Significant late Neogene east-west extension in northern Tibet

Field mapping in northern Tibet reveals that the normal slip along late Cenozoic north-south-trending faults is comparable to that estimated for equivalent structures in southern Tibet. The orientation of fault striations in two north-south-trending rifts suggests an eastnortheast-west-northwest direction of extension in northern Tibet, which in turn implies that northeast-striking active faults in northern Tibet have significant left-slip components. Initiation of rifting in northern Tibet postdates the early Oligocene, and possibly occurred after 4 Ma. The broad similarities in the magnitude 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 Tibet and requires a regional boundary condition as the cause of east-west extension for the entire Tibet plateau.