Journal of the Geological Society of India, Feb 1, 2011
... Associated rhyolites crystallized at ~987 Ma (zircon U-Pb age of rhyolites, Deb et al. 2001) ... more ... Associated rhyolites crystallized at ~987 Ma (zircon U-Pb age of rhyolites, Deb et al. 2001) and were later meta-... 2011 150 VADLAMANI RAVIKANT AND PR GOLANI semipelite (Sinha-Roy and Mohanty 1988, Bose et al. 1990; Deb and Sarkar 1990; Sugden et al. ...
Journal of Geological Society of India, Mar 1, 1998
A retrograde path inferred for the Schirmacher Hills granulites involves near ITD path following ... more A retrograde path inferred for the Schirmacher Hills granulites involves near ITD path following post-peak granulite facies metamorphism (M1/D1), preserved only in enclaves, followed by near IBC path, M3, post dating M2/D2 granulites facies metamorphism and deformation. Final uplift and cooling of the terrain occurred in the upper amphibolite facies metamorphic conditions, M4, syntectonic with respect to D3 deformation and emplacement of large volume of syntectonic granitoids. Fluids released during cooling and crystallization of these granitoids probably caused the large scale retrogression of granulite facies rocks to amphibolite facies gneisses.
Mafic and ultramafic enclaves from Schirmacher oasis preserve evidences for the earliest metamorp... more Mafic and ultramafic enclaves from Schirmacher oasis preserve evidences for the earliest metamorphic event. In this study, this event has been constrained through reaction textures, mineral chemistry and themobarometry by application of conventional and multireaction methods. Mafic enclaves comprise melanocratic Pargasite-Bearing gabbro, gabbroic anorthosite and ultramafic enclaves are spinel- and Garnet-Bearing websterite, Ortho- and clinopyroxenite which occur as deformed enclaves within foliated norite. Deformed metanorite dykes and metagabbro pods occur within metasedimentary granulite. Most of the enclaves are massive, without chromite layering, while few preserve deformed modal layering at Centimeter-Scale. It is likely that the enclaves represent mantle restites during a partial melting event. Reaction textures within enclaves indicate a decompressive sense of the P-T path inferred from Garnet-Bearing websterite, deformed metanorite dyke and melanocratic Pargasite-Bearing gab...
Kyanite-eclogite xenoliths from Wajrakarur are considered as remnants of subducted ocean-floor cr... more Kyanite-eclogite xenoliths from Wajrakarur are considered as remnants of subducted ocean-floor crust [1]. Here trace element concentration and isotopic data are presented in garnet (Grt) and kyanite (Ky) from xenoliths KL-2 E1-E4, characterized by [2]). We use the precise Sr/Sr host kimberlite groundmass perovskite ratio (0.70312-0.70333, [3]) as a proxy for the extent of kimberlitic magma infiltration at 1.1 Ga. The xenolithic Grt and Cr-rich (upto 1506 ppm) Ky have more radiogenic Sr/Sr values than kimberlite, at 1.1 Ga, of 0.703829-0.705203 and 0.703811-0.704502, respectively. Furthermore, the Grt and Ky Nd/Nd ratios, at 1.1 Ga, are 0.509321-0.511372 and 0.510951-0.511156, respectively, and are distinctly lower than those of the host kimberlite (0.511870-0.512290, [4]). This indicates that the infiltration of kimberlitic fluid has not altered the Sr/Sr and Nd/Nd ratios in the Grt and Ky, and therefore their isotope compositions must be inherited and predate the kimberlite magma g...
Orthogneiss with tabular to lensoid pyroxene-amphibolite enclaves, is exposed in the ice-free are... more Orthogneiss with tabular to lensoid pyroxene-amphibolite enclaves, is exposed in the ice-free areas of Payer and Weyprecht Mountains. Orthogneiss was emplaced late syntec- tonic to D2 deformation under amphibolite facies conditions which imparted a homogeneous foliation. The field relations and geochemical parameters suggest an I-type affinity for the granitic orthogneiss, while the pyroxene-amphibolite enclaves are metamorphosed products of basic igneous rocks.
ABSTRACT The timing of initiation of continent-continent collision between Asia and India is cont... more ABSTRACT The timing of initiation of continent-continent collision between Asia and India is controversial, but this major tectonic event is generally thought to have occurred in the Early Eocene, ca. 50 Ma. New and independent data from strontium isotopes, stable carbon isotopes, microfossil biostratigraphy, and mammal fossils from an Early Eocene marginal marine sequence (Cambay Shale) at the Vastan Lignite Mine of western India indicate that terrestrial faunal exchanges, and therefore continental collision, between Asia and the Indian subcontinent took place before 53.7 Ma. This age coincides with the second Eocene Thermal Maximum (ETM2), a short-lived warming episode that followed the Paleocene-Eocene Thermal Maximum (PETM) ca. 55.5 Ma. Our data also document, for the first time, a clear record of the ETM2 in terrestrial organic material from a low-latitude site, which is represented by a 3%-4% carbon isotope excursion (CIE) in lignite and dispersed organic carbon delta C-13 values. The magnitude of the CIE at this location closely matches that observed in marine cores from the Arctic Ocean, which supports an interpretation that this hyperthermal event, though of lower magnitude, was similar in character to that of the PETM, being a global phenomenon that affected both terrestrial and marine ecosystems.
Journal of the Geological Society of India, Feb 1, 2011
... Associated rhyolites crystallized at ~987 Ma (zircon U-Pb age of rhyolites, Deb et al. 2001) ... more ... Associated rhyolites crystallized at ~987 Ma (zircon U-Pb age of rhyolites, Deb et al. 2001) and were later meta-... 2011 150 VADLAMANI RAVIKANT AND PR GOLANI semipelite (Sinha-Roy and Mohanty 1988, Bose et al. 1990; Deb and Sarkar 1990; Sugden et al. ...
Journal of Geological Society of India, Mar 1, 1998
A retrograde path inferred for the Schirmacher Hills granulites involves near ITD path following ... more A retrograde path inferred for the Schirmacher Hills granulites involves near ITD path following post-peak granulite facies metamorphism (M1/D1), preserved only in enclaves, followed by near IBC path, M3, post dating M2/D2 granulites facies metamorphism and deformation. Final uplift and cooling of the terrain occurred in the upper amphibolite facies metamorphic conditions, M4, syntectonic with respect to D3 deformation and emplacement of large volume of syntectonic granitoids. Fluids released during cooling and crystallization of these granitoids probably caused the large scale retrogression of granulite facies rocks to amphibolite facies gneisses.
Mafic and ultramafic enclaves from Schirmacher oasis preserve evidences for the earliest metamorp... more Mafic and ultramafic enclaves from Schirmacher oasis preserve evidences for the earliest metamorphic event. In this study, this event has been constrained through reaction textures, mineral chemistry and themobarometry by application of conventional and multireaction methods. Mafic enclaves comprise melanocratic Pargasite-Bearing gabbro, gabbroic anorthosite and ultramafic enclaves are spinel- and Garnet-Bearing websterite, Ortho- and clinopyroxenite which occur as deformed enclaves within foliated norite. Deformed metanorite dykes and metagabbro pods occur within metasedimentary granulite. Most of the enclaves are massive, without chromite layering, while few preserve deformed modal layering at Centimeter-Scale. It is likely that the enclaves represent mantle restites during a partial melting event. Reaction textures within enclaves indicate a decompressive sense of the P-T path inferred from Garnet-Bearing websterite, deformed metanorite dyke and melanocratic Pargasite-Bearing gab...
Kyanite-eclogite xenoliths from Wajrakarur are considered as remnants of subducted ocean-floor cr... more Kyanite-eclogite xenoliths from Wajrakarur are considered as remnants of subducted ocean-floor crust [1]. Here trace element concentration and isotopic data are presented in garnet (Grt) and kyanite (Ky) from xenoliths KL-2 E1-E4, characterized by [2]). We use the precise Sr/Sr host kimberlite groundmass perovskite ratio (0.70312-0.70333, [3]) as a proxy for the extent of kimberlitic magma infiltration at 1.1 Ga. The xenolithic Grt and Cr-rich (upto 1506 ppm) Ky have more radiogenic Sr/Sr values than kimberlite, at 1.1 Ga, of 0.703829-0.705203 and 0.703811-0.704502, respectively. Furthermore, the Grt and Ky Nd/Nd ratios, at 1.1 Ga, are 0.509321-0.511372 and 0.510951-0.511156, respectively, and are distinctly lower than those of the host kimberlite (0.511870-0.512290, [4]). This indicates that the infiltration of kimberlitic fluid has not altered the Sr/Sr and Nd/Nd ratios in the Grt and Ky, and therefore their isotope compositions must be inherited and predate the kimberlite magma g...
Orthogneiss with tabular to lensoid pyroxene-amphibolite enclaves, is exposed in the ice-free are... more Orthogneiss with tabular to lensoid pyroxene-amphibolite enclaves, is exposed in the ice-free areas of Payer and Weyprecht Mountains. Orthogneiss was emplaced late syntec- tonic to D2 deformation under amphibolite facies conditions which imparted a homogeneous foliation. The field relations and geochemical parameters suggest an I-type affinity for the granitic orthogneiss, while the pyroxene-amphibolite enclaves are metamorphosed products of basic igneous rocks.
ABSTRACT The timing of initiation of continent-continent collision between Asia and India is cont... more ABSTRACT The timing of initiation of continent-continent collision between Asia and India is controversial, but this major tectonic event is generally thought to have occurred in the Early Eocene, ca. 50 Ma. New and independent data from strontium isotopes, stable carbon isotopes, microfossil biostratigraphy, and mammal fossils from an Early Eocene marginal marine sequence (Cambay Shale) at the Vastan Lignite Mine of western India indicate that terrestrial faunal exchanges, and therefore continental collision, between Asia and the Indian subcontinent took place before 53.7 Ma. This age coincides with the second Eocene Thermal Maximum (ETM2), a short-lived warming episode that followed the Paleocene-Eocene Thermal Maximum (PETM) ca. 55.5 Ma. Our data also document, for the first time, a clear record of the ETM2 in terrestrial organic material from a low-latitude site, which is represented by a 3%-4% carbon isotope excursion (CIE) in lignite and dispersed organic carbon delta C-13 values. The magnitude of the CIE at this location closely matches that observed in marine cores from the Arctic Ocean, which supports an interpretation that this hyperthermal event, though of lower magnitude, was similar in character to that of the PETM, being a global phenomenon that affected both terrestrial and marine ecosystems.
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