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

• Main Authors: Das, Kaushik, Bose, Sankar, Karmakar, Subrata, Dunkley, Daniel J., Dasgupta, Somnath
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: John Wiley and Sons 2011
• Subjects: QE Geology; Antarctic; East Antarctica; Rayner; Antarc*; Antarctica
• Online Access: http://repository.ias.ac.in/76390/; http://onlinelibrary.wiley.com/doi/10.1002/gj.1246/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 D 1 -D 2 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 (D 3 ) that produced deep crustal shears and mylonitic foliation (S 3m ) at low angles to D 1 -D 2 structures and was associated with slight loading, and possible partial melt extraction under granulite facies condition (M 2 ~7 kbar, 850°C), and (d) localized retrogression (M 3 ) in the presence of melt accompanying D 4 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 ( 207 Pb- 206 Pb age) that traces back the history of EGB with a lineage of the Mesoproterozoic supercontinent, Columbia. The UHT metamorphosed (peak M 1 at ca. 1000Ma) and subsequently cooled crustal segment (M1R) was subjected to strong tectonothermal reworking (M 2 ) 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 ( 207 Pb- 206 Pb 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.