Deep crustal structure of the southeastern Lhasa Terrane

doi:10.13745/j.esf.sf.2023.2.10

Abstract

Abstract:

The southern Lhasa Terrane is the foremost area to investigate plate boundary interactions in the India-Eurasia collision zone. Prior to Cenozoic continental collision, the southeastern Lhasa Terrane underwent multi-stage tectonic evolution under Mesozoic subduction of the Tethyan oceanic lithosphere, which resulted in a complex regional crustal structure that renders inconsistent observations of its deep structure using different geophysical methods with different resolving power. Presently, broadband seismic observation and deep seismic reflection data disagree on the location of the subduction front at the Indian plate. To gain further insight, a short-period dense array survey line was laid parallel to the previous survey line. By using high-resolution P-wave receiver functions, we discovered that the previously defined northward extension of the Indian lower crust based on broadband data is actually not continuous. In fact, the Indian crust exists only beneath the Yarlung Zangbo suture zone, which is consistent with deep seismic reflection results. The middle and upper crust of the Lhasa Terrane develops a thrust fault under south-north compression, while lower crustal eclogitization observed in the broadband seismic data is mainly located in the north of the Yarlung Zangbo suture zone in the middle Lhasa Terrane and southern part of the North Lhasa Terrane.

Key words: Lhasa Terrane, Yarlung Zangbo suture zone, short-period dense array, receiver functions

CLC Number:

P545

XU Xiao, YU Jiahao, XIANG Bo, GUO Xiaoyu, LI Chunsen, LUO Xucong, TONG Xiaofei, YUAN Zizhao, LIN Yanqi, SHI Hongcheng. Deep crustal structure of the southeastern Lhasa Terrane[J]. Earth Science Frontiers, 2023, 30(3): 221-232.

Figures/Tables 8

Fig.1 Tectonic units of southern Tibet (a) and distribution of previous geophysical observation lines (b, adapted from [4⇓⇓⇓⇓⇓⇓⇓⇓-13])

Fig.2 Lithospheric structure beneath the south-north trending rift zone of southeastern Tibet. Adapted from [31-32].

Fig.3 Location of short-period dense station array and distribution of seismic events. Adapted from [4,7].

Fig.4 Comparative analysis of interpreted nodal short-period station and broadband seismogaphic data. Adapted from [4].

Fig.5 Short-period dense station data improvement results using Gaussian overlay

Fig.6 Results of CCP superimposed imaging of Gangdese 92°E with Gaussian factor 2.5 (c-e) compared with previous result (a), and location of seismic profiles (b). Modified after [7].

Fig.7 (a) p-T curve for the metamorphic belts of the Lhasa Terrane and Himalayas (a, modified from [44]) and (b-d) results of CCP superimposed imaging of Gangdese 92°E with Gaussian factor 3.5

Fig.8 Crustal structural model of the Tethys Himalayan northern margin and Lhasa Terrane (not to scale)

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