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Multiple tectonometamorphic imprints in the lower crust: first evidence of ca. 950 Ma (zircon U-Pb SHRIMP) compressional reworking of UHT aluminous granulites from the Eastern Ghats Belt, India



Integrated structural, petrological and geochronological study on a suite of granulites from the central part of the Eastern Ghats Belt (EGB), India unveils polyphase tectonothermal evolution. We document (a) M1 ultrahigh temperature (UHT) metamorphism (∼1000°C at 6.5–8.5 kbar) on an anticlockwise PT trajectory simultaneously with early deformations D1–D2 involving partial melting, (b) cooling down to ∼ 800°C, 6 kbar that produced a variety of coronae/symplectites (M1R), (c) an unrelated compressional orogeny (D3) that produced deep crustal shears and mylonitic foliation (S3m) at low angles to D1–D2 structures and was associated with slight loading, and possible partial melt extraction under granulite facies condition (M2 ∼7 kbar, 850°C), and (d) localized retrogression (M3) in the presence of melt accompanying D4 deformation. This is the first record of the prograde PT path of the superimposed granulite facies metamorphism in the EGB. U-Pb SHRIMP data of zircon preserves an inherited grain domain of ca. 1700 Ma (207Pb-206Pb age) that traces back the history of EGB with a lineage of the Mesoproterozoic supercontinent, Columbia. The UHT metamorphosed (peak M1 at ca. 1000 Ma) and subsequently cooled crustal segment (M1R) was subjected to strong tectonothermal reworking (M2) along a clockwise PT path at 953 + 6 Ma (concordia age) that partially exhumed the rocks to mid-crustal levels. A later fluid-induced retrogressive event vis-à-vis melt crystallization occurred at ca. 900 Ma (207Pb-206Pb age). The post-peak evolution reveals striking similarities with those recorded in the rocks of the Rayner Complex of east Antarctica, thereby strengthening the notion of Indo-Antarctic correlation as part of Rodinia. Copyright © 2010 John Wiley & Sons, Ltd.