Quaternary Geology and Faulting in the Damxung‐Yangbajain Basin

Abstract

Abstract The detailed geological mapping, conducted in the Damxung‐Yangbajain basin, shows that there are many types of deposits formed since the Pliocene. The oldest sediments are formed during the Pliocene. The most prominent sediments are three sets of moraines and fluvioglacial deposits. The ESR, U‐series and OSL dates indicate they are formed about 700–500 ka B.P., 250–125 ka B.P. and 75–12 ka B.P. respectively and indicate that there are three glacial periods since the mid‐Pleistocene in the Nyainqentanglha Range. Along the southeast side of the Nyainqentanglha Range, the main southeast dipping fault zone which bounds the Damxung‐Yangbajain Graben on its western edge was mapped. The fault zone consists of three secondary fault zones and their initiation ages that the fault zones became active gradually decrease southeastward. Prominent faulting occurred in about 700–500 ka B.P., 350–220 ka B.P., ˜140 ka B.P. and 70–50 ka B.P. since the mid‐Pleistocene. The height of fault scarps which offset the sediments formed since the mid‐Pleistocene suggest that the vertical slip rates change between 0.4–2 mm/a and the cumulative average vertical movement at rates of 1.1±0.3 mm/a during the Quaternary period and the Holocene vertical throw rate is 1.4±0.6 mm/a along the fault zones on the western side of the Damxung‐Yangbajain Graben.