Kinematics of the Dadeldhura klippe shear zones (W Nepal): implications for the foreland evolution of the Himalayan metamorphic core

Authors


Correspondence: Borja Antolin, Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada. Tel.: +1 6135336169; email: antolin@geol.queensu.ca

Abstract

Mapping combined with structural analyses in the foreland edge of the metamorphic core of the Himalayas in SW Nepal highlights the existence of two north-dipping shear zones with opposite sense of shear. Here, the metamorphic core is mainly affected by non-coaxial top-to-the-south sense of shear at temperatures between 450 °C and 550 °C that switch to a top-to-the-north sense of shear at the top of the metamorphic core. We regionally correlate this upper shear zone with the South Tibetan detachment system. Ar-dating on white mica indicates that both shear zones operated between 23 Ma and 17 Ma. Restoration of the folded South Tibetan detachment in far western Nepal yields a minimum dip-slip distance of 190 km, compatible with predictions made by models of extrusion of a weak mid-crustal channel. Our results support an orogenic model in which channel flow in the hinterland coexisted with thrust wedge mechanics in the foreland.

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