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Petrology of gedrite-bearing rocks in mid-crustal ductile shear zones from the Eastern Ghats Belt, India 总被引:1,自引:0,他引:1
A suite of metapelitic, basic and quartzofeldspathic rocks intruded by enderbitic gneiss from the southernmost tip of the Eastern Ghats Belt, India, and metamorphosed at c. 750–800 °C, 6 kbar, were subjected to repeated ductile shear deformation, hydration, cooling and accompanying alkali metasomatism along narrow shear zones. Gedrite-bearing assemblages developed in the shear zones traversing metapelitic rocks. Interpretation of the reaction textures in an appropriate P–T grid in the system FMASH, an isothermal–isobaric μ H2O – μ Na2O grid in the system NFMASH, and geothermobarometric data suggest a complex evolutionary history for the gedrite-bearing parageneses. Initially, gedrite-bearing assemblages were produced due to increase in μ Na2O at nearly constant but high μ H2O accompanying cooling. Gedrite was partially destabilized to orthopyroxene+albite due to progressively increasing μ Na2O . During further cooling and at increased μ H2O a second generation of gedrite appeared in the rocks. 相似文献
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Somnath Dasgupta Jürgen Ehl Michael M. Raith Pulak Sengupta Pranesh Sengupta 《Contributions to Mineralogy and Petrology》1997,129(2-3):182-197
Pelitic rocks were thermally metamorphosed at the contact of the Chimakurthy mafic-ultramafic igneous complex, Eastern Ghats
Belt, India. The rocks show progressive change in mineralogy from biotite-sillimanite-quartz-garnet-K-feldspar (association
I, 150 m from the intrusive contact) to garnet-spinel-cordierite-K-feldspar-sillimanite (association II, 20–30 m from the
intrusive contact) to cordierite-K-feldspar-(cordierite-orthopyroxene-K-feldspar symplectite after osumilite)-spinel-FeTiAl
oxides with/without garnet (associations III and IV, 5 m from the intrusive contact), and finally to spinel-orthopyroxene-cordierite-K-feldspar
(association V, xenoliths). Oxide mineral clots in associations III and IV resemble emery-type rocks. Initial mineral reactions
involved biotite-dehydration melting with partial segregation of the melt. Down-temperature mineral reactions were largely
diffusion controlled and preservation of symplectitic and coronitic textures in microdomains is common. Interpretation of
reaction textures in relevant petrogenetic grids for the sytems KFMASH and FMAS and combined with geothermobarometry suggest
that the pelitic rocks were thermally metamorphosed at c. 6 kbar pressure along a heating-cooling trajectory within the temperature interval between c. 750 °C and c. 1000 °C.
Received: 20 October 1996 / Accepted: 17 June 1997 相似文献
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