are severely structurally damaged and contain numerous inclusions (Qzt, Pl, Kfsp, rare Opx

  16. Mineralogy and petrogenesis of lunar magnesian granulitic meteorite Northwest Africa 5744

    NASA Astrophysics Data System (ADS)

    Kent, Jeremy J.; Brandon, Alan D.; Joy, Katherine H.; Peslier, Anne H.; Lapen, Thomas J.; Irving, Anthony J.; Coleff, Daniel M.

    2017-09-01

    Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first-discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg-suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact-related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact-induced shock.

  17. Solution--Redeposition and the orthoclase-microcline transformation: Evidence from Adirondack granulites

    SciTech Connect

    Waldron, K.A. . Dept. of Geology); Parsons, I. . Dept. Geology and Geophysics); Brown, W.B. )

    1993-03-01

    Feldspar microtextures in Adirondack granulites suggest that the transformation of orthoclase to microcline has been accomplished by solution--redeposition. The orthoclase (Or)-rich part of an optically mesoperthitic alkali feldspar was found to be cryptoperthitic when examined by transmission electron microscopy. A two-stage thermal history is proposed to explain the coarse and fine textures, with the cryptoperthite forming by coherent exsolution below 350--400 C. Of particular interest are areas within the Or-rich cryptoperthite where the predominant tweed microtexture is cut by seams'' of microcline parallel to b and the cryptoperthite lamellae. The seams contain polygonal microcline subgrains and micropores (0.1--1.5 [mu]m in diameter). Micropores have been liked with fluid- assisted subgrain formation and turbidity in feldspars. Subgrains, micropores and the tweed/microcline interfaces within the seams often have simple crystallographic indices characteristic of the Adularia habit. The Adularia habit is characteristic of feldspar that has grown in low temperature veins or in sediments and appears to develop during in situ solution--redeposition of alkali feldspar. The crystal habit of the microcline subgrains, the presence of micropores within the seams and the textural relationship between the seams and cryptoperthite lamellae suggest that low temperature fluid infiltration resulted in solution--redeposition of the alkali feldspar on a remarkably fine scale. Subsolidus recrystallization of feldspars in this fashion may have important geochemical implications, particularly for [sup 18]O/[sup 16]O exchange.

  18. Metamorphism of cordierite gneisses from Eastern Ghat Granulite Terrain, Andhra Pradesh, South India

    NASA Technical Reports Server (NTRS)

    Murthy, D. S. N.; Charan, S. Nirmal

    1988-01-01

    Cordierite-bearing metapelites of the Eastern Ghat granulite terrain occur in close association of Khondalites, quartzites, calc-silicate rocks and charnockites. Rocks occurring between Bobbili in the north and Guntur in the south of Andhra Pradesh are studied. The association of the mineral and textural relationships suggest the following metamorphic reactions: Garnet + sillimanite + quartz = cordierite, hypersthene + sillimanite + quartz = cordierite, sillimanite + spinel = cordierite + corundum, and biotite + quartz + sillimanite = cordierite + K=feldspar. Generally the minerals are not chemically zoned except garnet-biotite showing zoning when they come in close contact with one another. The potential thermometers are provided by the Fe-Mg distribution of coexisting biotite-garnet and cordierite-garnet. Conflicting interpretation of the P/T dependence of these reactions involving cordierite are due to H2O in the cordierite. The presence of alkali feldspar-quartz assemblage which is common in these gneisses will be constrained from melting only if H2O activity is less than 0.5. The piezometric array inferred is convex towards the temperature array, indicating a rapid and isothermal crustal uplift probably aided by thrust tectonics.

  19. Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland

    USGS Publications Warehouse

    Whitehouse, M.J.

    1988-01-01

    A published Sm-Nd whole-rock isochron of 2,920 ?? 50 Myr, obtained from a wide range of lithologies in the Lewisian complex of north-west Scotland, was interpreted1 as the time of protolith formation. This date is ???260 Myr older than estimates for the timing of high-grade metamorphism in the complex at ??? 2,660 Myr2'3, and this period is considered to represent the duration of the Lewisian crustal accretion-differentiation superevent (CADS)4. Here we give new Sm-Nd data, obtained specifically from granulite facies tonalitic gneisses, that yield a date of 2,600 ??155 Myr. Although depleted-mantle model ages (tDM suggest >200 Myr of premetamorphic crustal residence, the regression date and its associated initial Nd-isotopic parameters demonstrate Nd-isotopic homogenization during the high-grade event, as well as the probability of general rare-earth-element (REE) mobility. Models for selective element depletion in the complex have previously assumed REE immobility since 2,920 Myr, but the data presented here suggest that a reappraisal of the depletion mechanism is required. ?? 1988 Nature Publishing Group.

  20. A granulite record of multistage metamorphism and REE behavior in the Dabie orogen: Constraints from zircon and rock-forming minerals

    NASA Astrophysics Data System (ADS)

    Wang, Shui-Jiong; Li, Shu-Guang; An, Shi-Chao; Hou, Zhen-Hui

    2012-04-01

    A combined study of mineral inclusions, U-Pb ages and trace elements was carried for zircon and coexisting minerals from granulite in the North Dabie Terrane (NDT) of the Dabie-Sulu ultrahigh-pressure metamorphic (UHP) zone, east-central China. The results provide insights into the exhumation history of NDT and into rare earth element (REE) behavior during retrogression. Besides inherited cores and one magmatic rim, zircons separated from the granulite record three episodes of metamorphism under different P-T conditions: (1) 223.8 ± 2.3 Ma for domains that contain Grt + Cpx ± Rt ± F - Ap ± Aln inclusions without plagioclase and show flat HREE patterns without negative Eu anomalies, representing peak eclogite-facies event; (2) 213.3 ± 2.1 Ma for domains that contain Pl ± Cpx ± Grt ± Qtz ± Ap inclusions and show rather flat HREE patterns with negative Eu anomalies, corresponding to granulite-facies retrogression; (3) 199.9 ± 3.3 Ma for domains that contain Amp ± Pl ± Qtz ± Ap inclusions and show high REE contents with steep HREE patterns and remarkable negative Eu anomalies, representing amphibolite-facies overprinting. Therefore, the UHP eclogite in NDT experienced decompression heating during the initial exhumation, with local hydration in the late stage of the Triassic continental collision. Garnet in the granulite is composed of a corroded core with embayed outline and spongy texture and an overgrowth rim. There is equilibrium distribution of HREE between garnet rim and granulite-facies zircon domain, confirming the geological interpretation of 213.3 ± 2.1 Ma for the granulite-facies metamorphism. There is the prograde HREE depletion in porphyroblastic garnet from core to rim and the continuous decrease of HREE from the eclogitic to granulitic zircons, suggesting that the metamorphic transformation from eclogite-facies to granulite-facies took place in a closed system. On the other hand, the amphibolitic zircons show steep HREE patterns and

  1. Tectonics of an exhumation zone in the Erzgebirge, N-Bohemian Massif: constraints from microstructures and EBSD data

    NASA Astrophysics Data System (ADS)

    Hallas, Peter; Kroner, Uwe

    2017-04-01

    The overthrusting of isothermally exhumed (U)HP units onto medium pressure gneiss complexes is a striking feature of the variscan Erzgebirge (N-Bohemian Massif). Because of a complex deformation history the exhumation mechanism of the deeply subducted rocks is controversially discussed. Here we present first results from detailed studies of the (U)HP / MP shear zone contact in the roof of the Catherine-Reitzenhain gneiss dome including field work, microscopic observation and EBSD texture analysis. Generally, the entire zone is characterized by a flat lying main foliation partly overprinting preexisting steeper inclined fabrics. The complex particle path in the shear zone is indicated by a large scatter of the x axis of the finite strain ellipsoid. In the medium-pressure units an initially NE-SW oriented stretching lineation is obliterated by a second elongation with WNW-ESE azimuth. In contrast, the (ultra)high-pressure units preserve a WSW-ENE oriented stretching lineation. Additionally, different exhumation paths are revealed by microkinematic indicators with top to the NE, (W)SW and (W)NW shearing. EBSD data from mica generally reveal plane to flattening strain with [001] point maxima near z and point maxima of [100] and [010] near x and y respectively as well as a girdle distribution of [100] and [010] in the xy plane of the finite strain ellipsoid. Textures of samples with an apparent constrictional strain geometry additionally contain a second [001] maxima deviating from the first one up to 90°. We explain this feature by stepwise deformation with different plane strain geometries rather than by a single constrictional process. Quartz shows all features of dynamic recrystallization by pervasive grain boundary migration. The texture is characterized by pronounced point [0001] maxima in y. However, in samples with multiple fabrics the finite quartz texture probably reflects incomplete overprinting of preexisting Crystal Preffered Orientations. In conclusion

  2. Two Lithologies in Lithospheric Mantle Beneath Nothern Margin of the Bohemian Massif (e Germany and SW Poland).

    NASA Astrophysics Data System (ADS)

    Matusiak-Małek, Magdalena; Puziewicz, Jacek; Ntaflos, Theodoros; Kukuła, Anna; Ćwiek, Mateusz

    2014-05-01

    The subcontinental lithospheric mantle (SCLM) occurring beneath Bohemian Massif in Central Europe has been sampled in Cenozoic times by numerous lavas. Recent studies (Puziewicz et al. 2011 and references therein) show that mantle in this region is mostly anhydrous, harzburgitic, and was subjected to various kinds of metasomatic events. Two major mantle lithologies characterized by different major element composition of peridotite- forming minerals occur in the SCLM Lower Silesia and Lusatia (op. cit. and unpublished results, 9 sites). Lithology "A" (minimal temperatures from 900 to 1000ºC or no equilibrium between cpx and opx) contains olivine Fo90.5 -92.0. Part of the population "A" peridotites contain clinopyroxene of mg# 94 - 95, typical for low temperatures of equilibration. The lithology "B" (equilibration temperatures close to 900 ºC) contains olivine Fo87.5-90.0. Elevated contents of LREE in clinopyroxene from both the lithologies "A" and "B" suggest their equilibration with one of the two metasomatic agents stated in this area: anhydrous silicate alkaline melt or carbonatite-silicate melt. Action of hydrous alkaline melts in the mantle in the region is recorded only locally (e.g. Wilcza Góra). In some sites (e.g. Krzeniów) the trace element patterns show that decreasing mg# of clinopyroxene in the "A" peridotites is due to gradual replacement of primary lower-temperature mineral assemblage by the later higher-temperature one. This suggests that the variation of mineral chemistry is rather due to chromatographic fractionation of metasomatic agents than due to vertical variation in lithospheric mantle temperatures (Christensen et al.,2001). The "B" peridotites originated due to "Fe-metasomatism" of more magnesian peridotites by silicate melts percolating through lithospheric mantle. The peridotites belonging to lithology "A" might have been partly the protolith of the lithology "B". The data on Central European lithospheric mantle are equivocal and thus

  3. Wagnerite-MA5BC From Granulite-Facies Paragneiss, Larsemann Hills, Prydz Bay, East Antarctica

    NASA Astrophysics Data System (ADS)

    Ren, L.; Grew, E. S.; Xiong, M.; Ma, Z.

    2003-04-01

    Wagnerite-Ma5bc, which is one of three new polytypes of (Mg,Fe)_2(PO_4)(F,OH) (Chopin, Armbruster &Leyx, this conference), occurs in paragneiss associated with banded cordierite-prismatine gneiss. It forms anhedral to euhedral grains mostly 0.5-2 mm across, some with a tabular habit. Textures are consistent with a primary assemblage wagnerite-Ma5bc + plagioclase + apatite + magnetite + ilmenite-hematite that crystallized under granulite-facies conditions (750 - ˜860^oC, 6-7 kbar). Also present are biotite, quartz, K-feldspar, monazite, xenotime, corundum, hercynite, sulfide. Electron microprobe analyses give P_2O_5 41.39, SiO_2 0.06, TiO_2 0.88, FeO 4.16, MnO 0.09, MgO 44.54, CaO 0.09, F 6.87, H_2O (calculated for OH + F = 1) 2.04, O=F -2.89, total 97.22 wt%, corresponding to (Mg1.88Fe0.10Ti0.02)(P0.99O_4)(F0.61OH0.39). Space group is Ia. Lattice parameters a = 9.645(2)Å, b = 31.659(6) Å , c = 11.914(2) Å, â=108.26 (3)^o, V= 3455(1) Å^3 for Z=40, Dcalc = 3.18(1) g/cm^3. The crystal structure has been solved by direct methods and refined to R_1=0.0413 for the independent 4521 reflections [I>2σ(I)] using MoKα radiation. The primary difference among the wagnerite polytypes is ordering of the (F,OH) positions. F can occupy one of two positions resulting in two distinct configurations along the a direction. In magniotriplite the sequence of configurations in the b direction is disordered, whereas in wagnerite-Ma2bc the sequence is ordered 121212... and in wagnerite-Ma5bc, 12112... Magniotriplite and the wagnerite polytypes do not overlap in composition: minerals richer in Fe and Mn (average ionic radius >= 0.76 Å) crystallize as the disordered minerals in the triplite group, whereas highly magnesian minerals (average ionic radius <= 0.73 Å or >= 86% of the Mg end member) crystallize as the ordered wagnerite polytypes. Magniotriplite formed at moderate temperatures (e.g., amphibolite-facies), whereas wagnerite-Ma2bc is found in rocks formed under a wide range

  4. Melt inclusions and origin of granite in migmatitic granulites from the Kerala Khondalite Belt, Southern India

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; Cesare, Bernardo; Salvioli Mariani, Emma; Cavallo, Andrea

    2010-05-01

    Both glassy and crystallized melt inclusions (MI) occur in garnet in metapelitic granulites from the Kerala Khondalite Belt. These rocks were metamorphosed and partially melted at UHT conditions during the Pan-African event, and MI represent droplets of the anatectic melt, originated by dehydration melting of biotite and trapped by garnet growth at supersolidus conditions. An extensive ESEM-BSE mapping study, along with EMPA analysis and re-heating experiments, has been carried out to characterize these anatectic MI. The inclusions range from 4 to 35 μm in diameter and occur as clusters in garnets. In spite of the long time it took for these rocks to cool below 350 °C (at least 60 m.y.), different degrees of crystallization were observed in the same cluster, ranging from totally crystallized to totally glassy. The crystallized MI are referred to as "nanogranites" (Cesare et al., 2009) and always contain quartz, Mg-rich biotite (XFe=0.23) and two feldspars in a fine-grained polycrystalline aggregate. Based on microstructural evidence, biotite crystallized as first phase, preferentially on the walls of the MI, while quartz and feldspars crystallized later, often forming graphic intergrowths and/or melt pseudomorph-like structures (≥ 50 nm) similar to coarser structures (≈ tens of microns scale) observed in the host rocks. The glassy inclusions are rare (about 15% of the total) and smaller in size (≤15 μm in diameter) compared to the crystallized nanogranite MI. Both MI types often show negative crystal-shape and contain trapped crystalline phases that are accessories in the host rock, including rutile, titanite, zircon, apatite and Zn-rich spinel. Partially crystallized MI have been also recognized, containing an amorphous phase identified as a residual melt Where Cl and Ca are preferentially partitioned. Re-heating experiments in a HT hearing stage succeeded in re-homogenizing the nanogranite inclusions. EMP data on 40 re-homogenized MI show an average SiO2

  5. Pseudotachylytes of the Deep Crust: Examples from a Granulite-Facies Shear Zone

    NASA Astrophysics Data System (ADS)

    Orlandini, O.; Mahan, K. H.; Regan, S.; Williams, M. L.; Leite, A.

    2013-12-01

    The Athabasca Granulite Terrane is an exhumed section of deep continental crust exposed in the western Canadian shield. The terrane hosts the 1.88 Ga Cora Lake shear zone, a 3-5 km wide sinistral and extensional oblique-slip system that was active at high-pressure granulite-grade conditions ( ~1.0 GPa, >800°C to ~0.8 GPa and 700 °C). Pseudotachylyte, a glassy vein-filling substance that results from frictional melting during seismic slip, is common in ultramylonitic strands of the shear zone, where veins run for tens of meters subparallel to foliation. Some but not all PST veins have been overprinted with the Cora Lake shear zone foliation, and undeformed PST locally bears microlitic garnet. The frictional melts that quench into PST may reach >1400 °C, but are extremely localized and cool to country rock temperatures within minutes, resulting in glass and/or microlitic mineral growths. The melt itself is thought by many to be in disequilibrium with the host rock due to its rapid nature, but during cooling equilibrium is probably reached at small scales. This allows for microprobe analysis of adjacent microlites for thermobarometric calculations. Preliminary results from undeformed (e.g., youngest of multiple generations) PST suggest that quenching occurred in upper amphibolite facies ambient conditions and is compatible with later stages of Cora Lake shear zone activity. Host-rock mylonites contain abundant garnet and pyroxene sigma clasts indicating sinistral shear, and where PST-bearing slip surfaces are found at low angles to the foliation, they display sinistral offset. The host rock contains abundant macroscopic and microscopic sinistral shear fracture systems (e.g., Riedel [R], Y, and P displacement surfaces) within the immediate proximity of PST veins, indicating a complex interplay of brittle and ductile behavior that is interpreted to be genetically related to the formation of the PST. The shear fracture systems are characterized by sharply bounded

  6. Partial fusion of basic granulites at 5 to 15 kbar: implications for the origin of TTG magmas

    NASA Astrophysics Data System (ADS)

    Springer, Wilhelm; Seck, Hans Adolf

    Partial fusion experiments with basic granulites (S6, S37) believed to represent the lower crust beneath the Eifel region (Germany) were performed at pressures from 5 to 15 kbar. Water-undersaturated experiments were carried out in the presence of 1 wt% H2O plus 2.44 or 0.81 wt% CO2 equivalent to mole fractions of H2O/(H2O+CO2) of 0.5 and 0.75, respectively, of the volatile components added. At temperatures from 850 to 1100 °C the weight proportions of melt range from 7 to 30 %. Melt compositions change from trondhjemitic over tonalitic to dioritic with increasing degree of partial melting. Crystalline residua are plagioclase/pyroxene dominated at 5 kbar to garnet/pyroxene dominated at 15 kbar. Dehydration melting was studied in granulite S35 similar in composition to S6. The magmatic precursors of the granulite xenoliths used in this study had geochemical characteristics of cumulate gabbro (metagabbro S37) and evolved melts (metabasalts S6, S35), respectively. Melts from granulite S37 match the major element compositions of natural trondhjemites and tonalites. At 5 kbar, their Al2O3 is relatively low, similar to tonalites from ophiolites. At 15 kbar, Al2O3 in the melts is high due to the near absence of plagioclase in the crystalline residua. The Al2O3 concentrations in 15 kbar melts from S6 ( 20 wt%) are higher than in natural tonalites. Depth constraints on the formation of tonalitic magmas in the continental crust are provided by REE (rare earth element) patterns of the synthetic melts calculated from the known REE abundances in metagabbro S37 and metabasalt S6 assuming batch melting and using partition coefficients from the literature. The REE patterns of tonalites from active continental margins and Archean trondhjemite-tonalite-granodiorite associations low in REE with LaN (chondrite normalised) from 10 to 30 and YbN from 1 to 2 are reproduced at pressures of 10 and 12.5 kbar from metagabbro S37 which displays a slightly L(light)REE enriched pattern with La

  7. 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.

  8. Fluid induced microstructures in granulites from the Reynolds Range, central Australia

    NASA Astrophysics Data System (ADS)

    Prent, Alexander; Beinlich, Andreas; Raimondo, Tom; Putnis, Andrew

    2016-04-01

    Fluids play a major role in the evolution of the Earth's crust, driving metamorphic reactions, facilitating transport of mass and heat, and changing the physical properties of rock. Shear zones present in intraplate orogens are ideal natural laboratories to study the relationship of fluid-driven rock weakening to deformation, and thus the impact of fluid availability on the tectonic reworking of continental interiors. Here we present preliminary observations from the Aileron Shear Zone (ASZ), Reynolds Range, central Australia, a major crustal-scale thrust of the Palaeozoic Alice Springs Orogen (ASO). This study focuses on the effects of fluids on the mineralogy and mineral chemistry of deep crustal rocks collected from a transect running through the ASZ. The ASZ is thought to have been of major importance during exhumation of the ASO, and exhumes a partly retrogressed suite of felsic and metasedimentary granulite facies gneisses. Hydration reactions associated with retrogression resulted in the partial replacement of orthopyroxene and numerous myrmekite textures associated with plagioclase and mica. In undeformed samples, orthopyroxene (En56 Fer44) rims are partly replaced by a zoned sequence of biotite (Phl70 Ann30), sub-parallel rims of magnetite, biotite and K-feldspar (Or87). Deformed samples gradually show an increase in dynamic recrystallization of quartz, with fully recrystallized bands of foam texture quartz defining the foliation together with biotite. Quartz and minor biotite replacement then dominates the mineral assemblage with increasing strain. The presence of fluid-driven mineral replacement reactions in undeformed samples suggests that hydration predates shearing and exhumation, and furthermore, that strain may have been localised in areas of intense hydration and rock weakening. Retrograde reactions and myrmekite textures suggest the availability of a silica-saturated fluid. Additional mass-balance calculations will be applied to constrain the

  9. Ultra-high temperature granulite-facies metamorphic rocks from the Mozambique belt of SW Tanzania

    NASA Astrophysics Data System (ADS)

    Sommer, H.; Kröner, A.

    2013-06-01

    The metamorphic rocks in the Neoproterozoic (Pan-African) Mozambique belt of southwestern Tanzania, around the town of Songea, can be subdivided into one- and two pyroxene bearing charnockitic gneisses, migmatitic granitoid gneisses and amphibolite-facies metapelites. Lower-grade amphibolite-facies rocks are rare and can be classified as sillimanite- and/or garnet-bearing metapelites. Most of the studied charnockitic gneisses show excellent corona textures with large orthopyroxene grains rimmed by clinopyroxene, followed by quartz and well developed garnet rims due to the reaction Opx + Pl = Grt + Cpx + Qtz that formed during isobaric cooling. These and other charnockitic gneisses show symplectites of orthopyroxene and An-rich plagioclase that resulted from the breakdown of garnet during isothermal decompression due to the reaction Grt + Cpx + Qtz = Opx + Pl. Geothermobarometric calculations yield up to ~ 1050 °C and up to ~ 12 kbar for peak metamorphic conditions. These are higher temperature and slightly lower pressure conditions than reported for other granulite-facies terrains in the Mozambique belt of Tanzania. Single zircon Pb-Pb evaporation and U-Pb SHRIMP ages for magmatic zircons extracted from two charnockitic and two granitic gneisses cluster in two groups, one at ~ 750 Ma and one at ~ 1150 Ma with the older reflecting the time of emplacement of the igneous precursors, and the younger approximating the time of charnockitization. These protolith ages are similar to those farther east in the Masasi area of southern Tanzania, as well as in northern Mozambique and in southern Malawi, and suggest that the Mozambique belt consists of chronologically heterogeneous assemblages whose pre-metamorphic tectonic setting remains obscure.

  10. Partial melting of apatite-bearing charnockite, granulite, and diorite: Melt compositions, restite mineralogy, and petrologic implications

    NASA Technical Reports Server (NTRS)

    Beard, James S.; Lofgren, Gary E.; Sinha, A. Krishna; Tollo, Richard P.

    1994-01-01

    Melting experiments (P = 6.9 kbar, T = 850-950 deg C, NNO is less than fO2 is less than HM) were done on mafic to felsic charnockites, a dioritic gneiss, and a felsic garnet granulite, all common rock types in the Grenville basement of eastern North America. A graphite-bearing granulite gneiss did not melt. Water (H2O(+) = 0.60 to 2.0 wt %) is bound in low-grade, retrograde metamorphic minerals and is consumed during the earliest stages of melting. Most melts are water-undersaturated. Melt compositions range from metaluminous, silicic granodiorite (diorite starting composition) to peraluminous or weakly metaluminous granites (all others). In general, liquids become more feldspathic, less silicic, and less peraluminous and are enriched in FeO, MgO, and TiO2 with increasing temperature. Residual feldspar mineralogy controls the CaO, K2O, and Na2O contents of the partial melts and the behavior of these elements can be used, particularly if the degree of source melting can be ascertained, to infer some aspects of the feldspar mineralogy of the source. K-feldspar, a common restite phase in the charnockite and granulite (but not the diorite) should control the behavior of Ba and, possibly, Eu in these systems and yield signatures of these elements that can distinguish source regions and, in some cases, bulk versus melt assimilation. Apatite, a common restite phase, is enriched in rare earth elements (REE), especially middle REE. Retention of apatite in the restite will result in steep, light REE-enriched patterns for melts derived from the diorite and charnockites.

  11. Silurian high-pressure granulites from Central Qiangtang, Tibet: Constraints on early Paleozoic collision along the northeastern margin of Gondwana

    NASA Astrophysics Data System (ADS)

    Zhang, Xiu-Zheng; Dong, Yong-Sheng; Li, Cai; Deng, Ming-Rong; Zhang, Le; Xu, Wang

    2014-11-01

    High-pressure (HP) granulites are commonly regarded as indicators of plate convergence and collision following the subduction of oceanic or continental crust. In this study we report the discovery of Silurian HP basic granulites from Central Qiangtang on the Tibetan Plateau. Detailed petrology and geochronology reveal a three-stage metamorphic history based on inclusions, reaction textures, and garnet zoning patterns. Peak metamorphism at 830-860 °C and 1.15-1.45 GPa (M1) is defined by high-Ca garnet cores, high-Al clinopyroxene, and high-Na plagioclase. Symplectites or coronas of orthopyroxene + plagioclase ± magnetite around garnet porphyroblasts indicate garnet breakdown reactions at ca. 810-830 °C and 0.65-0.85 GPa (M2). Kelyphites of amphibole + plagioclase around garnet formed during the cooling process at about 590-650 °C and 0.62-0.82 GPa (M3). These results help define a sequential P-T path containing near-isothermal decompression (ITD) and near-isobaric cooling (IBC) stages. Identification of mineral inclusion assemblages in zircons dated by U-Pb SHRIMP and LA-ICP-MS reveals peak HP metamorphism at ca. 427-422 Ma, subsequent near-isothermal decompression with associated retrograde reactions at ca. 392-389 Ma, and continued cooling at ca. 360 Ma. The P-T-t path of HP basic granulites reflects collision followed by extensional exhumation during early Paleozoic orogenesis. The present results indicate the occurrence of a collisional event along the northern margin of Indo-Australian Gondwana during the Silurian. Renewed Gondwana-directed subduction and subsequent collision probably led to the opening of the Paleo-Tethys Ocean.

  12. Constraints on formation and evolution of the lunar crust from feldspathic granulitic breccias NWA 3163 and 4881

    NASA Astrophysics Data System (ADS)

    McLeod, Claire L.; Brandon, Alan D.; Fernandes, Vera A.; Peslier, Anne H.; Fritz, Jörg; Lapen, Thomas; Shafer, John T.; Butcher, Alan R.; Irving, Anthony J.

    2016-08-01

    Lunar granulitic meteorites provide new constraints on the composition and evolution of the lunar crust as they are potentially derived from outside the Apollo and Luna landing sites. Northwest Africa (NWA) 3163, the focus of this study, and its paired stones NWA 4881 and NWA 4483, are shocked granulitic noritic anorthosites. They are petrographically and compositionally distinct from the Apollo granulites and noritic anorthosites. Northwest Africa 3163 is REE-depleted by an order of magnitude compared to Apollo granulites and is one of the most trace element depleted lunar samples studied to date. New in-situ mineral compositional data and Rb-Sr, Ar-Ar isotopic systematics are used to evaluate the petrogenetic history of NWA 3163 (and its paired stones) within the context of early lunar evolution and the bulk composition of the lunar highlands crust. The NWA 3163 protolith was the likely product of reworked lunar crust with a previous history of heavy REE depletion. The bulk feldspathic and pyroxene-rich fragments have 87Sr/86Sr that are indistinguishable and average 0.699282 ± 0.000007 (2σ). A calculated source model Sr TRD age of 4.340 ± 0.057 Ga is consistent with (1) the recently determined young FAS (Ferroan Anorthosite) age of 4.360 ± 0.003 Ga for FAS 60025, (2) 142Nd model ages for the closure of the Sm-Nd system for the mantle source reservoirs of the Apollo mare basalts (4.355-4.314 Ga) and (3) a prominent age peak in the Apollo lunar zircon record (c. 4.345 Ga). These ages are ∼100 Myr younger than predicted timescales for complete LMO crystallization (∼10 Myrs after Moon formation, Elkins-Tanton et al., 2011). This supports a later, major event during lunar evolution associated with crustal reworking due to magma ocean cumulate overturn, serial magmatism, or a large impact event leading to localized or global crustal melting and/or exhumation. The Ar-Ar isotopic systematics on aliquots of paired stone NWA 4881 are consistent with an impact event

  13. Regional variation in the Amitsoq gneisses related to crustal levels during late Archean granulite facies metamorphism: Southern west Greenland

    NASA Technical Reports Server (NTRS)

    Nutman, A. P.; Bridgwater, D.; Mcgregor, V. R.

    1986-01-01

    The dominant lithology at Kangimut sangmissoq is described as nebulitic tonalitic gneiss containing highly distended plagioclase phyric amphibolites. The gneiss amphibolite complex was intruded by Nuk gneiss between 3.05 and 2.90 Ga and later (2.6 to 2.7 Ga) by post granulite facies granitoid sheets. The amphibolites are though to be Ameralik dikes and the older gray gneiss are then Amitsoq by definition. The problem arises when the isotopic data are considered, none of which indicate rocks older that about 3.0 Ga.

  14. Magnetic Anomalies and Rock Magnetic Properties Related to Deep Crustal Rocks of the Athabasca Granulite Terrane, Northern Canada

    NASA Astrophysics Data System (ADS)

    Brown, L. L.; Williams, M. L.

    2010-12-01

    The Athabasca granulite terrane in northernmost Saskatchewan, Canada is an exceptional exposure of lower crustal rocks having experienced several high temperature events (ca 800C) during a prolonged period of deep-crustal residence (ca 1.0 GPa) followed by uplift and exhumation. With little alteration since 1.8 Ga these rocks allow us to study ancient lower crustal lithologies. Aeromagnetic anomalies over this region are distinct and complex, and along with other geophysical measurements, define the Snowbird Tectonic zone, stretching NE-SW across northwestern Canada, separating the Churchill province into the Hearne (mid-crustal rocks, amphibolite facies) from the Rae (lower crust rocks, granulite facies). Distinct magnetic highs and lows appear to relate roughly to specific rock units, and are cut by mapped shear zones. Over fifty samples from this region, collected from the major rock types, mafic granulites, felsic granulites, granites, and dike swarms, as well as from regions of both high and low magnetic anomalies, are being used to investigate magnetic properties. The intention is to investigate what is magnetic in the lower crust and how it produces the anomalies observed from satellite measurements. The samples studied reveal a wide range of magnetic properties with natural remanent magnetization ranging from an isolated high of 38 A/m to lows of 1 mA/m. Susceptibilities also range over several orders of magnitude, from 1 to 1 x10-4 SI. Magnetite is identified in nearly all samples using both low and high temperature measurements, but concentrations are generally very low. Hysteresis properties on 41 samples reveal nearly equal numbers of samples represented by PSD and MD grains, with a few samples (N=6) plotting in or close to the SD region. Low temperature measurements indicate that most samples contain magnetite, showing a marked Verway transition around 120K. Also identified in nearly half of the samples is pyrrhotite, noted by low temperature

  15. Gallium and germanium geochemistry during magmatic fractionation and post-magmatic alteration in different types of granitoids: a case study from the Bohemian Massif (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Gardenová, Nina; Kanický, Viktor; Vaculovič, Tomáš

    2013-06-01

    Contents of Ga and Ge in granites, rhyolites, orthogneisses and greisens of different geochemical types from the Bohemian Massif were studied using inductively coupled plasma mass spectrometry analysis of typical whole-rock samples. The contents of both elements generally increase during fractionation of granitic melts: Ga from 16 to 77 ppm and Ge from 1 to 5 ppm. The differences in Ge and Ga contents between strongly peraluminous (S-type) and slightly peraluminous (A-type) granites were negligible. The elemental ratios of Si/1000Ge and Al/1000Ga significantly decreased during magmatic fraction: from ca. 320 to 62 and from 4.6 to 1.2, respectively. During greisenization, Ge is enriched and hosted in newly formed hydrothermal topaz, while Ga is dispersed into fluid. The graph Al/Ga vs. Y/Ho seems to be useful tool for geochemical interpretation of highly evolved granitoids.

  16. (222)Rn activity concentration differences in groundwaters of three Variscan granitoid massifs in the Sudetes (NE Bohemian Massif, SW Poland).

    PubMed

    Przylibski, Tadeusz A; Gorecka, Joanna

    2014-08-01

    Based on research conducted in three Variscan granitoid massifs located within the crystalline Bohemian Massif, the authors confirmed that the higher the degree of their erosional dissection, the smaller the concentration of (222)Rn in groundwaters circulating in these massifs. This notion implies that radon waters and high-radon waters, from which at least some of the dissolved radon should be removed before feeding them as drinking water to the water-supply system, could be expected in granitoid massifs which have been poorly exposed by erosion. At the same time, such massifs must be taken into account as the areas of possible occurrence of radon medicinal waters, which in some countries can be used for balneotherapy in health resorts. Slightly eroded granitoid massifs should be also regarded as very probable radon prone areas or areas of high radon potential.

  17. U-Pb (LA-PIMMS) Ages of Inherited Zircons from Early Palaeozoic Granitoids of the W Sudetes, N Bohemian Massif, Central Europe: Implications for Neoproterozoic Continental Reconstructions

    NASA Astrophysics Data System (ADS)

    Crowley, Q. G.; Patocka, F.; Kachlík, V.

    2003-04-01

    A U-Pb laser ablation plasma ionisation multi-collector mass spectrometry (LA-PIMMS) geochronological study of zircons from early Palaeozoic (meta)granitoids of the Czech W Sudetes (E Saxothuringian Zone), NW Bohemian Massif, was carried out in order to determine the range of inherited age spectra preserved in these lithologies. Backscattered SEM images indicate that many zircons have distinct cores and rims. The majority of inherited zircon components yield concordant U-Pb ages that fall into the following age ranges: (1) 520-770 Ma, (2) 1.9-2.2 Ga and (3) ca. 3.0 Ga. These three age populations are typical of the W African Craton and the Armorican Terrane Assemblage of Europe. The age spectra correspond to Cadomian, Birimian / Icartian / Eburnean / Burkinian and Leonian events respectively. Some previous Pb-Pb zircon and whole rock Nd studies of similar lithologies from the W Sudetes (e.g. Hegner &Kröner, 2000) have attributed the presence of Mesoproterozoic 207Pb/206Pb ages to a peri-Amazonian provenance. Although some zircons from this study have yielded apparent Mesoproterozoic ages, they are discordant and can be resolved into early Palaeozoic to Neoproterozoic lower intercept and Palaeoproterozoic to Archaean upper intercept components. This unequivocally proves that an inherited Grenvillian component does not exist in these lithologies. We therefore favour derivation of the Saxothuringian zone and associated members of the Armorican Terrane Assemblage from a W African Craton Gondwanan setting. References: Hegner, E, &Kröner, A. 2000. Review of Nd data and xenocrystic and detrital ages from the pre-Variscan basement in the Eastern Bohemian Massif: speculations on palinspastic reconstructions. In: Franke, W., Altherr, R., Haak, V. &Oncken, O. (eds.), Orogenic Processes: Quantification and Modelling in the Variscan Belt of Central Europe Geological Society of London Special Publication, 179, 113-129.

  18. Indentation as an extrusion mechanism of lower crustal rocks: Insight from analogue and numerical modelling, application to the Eastern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Duretz, T.; Kaus, B. J. P.; Schulmann, K.; Gapais, D.; Kermarrec, J.-J.

    2011-05-01

    Recent petrological, structural and geochronological studies of the eastern margin of the Bohemian Massif (Czech Republic) suggest a conceptual geodynamical model to explain exhumation of lower crustal (20 kbar, 800 °C) felsic rocks. The model involves indentation of a weak orogenic lower crust by an adjacent rigid mantle lithosphere, resulting in crustal-scale buckling of the weak orogenic lower/middle crust interface followed by extrusion of a ductile nappe over the rigid promontory. The hypothesis has been investigated using both analogue and numerical models. Analogue experiments using a three layer sand-silicone setup were carried out in Rennes laboratory (France). Results show that the most important features of the conceptual model can be reproduced: extrusion of lowermost silicone over the indenter and flow of horizontal viscous channel underneath a rigid lid above the actively progressing promontory. Furthermore, experimental results show that a plateau develops above the channelling lower crust. Two sets of sandbox-scale numerical simulations were performed. The first set of experiments is designed to study the influence of viscosity stratification within the crust on the extrusion process. A second set of experiments were performed in order to quantify the influence of the viscosity and the geometry of the indentor. Non-dimensional scaling laws were derived to predict the maximum extrusion rates associated with the indentation mechanism. Such laws enable the computation vertical extrusion rates that are in good agreement with natural exhumation rates inferred from petrological data. Finally, we discuss the potential positive feedback of Rayleigh-Taylor instability on vertical extrusion for the case of Eastern Bohemian Massif.

  19. Underground electromagnetic activity in two regions with contrasting seismicity: a case study from the Eastern Alps and Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Baroň, Ivo; Koktavý, Pavel; Stemberk, Josef; Macků, Robert; Trčka, Tomáš; Škarvada, Pavel; Lenhardt, Wolfgang; Meurers, Bruno; Rowberry, Mattew; Marti, Xavi; Plan, Lukas; Grasemann, Berhnard; Mitrovic, Ivanka

    2016-04-01

    Electromagnetic emissions (EME) occur during the fracturing of solid materials under laboratory conditions and may represent potential earthquake precursors. We recorded EME from May 2015 to October 2015 in two caves situated in contrasting seismotectonic settings. Zbrašov Aragonite Caves are located close to the seismically quiescent contact between the Bohemian Massif and the Outer Western Carpathians while Obir Caves are located near the seismically active Periadriatic Fault on the southern margin of the Eastern Alps. The specific monitoring points are located at depths of tens of metres below the ground surface as such places are assumed to represent favourably shielded environments. The EME signals were continuously monitored by two custom-made Emission Data Loggers (EDLOG), comprising both analogue and digital parts. The crucial analogue component within the EDLOG is a wideband shielded magnetic loop antenna. To be able to observe EME related rock deformation and microfracturing we recorded signals between 10 and 200 kHz with a sampling frequency of 500 kHz. An ultralow noise preamplifier placed close to the antenna increases the signal-to-noise ratio. Further signal processing consisted of filtering, such as antialiasing and interference rejection, and additional amplification to fit the signal to the full scale range of the AD convertor. The digital part of the EDLOG comprises a range of PC components such as high-capacity replaceable data storage and unbuffered RAM, high-speed multichannel DAQ cards, and custom made control software in the programming environment LabVIEW. During our EME monitoring all the raw data were stored. This has allowed us to perform advanced data processing and detailed analysis. During the study period some artificial EME signals were observed in Zbrašov Aragonite Caves. This artificial noise may have overprinted any natural signals and is most likely to relate to the pumping of CO2. In contrast, markedly different signals were

  20. Multiple migmatite events and cooling from granulite facies metamorphism within the Famatina arc margin of northwest Argentina

    NASA Astrophysics Data System (ADS)

    Mulcahy, Sean R.; Roeske, Sarah M.; McClelland, William C.; Ellis, Joshua R.; Jourdan, Fred; Renne, Paul R.; Vervoort, Jeffrey D.; Vujovich, Graciela I.

    2014-01-01

    The Famatina margin records an orogenic cycle of convergence, metamorphism, magmatism, and extension related to the accretion of the allochthonous Precordillera terrane. New structural, petrologic, and geochronologic data from the Loma de Las Chacras region demonstrate two distinct episodes of lower crustal migmatization. The first event preserves a counterclockwise pressure-temperature path in kyanite-K-feldspar pelitic migmatites that resulted in lower crustal migmatization via muscovite dehydration melting at ˜12 kbar and 868°C at 461 ±1.7 Ma. The shape of the pressure temperature path and timing of metamorphism are similar to those of regional midcrustal granulites and suggest pervasive Ordovician migmatization throughout the Famatina margin. One-dimensional thermal modeling coupled with regional isotopic data suggests Ordovician melts remained at temperatures above their solidus for 20-30 Ma following peak granulite facies metamorphism, throughout a time period marked by regional oblique convergence. The onset of synconvergent extension occurred only after regional migmatites cooled beneath their solidus and was synchronous with the cessation of Precordillera terrane accretion at ˜436 Ma. The second migmatite event was regionally localized and occurred at ˜700°C and 12 kbar between 411 and 407 Ma via vapor saturated melting of muscovite. Migmatization was synchronous with extension, exhumation, and strike-slip deformation that likely resulted from a change in the plate boundary configuration related to the convergence and collision of the Chilenia terrane.

  1. Metamorphic history of garnet-rich gneiss at Ktiš in the Lhenice shear zone, Moldanubian Zone of the southern Bohemian Massif, inferred from inclusions and compositional zoning of garnet

    NASA Astrophysics Data System (ADS)

    Kobayashi, Tomoyuki; Hirajima, Takao; Kawakami, Tetsuo; Svojtka, Martin

    2011-05-01

    Multiple equilibrium stages were identified from garnet-rich gneiss at Ktiš in the Lhenice shear zone of the southern Bohemian Massif, Czech Republic. The matrix of the rock mainly comprises cordierite (Crd), sillimanite (Sil), biotite (Bt), garnet (Grt), quartz (Qtz), K-feldspar (Kfs) and plagioclase (Pl) along with accessory minerals such as spinel (Spl), apatite (Ap), monazite (Mnz) and zircon (Zrn). Bt, Sil, kyanite (Ky) and Pl occur as inclusion phases in Grt. Crd occurs only in the matrix both as isolated grains and as reaction coronas developed around Grt. Spl is closely correlated with the Crd corona. Some coarse-grained (> 3 mm) Grts show chemical heterogeneity both in major and trace elements. Grossular (Grs)-content is homogeneous and high {Xgrs = Ca / (Ca + Mg + Fe + Mn) = 0.27} in a center of the grain and smoothly decreases towards the grain margin (Xgrs = 0.02). However, pyrope (Prp)-content shows an inverse pattern against Grs-content; i.e., Prp-content is low and constant {Xprp = Mg / (Ca + Mg + Fe + Mn) = 0.03} in the center of the grain and gradually increases towards the margin (up to Xprp = 0.28). The contours of Grs- and Prp-contents show symmetrical hexagonal shapes. The distribution pattern of phosphorus, however, shows a striking contrast against Grs-content. The core of the grain is characterized by low-phosphorus content almost below the detection limit of the EPMA analysis but it is armored by the high-phosphorus rim accompanying with local development of phosphorus-poor outermost rim. The outline of phosphorus-poor core shows a hexagonal shape, which is symmetrical to those of Grs- and Prp-content contours, but it is located outside of higher-Grs (Xgrs = 0.27)- and lower-Prp (Xprp = 0.03)-content contours. These observations suggest that the outline of phosphorus-poor core should indicate the original shape of Grs-rich garnet developed during an early stage of the metamorphism. The zoning pattern of major/trace elements in garnet and

  2. Two-pyroxene syenitoids from the Moldanubian Zone of the Bohemian Massif: peculiar magmas derived from a strongly enriched lithospheric mantle source

    NASA Astrophysics Data System (ADS)

    Janoušek, Vojtěch; Holub, František; Gerdes, Axel; Verner, Kryštof

    2013-04-01

    (Ultra-)potassic plutonic rocks constitute a conspicuous association with metamorphic rocks of the high-grade, lower crustal/upper mantle Gföhl Unit (Moldanubian Zone). They can be subdivided into two contrasting suites: (1) coarse Kfs-phyric amphibole-biotite melagranite to quartz syenite (the durbachite series sensu Holub 1997), and (2) essentially even-grained biotite-two-pyroxene quartz syenites to melagranites (Tábor and Jihlava plutons). The latter, "syenitoid suite", characterized by an originally 'dry' mineral assemblage orthopyroxene + clinopyroxene + Mg-biotite, with accessoric zircon, apatite, ilmenite, monazite and/or rutile ± Cr-spinel, is a subject of the current study. Our conventional U-Pb ages for zircon (336.9 ± 0.6 Ma) and rutile (336.8 ± 0.8 Ma) from the Tábor Pluton, together with the age from the Jihlava body (U-Pb zircon: 335.1 ± 0.6 Ma; Kotková et al. 2010), provide a precise time bracket for the emplacement and rapid cooling of the syenitoids below c.600 ° C (closure temperature of U-Pb system in rutile: Cherniak 2000). This is in line with post-tectonic emplacement of hot dry melt into shallow levels of essentially consolidated orogenic crust. Comparably low temperatures obtained by zircon and rutile saturation calculations document probably a delayed onset of crystallization of the accessories in a hot, alkalis and ferromagnesian components-rich magma derived from a mantle source. Indeed, the structural relations inside and around the ultrapotassic plutons suggest that the most important regional HT/LP flat-lying fabric(s) in the Moldanubian Zone are closely related with the emplacement and crystallization of the durbachite suite at 343-338 Ma. They have formed prior to the relatively shallower emplacement of the essentially post-tectonic syenitoids dated at ~337-336 Ma (Žák et al. 2005; Verner et al. 2006, 2008). The two magmatic suites are thus essentially diachronous and not (nearly) contemporaneous (c. 335 Ma) intrusions at

  3. Remelting of Nanogranites in Peritectic Garnet from Granulites of Jubrique, Betic Cordillera, Southern Spain

    NASA Astrophysics Data System (ADS)

    Acosta-Vigil, A.; Barich, A.; Bartoli, O.; Poli, S.; Cesare, B.; Garrido, C. J.

    2014-12-01

    Peritectic minerals in migmatites can trap droplets of melt that form via incongruent melting during crustal anatexis. In most cases, these melts crystallize and form nanogranites upon slow cooling of the anatectic terrane. To obtain information on the primary compositions of crustal melts, nanogranites must be remelted and rehomogenized before analysis. A new occurrence of nanogranites was reported in granulitic gneisses at the bottom of the prograde metamorphic sequence of Jubrique, located on top of the Ronda peridotite slab (Betic Cordillera, S Spain). These nanogranites are trapped in garnet porphyroblasts. They show partially irregular to well facetted negative crystal shapes, and have variable size from ~5-10 μm and reach ~200 μm in diameter. They appear at the core and rim of large Grt crystals, and are composed of rare glass, daughter Qz, Pl, Kfs, Bt and Ms, and solid inclusions of Ky and less frequently Gr, Hc, Rt, Ilm, Zrn and Mnz. Ky was the main solid phase that favored the trapping of melt inclusions (MI) during Grt growth. The presence of Ky+Rt within MI, and their occurrence in the high-P cores of Grt, suggest that partial melting in the gneisses initiated at relatively high P conditions, and that most Grt in these rocks crystallized in the presence of melt. To recover the major and trace element composition of the primary melt during anatexis, we performed remelting experiments on chips of MI-bearing Grt separated from a sample of gneiss at Jubrique, using a piston cylinder apparatus. Experiments were run at 800, 825 and 850°C, 15 Kbar and dry conditions (i.e. no added H2O) for 24 hrs. Preliminary results of the first experiment at 850º show that nanogranites have been successfully remelted; they all contain glass regardless of their textural position. Glass is leucogranitic (SiO2≈65wt%; FeO+MgO≈2wt%), potassic (K#≈12), high in ASI (close to peraluminous) and hydrous (H2O≈11wt.%.). The degree of remelting, however, varies among

  4. The Palaeoproterozoic crustal evolution: evidences from granulite-gneiss belts, collisional and accretionary orogens

    NASA Astrophysics Data System (ADS)

    Mints, M. V.; Konilov, A. N.

    2003-04-01

    The Palaeoproterozoic juvenile assemblages were emplaced within two types of mobile belts: (1) high-grade or "granulite-gneiss" belts; (2) low- and medium-grade volcano-sedimentary and volcano-plutonic belts. Type (1) belts resulted from plume-induced heating, magmatism, emergence of riftogenic basins and volcano-tectonic depressions, their filling with rift-type sediments and juvenile but strongly contaminated lavas and ash-flow deposits, high-grade recrystallization of the lower- and mid-crustal assemblages including the filling of the basins and depressions that followed in intraplate and back-arc settings, and final thrusting and exhumation caused by collision-related tectonism. Type (2) belts represent sutures containing MORB- and arc-related assemblages, together with initial rift-related assemblages formed during evolution of the short-lived, mainly Red Sea-type oceans (intracontinental collisional orogens) and systems of oceanic, island-arc and back-arc terranes amalgamated along continent margins (peripheral accretionary orogens). Palaeoproterozoic history can be subdivided into five periods: (1) 2.51-2.44 Ga superplume activity and displacement of Fennoscandia; (2) 2.44-2.0 (2.11) Ga quiescent within-plate development complicated by local plume- and plate tectonics-related processes; (3) a 2.0-1.95 Ga superplume event; (4) 1.95-1.75 (1.71) Ga combined plume- and plate tectonics-related evolution, resulting in the partial disruption of the continental crust, and formation of accretionary orogens along some margins of the supercontinent and rebirth of the supercontinent entity, and (5) < 1,75 Ga post- and anorogenic magmatism and metamorphism. Magmatic and thermal activity during the early Palaeoproterozoic was almost exclusively concentrated within Laurentia (comprising North American and Fennoscandian cratons). In contrast, late Palaeoproterozoic assemblages are distributed within all continents. The simultaneous appearance of within-plate plume

  5. The Petrology and Geochemistry of Feldspathic Granulitic Breccia NWA 3163: Implications for the Lunar Crust

    NASA Technical Reports Server (NTRS)

    McLeod, C. L.; Brandon, A. D.; Lapen, T. J.; Shafer, J. T.; Peslier, A. H.; Irvine, A. J.

    2013-01-01

    Lunar meteorites are crucial to understand the Moon s geological history because, being samples of the lunar crust that have been ejected by random impact events, they potentially originate from areas outside the small regions of the lunar surface sampled by the Apollo and Luna missions. The Apollo and Luna sample sites are contained within the Procellarum KREEP Terrain (PKT, Jolliff et al., 2000), where KREEP refers to potassium, rare earth element, and phosphorus-rich lithologies. The KREEP-rich rocks in the PKT are thought to be derived from late-stage residual liquids after approx.95-99% crystallization of a lunar magma ocean (LMO). These are understood to represent late-stage liquids which were enriched in incompatible trace elements (ITE) relative to older rocks (Snyder et al., 1992). As a consequence, the PKT is a significant reservoir for Th and KREEP. However, the majority of the lunar surface is likely to be significantly more depleted in ITE (84%, Jolliff et al., 2000). Lunar meteorites that are low in KREEP and Th may thus sample regions distinct from the PKT and are therefore a valuable source of information regarding the composition of KREEP-poor lunar crust. Northwest Africa (NWA) 3163 is a thermally metamorphosed ferroan, feldspathic, granulitic breccia composed of igneous clasts with a bulk anorthositic, noritic bulk composition. It is relatively mafic (approx.5.8 wt.% FeO; approx.5 wt.% MgO) and has some of the lowest concentrations of ITEs (17ppm Ba) compared to the feldspathic lunar meteorite (FLM) and Apollo sample suites (Hudgins et al., 2011). Localized plagioclase melting and incipient melting of mafic minerals require localized peak shock pressures in excess of 45 GPa (Chen and El Goresy, 2000; Hiesinger and Head, 2006). NWA 3163, and paired samples NWA 4481 and 4883, have previously been interpreted to represent an annealed micro-breccia which was produced by burial metamorphism at depth in the ancient lunar crust (Fernandes et al., 2009

  6. Three-dimensional lithospheric electrical structure of Southern Granulite Terrain, India and its tectonic implications

    NASA Astrophysics Data System (ADS)

    Patro, Prasanta K.; Sarma, S. V. S.; Naganjaneyulu, K.

    2014-01-01

    crustal as well as the upper mantle lithospheric electrical structure of the Southern Granulite Terrain (SGT) is evaluated, using the magnetotelluric (MT) data from two parallel traverses: one is an 500 km long N-S trending traverse across SGT and another a 200 km long traverse. Data space Occam 3-D inversion was used to invert the MT data. The electrical characterization of lithospheric structure in SGT shows basically a highly resistive (several thousands of Ohm meters) upper crustal layer overlying a moderately resistive (a few hundred Ohm meters) lower crustal layer which in turn is underlain by the upper mantle lithosphere whose resistivity shows significant changes along the traverse. The highly resistive upper crustal layer is interspersed with four major conductive features with three of them cutting across the crustal column, bringing out a well-defined crustal block structure in SGT with individual highly resistive blocks showing correspondence to the geologically demarcated Salem, Madurai, and Trivandrum blocks. The 3-D model also brought out a well-defined major crustal conductor located in the northern half of the Madurai block. The electrical characteristics of this south dipping conductor and its close spatial correlation with two of the major structural elements, viz., Karur-Oddanchatram-Kodaikanal Shear Zone and Karur-Kamban-Painavu-Trichur Shear Zone, suggest that this conductive feature is closely linked to the subduction-collision tectonic processes in the SGT, and it is inferred that the Archean Dharwar craton/neoproterozoic SGT terrain boundary lies south of the Palghat-Cauvery shear zone. The results also showed that the Achankovil shear zone is characterized by a well-defined north dipping conductive feature. The resistive block adjoining this conductor on the southern side, representing the Trivandrum block, is shown to be downthrown along this north dipping crustal conductor relative to the Madurai block, suggesting a northward movement of

  7. What can we learn from melt inclusions in migmatites and granulites?

    NASA Astrophysics Data System (ADS)

    Cesare, Bernardo; Bartoli, Omar; Acosta-Vigil, Antonio; Ferrero, Silvio; Poli, Stefano; Remusat, Laurent

    2014-05-01

    The application of melt inclusion (MI) studies to migmatites and granulites is a recent, small-scale approach to a better understanding of melting in the continental crust. It builds on the discovery of glassy inclusions and of their crystallized counterparts ("nanogranites") in garnet and other host minerals from anatectic crustal enclaves in lavas and from regional migmatites. Unlike inclusions in igneous rocks, formed by magma cooling and crystallization, MI in migmatites are trapped during incongruent melting, generally along the up-temperature path of anatexis. Because of such peculiar origin, they can provide key microstructural and chemical information. Microstructurally, when MI appear trapped within potential peritectic minerals (garnet, cordierite, spinel, ilmenite) and display textural features pointing to a primary origin, they demonstrate the growth of their host in the presence of melt. Therefore MI represent one of the most reliable microstructural criteria for the former presence of melt in a rock, particularly in cases where deformation has erased previously present igneous microstructures. Not only MI indicate that a rock was partially melted, but also they add constraints to the mineral(s) which coexisted with the melt. In the case of hosts such as zircon or monazite, the occurrence of MI allows anatectic events to be dated with unprecedented confidence. Chemically, as the composition of anatectic MI is representative of that of the bulk melt in the system during anatexis, these tiny objects (rarely exceeding 15 μm) represent embryos of anatectic granites. With an appropriate characterization and analytical strategy they can provide the missing information on the primary composition of natural crustal melts before they undergo modification processes such as cumulus, fractional crystallization, mixing or entrainment of exotic material. Information on primary compositions includes the concentrations of volatile components, and hence the nature of

  8. Tectonic Implications of Ultrahigh-Temperature and High-Pressure Granulite Metamorphism in the Neoproterozoic Brasiliano Belts of SE Brazil

    NASA Astrophysics Data System (ADS)

    Brown, M.; Baldwin, J. A.; Moraes, R.; Reno, B. L.; Fuck, R. A.; Piccoli, P. M.; Trouw, R. A.

    2006-05-01

    The orogenic belts suturing Gondwana were a product of the Cryogenian-Cambrian Rodinia-to-Gondwana supercontinent breakup and reconfiguration. Ultrahigh temperature metamorphism is common throughout these belts, whereas high pressure granulite and ultrahigh pressure metamorphism are rarer. The suturing of W Gondwana is exemplified by the successive formation of the Brasilia, Ribeira and Cabo Frio orogenic belts of SE Brazil. In the Brasilia belt of Goias, UHTM granulites occur in the Anapolis-Itaucu complex, between the W margin of the Sao Francisco craton and the Goias magmatic arc. Peak P-T conditions of 0.875 GPa and 1025 C for an impure quartzite were calculated using THERMOCALC, within the Grt-Opx-Sil-Qtz divariant field in a FMAS pseudosection consistent with the peak assemblage (Baldwin et al., 2005), and less extreme than P-T estimated from published FMAS grids. Temperatures calculated using Ti-in-zircon thermometry (Watson et al., unpubl.) on metamorphic zircons are 850-950 C, and likely reflect prograde or retrograde growth; growth of new zircon from ilmenite breakdown appears to yield robust temperatures of 800-750 C, appropriate for post- peak cooling during exhumation. Rutile inclusions in garnet contain variable, but high amounts of Zr, indicating growth under high (or ultrahigh) temperature conditions, but the variability is inconsistent with partial diffusive re-equilibration. The retrograde P-T path involved decompression with production of Spr + Qtz followed by cooling and production of Crd. Dates on multiple single metamorphic zircons from four widely-spaced samples analyzed by TIMS suggest that the peak metamorphism occurred during the interval ca. 645-635 Ma, reflecting growth during a short-lived ultrahigh temperature event. The clockwise P-T evolution was a consequence of back-arc basin development during growth of the Goias magmatic arc and trench roll-back, followed by basin inversion with concomitant mafic magmatism, arc collision and core

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  10. Granulite formation in a Gondwana fragment: petrology and mineral equilibrium modeling of incipient charnockite from Mavadi, southern India

    NASA Astrophysics Data System (ADS)

    Endo, Takahiro; Tsunogae, Toshiaki; Santosh, M.; Shimizu, Hisako; Shaji, E.

    2013-10-01

    We report a new occurrence of incipient charnockite from Mavadi in the Trivandrum Granulite Block (TGB), southern India, and discuss the petrogenesis of granulite formation in an arrested stage on the basis of petrography, geothermobarometry, and mineral equilibrium modeling. In Mavadi, patches and lenses of charnockite (Kfs + Qtz + Pl + Bt + Grt + Opx + Ilm + Mag) of about 30 to 220 cm in length occur within Opx-free Grt-Bt gneiss (Kfs + Qtz + Pl + Bt + Grt + Ilm). The application of mineral equilibrium modeling on the charnockite assemblage in the NCKFMASHTO system to constrain the conditions of charnockitization defines a P- T range of 800 °C at 4.5 kbar to 850 °C at 8.5 kbar, which is broadly consistent with the results from the conventional geothermobarometry (810-880 °C at 7.7-8.0 kbar) on these rocks. The P- T conditions are lower than the peak metamorphic conditions reported for the ultrahigh-temperature granulites from this area ( T > 900 °C). The heterogeneity in peak P- T conditions within the same crustal block might be related to local buffering of metamorphic temperatures by the Opx-Bt-Kfs-Qtz assemblage. The result of T versus mole H2O (M(H2O)) modeling demonstrated that the Opx-free assemblage in the Grt-Bt gneiss is stable at M(H2O) = 0.3 to 1.5 mol%, and orthopyroxene occurs as a stable mineral at M(H2O) <0.3 mol%, which is consistent with the petrogenetic model of incipient charnockite related to the lowering of the water activity and stabilization of orthopyroxene through the breakdown of biotite by dehydration caused by the infiltration of CO2-rich fluid from external sources. We also propose a possible alternative mechanism to form charnockite from Grt-Bt gneiss through slight variations in bulk-rock chemistry (particularly for the K- and Fe-rich portion of Grt-Bt gneiss) that can enhance the stability of orthopyroxene rather than that of biotite, with K-metasomatism playing a possible role.

  11. Preliminary Analysis of Borosilicate Minerals in Pegmatitic Leucosomes within Aluminous Granulites at Ledge Mountain, Central Adirondack Highlands, New York

    NASA Astrophysics Data System (ADS)

    Gervais, S. M.; Metzger, E. P.

    2011-12-01

    The borosilicates tourmaline and dumortierite have been identified by polarized light microscopy and electron microprobe analysis in anatectic abyssal-type pegmatites within aluminum-rich granulite-facies migmatites at Ledge Mountain, Central Adirondacks, New York. No other boron-bearing minerals are found in these rocks, and neither borosilicate has been found in the adjacent host gneiss. Tourmaline is ubiquitous in the granulite and upper amphibolite-facies metamorphic rocks of the Central Adirondacks. Dumortierite has been reported from pegmatites of the Batchellerville Province of the Southern Adirondacks, approximately 66 km to the southeast of Ledge Mountain, but not previously at this locality. The tourmaline is alkali dravite-schorl with Mg# = 0.49- 0.53. It is present as anhedral grains less than 2 mm wide intergrown with perthitic microcline and quartz, and as euhedral megacrysts several centimeters in diameter. The dumortierite is strongly pleochroic, ranging from deep indigo blue and violet to colorless. Two strikingly different habits of dumortierite coexist within centimeters of one another in the same sample: bundles of fine prisms less than a few tenths of a millimeter across, and larger granular intergrowths with quartz and chlorite. Apatite and xenotime are also present in both leucosomes and melanosomes, indicating phosphate-enrichment and yttrium in the granulites. According to experimentally determined fields of stability for boron-bearing minerals, the presence of tourmaline and dumortierite and absence of other boron-bearing minerals, especially prismatine, in the pegmatites is consistent with estimated metamorphic conditions of approximately 695-770°C and 7.4-8.2 kbar, as previously determined for this locality using garnet-biotite thermometry and GASP barometry (Boone, 1978). The presence of borosilicates in the leucosomes of these migmatites and the conspicuous lack of them in the paleosome may suggest destabilization of boron

  12. Deciphering the timescales of Archean HT/UHT metamorphism in the Pikwitonei Granulite Domain using garnet petrochronology

    NASA Astrophysics Data System (ADS)

    Dragovic, B.; Guevara, V.; Caddick, M. J.; Couëslan, C. G.; Baxter, E. F.

    2016-12-01

    Sm-Nd garnet geochronology, trace element zoning, and the modeling of major and trace element diffusion in garnet are used to determine the timescales of high/ultrahigh temperature (HT/UHT) metamorphism in the 2.7 Ga Pikwitonei Granulite Domain (PGD), a >150,000 km2 area of dominantly granulite-facies rocks in the NW Superior Province. Combining these techniques with an appropriate pressure-temperature (P-T) path can help elucidate the mechanisms for crustal heating, and the formation of stable cratonic lithosphere, in the PGD. ID-TIMS Sm-Nd garnet geochronology has been performed on a wide range of granulite-facies lithologies, either by bulk garnet analysis (i.e. dating based upon multiple whole garnet crystals rather than portions thereof) or by zoned geochronology, where possible. The use of bulk garnet separates as a HT/UHT geochronometer has proven challenging, as the effects of a) polymetamorphism, b) long metamorphic durations, and c) slow cooling can result in scattered age distributions. However, garnet geochronology on distinct, microsampled growth zones can provide a far more accurate assessment of the rate and duration of metamorphism. Inferred peak T in the region, derived by Zr-in-rutile thermometry and phase equilibria modeling, ranges from 760ºC in the southernmost part of the PGD to 900-960ºC in the central/western PGD ( 40-60 km apart). While slow cooling from HT/UHT will result in some degree of intra-mineral age resetting, detailed isotopic study of a range of large garnet porphyroblasts from the PGD (crystals which are variably reset depending on peak T, grain size, and initial cooling rate) can reveal information about both prograde growth and initial cooling history of the region. Geospeedometry of major and trace element diffusion profiles in garnet can aid geochronologic data in determining timescales of prograde, peak, and retrograde metamorphism. Preliminary modeling in samples from the southern PGD (peak T of 760 ºC) suggests

  13. Deformation regime variations in an arcuate transpressional orogen (Ribeira belt, SE Brazil) imaged by anisotropy of magnetic susceptibility in granulites

    NASA Astrophysics Data System (ADS)

    Egydio-Silva, Marcos; Vauchez, Alain; Raposo, Maria Irene B.; Bascou, Jérôme; Uhlein, Alexandre

    2005-10-01

    The Ribeira belt of southeastern Brazil displays an arcuate shape, with a structural trend that varies from ˜NS in the northern domain to ENE-WSW in the southern domain. This curvature is accompanied by a transition from contraction-dominated to transcurrent-dominated tectonics. The transition in deformation regime is accommodated in the central domain of the belt where granulitic rocks dominate and mineral-stretching lineations are commonly concealed by metamorphic recrystallization. We present anisotropy of magnetic susceptibility (AMS) data from 664 samples from 62 sites in high-temperature gneisses, granulites and migmatites of the transitional, central domain of the belt, with the aim of investigating: (1) how well AMS allows one to map the mineral-stretching lineation and foliations in domains displaying a complex kinematic framework and (2) to investigate the kinematic pattern at the transition between the thrusting dominated and a wrench-faulting dominated orogenic segments. The mean magnetic susceptibility is 7.54×10 -3 SI. The degree of anisotropy varies from 1.32 up to 4.31, with an average value of 1.53. The shape parameter T is generally >0 meaning that the AMS ellipsoid is dominantly oblate. Magnetic lineations and foliations form a consistent pattern correlated with the modification of the structural characteristics observed along the Ribeira belt. In the southern wrench-fault-dominated domain, the magnetic lineation is subhorizontal, parallel to the trend of the steeply dipping magnetic foliation. This correlation with the fabric observed in mylonites suggests that the magnetic fabric is a valid proxy of the tectonic fabric in granulites. Results from the northern domain show that it comprises two sub-domains both displaying a ˜NS-trending magnetic foliation. Eastward, over a broad area, the magnetic foliation is consistently steeply dipping and bears a shallowly to moderately plunging magnetic lineation. Westward, the dip of the foliation

  14. Remelting of nanogranites in peritectic garnet from granulites of Jubrique, Betic Cordillera, Southern Spain

    NASA Astrophysics Data System (ADS)

    Barich, Amel; Bartoli, Omar; Acosta-Vigil, Antonio; Poli, Stefano; Cesare, Bernardo; Garrido, Carlos J.

    2014-05-01

    Peritectic minerals in migmatites can trap droplets of melt that form via incongruent melting reactions during crustal anatexis [1]. In most cases, these melts crystallize and form nanogranites upon slow cooling of the anatectic terrane [2]. To obtain information on the primary compositions of crustal melts, including volatile concentrations in melt and information on fluid regimes, nanogranites must be remelted and rehomogenized before analysis [3]. A new occurrence of nanogranites was recently reported in granulitic gneisses at the bottom of the prograde metamorphic sequence of Jubrique, located on top of the Ronda peridotite slab (Betic Cordillera, S Spain) [4]. These nanogranites are trapped in garnet porphyroblasts. They show partially irregular to well facetted negative crystal shapes, and have variable size from ~5-10 μm to several tens of μm or even ~200 μm in diameter. They appear at the core and rim of large Grt crystals, and are composed of rare glass, daughter Qz, Pl, Kfs, Bt and Ms, and solid inclusions of Ky and less frequently Gr, Hc, Rt, Ilm, Zrn and Mnz. Ky was the main solid phase that favored the trapping of melt inclusions (MI) by poisoning crystal surfaces during Grt growth. The presence of Ky+Rt within MI, and their occurrence in the high-P cores of Grt, suggest that partial melting in the gneisses initiated at relatively high P conditions, and that most Grt in these rocks crystallized in the presence of melt. To recover the major and trace element composition of the primary melt during anatexis, we performed remelting experiments on chips of MI-bearing Grt separated from a sample of gneiss at Jubrique, using a piston cylinder apparatus. Experiments were run at 800, 825 and 850° C, 15 Kbar and dry conditions (i.e. no added H2O) for 24 hrs. Preliminary results of the first experiment at 850º show that nanogranites have been successfully remelted; they all contain glass regardless of their textural position, i.e. at the core and rim of

  15. The Wuluma granite, Arunta Block, central Australia: An example of in situ, near-isochemical granite formation in a granulite-facies terrane

    NASA Astrophysics Data System (ADS)

    Collins, W. J.; Flood, R. H.; Vernon, R. H.; Shaw, S. E.

    1989-06-01

    The Wuluma granite is a small, elongate, relatively undeformed pluton in the Proterozoic Strangways Metamorphic Complex, central Australia. The complex constitutes a supracrustal assemblage that underwent granulite-facies metamorphism 1800 Ma ago. Metamorphism was associated with at least three phases of folding that ultimately produced upright, regional, doubly plunging F 3 folds and isobaric cooling ensued. Generation of the Wuluma granite occurred at ˜ 1750 Ma, based on RbSr isotopic data, during syn-D 3 regional retrogression and rehydration of the terrane. Contacts between the granite and gneisses are invariably gradational. At the pluton margin, banded gneisses grade along strike into granite containing abundant biotite schlieren that parallel regional structures. Granite and pegmatite dykes cut these rocks. Inwards from the contact, the granite is more homogeneous, containing diffuse parallel schlieren and small aligned rectangular feldspar crystals, indicating flow of magma. Rafts of unmelted granofels form a ghost layering; they mimic macroscopic F 3 folds and show only minor retrogressive metamorphic effects. At the pluton core, the granite is homogeneous and structurally isotropic, containing some subrounded granofelsic inclusions, very diffuse schlieren and disaggregated pegmatite dykes. Thus, it appears that an isoclinally folded, vertical body of quartzofeldspathic gneiss was melted "in situ" to form the pluton, which did not break away from the source. The body resembles a tapered diapir and we term this type of pluton a regional migmatite terrane granite. Geochemical data are consistent with the granite forming by anatexis of quartzofeldspathic migmatitic gneisses with appropriate composition. The chemical similarity of both rock types implies derivation of the granite by either partial melting and retention of residual material in the magma or more complete melting, followed by solidification virtually in situ. The latter interpretation is

  16. Late Quaternary tectonic switching of siliciclastic provenance in the strike-slip-dominated foreland of the Western Carpathians; Upper Morava Basin, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Novák, Aleš; Bábek, Ondřej; Kapusta, Jaroslav

    2017-06-01

    This study is focused on the lithology and provenance of late Quaternary fluvial deposits of the Upper Morava Basin a pull-apart basin situated at the contact of the Bohemian Massif and Western Carpathians. Late Cenozoic tectonic convergence between these two units caused differential subsidence along strike-slip faults of the Elbe-Odra zone, leading to a distinct horst-and-graben morphology of the Upper Morava Basin. The Pleistocene fluvial deposits are preserved in several terrace levels and partly buried under the present-day floodplain of the Morava River. This study is based on four cores (11-25 m deep) drilled in the floodplain of two major depocentres of the basin, the Lutín Graben, and the Upper Morava Basin sensu stricto. The drill cores were analysed for grain size, pebble- and heavy-mineral composition, chemical composition of detrital garnets, bulk magnetic susceptibility, sediment colour (visible-light spectral reflectance) and bulk element geochemistry. Age interpretations are based on eight optically stimulated luminescence (OSL) analyses. The Upper Pleistocene sediments were deposited in a gravelly braided to transitional braided-meandering river in both the Upper Morava Basin s.s. and the Lutín Graben (the oldest OSL age is 161.5 ka, corresponding to the late Saalian). Between the end of the Saalian and late Weichselian glaciations, the Morava River abandoned the Lutín Graben for the Upper Morava Basin s.s. where it flows up to the present day. The Pleistocene fluvial style contrasts with the present-day meandering to anastomosing fluvial style of the Morava River. The Pleistocene deposits were sourced from areas corresponding to the present-day Morava River catchment including crystalline units of the eastern Bohemian Massif and the Moravo-Silesian Carboniferous Basin. They also contain a considerable input from the Bohemian Cretaceous Basin. The composition of late Weichselian deposits from the Dub nad Moravou core (34.53 ± 3.42 ka and

  17. Magma-mixing in the genesis of Hercynian calc-alkaline granitoids: an integrated petrographic and geochemical study of the Sázava intrusion, Central Bohemian Pluton, Czech Republic

    NASA Astrophysics Data System (ADS)

    Janoušek, Vojtěch; Braithwaite, Colin J. R.; Bowes, D. R.; Gerdes, Axel

    2004-10-01

    The Devonian-early Carboniferous (354.1±3.5 Ma: conventional zircon U-Pb age) Sázava intrusion (biotite-amphibole quartz diorite, tonalite and granodiorite) of the Central Bohemian Pluton (CBP) associated with bodies of (olivine, pyroxene-) amphibole gabbro, gabbrodiorite, (quartz) diorite and rare hornblendite, gives an opportunity for a comparative study of a rather shallow, calc-alkaline magma-mixing zone at two levels, separated by a vertical difference of approximately 1 km. The deeper section (Příbram) displays the direct evidence for the existence of a long-lived, periodically tapped and replenished, floored magma chamber (MASLI). The contacts between the subhorizontal sheet-like basic bodies and the surrounding, commonly cumulus-rich, Sázava granitoid, are arcuate, and cut by a series of veins and ascending pipes. Shallow-dipping swarms of strongly elongated and flow-aligned mafic microgranular enclaves (MME), concordant with the contacts of the basic bodies, are commonplace. The higher level (Teletín) section shows relatively independent basic intrusions, some of them distinctly hybrid in character and mainly of quartz dioritic composition, surrounded by relatively homogeneous, nearly cumulus-free Sázava tonalite rich in texturally variable MME. Larger quartz microdiorite bodies and the MME, both interpreted as hybrids, contain varying proportions of highly heterogeneous plagioclase megacrysts with complex zoning, particularly well shown by cathodoluminescence (CL). Most often the megacrysts have cores of labradorite-anorthite, partly resorbed and overgrown by andesine rims but some are strongly brecciated and fragments have been annealed by rim growth. Also characteristic are long prisms of apatite, oikocrysts of quartz and K-feldspar and zoned amphibole. The latter has brown pargasite and magnesiohastingsite cores, resorbed and overgrown by magnesiohornblende, compositionally similar to the amphibole in the Sázava tonalite. The brown cores are

  18. Generation of trondhjemite from partial melting of dacite under granulite facies conditions: an example from the New Jersey Highlands, USA

    USGS Publications Warehouse

    Puffer, J.H.; Volkert, R.A.

    1991-01-01

    New field and geochemical data place the Losee Metamorphic Suite (a tonalite/trondhjemite complex) of northern New Jersey into the context of a major Proterozoic continental are represented by a discontinuous belt of northern Appalachian metadacite. Samples of Losee rock range from extremely leucocratic trondhjemite locally associated with amphibolite, to banded biotite, hornblende, pyroxene, and garnet-bearing tonalites. The major element and REE composition of the tonalite closely resembles dacite from continental are settings and model melts extracted from an eclogite residue by partial melting at 15 kbar. The REE composition of most Losee trondhjemite is enriched in REE, particularly HREE, compared with Losee tonalite, and is interpreted as the product of local anatectic melting of Losee tonalite (metadacite) that occurred in a granulite facies environment during the Grenville orogeny. ?? 1991.

  19. 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.

  20. Structural framework across the Bastar craton - the Eastern Ghats Granulite Belt interface: Implications for making of eastern Gondwana

    NASA Astrophysics Data System (ADS)

    Patole, Vishal; Nasipuri, Pritam

    2015-04-01

    The transformation of palaeo-continents involve breakup, dispersal and reassembly of cratonic blocks by collisional suturing that develop a network of orogenic (mobile) belts around the periphery of the stable cratons. During the collision, partial melting of the different crustal blocks produces migmatites at the craton-mobile belt interface. Thus, migmatites at the craton-mobile belt contact can provide valuable information regarding the pressure-temperature conditions of the melting of lower crust during supercontinent building processes. In this contribution, we document the structural framework across the Bastar craton- Eastern Ghats Granulite Belt (EGGB) interface that developed during the accretion of EGGB over Bastar craton. Near Bhawanipatna, Orissa, Eastern India, the granulites of the mobile belt are juxtaposed against the granitic rocks of the Bastar craton. Away from the contact domain, the cratonic granite is non-migmatitic and blasto-porphyritic in nature that gradually transforms to migmatitic variety towards the contact domain. In the non-migmatitic variety, the E-W trending stromatic leucozomes and biotite-hornblende rich fabric (S1) wraps around recrystallized K-feldspar augens. In the migmatitic variety towards the contact domain, NNE-SSW trending diatexite leucozomes (S2) are prominent and the intensity of melting and tightness of folding increases towards the contact domain. Structural measurements indicate that the S1 fabric is folded with the development of NNE-SSW axial plane with easterly plunging fold axis (50 -> 050N). To correlate the geological history of EGGB in the context of supercontinent reconstruction, the existence of a cratonic block consisting of India - Madagascar - Sri Lanka - Enderby Land-Kalahari ("IMSLEK") from 3000 Ma upto 750 Ma has been invoked by several authors. The apparent continuity of the Grenvillian metamorphic orogen along the East Antarctica-Australia-India margin has been taken as conclusive evidence for the

  1. P-T-t path for the Archean Pikwitonei Granulite Domain and Cross Lake Subprovince, Manitoba, Canada

    NASA Technical Reports Server (NTRS)

    Mezger, K.; Bohlen, S. R.; Hanson, G. N.

    1988-01-01

    The rationale was outlined for constructing pressure-temperature-time (P-T-t) paths by using U-Pb dating of garnet produced in thermobarometrically sensitive reactions. In an example from the Pikwitonei granulites of the Northwestern Superior Province of the Canadian Shield, garnets were formed at 2744-2742 Ma, 2700-2689 Ma, and 2605-2590 Ma, the latter events coinciding with times recorded by U-Pb zircon systems. Garnet grew during metamorphism at 6.5 kbar, 630 to 750 C and later at 7.2 to 7.5 kbar, 800 C; the later metamorphism apparently did not exceed the U-Pb closure temperature. The resultant P-T-t path is counterclockwise, with late isobaric cooling, interpreted to result from magmatic heating at an Andean margin.

  2. The Pan-African continental margin in northeastern Africa - Evidence from a geochronological study of granulites at Sabaloka, Sudan

    NASA Astrophysics Data System (ADS)

    Kroener, A.; Stern, R. J.; Dawoud, A. S.; Compston, W.; Reischmann, T.

    1987-09-01

    The evolution of the Pan-African ancient continental margin in northeastern Africa was investigated, using an Nd model age, ion-microprobe data on zircon ages, and Rb-Sr whole-rock dates on the high-grade gneiss terrain at Sabaloka, Sudan, a region which is formally considered to be part of the Archaean/early Proterozoic Nile craton. The analysis of these data indicates that the Sabaloka granulites and gneisses are not Archaen in age. Instead, they reflect Pan-African metamorphic events. The gneisses studied may represent the infrastructure of the ancient African continental margin onto which the juvenile arc assemblage of the Arabian-Nubian shield was accreted during intense horizontal shortening and crustal interstacking of a major collision event.

  3. Palaeoproterozoic high-pressure granulite overprint of the Archaean continental crust: evidence for homogeneous crustal thickening (Man Rise, Ivory Coast)

    NASA Astrophysics Data System (ADS)

    Pitra, Pavel; Kouamelan, Alain N.; Ballèvre, Michel; Peucat, Jean-Jacques

    2010-05-01

    The character of mountain building processes in the Palaeoproterozoic times is subject to much debate. The local observation of Barrovian-type assemblages and high-pressure granulite relics in the Man Rise (Côte d'Ivoire), led some authors to argue that Eburnean (Palaeoproterozoic) reworking of the Archaean basement was achieved by modern-style thrust-dominated tectonics (e.g., Feybesse & Milési, 1994). However, it has been suggested that crustal thickening and subsequent exhumation of high-pressure crustal rocks can be achieved by virtue of homogeneous, fold-dominated deformation of hot crustal domains even in Phanerozoic orogenic belts (e.g., Schulmann et al., 2002; 2008). We describe a mafic granulite of the Kouibli area (Archaean part of the Man Rise, western Ivory Coast) that displays a primary assemblage (M1) containing garnet, diopsidic clinopyroxene, red-brown pargasitic amphibole, plagioclase (andesine), rutile, ilmenite and quartz. This assemblage is associated with a subvertical regional foliation. Symplectites that develop at the expense of the M1 assemblage contain orthopyroxene, clinopyroxene, plagioclase (bytownite), green pargasitic amphibole, ilmenite and magnetite (M2). Multiequilibrium thermobarometric calculations and P-T pseudosections calculated with THERMOCALC suggest granulite-facies conditions of ca. 13 kbar, 850°C and <7 kbar, 700-800°C for M1 and M2, respectively. In agreement with the qualitative information obtained from reaction textures and chemical zoning of minerals, this suggests an evolution dominated by decompression accompanied by moderate cooling. A Sm-Nd garnet - whole-rock age of 2.03 Ga determined on this sample indicates that this evolution occurred during the Palaeoproterozoic. We argue that from the geodynamic point of view the observed features are best explained by homogeneous thickening of the margin of the Archaean craton, re-heated and softened due to the accretion of hot, juvenile Palaeoproterozoic crust, as

  4. Archaean associations of volcanics, granulites and eclogites of the Belomorian province, Fennoscandian Shield and its geodynamic interpretation

    NASA Astrophysics Data System (ADS)

    Slabunov, Alexander

    2013-04-01

    An assembly of igneous (TTG-granitoids and S-type leucogranites and calc-alkaline-, tholeiite-, kometiite-, boninite- and adakite-series metavolcanics) and metamorphic (eclogite-, moderate-pressure (MP) granulite- and MP amphibolite-facies rocks) complexes, strikingly complete for Archaean structures, is preserved in the Belomorian province of the Fennoscandian Shield. At least four Meso-Neoarchaean different-aged (2.88-2.82; 2.81-2.78; ca. 2.75 and 2.735-2.72 Ga) calc-alkaline and adakitic subduction-type volcanics were identified as part of greenstone belts in the Belomorian province (Slabunov, 2008). 2.88-2.82 and ca. 2.78 Ga fore-arc type graywacke units were identified in this province too (Bibikova et al., 2001; Mil'kevich et al., 2007). Ca.2.7 Ga volcanics were generated in extension structures which arose upon the collapse of an orogen. The occurrence of basalt-komatiite complexes, formed in most greenstone belts in oceanic plateau settings under the influence of mantle plumes, shows the abundance of these rocks in subducting oceanic slabs. Multiple (2.82-2.79; 2.78-2.76; 2.73-2.72; 2.69-2.64 Ga) granulite-facies moderate-pressure metamorphic events were identified in the Belomorian province (Volodichev, 1990; Slabunov et al., 2006). The earliest (2.82-2.79 Ga) event is presumably associated with accretionary processes upon the formation of an old continental crust block. Two other events (2.78-2.76; 2.73-2.72 Ga) are understood as metamorphic processes in suprasubduction setting. Late locally active metamorphism is attributed to the emplacement of mafic intrusions upon orogen collapse. Three groups of crustal eclogites with different age were identified in the Belomorian province: Mesoarchaean (2.88-2.86 and 2.82-2.80 Ga) eclogites formed from MORB and oceanic plateau type basalts and oceanic high-Mg rocks (Mints et al., 2011; Shchipansky at al., 2012); Neoarchaean (2.72 Ga) eclogites formed from MORB and oceanic plateau type basalts. The formation of

  5. Garnet Sm-Nd and Zircon U-Pb Ages Track Pluton Emplacement, Granulite Facies Metamorphism, Partial Melting, and Extension in the Lower Crust, Fiordland New Zealand

    NASA Astrophysics Data System (ADS)

    Stowell, H. H.; Klepeis, K. A.; Odom Parker, K.

    2011-12-01

    Extensional collapse of over thickened magmatic arc crust depends on crustal thickness variations and architecture. The structural architecture of the lower- and mid-crustal at the onset of extension may be complex due to lithologic variation resulting from structural juxtaposition of pre-arc lithologies, intrusion of plutons, and local partial melting. Additional complexity is introduced by the dynamic nature of arcs. Thus, robust ages for deformation, metamorphism, intrusion, and partial melting are essential for unraveling arc evolution and discerning the role of arc plutonism and metamorphism in strain localization during both contraction and extension. Eclogite and granulite facies metamorphic minerals indicate that Mesozoic arc crust in Fiordland was ≥ 50 km thick ca. 130 Ma prior to extensional collapse. This mid- to lower-crust records a history of mafic to intermediate magmatism, high-grade metamorphism, lower crustal melting, and the formation of extensional detachments that border eclogite- and granulite-cored gneiss domes. U-Pb zircon and Sm-Nd garnet ages indicate that intrusion of voluminous plutons, including the Western Fiordland Orthogneiss (WFO), and subsequent metamorphism occurred sequentially from north to south. Pluton emplacement occurred at 0.6-1.1 GPa in the north to 1.0-1.2 GPa in the south. In northern Fiordland [Milford Sound], intrusion of 135-128 Ma gabbroic magma was followed by 0.6-1.1 GPa 2-pyroxene granulite metamorphism at 126-135 Ma, and then 1.2-1.4 GPa garnet granulite metamorphism and partial melting ca. 126-123 Ma. To the south, WFO plutons have a similar history from north to south: the low-P 125-120.1 Ma Worsley was metamorphosed to garnet granulite at 1.2-1.4 GPa, ca. 115 Ma; the low-P ca. 120 Ma Misty was metamorphosed to garnet granulite at 1.2 GPa, ca. 115 Ma; the high-P 117.8-113.2 Ma Malaspina was metamorphosed to garnet granulite at 1.0-1.4 GPa, ca. 113 Ma along Doubtful Sound and 111.9±1.6 Ma to the south on

  6. Petrochronological and structural arguments for upper plate thickening and relamination of the lower plate buoyant material in the Variscan Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Peřestý, Vít; Holder, Robert; Lexa, Ondrej; Racek, Martin; Jeřábek, Petr

    2014-05-01

    Recent tectonic models for the Variscan evolution of the Bohemian Massif emphasize the role of Rayleigh-Taylor instability for the 355-340 Ma evolution of the Moldanubian domain. This model is based on the presence of weak, low-density felsic material tectonically underplating a high-density mafic layer and its subsequent gravity-driven overturn. However, earlier phases of the Variscan orogeny concerning the emplacement of felsic low-density material to the base of the upper plate are so far poorly documented. We contribute to this problem by deciphering of polyphase early-Variscan (~375 Ma) deformation and metamorphism close to the main Variscan suture. Detailed structural, pseudosection and microstructural analyses combined with LASS monazite dating were carried out in metapelites along the western margin of the upper plate represented by the Teplá Crystalline Complex (TCC). This region is represented by a ~25 km wide deformation zone with E-W metamorphic gradients associated with two distinct early-Variscan events (~380-375 and ~375-370 Ma). The first compressional event produced a vertical NNE-SSW trending fabric and a continuous and prograde Barrovian metamorphic sequence ranging from biotite to kyanite zones at a field geotherm of 20 to 25 °C/km. Subsequently, a gently SE dipping normal shear-zone associated with retrogression develops along the base of the TCC. This sub-horizontal fabric shows normal metamorphic zonation ranging from sillimanite, biotite to chlorite zones and indicates vertical shortening related to unroofing of high pressure metabasites of the underlying Mariánské-Lázně Complex. The first metamorphic fabric is interpreted to result from early thickening of the upper plate during continental underthrusting of Saxothuringian continent (380 to 375 Ma) while the second deformation and metamorphism (~370 Ma) reflects vertical shortening produced by buoyant uplift of accreted Saxothuringian felsic crust. This event is the unique yet

  7. 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

  8. Geochronology of granulite, charnockite and gneiss in the poly-metamorphosed Gaozhou Complex (Yunkai massif), South China: Emphasis on the in-situ EMP monazite dating

    NASA Astrophysics Data System (ADS)

    Chen, Cheng-Hong; Liu, Yung-Hsin; Lee, Chi-Yu; Xiang, Hua; Zhou, Han-Wen

    2012-07-01

    The in-situ EMP (electron microprobe) monazite age dating performed directly in the polished sections, in addition to the conventional U-Pb zircon and EMP monazite age dating on grains from heavy mineral concentrates, has been applied to the granulite, charnockite and gneiss in the Gaozhou Complex of the Yunkai massif in South China. While the conventional dating systems all give Caledonian ages, the in-situ EMP monazite ages provide more information to reveal not only detailed age groups pertaining to the Caledonian orogeny but also traces of later thermal events overprinting these rocks. For granulites, although some monazites present zoning (concentric, patchy and complex) in the BSE images, no discernable age differences are observed. Resetting of the Th-U-Pb monazite dating system under the high temperature condition could be the reason. Ages of homogeneous monazite in garnet porphyroblast (ca. 440 Ma) of the garnet-cordierite granulite that match nicely with the U-Pb zircon ages are systematically older than those in the matrix (ca. 430 Ma). The same case of two age groups is also present in the orthopyroxene-biotite granulite as revealed by monazite inclusions in plagioclase and orthopyroxene and those in quartz, respectively. For charnockites, despite similar ages of ca. 430 Ma are given by monazite in biotite and zircon in the rock, significant younger ages are obtained from monazites with particular features. Relict monazites with a breakdown texture to form successive layers of apatite and allanite in the rim as well as those which are close to the biotite-chlorite microvein always show a similar age of ca. 230 Ma. Moreover, tiny monazites in close association with the garnetiferous corona mainly surrounding orthopyroxene give rise to another age group around 370 Ma. For gneissic rocks, monazites enclosed by quartz give 434 Ma and those setting in the chlorite-epidote microvein of a paragneiss yield 237 Ma, consistent with the U-Pb zircon core-rim age

  9. Soil mesofauna in disturbed spruce forest stands near Čertovo and Plešné Lakes, the Bohemian Forest: preliminary results

    NASA Astrophysics Data System (ADS)

    Čuchta, Peter; Starý, Jozef

    2016-04-01

    The soil microarthropod communities were studied in disturbed spruce forest stands in the catchments areas of Čertovo (CT) and Plešné (PL) Lakes in the Bohemian Forest, Czech Republic. The study is focused on the impact of the windthrow, bark beetle outbreak damage and consecutive changes in the forest stands including soil environment. Within the soil microarthropods, two main groups, Collembola (Hexapoda) and Oribatida (Acari) are analysed. Four different treatments were selected for the study on both study areas: CT1 and PL1 stands - undamaged control forest stands, CT2 and PL2 stands - "dead" forest stands damaged by bark beetle, CT3 and PL3 stands - slightly managed windthrown forest stands left for the natural succession, and CT4 and PL4 stands - harvested windthrown stands. Soil samples were taken in June (CT1/PL1 - CT3/PL3), July and October (CT1/PL1 - CT4/PL4) 2012 from each treatment. Microarthropods were subsequently extracted in a modified high-gradient apparatus in the laboratory for seven days. Finally, the comparison of the microarthropod assemblages found at different treatment stands was performed. The most abundant groups in both study areas (Čertovo and Plešné Lakes) were Collembola and Oribatida with considerable diferences within particular treatments and in time as well.

  10. Granitic magma emplacement and deformation during early-orogenic syn-convergent transtension: The Staré Sedlo complex, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Tomek, Filip; Žák, Jiří; Chadima, Martin

    2015-07-01

    The Late Devonian Staré Sedlo complex, Bohemian Massif, was emplaced as a subhorizontal sheeted sill pluton into a transtension zone. The transtensional setting is documented by strong constrictional fabric, corroborated by the anisotropy of magnetic susceptibility (AMS), with variably developed subhorizontal magmatic to solid-state foliation suggesting vertical shortening. Intrusive contacts of the granitoids with metapelitic screens and tapered sill tips indicate that magma wedging was the dominant process of sill propagation. The sills exhibit two intrusive styles, ranging from thin lit-par-lit injections to widely spaced meter-thick sills. These two styles are interpreted as reflecting variable viscosities of intruding magma where low-viscosity magma percolated along foliation planes whereas high-viscosity magma produced more localized thicker sills. We propose that the magma/host rock system in transtension must have evolved from initial crack tip propagation and vertical expansion due to new magma additions through conduit flow to ductile thinning after the magma input had ceased. The sill emplacement and their subsequent deformation are then interpreted as recording early-orogenic syn-convergent sinistral transtension along the rear side of an upper-crustal wedge, which was extruded both upward and laterally in response to subduction and continental underthrusting.

  11. Fluid inclusion studies on the Koraput Alkaline Complex, Eastern Ghats Province, India: Implications for mid-Neoproterozoic granulite facies metamorphism and exhumation

    NASA Astrophysics Data System (ADS)

    Nanda, J.; Panigrahi, M. K.; Gupta, S.

    2014-03-01

    Following ultrahigh temperature granulite metamorphism at ˜1 Ga, the Eastern Ghats Province of India was intruded by the Koraput Alkaline Complex, and was subsequently re-metamorphosed in the granulite facies in the mid-Neoproterozoic time. Fluid inclusion studies were conducted on silica undersaturated alkali gabbro and syenites in the complex, and a pre-metamorphic pegmatitic granite dyke that intrudes it. High density (1.02-1.05 g/cc), pseudo-secondary pure CO2 inclusions are restricted to metamorphic garnets within the gabbro and quartz within the granite, whereas moderate (˜0.92-0.95 g/cc) and low density (˜0.75 g/cc) secondary inclusions occur in garnet, magmatic clinopyroxene, plagioclase, hornblende and quartz. The isochores calculated for high density pseudo-secondary inclusions pass very close to the peak metamorphic window (˜8 kbar, 750 °C), and are interpreted to represent the fluid present during peak metamorphism that was entrapped by the growing garnet. Microscopic round inclusions of undigested, relict calcite in garnet suggest that the CO2 present during metamorphism of the complex was internally derived through carbonate breakdown. Pure to low salinity (0.00-10.1 wt% NaCl equivalent) aqueous intra-/intergranular inclusions showing unimodal normal distribution of final ice-melting temperature (Tm) and temperature of homogenization (Th) are present only in quartz within the granite. These represent re-equilibrated inclusions within the quartz host that were entrapped at the metamorphic peak. Rare, chemically precipitated graphite along the walls of carbonic inclusions is interpreted as a post-entrapment reaction product formed during decompression. The fluid inclusion evidence is consistent with rapid exhumation of a thickened lower crust following the mid-Neoproterozoic granulite facies metamorphic event. The study suggests that mantle CO2, transported by alkaline magma into the crust, was locked up within carbonates and released during

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

  13. Spinel + quartz assemblage in granulites from the Achankovil Shear Zone, southern India: Implications for ultrahigh-temperature metamorphism

    NASA Astrophysics Data System (ADS)

    Shimizu, Hisako; Tsunogae, Toshiaki; Santosh, M.

    2009-09-01

    We report the finding of equilibrium spinel + quartz assemblage enclosed within garnet in garnet-orthopyroxene-cordierite granulites from Pakkandom within the Achankovil Shear Zone, a region which is considered as the trace of an accretionary suture in recent tectonic models on southern India. The spinel + quartz bearing granulites are composed of poikiloblastic garnet and subidioblastic orthopyroxene in the matrix of quartz, plagioclase, biotite, cordierite, and Fe-Ti oxides. Garnet contains numerous inclusions of sillimanite and biotite as well as spinel and quartz. The spinel in direct contact with quartz has moderate XMg (= Mg/(Fe 2+ + Mg) = 0.44-0.47), and is Zn and Fe 3+ poor ( XZn = Zn/(Fe 2+ + Mg + Zn) = 0.027-0.036, Fe 3+/(Fe 2+ + Fe 3+) = 0.12-0.17). Spinel is also present in the matrix surrounded by magnetite, but the matrix spinel contains more Zn( XZn = 0.067-0.072) and does not show any contact relationship with quartz. Such Zn- and Fe 3+-poor spinel in direct contact with quartz has been regarded as a diagnostic evidence of ultrahigh-temperature (UHT) metamorphism. The high-temperature stability of the spinel + quartz is also supported by the results of geothermobarometric calculation of garnet-orthopyroxene assemblages that provides robust evidence for peak UHT metamorphism at 920-980 °C and 8-10 kbar, which was further confirmed by Al-in-Opx and magnetite-ilmenite geothermometers (900-950 °C and ˜1000 °C, respectively). The peak UHT event was followed by decompression down to 4.0-4.2 kbar and 640-670 °C toward the stability of cordierite along a clockwise P-T path. Similar spinel + quartz assemblage enclosed in poikiloblastic garnet has also been reported from the Palghat-Cauvery Shear Zone system, the trace of a major suture zone within the Gondwana amalgam with evidence for prograde high-pressure ( P up to 20 kbar) metamorphism followed by UHT event. The fine-grained spinel + quartz may thus indicate decompression from higher pressure

  14. The evolution of a Gondwanan collisional orogen: A structural and geochronological appraisal from the Southern Granulite Terrane, South India

    NASA Astrophysics Data System (ADS)

    Plavsa, Diana; Collins, Alan S.; Foden, John D.; Clark, Chris

    2015-05-01

    Gondwana amalgamated along a suite of Himalayan-scale collisional orogens, the roots of which lace the continents of Africa, South America, and Antarctica. The Southern Granulite Terrane of India is a generally well-exposed, exhumed, Gondwana-forming orogen that preserves a record of the tectonic evolution of the eastern margin of the East African Orogen during the Ediacaran-Cambrian (circa 600-500 Ma) as central Gondwana formed. The deformation associated with the closure of the Mozambique Ocean and collision of the Indian and East African/Madagascan cratonic domains is believed to have taken place along the southern margin of the Salem Block (the Palghat-Cauvery Shear System, PCSS) in the Southern Granulite Terrane. Investigation of the structural fabrics and the geochronology of the high-grade shear zones within the PCSS system shows that the Moyar-Salem-Attur shear zone to the north of the PCSS system is early Paleoproterozoic in age and associated with dextral strike-slip motion, while the Cauvery shear zone (CSZ) to the south of the PCSS system can be loosely constrained to circa 740-550 Ma and is associated with dip-slip dextral transpression and north side-up motion. To the south of the proposed suture zone (the Cauvery shear zone), the structural fabrics of the Northern Madurai Block suggest four deformational events (D1-D4), some of which are likely to be contemporaneous. The timing of high pressure-ultrahigh temperature metamorphism and deformation (D1-D3) in the Madurai Block (here interpreted as the southern extension of Azania) is constrained to circa 550-500 Ma and interpreted as representing collisional orogeny and subsequent orogenic collapse of the eastern margin of the East African Orogen. The disparity in the nature of the structural fabrics and the timing of the deformation in the Salem and the Madurai Blocks suggest that the two experienced distinct tectonothermal events prior to their amalgamation along the Cauvery shear zone during the

  15. Chevkinite-group minerals from granulite-facies metamorphic rocks and associated pegmatites of East Antarctica and South India

    USGS Publications Warehouse

    Belkin, H.E.; Macdonald, R.; Grew, E.S.

    2009-01-01

    Electron microprobe data are presented for chevkinite-group minerals from granulite-facies rocks and associated pegmatites of the Napier Complex and Mawson Station charnockite in East Antarctica and from the Eastern Ghats, South India. Their compositions conform to the general formula for this group, viz. A4BC2D2Si4O22 where, in the analysed specimens A = (rare-earth elements (REE), Ca, Y, Th), B = Fe2+, Mg, C = (Al, Mg, Ti, Fe2+, Fe3+, Zr) and D = Ti and plot within the perrierite field of the total Fe (as FeO) (wt.%) vs. CaO (wt.%) discriminator diagram of Macdonald and Belkin (2002). In contrast to most chevkinite-group minerals, the A site shows unusual enrichment in the MREE and HREE relative to the LREE and Ca. In one sample from the Napier Complex, Y is the dominant cation among the total REE + Y in the A site, the first reported case of Y-dominance in the chevkinite group. The minerals include the most Al-rich yet reported in the chevkinite group (49.15 wt.% Al2O3), sufficient to fill the C site in two samples. Conversely, the amount of Ti in these samples does not fill the D site, and, thus, some of the Al could be making up the deficiency at D, a situation not previously reported in the chevkinite group. Fe abundances are low, requiring Mg to occupy up to 45% of the B site. The chevkinite-group minerals analysed originated from three distinct parageneses: (1) pegmatites containing hornblende and orthopyroxene or garnet; (2) orthopyroxene-bearing gneiss and granulite; (3) highly aluminous paragneisses in which the associated minerals are relatively magnesian or aluminous. Chevkinite-group minerals from the first two parageneses have relatively high FeO content and low MgO and Al2O3 contents; their compositions plot in the field for mafic and intermediate igneous rocks. In contrast, chevkinite-group minerals from the third paragenesis are notably more aluminous and have greater Mg/Fe ratios. ?? 2009 The Mineralogical Society.

  16. Brittle deformation in Southern Granulite Terrane (SGT): A study of pseudotachylyte bearing fractures along Gangavalli Shear Zone (GSZ), Tamil Nadu, India.

    NASA Astrophysics Data System (ADS)

    mohan Behera, Bhuban; Thirukumaran, Venugopal; Biswal, Tapas kumar

    2016-04-01

    High grade metamorphism and intense deformation have given a well recognition to the Southern Granulite Terrane (SGT) in India. TTG-Charnockite and basic granulites constitute the dominant lithoassociation of the area. Dunite-peridotite-anorthosite-shonkinite and syenites are the intrusives. TTG-charnockite-basic granulite have undergone F1 (isoclinal recumbent), F2 (NE-SW) and F3 (NW-SE) folds producing several interference pattern. E-W trending Neoarchean and Palaeoproterozoic Salem-Attur Shear Zone exhibits a low angle ductile thrust as well as some foot print of late stage brittle deformation near Gangavalli area of Tamil Nadu. The thrust causes exhumation of basic granulites to upper crust. Thrusting along the decollement has retrograded the granulite into amphibolite rock. Subsequently, deformation pattern of Gangavalli area has distinctly marked by numerous vertical to sub-vertical fractures mostly dominating along 0-15 and 270-300 degree within charnockite hills that creates a maximum stress (σ1) along NNW and minimum stress (σ3) along ENE. However, emplacement of pseudotachylyte vein along N-S dominating fracture indicates a post deformational seismic event. Extensive fractures produce anastomose vein with varying thickness from few millimeters to 10 centimeters on the outcrop. ICP-AES study results an isochemical composition of pseudotachylyte vein that derived from the host charnockitic rock where it occurs. But still some noticeable variation in FeO-MgO and Na2O-CaO are obtained from different parts within the single vein showing heterogeneity melt. Electron probe micro analysis of thin sections reveals the existence of melt immiscibility during its solidification. Under dry melting condition, albitic rich melts are considered to be the most favorable composition for microlites (e.g. sheaf and acicular micro crystal) re-crystallization. Especially, acicular microlites preserved tachylite texture that suggest its formation before the final coagulation

  17. Deformation microstructures and mechanisms in the high-pressure granulites of the Bacariza Formation (Cabo Ortegal, NW Spain): going up to the surface

    NASA Astrophysics Data System (ADS)

    Puelles, P.; Abalos, B.

    2009-04-01

    The Cabo Ortegal complex is a nappe stack formed by fragments of subducted continental and oceanic lithosphere emplaced onto the Gondwana edge during the Variscan orogeny. The nappe units of Cabo Ortegal were metamorphosed under different high-pressure (HP) conditions and currently are separated by ductile tectonic contacts. They include mappable ultramafic massifs, N-MORB eclogites, metagabbros, metaserpentinites, metaperidotites, ortho- and paragneisses, and the Bacariza Formation granulites. The primary structure consists of the ultramafic massifs tectonically resting on top of the granulites of the Bacariza Formation, which overlie eclogites and HP gneisses with eclogite boudins. Granulites of the Bacariza Formation are mainly basic to intermediate in composition, although granulitic, carbonate-rich or mineralogically more exotic varieties also exist. On the basis of modal variations in the abundance of mafic and felsic mineral several lithotypes have been differentiated in order of decreasing outcrop area: (G1) plagio-pyrigarnites or common mafic granulites, (G2) intermediate to felsic, plagioclase-rich granulites, (G3) Mg-rich mafic granulites, (G4) pyrigarnite, or plagioclase-poor ultramafic granulites, and (G5) granulitic orthogneisses. The Bacariza Formation recorded a high-pressure metamorphic event. This event was polyphasic and two deformational phases are differentiated, D1 and D2, namely. D2 is associated to amalgamation of eclogite, high-pressure granulitic rocks and ultramafic sheets in deep portions of a subduction channel during the initial exhumation of the complex. As a result, transposition of the previous D1 fabrics took place due to the development of spectacular shear zones at the contacts with the bounding units. Pressure and temperature conditions estimated from the D2 mineral assemblage in equilibrium yield values of ca. 1.4 GPa and 740 °C, respectively. In this work we present a detailed study of a D2 shear zone located at the contact

  18. The generation of voluminous S-type granites in the Moldanubian unit, Bohemian Massif, by rapid isothermal exhumation of the metapelitic middle crust

    NASA Astrophysics Data System (ADS)

    Žák, Jiří; Verner, Kryštof; Finger, Fritz; Faryad, Shah Wali; Chlupáčová, Marta; Veselovský, František

    2011-01-01

    This paper presents new structural, anisotropy of magnetic susceptibility (AMS), petrological, and geochronological data to examine the link between LP-HT metamorphism and S-type granite formation in the Moldanubian unit, Bohemian Massif. We first describe the intrusive relationships of an S-type granite to its host cordierite-bearing migmatites, superbly exposed in the Rácov locality, northeastern Moldanubian batholith. The knife-sharp contacts and rectangular stoped blocks establish that the migmatites cooled and were exhumed above the brittle-ductile transition prior to the granite emplacement. The U-Pb monazite geochronology combined with P-T estimations constrain the age and depth of migmatization at ~ 329 Ma and ~ 21 km (T ≈ 730 °C). The migmatite complex was then exhumed at a rate of 6-7 mm y-1 to a depth of < 9 km where it was intruded by the granite at ~ 327 Ma. These data indicate that the hot fertile metapelitic middle crust in this part of the Moldanubian unit, newly defined as the Pelhřimov complex, underwent rapid isothermal decompression at ~ 329-327 Ma, giving rise to biotite melting and generation of large volumes of S-type granite magma. We propose that the rapid ~ 329-327 Ma exhumation of the Pelhřimov complex may have been partly assisted by the crustal-scale Přibyslav mylonite zone, which delineates the underlying western edge of the Brunia microplate underthrust beneath the eastern half of the Moldanubian unit during the early Carboniferous. The front edge of Brunia thus acted as a rigid backstop at depth, localizing the exhumation of the Pelhřimov complex and separating the hot fertile middle crust to the west from the already cooled overthrust complexes to the east. The magnetic fabric of the granite around the migmatite blocks further reveals that the Pelhřimov complex was shortened vertically and extended in the ~ WNW-ESE direction during and after its exhumation, implying that the SSE-directed underthrusting of Brunia along the

  19. Crustal melting during subduction at mantle depth: anatomy of near-UHP nanogranites (Orlica-Śnieżnik Dome, Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Ferrero, Silvio; Ziemann, Martin; Walczak, Katarzyna; Wunder, Bernd; O'Brien, Patrick J.; Hecht, Lutz

    2015-04-01

    Small volumes (≤ 50µm) of hydrous melt were trapped as primary inclusions in peritectic garnets during partial melting of metagranitoids from the Orlica-Śnieżnik Dome (Bohemian Massif) at mantle depth [1]. Detailed microstructural/microchemical investigation confirmed the occurrence of a granitic assemblage (biotite+feldspars+quartz) in every investigated inclusion, i.e they are nanogranites [2]. MicroRaman mapping of unexposed inclusions showed the occurrence of residual, H2O-rich glass in interstitial position. Despite the oddity of this finding within a classic regional HP/HT terrain, an incomplete crystallization of the melt inclusions (MI) is consistent with the (relatively) rapid exhumation of the Orlica-Śnieżnik Dome proposed by some authors [e.g. 3]. Moreover glassy and partially crystallized MI have been already reported in lower-P (<1 GPa) migmatites [4]. MicroRaman investigation also showed the possible presence of kumdykolite, a high-temperature polymorph of albite reported in UHP rocks from the Kokchetav Massif as well as the Bohemian massif ([5] and references therein). Experimental re-homogenization of nanogranites was achieved using a piston cylinder apparatus at 2.7 GPa and 875°C under dry conditions, in order to investigate melt composition and H2O content with in situ techniques. The trapped melt is granitic, hydrous (6 wt% H2O) and metaluminous (ASI=1.03), and it is similar to those produced experimentally from crustal lithologies at mantle conditions. Re-homogenization conditions are consistent with the results of geothermobarometric calculations on the host rock, suggesting that no H2O loss occurred during exhumation - this would have caused a shift of the inclusion melting T toward higher values. Coupled with the absence of H2O-loss microstructural evidence, e.g. decrepitation cracks and/or vesciculation [4] in re-homogenized nanogranites, this evidence suggests that the nanogranites still preserves the original H2O content of the

  20. Contrasts in sillimanite deformation in felsic tectonites from anhydrous granulite- and hydrous amphibolite-facies shear zones, western Canadian Shield

    NASA Astrophysics Data System (ADS)

    Leslie, S. R.; Mahan, K. H.; Regan, S.; Williams, M. L.; Dumond, G.

    2015-02-01

    The deformation behavior of crustal materials in variably hydrated metamorphic environments can significantly influence the rheological and seismic properties of continental crust. Optical observations and electron backscatter diffraction (EBSD) analyses are used to characterize sillimanite deformation behavior in felsic tectonites from two deformation settings in the Athabasca granulite terrane, western Canadian Shield. Under estimated conditions of 0.8-1.0 GPa, 725-850 °C in the Cora Lake shear zone, the data suggest that sillimanite deformed by dislocation creep with slip in the [001] direction accompanied by subgrain rotation recrystallization. Where sillimanite locally remained undeformed, strain was concentrated in surrounding weaker phases. Under hydrated conditions of 0.4-0.6 GPa, 550-650 °C in the Grease River shear zone, textures and cathodoluminescence imaging point to dissolution-precipitation creep as the major deformation mechanism for sillimanite, resulting in synkinematic growth of foliation-parallel euhedral sillimanite in a preferred orientation with [001] parallel to the lineation. The results suggest that temperature, fluid content, and modal mineralogy of the surrounding phases may all have significant influence on sillimanite deformation but that preferential alignment of sillimanite [001] parallel to the lineation persists regardless of contrasts in the conditions or mechanisms of deformation.

  1. Pervasive horizontal fabric and rapid vertical extrusion: Lateral overturning and margin sub-parallel flow of deep crustal migmatites, northeastern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Pressler, R. E.; Schneider, D. A.; Petronis, M. S.; Holm, D. K.; Geissman, J. W.

    2007-10-01

    In the West Sudetes, northeastern Bohemia Massif, geochronometry provides evidence for repeated episodes of rapid cooling that contrasts sharply with an absence of structural evidence for significant tectonic exhumation by crustal extension. Instead, high-grade assemblages of the Orlica-Snieznik Complex have a regional sub-horizontal foliation and sub-horizontal lineations that trend parallel to narrow sub-vertical shear zones containing exhumed high-pressure assemblages. Mesoscopic petrofabrics combined with anisotropy of magnetic susceptibility (AMS) data from amphibolite facies to migmatitic meta-sedimentary and meta-igneous rocks reveal remarkably consistent average lineations that plunge shallowly to the SSW on both steep and sub-horizontal NNE-trending planar fabrics. The dominant SSW-NNE fabric orientation is parallel to the Bohemia-Brunia suture, which marks a major boundary along the eastern margin of the massif. The shape of the AMS ellipsoid is predominantly oblate, revealing flattened fabrics, with only local prolate ellipsoids. We envisage that the continental Brunian indentor operated as a rigid backstop and allowed the migmatized lower crustal orogenic root to be exhumed along the Bohemian margin shortly following terminal arc collision. Sub-vertical extrusion of the orogenic root was arrested in the mid-crust, where the lower ductile crust was laterally overturned at the base of rigid upper crustal blocks. Upon reaching the crustal high-strength lid the exhumed ductile mass of continental material laterally spread sub-parallel to the margin, underwent subsequent supra-Barrovian metamorphism, and quickly cooled. The application of AMS techniques to high-grade metamorphic rocks in concert with macroscopic structural observations is a powerful approach for resolving the deformation history of a terrane where visible rock fabrics can be tenuous.

  2. The Nysa-Morava Zone: an active tectonic domain with Late Cenozoic sedimentary grabens in the Western Carpathians' foreland (NE Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Špaček, Petr; Bábek, Ondřej; Štěpančíková, Petra; Švancara, Jan; Pazdírková, Jana; Sedláček, Jan

    2015-06-01

    We give an interpretive review of the geological evolution of the Nysa-Morava Zone (NMZ)—a Late Cenozoic tectonically active region of the NE Bohemian Massif located at its contact with the Western Carpathians' orogenic front. This crustal domain, delimited by generally NW-SE-striking fault system, is characterised by Oligo-Miocene and Plio-Pleistocene volcanic activity, regionally anomalous, weak historical and present-day seismicity and increased CO2 flux. The NMZ hosts several elongated, mostly NW-SE-trending, graben-like sedimentary basins (Upper Morava Basin System), which are filled by more than 300-m-thick succession of clastic fluvial/lacustrine sediments of Pliocene-Quaternary age. Based on geometric relations, basin architecture, coincidence of seismicity with CO2 escape and sparse focal mechanism data, a model is proposed, which explains this active domain as a transfer zone developed between major WNW-ESE and NW-SE faults in a right-lateral transpressional setting. It is suggested that slow horizontal slip at these faults resulted in local permutations of the largest and medium stress directions and formation of transtensional crustal domains in the NMZ. Moreover, relation of the NMZ to the Alpine-Carpathian system and sedimentary grabens in its foreland is discussed. The absence of Paleogene and Lower Miocene deposits suggests that subsidence in the NMZ was commenced later than in the European Cenozoic Rift System (ECRIS), which is in agreement with later thrusting in Western Carpathians at ~17 Ma. The quantitative contrasts to the ECRIS in terms of faulting and subsidence rates are explained by the absence of lithospheric/crustal thinning in the NMZ.

  3. Two-stage exhumation of subducted Saxothuringian continental crust records underplating in the subduction channel and collisional forced folding (Krkonoše-Jizera Mts., Bohemian Massif)

    NASA Astrophysics Data System (ADS)

    Jeřábek, Petr; Konopásek, Jiří; Žáčková, Eliška

    2016-08-01

    The Krkonoše-Jizera Massif in the northern part of the Variscan Bohemian Massif provides insight into the exhumation mechanisms for subducted continental crust. The studied region exposes a relatively large portion of a flat-lying subduction-related complex that extends approximately 50 km away from the paleosuture. wide extent of HP-LT metamorphism has been confirmed by new P-T estimates indicating temperatures of 400-450 °C at 14-16 kbar and 450-520 °C at 14-18 kbar for the easternmost and westernmost parts of the studied area, respectively. A detailed study of metamorphic assemblages associated with individual deformation fabrics together with analysis of quartz deformation microstructures and textures allowed characterisation of the observed deformation structures in terms of their subduction-exhumation memory. An integration of the lithostratigraphic, metamorphic and structural data documents a subduction of distal and proximal parts of the Saxothuringian passive margin to high-pressure conditions and their subsequent exhumation during two distinct stages. The initial stage of exhumation has an adiabatic character interpreted as the buoyancy driven return of continental material from the subduction channel resulting in underplating and progressive nappe stacking at the base of the Teplá-Barrandian upper plate. With the transition from continental subduction to continental collision during later stages of the convergence, the underplated high-pressure rocks were further exhumed due to shortening in the accretionary wedge. This shortening is associated with the formation of large-scale recumbent forced folds extending across the entire studied area.

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

    NASA Astrophysics Data System (ADS)

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

    2017-04-01

    Fundamental to every modern continent's early (Archean) history is the generation of high temperature conditions required to produce the dense, strong, relatively anhydrous rocks that comprise most of Earth's stable cratonic crust. While the thermal gradients supported in Archean terranes are better understood, the timescales over which these conditions occur are more enigmatic. Garnet petrochronology allows for the interrogation of a semi-continuous record of these tectonometamorphic conditions, by linking pressure-temperature-fluid conditions (using phase equilibria modeling, trace element thermometry, stable isotope geochemistry) to a precise chronologic/chronometric record (e.g. high-precision Sm-Nd geochronology, geospeedometry of major and trace element diffusion profiles). Here, we utilize techniques from this burgeoning field of study to elucidate the rates and conditions of high temperature/ultra-high temperature (HT/UHT) metamorphism in the 2.7 Ga Pikwitonei Granulite Domain (PGD). The PGD represents over 150,000 km2 of dominantly granulite-facies metamorphic rocks situated at the NW edge of the Superior Province. Peak temperatures in the region range from 760°C in the southernmost part of the PGD, to 900-960˚C in the central/western PGD ( 40-60 km apart). Previous studies have suggested that metamorphism was long-lived in the region, occurring over 100 Ma, from 2.71-2.60 Ga [1, 2, 3]. High-precision garnet geochronology on microsampled garnets provides a detailed growth history of several lithologies across the region. Where necessary, bulk garnet analysis (i.e. dating based upon multiple whole garnet crystals rather than portions thereof) was also performed. While cooling from HT/UHT will result in some degree of intra-mineral age resetting, a detailed isotopic study of a range of large garnet porphyroblasts from the PGD (those which would be variably reset depending on peak T, grain size, and initial cooling rate) can retain information about both

  5. The Suruli shear zone and regional scale folding pattern in Madurai block of Southern Granulite Terrain, south India

    NASA Astrophysics Data System (ADS)

    Srinivasan, V.; Rajeshdurai, P.

    2010-04-01

    Through the application of remote sensing techniques followed by field checks, the exact extension and nature of Suruli shear zone in Madurai block of southern granulite terrain (SGT) in south India is brought out for the first time in this work. The dominant rock type exposed in this area is charnockite intruded by granites. The Suruli ductile shear zone extends from just west of Kadaiyanallur in the south to Ganguvarpatti in the north over a length of 150 km. Between Kadaiyanallur and Kambam, the shear zone extends roughly in N-S direction. From Kambam, it swerves towards NE and then towards ENE near Ganguvarpatti. The strongly developed transposed foliation and mylonite foliation within the shear zone dip towards east only and so the eastern block (Varushanad hills) is the hanging wall and the western block (Cardamom hills) is the footwall of the shear zone. In the eastern block, three distinct phases of regional scale folding (F1, F2 and F3) are recognized. In complete contrast, the western block recorded only the last phase (F3) regional scale folding. As the more deformed eastern block (older terrain) moved over the relatively less deformed western block (younger terrain) along the Suruli shear zone, it is proposed that this shear zone is a thrust or reverse fault, probably of Proterozoic age. As there are evidences for decreasing displacement from north to south (i.e., from Ganguvarpatti to Kadaiyanallur), the Suruli shear zone could be a rotational thrust or reverse fault with the pivot located close to Kadaiyanallur. As the pivot is located near Achankovil shear zone which trends WNW-ESE (dip towards SSW), the Suruli shear zone could be splaying (branching) out from Achankovil shear zone. In a nutshell, the Suruli shear zone could be a splay, rotational thrust or reverse fault.

  6. Geochemical signatures of metasedimentary rocks of high-pressure granulite facies and their relation with partial melting: Carvalhos Klippe, Southern Brasília Belt, Brazil

    NASA Astrophysics Data System (ADS)

    Cioffi, Caue Rodrigues; Campos Neto, Mario da Costa; da Rocha, Brenda Chung; Moraes, Renato; Henrique-Pinto, Renato

    2012-12-01

    High-grade metasedimentary rocks can preserve geochemical signatures of their sedimentary protolith if significant melt extraction did not occur. Retrograde reaction textures provide the main evidence for trapped melt in the rock fabrics. Carvalhos Klippe rocks in Southern Brasília Orogen, Brazil, present a typical high-pressure granulite assemblage with evidence of mica breakdown partial melting (Ky + Grt + Kfs ± Bt ± Rt). The metamorphic peak temperatures obtained by Zr-in-Rt and ternary feldspar geothermometers are between 850 °C and 900 °C. The GASP baric peak pressure obtained using grossular rich garnet core is 16 kbar. Retrograde reaction textures in which the garnet crystals are partially to totally replaced by Bt + Qtz ± Fsp intergrowths are very common in the Carvalhos Klippe rocks. These reactions are interpreted as a result of interactions between residual phases and trapped melt during the retrograde path. In the present study the geochemical signatures of three groups of Carvalhos Klippe metasedimentary rocks are analysed. Despite the high metamorphic grade these three groups show well-defined geochemical features and their REE patterns are similar to average compositions of post-Archean sedimentary rocks (PAAS, NASC). The high-pressure granulite facies Grt-Bt-Pl gneisses with immature arenite (wacke, arkose or lithic-arenite) geochemical signatures present in the Carvalhos Klippe are compared to similar rocks in amphibolite facies from the same tectonic framework (Andrelândia Nappe System). The similar geochemical signatures between Grt-Bt-Pl gneisses metamorphosed in high-pressure granulite facies and Grt-Bt-Pl-Qtz schists from the Andrelândia and Liberdade Nappes, with minimal to absent melting conditions, are suggestive of low rates of melt extraction in these high-grade rocks. The rocks with pelitic compositions most likely had higher melt extraction and even under such circumstances nevertheless tend to show REE patterns similar to

  7. Metasedimentary rocks of the Angara-Kan granulite-gneiss block (Yenisey Ridge, south-western margin of the Siberian Craton): Provenance characteristics, deposition and age

    NASA Astrophysics Data System (ADS)

    Urmantseva, L. N.; Turkina, O. M.; Larionov, A. N.

    2012-04-01

    The Angara-Kan granulite-gneiss block (Yenisey Ridge) is one of the main basements uplift within the south-western margin of the Siberian Craton. The major part of the Angara-Kan block is composed of Early Precambrian high-grade metamorphic rocks. Metasedimentary association of the Kan granulitic complex is composed of garnet-bearing, garnet-orthopyroxene and orthopyroxene-bearing gneisses, garnet- and orthopyroxene-bearing gneisses with cordierite and sillimanite. Studied paragneisses were formed at the expense of granulite metamorphism of terrigenous rocks, ranging from graywacke to pelitic rock or mudstone. To estimate the time of sedimentation and metamorphism of the terrigenous deposits, the U-Pb zircon dating has been performed using the SHRIMP II ion microprobe. Detrital zircon cores from the biotite-orthopyroxene and high-alumina gneisses yield ages of 2.6-1.94 and 2.4-1.94 Ga, respectively. Together with the age of the magmatic zircons formed during high-grade metamorphism and partial melting (˜1.89 Ga) and metamorphic rims (˜1.87 Ga) it defines the time of sedimentation between 2.0-1.94 and 1.89-1.87 Ga. Detrital zircon ages indicate both Archean and Paleoproterozioc rocks in provenance source, that agrees with the Nd model ages of metasediments ranging in interval 2.4-2.8 Ga. Potential source of the Archean detrital zircons was the exposed basement of the southwestern Siberian Craton, whereas the Paleoproterozoic juvenile crustal source seems to be buried basement of the Tungus province of the Siberian Craton. Deposition of the Kan terrigeneous rocks was coeval with sedimentation in the southeastern part of the Sharyzhalgay uplift, where ages of detrital zircon cores and metamorphic rims from paragneisses bracket sediment deposition between 1.95 and 1.85 Ga.

  8. Garnet-biotite diffusion mechanisms in complex high-grade orogenic belts: Understanding and constraining petrological cooling rates in granulites from Ribeira Fold Belt (SE Brazil)

    NASA Astrophysics Data System (ADS)

    Bento dos Santos, Telmo M.; Tassinari, Colombo C. G.; Fonseca, Paulo E.

    2014-12-01

    Cooling rates based on the retrograde diffusion of Fe2+ and Mg between garnet and biotite inclusions commonly show two contrasting scenarios: a) narrow closure temperature range with apparent absence of retrograde diffusion; or b) high result dispersion due to compositional variations in garnet and biotite. Cooling rates from migmatites, felsic and mafic granulites from Ribeira Fold Belt (SE Brazil) also show these two scenarios. Although the former can be explained by very fast cooling, the latter is often the result of open-system behaviour caused by deformation. Retrogressive cooling during the exhumation of granulite-facies rocks is often processed by thrusting and shearing which may cause plastic deformation, fractures and cracks in the garnet megablasts, allowing chemical diffusion outside the garnet megablast - biotite inclusion system. However, a careful use of garnets and biotites with large Fe/Mg variation and software that reduces result dispersion provides a good correlation between closure temperatures and the size of biotite inclusions which are mostly due to diffusion and compositional readjustment to thermal evolution during retrogression. Results show that felsic and mafic granulites have low cooling rates (1-2 °C/Ma) at higher temperatures and high cooling rates (˜100 °C/Ma) at lower temperatures, suggesting a two-step cooling/exhumation process, whereas migmatites show a small decrease in cooling rates during cooling (from 2.0 to 0.5 °C/Ma). These results agree with previously obtained thermochronological data, which indicates that this method is a valid tool to obtain meaningful petrological cooling rates in complex high-grade orogenic belts, such as the Ribeira Fold Belt.

  9. A seismogenic zone in the deep crust indicated by pseudotachylytes and ultramylonites in granulite-facies rocks of Calabria (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Altenberger, U.; Prosser, G.; Grande, A.; Günter, C.; Langone, A.

    2013-10-01

    Pseudotachylyte veins frequently associated with mylonites and ultramylonites occur within migmatitic paragneisses, metamonzodiorites, as well as felsic and mafic granulites at the base of the section of the Hercynian lower crust exposed in Calabria (Southern Italy). The crustal section is tectonically superposed on lower grade units. Ultramylonites and pseudotachylytes are particularly well developed in migmatitic paragneisses, whereas sparse fault-related pseudotachylytes and thin mylonite/ultramylonite bands occur in granulite-facies rocks. The presence of sillimanite and clinopyroxene in ultramylonites and mylonites indicates that relatively high-temperature conditions preceded the formation of pseudotachylytes. We have analysed pseudotachylytes from different rock types to ascertain their deep crustal origin and to better understand the relationships between brittle and ductile processes during deformation of the deeper crust. Different protoliths were selected to test how lithology controls pseudotachylyte composition and textures. In migmatites and felsic granulites, euhedral or cauliflower-shaped garnets directly crystallized from pseudotachylyte melts of near andesitic composition. This indicates that pseudotachylytes originated at deep crustal conditions (>0.75 GPa). In mafic protoliths, quenched needle-to-feather-shaped high-alumina orthopyroxene occurs in contact with newly crystallized plagioclase. The pyroxene crystallizes in garnet-free and garnet-bearing veins. The simultaneous growth of orthopyroxene and plagioclase as well as almandine, suggests lower crustal origin, with pressures in excess of 0.85 GPa. The existence of melts of different composition in the same vein indicates the stepwise, non-equilibrium conditions of frictional melting. Melt formed and intruded into pre-existing anisotropies. In mafic granulites, brittle faulting is localized in a previously formed thin high-temperature mylonite bands. migmatitic gneisses are deformed into

  10. Petrology and mineral equilibrium modeling of incipient charnockite from the Lützow-Holm Complex, East Antarctica: implications for granulite formation in a Gondwana fragment

    NASA Astrophysics Data System (ADS)

    Tsunogae, Toshiaki

    2015-04-01

    Charnockite (orthopyroxene-bearing granitoid) is regarded as one of the fundamental lithologies in many high-grade metamorphic terranes including Neoproterozoic collisional orogen formed during the amalgamation of Gondwana supercontinent. Although both magmatic (massive) and metamorphic charnockites have been reported, several classic examples for the spectacular development of 'incipient charnockites' within orthopyroxene-free felsic gneisses are exposed in several quarry sections in Neoproterozoic granulite terrenes in southern India (e.g., Trivandrum Block) and Sri Lanka. (e.g., Wanni Complex). The charnockite-forming process in these localities is considered to have been triggered by the infiltration of CO2-rich anhydrous fluids along structural pathways within upper amphibolite facies gneisses, resulting in the lowering of water activity and stabilization of orthopyroxene through the breakdown of biotite. However, no detailed study of incipient charnockites in the Lützow-Holm Complex of East Antarctica, which is regarded as an extension of Neoproterozoic to Cambrian orogeny in India and Sri Lanka, has been reported so far. This study thus reports new petrological data of incipient charnockite patches in orthopyroxene-free felsic gneiss from Skallevikshalsen in the granulite-facies region of the Lützow-Holm Complex, East Antarctica, and discuss the timing and process of charnockite formation. Incipient charnockite (Opx + Qtz + Pl + Kfs + Grt) occurs as dark brownish patches of several cm in length within coarse-grained leucocratic gneiss (Qtz + Pl + Kfs + Grt) interlayered with various supracrustal lithologies such as mafic granulite, pelitic granulite, and marble. Orthopyroxene, which occurs only in garnet-bearing portion of the rock, probably formed by a FMAS continuous reaction: Grt + Qtz => Opx + Pl. Phase equilibrium modeling in the system NCKFMASH suggests a wide range of P-T stability (>780 C, >6 kbar), although the condition is broadly consistent with

  11. U-Pb monazite ages in amphibolite- to granulite-facies orthogneiss reflect hydrous mineral breakdown reactions: Sveconorwegian Province of SW Norway

    NASA Astrophysics Data System (ADS)

    Bingen, Bernard; van Breemen, Otto

    In the Rogaland-Vest Agder terrain of the Sveconorwegian Province of SW Norway, two main Sveconorwegian metamorphic phases are reported: a phase of regional metamorphism linked to orogenic thickening (M1) and a phase of low-pressure thermal metamorphism associated with the intrusion of the 931 +/- 2 Ma anorthosite-charnockite Rogaland igneous complex (M2). Phase M1 reached granulite facies to the west of the terrane and M2 culminated locally at 800-850 °C with the formation of dry osumilite-bearing mineral associations. Monazite and titanite U-Pb geochronology was conducted on 17 amphibolite- to granulite-facies orthogneiss samples, mainly from a suite of 1050 +2/-8 Ma calc-alkaline augen gneisses, the Feda suite. In these rocks, prograde negatively discordant monazite crystallized during breakdown of allanite and titanite in upper amphibolite facies at 1012-1006 Ma. In the Feda suite and other charnockitic gneisses, concordant to slightly discordant monazite at 1024-997 Ma probably reflects breakdown of biotite during granulite-facies M1 metamorphism. A spread of monazite ages down to 970 Ma in biotite +/- hornblende samples possibly corresponds to the waning stage of this first event. In the Feda suite, a well defined monazite growth episode at 930-925 Ma in the amphibolite-facies domain corresponds to major clinopyroxene formation at the expense of hornblende during M2. Growth or resetting of monazite was extremely limited during this phase in the granulite-facies domain, up to the direct vicinity of the anorthosite complex. The M2 event was shortly followed by cooling through ca. 610 °C as indicated by tightly grouped U-Pb ages of accessory titanite and titanite relict inclusions at 918 +/- 2 Ma over the entire region. A last generation of U-poor monazite formed during regional cooling below 610 °C, in hornblende-rich samples at 912-904 Ma. This study suggests: (1) that monazite formed during the prograde path of high-grade metamorphism may be preserved; (2

  12. Petrology, geochemistry and modelling of the granulitic-ultramafic rocks in Beni Bousera (Rif, Morocco): implications for direct crust-mantle interactions and melt-extraction systems

    NASA Astrophysics Data System (ADS)

    Manthei, C. D.; Álvarez-Valero, A.; Jagoutz, O. E.

    2011-12-01

    The Beni Bousera (N. Morocco) and Ronda (S. Spain) ultramafic massifs of the Betic-Rif orogenic belt are two of the most pristine exposures of upper-mantle/lower crustal material on Earth's surface. Unlike other samples of the mantle, they are relatively unaltered and preserve a record of ultra-high pressure conditions, within the diamond-stability field (e.g. Slodkevich, 1980; Pearson et al., 1989). The process of removing of the massifs from the diamond-stability field, and the ensuing emplacement into the continental crust, is an ongoing area of research in regional tectonics. Here, we focus specifically on Beni Bousera, and note that the up-risen material is of higher density than its host, prompting the development of models that use melt-induced buoyancy forces as the primary driver of exhumation (Jagoutz et al., 2006; Gerya and Burg, 2007). We find evidence for discrete reaction zones in the ultramafic rocks that were formed by pervasive infiltration of melt, which may have channelized, lowered the integrated bulk density of the massif (e.g., Jagoutz et al., 2006), and driven exhumation. Since key questions concerning the emplacement mechanisms are still unanswered, complementary studies of the surrounding crustal material -granulitic rocks, which are mostly metapelitic with local intercalation of mafic composition-, assist in deepening our understanding crust-mantle processes. We will discuss our ongoing research at Beni Bousera, focusing on: (1) the petrological, structural, geochronological and physical relationships between mantle and crust by combining field petrology, petrography and phase diagram modeling, geochemistry, zircons/monazite dating, and numerical modeling; (2) the emplacement mechanisms of ultramafic and granulitic rocks by proposing a new hypothesis of very rapid exhumation of the mantle material. This rapid ascent is currently being constrained/tested by combining geobarometric calculations and high precision U-Pb zircon geochronology on

  13. Laboratory-scale experimental burning of selected Palaeozoic limestones from the Barrandian area (Prague Basin, Bohemian Massif, Czech Republic): re-evaluation of properties of historical raw material

    NASA Astrophysics Data System (ADS)

    Kozlovcev, Petr; Prikryl, Richard; Stastna, Aneta

    2013-04-01

    Palaeozoic limestones from the Barrandian area (Prague Basin, Bohemian Massif, Czech Republic) have been quarried and utilized, among others, for manufacturing of inorganic binders. Certain beds, e.g. Devonian dvorecko-prokopské limestones were historically burnt for high quality hydraulic lime which is not produced recently. Aiming to evaluate potential of this specific raw material for small-scale production of restoration hydraulic lime, we have conducted some laboratory experimental burning tests in an electrical furnace up to 1200°C. Prior to the burning, all studied lithotypes (4 in total) have been examined for their mineralogy (optical microscopy, cathodoluminescence study, X-ray diffraction of insoluble residue) and geochemistry (wet chemical analyses). Studied biomicritic limestones can be classified as wackstones to packstones. Carbonate content varies from 80 to 90 %, the rest is due to dominant illite and silica, and subordinate kaolinite, feldspars, and/or chlorite. Specific composition of non-carbonate component (specifically high content of illite and silica) positively influences formation of CS, Ca, and/or CAS phases when burnt at calcination temperatures from 850 to 1200°C (in steps of 50°C). In the products formed during firing, mineral phases typical for hydraulic lime, such as larnite, brownmillerite, and gehlenite, along with free lime, quartz and silica phases, and portlandite were identified by X-ray diffraction. The amount of the dominant hydraulic phase, larnite, increased with higher firing temperature. On the other hand, content of free lime, quartz and silica decreased. The amount of portlandite was almost independent of the firing temperature. Higher amounts of larnite and other hydraulic phase were detected during the peak firing temperature of 1200°C in specimens containing higher amount of insoluble residue. From the study performed, it is evident that studied dvorecko-prokopské limestone, which included favourable amount of

  14. Re-Os and Lu-Hf isotopic constraints on the formation and age of mantle pyroxenites from the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Bizimis, Michael; Haluzová, Eva; Sláma, Jiří; Svojtka, Martin; Hirajima, Takao; Erban, Vojtěch

    2016-07-01

    We report on the Lu-Hf and Re-Os isotope systematics of a well-characterized suite of spinel and garnet pyroxenites from the Gföhl Unit of the Bohemian Massif (Czech Republic, Austria). Lu-Hf mineral isochrons of three pyroxenites yield undistinguishable values in the range of 336-338 Ma. Similarly, the slope of Re-Os regression for most samples yields an age of 327 ± 31 Ma. These values overlap previously reported Sm-Nd ages on pyroxenites, eclogites and associated peridotites from the Gföhl Unit, suggesting contemporaneous evolution of all these HT-HP rocks. The whole-rock Hf isotopic compositions are highly variable with initial εHf values ranging from - 6.4 to + 66. Most samples show a negative correlation between bulk rock Sm/Hf and εHf and, when taking into account other characteristics (e.g., high 87Sr/86Sr), this may be explained by the presence of recycled oceanic sediments in the source of the pyroxenite parental melts. A pyroxenite from Horní Kounice has decoupled Hf-Nd systematics with highly radiogenic initial εHf of + 66 for a given εNd of + 7.8. This decoupling is consistent with the presence of a melt derived from a depleted mantle component with high Lu/Hf. Finally, one sample from Bečváry plots close to the MORB field in Hf-Nd isotope space consistent with its previously proposed origin as metamorphosed oceanic gabbro. Some of the websterites and thin-layered pyroxenites have variable, but high Os concentrations paralleled by low initial γOs. This reflects the interaction of the parental pyroxenitic melts with a depleted peridotite wall rock. In turn, the radiogenic Os isotope compositions observed in most pyroxenite samples is best explained by mixing between unradiogenic Os derived from peridotites and a low-Os sedimentary precursor with highly radiogenic 187Os/188Os. Steep increase of 187Os/188Os at nearly uniform 187Re/188Os found in a few pyroxenites may be connected with the absence of primary sulfides, but the presence of minor

  15. Ultrapotassic dykes in the Moldanubian Zone and their significance for understanding of the post-collisional mantle dynamics during Variscan orogeny in the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Kubínová, Šárka; Faryad, Shah Wali; Verner, Kryštof; Schmitz, Mark; Holub, František

    2017-02-01

    We report mineral textures, geochemistry and age relations of two ultrapotassic dykes from a dyke swarm in the Western part of the Moldanubian Zone at contact to the Teplá-Barrandian Block. The dykes have orientation almost perpendicular to the NNE-SSW trending Central Bohemian plutonic complex and cross cut metamorphic foliation in basement gneisses and migmatites. Based on mineral compositions and geochemistry, the dykes show close relations to Mg-K syenite plutons in the Moldanubian Zone. The two dykes are vaugnerite and syenite in compositions and contain talc pseudomorphs after olivine within a fine-grained matrix that consists of K-feldspar, phlogopite with small amounts of clinopyroxene and accessory quartz, apatite, titanite and sulphides of Fe, Cu, Ni. The syenite porphyry dyke cross cuts the vaugnerite. It contains quartz phenocrysts and comparing to vaugnerite has lower modal content of talc pseudomorphs. The vaugnerite and syenite porphyry have high K2O (6 to 7 wt.%) and mg-number (0.66-0.74), but low CaO and Na2O contents. The vaugnerite is markedly rich in P2O5 (> 2 wt.%) and comparing to syenite porphyry has higher amount of mantle-incompatible elements (e.g. Rb, Cs, Ba, Pb, Th, U), V and Cr. ID-TIMS analyses on titanite in vaugnerite and on zircon in syenite porphyry yielded 338.59 ± 0.68 and 337.87 ± 0.21 Ma, respectively. Mineral and bulk rock chemistry of the dykes indicates that the source magma was formed by a low degree of partial melting of a highly anomalous domain in the upper mantle which subsequently fractionated and was contaminated with crustal material during its ascent. Formation of ultrapotassic magma is explained by transcurrent shear zones in the mantle lithosphere that occurred due to block rotation and post-collisional mantle dynamics initiated by slab break-off and asthenosphere upwelling into the Moldanubian accretionary complex during the Variscan Orogeny.

  16. Human impacts of hydrometeorological extremes in the Bohemian-Moravian Highlands derived from documentary sources in the 18th-19th centuries

    NASA Astrophysics Data System (ADS)

    Dolák, Lukáš; Brázdil, Rudolf; Valášek, Hubert

    2014-05-01

    The extent of damage caused by hydrometeorological events or extremes (HME) has risen up in the entire world in the last few years. Especially the floods, flash floods, torrential rains and hailstorms are the most typical and one of the most frequent kind of natural disasters in the central Europe. Catastrophes are a part of human history and people were forced to cope with their consequences (e. g. material damage, economical losses, impacts on agriculture and society or losses of human lives). This paper analyses the human impacts of HME in the Bohemian-Moravian Highlands (central part of the Czech Republic) on the basis of documentary sources from the 18th-19th centuries. The paper presents various negative impacts of natural disasters on lives and property and subsequent inconveniences of Czech peasants. The preserved archival documents of estates or domains became the primary sources of data (e. g. taxation reliefs, damaged records, reports of afflicted farmers, administrative correspondence etc.). Particularly taxation reliefs relate to taxation system in the Czech lands during the 17th-19th centuries allowing to farmers to ask for tax alleviation when their crops were significantly damaged by any HME. These archival documents are a highly valuable source for the study of human impacts of natural disasters. Devastating consequences of these extremes affected individual farmers much more than the aristocracy. Floods caused inundations of farmer's fields, meadows, houses and farm buildings, washed away the arable land with crops, caused losses of cattle, clogged the land with gravel and mud and destroyed roads, bridges or agricultural equipment. Afflicted fields became worthless and it took them many years to become became fertile again. Crop was also damaged by hailstorms, droughts or late/early frosts. All these events led to lack of food and seeds in the following year and it meant the decrease of living standard, misery and poverty of farmers. Acquired

  17. Behavior of trace elements in quartz from plutons of different geochemical signature: A case study from the Bohemian Massif, Czech Republic

    NASA Astrophysics Data System (ADS)

    Breiter, Karel; Ackerman, Lukáš; Svojtka, Martin; Müller, Axel

    2013-08-01

    In this study, the trace-element content in igneous quartz from granitoids of different geochemical types was investigated using the laser ablation ICP-MS technique. The Variscan granitoids in the Bohemian Massif provide an excellent opportunity to study the chemical composition of magmatic quartz from the following granite types: (1) geochemically primitive I-type tonalites and granodiorites, (2) peraluminous S-type two-mica granites, (3) moderately fractionated A-type volcano-plutonic complexes of the Teplice caldera, and (4) highly fractionated S- and A-type rare-metal granites. This diversity of granitoids permitted the study of the chemical composition of magmatic quartz as the result of (i) different magma protoliths and (ii) variable degrees of differentiation. There were only small differences in the quartz trace-element contents, ranging from weakly to moderately differentiated plutons of all geochemical types: Al (mostly in the range between 20 and 250 ppm), Ti (mostly 20-110 ppm), B (< 13 ppm), Be (< 0.7 ppm), Ge (< 1 ppm), Li (< 30 ppm), and Rb (< 2 ppm). Only the S-type granites from western Erzgebirge contain Al-enriched quartz (mostly 200-400 ppm Al) since the beginning of its evolution. However, quartz from the highly fractionated granites (group 4) differs significantly: this quartz is generally poor in Ti (< 20 ppm Ti) and enriched in Al (up to 600 ppm in A-type, and up to 1000 ppm in S-type granites), Be (up to 3.2 ppm), Ge (up to 5.7 ppm), Li (up to 132 ppm, particularly in the S-type granites), and Rb (up to 15 ppm). The contents of the analyzed lithophile elements in the quartz from the highly fractionated granites are similar to the contents reported to be present in evolved complex pegmatites. Although the input of Ti into quartz is controlled mainly by the temperature and pressure of quartz crystallization, the entry of Al into quartz increases as a function of the water and fluorine content of the residual melt. The contents of Ge and Li

  18. Magnetic Characteristics of the Lower Crust: Examples from the Chipman Tonalite, Chipman Dikes, and Fehr Granite, Athabasca Granulite Terrane, Northern Canada

    NASA Astrophysics Data System (ADS)

    Brown, L. L.; Koteas, C.; Seaman, S. J.; Williams, M. L.

    2011-12-01

    The Athabasca granulite terrane (AGT) in northernmost Saskatchewan, Canada is an outstanding exposure of lower crustal rocks having experienced high temperature (~800°C) and high pressure (>1.0 GPa) conditions followed by uplift and exhumation to the surface. With little alteration since 1.9 Ga these rocks allow us to study ancient lower crustal lithologies. Aeromagnetic anomalies over this region are distinct and complex, and along with other geophysical measurements, define the Snowbird Tectonic zone, stretching NE-SW across the Canadian Shield and separating the Churchill province into the Hearne domain (mid-crustal rocks, lower metamorphism) from the Rae domain (lower crust rocks, higher metamorphism). The eastern part of the AGT is dominated by the Chipman tonalite batholith (3.3 Ga), and on the far east the Fehr Granite (2.4 Ga). Both units were intruded by the extensive mafic Chipman dike swarm at ~1.9 Ga. On-going magnetic studies of these three units are aimed at characterizing the rock magnetism and remanence of each group as well as relating magnetic properties to the observed aeromagnetic signatures. The Fehr granite is weakly magnetic, with susceptibilities ranging from 9.4 x 10-6 to 2.1 x 10-4 with an average of 9 x 10-5 SI. The remanence held by many Fehr granite samples is weak, but stronger than expected at ~1 mA/m. The bland aeromagnetic signature over the Fehr granite reflects low susceptibility and low remanence. Chipman tonalite samples show a wide range of magnetic properties including distinct oxide zones with susceptibilities of 0.3 SI and remanence values greater than 10 A/m to relatively non-magnetic areas with susceptibilities of 1x 10-4 SI and magnetization of .01 A/m. Hysteresis properties indicate a range of behavior from single-domain to multi-domain magnetite with a majority of samples indicating pseudo-single-domain behavior (average Mr/Ms = 0.13, Hcr/Hc = 3.3). Low temperature experiments confirm the presence of magnetite, and

  19. The Rožná uranium deposit (Bohemian Massif, Czech Republic): shear zone-hosted, late Variscan and post-Variscan hydrothermal mineralization

    NASA Astrophysics Data System (ADS)

    Kříbek, Bohdan; Žák, Karel; Dobeš, Petr; Leichmann, Jaromír; Pudilová, Marta; René, Miloš; Scharm, Bohdan; Scharmová, Marta; Hájek, Antonín; Holeczy, Daniel; Hein, Ulrich F.; Lehmann, Bernd

    2009-01-01

    Three major mineralization events are recorded at the Rožná uranium deposit (total mine production of 23,000 t U, average grade of 0.24% U): (1) pre-uranium quartz-sulfide and carbonate-sulfide mineralization, (2) uranium, and (3) post-uranium quartz-carbonate-sulfide mineralization. (1) K-Ar ages for white mica from wall rock alteration of the pre-uranium mineralization style range from 304.5 ± 5.8 to 307.6 ± 6.0 Ma coinciding with the post-orogenic exhumation of the Moldanubian orogenic root and retrograde-metamorphic equilibration of the high-grade metamorphic host rocks. The fluid inclusion record consists of low-salinity aqueous inclusions, together with H2O-CO2-CH4, CO2-CH4, and pure CH4 inclusions. The fluid inclusion, paragenetic, and isotope data suggest that the pre-uranium mineralization formed from a reduced low-salinity aqueous fluid at temperatures close to 300°C. (2) The uraniferous hydrothermal event is subdivided into the pre-ore, ore, and post-ore substages. K-Ar ages of pre-ore authigenic K-feldspar range from 296.3 ± 7.5 to 281.0 ± 5.4 Ma and coincide with the transcurrent reorganization of crustal blocks of the Bohemian Massif and with Late Stephanian to Early Permian rifting. Massive hematitization, albitization, and desilicification of the pre-ore altered rocks indicate an influx of oxidized basinal fluids to the crystalline rocks of the Moldanubian domain. The wide range of salinities of fluid inclusions is interpreted as a result of the large-scale mixing of basinal brines with meteoric water. The cationic composition of these fluids indicates extensive interaction with crystalline rocks. Chlorite thermometry yielded temperatures of 260°C to 310°C. During this substage, uranium was probably leached from the Moldanubian crystalline rocks. The hydrothermal alteration of the ore substage followed, or partly overlapped in time, the pre-ore substage alteration. K-Ar ages of illite from ore substage alteration range from 277.2 ± 5.5 to

  20. Petrology, phase equilibria and monazite geochronology of granulite-facies metapelites from deep drill cores in the Ordos Block of the North China Craton

    NASA Astrophysics Data System (ADS)

    He, Xiao-Fang; Santosh, M.; Bockmann, Kiara; Kelsey, David E.; Hand, Martin; Hu, Jianmin; Wan, Yusheng

    2016-10-01

    Among the various Precambrian crustal blocks in the North China Craton (NCC), the geology and evolution of the Ordos Block remain largely enigmatic due to paucity of outcrop. Here we investigate granulite-facies metapelites obtained from deep-penetrating drill holes in the Ordos Block and report petrology, calculated phase equilibria and in-situ monazite LA-ICP-MS geochronology. The rocks we studied are two samples of cordierite-bearing garnet-sillimanite-biotite metapelitic gneisses and one graphite-bearing, two-mica granitic gneiss. The peak metamorphic age from LA-ICP-MS dating of monazite in all three samples is in the range of 1930-1940 Ma. The (U + Pb)-Th chemical ages through EPMA dating reveals that monazite occurring as inclusions in garnet are older than those in the matrix. Calculated metamorphic phase diagrams for the cordierite-bearing metapelite suggest peak P-T conditions ca. 7-9 kbar and 775-825 °C, followed by decompression and evolution along a clockwise P-T path. Our petrologic and age data are consistent with those reported from the Khondalite Belt in the Inner Mongolia Suture Zone in the northern part of the Ordos Block, suggesting that these granulite-facies metasediments represent the largest Paleoproterozoic accretionary belt in the NCC.

  1. 1.45 Ga granulites in the southwestern Grenville province: Geologic setting, P-T conditions, and U-Pb geochronology

    NASA Astrophysics Data System (ADS)

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

    1994-03-01

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

  2. U Pb zircon (TIMS and SIMS) and Sm Nd whole-rock geochronology of the Gour Oumelalen granulitic basement, Hoggar massif, Tuareg shield, Algeria

    NASA Astrophysics Data System (ADS)

    Peucat, Jean Jacques; Drareni, Amar; Latouche, Louis; Deloule, Etienne; Vidal, Philippe

    2003-11-01

    Two major granulitic units are recognized in the Gour Oumelalen area. One of the units is composed partially of Archean gneisses (Red Gneiss complex) with U-Pb zircon SIMS and TIMS ages of approximately 2.7 Ga. Although they were formed from 3.0- to 3.2-Ga-old precursors, as indicated by Nd model ages, we find no evidence of any older history (≈3.5 Ga) as suggested by previous Pb-Pb ages. The other formation (Gour Oumelalen supergroup) is a metasedimentary sequence at least partly of Paleoproterozoic age, as indicated by zircon dates of a metavolcanic rock at approximately 2.2 Ga. A later magmatic event is recorded at approximately 1.9 Ga in both units and related to coeval granulite-facies metamorphism that affected both units. Nd model ages at approximately 2.0 Ga suggest an accretion of juvenile crust formation at that time. The existence of T DM Nd model ages intermediate between 2.5 and 2.9 Ga could result from the mixing of 3.2 and 2.0-Ga-old material or may reflect separate events.

  3. Discovery of ultrahigh-T spinel-garnet granulite with pure CO2fluid inclusions from the Altay orogenic belt, NW China*

    PubMed Central

    Li, Zi-long; Chen, Han-lin; Santosh, M; Yang, Shu-feng

    2004-01-01

    We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene, spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the orthopyroxenes have high XMg and Al2O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around −56.7 °C, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3–23.8 °C translating into CO2 densities of the order of 0.86–0.88 g/cm3. Based on preliminary mineral paragenesis, reaction textures and petrogenetic grid considerations, we infer that the rock was subjected to UHT conditions. The CO2-rich fluids were trapped during exhumation along a clockwise P-T path following isothermal decompression under UHT conditions. PMID:15362187

  4. Internal Microstructure and Breakdown of Garnet from Moldanubian Granulites (Gföhl Unit, Dunkelsteinerwald, Lower Austria)

    NASA Astrophysics Data System (ADS)

    Bourgin, Nathalie; Abart, Rainer; Petrakakis, Konstantin

    2014-05-01

    Symplectites in some conspicuous granulite facies rocks from the Moldanubian Gföhl Unit in Lower Austria show an unusual bulk composition with very high Mg, Ca contents and 14 mole% normative corundum. It contains garnet (XPyr>0,5), clinopyroxene (XMg: 14 mole%; XCaTs: 0,3), pargasitic hornblende (XMg: 17 mole%), and plagioclase (XAn>0,8). The primary microstructure is granular, medium-grained and well equilibrated. Clinopyroxene often shows exsolution lamellae and inclusions of amphibole and plagioclase. Garnets of about 2-3cm size are common. Often they are resorbed and therefore significantly smaller. The large garnets display numerous inclusions, e.g. of kyanite. The garnets show internal deformation domains. The lattice orientations of the different domains show displacements around a common rotation axis approximately parallel to [211]. This points to incipient polygonalization of garnet during crystal plastic deformation at obviously high strain rates under high grade metamorphic conditions. Along garnet margins and within cracks, various replacement symplectites were formed comprising distinct assemblages among orthopyroxen, spinel, anorthite, Al-rich amphibole, tschermakitic diopside, sapphirine and corundum. Symplectite formation was induced by decompression feature. The last peak metamorphic conditions of the Gföhl Unit has been estimated in previous studies with pressures and temperatures around resp. 8-11 kbar and 700-800°C. The rocks then experienced isothermal decompression followed by isobaric cooling around 5-6 kbar (e.g. Petrakakis 1997). The temperature during the formation of the symplectites has been estimated by garnet-orthopyroxene thermometry and resulted in values of approx. 700°C for the pressure-range of 5-6 kbar, indicating essentially isothermal decompression. The rims of breaking down garnets adjacent to Opx+Spl+Pl-symplectite show diffusional zoning patterns allowing geospeedometry modelling. This zoning is continuous displaying

  5. Rockmagnetism in relation to magnetic mineralogy of anorthosites in the southern granulite region of the Indian shield

    NASA Astrophysics Data System (ADS)

    Soumya, G. S.; Asanulla, R. Mohamed; Radhakrishna, T.

    2017-06-01

    Anorthosite occurrences in the south Indian shield are well known. Recent studies obtained Neoproterozoic age for many of them, yet their petrological and mineralogical data are very limited. This paper presents first comprehensive report of the physical attributes of petrography and rockmagnetism of two prominent anorthosite occurrences, one from the Oddanchatram and the other from the Kadavur in the southern granulite terrain of India. Petrography highlights the occurrence of exsolution lamellae of magnetite in plagioclase with clouding appearance in the Oddanchatram anorthosite (ODAN). The Kadavur anorthosite (KDAN) contains magnetite in the form of discrete grains. The distinctions are sharply reflected in the rockmagnetic attributes also. The Oddanchatram occurrence is characterized by high Koenigsberger ratios (Q value mostly >10), median destructive field (MDF > 50 mT) and coercivity of remanence (Hcr; 45-86 mT), dominance of remanence magnetism over induced magnetism, harder natural remanence over saturation isothermal remanence, Curie temperatures of 570-580 °C and high ratio of saturation remanence magnetization to saturation magnetization (Mrs/Ms: 0.08-0.35) with low ratio of Hcr to coercive force (Hcr/Hc:1.78-2.27) as determined from hysteresis loops indicating single (SD)/pseudo-single-domain (PSD) magnetite as the chief magnetic carrier. In contrast, the Kadavur occurrence is characterized by lower Q value (mostly <1), MDF (<10 mT) and Hcr (23-65 mT), dominance of induced magnetism over remanence, harder saturation isothermal remanence over natural remanence, Curie temperatures of 580-600 °C and low Mrs/Ms (0.02-0.04) with high Hcr/Hc (2.61-3.76) indicating presence of a dominant multidomain magnetite along with small quantities of canted antiferromagnetic mineral (haemo-ilmenites). These differences in physical attributes are explained in terms of crustal depths of their emplacement. The ODAN possessing SD/PSD exsolved magnetite lamellae in

  6. Oxygen isotope variations in granulite-grade iron formations: constraints on oxygen diffusion and retrograde isotopic exchange

    USGS Publications Warehouse

    Sharp, Z.D.; O'Neil, J.R.; Essene, E.J.

    1988-01-01

    The oxygen isotope ratios of various minerals were measured in a granulite-grade iron formation in the Wind River Range, Wyoming. Estimates of temperature and pressure for the terrane using well calibrated geothermometers and geobarometers are 730??50?? C and 5.5??0.5 kbar. The mineral constraints on fluid compositions in the iron formation during retrogression require either very CO2-rich fluids or no fluid at all. In the iron formation, isotopic temperature estimates from quartz-magnetite fractionations are controlled by the proximity to the enclosing granitic gneiss, and range from 500?? C (??qz - mt=10.0???) within 2-3 meters of the orthogneiss contact to 600?? C (??qz - mt=8.0???) farther from the contact. Temperature estimates from other isotopic thermometers are in good agreement with those derived from the quartz-magnetite fractionations. During prograde metamorphism, the isotopic composition of the iron formation was lowered by the infiltration of an external fluid. Equilibrium was achieved over tens of meters. Closed-system retrograde exchange is consistent with the nearly constant whole-rock ??18Owr value of 8.0??0.6???. The greater ??qz-mt values in the iron formation near the orthogneiss contact are most likely due to a lower oxygen blocking temperature related to greater exchange-ability of deformed minerals at the contact. Cooling rates required to preserve the quartz-magnetite fractionations in the central portion of the iron formation are unreasonably high (???800?? C/Ma). In order to preserve the 600?? C isotopic temperature, the diffusion coefficient D (for ??-quartz) should be two orders of magnitude lower than the experimentally determined value of 2.5??10-16 cm2/s at 833 K. There are no values for the activation energy (Q) and pre-exponential diffusion coefficient (D0), consistent with the experimentally determined values, that will result in reasonable cooling rates for the Wind River iron formation. The discrepancy between the diffusion

  7. Oxygen isotope variations in granulite-grade iron formations: constraints on oxygen diffusion and retrograde isotopic exchange

    NASA Astrophysics Data System (ADS)

    Sharp, Z. D.; O'Neil, J. R.; Essene, E. J.

    1988-04-01

    The oxygen isotope ratios of various minerals were measured in a granulite-grade iron formation in the Wind River Range, Wyoming. Estimates of temperature and pressure for the terrane using well calibrated geothermometers and geobarometers are 730±50° C and 5.5±0.5 kbar. The mineral constraints on fluid compositions in the iron formation during retrogression require either very CO2-rich fluids or no fluid at all. In the iron formation, isotopic temperature estimates from quartz-magnetite fractionations are controlled by the proximity to the enclosing granitic gneiss, and range from 500° C ( Δ qz - mt=10.0‰) within 2 3 meters of the orthogneiss contact to 600° C ( Δ qz - mt=8.0‰) farther from the contact. Temperature estimates from other isotopic thermometers are in good agreement with those derived from the quartz-magnetite fractionations. During prograde metamorphism, the isotopic composition of the iron formation was lowered by the infiltration of an external fluid. Equilibrium was achieved over tens of meters. Closed-system retrograde exchange is consistent with the nearly constant whole-rock δ 18Owr value of 8.0±0.6‰. The greater Δ qz-mt values in the iron formation near the orthogneiss contact are most likely due to a lower oxygen blocking temperature related to greater exchange-ability of deformed minerals at the contact. Cooling rates required to preserve the quartz-magnetite fractionations in the central portion of the iron formation are unreasonably high (˜800° C/Ma). In order to preserve the 600° C isotopic temperature, the diffusion coefficient D (for α-quartz) should be two orders of magnitude lower than the experimentally determined value of 2.5×10-16 cm2/s at 833 K. There are no values for the activation energy ( Q) and pre-exponential diffusion coefficient ( D 0), consistent with the experimentally determined values, that will result in reasonable cooling rates for the Wind River iron formation. The discrepancy between the

  8. The Krásná Hora, Milešov, and Příčovy Sb-Au ore deposits, Bohemian Massif: mineralogy, fluid inclusions, and stable isotope constraints on the deposit formation

    NASA Astrophysics Data System (ADS)

    Němec, Matěj; Zachariáš, Jiří

    2017-04-01

    The Krásná Hora-Milešov and Příčovy districts (Czech Republic) are the unique examples of Sb-Au subtype orogenic gold deposits in the Bohemian Massif. They are represented by quartz-stibnite veins and massive stibnite lenses grading into low-grade, disseminated ores in altered host rocks. Gold postdates the stibnite and is often replaced by aurostibite. The ore zones are hosted by hydrothermally altered dikes of lamprophyres (Krásná Hora-Milešov) or are associated with local strike-slip faults (Příčovy). Formation of Sb-Au deposits probably occurred shortly after the main gold-bearing event (348-338 Ma; Au-only deposits) in the central part of the Bohemian Massif. Fluid inclusion analyses suggest that stibnite precipitated at 250 to 130 °C and gold at 200 to 130 °C from low-salinity aqueous fluids. The main quartz gangue hosting the ore precipitated from the same type of fluid at about 300 °C. Early quartz-arsenopyrite veins are not associated with the Sb-Au deposition and formed from low-salinity, aqueous-carbonic fluid at higher pressure and temperature ( 250 MPa, 400 °C). The estimated oxygen isotope composition of the ore-bearing fluid (4 ± 1‰ SMOW; based on post-ore calcite) suggests its metamorphic or mixed magmatic-metamorphic origin and excludes the involvement of meteoric water. Rapid cooling of warm hydrothermal fluids reacting with "cold" host rock was probably the most important factor in the formation of both stibnite and gold.

  9. Age and mineralogy of supergene uranium minerals — Tools to unravel geomorphological and palaeohydrological processes in granitic terrains (Bohemian Massif, SE Germany)

    NASA Astrophysics Data System (ADS)

    Dill, H. G.; Gerdes, A.; Weber, B.

    2010-04-01

    Uranyl phosphates (torbernite, autunite, uranocircite, saleeite) and hydrated uranyl silicates (normal and beta-uranophane) found in various erosion levels and structures in the Late Variscan granites at the western edge of the Bohemian Massif, Germany, were the target of mineralogical investigations and age dating, using conventional and more advanced techniques such as Laser-Ablation-Inductive-Coupled-Plasma Mass Spectrometry (LA-ICP-MS). Supergene U minerals have an edge over other rock-forming minerals for such studies, because of their inherent ‘clock’ and their swift response to chemical and physical environmental changes on different scales. Uraniferous phoscretes and silcretes, can be used to characterize the alkalinity/acidity of meteoric/per descensum fluids and to constrain the redox conditions during geomorphic processes. This study aims to decipher the geomorphological and palaeohydrological regime that granitic rocks of the Central European Variscides (Moldanubian and Saxothuringian zones) went through during the Neogene and Quaternary in the foreland of the rising Alpine mobile fold belt. The study provides an amendment to the current sub-division of the regolith by introducing the term “hydraulith”, made up of percolation and infiltration zones, for the supergene alteration zone in granitic terrains. It undercuts the regolith at the brink of the phreatic to vadose hydrological zones. Based upon the present geomorphological and mineralogical studies a four-stage model is proposed for the evolution of the landscape in a granitic terrain which might also be applicable to other regions of the European Variscides, considering the hydrological facies changes along with paleocurrent and paleoslope in the basement and the development of the fluvial drainage system in the foreland. Stage I (U mineralization in the infiltration zone) is a mirror image of the relic granitic landscape with high-altitude divides and alluvial-fluvial terraces. Its

  10. Internal morphology, habit and U-Th-Pb microanalysis of amphibolite-to-granulite facies zircons: geochronology of the Ivrea Zone (Southern Alps)

    NASA Astrophysics Data System (ADS)

    Vavra, Gerhard; Schmid, Rolf; Gebauer, Dieter

    Several types of growth morphologies and alteration mechanisms of zircon crystals in the high-grade metamorphic Ivrea Zone (IZ) are distinguished and attributed to magmatic, metamorphic and fluid-related events. Anatexis of pelitic metasediments in the IZ produced prograde zircon overgrowths on detrital cores in the restites and new crystallization of magmatic zircons in the associated leucosomes. The primary morphology and Th-U chemistry of the zircon overgrowth in the restites show a systematic variation apparently corresponding to the metamorphic grade: prismatic (prism-blocked) low-Th/U types in the upper amphibolite facies, stubby (fir-tree zoned) medium-Th/U types in the transitional facies and isometric (roundly zoned) high-Th/U types in the granulite facies. The primary crystallization ages of prograde zircons in the restites and magmatic zircons in the leucosomes cannot be resolved from each other, indicating that anatexis in large parts of the IZ was a single and short lived event at 299+/-5Ma (95% c. l.). Identical U/Pb ages of magmatic zircons from a metagabbro (293+/-6Ma) and a metaperidotite (300+/-6Ma) from the Mafic Formation confirm the genetic context of magmatic underplating and granulite facies anatexis in the IZ. The U-Pb age of 299+/-5Ma from prograde zircon overgrowths in the metasediments also shows that high-grade metamorphic (anatectic) conditions in the IZ did not start earlier than 20Ma after the Variscan amphibolite facies metamorphism in the adjacent Strona-Ceneri Zone (SCZ). This makes it clear that the SCZ cannot represent the middle to upper crustal continuation of the IZ. Most parts of zircon crystals that have grown during the granulite facies metamorphism became affected by alteration and Pb-loss. Two types of alteration and Pb-loss mechanisms can be distinguished by cathodoluminescence imaging: zoning-controlled alteration (ZCA) and surface-controlled alteration (SCA). The ZCA is attributed to thermal and/or decompression pulses

  11. High-pressure pelitic granulites from the Jiao-Liao-Ji Belt, North China Craton: A complete P-T path and its tectonic implications

    NASA Astrophysics Data System (ADS)

    Zou, Yi; Zhai, Mingguo; Santosh, M.; Zhou, Ligang; Zhao, Lei; Lu, Junsheng; Shan, Houxiang

    2017-02-01

    The Paleoproterozoic khondalite series rocks were widely distributed along the Jiao-Liao-Ji Belt (JLJB), North China Craton (NCC). Metamorphic investigations on these rocks can definitely shed light on the tectonic evolution of the JLJB and provide some clues for Paleoproterozoic history of the NCC. Here we present a comprehensive metamorphic study of high-pressure (HP) pelitic granulites from the Jiaobei terrane in the southern part of the JLJB and combine microstructure, mineral chemistry, Raman spectroscopy, thermobarometry, and P-T-X pseudosections in NCKFMASHTO to trace the metamorphic evolution of these rocks. Staurolite inclusion in kyanite was firstly reported using Raman spectroscopy and four successive mineral assemblages (M1-M4) were identified. Integrated method of thermobarometry and pseudosection modeling constrains P-T conditions of 6-8 kbar at below 660 °C, 15-16.6 kbar at 850-860 °C, 8.8-10.5 kbar at 830-870 °C, 5.8-7.8 kbar at 660-700 °C, for M1-M4, respectively. By employing the melt-reintegrated method, a prograde P-T trajectory is evaluated and hence a complete P-T path is defined that involves a prograde trajectory with marked increase both in pressure and temperature to peak metamorphism, followed by isothermal decompression and subsequent near-isobaric cooling. Such a P-T path implies that a subduction process before collision followed by subsequent extension and cooling processes, was involved in the formation the JLJB, consistent with an orogenic event. Available geochronological data suggests that HP granulites-facies metamorphism probably initiated at 1.90-1.95 Ga and that exhumation and cooling of the metamorphic terrane occurred at 1.80-1.85 Ga, indicating a long-lived hot orogeny during Paleoproterozoic. This contribution provides mineralogical evidence for low-pressure prograde metamorphism in HP pelitic granulites and hence gives a complete P-T path, placing a more rigorous metamorphic constraint on evolution of the JLJB.

  12. Zr-in-rutile resetting in aluminosilicate bearing ultra-high temperature granulites: Refining the record of cooling and hydration in the Napier Complex, Antarctica

    NASA Astrophysics Data System (ADS)

    Mitchell, Ruairidh J.; Harley, Simon L.

    2017-02-01

    The relative validity and closure temperature of the Zr-in-rutile thermometer for recording UHT metamorphism are process dependent and hotly debated. We present an integrated petrological approach to Zr-in-rutile thermometry including phase equilibrium (pseudosection) modelling in complex chemical systems with updated mineral a-X models and systematic in-situ microanalysis of rutile. This study is centred on high-pressure rutile bearing UHT granulites from Mt. Charles, Napier Complex, Antarctica. P-T phase equilibrium modelling of two garnet bearing granulites (samples 49677, 49701) constrains an overall post-peak near isobaric cooling (IBC) evolution for the Napier Complex at Mt. Charles; from 14 kbar, 1100 °C with moderate decompression to 11 kbar, 800-900 °C. Local hydration on cooling over this temperature range is recorded in a kyanite bearing granulite (sample 49688) with an inferred injection of aqueous fluid equivalent to up to 9 mol% H2O from T-MH2O modelling. Further late stage cooling to < 740 °C is recorded by voluminous retrograde mica growth and partial preservation of a ky-pl-kfs-bt-liq bearing equilibrium assemblage. Overall, Zr-in-rutile temperatures at 11 kbar (Tomkins et al., 2007) are reset to between 606 °C and 780 °C across all samples, with flat core-rim Zr concentration profiles in all rutiles. However, zircon precipitates as inclusions, needle exsolutions, or rods along rutile grain boundaries are recrystallised from rutiles in qz/fsp domains. Reintegrating the Zr-in-rutile concentration 'lost' via the recrystallisation of these zircon precipitates (e.g. Pape et al., 2016) can recover maximum concentrations of up to 2.2 wt% and thus maximum peak temperatures of 1149 °C at 11 kbar. Rutile Nb-Ta signatures and rounded rutile grains without zircon precipitates in hydrated mica domains in sample 49688 provide evidence for fluid-mediated mobility of Zr and Nb during retrograde cooling in hydrated lithologies. Aqueous fluid supplemented

  13. Neoproterozoic eclogite- to high-pressure granulite-facies metamorphism in the Mozambique belt of east-central Tanzania: A petrological, geochemical and geochronological approach

    NASA Astrophysics Data System (ADS)

    Sommer, H.; Kröner, A.; Lowry, J.

    2017-07-01

    This study investigated Neoproterozoic (Pan-African) eclogite- and high-pressure-granulite (E-HPG) facies rocks from the Mozambique belt of east-central Tanzania, collected close to the town of Ifakara and the adjacent Furua area from different tectonic settings, the Palaeoproterozoic Usagaran and the Neoproterozoic Mozambique belt. The studied rocks are E-HPG facies granite- and diorite-gneisses and a meta-gabbroic rock, which are retrogressed to amphibolite- and greenschist-facies conditions. Four different clockwise P-T paths were constructed. The first P-T path for a granodioritic gneiss displays peak metamorphic conditions at 830 °C and 13.0 kbar. The second P-T path for a quartz dioritic gneiss shows peak metamorphic conditions of 920 °C and 14.9 kbar. The third P-T path for a mafic granulite shows peak metamorphic conditions of 820 °C and 13.2 kbar. A fourth P-T path for a monzodioritic gneiss also displays peak metamorphic conditions of up to 810 °C and 14.9 kbar. Evidence for all four P-T paths is provided by mineral chemical and modal abundance calculations in combination with textural observations in thin sections. Zircon ages indicate that the east-central part of the Mozambique belt in Tanzania consists of granite-, granodiorite- and monzodiorite gneisses with Mesoarchaean ( 2915 Ma), Neoarchaean ( 2637-2676 Ma) and Palaeoproterozoic ( 1873-1926 Ma) protolith ages. Early Neoproterozoic (Tonian) igneous zircons were found in the mafic granulite with an age of 989 Ma. Late Neoproterozoic (Cyrogenian) igneous zircons were found in a dioritic and monzodiorite gneiss with ages of 748 Ma and 718 Ma, respectively. Metamorphic zircons extracted from Qtz-monzodiorite and granodiorite gneisses yielded ages of 640 Ma and are considered to approximate the peak of regional E-HPG metamorphism. We suggest that this high-grade metamorphic event was caused by the collision of fragments of East and West Gondwana during the Pan-African orogeny, associated with ocean

  14. Ion microprobe analysis of oxygen isotope ratios in granulite facies magnetites: diffusive exchange as a guide to cooling history

    NASA Astrophysics Data System (ADS)

    Valley, John W.; Graham, Colin M.

    1991-03-01

    Ion microprobe analysis of magnetites from the Adirondack Mountains, NY, yields oxygen isotope ratios with spatial resolution of 2 8 μm and precision in the range of 1‰ (1 sigma). These analyses represent 11 orders of magnitude reduction in sample size compared to conventional analyses on this material and they are the first report of routinely reproducible precision in the 1 per mil range for analysis of δ18O at this scale. High precision micro-analyses of this sort will permit wide-ranging new applications in stable isotope geochemistry. The analyzed magnetites form nearly spherical grains in a calcite matrix with diopside and monticellite. Textures are characteristic of granulite facies marbles and show no evidence for retrograde recrystallization of magnetite. Magnetites are near to Fe3O4 in composition, and optically and chemically homogeneous. A combination of ion probe plus conventional BrF5 analysis shows that individual grains are homogeneous with δ18O=8.9±1‰ SMOW from the core to near the rim of 0.1 1.2 mm diameter grains. Depth profiling into crystal growth faces of magnetites shows that rims are 9‰ depleted in δ18O. These low δ18O values increase in smooth gradients across the outer 10 μm of magnetite rims in contact with calcite. These are the sharpest intracrystalline gradients measured to date in geological materials. This discovery is confirmed by bulk analysis of 150 350 μm diameter magnetites which average 1.2‰ lower in δ18O than coarse magnetites due to low δ18O rims. Conventional analysis of coexisting calcite yields °18O=18.19, suggesting that bulk Δ18O (Cc-Mt)=9.3‰ and yielding an apparent equilibration “temperature” of 525° C, over 200° C below the temperature of regional metamorphism. Consideration of experimental diffusion data and grain size distribution for magnetite and calcite suggests two contrasting cooling histories. The data for oxygen in calcite under hydrothermal conditions at high P(H2O) indicates that

  15. Magnetic fabric as a strain marker in polydeformed granulites? An example from the Mt. Hay block, central Australia

    NASA Astrophysics Data System (ADS)

    Waters-Tormey, C. L.; Kelso, P. R.; White, R. J.; Wepasnick, K.

    2009-12-01

    The >5-km thick Capricorn ridge shear zone (Mt. Hay block, Arunta region, central Australia) is a steeply dipping, normal sense shear zone with a steeply inclined lineation. It is an excellent place to study magnetic fabric development in high grade terranes because its map- and mesoscale structures are well understood (Waters-Tormey and Tikoff, 2007), contains rock types thought to be common in the deep crust worldwide, and has been penetratively deformed at granulite facies conditions. Mesoscale structures and fabric gradients record a combination of shear and flattening (D3) which has completely transposed the earlier D1 and D2 structures. Multiple tectonothermal events often recorded in high grade terranes, as in the Capricorn ridge shear zone, complicate the interpretation of their fabrics as strain markers. Magnetic fabric analysis is a potentially useful tool in high grade terranes where there are few strain markers but, as expected, detailed analysis is required to interpret the magnetic fabric. Shape-preferred measurements (SPO) in two rock types (quartzofeldspathic and gabbroic) across a strain gradient demonstrate that no one fabric element records the “bulk” deformation, although patterns across the gradient are consistent with the transposition of a heterogeneous older fabric by a flattening deformation. Both bulk and magnetic anisotropy characteristics vary significantly at many sampling sites (typically <10m2), even at the 10 cm-scale. For example, one site may contain strongly prolate and oblate fabric types, yet have similar fabric intensities and magnetic fabric axis orientations. The “simplest” subset of rock types is a gabbroic gneiss in which the dominant magnetic carrier is pseudo-single to multi-domain magnetite. Evidence of exsolution, single domain grains, or reactions that would complicate magnetic carrier fabric are not observed. Statistically significant patterns in the anisotropy of anhysteretic remanent magnetization (AARM) and

  16. Graphite-bearing CO 2-fluid inclusions in granulites: Insights on graphite precipitation and carbon isotope evolution

    NASA Astrophysics Data System (ADS)

    Satish-Kumar, Madhusoodhan

    2005-08-01

    Graphite in deep crustal enderbitic (orthopyroxene + garnet + plagioclase + quartz) granulites (740°C, 8.9 kb) of Nilgiri hills, southern India were investigated for their spectroscopic and isotopic characteristics. Four types of graphite crystals were identified. The first type (Gr I), which is interstitial to other mineral grains, can be grouped into two subtypes, Gr IA and Gr IB. Gr IA is either irregular in shape or deformed, and rough textured with average δ 13C values of -12.7 ± 0.4‰ ( n = 3). A later generation of interstitial graphite (Gr IB) shows polygonal crystal shapes and highly reflecting smooth surface features. These graphite grains are more common and have δ 13C values of -11.9 ± 0.3‰ ( n = 14). Both subtypes show well-defined Raman shifts suggesting a highly crystalline nature. Cores of interstitial graphite grains have, on average, lower δ 13C values by ˜0.5‰ compared to that of the rim. The second type of graphite (Gr II) occurs as solid inclusions in silicate minerals, commonly forming regular hexagonal crystals with a slightly disordered structure. The third type of graphite (Gr III) is associated with solid inclusions (up to 100 μm) that have decrepitation halos of numerous small (<15 μm) satellite fluid inclusions of pure CO 2 with varying density (1.105 to 0.75 g/cm 3). The fourth type of graphite (Gr IV) is found as daughter crystals within primary type CO 2-fluid inclusions in garnet and quartz. These fluid inclusions have a range of densities (1.05 to 0.90 g/cm 3), but in general are significantly less dense than graphite-free primary, pure CO 2 fluid inclusions (1.12 g/cm 3). Raman spectral characteristics of graphite inside fluid inclusions suggest graphite crystallization at low temperature (˜ 500°C). The precipitation of graphite probably occurred during the isobaric cooling of CO 2-rich peak metamorphic fluid as a result of oxyexsolution of oxide phases. The oxyexsolution process is evidenced by the magnetite

  17. Rb depletion in biotites and whole rocks across an amphibolite to granulite facies transition zone, Tamil Nadu, South India

    NASA Astrophysics Data System (ADS)

    Hansen, Edward; Ahmed, Khurram; Harlov, Daniel E.

    2002-09-01

    Relatively low concentrations of Rb and high K/Rb ratios are characteristic of many granulite facies terranes. This depletion in Rb has been attributed to both the removal of a partial melt and exchange with a metamorphic fluid phase. These models have been tested using Rb concentrations in biotites and whole rocks from intermediate and felsic gneisses collected along a traverse from just north of Krishnagiri to just north of Salem in Tamil Nadu State, South India. Along this traverse, the northern amphibolite-facies zone gives way to a clinopyroxene zone in which clinopyroxene appears in intermediate and felsic gneisses. Further south is the lowland charnockite zone characterised by the presence of orthopyroxene and the scarcity of clinopyroxene in intermediate to felsic gneisses. The abundance of orthopyroxene increases southwards and it is the dominant ferromagnesium silicate in the highland charnockite zone. There is a good correlation between Rb in biotite and whole-rock Rb in samples collected throughout the traverse. Intermediate and felsic gneisses in the northern portion of this traverse have relatively high modal abundances of biotite, low Ti concentrations in the biotites, high whole-rock Rb concentrations, low K/Rb ratios and high Rb concentrations within the biotites. Ti concentrations in the biotites increase southward into the clinopyroxene zone and then remain relatively constant. High K/Rb ratios first appear at the southern boundary of the clinopyroxene zone. In the lowland and highland charnockite zones, the majority of the rocks have relatively low Rb concentrations and high K/Rb ratios. Low Rb concentrations in biotites (at or near the detection limit of 65 ppm) first appear in the lowland charnockite zone and persist into the highland charnockite zone. A smaller group of rocks in the highland charnockite zone contain biotites with moderate Rb concentrations. Most of these rocks also contain anomalously high biotite concentrations and low K

  18. Magmatic Activity and Crustal Melting During Orogenesis: Laser-ablation U-Pb Geochronology of Dike and Leucosome Generations in Granulites of the Gruf Complex, Central Alps

    NASA Astrophysics Data System (ADS)

    Savage, J. A.; Oalmann, J.; Bousquet, R.; Moeller, A.

    2012-12-01

    Magmatic leucosomes and dikes in metamorphic terranes provide an opportunity to correlate accessory phase crystallization ages with the timing of deformation and metamorphic events, as well as larger scale magmatic intrusions. The Gruf Complex consists of upper amphibolite to lower granulite facies migmatitic gneisses and scarce, UHT sapphirine granulites and is bordered by the c. 31 Ma tonalite-granodiorite Bergell Intrusion and the c. 24 Ma Novate S-type leucogranite. Several mineralogically distinct types of leucosomes and dikes have been identified: 1) biotite-bearing leucosomes, which define the main foliation and are commonly folded; 2) hornblende- and biotite-bearing dikes, which are either boudinaged or crosscut the main foliation; 3) pegmatitic muscovite-, garnet-, beryll-bearing dikes, which commonly crosscut all other rock types. These field observations indicate a change in melt composition during and after the regional metamorphic event and its associated deformation. To correlate these melt types with the timing of metamorphism of the Gruf Complex, and the Bergell and Novate intrusions, U-Pb zircon ages were obtained from several dike and leucosome samples. Grains were separated, mounted in epoxy, and imaged by cathodoluminescence prior to U-Pb isotope analysis by LA-ICP-MS. The outermost zircon growth zones were targeted in order to determine the crystallization age of the host magma. All of the analyzed samples contain oscillatory-zoned domains with ages between 250 Ma and 300 Ma. A leucosome sample from within a brecciated metaperidotite enclave in the granulites contains equant, sector-zoned "soccer ball" zircon grains with an age of 32.4±1.0 Ma. Most dike samples contain unzoned or sector-zoned rims or mantles that range from 30-33 Ma. Most of the pegmatitic samples, regardless of their degree of deformation, contain zircon crystals with weakly zoned rims ranging from 24-27 Ma. However, some undeformed pegmatitic samples lack zircon domains

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

    NASA Astrophysics Data System (ADS)

    Brown, M.

    2006-12-01

    Essene's contributions began pre-plate tectonics more than 40 years ago; they range from mineralogy to tectonics, from experiments and thermobarometry to elements and isotopes, and from the Phanerozoic to the Precambrian. Eric is a true polymath! Assessing the P-T conditions and age distribution of crustal metamorphism is an important step in evaluating secular change in tectonic regimes and geodynamics. In general, Archean rocks exhibit moderate-P - moderate-to-high-T facies series metamorphism (greenstone belts and granulite terranes); neither blueschists nor any record of deep continental subduction and return are documented and only one example of granulite facies ultrahigh-temperature metamorphism is reported. Granulite facies ultrahigh temperature metamorphism (G-UHTM) is documented in the rock record predominantly from Neoarchean to Cambrian, although G-UHTM facies series rocks may be inferred at depth in younger orogenic systems. The first occurrence of G-UHTM in the rock record signifies a change in geodynamics that generated transient sites of very high heat flow. Many G-UHTM belts may have developed in settings analogous to modern continental backarcs. On a warmer Earth, the formation and breakup of supercontinents, particularly by extroversion, which involved destruction of ocean basins floored by thinner lithosphere, may have generated hotter continental backarcs than those around the modern Pacific rim. Medium-temperature eclogite - high-pressure granulite metamorphism (E-HPGM) also is first recognized in the Neoarchean rock record, and occurs at intervals throughout the Proterozoic and Paleozoic rock record. E- HPGM belts are complementary to G-UHTM belts, and are generally inferred to record subduction-to-collision orogenesis. Blueschists become evident in the Neoproterozoic rock record; lawsonite blueschists and eclogites (high-pressure metamorphism, HPM), and ultrahigh pressure metamorphism (UHPM) characterized by coesite or diamond are

  20. Feldspathic granulite 79215 - Limitations on T-fo2 conditions and time of metamorphism. [temperature-oxygen fugacity relationship in annealed lunar polymict beccia

    NASA Technical Reports Server (NTRS)

    Mcgee, J. J.; Bence, A. E.; Eichhorn, G.; Schaeffer, O. A.

    1978-01-01

    Feldspathic granulite 79215, an annealed polymict breccia which has a bulk composition between anorthositic gabbro and gabbroic anorthosite, contains numerous oxide complexes in the matrix. An Ar-39-Ar-40 stepwise heating experiment gives a well-defined plateau corresponding to an age of 4.03 + or - 0.02 AE. The polmict character of this breccia and the variability of the complexes suggest that they formed as a consequence of reactions between spinel-rich clasts and matrix under the high-T low-P conditions of an ejecta blanket. The duration of annealing is estimated to have been less than 10 million yr; the absence of a KREEP component may indicate an inhomogeneous distribution of this component at the lunar surface at 4.0 AE.

  1. Tectono-metamorphic evolution of a hot orogen during Gondwanaland assembly: a case study from Palni hills metapelite granulite, south India

    NASA Astrophysics Data System (ADS)

    Bhadra, S.; Nasipuri, P.

    2012-04-01

    This study deals with the tectono-metamorphic evolution of Sapphirine-cordierite-bearing metapelite granulite at Perumalmalai, south India, that occurs as enclave within deformed migmatitic enderbite gneiss of Kodaikanal massif, Madurai granulite block (MB), south India. Pre-peak mineral paragenesis is represented by an inclusion assemblage of sillimanite + plagioclase + Ti-rich biotite ±quartz in Al-rich orthopyroxene. Dehydration melting of biotite marked the onset of ultra-high temperature metamorphism (M1A, ~1000 °C, 10 Kbar). Early stage of retrograde metamorphism (M1B) is characterized by the development of type1-symplectite and corona textures. In type1-symplectite an innermost vermicular sapphirine (Spr - XMg: 0.90, Al/Si: 6.17) - cordierite (Crd) symplectite on sillimanite is followed by cordierite (XMg: 0.94) moat. A meso-perthitic layer laced the interface between cordierite moat and orthopyroxene porphyroblast, the latter showing prominent rim-ward decrease in Al2O3 (up to 3 wt%). The cordierite rim at the interface between sillimanite and orthopyroxene characterizes corona texture. Type1-symplectite and corona domains are circumnavigated by Ti-poor biotite (TiO2: ~3.2 wt%) showing shape preferred alignment, and set in a feldspar matrix showing wide compositional range. By implication, leucosome crystallization was possibly prolonged and enhanced by deformation. Type1-symplectite and corona textures were resulted from melt-solid interaction or silica-metasomatism during early stage of retrogression, Opx+Sil = Spr+Crd → Opx+Sil+melt = Crd. The retrograde metamorphism is constrained at 9 kbar and 950°C, implying an early stage of near-isothermal decompression. Late stage retrograde metamorphism (M2) is also characterized by symplectite textures, type2-symplectite, with innermost sapphirine-cordierite symplectite followed by cordierite corona. Sapphirine in type2-symplectite domain (XMg: 0.89; Al/Si: 5.92), which occurs as inclusion in Opx, is

  2. Feldspathic granulite 79215 - Limitations on T-fo2 conditions and time of metamorphism. [temperature-oxygen fugacity relationship in annealed lunar polymict beccia

    NASA Technical Reports Server (NTRS)

    Mcgee, J. J.; Bence, A. E.; Eichhorn, G.; Schaeffer, O. A.

    1978-01-01

    Feldspathic granulite 79215, an annealed polymict breccia which has a bulk composition between anorthositic gabbro and gabbroic anorthosite, contains numerous oxide complexes in the matrix. An Ar-39-Ar-40 stepwise heating experiment gives a well-defined plateau corresponding to an age of 4.03 + or - 0.02 AE. The polmict character of this breccia and the variability of the complexes suggest that they formed as a consequence of reactions between spinel-rich clasts and matrix under the high-T low-P conditions of an ejecta blanket. The duration of annealing is estimated to have been less than 10 million yr; the absence of a KREEP component may indicate an inhomogeneous distribution of this component at the lunar surface at 4.0 AE.

  3. Interpretation of zircon coronae textures from metapelitic granulites of the Ivrea-Verbano Zone, northern Italy: two-stage decomposition of Fe-Ti oxides

    NASA Astrophysics Data System (ADS)

    Kovaleva, Elizaveta; Austrheim, Håkon O.; Klötzli, Urs S.

    2017-07-01

    In this study, we report the occurrence of zircon coronae textures in metapelitic granulites of the Ivrea-Verbano Zone. Unusual zircon textures are spatially associated with Fe-Ti oxides and occur as (1) vermicular-shaped aggregates 50-200 µm long and 5-20 µm thick and as (2) zircon coronae and fine-grained chains, hundreds of micrometers long and ≤ 1 µm thick, spatially associated with the larger zircon grains. Formation of such textures is a result of zircon precipitation during cooling after peak metamorphic conditions, which involved: (1) decomposition of Zr-rich ilmenite to Zr-bearing rutile, and formation of the vermicular-shaped zircon during retrograde metamorphism and hydration; and (2) recrystallization of Zr-bearing rutile to Zr-depleted rutile intergrown with quartz, and precipitation of the submicron-thick zircon coronae during further exhumation and cooling. We also observed hat-shaped grains that are composed of preexisting zircon overgrown by zircon coronae during stage (2). Formation of vermicular zircon (1) preceded ductile and brittle deformation of the host rock, as vermicular zircon is found both plastically and cataclastically deformed. Formation of thin zircon coronae (2) was coeval with, or immediately after, brittle deformation as coronae are found to fill fractures in the host rock. The latter is evidence of local, fluid-aided mobility of Zr. This study demonstrates that metamorphic zircon can nucleate and grow as a result of hydration reactions and mineral breakdown during cooling after granulite-facies metamorphism. Zircon coronae textures indicate metamorphic reactions in the host rock and establish the direction of the reaction front.

  4. The Cora Lake Shear Zone: Strain Localization in an Ultramylonitic, Deep Crustal Shear Zone, Athabasca Granulite Terrain, Western Churchill Province, Canada

    NASA Astrophysics Data System (ADS)

    Regan, S.; Williams, M. L.; Mahan, K. H.; Orlandini, O. F.; Jercinovic, M. J.; Leslie, S. R.; Holland, M.

    2012-12-01

    Ultramylonitic shear zones typically involve intense strain localization, and when developed over large regions can introduce considerable heterogeneity into the crust. The Cora Lake shear zone (CLsz) displays several 10's to 100's of meters-wide zones of ultramylonite distributed throughout its full 3-5 km mylonitized width. Detailed mapping, petrography, thermobarometry, and in-situ monazite geochronology suggest that it formed during the waning phases of granulite grade metamorphism and deformation, within one of North America's largest exposures of polydeformed lower continental crust. Anastomosing zones of ultramylonite contain recrystallized grain-sizes approaching the micron scale and might appear to suggest lower temperature mylonitization. However, feldspar and even clinopyroxene are dynamically recrystallized, and quantitative thermobarometry of syn-deformational assemblages indicate high P and T conditions ranging from 0.9 -10.6 GPa and 775-850 °C. Even at these high T's, dynamic recovery and recrystallization were extremely limited. Rocks with low modal quartz have extremely small equilibrium volumes. This is likely the result of inefficient diffusion, which is further supported by the unannealed nature of the crystals. Local carbonate veins suggests that H2O poor, CO2 rich conditions may have aided in the preservation of fine grain sizes, and may have inhibited dynamic recovery and recrystallization. The Cora Lake shear zone is interpreted to have been relatively strong and to have hardened during progressive deformation. Garnet is commonly fractured perpendicular to host rock fabric, and statically replaced by both biotite and muscovite. Pseudotachylite, with the same sense of shear, occurs in several ultramylonitized mafic granulites. Thus, cataclasis and frictional melt are interpreted to have been produced in the lower continental crust, not during later reactivation. We suggest that strengthening of rheologically stiffer lithologies led to

  5. Measured and calculated elastic wave speeds in partially equilibrated mafic granulite xenoliths: Implications for the properties of an underplated lower continental crust

    NASA Astrophysics Data System (ADS)

    Rudnick, Roberta L.; Jackson, Ian

    1995-06-01

    Ultrasonic compressional wave velocities measured at 1.0 GPa and room temperature are compared with calculated velocities (based on single-crystal data and modal mineralogy) for a suite of mafic granulite xenoliths from the Chudleigh volcanic province, north Queensland, Australia. The xenoliths have nearly constant major element compositions but widely variable modal mineralogy, reflecting recrystallization under variable pressure-temperature conditions at depth in the continental crust (20-45 km). They thus provide an excellent opportunity to investigate velocity variation with depth in a mafic lower crust. Measured P wave velocities, corrected for the decompression-induced breakdown of garnet, range from 6.9 to 7.6 km/sec and correlate with derivation depth. These velocities are 5-12% lower than the calculated velocities (7.5-8.0 km/sec), apparently as a result of grain boundary alteration as well as irreversible changes that occurred in the xenoliths during rapid decompression. Calculated P wave velocities are similar to those estimated by Furlong and Fountain (1986) and Sobolev and Babeyko (1989) for mafic granulites formed through basaltic underplating of the continental crust. Depending upon in situ temperature, P wave velocities in the deepest samples may be interpreted as crustal (e.g., 7.3-7.6 km/sec, if heat flow is high) or mantle (7.7-7.8 km/sec, in areas of low heat flow). The range of velocities in the xenolith suite is larger than predicted for a fully equilibrated underplated basaltic layer, highlighting the importance of kinetic effects in determining the ultimate velocity profile of magmatically underplated crust. Comparison of our results with seismic profiles illustrates that the lower crust rarely reaches such high velocities, suggesting quartz-bearing rocks (country rocks?) are present within magmatically underplated layers of the deep crust.

  6. Geotherms and heat flow estimates in the Odra Fault Zone (NE margin of Bohemian Massif, Central Europe) and its relationships to geological structure of NE termination of the European Variscan Orogen

    NASA Astrophysics Data System (ADS)

    Puziewicz, Jacek; Czechowski, Leszek; Majorowicz, Jacek; Pietranik, Anna; Grad, Marek

    2017-04-01

    The NE margin of Variscan Orogen in Europe comprises Sudety Mts., Fore-Sudetic Block, Odra Fault Zone and Fore-Sudetic Homocline. The Sudety Mts. together with the located to the NE Fore-Sudetic Block form NE part of the Bohemian Massif. The Variscan crystalline basement is exposed at the surface here. The Odra Fault Zone is situated further to the NE. It is a ca. 20 km wide horst of crystalline basement, hidden beneath relatively thin (< 1000 m) Permian-Mesozoic and Cenozoic sedimentary sequences and is called the Odra Horst in the following. This horst marks the margin of stretching to NE Fore-Sudetic Homocline, in which the crystalline basement is dipping to NE under thickening Permo-Mesozoic strata, covered by few hundred meter thick Cenozoic sedimentary layer (Żelaźniewicz et al. 2016 and references therein). The Odra Horst is possibly a continuation of the Mid German Crystalline High at the NE side of the Bohemian Massif (Dörr et al. 2006). The copper mines located at the central part of the Odra Horst at depth 600 - 1000 m enable the numerous high-quality temperature measurements. However, complicated geometry of geological units requires 3D simulations. We use 3D numerical thermal model for the considered region. The heat flow in the region is 80 mW/m2 (corrected for paleclimate). This value is higher than in the neighbouring parts of Sudetes and Fore-Sudetic Block ( 70 mW/m2) and compares rather to positive heat flow anomaly stretching NW-SE in Wielkopolska region north of the Dolsk Fault and continuing to NE Germany. This anomaly corresponds crudely to the extent of the Permian volcanic province of Polish and North-East German Basin. Unfortunately, preliminary results of the model are not conclusive, because they depend on many parameters, (compare e.g. Puziewicz et al 2012). It remains an open question if this anomaly could be related to the lithospheric mantle thermal anomalies (Tesauro et al. 2009) or is rather due to crustal rock contributions

  7. Body lice

    MedlinePlus

    ... Body lice are tiny insects (scientific name is Pediculus humanus corporis ) that are spread through close contact ... disease Images Body louse Lice, body with stool (Pediculus humanus) Body louse, female and larvae Head louse ...

  8. Petrology and geochemistry of charnockites (felsic ortho-granulites) from the Kerala Khondalite Belt, Southern India: Evidence for intra-crustal melting, magmatic differentiation and episodic crustal growth

    NASA Astrophysics Data System (ADS)

    Ravindra Kumar, G. R.; Sreejith, C.

    2016-10-01

    The Kerala Khondalite Belt (KKB) of the southern India encompasses volumetrically significant magmatic components. Among these, orthopyroxene-bearing, felsic ortho-granulites, popularly known as charnockites in Indian context, constitute an important lithology. In contrast to the well-known phenomena of arrested charnockitization, the geochemical characteristics and petrogenesis of these ortho-granulite suites remain poorly studied, leaving geodynamic models envisaged for the KKB highly conjectural. In this paper, we try to bridge this gap with detailed results on orthopyroxene-bearing, felsic ortho-granulites spread over the entire KKB and propose a new petrogenetic and crustal evolution model. Based on geochemical characteristics, the orthopyroxene-bearing, felsic ortho-granulites (charnockites sensu lato) of KKB are classified into (1) tonalitic (TC), (2) granitic (GC), and (3) augen (AC) suites. Members of the TC follow sodic (characterized by decreasing CaO/Na2O), whereas those of the GC and AC follow calc-alkaline trends of differentiation. Geochemical patterns of the TC resemble those of the Archaean tonalite-trondhjemite-granodiorite (TTG) suites, with slightly magnesian character (average Mg# = 33), moderate LREE (average LaN = 154), low HREE (average YbN = 6) and Y (1-53 ppm; average 11 ppm). The TC is also characterized by positive to slightly negative europium anomalies (Eu/Eu* = 0.7 to 1.67). The GC and AC suites, on the other hand, resemble post-Archaean arc-related granites. The GC displays ferroan nature (average Mg# = 22), low to moderate degrees of REE fractionation (average [La/Yb]N = 34.84), high contents of Y (5-128 ppm; average 68), and low Sr/Y (1-98) ratios. Significant negative Eu anomalies (Eu/Eu* = 0.18-0.91; average 0.50) and low Sr (65-690 ppm) are also noted in the GC. Similar chemical characteristics are shown by the AC, with ferroan nature (average Mg# = 21), low to moderate degrees of REE fractionation (average [La/Yb]N = 26), high

  9. Zircon U-Pb and trace element zoning characteristics in an anatectic granulite domain: Insights from LASS-ICP-MS depth profiling

    NASA Astrophysics Data System (ADS)

    Marsh, Jeffrey H.; Stockli, Daniel F.

    2015-12-01

    Understanding the geochemical characteristics of metamorphic zircon, and how they may be modified by recrystallization processes, is fundamental to defining the timescales of tectonic processes affecting continental lithosphere. We utilize laser ablation split-stream (LASS)-ICP-MS depth-profiling analysis to obtain a continuous rim-to-core record of the U-Pb ages and trace-element composition preserved within variably recrystallized zircon from different rock types within a well-studied granulite domain in the western Grenville Province, Canada. Detailed analysis of the depth-resolved signal enables definition of chemically distinct (homogeneous) internal domains and heterogeneous intervening zones that can generally be correlated with textural features observed in CL. Three age populations have been distinguished within the ~ 35 μm deep profiles that correlate well with the established timing of protolith formation, granulite-facies metamorphism, and amphibolite-facies shearing, respectively. The U-Pb isotopic system and Th/U ratios in much of the crystal interiors have undergone considerable modification, as evidenced by a linear correlation between 207Pb/206Pb age and Th/U ratio. Interior and rim domains commonly contain blurred or faded oscillatory zoning patterns, suggesting that solid-state recrystallization is at least partially responsible for the modified U-Th-Pb composition. A number of systematic trends in trace element composition are also observed between interior domains and recrystallized rims, including 1) decreased Th/U (to ~ 0.1), 2) tighter clustering of Hf concentrations, 3) decreased total REE, 4) unchanged Eu anomalies, and 5) a widened spread of HREE enrichment values (YbN/GdN). Both YbN/GdN vs. Th/U and U/Ce vs. Th plots show increasing degree of compositional differentiation from protolith zircon as a function of metamorphic reworking processes (i.e. sample type). The transition zones between interior and rim domains exhibit textural

  10. Zircon and monazite geochronology of the granulites and associated gneisses from the Rengali Province, India: Growth of the southern margin of the Singhbhum Craton

    NASA Astrophysics Data System (ADS)

    Bose, S.; Das, K.; Kimura, K.; Hayasaka, Y.; Hidaka, H.; Dasgupta, A.; Ghosh, G.; Mukhopadhyay, J.

    2013-12-01

    Geological evidences show that cratons grew in size by multiple orogenic cycles which can best be studied in their marginal orogenic belts. Rengali Province, occurring at the southern margin of the Singhbhum Craton, India is one such belt, characterized by low- to high-grade metamorphic signatures. This is sharply different from the virtually unmetamorphosed cratonic rocks in north and ultrahigh temperature metamorphosed rocks of the Eastern Ghats Province in south. High-grade gneisses and granitoids (including charnockite) constitute the central highland of this province. Several large-scale faults and shear zones juxtapose rocks of contrasting metamorphic grades. Our geochronological investigation from samples of high-grade orthogneiss and paragneiss along with the intrusive granitoids from central and eastern part of the Rengali Province using zircon (SHRIMP) and monazite chemical techniques reveal a complex evolutionary history. Zircon grains of the metapelitic granulites from the eastern segment yield detrital ages in the time span of ca. 3528-3087 Ma, without perceptible evidence of subsequent metamorphism. In contrast, monazite grains from the same samples record strong metamorphic signature at ca. 2.8-2.7 Ga along with inherited populations of ca. 3.0-2.9 Ga. Charnockite from the eastern segment has protolith age of 3058×15 Ma while that from the central segment records high-grade metamorphism at 2818×15 Ma. Mafic granulite from the central segment preserves the oldest core age of 2844×7 Ma. Synkinematic leucogranite in the central and undeformed granitoid in the eastern segment were emplaced at 2807×13 Ma and 2809×13 Ma respectively. Most of the samples show zircon overgrowth at ca. 2500 Ma, which possibly caused by a separate tectonothermal overprinting. From the available geochronological data, we postulate the existence of marine basin which opened at ca. 3050 Ma, received sediments from the adjacent cratonic hinterland, switched to an active

  11. Thermochronology of mid-Cretaceous dioritic granulites adjacent "Big Bend" in Australia-Pacific plate boundary, northern South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Sagar, M.; Seward, D.; Heizler, M. T.; Palin, J. M.; Toy, V. G.; Tulloch, A. J.

    2012-12-01

    The Western Fiordland Orthogneiss (WFO), situated south-east of the Australian-Pacific plate boundary (Alpine Fault), southern South Island, New Zealand is the largest suite of plutonic rocks intruded into the Pacific margin of Gondwana during the final stages of arc plutonism preceding break-up of the supercontinent in the Late Cretaceous. Dextral motion of c. 480 km along the Alpine Fault during the Cenozoic has offset originally contiguous Pacific Gondwana margin rocks in northern and southern South Island. The Glenroy Complex in northern South Island, west of the Alpine Fault is dominated by two-pyroxene+hornblende granulite facies monzodioritic gneisses. U-Pb zircon geochronological and geochemical data indicate the Glenroy Complex was emplaced between 128-122 Ma and is a correlative of the WFO. The Glenroy Complex forms the lower-most block bounded by an east-dipping set of imbricate thrusts that developed during the late Cenozoic to the west of the largest S-shaped restraining bend ("Big Bend") in the Alpine Fault. New 40Ar/39Ar and fission-track thermochronological data, combined with previous geological field-mapping, demonstrate that the Glenroy Complex cooled rapidly (c. 30° C/Ma) after emplacement and granulite facies metamorphism (c. 850°C) at c. 120 Ma, through c. 550 °C by c. 110-100 Ma. The average cooling rate during the Late Cretaceous-Cenozoic was relatively slow, and initial exposure in the late Early Miocene (c. 16 Ma) was followed by reburial to c. 3-4 km (c. 80-100 °C) before final exhumation post-Pliocene. This thermal history is similar to the WFO, which cooled rapidly through c. 350 °C during mid-Cretaceous continental extension, followed by slow cooling during the Late Cretaceous and Cenozoic until development of the Australian-Pacific boundary through New Zealand facilitated rapid, exhumation-related cooling from c. 240 °C at c. 20 Ma and final exhumation post-10 Ma (Davids, 1999). However, the Glenroy Complex cooled at a faster

  12. U-Pb and Sm-Nd systematics of monazite in high-pressure felsic granulites: an example from the Snowbird tectonic zone, northern Saskatchewan, Canada

    NASA Astrophysics Data System (ADS)

    Baldwin, J. A.; Bowring, S. A.; Williams, M. L.; Mahan, K. H.

    2004-05-01

    U-Pb and Sm-Nd systematics of monazite (Mnz) from felsic granulites of the Snowbird tectonic zone, northern Saskatchewan, have been investigated through an integrated electron microprobe (EMP) and ID-TIMS study. The granulites contain the assemblage Grt+Ky+ternary Fsp and were metamorphosed at conditions of 1.5-2.0 GPa and 900-1000° C. The Mnz occurs in a variety of textural settings, including both well-armored and un-armored inclusions in Grt, as well as matrix grains that are interstitial to Ky and/or alkali Fsp. EMP and ID-TIMS studies reveal a polyphase Mnz growth history. Well-armored Mnz inclusions in Grt yield the oldest U-Pb dates at 2.62 Ga. In contrast, matrix grains and un-armored inclusions in Grt rims show more complicated U-Pb systematics with age domains from 2.6 Ga to 1.9 Ga. This is interpreted to largely reflect the reactivity of Mnz with fluids and/or melt in the lower crust. Numerous small (5-10 μ m) grains yield Paleoproterozoic EMP dates (ca. 1.9 Ga), whereas only one matrix Mnz yielded a TIMS date of 1.90 Ga, reflecting the bias of grain separates to larger, and in this case, older populations. Sm-Nd isotope systematics of Mnz grains included in Grt are similar to the whole rock with a limited range of slightly negative ɛ Nd(i). In contrast, grains that show more complex histories have more positive ɛ Nd(i), indicating Nd derivation from a source containing Grt. Further, inclusions in Grt show higher Y, Th, U, Nd, and other REEs compared to the matrix grains. We suggest that the Archean Mnz grew in the absence of Grt; Proterozoic Mnz grew after significant Grt growth and whole-rock melting. These results have important implications for the U-Pb systematics of Mnz under high-T conditions, and show empirically that at temperatures of 1000° C there has not been any significant diffusional Pb loss consistent with the experimental data of Cherniak et al. 2004. Moreover, the two episodes of Mnz growth record the evolving composition and

  13. Geochemical and geochronological study of the non-granitic pegmatite body "La Panchita", Oaxaca state, Southern Mexico

    NASA Astrophysics Data System (ADS)

    Shchepetilnikova, Valentina; Solé, Jesús; Solari, Luigi; Abdullin, Fanis

    2014-05-01

    The La Panchita pegmatite body intrudes a >10 m thick pyroxenite dike that in turn is cutting the central portion of ~1Ga Oaxacan Complex rocks, Southern Mexico. The Oaxacan Complex is the largest exposure in Mexico of Neoproterozoic basement rocks metamorphosed up to the granulite facies during the Grenville orogeny. This Complex has multiple intrusions of pegmatite bodies along its extension, some mineralogically simple, some complex. As for the mineralogy, the La Panchita pegmatite is distinct from other pegmatites of the Oaxacan Complex. It contains unusual minerals for a pegmatite, like scapolite and calcite, and it is a non-granitic pegmatite, as suggested before. This work presents preliminary geochemical and geochronological results of this pegmatite body and a discussion about its possible origin. The geochronological study shows that the time of emplacement of this pegmatite is 981.4 ± 7.4 Ma and it is post-tectonic with respect to the granulite facies metamorphic event of the Oaxacan Complex. The geochemical study shows that the pegmatite La Panchita formed during the evolution of an anorogenic magmatic source of carbonatitic-alkaline composition related to a post-Grenvillian rifting event. Medium to low-temperature thermochronometers (K-Ar, fission track and U-Th-He) from this pegmatite are under progress and the results will be given at the meeting.

  14. Late Paleozoic tectono-metamorphic evolution of the Altai segment of the Central Asian Orogenic Belt: Constraints from metamorphic P-T pseudosection and zircon U-Pb dating of ultra-high-temperature granulite

    NASA Astrophysics Data System (ADS)

    Li, Zilong; Yang, Xiaoqiang; Li, Yinqi; Santosh, M.; Chen, Hanlin; Xiao, Wenjiao

    2014-09-01

    Ultra-high-temperature (UHT) granulite-facies rocks offer important constraints on crustal evolution processes and tectonic history of orogens. UHT granulites are generally rare in Phanerozoic orogens. In this study, we investigate the late Paleozoic pelitic UHT granulites from Altai in the western segment of the Central Asian Orogenic Belt (CAOB). The diagnostic minerals in these rocks include high alumina orthopyroxene (Al2O3 up to 9.76 wt.%, and y(opx) = AlVI in orthopyroxene up to 0.21) coexisting with sillimanite and quartz, and low Zn spinel (ZnO = 1.85-2.50 wt.%) overgrowth with quartz. Cordierite corona separates sillimanite from orthopyroxene. The high alumina orthopyroxene is replaced by symplectites of low-alumina orthopyroxene (~ 5.80 wt.% Al2O3) and cordierite. These textural observations are consistent with a significant decompression following the peak UHT metamorphism. Phase equilibrium modeling using pseudosections and the y(opx) isopleths indicate an anti-clockwise P-T path for the exhumation of the Altai orogenic belt. The pre-peak assemblage of spinel + quartz in garnet is stable at high- to ultra-high-temperature and low-pressure conditions (P < 5.8 kbar at T ~ 900 °C). The peak P-T values recorded by high aluminium orthopyroxene is > 940 °C and 7.8 to 10 kbar. Subsequent near-isothermal decompression occurred at 890 to 940 °C and 5 to 6 kbar. The final-stage cooling is recorded at 750 and 800 °C and 4 to 5 kbar accompanied by a decrease in the y(opx) values (0.11-0.12). In the UHT granulite, zircon grains are commonly enclosed within cordierite. The overgrowth rims of the zircon grains yield a weighted mean 206Pb/238U age of 277 ± 2 Ma using LA-ICP-MS zircon dating, which is interpreted to mark the timing of decompression and cooling. We propose that the anti-clockwise P-T path of the UHT granulite in the Altai orogenic belt could be related to an extensional event related to the sinistral strike-slip along the Irtish tectonic belt after

  15. Scapolite phase equilibria and carbon isotope variations in high grade rocks: Tests of the CO sub 2 -flooding hypothesis of granulite gneiss

    SciTech Connect

    Moecher, D.P.

    1988-01-01

    Scapolite decarbonation reactions and carbon isotope analysis of CO{sub 2} extracted from scapolite are used to determine the presence, composition, and source of fluid components in high grade rocks. Scapolite-plagioclase-garnet-quartz assemblages, common to many lithologies in high grade terranes, monitors CO{sub 2} activity (aCO{sub 2}) by the reaction 2 Meionite + Quarts = 5 Anorthite + Grossular + 2 CO{sub 2}. The P-T-X location of this reaction was calculated using an internally consistent thermodynamic data set for meionite and phases in the CASCH system. Activity-composition relations for meionite in scapolite were calculated from the thermodynamic data set and compositional data on natural scapolite-plagioclase-calcite assemblages. Equilibration pressures of scapolite assemblages were calculated from clinopyroxene-garnet-plagioclass-quartz barometers calibrated for this study. The aCO{sub 2} was calculated for a variety of high grade gneisses from the southwestern Grenville Province and other terranes. Granulites typically yield low to moderate values of aCO{sub 2} (less than 0.5). Calc-silicates and meta-anorthosite yield moderate aCO{sub 2}. Deep crustal xenoliths yield a range of aCO{sub 2}.

  16. Body Composition.

    ERIC Educational Resources Information Center

    Mayhew, Jerry L.

    1981-01-01

    Body composition refers to the types and amounts of tissues which make up the body. The most acceptable method for assessing body composition is underwater weighing. A subcutaneous skinfold provides a quantitative measurement of fat below the skin. The skinfold technique permits a valid estimate of the body's total fat content. (JN)

  17. Body Composition.

    ERIC Educational Resources Information Center

    Mayhew, Jerry L.

    1981-01-01

    Body composition refers to the types and amounts of tissues which make up the body. The most acceptable method for assessing body composition is underwater weighing. A subcutaneous skinfold provides a quantitative measurement of fat below the skin. The skinfold technique permits a valid estimate of the body's total fat content. (JN)

  18. Body lift.

    PubMed

    Capella, Joseph F

    2008-01-01

    The body in the patient who has lost a massive amount of weight presents an extreme form of traditional esthetic and functional body contour concerns. Routine body contouring procedures usually produce only suboptimal results in this patient population. The body lift described herein is an excellent alternative to treat the body contour deformity of the patient who has undergone bariatric surgery. As with every technique, careful patient selection, education, and preparation are critical to minimizing complications and optimizing outcome.

  19. Monitoring and validating the temporal dynamics of interday streamflow from two upland head micro-watersheds with different vegetative conditions during dry periods of the growing season in the Bohemian Massif, Czech Republic.

    PubMed

    Deutscher, Jan; Kupec, Petr

    2014-06-01

    At present, dynamic land use, climate change, and growing needs for fresh water are increasing the demand on the ecosystem effects of forest vegetation. Mountainous areas are at the forefront of scientific interest in European forest ecology and forest hydrology. Although uplands cover a significant area of the Czech Republic and other countries and are often covered with forest formations, they do not receive an appropriate amount of attention. Therefore, two experimental upland head micro-watersheds in the Bohemian Massif were selected for study because they display similar natural conditions, but different vegetative conditions (forest versus meadow). During the 2011 growing season, short-term streamflow measurements were carried out at the discharge profiles of both catchments and were evaluated in relation to climatic data (rainfall and temperature). The basic premise was that the streamflow in a forested catchment must exhibit different temporal dynamics compared to that in treeless areas and that these differences can be attributed to the effects of woody vegetation. These conclusions were drawn from measurements performed during dry periods lasting several days. A decreasing streamflow trend during the day part of the day (0900-1900 hours) was observed in both localities. The decrease reached approx. 44 % of the initial morning streamflow (0.24 dm(3) s(-1) day(-1)) in the treeless catchment and approx. 20 % (0.19 dm(3) s(-1) day(-1)) in the forested catchment. At night (1900-0900 hours), the streamflow in the forested catchment increased back to its initial level, whereas the streamflow in the treeless catchment stagnated or slowly decreased. We attribute these differences to the ecosystem effects of woody vegetation and its capacity to control water loss during the day. This type of vegetation can also function as a water source for the hydrographic network during the night.

  20. Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U-Pb zircon and Sr-Nd isotopic evidence from the Brunovistulian Domain, eastern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Soejono, Igor; Janoušek, Vojtěch; Žáčková, Eliška; Sláma, Jiří; Konopásek, Jiří; Machek, Matěj; Hanžl, Pavel

    2017-09-01

    Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and geotectonic affinity of some of pre-Variscan (meta-)igneous rock complexes from this domain are still unknown. Geochronological and geochemical study of the granitic rocks across the Brunovistulian Domain reveals new information about the timing and nature of this magmatic activity originally situated along the northern margin of Gondwana. Zircon U-Pb data (601 ± 3 Ma, Brno Massif; 634 ± 6 Ma, paraautochtonous core of the Svratka Dome; 568 ± 3 Ma, Bíteš orthogneiss) from the allochtonous Moravicum indicate the prolonged magmatic activity within the Brunovistulian Domain during the Ediacaran. The major- and trace-element and Sr-Nd isotopic signatures show heterogeneous geochemical characteristics of the granitic rocks and suggest a magmatic-arc geotectonic setting. The two-stage Depleted Mantle Nd model ages ( c. 1.3-2.0 Ga) indicate derivation of the granitic rocks from a relatively primitive crustal source, as well as from an ancient and evolved continental crust of the Brunovistulian Domain. These results constrain the magmatic-arc activity to c. 635-570 Ma and provide a further evidence for a long-lived (at least c. 65 Myr) and likely episodic subduction-related magmatism at the northern margin of Gondwana. The presence of granitic intrusions derived from variously mature crustal sources at different times suggests heterogeneous crustal segments to having been involved in the magmatic-arc system during its multistage evolution.

  1. Long-lasting Cadomian magmatic activity along an active northern Gondwana margin: U-Pb zircon and Sr-Nd isotopic evidence from the Brunovistulian Domain, eastern Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Soejono, Igor; Janoušek, Vojtěch; Žáčková, Eliška; Sláma, Jiří; Konopásek, Jiří; Machek, Matěj; Hanžl, Pavel

    2016-11-01

    Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and geotectonic affinity of some of pre-Variscan (meta-)igneous rock complexes from this domain are still unknown. Geochronological and geochemical study of the granitic rocks across the Brunovistulian Domain reveals new information about the timing and nature of this magmatic activity originally situated along the northern margin of Gondwana. Zircon U-Pb data (601 ± 3 Ma, Brno Massif; 634 ± 6 Ma, paraautochtonous core of the Svratka Dome; 568 ± 3 Ma, Bíteš orthogneiss) from the allochtonous Moravicum indicate the prolonged magmatic activity within the Brunovistulian Domain during the Ediacaran. The major- and trace-element and Sr-Nd isotopic signatures show heterogeneous geochemical characteristics of the granitic rocks and suggest a magmatic-arc geotectonic setting. The two-stage Depleted Mantle Nd model ages (c. 1.3-2.0 Ga) indicate derivation of the granitic rocks from a relatively primitive crustal source, as well as from an ancient and evolved continental crust of the Brunovistulian Domain. These results constrain the magmatic-arc activity to c. 635-570 Ma and provide a further evidence for a long-lived (at least c. 65 Myr) and likely episodic subduction-related magmatism at the northern margin of Gondwana. The presence of granitic intrusions derived from variously mature crustal sources at different times suggests heterogeneous crustal segments to having been involved in the magmatic-arc system during its multistage evolution.

  2. Durbachites from the Eastern Moldanubicum (Bohemian Massif): erosional relics of large, flat tabular intrusions of ultrapotassic melts—geophysical and petrological record

    NASA Astrophysics Data System (ADS)

    Leichmann, J.; Gnojek, I.; Novák, M.; Sedlák, J.; Houzar, S.

    2017-01-01

    The results of the airborne survey comprising gamma-ray spectrometry and proton magnetometry, ground gravity survey, and field geological observations (e.g., deep borehole profiles, contact aureole in dolomite marbles, distribution of granitic pegmatites within the Třebíč pluton) suggest that the ultrapotassic Třebíč and Jihlava plutons are flat intrusions. They intruded distinct deep levels of the crust, 2-4 kbar for Třebíč pluton, and 5-7 kbar for Jihlava-pluton. Current thickness of the intrusions is generally less than 2 km, with two exceptions: (1) central part of the Jihlava pluton and (2) a small body near Věžnice, where the estimated depth of tube-shaped stocks of shoshonitic and ultrapotassic gabbros or monzogabbros is around 2.5 km. These stocks could represent feeding pipes of basic and alkaline and dry magmas protruding to the upper crust level. The NE part of the Třebíč pluton is a bottom part of this body, whereas the NW corner and the southern promontory of the pluton could represent an upper (roof) part of the intrusion. Small isolated durbachite bodies located within the Moldanubian gneisses and migmatites of the Strážek Unit represent rootless remnants of a former large and flat durbachite body initially extending significantly more to N and NE and eroded since Lower Carboniferous. Discrepancy between the long-wave magnetic and gravity anomalies, and surface geological structure of the eastern part of the Moldanubian Zone indicates a crucial role of the thrust tectonics.

  3. The Role of Brines in the Fluid Induced Dehydration of the Mafic Lower Crust from Amphibolite to Granulite Grade: Nature and Experiment

    NASA Astrophysics Data System (ADS)

    Harlov, D. E.

    2016-12-01

    Natural evidence for the role of low H2O activity fluids (CO2 or concentrated brines) in the dehydration of H2O-rich, mafic amphibolite-facies rocks to H2O-poor, Opx-bearing granulite-facies rocks (700-900 °C and 500-1000 MPa) for both highly localised dehydration zones (CO2; cm's) (Harlov et al. 2006, J Petrol, 47, 3) as well as regional terranes (NaCl-KCl brines; km's) (Harlov and Förster 2002, J Petrol, 43, 769; Hansen and Harlov 2007, 48, 1641) include the presence of Kfs micro-veins along Qtz-Plg grain boundaries; Plg grains metasomatised in a K-rich fluid; Mnz and/or Xn inclusions in the FAp grains; Bt enriched in Ti, F, and Cl; and FAp enriched in Cl and F. These features are not seen in the "source" amphibolite facies terrane along the same traverse. When log(fHF/fH2O) for either Bt or FAp is plotted as a function of the distance from the fluid/heat source, a uniform decrease in log(fHF/fH2O) is observed across the granulite to amphibolite facies traverse suggesting the presence of a uniform low H2O activity uniform fluid front. Dehydration experiments (900 °C; 1000 MPa; 3 weeks; Au capsule; quenched) involving a cylinder of natural tonalitic Bt gneiss (Plg, Qtz, Bt) (220 mg) and a concentrated KCl brine (20-30 % H2O; 70-80 % KCl) (8 mg) placed at the base of the cylinder have been conducted in the piston cylinder apparatus (CaF2 setup). Micro-veins primarily of Kfs, with some evidence of partial melting, formed along Qtz/Plg grain boundaries though only where Bt and Qtz were in contact. Here the Bt reacted with Qtz to form numerous small Opx and Cpx grains as well as minor Ilm from the 2-3 wt % of TiO2 present in the Bt. The two principle reactions responsible for both the formation of the Kfs micro-veins as well as the pyroxenes include: (1) An (in Plg) + Qtz + KCl (in fluid) = Kfs + CaCl2 (in fluid) and (2) Bt + Qtz = Opx + Kfs + H2O. The same experiment performed under the same P-T conditions involving either a concentrated NaCl brine (20-30 % H2O

  4. LASS U-Th-Pb monazite and rutile geochronology of felsic high-pressure granulites (Rhodope, N Greece): Effects of fluid, deformation and metamorphic reactions in local subsystems

    NASA Astrophysics Data System (ADS)

    Wawrzenitz, Nicole; Krohe, Alexander; Baziotis, Ioannis; Mposkos, Evripidis; Kylander-Clark, Andrew R. C.; Romer, Rolf L.

    2015-09-01

    The specific chemical composition of monazite in shear zones is controlled by the syndeformation dissolution-precipitation reactions of the rock-forming minerals. This relation can be used for dating deformation, even when microfabric characteristics like shape preferred orientation or intracrystalline deformation of monazite itself are missing. Monazite contemporaneously formed in and around the shear zones may have different compositions. These depend on the local chemical context rather than reflecting successive crystallization episodes of monazite. This is demonstrated in polymetamorphic, mylonitic high-pressure (HP) garnet-kyanite granulites of the Alpine Sidironero Complex (Rhodope UHP terrain, Northern Greece). The studied mylonitic rocks escaped from regional migmatization at 40-36 Ma and from subsequent shearing through cooling until 36 Ma. In-situ laser-ablation split-stream inductively-coupled plasma mass spectrometry (LASS) analyses have been carried out on monazite from micro-scale shear zones, from pre-mylonitic microlithons as well as of monazite inclusions in relictic minerals complimented by U-Pb data on rutile and Rb-Sr data of biotite. Two major metamorphic episodes, Mesozoic and Cenozoic, are constrained. Chemical compositions, isotopic characteristics and apparent ages systematically vary among monazite of four different microfabric domains (I-IV). Within three pre-mylonitic domains (inclusions in (I) pre-mylonitic kyanite and (II) garnet porphyroclasts, and (III) in pre-mylonitic microlithons) monazite yields ages of ca. 130-150 Ma for HP-granulite metamorphism, in line with previous geochronological results in the area. Patchy alteration of the pre-mylonitic monazite by intra-grain dissolution-precipitation processes variably increased negative Eu anomaly and reduced the HREE contents. The apparent age of this altered monazite is reduced. Monazite in the syn-mylonitic shear bands (IV) differs in chemical composition from unaltered and

  5. Anomalous Seismic Velocity Drop in Iron and Biotite Rich Amphibolite to Granulite Facies Transitional Rocks from Deccan Volcanic Covered 1993 Killari Earthquake Region, Maharashtra (India): a Case Study

    NASA Astrophysics Data System (ADS)

    Pandey, O. P.; Tripathi, Priyanka; Vedanti, Nimisha; Srinivasa Sarma, D.

    2016-07-01

    65 Ma Deccan Volcanic Province of western India forms one of the largest flood basaltic eruptions on the surface of the earth. The nature of the concealed crust below this earthquake prone region, which is marked by several low velocity zones at different depths has hardly been understood. These low velocity zones have been invariably interpreted as fluid-filled zones, genetically connected to earthquake nucleation. While carrying out detailed geological and petrophysical studies on the Late Archean basement cores, obtained from a 617 m deep KLR-1 borehole, drilled in the epicentral zone of 1993 Killari earthquake region of the southern Deccan Volcanic Province, we came across several instances where we observed remarkable drop in measured P-wave velocity in a number of high density cores. We provide detailed petrographic and geological data on 11 such anomalous samples which belong to mid-crustal amphibolite to granulite facies transitional rocks. They are associated with a mean P-wave velocity of 6.02 km/s (range 5.82-6.22 km/s) conforming to granitic upper crust, but in contrast have a high mean density of 2.91 g/cm3 (range 2.75-3.08 g/cm3), which characterise mid to lower crust. This velocity drop, which is as much as 15 % in some cores, is primarily attributed to FeOT enrichment (up to about 23 wt%) during the course of mantle-fluid driven retrogressive metasomatic reactions, caused by exhumation of deep-seated mafic rocks. Presence of Iron content (mainly magnetite), widely seen as opaques in thin sections of the rocks, seems to have resulted into sharp increase in density, as well as mean atomic weight. Our study indicates that the measured V p is inversely related to FeOT content as well as mean atomic weight of the rock.

  6. Granulite-Facies High-sulfidation VHMS-like Hydrothermal System in the La Romaine Area, Eastern Grenville Province, Quebec: a Metamorphic and Geochemical Overview

    NASA Astrophysics Data System (ADS)

    Bonnet, A.; Corriveau, L.; Laflèche, M. R.

    2004-05-01

    An extensive Cu-mineralized hydrothermal system has been recognized among the 1.5 Ga La Romaine volcano-sedimentary belt, in the eastern Grenville Province. This high-grade metamorphosed supracrustal belt occurs as a narrow basin within coeval granitoids. Granulite-facies alteration halos, encompassing rocks diagnostic of advanced argillic alteration (sillimanite-garnet-cordierite gneiss), silicification (quartz-cordierite gneiss) and sericite alteration (quartz-muscovite-sillimanite-iron oxide nodules or veins), are mapped among rhyolitic to dacitic tuffs and lapillistones. Some of these altered rocks have preserved primary lapilli textures. Amphibolite units of uncertain volcanic or intrusive origin overly the felsic pyroclastics and form a structurally coherent, east-west oriented unit. A narrow zone of ironstones (magnetite-rich amphibolite and biotite gneiss), carbonated zones (epidote-, diopside-, anorthite-, Ca garnet-, and/or calcite-rich calc-silicate rocks) and disseminated Cu sulphides, is found across its trend and testify of focused fluid discharge and mineralization. Structural and petrographic data suggest that mineralization and alteration are controlled by synvolcanic faults, with the amphibolite unit serving as a cap rock. Despite high-grade metamorphism, the volcanic and granitic rocks preserve a reproducible signature of calc-alkaline affinity. Element ratios analysis indicates that these rocks have not experienced significant LILE depletion and that metamorphism was, for the most part, isochemical. Element mobility of altered rocks is thus interpreted as produced by hydrothermal activity. AFM, ACF and AKF ternary plots of altered rocks and their protolith, define diagnostic alteration vectors, which reflect major elements mobility for the various alteration facies. Strong silica mobility is revealed by mass-balance calculations for altered pyroclastics. REE patterns of these rocks also show the mobility of heavy REE, in particular Tb, Dy and Ho

  7. Mass transfer in the lower crust: Evidence for incipient melt assisted flow along grain boundaries in the deep arc granulites of Fiordland, New Zealand

    NASA Astrophysics Data System (ADS)

    Stuart, Catherine A.; Piazolo, Sandra; Daczko, Nathan R.

    2016-09-01

    Knowledge of mass transfer is critical in improving our understanding of crustal evolution, however mass transfer mechanisms are debated, especially in arc environments. The Pembroke Granulite is a gabbroic gneiss, passively exhumed from depths of >45 km from the arc root of Fiordland, New Zealand. Here, enstatite and diopside grains are replaced by coronas of pargasite and quartz, which may be asymmetric, recording hydration of the gabbroic gneiss. The coronas contain microstructures indicative of the former presence of melt, supported by pseudosection modeling consistent with the reaction having occurred near the solidus of the rock (630-710°C, 8.8-12.4 kbar). Homogeneous mineral chemistry in reaction products indicates an open system, despite limited metasomatism at the hand sample scale. We propose the partial replacement microstructures are a result of a reaction involving an externally derived hydrous, silicate melt and the relatively anhydrous, high-grade assemblage. Trace element mapping reveals a correlation between reaction microstructure development and bands of high-Sr plagioclase, recording pathways of the reactant melt along grain boundaries. Replacement microstructures record pathways of diffuse porous melt flow at a kilometer scale within the lower crust, which was assisted by small proportions of incipient melt providing a permeable network. This work recognizes melt flux through the lower crust in the absence of significant metasomatism, which may be more common than is currently recognized. As similar microstructures are found elsewhere within the exposed Fiordland lower crustal arc rocks, mass transfer of melt by diffuse porous flow may have fluxed an area >10,000 km2.

  8. Body Measurement.

    ERIC Educational Resources Information Center

    Neufeld, K. Allen

    1989-01-01

    Described are activities for measuring the human body. The activities include measurements and calculations, calculating volume and density, problems related to body measurement, and using a nomogram. Several charts, illustrations, and a nomogram are provided. (YP)

  9. Body Measurement.

    ERIC Educational Resources Information Center

    Neufeld, K. Allen

    1989-01-01

    Described are activities for measuring the human body. The activities include measurements and calculations, calculating volume and density, problems related to body measurement, and using a nomogram. Several charts, illustrations, and a nomogram are provided. (YP)

  10. Ringworm (Body)

    MedlinePlus

    Ringworm (body) Overview Ringworm of the body is a fungal infection that develops on the top layer of your skin. It's characterized by ... clearer skin in the middle. It may itch. Ringworm gets its name because of its appearance. No ...

  11. 2.69-2.68 Ga granulite facies metamorphism in the Wyoming Craton revealed by Sm-Nd garnet geochronology and trace element zoning, eastern Beartooth Mountains, Montana and Wyoming, USA

    NASA Astrophysics Data System (ADS)

    Guevara, V.; Dragovic, B.; Caddick, M. J.; Baxter, E. F.

    2014-12-01

    The Beartooth Mountains in Montana and Wyoming, USA, form an extensive exposure of Archean rocks of the Wyoming Craton and are dominantly comprised of a ~2.8 Ga granitoid batholith known as the Long Lake Magmatic Complex (LLMC). Contained within the LLMC are numerous m- to km-scale enclaves of metasedimentary granulites. P-T pseudosection modeling indicates that these granulites reached peak pressure-temperature (P-T) conditions of 800 °C, 7-8 kbar. This has previously been interpreted to result from contact heating with the LLMC. However, substantial field evidence from multiple localities suggests that the texturally dominant phase of HT metamorphism in the metasediments postdates LLMC emplacement. Further, Sm-Nd garnet (grt) dates from the metasediments are in the range ~2.69-2.68 Ga ('bulk' dates incorporating crystal cores and rims), ~100 Myrs younger than LLMC emplacement (based on U-Pb zircon ages, 1). Trace element zoning in grt suggests that these dates record the age of granulite facies metamorphism. Euhedral high-Ca overgrowths in Grt from a residual pelite are coincident with a high Eu spike, interpreted to result from plagioclase breakdown during partial melting. These overgrowths are also coincident with high Sm and Nd annuli, and we thus interpret the bulk grt date (2689±4 Ma) to record timing of the late stages of grt growth during migmatisation near peak T. Coupled with major element zoning, retention of Sm and Nd zoning in euhedral grt from the leucosome of another sample suggest that its bulk date (2681±1 Ma) also represents peritectic grt growth rather than subsequent diffusion. Grt from a lithology that did not experience melting records a date of 2686±1 Ma. Together, these ages indicate that granulite facies metamorphism persisted in the area for at least ~3 Myrs (inner bounds of the 2σ dates), ~100 Myrs after batholith emplacement. Limited evidence for this later event in the plutonic rocks is consistent with their experiencing little

  12. Atypical geochemistry of the lherzolite enclave in the Paleoarchean Bug Granulite complex - participation of the chondrite material?

    NASA Astrophysics Data System (ADS)

    Lobach-Zhuchenko, Svetlana; Egorova, Yuliya

    2017-04-01

    An enclave of a small ( 30 * 300 sm) lens-like body [N56°30`, E13°50`] of spinel lherzolite occurs in the Paleoarchean orthogneiss of the Bug complex of the Ukrainian Shield which experienced multistage metamorphism and deformation [Claesson et al., 2006; Lobach-Zhuchenko et al., 2016]. The spinel lherzolite lens is mantled by a thin rim of a phlogopite websterite at the contact with the host orthogneiss. The spinel lherzolite consists of Ol (Fo 85), Opx (#Mg 0.86), Cpx (#Mg 0.92), minor Phl (#Mg 0.92), Cr- Spl, Srp, Pn (Fe 4.3 Ni 4.6 S 8), Mel, Ccp, Crb, Mag, Ap. A mineral assemblage of the websterite is the same except for the minor or absence of Ol and more concentration of Phl. While the mineral composition of the lherzolite is usial for the mantle ultramafic rocks its geochemistry is atypical (SiO2 - 41.04 wt%, TiO2 - 0.26, Al2O3 - 1.62, Fe2O3 - 3.88, FeO - 7.75, MnO - 0.18, MgO - 38.90, CaO - 0.61, Na2O - 0.09, K2O - 1.12, P2O5 - 0.02, LOI - 3.37, CO2 - 0.85, S - 0.08 wt%). The main distinctions of this rock include (1) low # Mg (0.86) relative to PM and mantle xenoliths [Pearson et al., 2003], (2) high abundance of Ni - average 3737 ppm versus 1960 ppm in PM [Palme & O`Neil, 2003] and as a consequence olivine enriched in Ni relative to its Mg-number [Mysen, 2006; Herzberg et al., 2016], (3) high Ni/Cr = 4.76 and Ni/Co = 21.56 versus PM with Ni/Cr = 0.74; Ni/Co = 18.20 [Palme & O`Neil, 2003] and as compared with other terrestrial ultramafics, for instance, relative to orogenic lehrzolite (Ni = 2024; Ni/Cr = 0.78; Ni/Co = 18.4) [Lorand et al., 2000]. It is known that such high ratios are typical for all types of chondrites, e.g., the ratios in C1, C2, C3, L, E chondrites are: Ni/Cr = 2.9-5.3, Ni/Co = 21-29 [Mason, 1971; Sobotovich, 1986]. Probably, the geochemistry of the studied lherzolite inclusion assumes participation of the chondrite material in its formation during some impact event in the past.

  13. Granodiorites of the South Mountain Batholith (Nova Scotia, Canada) derived by partial melting of Avalonia granulite rocks beneath the Meguma terrane: Implications for the heat source of the Late Devonian granites of the Northern Appalachians

    NASA Astrophysics Data System (ADS)

    Shellnutt, J. Gregory; Dostal, Jaroslav

    2015-08-01

    The Late Devonian South Mountain Batholith (SMB) of Nova Scotia is the largest batholith of the northern Appalachians. The peraluminous granitic rocks range from biotite granodiorite to leucogranite. Samples collected from a drill core of the Scrag Lake granodioritic pluton of the western SMB are chemically homogeneous from the surface to a depth of ~ 1425 m. The homogeneous composition implies that the granodiorite was derived from a relatively homogeneous source and that country rock assimilation was not an important source for the parental magma. Equilibrium partial melt modeling of underlying sub-Meguma granulite rocks indicates that they are the primary source rocks of the granodiorites. We suggest that mantle-derived magmas intruded the lower crust and induce large-scale melting of the granulite basement rocks to produce the granodiorites. Fractional crystallization of the granodiorites plus assimilation of Meguma Supergroup metasediments likely produces the silica-rich rocks of the SMB. The cause of mantle melting is uncertain however it may be related to the transitioning of the northern Appalachians from a position above the deep mantle Pacific large low shear velocity province (LLSVP) to a higher shear velocity region of the mantle.

  14. Prograde infiltration of Cl-rich fluid into the granulitic continental crust from a collision zone in East Antarctica (Perlebandet, Sør Rondane Mountains)

    NASA Astrophysics Data System (ADS)

    Kawakami, Tetsuo; Higashino, Fumiko; Skrzypek, Etienne; Satish-Kumar, M.; Grantham, Geoffrey; Tsuchiya, Noriyoshi; Ishikawa, Masahiro; Sakata, Shuhei; Hirata, Takafumi

    2017-03-01

    Utilizing microstructures of Cl-bearing biotite in pelitic and felsic metamorphic rocks, the timing of Cl-rich fluid infiltration is correlated with the pressure-temperature-time (P-T-t) path of upper amphibolite- to granulite-facies metamorphic rocks from Perlebandet, Sør Rondane Mountains (SRM), East Antarctica. Microstructural observation indicates that the stable Al2SiO5 polymorph changed from sillimanite to kyanite + andalusite + sillimanite, and P-T estimates from geothermobarometry point to a counterclockwise P-T path characteristic of the SW terrane of the SRM. In situ laser ablation inductively coupled plasma mass spectrometry for U-Pb dating of zircon inclusions in garnet yielded ca. 580 Ma, likely representing the age of garnet-forming metamorphism at Perlebandet. Inclusion-host relationships among garnet, sillimanite, and Cl-rich biotite (Cl > 0.4 wt%) reveal that formation of Cl-rich biotite took place during prograde metamorphism in the sillimanite stability field. This process probably predated partial melting consuming biotite (Cl = 0.1-0.3 wt%). This was followed by retrograde, moderately Cl-bearing biotite (Cl = 0.1-0.3 wt%) replacing garnet. Similar timings of Cl-rich biotite formation in different samples, and similar f(H2O)/f(HCl) values of coexisting fluid estimated for each stage can be best explained by prograde Cl-rich fluid infiltration. Fluid-present partial melting at the onset of prograde metamorphism probably contributed to elevate the Cl concentration (and possibly salinity) of the fluid, and consumption of the fluid resulted in the progress of dehydration melting. The retrograde fluid was released from crystallizing Cl-bearing partial melts or derived externally. The prograde Cl-rich fluid infiltration in Perlebandet presumably took place at the uppermost part of the footwall of the collision boundary. Localized distribution of Cl-rich biotite and hornblende along large-scale shear zones and detachments in the SRM supports external

  15. Mid-Neoproterozoic intraplate magmatism in the northern margin of the Southern Granulite Terrane, India: Constraints from geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Deeju, T. R.; Santosh, M.; Yang, Qiong-Yan; Pradeepkumar, A. P.; Shaji, E.

    2016-11-01

    The northern margin of the Southern Granulite Terrane in India hosts a number of mafic, felsic and alkaline magmatic suites proximal to major shear/paleo-suture zones and mostly represents magmatism in rift-settings. Here we investigate a suite of gabbros and granite together with intermediate (dioritic) units generated through mixing and mingling of a bimodal magmatic suite. The massive gabbro exposures represent the cumulate fraction of a basic magma whereas the granitoids represent the product of crystallization in felsic magma chambers generated through crustal melting. Diorites and dioritic gabbros mostly occur as enclaves and lenses within host granitoids resembling mafic magmatic enclaves. Geochemistry of the felsic units shows volcanic arc granite and syn-collisional granite affinity. The gabbro samples show mixed E-MORB signature and the magma might have been generated in a rift setting. The trace and REE features of the rocks show variable features of subduction zone enrichment, crustal contamination and within plate enrichment, typical of intraplate magmatism involving the melting of source components derived from both depleted mantle sources and crustal components derived from older subduction events. The zircons in all the rock types show magmatic crystallization features and high Th/U values. Their U-Pb data are concordant with no major Pb loss. The gabbroic suite yields 206Pb/238U weighted mean ages in the range of 715 ± 4-832.5 ± 5 Ma marking a major phase of mid Neoproterozoic magmatism. The diorites crystallized during 206Pb/238U weighted mean age of 724 ± 6-830 ± 2 Ma. Zircons in the granite yield 206Pb/238U weighted mean age of 823 ± 4 Ma. The age data show broadly similar age ranges for the mafic, intermediate and felsic rocks and indicate a major phase of bi-modal magmatism during mid Neoproterozoic. The zircons studied show both positive and negative εHf(t) values for the gabbros (-6.4 to 12.4), and negative values for the diorites (-7

  16. Sm-Nd chronology of porphyroblastic garnets from granulite facies metabasic rocks in Calabria (Southern Italy): inferences for preserved isotopic memory and resetting

    NASA Astrophysics Data System (ADS)

    Duchene, S.; Fornelli, A.; Micheletti, F.; Piccarreta, G.

    2013-08-01

    Metabasic rocks related to pre-Cambrian protoliths from the lower portion of the deep crust of the Serre (Calabria, southern Italy) contain porphyroblastic garnet up to 5-6 cm in diameter. Garnet forms coronas around the inclusions of clinopyroxene and is in contact with various matrix minerals. Both inner and outer coronas formed under granulite facies conditions after the thermal peak during the Hercynian reworking. Six porphyroblastic garnets (≥1 cm in diameter) from four samples have been dated with the Sm-Nd method to constrain the distinct metamorphic stages and, possibly, to investigate the diffusion of Sm and Nd in garnet. They show in the core major element flat profiles whereas one of these, analyzed for REEs, preserves only a feeble zoning. This suggests that the diffusion rates of REEs are effective at the crystal scale. The apparent Nd ages range from 354 to 88 Ma, without any reproducibility in each and in all rock samples. The oldest age of 354 Ma is interpreted as the primary isotopic signatures linked to prograde metamorphism. The interpretation of younger ages (309, 272, 215, 143 and 88 Ma) requires a detailed discussion about: (i) possible modification of chemical and isotopic composition of the rocks during and after garnet growth, (ii) possible contamination by inclusions in garnet, (iii) inherited isotopic disequilibrium, (iv) new growth or recrystallization of garnet and (v) possible isotopic resetting of large crystals which, in principle, is hampered by the slow diffusion of REE's in garnet. Some of the Nd ages are similar to U-Pb ages of zircon from the metabasic rocks of deep crustal rocks of the Serre (350, 300 and 280 Ma). This convergence of apparent ages can hardly be considered as simply fortuitous. Thus, since: (i) corona formation was fluid-assisted and (ii) all porphyroblasts were broken up into several fragmented subgrains by sets of fractures resulting in smaller volumes, the volume diffusion and the possible role of high

  17. Crustal Provenance and Early Palaeozoic Continenal Break-up of N Gondwana: A Nd Isotope and REE Study of (meta)Granitoids from the Pre-Variscan Basement, N Bohemian Massif, Central Europe

    NASA Astrophysics Data System (ADS)

    Crowley, Q. G.; Patocka, F.; Kachlík, V.

    2003-04-01

    Pre-Variscan (meta)granitoids occurring in the Krkonose-Jizera region of the NW Bohemian Massif (Czech W Sudetes) were emplaced at ca 500 Ma (Kröner et al 2001). They are calc-alkaline in character and generally predate or are coeval with minor felsic metavolcanic rocks and voluminous metabasites (the former are mostly WPG-like, the latter display a wide spectrum of compositions from N-MORB to alkali WPB types) that were generated in an extensional regime related to fragmentation of the N Gondwanan margin (Crowley et al 2000). The (meta)granitoids vary considerably in LREE enrichment ((Ce/Yb)_N = 2 to 8), whereas two felsic metavolcanics included in the study display (Ce/Yb)_N = 3 and 4. The (meta)granitoids are characterised by ɛNd(t) values of -4.8 to -3.2 and have two stage TDM ages of 1.5 to 1.2 Ga. The felsic metavolcanics display ɛNd(t) values of +5.6 to +6.2. This indicates that the felsic metavolcanics formed from a depleted mantle source and did not experience any major crustal contamination. The (meta)granitoids however, predominantly formed by recycling of pre-existing continental crust. The (meta)granitoid TDM ages do not necessarily signify a crustal component of this age and only provide a lower age limit on the older components involved in their petrogenesis. It is possible that a mixture of Archaean, Palaeoproterozoic and Neoproterozoic aged sources were utilised in this early Palaeozoic granitoid magmatic event. References: Crowley, Q.G., Floyd, P.A., Winchester, J.A., Franke, W. &Holland, J.G. 2000. Early Palaeozoic rift-related magmatism in Variscan Europe: fragmentation of the Armorican Terrane Assemblage. Terra Nova, 2, 171-180. Kröner, A. Jaeckel, P. Hegner, E., Opetal, M. 2001. Single zircon ages and whole-rock Nd isotopic systematics of early Palaeozoic gneisses from the Czech and Polish Sudetes. International Journal of Earth Sciences, 0, 304-324.

  18. Geochemical characteristics and petrogenesis of phonolites and trachytic rocks from the České Středohoří Volcanic Complex, the Ohře Rift, Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Ackerman, Lukáš; Ulrych, Jaromír; Řanda, Zdeněk; Erban, Vojtěch; Hegner, Ernst; Magna, Tomáš; Balogh, Kadosa; Frána, Jaroslav; Lang, Miloš; Novák, Jiří K.

    2015-05-01

    distinct fluids are implicated from the Li-Cs correlations. The derivation of these melts/liquids from sedimentary and/or meta-sedimentary crustal sources is underscored by variable but overall light Li isotopic compositions. Some phonolites exhibit enrichments in high-field-strength elements coupled with increased Zr/Nb ratios. In contrast to previous studies, we show that this feature, apparent in many volcanic rocks from the Bohemian Massif, can be explained with progressive melt fractionation of parental magmas involving amphibole and plagioclase.

  19. Body Basics

    MedlinePlus

    ... more about how the body works, what basic human anatomy is, and what happens when parts of the body don't function properly. Blood Bones, Muscles, and Joints Brain and Nervous System Digestive System Endocrine System Eyes Female Reproductive System ...

  20. Low-Enthalpy Geothermal Potential of the Czech Republic with Particular Focus on Waters of Metalliferous Mining Districts in Crystalline Structures of the Bohemian Massif

    NASA Astrophysics Data System (ADS)

    Stibitz, M.; Jirakova, H.; Frydrych, V.

    2012-04-01

    mixing with the warmer mine water. Various technical solutionsfor the exploitation of energetic potential of mine water are relatively well known - geothermal heat from operating mines, geothermal heat capacity of the flooded mines, groundwater bodies in flooded mines used for heat storage. Regarding the fact that the temperature conditions of the mine water are very stable and the time scale of the mine water temperature decrease is over several centuries, mine waters represent a promising source of geothermal energy. Regional and local demand for heat is being quantified; technical solutions of mine water heat utilization are being investigated along with development of legal framework in the Czech Republic.

  1. Body Image

    MedlinePlus

    ... spider veins Body dysmorphic disorder (BDD) Eating disorders Anorexia nervosa Binge eating disorder Bulimia nervosa Over-exercising ... conditions? Visit our Mental health section. Fact sheets Anorexia nervosa Binge eating disorder Bulimia nervosa Cosmetics and ...

  2. Bog bodies.

    PubMed

    Lynnerup, Niels

    2015-06-01

    In northern Europe during the Iron Age, many corpses were deposited in bogs. The cold, wet and anaerobic environment leads in many cases to the preservation of soft tissues, so that the bodies, when found and excavated several thousand years later, are remarkably intact. Since the 19th century the bog bodies have been studied using medical and natural scientific methods, and recently many bog bodies have been re-examined using especially modern, medical imaging techniques. Because of the preservation of soft tissue, especially the skin, it has been possible to determine lesions and trauma. Conversely, the preservation of bones is less good, as the mineral component has been leached out by the acidic bog. Together with water-logging of collagenous tissue, this means that if the bog body is simply left to dry out when found, as was the case pre-19th century, the bones may literally warp and shrink, leading to potential pitfalls in paleopathological diagnostics. Bog bodies have in several instances been crucial in determining the last meal, as gut contents may be preserved, and thus augment our knowledge on pre-historic diet by adding to, for example, stable isotope analyses. This article presents an overview of our knowledge about the taphomic processes as well as the methods used in bog body research.

  3. Comment on ;Evolution of high-pressure mafic granulites and pelitic gneisses from NE Madagascar: Tectonic implications;. Tectonophysics, 662, 219-242 (2015) by Ishwar-Kumar et al.

    NASA Astrophysics Data System (ADS)

    Goncalves, Philippe; Brandt, Sönke; Nicollet, Christian; Tucker, Robert

    2017-05-01

    Determining the possible tectonic regimes active during the Neoproterozoic is crucial for the knowledge of the evolution of the super-continent Gondwana. In Madagascar, that occupies a key position in Gondwana, there is an on-going debate regarding the location of possible suture zones and the implications in terms of paleo-geography. Recognizing high-pressure to ultra-high pressure conditions in mafic rocks is commonly viewed as a strong argument for paleo-subduction zones. Ishwar-Kumar et al. (2015) report unusual high pressure conditions (24 kbar) in Neoproterozoic to Cambrian rocks from North-Central Madagascar (Andriamena Complex). They propose a geodynamic model in which exhumation of the high pressure terranes from up to 80 km to 40 km occurred via vertical extrusion during the collision of various crustal blocks after subduction and closure of an oceanic domain during the formation of Gondwana in the late Neoproterozoic to Cambrian. We question this model and in particular the (ultra-)high pressure conditions reported, because their estimation is based on a misinterpretation of the petrography and inaccurate thermodynamic modeling for the crucial metabasite sample. The authors suggest that garnet-quartz coronas around orthopyroxene and ilmenite coexist with clinopyroxene. The postulated garnet-clinopyroxene-quartz assemblage is interpreted to document an eclogite facies overprint. However, the presence of abundant plagioclase in the sample and the lack of high jadeite content in clinopyroxene clearly refute the postulated eclogite facies conditions. According to the presented photographs clinopyroxene is part of the rock matrix. We therefore suggest that the sample represents a common two-pyroxene granulite, formed at mid- to low-pressure granulite facies conditions of > 700 °C and < 6 kbar, consistent with PT data of former studies for the Andriamena Complex. Garnet-quartz-bearing coronas produced at the expense of the granulite-facies assemblage could

  4. Cryogenian alkaline magmatism in the Southern Granulite Terrane, India: Petrology, geochemistry, zircon U-Pb ages and Lu-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Santosh, M.; Yang, Qiong-Yan; Ram Mohan, M.; Tsunogae, T.; Shaji, E.; Satyanarayanan, M.

    2014-11-01

    The Southern Granulite Terrane (SGT) in India preserves the records of the formation and recycling of continental crust from Mesoarchean through Paleoproterozoic to Neoproterozoic and Cambrian, involving multiple subduction-accretion-collision associated with major orogenic cycles. A chain of unmetamorphosed and undeformed alkaline magmatic intrusions occurs along the northern margin of the SGT aligned along paleo-suture zones. Here we investigate two representative plutons from this suite, the Angadimogar syenite (AM) and the Peralimala alkali granite (PM) through field, petrological, geochemical, zircon U-Pb and Lu-Hf studies. Magma mixing and mingling textures and mineral assemblages typical of alkaline rocks are displayed by these plutons. The whole-rock major and trace element data characterize their alkaline nature. In trace element discrimination diagrams, the AM rocks straddle between the VAG (volcanic-arc granites) and WPG (within plate granites) fields with most of the samples confined to the VAG field, whereas the PM rocks are essentially confined to the WPG field. The diversity in some of the geochemical features between the two plutons is interpreted to be the reflection of source heterogeneities. Most zircon grains from the AM and PM plutons display oscillatory zoning typical of magmatic crystallization although some grains, particularly those from the PM pluton, show core-rim structures with dark patchy zoned cores surrounded by irregular thin rims resulting from fluid alteration. The weighted mean 206Pb/238U ages of the magmatic zircons from three samples of the AM syenite are in the range of 781.8 ± 3.8 Ma to 798 ± 3.6 Ma and those from two samples of the PM alkali granite yield ages of 797.5 ± 3.7 Ma and 799 ± 6.2 Ma. A mafic magmatic enclave from the AM pluton shows weighted mean 206Pb/238U age of 795 ± 3.3 Ma. The AM and PM plutons also carry rare xeneocrystic zircons which define upper intercept concordia ages of 3293 ± 13 Ma and 2530

  5. Body Imaging

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The high-tech art of digital signal processing (DSP) was pioneered at NASA's Jet Propulsion Laboratory (JPL) in the mid-1960s for use in the Apollo Lunar Landing Program. Designed to computer enhance pictures of the Moon, this technology became the basis for the Landsat Earth resources satellites and subsequently has been incorporated into a broad range of Earthbound medical and diagnostic tools. DSP is employed in advanced body imaging techniques including Computer-Aided Tomography, also known as CT and CATScan, and Magnetic Resonance Imaging (MRI). CT images are collected by irradiating a thin slice of the body with a fan-shaped x-ray beam from a number of directions around the body's perimeter. A tomographic (slice-like) picture is reconstructed from these multiple views by a computer. MRI employs a magnetic field and radio waves, rather than x-rays, to create images. In this photograph, a patient undergoes an open MRI.

  6. Body Imaging

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The high-tech art of digital signal processing (DSP) was pioneered at NASA's Jet Propulsion Laboratory (JPL) in the mid-1960s for use in the Apollo Lunar Landing Program. Designed to computer enhance pictures of the Moon, this technology became the basis for the Landsat Earth resources satellites and subsequently has been incorporated into a broad range of Earthbound medical and diagnostic tools. DSP is employed in advanced body imaging techniques including Computer-Aided Tomography, also known as CT and CATScan, and Magnetic Resonance Imaging (MRI). CT images are collected by irradiating a thin slice of the body with a fan-shaped x-ray beam from a number of directions around the body's perimeter. A tomographic (slice-like) picture is reconstructed from these multiple views by a computer. MRI employs a magnetic field and radio waves, rather than x-rays, to create images.

  7. Body Imaging

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The high-tech art of digital signal processing (DSP) was pioneered at NASA's Jet Propulsion Laboratory (JPL) in the mid-1960s for use in the Apollo Lunar Landing Program. Designed to computer enhance pictures of the Moon, this technology became the basis for the Landsat Earth resources satellites and subsequently has been incorporated into a broad range of Earthbound medical and diagnostic tools. DSP is employed in advanced body imaging techniques including Computer-Aided Tomography, also known as CT and CATScan, and Magnetic Resonance Imaging (MRI). CT images are collected by irradiating a thin slice of the body with a fan-shaped x-ray beam from a number of directions around the body's perimeter. A tomographic (slice-like) picture is reconstructed from these multiple views by a computer. MRI employs a magnetic field and radio waves, rather than x-rays, to create images.

  8. Body Imaging

    NASA Technical Reports Server (NTRS)

    2001-01-01

    The high-tech art of digital signal processing (DSP) was pioneered at NASA's Jet Propulsion Laboratory (JPL) in the mid-1960s for use in the Apollo Lunar Landing Program. Designed to computer enhance pictures of the Moon, this technology became the basis for the Landsat Earth resources satellites and subsequently has been incorporated into a broad range of Earthbound medical and diagnostic tools. DSP is employed in advanced body imaging techniques including Computer-Aided Tomography, also known as CT and CATScan, and Magnetic Resonance Imaging (MRI). CT images are collected by irradiating a thin slice of the body with a fan-shaped x-ray beam from a number of directions around the body's perimeter. A tomographic (slice-like) picture is reconstructed from these multiple views by a computer. MRI employs a magnetic field and radio waves, rather than x-rays, to create images. In this photograph, a patient undergoes an open MRI.

  9. Body parts

    NASA Astrophysics Data System (ADS)

    Ayiter, Elif

    2010-01-01

    In this project, the artist wishes to examine corporeality in the virtual realm, through the usage of the (non)-physical body of the avatar. An art installation created in the virtual world of Second Life, which is meant to be accessed with site specific avatars, will provide the creative platform whereby this investigation is undertaken. Thus, "body parts" seeks to challenge the residents of virtual environments into connecting with the virtual manifestations, i.e., avatars of others in an emotionally expressive/intimate manner.

  10. Body Imaging

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Magnetic Resonance Imaging (MRI) and Computer-aided Tomography (CT) images are often complementary. In most cases, MRI is good for viewing soft tissue but not bone, while CT images are good for bone but not always good for soft tissue discrimination. Physicians and engineers in the Department of Radiology at the University of Michigan Hospitals are developing a technique for combining the best features of MRI and CT scans to increase the accuracy of discriminating one type of body tissue from another. One of their research tools is a computer program called HICAP. The program can be used to distinguish between healthy and diseased tissue in body images.

  11. Late Devonian - Early Carboniferous polyphase metamorphic evolution of the Orlica-Śnieżnik Dome (NE Bohemian Massif, Poland): evidence from Th-U-total Pb monazite dating

    NASA Astrophysics Data System (ADS)

    Budzyń, Bartosz; Jastrzębski, Mirosław; Stawikowski, Wojciech

    2014-05-01

    The Orlica-Śnieżnik Dome, located in the NE part of the Bohemian Massif, mainly consists of Cambro-Ordovician orthogneisses and the metavolcano-sedimentary Młynowiec and Stronie Formations. This study constrains electron microprobe Th-U-total Pb ages of monazite in (1) orthogneisses, (2) paragneisses of the Młynowiec Formation (MF), (3) mica schists of the Stronie Formation (SF) and (4) light quartzites. The latter light quartzites form a continuous 'horizon' between two metavolcano-sedimentary formations, however, they are traditionally treated as the lowest member of the Stronie Formation (SF). Our field and structural studies conducted along the transects crossing the boundaries between the above-mentioned rocks indicate that there is a stratigraphic and structural continuity between the Młynowiec and Stronie Formations. Samples for the monazite dating were collected at different distances from the contact between orthogneisses and metasediments. The aim of this study was to provide a new data to verify a hypothesis of Cambro-Ordovician contact or regional metamorphism of the Młynowiec-Stronie Group and to constrain age of the Variscan metamorphic events in the Orlica-Śnieżnik Dome. Monazite from medium-grained orthogneiss yield dates ranging from 546 to 322 Ma, while three age domains of ca. 481 Ma, ca. 421 Ma and ca. 370 Ma are defined in fine-grained orthogneiss. Monazite in two porphyroblastic paragneisses (MF) yields two age domains of 369-361 Ma and 340-336 Ma. It should be noted that the older ages are recorded by inclusions of monazite in staurolite and plagioclase, as well as by matrix monazite. Monazite in leucosome of the migmatized paragneiss (MF) yields ca. 337 Ma age, while matrix monazite in melanosome yields ages of ca. 331 Ma age and a faint record of ca. 355 Ma. In two K-feldspar bearing light quartzites (SF), older spectrum of ages within 524-463 Ma, as well as younger ages of ca. 358 Ma and 347 Ma are obtained. On the other hand, only

  12. 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

    SciTech Connect

    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, reveals 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.

  13. Evolution of the Chilka Lake granulite complex, northern Eastern Ghats Belt, India: First evidence of ~ 780 Ma decompression of the deep crust and its implication on the India-Antarctica correlation

    NASA Astrophysics Data System (ADS)

    Bose, S.; Das, K.; Torimoto, J.; Arima, M.; Dunkley, D. J.

    2016-10-01

    High-grade para- and orthogneissic rocks near the Chilka Lake granulite complex, northern part of the Eastern Ghats Belt show complex structural and petrological history. Based on field and petrographic characters, five (M1-M5) metamorphic events could be identified. The earliest metamorphic event (M1) produced amphibolite grade mineral assemblage which produced the peak granulite (M2) assemblages at 900-950 °C, 8.5-9.0 kbar. The third metamorphic event caused decompression of the deeper crust up to 700-800 °C, 6.0-6.5 kbar. This was followed by cooling (M4) and subsequent thermal overprinting (M5). Fluid-composition during M3 was dominated by high-density CO2 and changed to low-density mixed CO2-H2O during the M3. Zircon U-Pb SHRIMP data suggest 781 ± 9 Ma age for M3 event. Texturally constrained monazite U-Th-Pb EPMA data, on the other hand, yield a group age of 988 ± 23 Ma from grain interior, which can signifies the age of M2 event. Few spots with younger dates in the range of 550-500 Ma are also noted. This interpretation changes the existing tectonothermal history of northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories. While the central Domain 2 evolved through early anticlockwise P-T path culminating in ultrahigh temperature, the northern Domain 3 evolved through a clockwise P-T path. It appears that the Domain 3 was contiguous to East Antarctica and became part of the Eastern Ghats Belt during the assembly of Gondwana. The ca. 780 Ma decompression event in the northern Eastern Ghats Belt opens up new possibilities for interpreting the breakup of Rodinia.

  14. Body Language.

    ERIC Educational Resources Information Center

    Pollard, David E.

    1993-01-01

    Discusses how the use of body language in Chinese fiction strikes most Westerners as unusual, if not strange. Considers that, although this may be the result of differences in gestures or different conventions in fiction, it is a problem for translators, who handle the differences by various strategies, e.g., omission or expansion. (NKA)

  15. "The Bohemian Life": Opera and Gifted Education.

    ERIC Educational Resources Information Center

    White, David A.; Sprague, Cynthia

    2002-01-01

    This article discusses how a social studies teacher taught her middle school students about the components of an opera and prepared her students for putting on an opera. The development of the opera and how the opera training related to the social studies, language arts, and music curriculum are addressed. (Contains 1 reference.) (CR)

  16. Lewy bodies

    PubMed Central

    Shults, Clifford W.

    2006-01-01

    Lewy bodies (LB) in the substantia nigra are a cardinal pathological feature of Parkinson's disease, but they occur in a number of neurodegenerative diseases and can be widespread in the nervous system. The characteristics, locations, and composition of LB are reviewed, with particular attention to α-synuclein (α-SYN), which appears to be the major component of LB. The propensity for α-SYN, a presynaptic protein widely expressed in the brain, to aggregate is because of an amyloidogenic central region. The factors that favor the aggregation of α-SYN and mechanisms of toxicity are examined, and a mechanism through which aggregates of α-SYN could induce mitochondrial dysfunction and/or release of proapoptotic molecules is proposed. PMID:16449387

  17. 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

  18. [Multifaceted body. I. The bodies of medicine].

    PubMed

    Saraga, M; Bourquin, C; Wykretowicz, H; Stiefel, F

    2015-02-11

    The human body is the object upon which medicine is acting, but also lived reality, image, symbol, representation and the object of elaboration and theory. All these elements which constitute the body influence the way medicine is treating it. In this series of three articles, we address the human body from various perspectives: medical (1), phenomenological (2), psychosomatic and socio-anthropological (3). This first article discusses four distinct types of representation of the body within medicine, each related to a specific epistemology and shaping a distinct kind of clinical legitimacy: the body-object of anatomy, the body-machine of physiology, the cybernetic body of biology, the statistical body of epidemiology.

  19. Body Image and Body Contouring Procedures.

    PubMed

    Sarwer, David B; Polonsky, Heather M

    2016-10-01

    Dissatisfaction with physical appearance and body image is a common psychological phenomena in Western society. Body image dissatisfaction is frequently reported by those who have excess body weight, but also is seen in those of normal body weight. For both groups of individuals, this dissatisfaction impacts self-esteem and quality of life. Furthermore, it is believed to be the motivational catalyst to a range of appearance-enhancing behaviors, including weight loss efforts and physical activity. Body image dissatisfaction is also believed to play a role in the decision to seek the wide range of body contouring procedures offered by aesthetic physicians. Individuals who seek these procedures typically report increased body image dissatisfaction, focus on the feature they wish to alter with treatment, and often experience improvement in body image following treatment. At the same time, extreme body image dissatisfaction is a symptom of a number of recognized psychiatric disorders. These include anorexia nervosa, bulimia nervosa, and body dysmorphic disorder (BDD), all of which can contraindicate aesthetic treatment. This special topic review paper provides an overview of the relationship between body image dissatisfaction and aesthetic procedures designed to improve body contouring. The review specifically focuses on the relationship of body image and body weight, as well as the presentation of body image psychopathology that would contraindicate aesthetic surgery. The overall goal of the paper is to highlight the clinical implications of the existing research and provide suggestions for future research on the psychological aspects of body contouring procedures.

  20. [Multifaceted body. 2. The lived body].

    PubMed

    Wykretowicz, H; Saraga, M; Bourquin, C; Stiefel, F

    2015-02-11

    The human body is the object upon which medicine is acting, but also lived reality, image, symbol, representation and the object of elaboration and theory. All these elements which constitute the body influence the way medicine is treating it. In this series of three articles, we address the human body from various perspectives: medical (1), phenomenological (2), psychosomatic and socio-anthropological (3). This second article distinguishes between the body as an object of knowledge or representation and the way the body is lived. This distinction which originates in phenomenological psychiatry aims to understand how the patient experiences his body and to surpass the classical somatic and psychiatric classifications.

  1. Timing of Early Proterozoic collisional and extensional events in the granulite-gneiss-charnockite-granite complex, Lake Baikal, USSR: A U-Pb, Rb-Sr, and Sm-Nd isotopic study

    SciTech Connect

    Aftalion, M. ); Bibikova, E.V. ); Bowes, D.R. ); Hopwood, A.M. ); Perchuk, L.L. )

    1991-11-01

    In the Sharyzhalgay Complex of the Lake Baikal region in eastern Siberia Early Proterozoic collisional and extensional events were separated by ca. 100 m.yr. The earlier collisional event, associated with the development of granulites and gneisses as the result of high-grade dynamothermal metamorphism, took place close to 1965 {plus minus} 4 Ma. A {sup 207}Pb/{sup 204}Pb vs. {sup 206}Pb/{sup 204}Pb isochron for zircon from five size fractions and a six point Rb-Sr whole-rock errorchron give generally corresponding ages of 1956 {plus minus} 8 and 1963 {plus minus} 163 Ma, respectively. The later extensional event, associated with charnockitization due to the uprise of fluids and heat in a regime corresponding to the middle to upper crustal levels of a Basin and Range-type province, was initiated in the 1880-1860 Ma period. The event was continued with magmatic emplacement of granitic masses into the deep levels of caldera-like structures, possibly during the upper time range of lower concordia intercept ages of 1817 +30/{minus}32 and 1797 +40/{minus}44 Ma for two distinctly different zircon populations in a pyroxene-bearing granodiorite interpreted as an evolved (and contaminated) product of the mantle-derived magma that was the source of CO{sub 2} involved in the charnockitization. Upper intercept ages of 2784 +48/{minus}45 and 2775 +61/{minus}55 Ma indicate late Archean crust at depth as the source region of the incorporated zircon. T{sub DM} ages from Sm-Nd isotopic data show that the protolith of the lithologically layered supracrustal assemblage, subsequently polyphase deformed and polymetamorphosed in Early Proterozoic times, was also formed in Early Proterozoic (not Archean) times.

  2. The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India

    NASA Astrophysics Data System (ADS)

    Das, Kaushik; Tomioka, Naotaka; Bose, Sankar; Ando, Jun-ichi; Ohnishi, Ichiro

    2017-06-01

    We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91-1.94Fe0.06-0.07Ca<0.01) (P0.99-1.00O4)(OH0.02-0.17F0.98-0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites ( 1000 °C, 8-9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800-850 °C, 6-6.5 kbar) as deduced from their pressure -temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with high X Mg and/or fO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.

  3. The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India

    NASA Astrophysics Data System (ADS)

    Das, Kaushik; Tomioka, Naotaka; Bose, Sankar; Ando, Jun-ichi; Ohnishi, Ichiro

    2016-09-01

    We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91-1.94Fe0.06-0.07Ca<0.01) (P0.99-1.00O4)(OH0.02-0.17F0.98-0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites (~1000 °C, 8-9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800-850 °C, 6-6.5 kbar) as deduced from their pressure-temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with high X Mg and/or fO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.

  4. [Perspectives on body: embodiment and body image].

    PubMed

    Chang, Shiow-Ru; Chao, Yu-Mei Yu

    2007-06-01

    "Body" is a basic concept of both the natural and human sciences. This extensive review of the literature explores the various philosophical approaches to the body, including empiricism, idealism, existentialism and phenomenology, as well as the relationship between body and mind. Embodiment and body image are the two main concepts of body addressed in this article. Merleau-Ponty's perspective on embodiment, an important new area of theory development, emphasizes that embodiment research must focus on life experiences, such as the study of body image. Using Schilder's framework of psychosocialology, this article provides a comprehensive understanding of the concept of body image and women's perspectives on the "body" in both Western culture and Eastern cultures. Body size and shape significantly influence the self-image of women. Body image is something that develops and changes throughout one's life span and is continually being constructed, destructed, and reconstructed. Personal body image has important psychological effects on the individual, especially women. This integrative review can make a significant contribution to knowledge in this area and, consequently, to related practice and research.

  5. Sweating and Body Odor

    MedlinePlus

    Sweating and body odor Overview By Mayo Clinic Staff Sweating and body odor are facts of life for ... stress. Your body has two main types of sweat glands, and they produce two very different types ...

  6. Lewy Body Disease

    MedlinePlus

    Lewy body disease is one of the most common causes of dementia in the elderly. Dementia is the loss of mental ... to affect normal activities and relationships. Lewy body disease happens when abnormal structures, called Lewy bodies, build ...

  7. "You have no good blood in your body". Oral communication in sixteenth-century physicians' medical practice.

    PubMed

    Stolberg, Michael

    2015-01-01

    In his personal notebooks, the little known Bohemian physician Georg Handsch (1529-c. 1578) recorded, among other things, hundreds of vernacular phrases and expressions he and other physicians used in their oral interaction with patients and families. Based primarily on this extraordinary source, this paper traces the terms, concepts and images to which sixteenth-century physicians resorted when they explained the nature of a patient's disease and justified their treatment. At the bedside and in the consultation room, Handsch and his fellow physicians attributed most diseases to a local accumulation of impure, putrid or otherwise pathological humours. The latter were commonly said to result, in turn, from an insufficient concoction and assimilation of food and drink in the stomach and the liver or from an obstruction of the humoral flow inside the body and across its borders. By contrast, other notions and explanatory models, which had a prominent place in contemporary learned medical writing, hardly played a role at all in the physicians' oral communication. Specific disease terms were rarely used, a mere imbalance of the four natural humours in the body was almost never inculpated, and the patient's personal life-style and other non-naturals did not attract much attention either. These striking differences between the ways in which physicians explained the patients' diseases in their daily practice and the explanatory models we find in contemporary textbooks, are attributed, above all, to the physicians' precarious situation in the early modern medical marketplace. Since dissatisfied patients were quick to turn to another healer, physicians had to explain the disease and justify their treatment in a manner that was comprehensible to ordinary lay people and in line with their expectations and beliefs, which, at the time, revolved almost entirely around notions of impurity and evacuation.

  8. [Body image and body image distortion].

    PubMed

    Ábrahám, Ildikó; Jambrik, Máté; John, Balázs; Németh, Adrienn Réka; Franczia, Nóra; Csenki, Laura

    2017-05-01

    The aim of this literature review is to integrate the results of various studies regarding body image and body image distortion into a unified framework. The concept of body image is complex and can be interpreted from multiple points of view. The first part of the study touches upon different age characteristics, attentional focus on the body, the early and important role of the body in identity formation, specific features in adolescence, gender differences, and the often-observed stability of body image (distortion), which may be present as a (trait) marker throughout the lifespan. The second part focuses on the organization of body image. The results of different studies on cognitive information processing are reviewed, the question of perceptual accuracy is addressed and the concepts of embodiment are examined. The third topic is body image distortion. First, the concept is contextualized along different continua, then discussed in a clinical sense along with the complexity of diagnostic methods, as well as the state and trait aspects of body image distortion. Orv Hetil. 2017; 158(19): 723-730.

  9. [Multifaceted body. 3. The contextualised body].

    PubMed

    Bourquin, C; Wykretowicz, H; Saraga, M; Stiefel, F

    2015-02-11

    The human body is the object upon which medicine is acting, but also lived reality, image, symbol, representation and the object of elaboration and theory. All these elements which constitute the body influence the way medicine is treating it. In this series of three articles, we address the human body from various perspectives: medical (1), phenomenological (2), psychosomatic and socio-anthropological (3). This third and last article focuses on the psychosomatic and socio-anthropological facets of the body and their contribution to its understanding.

  10. Adolescence and Body Image.

    ERIC Educational Resources Information Center

    Weinshenker, Naomi

    2002-01-01

    Discusses body image among adolescents, explaining that today's adolescents are more prone to body image distortions and dissatisfaction than ever and examining the historical context; how self-image develops; normative discontent; body image distortions; body dysmorphic disorder (BDD); vulnerability of boys (muscle dysmorphia); who is at risk;…

  11. Adolescence and Body Image.

    ERIC Educational Resources Information Center

    Weinshenker, Naomi

    2002-01-01

    Discusses body image among adolescents, explaining that today's adolescents are more prone to body image distortions and dissatisfaction than ever and examining the historical context; how self-image develops; normative discontent; body image distortions; body dysmorphic disorder (BDD); vulnerability of boys (muscle dysmorphia); who is at risk;…

  12. Fine-scale isotopic heterogeneities and fluids in the deep crust: a 40Ar/ 39Ar laser ablation and TEM study of muscovites from a granulite-eclogite transition zone

    NASA Astrophysics Data System (ADS)

    Boundy, T. M.; Hall, C. M.; Li, G.; Essene, E. J.; Halliday, A. N.

    1997-04-01

    Spectacular exposures on Holsnøy Island, western Norway, reveal that eclogites formed in situ from adjacent anhydrous granulites as a result of the localized infiltration of fluids. Stepwise and laser 40Ar/ 39Ar experiments on muscovite from the eclogites have been used in conjunction with electron microprobe and transmission electron microscopy (TEM) analysis to examine the behavior of argon under high pressure metamorphism and subsequent cooling. Muscovites with 0.10-0.17Na/(Na + K) yield 40Ar/ 39Ar plateau and integrated ages in the range 450-465 Ma, 20-35 Myr older than 40Ar/ 39Ar muscovite plateau ages from adjacent eclogite samples. Laser 40Ar/ 39Ar analyses on ˜ 75 μm spots across two single muscovite grains from these samples are approximately uniform at 444.2 ± 1.9 (21 spots) and 443.3 ± 1.7 Ma (26 spots). However, incremental heating of high sodic (0.18-0.32 (Na/(Na + K)) muscovite failed to yield a plateau. Laser 40Ar/ 39Ar analyses of 100 areas from two single grains from this sample reveal complex two-dimensional patterns with variable apparent ages in the range of 445-625 Ma. Electron microprobe measurements obtained from one of the grains reveal that the paragonite content is also highly variable both parallel and perpendicular to (001). All the TEM bright field images obtained from this mica yield information consistent with a single homogeneous phyllosilicate phase, yet several of the selected area electron diffraction (SAED) analyses document locally intergrown muscovite and sodic muscovite, possibly in an exsolution relationship on a unit cell scale. Analytical electron microscopy (AEM) analyses obtained over a 5-100 nm scale on the same sample reveal great range and heterogeneity inNa/K, including pure muscovite, although no separate paragonite domains were found. In contrast, muscovite grains with consistent laser spot fusion and plateau ages show little heterogeneity inNa/K at the microprobe level. These data provide evidence of variable

  13. Avatar body dimensions and men's body image.

    PubMed

    Cacioli, Jon-Paul; Mussap, Alexander J

    2014-03-01

    Two online surveys examined the significance of the visual analogues, or 'avatars', men (total N=266) create and use online. Two-dimensional (adiposity×muscle) somatomorphic matrices revealed that avatars are generally thinner than their creator's actual body and similar to their ideal, but more muscular than either their actual or ideal. Men's ratings of the importance of their avatar's appearance correlated with their actual weight and muscle concerns, and disparity between their avatar and actual body dimensions predicted their offline context body change concerns additional to that accounted for by disparity between their ideal and actual bodies. Together with the observation that men also reported higher self-esteem, less social interaction anxiety and less social phobia while online (which correlated with the time they spent online), these results suggest that the physical dimensions of avatars used in social interactions online may serve a compensatory function. Copyright © 2013 Elsevier Ltd. All rights reserved.

  14. Media and Body Image

    MedlinePlus

    ... weight/body are not helpful.” What are the warning signs of an unhealthy body image? You may ... Legislative Priorities GR & Outreach State Advocacy Underserved Women Global Women's Health Council on Patient Safety For Patients ...

  15. Body Dysmorphic Disorder

    MedlinePlus

    ... compulsive disorder. Environment. Your environment, life experiences and culture may contribute to body dysmorphic disorder, especially if they involve negative social evaluations about your body or self-image, or ...

  16. Lewy Body Dementia

    MedlinePlus

    ... People with Lewy body dementia may experience visual hallucinations, and changes in alertness and attention. Other effects ... body dementia signs and symptoms may include: Visual hallucinations. Hallucinations may be one of the first symptoms, ...

  17. Stereometric body volume measurement

    NASA Technical Reports Server (NTRS)

    Herron, R. E.

    1975-01-01

    The following studies are reported: (1) effects of extended space flight on body form of Skylab astronauts using biostereometrics; (2) comparison of body volume determinations using hydrostatic weighing and biostereometrics; and (3) training of technicians in biostereometric principles and procedures.

  18. BAM! Body and Mind

    MedlinePlus

    ... Search Controls Search Form Controls Cancel Submit BAM! Body and Mind Note: Javascript is disabled or is not supported ... please visit this page: About CDC.gov . BAM! Body and Mind Diseases Disease Detectives Immune Platoon Learn How Your ...

  19. Literacies in the Body

    ERIC Educational Resources Information Center

    Jones, Stephanie

    2013-01-01

    In this commentary, the author invites readers to consider the body and its central place in literacy pedagogy, practice and research. She emphasizes two interrelated paths for teachers and researchers interested in literacies to tend to the body: (1) the ways literacies are engaged and cultivated for making sense of bodies, and (2) the literacies…

  20. Literacies in the Body

    ERIC Educational Resources Information Center

    Jones, Stephanie

    2013-01-01

    In this commentary, the author invites readers to consider the body and its central place in literacy pedagogy, practice and research. She emphasizes two interrelated paths for teachers and researchers interested in literacies to tend to the body: (1) the ways literacies are engaged and cultivated for making sense of bodies, and (2) the literacies…

  1. [Foreign Body in Esophagus].

    PubMed

    Domeki, Yasushi; Kato, Hiroyuki

    2015-07-01

    An esophageal foreign body is the term for a foreign body in the esophagus. The 2 age groups most prone to this condition are children age 9 and under (and especially toddlers age 4 and under) and elderly individuals age 70 and over. A foreign body often lodges where the esophagus is most constricted. In toddlers, the foreign body is often currency or coins or a toy. In adults, the body is often a piece of fish, dentures, a piece of meat, a pin or needle, or a drug in its blister pack packaging. In children, an esophageal foreign body is treated by fluoroscopically guided removal of the body with a balloon catheter or magnetic catheter or removal of the body via endoscopy or direct esophagoscopy under general anesthesia. In adults, the best choice for treating an esophageal foreign body is removing the body with an endoscope but there are instances where surgery is performed because the body is hard to remove endoscopically, a puncture has occurred, or empyema or mediastinitis has developed. This paper reviews the diagnosis and treatment of an esophageal foreign body.

  2. Densified Carbonaceous bodies

    SciTech Connect

    Hucke, E.E.

    1990-01-16

    This patent describes a densified carbonaceous body. It comprises: a permeable carbonaceous body, the pores of the body being filled with the pyrolyzation product of a resin obtained by polymerizing a liquid impregnant containing furfural, furfural alcohol or a mixture thereof, an acid catalyst, and a glycol of mixture of glycols.

  3. PML nuclear bodies.

    PubMed

    Lallemand-Breitenbach, Valérie; de Thé, Hugues

    2010-05-01

    PML nuclear bodies are matrix-associated domains that recruit an astonishing variety of seemingly unrelated proteins. Since their discovery in the early 1960s, PML bodies have fascinated cell biologists because of their beauty and their tight association with cellular disorders. The identification of PML, a gene involved in an oncogenic chromosomal translocation, as the key organizer of these domains drew instant interest onto them. The multiple levels of PML body regulation by a specific posttranslational modification, sumoylation, have raised several unsolved issues. Functionally, PML bodies may sequester, modify or degrade partner proteins, but in many ways, PML bodies still constitute an enigma.

  4. PML Nuclear Bodies

    PubMed Central

    Lallemand-Breitenbach, Valérie; de Thé, Hugues

    2010-01-01

    PML nuclear bodies are matrix-associated domains that recruit an astonishing variety of seemingly unrelated proteins. Since their discovery in the early 1960s, PML bodies have fascinated cell biologists because of their beauty and their tight association with cellular disorders. The identification of PML, a gene involved in an oncogenic chromosomal translocation, as the key organizer of these domains drew instant interest onto them. The multiple levels of PML body regulation by a specific posttranslational modification, sumoylation, have raised several unsolved issues. Functionally, PML bodies may sequester, modify or degrade partner proteins, but in many ways, PML bodies still constitute an enigma. PMID:20452955

  5. [Disorders of body schema].

    PubMed

    Tsuruya, Natsuko; Kobayakawa, Mutsutaka

    2014-04-01

    A variety of disorders have been associated with the concept of body schema. However, this concept has been interpreted in many ways, and there is no consensus on the nature and cognitive mechanisms of body schema. Historically, two major issues have been discussed. One was the body-specificity of the body schema, and the other was the relationship between input and output modality. Autotopagnosia, an inability to localize and orient different parts of the body, has been a focus of attention because it is thought to provide insight into the function of body schema. Although there have not been many cases of pure autotopagnosia, a double dissociation indicating the independence of body-specific system. There are a few working hypotheses for cognitive models of body schema, which can explain the different types of autotopagnosia. One model includes multiple representation subsystems for body processing, while another assumes the use of intrinsic and extrinsic egocentric coordinates to maintain on-line processing for body state. The consistency of these accounts should be examined in light of extensive neuroimaging and psychological data, to construct a plausible model for body schema.

  6. Large meteor bodies

    NASA Astrophysics Data System (ADS)

    Terentjeva, A. K.

    A population of 69 large meteor bodies with extra-atmospheric masses from several kilograms up to several tens of tons detected from photographic observations of bright fireballs of Prairie and European networks is investigated. A half of these objects are "meteorite producers". A relationship between large meteor bodies and meteor streams is analysed. A unique group of meteorite producers moving along extremely short period orbits is considered. Orbits of these bodies are entirely located inside the Earth's orbit similarly to the orbits of system of the Eccentrid meteor bodies, has been discovered by the author in 1981. Interrelationship between all of these bodies and meteor streams is investigated. Some associations have been revealed. Families may exist inside the complex of minor bodies which consist of meteor streams, asteroids of Aten, Apollo and Amor type and large meteor bodies, including meteorite producers.

  7. Petrogenesis of metaophiolitic granulites from SE Anatolia

    NASA Astrophysics Data System (ADS)

    Awalt, Mitchell Burgess

    The problem of synthesizing online optimal flight controllers in the presence of multiple objectives is considered. A hybrid adaptive-optimal control architecture is presented, which is suitable for implementation on systems with fast, nonlinear and uncertain dynamics subject to constraints. The problem is cast as an adaptive Multi-Objective Optimization (MO-Op) flight control problem wherein control policy is sought that attempts to optimize over multiple, sometimes conflicting objectives. A solution strategy utilizing Gaussian Process (GP)-based adaptive-optimal control is presented, in which the system uncertainties are learned with an online updated budgeted GP. The mean of the GP is used to feedback-linearize the system and reference model shaping Model Predictive Control (MPC) is utilized for optimization. To make the MO-Op problem online-realizable, a relaxation strategy that poses some objectives as adaptively updated soft constraints is proposed. The strategy is validated on a nonlinear roll dynamics model with simulated state-dependent flexible-rigid mode interaction. In order to demonstrate low probability of failure in the presence of stochastic uncertainty and state constraints, we can take advantage of chance-constrained programming in Model Predictive Control. The results for the single objective case of chance-constrained MPC is also shown to reflect the low probability of constraint violation in safety critical systems such as aircrafts. Optimizing the system over multiple objectives is only one application of the adapive-optimal controller. Another application we considered using the adaptive-optimal controller setup is to design an architecture capable of adapting to the dynamics of different aerospace platforms. This architecture brings together three key elements, MPC-based reference command shaping, Gaussian Process (GP)-based Bayesian nonparametric Model Reference Adaptive Control (MRAC) which both were used in the previous application as well, and online GP clustering over nonstationary (time-varying) GPs. The key salient feature of our architecture is that not only can it detect changes, but it uses online GP clustering to enable the controller to utilize past learning of similar models to significantly reduce learning transients. Stability of the architecture is argued theoretically and performance is validated empirically.

  8. The Athletic Body.

    PubMed

    Edgar, Andrew

    2016-09-10

    This paper seeks to explore the attraction and the beauty of the contemporary athletic body. It will be suggested that a body shaped through muscular bulk and definition has come to be seen as aesthetically normative. This body differs from the body of athletes from the early and mid-twentieth century. It will be argued that the contemporary body is not merely the result of advances in sports science, but rather that it is expressive of certain meanings and values. The visual similarity of the contemporary athletic body and that of the comic book superhero suggests that both bodies carry a similar potential for narrative story-telling, and that their attraction is bound up with this narrative potential. The superhero and athlete live meaningful lives, pursuing clear and morally unambiguous goals. The aesthetic attraction of the body lies in its capacity to facilitate the articulation of a story of a meaningful life, and to do so in the face of the growing anomie and thus meaninglessness of life as experienced in contemporary society. Athleticism offers an illusion of meaning, serving to reproduce dominant justificatory narratives and social stereotypes. Yet, as an illusion of meaning, it may be challenged and negotiated, not least with respect to its bias towards a certain form of the male body. The female athletic body disrupts the illusion, opening up new existential possibilities, new ways of living and being, and thus new, and potentially disruptive, narratives.

  9. In situ Pb-Pb dating of rutile from slowly cooled granulites by LA-MC-ICP-MS: confirmation of the high closure temperature (>=600°C) for Pb diffusion in rutile

    NASA Astrophysics Data System (ADS)

    Vry, J.; Baker, J.; Waight, T.

    2003-04-01

    We have analysed Pb isotopes in natural rutile crystals by laser ablation MC-ICP-MS to assess the potential of rapid Pb-Pb dating of rutile with this method. The rutile samples are from granulite-facies Mg- and Al-rich rocks from the Reynolds Range, Northern Territory, Australia. This metamorphic terrane has a well-constrained high-T cooling history (ca. 3^oC/Myr) defined by previous U-Pb dating of monazite and zircon (peak metamorphism at 1584 Ma), which we have supplemented with additional Rb-Sr dates of phlogopite, biotite and muscovite. The dated rutiles vary in size from 3 to 0.05 mm, have Pb concentrations of ca. 20 ppm, and were analysed with a 266 nm laser coupled to an AXIOM MC-ICP-MS (spot size of 200-50 μm). Individual larger crystals (>= 200 μm) exhibit sufficient Pb isotopic heterogeneity (206Pb/204Pb = 10000-80000) to perform isochron calculations on several short analyses of a single grain (30-60 s). The largest rutiles yielded Pb-Pb isochron ages of 1540-1555 Ma with typical uncertainties of ± 1 to 10 Ma. 207Pb/206Pb ages are typically within 1% of the Pb-Pb isochron ages testifying to the radiogenic nature of Pb in the rutile. A mean age for all the analysed rutiles was 1548.4 ± 9.1 Ma (n = 33). Comparable 207Pb/206Pb ages were also obtained from individual smaller crystals (50 μm) where the 204Pb ion beam could not be measured precisely. The results demonstrate that even small rutile crystals are extremely resistant to isotopic resetting, and that this mineral is a high-T chronometer. Phlogopite and muscovite Rb-Sr ages are <1454 and 1400-1480 Ma, respectively, with some of the phlogopite and biotite micas having been partially reset by later thermal events younger than 400 Ma. All the mica ages are considerably younger (100-70 My) than the rutile ages, which approach U-Pb ages for monazite and zircon overgrowths, even though the mica closure temperatures (350-500^oC) are comparable or slightly higher than earlier geological estimates [1] of

  10. Religion and body weight.

    PubMed

    Kim, K H; Sobal, J; Wethington, E

    2003-04-01

    Relationships between religion and body weight were examined in a US national sample. Data from the National Survey of Midlife Development in the United States (MIDUS), collected through telephone and postal questionnaires, were analyzed for 3032 adults aged 25-74. Religious denomination was significantly related to higher body weight in men after accounting for sociodemographic controls. Conservative Protestant men had a 1.1 +/- 0.45 higher body mass index (BMI) than those reporting no religious affiliation. Other religion variables that initially had significant relationships with greater body weight before adjusting for control variables became nonsignificant after smoking was controlled. No significant relationships between religion and body weight were present in women. Religious denomination was related to body weight in men. Other dimensions of religiosity showing a relationship with higher BMI appeared to be because of the lower rates of smoking among more religious individuals.

  11. My body, my property.

    PubMed

    Andrews, L B

    1986-10-01

    Two recent cases raise the question: Should the body be considered a form of property? Patients generally do not share in the profits derived from the applications of research on their body parts and products. Nor is their consent for research required so long as the body part is unidentified and is removed in the course of treatment. A market in body parts and products would require consent to all categories of research and ensure that patients are protected from coercion and given the chance to be paid fairly for their contributions. Such a market might force us to rethink our policies prohibiting organ sales. Donors, recipients, and society will benefit from a market in body parts so long as owners--and no one else--retain control over their bodies.

  12. Portable Body Temperature Conditioner

    DTIC Science & Technology

    2013-10-18

    also have decreased thermoregulation due to blood loss. Normal core body temperature is defined as 37oC and core body temperature below 35oC and above...environmental exposure during transport and decreased ability of thermoregulation due to blood loss. Normal core body temperature is defined at 37oC and...require efficient and reliable equipment for the thermoregulation of either injured or ill patients. However, effective methods for warming/cooling

  13. Portable Body Temperature Conditioner

    DTIC Science & Technology

    2012-10-01

    thermoregulation due to blood loss. Normal core body temperature is defined as 37 o C and core body temperature below 35 o C and above 40 o C is defined as...environmental exposure during transport and decreased ability of thermoregulation due to blood loss. Normal core body temperature is defined at 37 o...medical installations require efficient and reliable equipment for the thermoregulation of either injured or ill patients. However, effective methods for

  14. Body, biometrics and identity.

    PubMed

    Mordini, Emilio; Massari, Sonia

    2008-11-01

    According to a popular aphorism, biometrics are turning the human body into a passport or a password. As usual, aphorisms say more than they intend. Taking the dictum seriously, we would be two: ourself and our body. Who are we, if we are not our body? And what is our body without us? The endless history of identification systems teaches that identification is not a trivial fact but always involves a web of economic interests, political relations, symbolic networks, narratives and meanings. Certainly there are reasons for the ethical and political concerns surrounding biometrics but these reasons are probably quite different from those usually alleged.

  15. Vehicle body cover

    SciTech Connect

    Hirose, T.

    1987-01-13

    This patent describes a vehicle body covered with a vehicle body cover which comprises: a front cover part, a rear cover part, a pair of side cover parts, and a roof cover part: the front cover part having portions adapted to cover only a hood, an area around a windshield and tops of front fenders of a vehicle body. The portion covering the hood is separated from the portions covering the tops of the fenders by cuts in the front cover part, the front cover part having an un-cut portion corresponding to a position at which the hood is hinged to the car body. The front cover part has a cut-out at a position corresponding to the windshield of the vehicle body and the front cover part has at least one cut-out at a position corresponding to where a rear view mirror is attached to the vehicle body; and the rear cover part having portions adapted to cover an area around a rear window, a trunk lid and a rear end of the vehicle body, the portion covering the trunk lid separated from the rest of the rear cover part by cuts corresponding to three sides of the trunk lid and an un-cut portion corresponding to a position at which the trunk lid is hinged to the vehicle body. The rear cover part has a hole at position corresponding to a trunk lid lock, a cut-out portion at a position corresponding to the rear window of the vehicle body, a cut-out at a position corresponding to a license plate of the vehicle body and cut-outs at positions corresponding to rear taillights of the vehicle body.

  16. Guy's Guide to Body Image

    MedlinePlus

    ... Healthy Breakfasts Shyness A Guy's Guide to Body Image KidsHealth > For Teens > A Guy's Guide to Body ... image can be a problem. Why Is Body Image Important? Body image is a person's opinions, thoughts, ...

  17. Disorders of body temperature.

    PubMed

    Gomez, Camilo R

    2014-01-01

    The human body generates heat capable of raising body temperature by approximately 1°C per hour. Normally, this heat is dissipated by means of a thermoregulatory system. Disorders resulting from abnormally high or low body temperature result in neurologic dysfunction and pose a threat to life. In response to thermal stress, maintenance of normal body temperature is primarily maintained by convection and evaporation. Hyperthermia results from abnormal temperature regulation, leading to extremely elevated body temperature while fever results from a normal thermoregulatory mechanism operating at a higher set point. The former leads to specific clinical syndromes with inability of the thermoregulatory mechanism to maintain a constant body temperature. Heat related illness encompasses heat rash, heat cramps, heat exhaustion and heat stroke, in order of severity. In addition, drugs can induce hyperthermia and produce one of several specific clinical syndromes. Hypothermia is the reduction of body temperature to levels below 35°C from environmental exposure, metabolic disorders, or therapeutic intervention. Management of disorders of body temperature should be carried out decisively and expeditiously, in order to avoid secondary neurologic injury. © 2014 Elsevier B.V. All rights reserved.

  18. The Body Bites Back!

    ERIC Educational Resources Information Center

    Alsop, Steve

    2011-01-01

    How should we think about the body in science education? What ought it mean to be alive and live within epistemologies and pedagogies? What does it mean to be human in science education? In response to Auli Arvola Orlander and Per-Olof Wickram's article, this essay explores some of the possibilities and questions that the body evokes in science…

  19. [Body and philosophy].

    PubMed

    Paturet, Jean-Bernard

    2011-06-01

    Reflections on the body and its representations have marked every era throughout the history of mankind. Philosophical, religious, political, social, etc. the body is multi-faceted. It is a "living object" which is part of the fabric of the world.

  20. Body satisfaction during pregnancy.

    PubMed

    Loth, Katie A; Bauer, Katherine W; Wall, Melanie; Berge, Jerica; Neumark-Sztainer, Dianne

    2011-06-01

    The current study examines how body satisfaction of pregnant women compares to that of nonpregnant women. The sample included 68 pregnant and 927 nonpregnant young women who participated in a population-based longitudinal study examining eating and weight concerns in young adults. Body satisfaction was assessed using a 10-item modified version of the Body Shape Satisfaction Scale. The longitudinal design allowed for the assessment of body satisfaction among women both prior to and during their pregnancy. Mean body satisfaction was higher in pregnant women (32.6, 95% CI: 30.7-34.5) than nonpregnant women (29.6, 95% CI: 29.1-30.1) with moderate effect size 0.32, after adjusting for body satisfaction and body mass index prior to pregnancy, indicating that pregnant women experienced a significant increase in body satisfaction from the time prior to their pregnancy (p=.003) despite weight gain. These findings have important implications for clinicians delivering weight-related messages to women during pregnancy. Published by Elsevier Ltd.

  1. Porous body infiltrating method

    DOEpatents

    Corman, Gregory Scot

    2002-01-01

    A mixture is formed that comprises at least some to about 10 wt % boron nitride and silicon. A body comprising a component that is wetted by or reacts with silicon is contacted with the mixture and the contacted body is infiltrated with silicon from the mixture.

  2. The Cajal Body and Histone Locus Body

    PubMed Central

    Nizami, Zehra; Deryusheva, Svetlana; Gall, Joseph G.

    2010-01-01

    The Cajal body (CB) is a nuclear organelle present in all eukaryotes that have been carefully studied. It is identified by the signature protein coilin and by CB-specific RNAs (scaRNAs). CBs contain high concentrations of splicing small nuclear ribonucleoproteins (snRNPs) and other RNA processing factors, suggesting that they are sites for assembly and/or posttranscriptional modification of the splicing machinery of the nucleus. The histone locus body (HLB) contains factors required for processing histone pre-mRNAs. As its name implies, the HLB is associated with the genes that code for histones, suggesting that it may function to concentrate processing factors at their site of action. CBs and HLBs are present throughout the interphase of the cell cycle, but disappear during mitosis. The biogenesis of CBs shows the features of a self-organizing structure. PMID:20504965

  3. The body as art.

    PubMed

    Barker, D J; Barker, M J

    2002-07-01

    For millennia people have altered the appearance of their bodies with cosmetics, jewellery, tattoos, piercings, and other surgical procedures. It would appear that they wish to conform to a perceived 'ideal body', although the actual appearance of such a body is subject to temporal, cultural and geographical change. In contemporary society the media are largely responsible for providing the yardsticks against which individual body shape is measured. Today the desired form is generally young, slim, tanned and blemish-free. Sadly, dissatisfaction with body image can be the source of great unhappiness and may even lead to suicide. Interested scholars have debated the meaning of beauty for centuries but it seems that every human society has its own standards. At the simplest it would appear that youth and symmetry are the most highly prized ingredients. There is no doubt that those who fit the conventional standards of attractiveness are treated better by society. Individuals have an inalienable right to their own body appearance, and to alter it as they see fit, however such modifications may not always be in their own best interests. Practitioners of cosmetic procedures must be alert to clients with histories of weight fluctuation, unrealistic body image, or low self-esteem. Psychological disorders may present with dysmorphophobic symptoms. Doctors providing cosmetic services need to be adept at diagnosing psychological illness.

  4. Railway vehicle body structures

    SciTech Connect

    Not Available

    1985-01-01

    The strength and durability of railway vehicle structures is a major topic of engineering research and design. To reflect this importance the Railway Division of the Institution of Mechanical Engineers organised a conference to discuss all matters relating to railway vehicle design. This book presents the papers discussed in that conference. The contents include: Vehicle body design and the UIC's international contribution; LUL prototype 1986 stock - body structure; vehicle structure for the intermediate capacity transmit system vehicles; car body technology of advanced light rapid transit vehicles; concepts, techniques and experience in the idealization of car body structures for finite element analysis; Calcutta metropolitan railway; design for a lightweight diesel multiple unit body; the design of lightweight inter-city coal structures; the BREL international coach body shell structure; new concepts and design techniques versus material standards; structures of BR diesel electric freight locomotives; structural design philosophy for electric locomotives; suspension design for a locomotive with low structural frequencies; freight wagon structures; a finite element study of coal bodyside panels including the effects of joint flexibility; a fresh approach to the problem of car body design strength; energy absorption in automatic couplings and draw gear; passenger vehicle design loads and structural crashworthiness; design of the front part of railway vehicles (in case of frontal impact); the development of a theoretical technique for rail vehicle structural crashworthiness.

  5. Rushton bodies: an update.

    PubMed

    Babburi, Suresh; Rudraraju, Amrutha Rajesh; V, Aparna; P, Sowjanya

    2015-02-01

    Rushton bodies are peculiar, eosinophilic, linear, curved or straight, polycyclic, glassy structures occurring with variable frequency in the epithelial lining of odontogenic cysts, whose presence occasionally contributes to the diagnosis. Presence of these structures depends upon the sectioning plane of specimen. They are easily identifiable by their peculiar morphological and staining patterns. There is considerably ambiguity about the nature and epithelial, vascular, odontogenic or keratinous origin of these hyaline bodies. This article highlights the occurrence, light and electron microscopic features and histogenesis of Rushton bodies.

  6. Rushton Bodies: An Update

    PubMed Central

    Rudraraju, Amrutha Rajesh; V, Aparna; P, Sowjanya

    2015-01-01

    Rushton bodies are peculiar, eosinophilic, linear, curved or straight, polycyclic, glassy structures occurring with variable frequency in the epithelial lining of odontogenic cysts, whose presence occasionally contributes to the diagnosis. Presence of these structures depends upon the sectioning plane of specimen. They are easily identifiable by their peculiar morphological and staining patterns. There is considerably ambiguity about the nature and epithelial, vascular, odontogenic or keratinous origin of these hyaline bodies. This article highlights the occurrence, light and electron microscopic features and histogenesis of Rushton bodies PMID:25859536

  7. Magnetic human body communication.

    PubMed

    Park, Jiwoong; Mercier, Patrick P

    2015-01-01

    This paper presents a new human body communication (HBC) technique that employs magnetic resonance for data transfer in wireless body-area networks (BANs). Unlike electric field HBC (eHBC) links, which do not necessarily travel well through many biological tissues, the proposed magnetic HBC (mHBC) link easily travels through tissue, offering significantly reduced path loss and, as a result, reduced transceiver power consumption. In this paper the proposed mHBC concept is validated via finite element method simulations and measurements. It is demonstrated that path loss across the body under various postures varies from 10-20 dB, which is significantly lower than alternative BAN techniques.

  8. Body Fluids Monitor

    NASA Technical Reports Server (NTRS)

    Siconolfi, Steven F. (Inventor)

    2000-01-01

    Method and apparatus are described for determining volumes of body fluids in a subject using bioelectrical response spectroscopy. The human body is represented using an electrical circuit. Intra-cellular water is represented by a resistor in series with a capacitor; extra-cellular water is represented by a resistor in series with two parallel inductors. The parallel inductors represent the resistance due to vascular fluids. An alternating, low amperage, multifrequency signal is applied to determine a subject's impedance and resistance. From these data, statistical regression is used to determine a 1% impedance where the subject's impedance changes by no more than 1% over a 25 kHz interval. Circuit component, of the human body circuit are determined based on the 1% impedance. Equations for calculating total body water, extra-cellular water, total blood volume, and plasma volume are developed based on the circuit components.

  9. BODY ENERGY HOMEOSTASIS

    PubMed Central

    Keesey, Richard E.; Powley, Terry L.

    2008-01-01

    Evidence for the regulation of body energy is reviewed from the homeostatic perspective of Claude Bernard and Walter Cannon. Considered are the complementary roles of food intake and energy expenditure in the maintenance and defense of energy balance. Particular attention is paid to the roles adjustments in energy expenditure play in this process and to recent investigations identifying their metabolic underpinnings. This is followed by a consideration of the many newly-identified signals of body energy status and the pathways and feedback loops they utilize to inform the central regulating system. Finally, various naturally-occurring and experimentally-induced alterations in the regulated level of body energy are described and discussed. It is concluded that, though early investigators did not expressly consider energy a regulated feature of the milieu interieur, more recent research has provided a sound basis for judging the regulation of body energy to be another homeostatic process. PMID:18647629

  10. Spray Sprinkler Bodies

    EPA Pesticide Factsheets

    Landscape irrigation sprinklers are often installed at sites where the system pressure is higher than what is recommended for the sprinkler nozzle, which can lead to water waste. WaterSense labeled sprinkler bodies help control pressure.

  11. Bodies, rights and abortion.

    PubMed

    McLachlan, H V

    1997-06-01

    The issue of abortion is discussed with reference to the claim that people have a right of control over their own bodies. Do people "own" their own bodies? If so, what would be entailed? These questions are discussed in commonsense terms and also in relation to the jurisprudence of Hohfeld, Honore, Munzer and Waldron. It is argued that whether or not women are morally and/or should be legally entitled to have abortions, such entitlements cannot be derived from a general moral entitlement to do what we will with our own bodies since there is no such entitlement. Whether or not we "own" them, we can have rights duties, liabilities, restrictions and disadvantages as well as rights concerning our own bodies.

  12. Multichannel Human Body Communication

    NASA Astrophysics Data System (ADS)

    Przystup, Piotr; Bujnowski, Adam; Wtorek, Jerzy

    2016-01-01

    Human Body Communication is an attractive alternative for traditional wireless communication (Bluetooth, ZigBee) in case of Body Sensor Networks. Low power, high data rates and data security makes it ideal solution for medical applications. In this paper, signal attenuation for different frequencies, using FR4 electrodes, has been investigated. Performance of single and multichannel transmission with frequency modulation of analog signal has been tested. Experiment results show that HBC is a feasible solution for transmitting data between BSN nodes.

  13. WELDED JACKETED URANIUM BODY

    DOEpatents

    Gurinsky, D.H.

    1958-08-26

    A fuel element is presented for a neutronic reactor and is comprised of a uranium body, a non-fissionable jacket surrounding sald body, thu jacket including a portion sealed by a weld, and an inclusion in said sealed jacket at said weld of a fiux having a low neutron capture cross-section. The flux is provided by combining chlorine gas and hydrogen in the intense heat of-the arc, in a "Heliarc" welding muthod, to form dry hydrochloric acid gas.

  14. Experience with Free Bodies

    NASA Technical Reports Server (NTRS)

    Butler, T. G.

    1985-01-01

    Some of the problems that confront an analyst in free body modeling, to satisfy rigid body conditions are discussed and with some remedies for these problems are presented. The problems of detecting these culprits at various levels within the analysis are examined. A new method within NASTRAN for checking the model for defects very early in the analysis without requiring the analyst to bear the expense of an eigenvalue analysis before discovering these defects is outlined.

  15. Beyond body mass index.

    PubMed

    Prentice, A M; Jebb, S A

    2001-08-01

    Body mass index (BMI) is the cornerstone of the current classification system for obesity and its advantages are widely exploited across disciplines ranging from international surveillance to individual patient assessment. However, like all anthropometric measurements, it is only a surrogate measure of body fatness. Obesity is defined as an excess accumulation of body fat, and it is the amount of this excess fat that correlates with ill-health. We propose therefore that much greater attention should be paid to the development of databases and standards based on the direct measurement of body fat in populations, rather than on surrogate measures. In support of this argument we illustrate a wide range of conditions in which surrogate anthropometric measures (especially BMI) provide misleading information about body fat content. These include: infancy and childhood; ageing; racial differences; athletes; military and civil forces personnel; weight loss with and without exercise; physical training; and special clinical circumstances. We argue that BMI continues to serve well for many purposes, but that the time is now right to initiate a gradual evolution beyond BMI towards standards based on actual measurements of body fat mass.

  16. [Dental foreign body sinusitis].

    PubMed

    Thévoz, F; Arza, A; Jaques, B

    2000-01-01

    Unilateral chronic maxillary sinusitis is frequently attributed to dental origin. The goal of this retrospective study is to determine the frequency of maxillary sinusitis due to a foreign body of dental origin and its characteristics. Review of 197 sinusitis cases with maxillary sinus involvement operated in our department from 1991 to 1999. Selection of the 17 cases preoperatively suspect to be due to a foreign body of dental origin. 9% of the 197 maxillary sinusitis were classified "odontogenic". Intra-sinusal foreign bodies were identified in 5%: 2% of dental origin, 1% dental or radicular remnants, 2% of "pseudo" foreign bodies of mycotic origin. Chronic maxillary sinusitis attributable to a dental foreign body is rare and overestimated. There exists an important disproportion between the number of intra-sinusal dental foreign bodies and the number of patients who are symptomatic. Treatment is surgical by oral antrotomy and/or endonasal meatotomy. Only a prospective study could give a real estimation of the proportion of symptomatic cases and determine the predisposing factors.

  17. Mind–body interventions

    PubMed Central

    Wahbeh, Helané; Elsas, Siegward-M.; Oken, Barry S.

    2010-01-01

    Objective Half of the adults in the United States use complementary and alternative medicine with mind–body therapy being the most commonly used form. Neurology patients often turn to their physicians for insight into the effectiveness of the therapies and resources to integrate them into their care. The objective of this article is to give a clinical overview of mind–body interventions and their applications in neurology. Methods Medline and PsychInfo were searched on mind–body therapies and neurologic disease search terms for clinical trials and reviews and published evidence was graded. Results Meditation, relaxation, and breathing techniques, yoga, tai chi, and qigong, hypnosis, and biofeedback are described. Mind–body therapy application to general pain, back and neck pain, carpal tunnel syndrome, headaches, fibromyalgia, multiple sclerosis, epilepsy, muscular dysfunction, stroke, aging, Parkinson disease, stroke, and attention deficit–hyperactivity disorder are reviewed. Conclusions There are several conditions where the evidence for mind–body therapies is quite strong such as migraine headache. Mind–body therapies for other neurology applications have limited evidence due mostly to small clinical trials and inadequate control groups. PMID:18541886

  18. The neural basis of body form and body action agnosia.

    PubMed

    Moro, Valentina; Urgesi, Cosimo; Pernigo, Simone; Lanteri, Paola; Pazzaglia, Mariella; Aglioti, Salvatore Maria

    2008-10-23

    Visual analysis of faces and nonfacial body stimuli brings about neural activity in different cortical areas. Moreover, processing body form and body action relies on distinct neural substrates. Although brain lesion studies show specific face processing deficits, neuropsychological evidence for defective recognition of nonfacial body parts is lacking. By combining psychophysics studies with lesion-mapping techniques, we found that lesions of ventromedial, occipitotemporal areas induce face and body recognition deficits while lesions involving extrastriate body area seem causatively associated with impaired recognition of body but not of face and object stimuli. We also found that body form and body action recognition deficits can be double dissociated and are causatively associated with lesions to extrastriate body area and ventral premotor cortex, respectively. Our study reports two category-specific visual deficits, called body form and body action agnosia, and highlights their neural underpinnings.

  19. [Body image as a process or object and body satisfaction].

    PubMed

    Zarek, Aleksandra

    2009-01-01

    This work focused on categorization of elements of body image viewed as an object or process, as well as on the relationship between body satisfaction and manner of perceiving the body. The study was carried out in 177 subjects aged 19 to 53 years (148 females and 29 males). Body image was measured with the Body Image Questionnaire based on the Body Cathexis Scale of P.F. Secord and S.J. Jourard. Participation was anonymous. The procedure of attributing an element of the body to the function scale or body parts scale was based on the method described by S. Franzoi. Elements of body image recognized as body parts were characterized in the context of appearance (static object), while elements of body image recognized as body functions were considered in the context of operation (dynamic process). This relationship, however, was not symmetrical as elements of the body not characterized as body functions could also be evaluated in the context of operation. The level of body satisfaction was associated with perception of an element of the body in the aspect of appearance or operation, whereas its perception as body part or body function was of lesser importance.

  20. Bacterial body plans

    PubMed Central

    Rieger, Tomáš; Neubauer, Zdeněk; Blahůšková, Anna; Cvrčková, Fatima

    2008-01-01

    The bacterium Serratia marcescens produces a plethora of multicellular shapes of different colorations on solid substrates, allowing immediate visual detection of varieties. Such a plasticity allows studies on multicellular community scale spanning two extremes, from well-elaborated individual colonies to undifferentiated cell mass. For a single strain and medium, we obtained a range of different multicellular bodies, depending on the layout of initial plating. Four principal factors affecting the morphogenetic pathways of such bodies can be distinguished: (1) amount, density and distribution pattern of founder cells; (2) the configuration of surrounding free medium; (3) the presence and character of other bacterial bodies sharing the same niche; and (4) self-perception, resulting in delimitation towards other bodies. The last feature results in an ability of well-formed multicellular individuals to maintain their identity upon a close mutual contact, as well as in spontaneous separation of cell masses in experimental chimeras. We propose an “embryo-like” colony model where multicellular bacterial bodies develop along genuine ontogenetic pathways inherent to the given species (clone), while external shaping forces (like nutrient gradients, pH, etc.,) exert not formative, but only regulative roles in the process. PMID:19513204

  1. Inclusion Body Myositis

    PubMed Central

    Dimachkie, Mazen M.; Barohn, Richard J.

    2012-01-01

    The idiopathic inflammatory myopathies are a group of rare disorders that share many similarities. These include dermatomyositis (DM), polymyositis (PM), necrotizing myopathy (NM), and sporadic inclusion body myositis (IBM). Inclusion body myositis is the most common idiopathic inflammatory myopathy after age 50 and it presents with chronic proximal leg and distal arm asymmetric mucle weakness. Despite similarities with PM, it is likely that IBM is primarily a degenerative disorder rather than an inflammatory muscle disease. Inclusion body myositis is associated with a modest degree of creatine kinase (CK) elevation and an abnormal electromyogram demonstrating an irritative myopathy with some chronicity. The muscle histopathology demonstrates inflammatory exudates surrounding and invading nonnecrotic muscle fibers often times accompanied by rimmed vacuoles. In this chapter, we review sporadic IBM. We also examine past, essentially negative, clinical trials in IBM and review ongoing clinical trials. For further details on DM, PM, and NM, the reader is referred to the idiopathic inflammatory myopathies chapter. PMID:23117948

  2. [Polar body diagnosis].

    PubMed

    Montag, M; van der Ven, K; van der Ven, H

    2009-01-01

    Polar body diagnosis (PBD) is a diagnostic method for the indirect genetic analysis of oocytes. Polar bodies are by-products of the meiotic cell cycle which have no influence on further embryo development. The biopsy of polar bodies can be accomplished either by zona drilling or laser drilling within a very short time period. The paternal contribution to the genetic constitution of the developing embryo cannot be diagnosed by PBD. The major application of PBD is the detection of maternally derived chromosomal aneuploidies and translocations in oocytes. For these indications, PBD may offer a viable alternative to blastomere biopsy as the embryo's integrity remains unaffected in contrast to preimplantation genetic diagnosis by blastomere biopsy. The fast development in the field of molecular diagnostics will also influence PBD and probably allow a more general diagnosis in the future.

  3. Hurling body wastes.

    PubMed

    1998-03-20

    Pennsylvania Governor Tom Ridge signed legislation toughening penalties for HIV-positive prisoners who spit or throw body wastes at corrections officers and police. The legislation creates three separate offenses: a second-degree felony for prisoners who cause others to come into contact with blood or body fluids, an aggravated harassment charge for the same conduct by HIV-negative prisoners, and stronger penalties for prisoners on death row or serving a life sentence. The bill is part of an overall revision of the State criminal laws.

  4. [Complications of body piercing].

    PubMed

    Friedrich, L; Madrid, C; Odman-Jaques, M; Yersin, B; Carnon, P N

    2014-03-19

    The trend of body piercing has grown in popularity in the past decade within the general population and especially among young adults. Complications of body piercing include local inflammation and infections, but severe complications are also possible and largely underestimated. People are usually not aware of the risks before making a piercing, and their medical history, medication and comorbidities are largely neglected by the people who realise the piercing. This article presents a review of the complications that a primary care physician may observe, for a patient who wishes to make a piercing, or presents complications due to the implementation of such a device.

  5. Women gaze behaviour in assessing female bodies: the effects of clothing, body size, own body composition and body satisfaction.

    PubMed

    Cundall, Amelia; Guo, Kun

    2017-01-01

    Often with minimally clothed figures depicting extreme body sizes, previous studies have shown women tend to gaze at evolutionary determinants of attractiveness when viewing female bodies, possibly for self-evaluation purposes, and their gaze distribution is modulated by own body dissatisfaction level. To explore to what extent women's body-viewing gaze behaviour is affected by clothing type, dress size, subjective measurements of regional body satisfaction and objective measurements of own body composition (e.g., chest size, body mass index, waist-to-hip ratio), in this self-paced body attractiveness and body size judgement experiment, we compared healthy, young women's gaze distributions when viewing female bodies in tight and loose clothing of different dress sizes. In contrast to tight clothing, loose clothing biased gaze away from the waist-hip to the leg region, and subsequently led to enhanced body attractiveness ratings and body size underestimation for larger female bodies, indicating the important role of clothing in mediating women's body perception. When viewing preferred female bodies, women's higher satisfaction of a specific body region was associated with an increased gaze towards neighbouring body areas, implying satisfaction might reduce the need for comparison of confident body parts; furthermore undesirable body composition measurements were correlated with a gaze avoidance process if the construct was less changeable (i.e. chest size) but a gaze comparison process if the region was more changeable (i.e. body mass index, dress size). Clearly, own body satisfaction and body composition measurements had an evident impact on women's body-viewing gaze allocation, possibly through different cognitive processes.

  6. Very Young Children's Body Image: Bodies and Minds under Construction

    ERIC Educational Resources Information Center

    Birbeck, David; Drummond, Murray

    2006-01-01

    In recent years research has recognised that notions of body image, body image ideals and body dissatisfaction develop much earlier than was once thought. Forty-seven children (25 male; 22 female) aged between 5 and 6 years were interviewed on three occasions over 12 months regarding their perceptions of body image. The interviews revealed…

  7. The "Body Beautiful": English Adolescents' Images of Ideal Bodies.

    ERIC Educational Resources Information Center

    Dittmar, Helga; Lloyd, Barbara; Dugan, Shaun; Halliwell, Emma; Jacobs, Neil; Cramer, Helen

    2000-01-01

    Two studies examine qualities capturing adolescents' images of ideal bodies for both genders. Data from questionnaires and discussions of photographs indicate that body-image ideals are multidimensional, show systematic gender differences, and become more conventional with age. Adolescents' own body mass links systematically to body-image…

  8. Body Mass Index

    PubMed Central

    Nuttall, Frank Q.

    2015-01-01

    The body mass index (BMI) is the metric currently in use for defining anthropometric height/weight characteristics in adults and for classifying (categorizing) them into groups. The common interpretation is that it represents an index of an individual’s fatness. It also is widely used as a risk factor for the development of or the prevalence of several health issues. In addition, it is widely used in determining public health policies.The BMI has been useful in population-based studies by virtue of its wide acceptance in defining specific categories of body mass as a health issue. However, it is increasingly clear that BMI is a rather poor indicator of percent of body fat. Importantly, the BMI also does not capture information on the mass of fat in different body sites. The latter is related not only to untoward health issues but to social issues as well. Lastly, current evidence indicates there is a wide range of BMIs over which mortality risk is modest, and this is age related. All of these issues are discussed in this brief review. PMID:27340299

  9. Porous metallic bodies

    DOEpatents

    Landingham, R.L.

    1984-03-13

    Porous metallic bodies having a substantially uniform pore size of less than about 200 microns and a density of less than about 25 percent theoretical, as well as the method for making them, are disclosed. Group IIA, IIIB, IVB, VB, and rare earth metal hydrides a

  10. Lewy Body Dementia Research

    MedlinePlus

    ... of LBD research papers published by the journal Alzheimer’s Research & Therapy. Memantine Improves Attention and Episodic Memory in Mild to Moderate Lewy Body Dementias Sept, 2014 - A recent study ... used for Alzheimer’s disease, improves two important areas of cognitive function ...

  11. Weightlessness and Free Bodies.

    ERIC Educational Resources Information Center

    Easton, D.

    1983-01-01

    Provides additional information on a demonstration described in the March 1981 issue of "The Physics Teacher" involving free-falling objects using styrofoam cups, rubber bands, and weights. Approaches the subject using free-body diagrams (included) and discusses the mechanism by which the weights are pulled into the cup. (JM)

  12. Body of Knowledge.

    ERIC Educational Resources Information Center

    Stinson, Susan W.

    1995-01-01

    This paper explores how a dance scholar's experience in dance is represented in her educational research. Discussion covers perceptions of art, body-mind dualities in schools and educational practice, the process and products of research and choreography, and crafting the choreography of research. (JB)

  13. Body Motion and Graphing.

    ERIC Educational Resources Information Center

    Nemirovsky, Ricardo; Tierney, Cornelia; Wright, Tracy

    1998-01-01

    Analyzed two children's use of a computer-based motion detector to make sense of symbolic expressions (Cartesian graphs). Found three themes: (1) tool perspectives, efforts to understand graphical responses to body motion; (2) fusion, emergent ways of talking and behaving that merge symbols and referents; and (3) graphical spaces, when changing…

  14. Review body reaction.

    PubMed

    Chilver, Karen

    2017-07-19

    Health secretary Jeremy Hunt has pledged to listen to what the pay review body (RB) has to say about the pay cap for nurses. That's all very well, but it is worth remembering that he voted against scrapping the cap in a Commons vote in June. So we won't be holding our breaths for a change of heart.

  15. Portable Body Temperature Conditioner

    DTIC Science & Technology

    2013-12-01

    environmental exposure during transport. These patients also have decreased thermoregulation due to blood loss. Normal core body temperature is defined...patients become hypothermic after severe injury due to environmental exposure during transport and decreased ability of thermoregulation due to blood loss...device. CONCLUSIONS: Defense medical installations require efficient and reliable equipment for the thermoregulation of either injured or ill

  16. Automotive Body Repair Competencies.

    ERIC Educational Resources Information Center

    D'Armond, Jack; And Others

    Designed to provide a model curriculum and guidelines, this manual presents tasks that were identified by employers, employees, and teachers as important in a postsecondary auto body repair curriculum. The tasks are divided into ten major component areas of instruction: metalworking and fiberglass, painting, frame and suspension, glass and trim,…

  17. Bacterial inclusion body purification.

    PubMed

    Seras-Franzoso, Joaquin; Peternel, Spela; Cano-Garrido, Olivia; Villaverde, Antonio; García-Fruitós, Elena

    2015-01-01

    Purification of bacterial inclusion bodies (IBs) is gaining importance due to the raising of novel applications for this type of submicron particulate protein clusters, with potential uses in the biomedical field among others. Here, we present two optimized methods to purify IBs adapting classical procedures to the material nature as well as the requirements of its final application.

  18. Carotid Body Tumor.

    PubMed

    Bakshi, Satvinder S; Kumar T, Lokesh

    2017-08-14

    A 17 year old girl presented with a progressively increasing swelling in her neck since 9 months. On examination a2*3 cm, firm, pulsatile swelling was felt in the left anterior triangle. The CT scan of the mass was suggestive of a carotid body tumor and urinary cathecholamines were negative. The mass was excised completely.

  19. Marijuana and body weight.

    PubMed

    Sansone, Randy A; Sansone, Lori A

    2014-07-01

    Acute marijuana use is classically associated with snacking behavior (colloquially referred to as "the munchies"). In support of these acute appetite-enhancing effects, several authorities report that marijuana may increase body mass index in patients suffering from human immunodeficiency virus and cancer. However, for these medical conditions, while appetite may be stimulated, some studies indicate that weight gain is not always clinically meaningful. In addition, in a study of cancer patients in which weight gain did occur, it was less than the comparator drug (megestrol). However, data generally suggest that acute marijuana use stimulates appetite, and that marijuana use may stimulate appetite in low-weight individuals. As for large epidemiological studies in the general population, findings consistently indicate that users of marijuana tend to have lower body mass indices than nonusers. While paradoxical and somewhat perplexing, these findings may be explained by various study confounds, such as potential differences between acute versus chronic marijuana use; the tendency for marijuana use to be associated with other types of drug use; and/or the possible competition between food and drugs for the same reward sites in the brain. Likewise, perhaps the effects of marijuana are a function of initial weight status-i.e., maybe marijuana is a metabolic regulatory substance that increases body weight in low-weight individuals but not in normal-weight or overweight individuals. Only further research will clarify the complex relationships between marijuana and body weight.

  20. Body of Knowledge.

    ERIC Educational Resources Information Center

    Stinson, Susan W.

    1995-01-01

    This paper explores how a dance scholar's experience in dance is represented in her educational research. Discussion covers perceptions of art, body-mind dualities in schools and educational practice, the process and products of research and choreography, and crafting the choreography of research. (JB)

  1. Automotive Body Repair Competencies.

    ERIC Educational Resources Information Center

    D'Armond, Jack; And Others

    Designed to provide a model curriculum and guidelines, this manual presents tasks that were identified by employers, employees, and teachers as important in a postsecondary auto body repair curriculum. The tasks are divided into ten major component areas of instruction: metalworking and fiberglass, painting, frame and suspension, glass and trim,…

  2. Adolescent Development: Body Blues.

    ERIC Educational Resources Information Center

    Yates, Alayne; Brodkin, Adele M.

    1994-01-01

    When early adolescents equate body image with self-image, they risk eating and exercise disorders, with dangerous results. Interviews with two experts present information to help middle school teachers understand the problem and intervene with students whose preoccupation with appearance or prowess can, taken to the extreme, be fatal. (SM)

  3. Lewy Body Dementia Diagnosis

    MedlinePlus

    ... as part of their protocols. Participating in research studies is a good way to benefit others with Lewy body dementia. Medications Medications are one of the most controversial subjects in dealing with LBD. A medication that doesn't work for one person may work for another person. ...

  4. Body inversion effect without body sense: insights from deafferentation.

    PubMed

    Bosbach, Simone; Knoblich, Guenther; Reed, Catherine L; Cole, Jonathan; Prinz, Wolfgang

    2006-01-01

    Like faces, human bodies are recognized via the configuration of their parts; their recognition is impaired by inversion. Processing of configural relations has been shown to depend on perceptual expertise with certain classes of objects. Because people see their own body and others' bodies frequently, humans are experts in the visual processing of human body postures. In addition, the observer's own on-line, multimodal body representation which heavily relies on current proprioception may play a crucial role in recognizing human body postures. We investigated whether static body posture recognition relied on current proprioceptive inputs or whether visual familiarity and stored body representations were sufficient. IW, who is deafferented (lost cutaneous touch and proprioception from his body), was tested on the recognition of upright and inverted human body postures, faces, and houses. As controls, IW showed an inversion effect for abstract, common, and rare human body postures as well as faces, but not houses. Results rule out a strong contribution of current afferent inputs to the recognition of human postures. The findings are discussed in terms of the role of the body schema in body posture recognition and how other contributions from one's own body may be involved in the visual processing of human bodies.

  5. Body Image Satisfaction among Blacks

    ERIC Educational Resources Information Center

    Gustat, Jeanette; Carton, Thomas W.; Shahien, Amir A.; Andersen, Lori

    2017-01-01

    Satisfaction with body image is a factor related to health outcomes. The purpose of this study is to examine the relationship between body image satisfaction and body size perception in an urban, Black community sample in New Orleans, Louisiana. Only 42.2% of respondents were satisfied with their body image and 44.1% correctly perceived their body…

  6. Body Art: A Panel Discussion.

    ERIC Educational Resources Information Center

    Surgenor, Peter; And Others

    1997-01-01

    Three camp directors discuss their policies regarding body art and body piercing. Only one director reported a strict policy prohibiting tattoos or body art based on standards that the camp portrays to families. However, all directors enforced policies prohibiting clothing or body art that mentions alcohol, tobacco, drug use, or inappropriate…

  7. Inclusion bodies in Plesiomonas shigelloides.

    PubMed Central

    Pastian, M R; Bromel, M C

    1984-01-01

    Inclusion bodies were discovered in seven environmental isolates of Plesiomonas shigelloides and the P. shigelloides control (ATCC 14029). Differential staining indicated that the inclusion bodies may be composed of polyphosphates, and developmental stages of the bodies may occur. The inclusion bodies may be useful for rapid presumptive identification of this organism. Images PMID:6320723

  8. Body Art: A Panel Discussion.

    ERIC Educational Resources Information Center

    Surgenor, Peter; And Others

    1997-01-01

    Three camp directors discuss their policies regarding body art and body piercing. Only one director reported a strict policy prohibiting tattoos or body art based on standards that the camp portrays to families. However, all directors enforced policies prohibiting clothing or body art that mentions alcohol, tobacco, drug use, or inappropriate…

  9. Body Image Satisfaction among Blacks

    ERIC Educational Resources Information Center

    Gustat, Jeanette; Carton, Thomas W.; Shahien, Amir A.; Andersen, Lori

    2017-01-01

    Satisfaction with body image is a factor related to health outcomes. The purpose of this study is to examine the relationship between body image satisfaction and body size perception in an urban, Black community sample in New Orleans, Louisiana. Only 42.2% of respondents were satisfied with their body image and 44.1% correctly perceived their body…

  10. Early Adolescence: Whole Body Learning.

    ERIC Educational Resources Information Center

    Cannon, Roger K., Jr.; Padilla, Michael J.

    1982-01-01

    "Whole body" denotes using the entire body to sense and experience a concept or idea. Typical whole body learning activities involve use of several senses: muscle sense, temperature, pain, pressure, and sense of equilibrium. Four whole body science activities are described, including identifying trees by touch. (Author/JN)

  11. Early Adolescence: Whole Body Learning.

    ERIC Educational Resources Information Center

    Cannon, Roger K., Jr.; Padilla, Michael J.

    1982-01-01

    "Whole body" denotes using the entire body to sense and experience a concept or idea. Typical whole body learning activities involve use of several senses: muscle sense, temperature, pain, pressure, and sense of equilibrium. Four whole body science activities are described, including identifying trees by touch. (Author/JN)

  12. Body image inflexibility mediates the relationship between body image evaluation and maladaptive body image coping strategies.

    PubMed

    Mancuso, Serafino G

    2016-03-01

    Body image inflexibility, the unwillingness to experience negative appearance-related thoughts and emotions, is associated with negative body image and eating disorder symptoms. The present study investigated whether body image inflexibility mediated the relationship between body image evaluation and maladaptive body image coping strategies (appearance-fixing and experiential avoidance) in a college and community sample comprising 156 females aged 18-51 years (M=22.76, SD=6.96). Controlling for recruitment source (college vs. community), body image inflexibility fully mediated the relationship between body image evaluation and maladaptive body image coping strategies. Results indicated that an unwillingness to experience negative appearance-related thoughts and emotions is likely responsible for negative body image evaluation's relationship to appearance-fixing behaviours and experiential avoidance. Findings support extant evidence that interventions that explicitly target body image inflexibility, such as Acceptance and Commitment Therapy, may have utility in treating body dissatisfaction in nonclinical populations.

  13. BODY VOLUME OF ADULT MEN

    DTIC Science & Technology

    The ideal weight given on the USAF standard weight table was found to have a correlation coefficient of only .672 with calculated percent body fat....volume from height and weight revealed the chart to be biased for adult men. Body volume was found to correlate well with body weight ( correlation ... coefficient of .996). Body volume of men in liters, V, may be estimated from body weight in kilograms, W, by using the formula: V = -4.7573 + 1.0153 W

  14. The body bites back!

    NASA Astrophysics Data System (ADS)

    Alsop, Steve

    2011-09-01

    How should we think about the body in science education? What ought it mean to be alive and live within epistemologies and pedagogies? What does it mean to be human in science education? In response to Auli Arvola Orlander and Per-Olof Wickram's article, this essay explores some of the possibilities and questions that the body evokes in science education research and practice. Drawing on selected theorizing in science education, environmental education and science and technology studies, the author suggests that we should strive to be more in tune with the seemingly mundane corporeal aspects of our performances and representations. This shift in attention has the potential to open up research, policy and practice agendas associated with relationships between pedagogies and embodied and disembodied knowledge and knowing. Such agendas might start by considering situated and embodied emotions in science education.

  15. Measuring body temperature.

    PubMed

    McCallum, Louise; Higgins, Dan

    Body temperature is one of the four main vital signs that must be monitored to ensure safe and effective care. Temperature measurement is recommended by the National Institute of Clinical Excellence a part of the initial assessment in acute illness in adults (NICE, 2007) and by the Scottish Intercollegiate Guidelines Network guidelines for post-operative management in adults (SIGN, 2004). Despite applying in all healthcare environments, wide variations exist on the methods and techniques used to measure body temperature. It is essential to use the most appropriate technique to ensure that temperature is measured accurately. Inaccurate results may influence diagnosis and treatment, lead to a failure to identify patient deterioration and compromise patient safety. This article explains the importance of temperature regulation and compares methods of its measurement.

  16. Myxobacteria Fruiting Body Formation

    NASA Astrophysics Data System (ADS)

    Jiang, Yi

    2006-03-01

    Myxobacteria are social bacteria that swarm and glide on surfaces, and feed cooperatively. When starved, tens of thousands of cells change their movement pattern from outward spreading to inward concentration; they form aggregates that become fruiting bodies, inside which cells differentiate into nonmotile, environmentally resistant spores. Traditionally, cell aggregation has been considered to imply chemotaxis, a long-range cell interaction mediated by diffusing chemicals. However, myxobacteria aggregation is the consequence of direct cell-contact interactions. I will review our recent efforts in modeling the fruiting body formation of Myxobacteria, using lattice gas cellular automata models that are based on local cell-cell contact signaling. These models have reproduced the individual phases in Myxobacteria development such as the rippling, streaming, early aggregation and the final sporulation; the models can be unified to simulate the whole developmental process of Myxobacteria.

  17. Body art and pregnancy.

    PubMed

    Kluger, Nicolas

    2010-11-01

    Body art has gained tremendously in popularity over the past 20 years, and a substantial number of pregnant women may have tattoos or piercings. In most cases, pregnancy will be uneventful. However, on rare occasions, body art may become an issue or cause complications. Navel and abdominal surface piercing and microdermal implants may cause unsightly stretch marks from gravid distension. Nipple piercing could impair breastfeeding. In emergency situations, oral piercing may interfere with airway management and nasal jewelry can be inhaled or swallowed during orotracheal intubation. Tattoos may become distorted if placed on a distended area or they may cover surgical incision lines. The risk of introducing tattoo pigments during epidural analgesia, with the potential for tumor growth, is currently under debate, although the arguments are highly speculative and without solid basis.

  18. Dementia with Lewy bodies

    PubMed Central

    Ferman, Tanis J.; Boeve, Bradley F.

    2009-01-01

    Synopsis The advent of new immunostains have improved our ability to detect limbic and cortical Lewy bodies, and it is now evident that Dementa with Lewy bodies (DLB) is the second most common neurodegenerative dementia, after Alzheimer’s disease (AD). Distinguishing DLB from AD has important implications for treatment, in terms of substances that may worsen symptoms (i.e., anticholinergic and certain neuroleptic medications) and those that may improve them (i.e., cholinesterase inhibitors, carbidopa-levodopa). Neurocognitive patterns, psychiatric features, extrapyramidal signs and sleep disturbance are helpful in differentiating DLB from AD early in the disease course. Differences in the severity of cholinergic depletion as well as type and distribution of neuropathology contribute to these clinical differences, though DLB patients with a high density of co-occuring AD pathology are less clinical distinguishable from AD. PMID:17659188

  19. Imaging body armor.

    PubMed

    Harcke, H Theodore; Schauer, David A; Harris, Robert M; Campman, Steven C; Lonergan, Gael J

    2002-04-01

    This study examined the feasibility of performing radiographic studies on patients wearing standard-issue body armor. The Kevlar helmet, fragmentation vest, demining suit sleeve, and armor plate were studied with plain film and computed tomography in a simulated casualty situation. We found that the military helmet contains metal screws and metal clips in the headband, but diagnostic computed tomographic images can be obtained. Kevlar, the principal component of soft armor, has favorable photon attenuation characteristics. Plate armor of composite material also did not limit radiographic studies. Therefore, when medically advantageous, patients can be examined radiographically while wearing standard military body armor. Civilian emergency rooms should be aware of these observations because law enforcement officers wear similar protective armor.

  20. [Body-contouring surgery].

    PubMed

    Pitanguy, Ivo

    2003-01-01

    Concepts of beauty have been continuously evolving throughout the history of mankind. The voluptuous figures that were idealized by artists in the past have been substituted by slimmer forms. Medical advances in this century have permitted safe and efficient surgical correction of contour deformities. Until recently, these alterations were mostly hidden under heavy clothing or were reluctantly accepted. Current fashion trends generally promote body-revealing attire. The media frequently encourages the importance of fitness and good health linking these qualities with youthfulness and beauty. The subliminal as well as overt message is that these are necessary and desirable requirements for social acceptance and professional success. On the other hand, current sedentary lifestyle and dietary excesses, associated with factors such as genetic determination, pregnancy and the aging process, contribute to alterations of body contour that result in the loss of the individual's body image. This creates a strong psychological motivation for surgical correction. Localized fat deposits and skin flaccidity are sometimes resistant to the most sincere efforts in weight loss and sport activities. This ever-increasing request for contour surgery has been favorably met by safe and effective anesthesiology as well as efficient surgical techniques, resulting in a high degree of patient satisfaction. It is essential that today's aesthetic surgeon understand the motivations of patients who present with body contour deformities. A request for surgical treatment should be seen as a legitimate desire to achieve a physical form that approximates the individual with his or her ideal self-image. Additionally, the surgeon must always consider the possible benefit of including the participation of a multidisciplinary team approach. Depending on each case, this team should include consultants in endocrinology, dermatology, oculoplastics, pediatrics and other appropriate specialties.

  1. N-body models

    NASA Technical Reports Server (NTRS)

    Miller, R. H.

    1990-01-01

    The experimental discovery of an overstability in the central regions of galaxies is briefly discussed, and numerical methods for integrating orbits are briefly addressed. The overstability manifests itself as a growing amplitude in the orbit of a galaxy's nucleus about its mass centroid. This finding may complicate studies of the topological properties of orbits and studies of the bifurcation structure of orbits. A sample problem is used to illustrate the importance of a Liouville theorem in N-body calculations.

  2. Few-body physics

    SciTech Connect

    Briceno, Raul

    2015-05-01

    Few-body hadronic observables play an essential role in a wide number of processes relevant for both particle and nuclear physics. In order for Lattice QCD to offer insight into the interpretation of few-body states, a theoretical infrastructure must be developed to map Euclidean-time correlation functions to the desired Minkowski-time few-body observables. In this talk, I will first review the formal challenges associated with the studies of such systems via Lattice QCD, as first introduced by Maiani and Testa, and then review methodology to circumvent said limitations. The first main example of the latter is the formalism of Luscher to analyze elastic scattering and a second is the method of Lellouch & Luscher to analyze weak decays. I will then proceed to discus recent theoretical generalizations of these frameworks that allow for the determination of scattering amplitudes, resonances, transition and elastic form factors. Finally, I will outline outstanding problems, including those that are now beginning to be addressed.

  3. Body as subject1

    PubMed Central

    MEIR, IRIT; PADDEN, CAROL A.; ARONOFF, MARK; SANDLER, WENDY

    2011-01-01

    The notion of subject in human language has a privileged status relative to other arguments. This special status is manifested in the behavior of subjects at the morphological, syntactic, semantic and discourse levels. Here we bring evidence that subjects have privileged status at the lexical level as well, by analyzing lexicalization patterns of verbs in three different sign languages. Our analysis shows that the sublexical structure of iconic signs denoting state of affairs in these languages manifests an inherent pattern of form–meaning correspondence: the signer’s body consistently represents one argument of the verb, the subject. The hands, moving in relation to the body, represent all other components of the event – including all other arguments. This analysis shows that sign languages provide novel evidence in support of the centrality of the notion of subject in human language. It also solves a typological puzzle about the apparent primacy of object in sign language verb agreement, a primacy not usually found in spoken languages, in which subject agreement ranks higher. Our analysis suggests that the subject argument is represented by the body and is part of the lexical structure of the verb. Because it is always inherently represented in the structure of the sign, the subject is more basic than the object, and tolerates the omission of agreement morphology. PMID:23066169

  4. Géochimie / Geochemistry Géomatériaux / Geomaterials Géochimie (éléments majeurs et terres rares) des granulites méta-sédimentaires en xénolithes dans les basaltes alcalins quaternaires du Moyen Atlas (Maroc): Arguments en faveur de la nature pour partie restitique de la croûte inférieure

    NASA Astrophysics Data System (ADS)

    Moukadiri, Ali; Pin, Christian

    1998-11-01

    High-alumina granulite xenoliths equilibrated under lower crustal conditions (850-900 C; 9 ± 1 kbar) have been found in the Tafraout maars and analysed for major and rare earth elements. Starting from a protolith of pelitic composition, a strong decrease of SiO 2 and alkalis and a concomitant increase of Al 2O 3, Fe 2O 3 and MgO are observed. These variations are interpreted to reflect partial melting and extraction of granitic magmas. Lanthanide elements show a progressive depletion of LREE combined with a marked increase of HREE. These variations result, in the most restitic samples, in V-shaped chondrite-normalized patterns. These peculiar patterns are interpreted in terms of incomplete separation between a garnet-sillimanite-rich refractory residue, highly depleted in LREE and enriched in HREE, and a small amount of trapped partial melt, containing most of the LREE. Negative Eu anomalies, inherited from the pelitic protolith, occur throughout. They are not erased, but rather enhanced, by partial melting and granitic magma removal. A simple modeling, based on K 2O and La concentrations, allows us to propose that most of the xenoliths represent refractory residues derived from high degrees (about 65 %) of partial melting of evolved sources similar to average post-Archean shales. In the most restitic samples, the amount of partial melt left behind in the sour