Miocene Jiali faulting and its implications for Tibetan tectonic evolution

The Karakoram-Jiali Fault Zone (KJFZ) comprises a series of right-lateral shear zones that southerly bound the eastward extrusion of northern, Tibet relative to India and stable Eurasia. Here we present new 40Ar/39Ar age data from the Puqu and Parking faults, two easternmost branches of the Jiali fault zone, which indicate a main phase of the KJFZ shearing from similar to18 to 12 Ma. Thus, the Tibetan eastward extrusion bounded by principal strike-slip fault zones started and was probably most active around the middle Miocene, an interval marked also by active east-west extension in southern Tibet. The coincidence of these two tectonic events strongly suggests a common causal mechanism, which is best explained as oblique convergence between India and Asia. Under the framework of this mechanism, the extension in southern Tibet is not a proxy for the plateau uplift. The KJFZ activity was furthermore coincident with right-lateral displacements along the Gaoligong and Sagaing faults in southeast Asia. This defines a Miocene deformation record for the regional dextral accommodation zone that, in response to the continuing India Asia collision, may have accounted for the initiation and prolonged history of clockwise rotation of the Tibetan extrusion around the eastern Himalayan Syntaxis. (C) 2002 Elsevier Science B.V. All rights reserved.