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

Abstract

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 6.5-8.5kbar) on an anticlockwise P-T 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 (M_1R), (c) an unrelated compressional orogeny (D₃) that produced deep crustal shears and mylonitic foliation (S_3m) 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 P-T path of the superimposed granulite facies metamorphism in the EGB. U-Pb SHRIMP data of zircon preserves an inherited grain domain of ca. 1700Ma (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. 1000Ma) and subsequently cooled crustal segment (M1R) was subjected to strong tectonothermal reworking (M₂) along a clockwise P-T path at 953+6Ma (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. 900Ma (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.