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

Abstract

AbstractIntegrated 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) M1ultrahigh temperature (UHT) metamorphism (∼1000°C at 6.5–8.5 kbar) on an anticlockwiseP–Ttrajectory simultaneously with early deformations D1–D2involving 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–D2structures 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 D4deformation. This is the first record of the progradeP–Tpath of the superimposed granulite facies metamorphism in the EGB. U‐Pb SHRIMP data of zircon preserves an inherited grain domain ofca. 1700 Ma (207Pb‐206Pb age) that traces back the history of EGB with a lineage of the Mesoproterozoic supercontinent, Columbia. The UHT metamorphosed (peak M1atca. 1000 Ma) and subsequently cooled crustal segment (M1R) was subjected to strong tectonothermal reworking (M2) along a clockwiseP–Tpath at 953 + 6 Ma (concordia age) that partially exhumed the rocks to mid‐crustal levels. A later fluid‐induced retrogressive eventvis‐à‐vismelt crystallization occurred atca. 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.