Opposite vergent synclines on the flanks of a large-scale box fold in the Chamba–Lahaul region, northwest Himalaya, India

Abstract

This article focuses on two regional-scale synclines of the Chamba Thrust Sheet, northwest Himalaya. These synclines were explained by two different tectonic events. Earlier studies ascribe the NE vergent Tandi syncline and the SW vergent Chamba syncline to the older NE-directed nappe stacking and the younger SW-directed Himalayan deformation events, respectively. The new field data and structural analysis reveal that these synclines define the flanks of a large-scale asymmetric box fold referred to here as the Hadsar–Chobia box fold and to a common phase of deformation. The box fold in the Chamba Thrust Sheet has developed over a ductile–brittle substrate referred to here as the Chamba Thrust. This thrust has translated a portion of the Tethys Himalaya over both the Higher Himalayan Crystallines and the Lesser Himalaya. Structural analysis, particularly the parallelism between the trends of hinge lines of the Hadsar–Chobia box fold and the strike of the regional thrust planes indicate that the folding and translation may have occurred simultaneously during the D1 deformation episode.