Thin-skinned N-S extension within the convergent Himalayan region: gravitational collapse of a Miocene topographic front

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Abstract
Summary: Recent work by Burg et al. indicates the presence of E-W striking, gently N-dipping normal faults in the High Himalayas and southern Tibet, that formed during the post-collisional convergence of India and Tibet. These faults extend for at least 600 km along strike. We interpret them as probable late (?) Miocene extensional features with perhaps several tens of kilometres downward northerly displacement. A simple elastic model suggests that these normal faults may have formed during gravitational collapse of the Miocene topographic front between India and Tibet. In this interpretation, gravitational collapse occurred by southward motion, relative to India and Tibet, of a wedge of crustal rock bounded above by gently dipping normal faults and below by thrust faults that probably dip N. N-S extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere. Such faults may be common, but so far mainly unrecognized, features developed during convergence in many orogenic belts.