Penetration of mid-crustal low velocity zone across the Kunlun Fault in the NE Tibetan Plateau revealed by ambient noise tomography

- A 3D Vsv model with a resolution of ∼30-50 km is constructed in the NE Tibetan Plateau.
- Widespread mid-crustal LVZs are observed in the NE Tibetan Plateau.
- LVZs have penetrated northward into the East Kunlun and Qinling Orogen over ∼100 km.
- The distribution of mid-crustal LVZs is consistent with the mid/lower crustal channel flow model.

The NE Tibetan Plateau, composed of the Mesozoic accretions of Lhasa, Qiangtang and Songpan-Ganze Terranes, are bounded by the east Kunlun-Qaidam Block in the north with the boundary delineated by the Kunlun Fault. The NE Tibetan Plateau is at a nascent stage of plateau growth resulting from the collision between the Indian and Eurasian plate starting ∼50 million years ago, and is one of the best areas to study the growth mechanism of the Tibetan Plateau. In this study, we process continuous ambient noise data collected from ∼280 stations during 2007 and 2010 and generate Rayleigh wave phase velocity maps at 10-60 s periods with a lateral resolution of ∼30-50 km for most of the study region. By adopting a Bayesian Monte Carlo method, we then construct a 3-D Vsv model of the crust using the Rayleigh wave dispersion maps. Our 3-D model reveals that strong LVZs exist in the middle crust across the NE Tibetan Plateau; and the lateral distribution of LVZs exhibit significant west-east variations along the Kunlun Fault. In the west of 98°E, LVZs are confined to regions of the Kunlun Fault and the eastern Kunlun Ranges, but absent beneath the Qaidam Basin; while in the east of 98°E, LVZs extend and penetrate northward into the east Kunlun and Qinling Orogens over ∼100 km across the Kunlun Fault. The strong contrast of the LVZs distribution along the Kunlun Fault may be related to the distinct neighboring tectonic units in the north: a strong crust of the Qaidam Basin in the west blocking the penetration of LVZs, but a weak crust in the Qinling Orogens facilitating the extrusion of LVZs. The distribution of LVZs in the NE Tibetan Plateau is consistent with the crustal channel flow model, which predicts a branch of north-eastward mid-crustal channel flow. Our 3D model clearly delineates the north extent of the mid-crustal LVZs, probably reflecting the status of channel flow in the NE Tibetan Plateau.