Structural and Metamorphic Traverse across the northwestern Kathmandu Nappe, central Nepal

A. Alexander G. Webb, and Bishal Nath Upreti

This contribution describes an easy-access, one-day field excursion across the northwestern Kathmandu Nappe along the Kathmandu-Pokhara Highway. The Kathmandu Nappe is one of the best-studied members of the Lesser Himalayan Crystalline Nappes, an enigmatic series of klippen and half-klippen that occur across the central southern Himalaya. Various workers have assigned different tectonic affinities to these Nappes, with possibilities including all of the three major Himalayan units (the Lesser Himalayan Sequence, Greater Himalayan Crystalline complex, and Tethyan Himalayan Sequence) or some combination thereof. The field trip introduces the basic geology of the Kathmandu Nappe, and allows participants to explore the possible implications of long-standing and recent findings from this area for our understanding of Himalayan thrust tectonics. Highlights include stops at the Mahabharat thrust and the Galchi shear zone, which may represent the major faults bounding the Greater Himalayan Crystalline complex. The Mahabharat thrust is widely interpreted as the southern trace of the Main Central thrust, whereas the Galchi shear zone is proposed to represent the southern strand of the South Tibet detachment. These interpretations and their broader implications, including the possibility that the Greater Himalayan Crystallline complex was not extruded towards the surface between its bounding faults, can be readily explored during this one-day excursion.

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