Deformation of terrane boundary shear zone (Lakhna shear zone) between Eastern Ghats Mobile Belt and Bastar Craton in Balangir and Kalahandi Districts, Orissa

The terrane boundary between Eastern Ghats Mobile Belt and the Bastar Crato n in Balangir and Kalahandi Districts of Orissa is distinctly marked by nea rly two kilometer wide southeasterly dipping ductile shear zone, designated as the Lakhna shear zone. The shear zone has largely developed in the cott on, but for a narrow width within the Eastern Ghats. It is dominated by qua rtzofeldspathic mylonites characterised by S-C fabric, asymmetric winged po rphyroclasts, quartz ribbons and intragranular faults. These structures hav e been effectively utilized in deducing the sense of shear and evaluating t he amount of strain. The results show thrusting of the Eastern Ghats over t he Bastar Craton. The minimum amount of throw along the thrust has been est imated to be around 2.5 to 4.7 km assuming a dominant simple shear deformat ion.