Crustal Velocity Structure of the Northeastern Tibetan Plateau from Ambient Noise Surface-Wave Tomography and Its Tectonic Implications

Limited southward underthrusting of the Asian lithosphere and material extrusion beneath the northeastern margin of Tibet, inferred from teleseismic Rayleigh wave tomography

“…In the middle‐to‐lower crust, our results (Figure a) show structural features similar to other seismic studies. For example, two low‐velocity zones are consistently observed [ Bao et al , ; Zhang et al , ; X. Li et al , ; Jiang et al , ]: the first one is underneath the Songpan‐Ganzi Terrane and the West Qinling Orogen (east of 101°E) and the second one is underneath the Shanxi‐Shaanxi Rift. Moreover, the middle‐to‐lower crust of the eastern part of Ordos Block exhibits a velocity of ∼3.60 km/s, in agreement with the results from ambient noise analysis and receiver function imaging showing a low‐velocity crustal layer inside the craton [ Zheng et al , ; Cheng et al , ].…”

“…However, detailed structures beneath this part of Tibet are under ardent debate recently. Many geophysical investigations agree on the existence of crustal low‐velocity zones under the Songpan‐Ganzi Terrane and the western part of Qilian Orogen [ Li et al , ; Bao et al , ; H. Li et al , ; X. Li et al , ; Jiang et al , ; Yu et al , ; Zheng et al , ], which might correspond to the proposed middle‐to‐lower crustal flow [ Royden et al , ; Beaumont et al , , ], but these zones are not as widespread and well connected as expected. On the other hand, geophysical results diverge on the mantle lithosphere structure.…”

Lateral extrusion along the Altyn Tagh Fault, Qilian Shan (NE Tibet): insight from a 3D crustal budget

“…The occurrence of lower crustal flow in the north‐eastern Tibetan Plateau has recently been rejected (e.g. Lease et al ., ; Li et al ., ). From this conclusion and the lack of Cenozoic magmatism in the Qaidam Basin and Qilian Shan (Yin and Harrison, ), we conclude that the Cenozoic crust–mantle interaction and transition is sufficiently weak to be neglected in our model, and we simplify the mass balance to volume balance.…”

“…The present‐day crustal thickness ( H 1 ) in the Qilian Shan was calculated by adding the average crustal thickness below sea‐level (~60 km; Fig. C; Tian and Zhang, ; Li et al ., ), the average amount of Cenozoic exhumation (~6 km) estimated from fission‐track analysis (Jolivet et al ., ) and the average elevation of the range (~4 km) measured on Google Earth. The obtained value for H 1 is ~70 km.…”

“…(C) SRTM ‐based present‐day crustal‐thickness map of the northern Tibetan Plateau and the surrounding region, modified from Li et al . (). The white solid triangles represent the locations of seismic stations, and numbers refer to the corresponding crustal thickness.…”