| Reference Type | Journal (article/letter/editorial) |
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| Title | Transitional granulite-eclogite facies metamorphism of basic supracrustal rocks in a shear zone complex in the Precambrian shield of south India |
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| Journal | Mineralogical Magazine | ISSN | 0026-461X |
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| Authors | Mukhopadhyay, Biswajit | Author |
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| Bose, Mihir K. | Author |
| Year | 1994 (March) | Volume | 58 |
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| Issue | 390 |
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| Publisher | Mineralogical Society |
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| Download URL | https://rruff.info/doclib/MinMag/Volume_58/58-390-97.pdf+ |
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| DOI | doi:10.1180/minmag.1994.058.390.10Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 2007 | Long-form Identifier | mindat:1:5:2007:1 |
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| GUID | 0 |
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| Full Reference | Mukhopadhyay, Biswajit, Bose, Mihir K. (1994) Transitional granulite-eclogite facies metamorphism of basic supracrustal rocks in a shear zone complex in the Precambrian shield of south India. Mineralogical Magazine, 58 (390) 97-118 doi:10.1180/minmag.1994.058.390.10 |
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| Plain Text | Mukhopadhyay, Biswajit, Bose, Mihir K. (1994) Transitional granulite-eclogite facies metamorphism of basic supracrustal rocks in a shear zone complex in the Precambrian shield of south India. Mineralogical Magazine, 58 (390) 97-118 doi:10.1180/minmag.1994.058.390.10 |
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| In | (1994, March) Mineralogical Magazine Vol. 58 (390) Mineralogical Society |
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| Abstract/Notes | AbstractThe phase petrology of two bodies of basic granulites occurring in association with supracrustal sequences within a dextral oblique-slip shear complex in the high-grade terrain of south India, have been studied. Some metabasites are characterized by garnet + clinopyroxene assemblages such as Grt + Cpx + PI ± Hbl ± Opx ± Qtz + Fe-Ti oxide(s) which are high-pressure granulites (garnet-clinopyroxene subfacies) transitional between the intermediate-pressure granulites (orthopyroxene-plagioclase subfacies) and eclogite. Mineralogical characteristics suggest that metamorphic conditions did not reach the eclogite facies but certainly approached that level. Close spatial association of the garnetiferous varieties with garnet-free assemblages (Opx + Hbl + Pl ± Cpx) and intimate juxtaposition of anhydrous and hydrous assemblages indicate a complex interplay of variable μH2O and bulk composition, especially αSiO2. Due to variable and low closure temperature of Fe-Mg exchange reactions between coexisting pyroxene and garnet, reliable estimation of peak temperatures during this near eclogite-facies metamorphism is problematic. A combination of a garnet-clinopyroxene barometer and various temperature estimates suggests P-T conditions of 875 ± 25°C and 8 ± 1 kbar for the Mettuppalaiyam samples and 900 ± 50°C and 14 ± 2 kbar for the Kanjamalai samples. Bulk rock chemical differences in terms of SiO2-content can account for the development of similar mineral assemblages along a near adiabatic metamorphic gradient between these two localities. These assemblages represent some of the highest grade granulite facies rocks in south India. The high-pressure granulites are not in situ samples of ancient lower continental crust, but low-pressure protoliths buried at depth. Textural features suggest that the high-pressure garnet-clinopyroxene subfacies rocks evolved from an amphibolitic assemblage by formation of garnet at the expense of hornblende and plagioclase and this high-pressure assemblage underwent an isothermal decompression indicating a clockwise P-T-t path resulting from crustal thickening and exhumation. A later isobaric cooling, possibly accompanying shearing and high H2O influx (aH2O≈0.78) gave rise to the coexisting orthopyroxeneplagioclase subfacies rocks (intermediate pressure granulites). |
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