Lithospheric structures of and tectonic implications for the central–east Tibetan plateau inferred from joint tomography of receiver functions and surface waves

Abstract

Summary We present an updated joint tomographic method to simultaneously invert receiver function waveforms and surface-wave dispersions for a 3-D S-wave velocity (Vs) model. By applying this method to observations from ∼900 seismic stations and with a priori Moho constraints from previous studies, we construct a 3-D lithospheric S-wave velocity model and crustal-thickness map for the central–east Tibetan plateau. Data misfit/fitting shows that the inverted model can fit the receiver functions and surface-wave dispersions reasonably well, and checkerboard tests show the model can retrieve major structural information. The results highlight several features. Within the plateau crustal thickness is > 60 km and outwith the plateau it is ∼40 km. Obvious Moho offsets and lateral variations of crustal velocities exist beneath the eastern (Longmen Shan Fault), northern (central-east Kunlun Fault) and northeastern (east Kunlun Fault) boundaries of the plateau, but with decreasing intensity. Segmented high upper-mantle velocities have varied occurrences and depth extents from south/southwest to north/northeast in the plateau. A Z-shaped upper-mantle low-velocity channel, which was taken as Tibetan lithospheric mantle, reflecting deformable material lies along the northern and eastern periphery of the Tibetan plateau, seemingly separating two large high-velocity mantle areas that respectively correspond to the Indian and Asian lithospheres. Other small high-velocity mantle segments overlain by the Z-shaped channel are possibly remnants of cold micro-plates/slabs associated with subductions/collisions prior to the Indian-Eurasian collision during the accretion of the Tibetan region. By integrating the Vs structures with known tectonic information, we derive that the Indian slab generally underlies the plateau south of the Bangong–Nujiang suture in central Tibet and the Jinsha River suture in eastern Tibet and west of the Lanchangjiang suture in southeastern Tibet. The eastern, northern, northeastern and southeastern boundaries of the Tibetan plateau have undergone deformation with decreasing intensity. The weakly resisting northeast and southeast margins, bounded by a wider softer channel of uppermost mantle material, are two potential regions for plateau expansion in the future.

Lateral Seismic Anisotropy Variations Record Interaction Between Tibetan Mantle Flow and Plume‐Strengthened Yangtze Craton

“…Xu et al., 2001). Furthermore, recent seismic tomographic images also depict an asthenospheric corridor with upper mantle low‐velocity anomaly beneath the TRZ, which is contrasting to the thick upper mantle high‐velocity anomaly beneath the western Yangtze Craton (e.g., Feng et al., 2020; F. Zhang et al., 2018). It is therefore of great interest to know how the mantle extrusion along the asthenospheric corridor might interact with the craton impacted by an ancient mantle plume, and the XKS splittings could provide an approach to inspect the related dynamics happened there.…”

“…Purple filled regions represent the Eocene-Oligocene potassic rocks (Chung et al, 1998) The continental extrusion was apparently accompanied by the mantle extrusion process along the west edge of the Yangtze Craton, given the geochemical signatures of an exotic lithospheric mantle linked to Tibet by the dispersed, small-volume potassic volcanics exposed from the central Tibet to the Indochina Block (Figure 1a) (Flower et al, 1998;Mo et al, 2006;Y.-G. Xu et al, 2001). Furthermore, recent seismic tomographic images also depict an asthenospheric corridor with upper mantle low-velocity anomaly beneath the TRZ, which is contrasting to the thick upper mantle high-velocity anomaly beneath the western Yangtze Craton (e.g., Feng et al, 2020;F. Zhang et al, 2018).…”

The lithospheric S-wave velocity structure beneath the NE Tibetan Plateau and its surrounding craton basins

“…The S-wave velocity structure beneath sections along (A) latitude line of 38 °N (A) and (B) longitude line of 102 °E from this study and previous studies (Wang, et al, 2017;Feng, et al, 2020;Han, et al, 2022;Wu, et al, 2022).…”

“…By using double-difference tomography, Han, et al ( 2022) obtained high-resolution longitudinal and shear wave velocity models in China. For similar researches in NE Tibetan Plateau and the surrounding areas, some studies used part of the data set and the same method as the current study (e.g., Wang et al, 2017;Wu et al, 2022), and some studies used completely different data set and different methods (e.g., Feng et al, 2017Feng et al, , 2020. We compare our results with four previous studies (Wang et al, 2017;Feng et al, 2020;Han et al, 2022;Wu et al, 2022) beneath two profiles along the latitude line of 38 °N and longitude line of 102 °E, as shown in Figure 10.…”

Uppermost Mantle Seismic Pn‐Velocity in Continental China and Its Tectonic Implications

“…Similarly, we attribute the high Pn ‐velocity anomaly beneath the southeastern Tibetan Plateau (HV10) to low temperatures of the cold cratonic root of the Indian lithospheric mantle subducted beneath the Lhasa block and the remnant cratonic root of the Lhasa lithospheric mantle subducted beneath the Qiangtang block. This conclusion is supported by the following lines of evidence: (a) a high‐velocity body in the uppermost mantle was reported to reach the Jinshajiang suture (JS) in the eastern Tibetan Plateau (M. Chen et al., 2015, 2017; Feng et al., 2020; Hearn et al., 2004, 2019; Kim et al., 2021; Li & Song, 2018; Liang & Song, 2006; Replumaz et al., 2014; Tilmann et al., 2003), (b) a dislocated lithosphere‐asthenosphere‐boundary beneath the Bangong‐Nujiang suture (BNS) was observed in the eastern Tibetan Plateau (Zhao et al., 2010, 2011), possibly indicating the presence of two types of lithospheres (i.e., the Indian lithosphere and the Lhasa lithosphere), and (c) a significant lithospheric mantle discontinuity between the BNS and the JS was reported (Yue et al., 2012), possibly indicating the presence of the subducted Lhasa lithospheric mantle beneath the Qiangtang block.…”