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

• Published in: Journal of geophysical research. Solid earth 2023-04, Vol.128 (4), p.n/a
• Main Authors: Nie, Shitan, Tian, Xiaobo, Liang, Xiaofeng, Wan, Bo
• Format: Article
• Language: English
• Subjects: Broadband; crustal channel‐flow; Deformation; Flow; Geological faults; Geophysics; joint inversion; Plateaus; receiver function; Resolution; Rock; Rocks; S waves; Seismic arrays; Seismic data; Seismic velocities; Seismological data; Structures; Surface water waves; surface wave; Surface waves; Tibetan Plateau; Velocity; Wave dispersion; Wave velocity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2022JB025747

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. Plain Language Summary The crustal channel‐flow model suggests that the middle‐lower crust partially melts, resulting in flow from central Tibet to its eastern margin. Therefore, basal shear is exerted on the upper crust and generates east‒west extensional structures, such as the north‐south‐trending rifts in the Lhasa and Qiangtang terranes and the conjugate strike‐slip faults along the Bangong‐Nujiang suture. Seismic low‐velocity layers (LVLs) have been reported in the middle‐lower crust beneath the central plateau and treated as the signature of crustal channel‐flow. However, there is no clear evidence to support that the LVLs are weak enough to result in flow. To generate crustal channel‐flow, the melt volume percentage (MVP) should be larger than 7% to form an interconnected network, which will decrease the rock strength by one order of magnitude. We imaged the crustal velocity structure with high vertical resolution in central Tibet using broadband seismic data. However, the S‐wave velocities in the LVLs are almost within 3.0–3.4 km/s, which corresponds to an MVP lower than 7%. This implies that there is no massive crustal channel‐flow in the central plateau. We suggest that east‒west extension structures are the result of ductile deformation rather than crustal channel‐flow in the