Less-Well-Developed Crustal Channel-Flow in the Central Tibetan Plateau Revealed by Receiver Function and Surface Wave Joint Inversion

A crustal channel-flow model has been previously used to explain the formation of crustal extensional structures in the Tibetan Plateau. However, the existence of massive crustal channel-flow in the central plateau is still controversial. To reveal the crustal S-wave velocity structure with high vertical resolution, we conducted a joint inversion of receiver functions and surface wave dispersions from the 2-D broadband seismic array SANDWICH deployed in the central plateau. Our results show a low-velocity layer (LVL) in the middle-lower crust beneath all stations. The minimum S-wave velocity in each LVL is mostly within 3.0-3.4 km/s, which result in the maximum velocity reductions are less than 17.5%. It deduces a melt volume percentage (MVP) less than 7% even attributing all velocity reduction to partial melting of rocks. Our study suggests that there is not a high enough melt volume in central Tibet to develop crustal channel-flow, which requires a larger MVP to decrease rock strength more than an order of magnitude. The formation of extensional structures in the central plateau may contribute to ductile deformation in the middle-lower crust but not crustal channel-flow.