Tearing of Indian mantle lithosphere from high-resolution seismic images and its implications for lithosphere coupling in southern Tibet

Abstract

What happened to the Indian mantle lithosphere (IML) during the Indian-Eurasian collision and what role it has played on the plateau growth are fundamental questions that remain unanswered. Here, we show clear images of the IML from high-resolution P and S tomography, which suggest that the subducted IML is torn into at least four pieces with different angles and northern limits, shallower and extending further in the west and east sides while steeper in the middle. Intermediate-depth earthquakes in the lower crust and mantle are located almost exclusively in the high-velocity (and presumably strong) part of the Indian lithosphere. The tearing of the IML provides a unified mechanism for Late Miocene and Quaternary rifting, current crustal deformation, and intermediate-depth earthquakes in the southern and central Tibetan Plateau and suggests that the deformations of the crust and the mantle lithosphere are strongly coupled.

East‐West Differential Underthrusting of the Indian Lithospheric Plate Beneath Central Tibet Revealed by Imaging VP/VS

“…This model is consistent with previous studies that concluded that the IML is underthrusting beneath southern Tibet with an eastward increase in dip angle (Chen et al, ; Li et al, ; Zhao et al, ) and is supported by the latest Pn tomography result (Li & Song, ), in which a remarkable tear is seen to exist at almost the same position. In addition, crustal scale studies by deep seismic reflection profiling (Guo et al, ) also revealed a consistent geometric variation of eastward steepening of the subducting Indian crust, but with a limited advancing extent relative to the IML, reflecting the coupling of crust‐mantle deformation in the vertical direction and decoupling of advancement in the horizontal direction.…”

“…With the continually northward underthrusting of the Indian lithospheric slab beneath Tibet, slab‐tearing subparallel to the convergence direction occurred because of the differential rollback velocities of the slab. Previous shear wave birefringence (Chen et al, ), tomography studies (Li et al, ; Li & Song, ; Liang, Chen, et al, ), and deep seismic reflection images (Guo et al, ) have led to a similar model. Meanwhile, the downgoing plate would have an important effect on the mantle flow, as revealed by seismic anisotropy observations (Long & Silver, , ), driving subslab mantle flow in the direction of the subslab.…”

“…As discussed above, the velocity ratio structures differ significantly between the two sides of 90°E in response of different geometries of the underthrusting Indian lithospheric slab beneath Tibet. Combined with previous seismic studies (Agius & Lebedev, 2013;Guo et al, 2018;Li & Song, 2018;Nunn et al, 2014;Tian et al, 2015), we outline the geometries of the IML beneath central Tibet with Figure 10. From our result, we propose that the IML has been mainly torn into two parts beneath our research area, and the tear corresponds in position with the YGR.…”

“…First, the extent of underthrusting to the north under the southern portion is not consistent. Tomography results suggest that the entire plateau is underlain by relatively cold lithospheric mantle (to 225–250 km in depth; Shapiro & Ritzwoller, ; Zhou & Murphy, ), whereas other results indicate that the subducted IML only lies under the southern portion of the Tibetan Plateau (Li et al, ; Li & Song, ; Liang et al, ; Tilmann & Ni, ; Zhang et al, ) or that its frontier has passed through the Bangong‐Nujiang suture (BNS) and extended northward beneath the Qiangtang terrane (He et al, ; Hung et al, ; Qiang et al, ), which is consistent with inefficient Sn propagation, low seismic velocities (Barron & Priestley, ), and strong seismic anisotropy (Huang et al, ) beneath northern Tibet. Previous results reveal different geometries of the IML under central Tibet.…”

Early‐Stage Lithospheric Foundering Beneath the Eastern Tibetan Plateau Revealed by Full‐Wave Pn Tomography

“…Our model thus suggests an east-west boundary of the northern Tibetan Plateau at approximately 93°E. This overall pattern of velocity variations agrees with previous P n studies (Hearn et al, 2019;J. T. Li & Song, 2018;Zhou & Lei, 2016).…”