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

Abstract

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".

Exhumation history of the NW Indian Himalaya revealed by fission track and 40Ar/39Ar ages

“…Metamorphic grade ranges from the prehnite-pumpellyite zone in the Baralacha La-upper Chandra region ( Fig. 1; Steck et al, 1993;Vannay, 1993;Steck, 2003;Epard and Steck, 2004) to the sillimanite + K-feldspar + melt zone in the High Himalayan Crystalline dome south of Zanskar (Honegger, 1983;Honegger et al, 1982;Searle et al, 1992, 1999; Robyr et al, 2002Robyr et al, , 2006. The Zanskar shear zone was intruded during its formation by the 22.2 ± 0.2 Ma Gumburanjun leucogranite (Dèzes et al, 1999).…”

“…Its eastern en echelon continuation is defined by the Tapachan and Dutung-Thaktote low angle normal faults. The Zanskar and Tapachan faults are crosscut by the high angle conjugate Sarchu normal faults (Epard and Steck, 2004;Girard et al, , 2001). (6) The High Himalayan nappe contains the same rock sequences as the North Himalayan nappes (Frank et al, 1995.…”

“…(5) The South Tibetan (Burchfiel and Royden, 1985) or Central Himalayan detachment (Fig. 1, Steck, 2003;Epard and Steck, 2004), which overprints the front of the North Himalayan nappes. This detachment zone includes the high-grade ductile Zanskar shear zone on the northern slope of the High Himalayan Crystalline dome (Herren, 1987;Dèzes et al, 1999).…”

Temperature and age constraints on the metamorphism of the Tethyan Himalaya in Central Nepal: A multidisciplinary approach

“…The latter one carries Upper Liassic/Dogger carbonates from the Ratna nappe above Triassic sediments. No other geological surveys have ever revealed thrusts in northern Nepal although they are common far to the W in Zanskar (i.e., Steck et al, 1993;Epard and Steck, 2004).…”

Doming in compressional orogenic settings: New geochronological constraints from the NW Himalaya

“…BT, Baralacha La Thrust; DTFZ, Dutung-Thaktote Fault Zone; HHCZ, High Himalayan Crystalline Zone; JD, Jahla Detachment; KSZ, Khanjar Shear Zone; LHC, Lesser Himalayan Crystalline; LT, Lagudarsi La Thrust; MBT, Main Boundary Thrust; MCT, Main Central Thrust; MTZ, Miyar Thrust; PT, Parang Thrust; SD, Sangla Detachment; SF, Sarchu Fault; ZSZ, Zanskar Shear Zone. a consequence, the tectonometamorphic evolution of this part of the range is well constrained [e.g., Honegger et al, 1982;Kündig, 1989;Stäubli, 1989;Patel et al, 1993;Dèzes, 1999;Searle et al, 1999;Walker et al, 1999;Stephenson et al, 2000;Epard and Steck, 2004]. In contrast, the timing of the metamorphic and tectonic evolution of the southern limb of the Gianbul dome is still poorly constrained.…”