Jiali Fault Research Articles

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 Parlung faults, two easternmost branches of the Jiali fault zone, which indicate a main phase of the KJFZ shearing from ∼18 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.

Travel time tomography inversion and the deep structure of the southern Tibet

2312 P and some S arrival times were picked from 80 earthquakes recorded by 51 seismographs deployed on a profile that followed the southern Tibetan highway during 1992 Sino-French seismic experiment. We analysed the azimuthal and distance variations of P, PKP residuals and S-P travel time residuals along the profile and their tectonic implication, and finally, we applied the "ACH" inversion scheme to calculate the velocity perturbation in the crust and upper mantle. The initial results from our study are: (1) the upper mantle velocity beneath Tibetan Plateau is lower than that of normal continents, the lowest mantle velocity is found beneath QiangTang block. The early PKP residuals in the north (north to Sangxiong) of the profile indicates a shallower Moho depth. (2) The abrupt increase of S-P travel time residuals northward from Indus-Tsangpo Suture (ITS) and the low velocity crust feature in this area from tomography inversion evidenced the existence of partial melting within the crust. (3) Karakorum Jiali Fault Zones (KJFZ) may be the southern branch of Banggong-Nujiang Suture (BNS), the southern boundary of Qiangtang block. (4) The high velocity anomaly beneath north Himalaya revealed by tomography inversion may represents the the front of the underthrusting Indian lithosphere. The lower velocity anomaly beneath the center of the profile may reflect the physical state change related to high temperature.