Abstract: ?00 000 geological mapping reveals a series of thrust nappes and folds in the Cretaceous in the Coqên area, west central Tibet, which are cut by plutons and overlain unconformably by undeformed volcanic tuffs. Ar Ar ages of the K feldspar and hornblende in plutons and altered plagioclase in the tuffs, composition of sedimentary materials and spatial distribution of the sedimentary strata suggest that the thrusts and folds developed in the Late Cretaceous, earlier than the Early Teritary. Regional geological data shows that Late Mesozoic structural deformation was prevalent in the Lasha block.