Indian plate blocked by the thickened Eurasian crust in the middle of the continental collision zone of southern Tibet

• Published in: Earthquake research advances Vol. 3; no. 3; p. 100233
• Main Authors: Wang, Gaochun, Tian, Xiaobo, Li, Yibing, Xu, Tao, Wan, Bo, Chen, Yi, Nie, Shitan, Yang, Xusong, Zuo, Sicheng, Zhang, Jianli
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2023; KeAi Communications Co. Ltd
• Subjects: Crustal P- wave velocity structure; Crustal thickening; Indian lithospheric slab; Qinghai-Tibetan Plateau; Wide-angle reflection/refraction; Wide-angle reflection/refraction; Indian lithospheric slab; Crustal P- wave velocity structure; Qinghai-Tibetan Plateau; Crustal thickening
• ISSN: 2772-4670; 2772-4670
• DOI: 10.1016/j.eqrea.2023.100233

The relationship of the crustal contact between the Indian and Eurasian plates is a key issue in understanding crustal thickening and the subduction of the Indian lithosphere beneath the Qinghai-Tibetan Plateau. Across the middle of the Yarlung-Zangbo Suture (YZS), we deployed an ∼450-km-long SN-trending wide-angle reflection/refraction profile to observe the P-wave velocity (vP) structure beneath the northern Himalaya and the southern plateau. Our results show that, 1. the high vP (∼7.1 ​km/s) indicates that the Indian lower crust extends no more than 50 ​km north of the YZS. 2. The lower crust beneath the southern part of the plateau features an extremely low vP (<6.7 ​± ​0.2 ​km/s). 3. Compared with the velocities of several typical crustal lithologies in different temperature regimes, the low vP in the lower crust can be explained by felsic-intermediate granulite, which has prevented the lower crust from further eclogitization. We propose that the dip angle of the Indian lithospheric slab beneath the YZS is partly controlled by the composition of the lower crust of the plateau. In the northern middle YZS, the crust of the southern plateau is too thick and blocks the northward advancement of the Indian lower crust, resulting in the subduction of the Indian lithospheric slab into the upper mantle. The lower crust in western and eastern Lhasa is dominated by a mafic composition, and it was delaminated after eclogitization before the Miocene. The void zone generated by delamination favors the flattening and underthrusting of the Indian lower crust. •High Vp shows the Indian lower crust is subducting into the upper mantle rather than flat underthrusting beneath the Suture.•An extremely low Vp (<6.7 km/s) of the lower crust beneath the Lhasa terrane indicates a felsic-intermediate composition.•The subducting angle of the Indian slab depends on the nature of lower crust and thickness of the overriding Eurasian plate. Plain language summary: The relationship of the contact between India and Eurasia and the rock type of the lower crust beneath the Tibetan Plateau are key issues in understanding continental collision and the formation of the plateau. Across the middle of the collision zone, a seismic sounding profile was deployed to observe the P-wave velocity (Vp) structure. In our results, the Indian lower crust features high Vp subduction into the upper mantle rather than flat underthrusting northward beneath the suture. The crust is as thick as ∼80 ​km beneath the southern part of the plateau, but its lower crust presents an extremely low Vp. The low Vp is an indicator of the lower crust being composed of felsic-intermediate granulite, which has prevented the lower crust from further eclogitization. We propose that the plateau crust beneath the middle of the collision is too thick and blocks the northward advancement of the Indian lower crust, resulting in subduction of the Indian slab into the upper mantle. In contrast, a lower crust dominated by a mafic composition is delaminated after eclogitization during crustal thickening. The delamination provides a void zone for the flattening and underthrusting of the Indian lower crust beneath western and eastern Lhasa.