TECTONIC AND METAMORPHIC EVOLUTION

OF THE CENTRAL HIMALAYAN DOMAIN

IN SOUTHEAST ZANSKAR

by Pierre Dèzes

4. TECTONICS

Nothing I had ever read or imagined prepared me for the splendour and majesty of the mountains that first day; that was the first gift Ladakh gave me, a silence before that phantasmagoria of stone, those vast wind-palaces of red and ochre and purple rock, those rock faces the wind and snow had worked over thousands of years into shapes so unexpected and fantastical the eye could hardly believe them [...] rocks tortured in as many thousand ways as the mountains they are torn from.

«A Journey tp Ladakh» Andrew Harvey

4.1 Introduction

We have seen in the previous chapters that the Tethys Himalaya and part of the High Himalayan Crystalline Sequence are formed by a thick pile of sedimentary rocks, deposited on the northern margin of the Indian continent and that the normal stratigraphic succession of these sediments was disturbed in places by a succession of tectonic events, that occurred mainly during the Paleozoic. The stress these events exerted on the sedimentary series are however moderate compared to the huge forces that were applied on them during the collision between India and Asia. Most of the deformations that can be observed within the Tethys Himalaya and the High Himalayan Crystalline Sequence are thus the consequence of the Himalayan orogen.

A considerable amount of work has already been done by previous researchers to decipher the rather complex Himalayan tectonic evolution of the Ladakh - Zanskar - Lahul area (Frank et al. 1973, 1977, 1987; Thöni, 1977; Bassoulet et al. 1980; Srikantia et al., 1980; Fuchs, 1982, 1987, 1989; Honegger, 1983; Keleman and Sonnenfeld, 1983; Baud et al. 1984; Gaetani et al. 1985; Colchen et al. 1986; Gilbert, 1986; Searle, 1986; Stutz and Steck, 1986; Herren, 1987; Kündig, 1988; Searle et al., 1988, 1997; McElroy et al. 1990; Pêcher, 1991; Gapais et al., 1992; Güntli, 1993; Patel et al. 1993; Routh, 1993; Steck et al., 1993, 1998; Spring, 1993; Vannay, 1993; Epard et al., 1995; Fuchs et al. 1995; Vannay and Steck, 1995; Wyss et al., in press). These studies, although sometimes contradictory, lead to a better understanding of the northwestern Himalayan tectonic history.

The tectonic evolution of the Ladakh-Zanskar-Lahul region can be subdivided in two major episodes: the first one is marked by compression tectonics related to the collision between India and Asia. This first event was responsible for crustal shortening, thickening and Barrovian metamorphic imprint on the sedimentary series of the Indian continental margin. Deformation was accommodated by thrusting, folding and the formation of both SW- and NE-directed nappes. The second major episode is marked by extensional tectonic structures related to the exhumation of the high-grade metamorphic rocks of the High Himalayan Crystalline Sequence. This second episode of syn-orogenic extension occurred while the Himalaya was still globally in compression and is expressed by ductile normal shearing, doming and brittle normal faulting.