Evolution of normal faults within the Higher Himalaya - local phenomenon or regional trend?

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One of the most challenging problems in understanding the evolution of ancient and active mountain belts are normal faults in the setting which is otherwise characterized by structures related to shortening. Observations in the Andes, the Alps, as well as in the Himalaya shows that extension and normal faulting at upper crustal levels can occur contemporaneously with shortening and thrusting at lower crustal levels or in areas of low topography. In the internal sectors of the Himalayan orogen, active N-S striking extensional fault systems at high elevations are well documented. These closely spaced faults are the youngest structural features and cut all pre-existing compressional structures. However, their spatiotemporal propagation, as well as the reason for their formation remains largely unclear. For example, in the NW Himalaya, it is not known whether these fault systems are local phenomena and are related to ongoing exhumation of the Leo Pargil metamorphic dome or if they are an integral part of a structural framework of regional importance. Extensional fault plane solutions of recent earthquakes, structural, and geomorphic observations indicate active normal faulting in the Sutlej Valley (Himachal Pradesh, NW India), where individual faults extend southward toward the Himalayan front and northward into the southern Tibetan plateau. To the south of this region exists an ellipsoidal sector in the orogen, where high exhumation rates correlate with focused, high monsoonal precipitation, and pronounced local relief. Thermochronological data from this area indicate rapid exhumation irrespective of formerly generated structural boundaries, thus emphasizing the importance of erosion-controlled exhumation. In contrast to the region farther north in the Higher Himalaya, this sector of the orogen is characterized by seismicity indicating N-S shortening. The spatial correlation of these three phenomena suggests climatically controlled exhumation until present. A rigorous analysis of existing seismicity data from local networks and data to be obtained from our own network will help better understand the cause of these disparities in orogenic evolution. Additional paleoseismic analysis of Quaternary deposits will further help reveal the temporal development of normal faulting in the Higher Himalaya.