Abstract:

Lhozhag fault,the eastern segment of the famous Dingri-Lhozhag Fault,is a tectonically significant structure in the Himalayan orogen, but it remains poorly constrained so far. Geologic mapping and structural analysis of Lhozhag fault in Lhozhag area, southeastern Tibet, were carried out to reveal its geometry, kinematics, evolutional history and tectonic significance. The major structural features of Lhozhag fault are described as follows:(1)Lhozhag fault is now mainly characterized by a large brittle, brittle-ductile normal fault with a SWW-NEE strike and steep NNW dipping. The fault zone materials are comprised of cleavages, fault gouge, fault breccia,etc. (2)Two blocks in Tethys Himalaya unit separated by Lhozhag fault have significantly different deformation characteristics, the south with gentle deformation, and the north with strong deformation. (3)Lhozhag fault has experienced five deformation events,i.e.normally faulting during the Mesozoic, thrusting during the Paleogene, ductile extension during the Miocene, thrusting during the late Miocene, and normally faulting during the Pliocene and Quaternary. Present fault features show more of the last episode of the activities.(4)Lhozhag fault on its large scale, multi-phase activities, and controlling the deformational and sedimentary differences between the northern and southern blocks, reveals that it plays the role of separating tectonic units on Himalayan orogeny.(5)Both Lhozhag fault and the south Tibetan detachment fault (STD) outcrop in Lhozhag area, and in some places,they are close to each other. Field data show steep Lhozhag fault has cut gentle STD. Lhozhag fault is a regional fault with a longer geological history than STD, but the latter’s activities since Miocene have attracted more attention.

Key words: Lhozhag fault, regional fault, multi-phase activity, south Tibetan detachment fault, ESR dating