The Eastern prolongation of the Zanskar Shear Zone (Western Himalaya)

This paper aims to describe the possible SE extension of the Zanskar Shear Zone and its relation with other extensional and compressional structures, New structural and metamorphic data were collected in the Baralacha La, Yunam, Lingti region and a new geologic map of the studied area is proposed. The new data reveal that an E-verging syncline (the Kenlung Serai fold), formerly interpreted as a late backfold is, in fact, related to an early northward underthrusting of India below Asia before the main NE movement related to nappes emplacement. This succession of movements is coherent with the displacement of India postulated by several authors from paleomagnetic data. The well defined Zanskar Shear Zone can be followed towards the SE in a zone of low angle normal faults (the Tapachan normal fault zone) located at the front of the North Himalayan nappes. The change in style from a ductile shear zone to a set of low angle normal faults is related to a change of tectonic level and metamorphic grade. The location of these extensional structures at the front of the North Himalayan nappes as well as their tectonometamorphic history is totally similar to what is known farther NW for the Zanskar Shear Zone. High angle normal faults such as the Sarchu faults are late structures related to vertical extrusion accommodated by doming. Late NE-verging backfolds develop mainly in the hanging wall of the high angle normal faults and are therefore associated with the doming event. The new data are incorporated into a kinematic model for the "Crystalline nappe".