Microstructural and fluid inclusion constraints on the evolution of Jakhri Thrust Zone in the Satluj valley of NW Himalaya

The regional structures, microstructure and fluid inclusion trail pattern have been employed to work out the evolution of the Jakhri Thrust Zone (JTZ) exposed in the Satluj valley of NW Himalaya. It is a NE-dipping, SW-propagating out-of-sequence thrust cutting across the folded Lesser Himalayan crystalline nappe and lies in the seismically active inner Lesser Himalayan zone. The recrystallization microstructure in the footwall quartzite suggests deformation in the lower green schist facies condition with a progressively decreasing finite strain away from the thrust. The microstructures and fluid inclusion trails (secondary) show analogous pattern and have formed during the same deformation event in the footwall. The CO2-H2O and H2O-NaCl fluid inclusions have been identified. The former has been re-equilibrated during the peak deformation whereas the latter has evolved and been re-equilibrated during exhumation. The isochores of CO2-H2O and H2O-NaCl inclusions suggest an isothermal exhumation path from a depth of similar to 15-17 km, considering a lithostatic condition. These results suggest that the JTZ is a deep-seated thrust, probably a steep imbrication on the main decollement fault.