Abstract
Himalayan tectonic activity is triggered by downward penetration of the Indian plate beneath the Asian plate. The subsurface geometry of this interaction has not been fully investigated. This study presents novel constraints on this geometry provided by two newly obtained, deep seismic reflection profiles. The profiles cover 100- and 60-km transects across the Yarlung-Zangbo suture of the Himalaya-Tibet orogen at c. 88°E. Both profiles show a crustal-scale outline of the subducting Indian crust. This outline clearly shows Indian understhrusting southern Tibet, but only to a limited degree. When combined with a third seismic reflection profile of the western Himalayas, the new profiles reveal progressive, eastward steepening and shortening in the horizontal advance of the subducting Indian crust.
Highlights
The Himalayan-Tibetan Plateau is currently the world’s largest example of an active continent-continent collisional orogen
New high-resolution seismic reflection profiles described here reveal that India is underthrusting southern Tibet but only to a limited degree
Together with the deep seismic reflection profile in the western Himalayas, the results outlined the limited thickness of Indian crust subduction beneath southern Tibet
Summary
Xiaoyu Guo[1], Wenhui Li2, Rui Gao[1,2], Xiao Xu1, Hongqiang Li2, Xingfu Huang[1], Zhuo Ye2, Zhanwu Lu2 & Simon L. Surface structural investigations have documented top-to-the north displacement bounding the ophiolitic mélange[17], which appeared in the INDEPTH seismic reflection profile across the Yarlung-Zangbo suture zone[16] This observation runs contrary to the assumption that faults bordering the exposed suture zone trend parallel to the direction of subduction. Given the well-documented crustal-scale duplexing that has transferred material from the lower to the upper plate in the western Himalayas[24], we interpret this anomalous zone (bright-spot) as consisting of fragments of ophiolitic mélange from the Yarlung-Zangbo suture (Figs 2d and 3d) dislocated during crustal-scale duplexing of the subducted Indian crust along the MHT at its base[24] (Figs 2d and 3d). The overall crustal geometry imaged by these seismic reflection profiles (seismic lines A, B and C in Fig. 1a) affirms lateral variation along the subductive margin and indicates progressive eastward steepening of the down-going Indian crust
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