Late brittle tectonics in a Precambrian ductile belt: evidence from brittle structures in the Singhbhum Shear Zone, eastern India

The Singhbhum Shear Zone, a 200 km long tectonic lineament, passes close to the boundary between the Archaean ‘Singhbhum craton’ and the Proterozoic ‘Singhbhum mobile belt’. Evidence from meso-structures reveals development of this shear zone in a ductile tectonic regime (1.6–2.2 Ga.) by thrusting of the northern block over the southern block along the N-dipping shear surface. A hitherto unrecognized, late brittle tectonic regime (≤1.6 Ga.) comprising two discrete phases is established from dynamic analysis of the fractures and veins in the shear zone. Episodic extension parallel and normal to the shear zone was a major consequence of this middle Proterozoic (≤1.6 Ga.) brittle tectonic episode, and was associated with the intrusion of a swarm of basic dykes.