Significant late Neogene east-west extension in northern Tibet

Field mapping in northern Tibet reveals that the normal slip along late Cen ozoic north-south-trending faults is comparable to that estimated for equiv alent structures in southern Tibet. The orientation of fault striations in two north-south-trending rifts suggests an east-northeast-west-northwest di rection of extension in northern Tibet, which in turn implies that northeas t-striking active faults in northern Tibet have significant left-slip compo nents. Initiation of rifting in northern Tibet postdates the early Oligocen e, and possibly occurred after 4 Ma. The broad similarities in the magnitud e of slip and the direction of extension for normal faults in both northern and southern Tibet imply that the entire plateau has been extending. This precludes significant eastward extrusion of north Tibet relative to south T ibet and requires a regional boundary condition as the cause of east-west e xtension for the entire Tibet plateau.