Geometry of accretion and oceanic thrusting of the Spongtang Ophiolite, Ladakh-Himalaya

Abstract

Ductile mylonitic shear zones, which in ophiolitic peridotites over-print high-temperature ductile flow, have been commonly associated with intra-oceanic thrusting, if situated at the base of the peridotites1,2. In fewer cases, such shear zones have been related to the vicinity of transform faults cutting the spreading ridge3–9. In the Spongtang nappe, one of the few well preserved Himalayan ophiolite slabs, obducted southward from the Indus–Tsangpo suture zone, two successive mylonitic ductile shear events in the peridotites have been observed. The first can be related to a transform fault, the second to intra-oceanic thrusting, resulting in the superposition of two peridotite sheets10,11. Poor development of the crustal sequence also indicates the presence of a transform fault, and/or to a very slowly spreading ridge. Here a three-dimensional geometry of the accretional and successive oceanic environment in the context of the eastern Neo-Tethys is proposed.