An overview of thrusts and nappes of western Himalaya

Abstract

The Shali-Deoban Parautochthon, Krol Berinag Nappes and Outer Crystallines Nappes are the main lithostructural units of the Lesser Himalaya of Kumaun, Garhwal and eastern Himachal. Two thrust sheets, the Chail Nappe and the Jutogh Nappe are recognized in the Outer Crystallines Nappes. The Chail Nappe forms a separate thrust sheet, and the Jutogh Nappe overlying it represents a southward extension of the Central Crystallines Nappe of the Higher Himalaya. The Chail Nappe rocks constitute the base of the Palaeozoic-Mesozoic sequence of the Kashmir-Chamba Parautochthon, whereas the Central Crystallines Nappe forms the basement for the late Precambrian-Cretaceous sequence of the Tethyan Zone in the Kumaun, Spiti and Zaskar regions. The Central Crystallines Nappe shows a progressive regional metamorphism, chlorite to sillimanite grade, whereas the metamorphism of the Chail Nappe is mainly confined to the greenschist facies. Metamorphic inversion is a characteristic feature of the Jutogh Nappe which occurs as crystalline klippen in the Lesser Himalaya Zone. The ophiolite suite of rocks of the Indus-Tsangpo suture occurs also as klippen above the sediments of the Tethys Himalaya and metamorphics of the Tso Morari Dome. They appear to have resulted from squeezing out from the root zone and subsequent gravity gliding. The Indus Suture Zone is unique with regard to its thrust tectonics, in that, whereas all the principal thrusts elsewhere in the Himalaya are directed towards the S, within this zone they are directed only toward the N.