The boundary between the Indian and Asian tectonic plates below Tibet

Abstract

The fate of the colliding Indian and Asian tectonic plates below the Tibetan high plateau may be visualized by, in addition to seismic tomography, mapping the deep seismic discontinuities, like the crust-mantle boundary (Moho), the lithosphere-asthenosphere boundary (LAB), or the discontinuities at 410 and 660 km depth. We herein present observations of seismic discontinuities with the P and S receiver function techniques beneath central and western Tibet along two new profiles and discuss the results in connection with results from earlier profiles, which did observe the LAB. The LAB of the Indian and Asian plates is well-imaged by several profiles and suggests a changing mode of India-Asia collision in the east-west direction. From eastern Himalayan syntaxis to the western edge of the Tarim Basin, the Indian lithosphere is underthrusting Tibet at an increasingly shallower angle and reaching progressively further to the north. A particular lithospheric region was formed in northern and eastern Tibet as a crush zone between the two colliding plates, the existence of which is marked by high temperature, low mantle seismic wavespeed (correlating with late arriving signals from the 410 discontinuity), poor Sn propagation, east and southeast oriented global positioning system displacements, and strikingly larger seismic (SKS) anisotropy.Tibetan lithosphere | receiver functions | anisotropy I t has long been recognised that the Tibetan plateau was created by the collision of the northward moving Indian plate and the relatively stationary Asian plate, which began about 50 million yr ago (1). However, the mode of deformation of the mantle lithospheres (2) remained largely unknown. A fundamental question is whether the postcollision convergence of India and Asia, estimated at >2;000 km (3, 4), was accommodated by homogeneous thickening or plate subduction (2). Global positioning systems (GPS) measurements have shown that at present an eastward motion dominates the surface deformation of northern and eastern Tibet (5). GPS and seismic anisotropy (6) indicate extrusion also of the deep Tibetan lithosphere to the east and southeast. Most surface wave studies revealed a thick lithosphere beneath much of the plateau (7-12), whereas body wave tomography observed the subducted Indian mantle lithosphere characterized by high wavespeed, in contrast to the Asian mantle lithosphere (13-15). Recently a high resolution P travel time tomographic study (15) imaged the high velocity Indian lithosphere in western Tibet below the entire plateau down to 300-400 km depth. In eastern Tibet, however, the front of the Indian plate is located south of the Yarlong-Zangbo Suture (YZS) (15). Relatively slow wave speeds are found in the upper mantle below the central and northeastern parts of the plateau. Modeling indicates that the Tibetan part of the lithosphere originated from the progressive accretion of a number of continental or island-arc type blocks before India came into direct contact with Asia (16) or stepwise subduction of the Asian pl...

Effects of crustal eclogitization on plate subduction/collision dynamics: Implications for India-Asia collision

“…A large number of speculative hypotheses on the Tibetan evolution have been proposed, e.g., crustal shortening and thickening (England and Houseman, 1986), eastward strike-slip extrusions of SE Asia (Li et al, 2013;Tapponnier et al, 2001Tapponnier et al, , 1982, underthrust of the Indian lithosphere beneath Asia (Li et al, 2011;Haines et al, 2003;DeCelles et al, 2002;Chemenda et al, 2000;Owens and Zandt, 1997;Powell, 1986;Klootwijk et al, 1985), destabilization and collapse of the tectonically thickened lithospheric root (Chung et al., 2009, 2005Platt and England, 1994;Houseman et al, 1981), northward crustal injection model (Chemenda et al, 2000;Zhao and Morgan, 1985), and southward subduction of the Asian lithosphere beneath Tibet (Paul et al, 2001;Roger et al, 2000;Willett and Beaumont, 1994). Recent geological, geophysical and geochemical studies suggest that the Tibetan Plateau possesses lateral variations of the subduction-related mantle structure (e.g., Chen Y et al, 2015;Chen L et al, 2013;Liang et al, 2012;Searle et al, 2011;Zhao W et al, 2011;Zhao J et al, 2010;Li et al, 2008;Yang et al, 2015) and temporal-spatial variations in post-collisional magmatism(e.g., Wang R et al, 2015;Zhang et al, 2014;Zhu et al, 2013;Chung et al, 2005Chung et al, , 2003Ding et al, 2003), which indicate that the Tibetan Plateau might have been deformed through complex tectonic events.…”

Greater India Basin hypothesis and a two-stage Cenozoic collision between India and Asia

“…4). A third conspicuous body imaged horizontally below Tibet over a distance of approximately 500 km from the Himalayan front represents Indian continental lithosphere that has underthrust Asia since the last phase of slab break-off (39,41). Taking Asian shortening (14) into account, this horizontal body represents the last 10-15 Ma of India-Asia convergence.…”

Crustal structure of the central Tibetan plateau and geological interpretation

“…The crustal positive amplitude arrivals, seen at a depth of 40-55 km, probably imply the presence of partial eclogitic layers as well. Previous studies have shown that the Indian subduction lithosphere has thrusted northward and reached toward the BNS in the central Tibetan plateau Zhao et al, 2010;Zhao et al, 2011). Therefore, the eclogitic layer north of the BNS probably formed due to the collision of the Qiangtang and Lhasa terranes in the Middle-Late Jurassic.…”

“…The fundamental structures that compose the lithosphere under the extreme topography of the Tibetan plateau have been gradually discovered over time, allowing us to work towards deciphering the geodynamic mechanisms that have led to the growth of the plateau. The subducting Indian lithosphere is northward-thrusting under the Tibetan plateau at an increasingly shallow angle, and reaches progressively further toward the Jinsha suture in western Tibet, the Bangong-Nujiang suture in the center, and the middle of the Lhasa terrane in the east, which has been resolved using receiver function and travel-time tomography studies (Li et al, 2008;Kind and Yuan, 2010;Zhao et al, 2010;Zhao et al, 2011). In the Himalaya and the central Tibet, doublet crustal structures are presented (Kind et al, 2002;Schulte-Pelkum et al, 2005;Nábělek et al, 2009;Wittlinger et al, 2009), which partially explains approximately 2 000 km of post-collision convergence between India and Eurasia (Molnar and Tapponnier, 1975;Patriat and Achache, 1984;Besse and Courtillot, 1988;Patzelt et al, 1996;Yi et al, 2011).…”