Structural evolution across the Eastern Ghats Mobile Belt–Bastar craton boundary, India: hot over cold thrusting in an ancient collision zone

Along the western margin of the Eastern Ghats Mobile Belt (EGMB), ultrahigh-temperature granulites are thrust westward over hornblende granites and sedimentary rocks of the Bastar craton. Multiply deformed migmatitic gneisses, and porphyritic charnockite of the EGMB unit preserve thrust-related shear fabrics (S3M). In the cratonic foreland, undeformed granites show a progressive decrease in grain-size and increase in penetrative foliation to the east, evolving into orthogneiss near the mylonitized contact zone with charnockite. Foreland fabrics with a consistent top-to-the-west shear sense are conformable with S3M in charnockite and correlate with S3B in polydeformed orthogneisses of cratonic windows. S3B in the windows parallels S3M in overlying EGMB migmatitic gneisses. While S3M accompanied granulite metamorphism in the EGMB, S3B temperature estimates vary from T>700 °C in the windows to T<550 °C in the west. Decreasing temperature and later fabric formation in the west are explained by an evolving thermal profile in the cold craton, which is caused by thrusting against hot lower crustal EGMB rocks. on lithologic, structural and metamorphic variations across the contact, and resemblances between the EGMB and Rayner Complex, the craton–mobile belt boundary is considered a result of Indo-Antarctic collision, leading to the formation of an ancient supercontinent.