Fold-thrust belt and synkinematic alkali magmatism along terrane boundary shear zone of the Eastern Ghats Mobile Belt: Does the Rayner-Napier boundary of East Antarctica reflect that?

摘要

The terrane margin of the Eastern Ghats Mobile Belt (EGMB) with the surrounding cratons of Indian Peninsula is considered to abut against the Rayner-Napier boundary of Enderby Land in the East Gondwanaland assembly. In this paper, a detailed structural analysis of NW part of the Eastern Ghats terrane margin is attempted. The NW front shows fold-thrust belt structure consisting of Sinapalli, Lathore and Turekela nappes. The basal decollement is exposed as a terrane boundary shear zone that demarcates the high grade Eastern Ghats belt from the surrounding craton. It shows splay thrusts forming schuppen or imbricate structure. Further, the decollement passes over a lateral ramp across which a variation in the rock association is noticed. Nepheline syenite plutons are emplaced along the terrane boundary shear zone. The plutons show transitional fabric from magmatic to solid state, thus ascribing the compressional origin of the alkaline melt and synkinematic emplacement of the pluton with thrusting. The fold-thrust belt development and synkinematic alkaline magmatism characterising the NW margin of the EGMB should also be looked into the tectonic correlative Rayner-Napier boundary.