Tectonic evolution of Kishtwar Window with respect to the Main Central Thrust, northwest Himalaya, India

Abstract

The crystalline rocks of the Himalaya (High Himalayan Crystallines, Central Crystallines, etc.) are bounded to the north by the South Tibetan Detachment/Zanskar Shear Zone/Trans Himadri Fault System at the top and to the south by the Main Central Thrust (MCT) at the base. To the south and tectonically below the MCT lies the Lesser Himalaya comprising low grade meta-sedimentary thrust sheets and the crystallines klippen. North and tectonically above the Zanskar Shear Zone lies the sedimentary succession of the Tethys Himalaya. However, there is a different geological set-up to the northwest of Beas valley, which defies this normal set-up, i.e., the Tethyan rocks either lie in contact with the Lesser Himalayan thrust sheets or they, to a large extent, surround the High Himalayan Crystallines (HHC). This unique set-up is documented around areas comprising Chamba, Kishtwar and Zanskar regions in the northwest Himalaya. The Lesser Himalayan imbricated sequence, extending progressively into deeper structural level beneath and crops-out as Kishtwar Window within the HHC. This tectonic contact along the window was described as the MCT. However, the present study of the window indicates that its western side is bounded by a high angle NE dipping reverse fault (Kishtwar Thrust). The structural analyses reveal that this fault is younger than the MCT and is interpreted here as Breach Thrust. Present observations suggest that the rocks of the window and the northeasterly lying HHC have been folded and exhumed together as an antiform along the Kishtwar Thrust. The HHC occurring south of the Kishtwar Window have actually been thrust over the Lesser Himalayan thrust sheet. This contact is observed and marked for the first time and is accordingly described as the Main Central Thrust as per convention along the length of the Himalayan belt. Northeast and in the hangingwall of the MCT, the repetition of the contact of the Lesser Himalayan rocks and the HHC is interpreted here as the deeper part of the MCT brought to the surface by Kishtwar Thrust.