The role of extension during brittle deformation within the NW Indian Himalaya

Synorogenic extension has been recognized as an integral structural constituent of mountain belts and high‐elevation plateaus during their evolution. In the Himalaya, both orogen‐parallel and orogen‐normal extension has been recognized. However, the underlying driving forces for extension and their timing are still a matter of debate. Here we present new fault kinematic data based on systematic measurements of hundreds of outcrop‐scale brittle fault planes in the NW Indian Himalaya. This new data set, as well as field observations including crosscutting relationships, mineral fibers on fault planes, and correlations with deformation structures in lake sediments, allows us to distinguish different deformation styles. The overall strain pattern derived from our data reflects the large regional contractional deformation pattern very well but also reveals significant extensional deformation in a region, which is dominated by shortening. In total, we were able to identify six deformation styles, most of which are temporally and spatially linked, representing protracted shortening. Our observations also furnish the basis for a detailed overview of the younger deformation history in the NW Himalaya, which has been characterized by extension overprinting previously generated structures related to shortening. The four dominant deformation styles are (1) shortening parallel to the regional convergence direction; (2) arc‐normal extension; (3) arc‐parallel extension; and finally, (4) E–W extension. This is the first data set where a succession of both arc‐normal and E–W extension has been documented in the Himalaya. Importantly, our observations help differentiate E–W extension triggered by processes within the Tibetan Plateau from arc‐parallel and arc‐normal extension originating from the curvature of the Himalayan orogen.