Joint inversion of surface waves and teleseismic body waves across the Tibetan collision zone: the fate of subducted Indian lithosphere (original) (raw)
Related papers
Earth and Planetary Science Letters, 2016
Closely-spaced receiver-function profiles in the east-central India-Tibet collision zone reveal drastic west-east changes of the crustal and upper mantle structure. West of ~91.5°E, we show the Indian crust-mantle boundary (Moho) extending subhorizontally from ~50 km depth below sea level under the High Himalaya to ~90 km under the central Lhasa terrane. Further north, this boundary transitions to become the top of the Indian lithospheric mantle and, becoming faint but still observable, it can be tracked continuously to ~135 km depth near 19~3 1.5°N. The top of the Indian lithospheric mantle is clearly beneath the Tibetan Moho that is also a conspicuous boundary, undulatory at 60-75 km depth from the central Lhasa terrane to the north end of our profile at ~34°N. This geometry is consistent with underthrusting of Indian lower crust and underplating of the Indian plate directly beneath southern Tibet. In contrast, east of ~91.5°E, the Indian Moho is only seen under the southernmost margin of the Tibetan plateau, and eludes imaging from ~50 km south of the Yarlung-Zangbo suture to the north. The Indian lower crust thins greatly and in places lacks a clear Moho. This is in contrast to our observation west of ~91.5°E, that the Indian lower crust thickens northwards. A clear depression of the top of the Indian lower crust is also observed along west-east oriented profiles, centered above the region where the Indian Moho is not imaged. Our observations suggest that roll-back of the Indian lithospheric mantle has occurred east of ~91.5°E, likely due to delamination associated with density instabilities in eclogitized Indian lower crust, with the center of foundering beneath the southern Lhasa terrane slightly east of 91.5°E.
Due to the non-uniform seismic station coverage in Tibet, critically important questions remain about the existence of southward continental subduction of Eurasia beneath northern Tibet from north, and the nature of the underthrusting Indian lithosphere underneath southern Tibet from south. Using differential P-and S-wave travel-times measured from 301 stations of all the temporary experiments deployed throughout Tibet, we constructed a comprehensive tomographic model. The upper mantle of northern Tibet consists of a rather homogeneous low velocity zone with no evidence of southward Asian continental subduction. In contrast the upper mantle from the Himalayas to central Tibet exhibits laterally variable P-and S-wave velocities. Significant low velocity zones are observed that are elongated in a north-south direction and extending to at least 150 km depth, which we interpret as evidences for fragmentation of the underthrusting Indian continental lithosphere.
The boundary between the Indian and Asian tectonic plates below Tibet
Proceedings of the National Academy of Sciences, 2010
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...
Convergence of the Indian and Eurasian plates under eastern Tibet revealed by seismic tomography
Geochemistry, Geophysics, Geosystems, 2012
1] A three-dimensional P wave velocity model of the crust and upper mantle down to 400-km depth beneath eastern Tibet is obtained using many temporary seismic stations of the ASCENT project and the Namche Barwa Broadband Seismic Network. We collected 16,508 arrival times of P, Pn and Pg phases from 573 local and regional earthquakes and 7,450 P wave arrivals from seismograms of 435 teleseismic events. Our high-quality data set enables us to reconstruct the 3-D velocity structure under eastern Tibet in more detail than the previous studies. In the shallow depth, our results show that the low velocity zones are not interconnected well (no wide-spread low velocity zones), which may reflect the complex pattern of material flowing in the study region. Below the Moho, we find that the Indian lithospheric mantle underthrusts sub-horizontally under eastern Tibet, and the extent of the northward advancing Indian lithosphere decreases from west to east. In the north, the Asian lithospheric mantle is detected under the vicinity of the Qaidam Basin. Between the Indian and Asian lithospheric mantles, there is an obvious low-velocity anomaly which may reflect an upwelling mantle diapir.
Small 660-km seismic discontinuity beneath Tibet implies resting ground for detached lithosphere
Journal of Geophysical Research, 2007
1] Using seismic profiles comprising of high-resolution, triplicate waveforms across apertures of over 1,000 km, we show that because of high P wave speed (V P ) near the bottom of the mantle transition zone, the contrast in V P across the 660-km discontinuity beneath central Tibet is small: only about 70% of that beneath the northern Indian shield. This subhorizontal anomaly of high V P is most likely a remnant of detached mantle lithosphere that recently sank to depth, thus providing key evidence for a direct connection between continental collision near the surface and deep-seated dynamics in the mantle.
Geophysical Journal International, 2019
Using P n-wave traveltimes from three regional distance ranges we generated P n tomography models to investigate the 3-D nature of the uppermost mantle lid P-wave velocity structure beneath the Tibetan Plateau and surrounding regions. Significant velocity variations spatially and with depth are observed. High-velocity regions are found beneath the Himalayas and most parts of southern Tibet. These high-velocity regions can be interpreted as subducting Indian continental mantle lithosphere, accreted terranes and a cold, non-convective mantle wedge beneath central Plateau. They are disjointed suggesting that the subducting Indian lithosphere is fragmented laterally. In the western Tibetan Plateau, the high-velocity region extends northwards to the middle of Qiangtang Terrane. In the central Plateau, the highvelocity region reaches near the Bangong-Nujiang suture. The northern extent of the subducted Indian continent cannot be determined uniquely from P n models because the Indian plate dips moderately beneath southeastern Tibet. Around the Plateau, Tarim, Qaidam, Gonghe and Sichuan basins are floored by high-velocity Asian continental blocks that keep the elevation of these basins lower than surrounding regions. We found no evidence of an ongoing southward subduction of Asian lithosphere beneath central to northeastern Tibetan Plateau. Two major P n low-velocity anomalies are found beneath northern and northeastern Tibet, primarily within the Qiangtang and Songpan-Ganzi Terranes. The northern Tibet low-velocity mantle is situated in a continental backarc of the India-Asia continental subduction zone, and hence we interpreted this region as thin thermal lithosphere with upwelling mantle driving by the subducting Indian lithosphere. The Qilianshan is also underlain by a low-velocity mantle structure and could be related to the same upwelling in this continental backarc. A narrow N-S trending low-velocity anomaly is found beneath the Yadong-Gulu Rift and confirmed that the Lhasa Terrane is not limited to the crust, but involves the entire lithosphere. Another pronounced low P n velocity region is observed in the southeastern Tibetan Plateau, southern Yunnan and northeastern Myanmar. This feature is probably related to backarc convection associated with the subduction and rollback of Indian oceanic slab beneath Myanmar and Yunnan province, China.International Seismological Centre, On-line Bulletin, http://www.isc.ac.uk, Internatl. Seismol. Cent.
Earth, Planets and Space, 2014
A number of tectonic models have been proposed for the Tibetan Plateau, which origin, however, remains poorly understood. In this study, investigations of the shear wave velocity (Vs) and density (ρ) structures of the crust and upper mantle evidenced three remarkable features: (1) There are variations in Vs and ρ of the metasomatic mantle wedge in the hanging wall of the subduction beneath different tectonic blocks of Tibet, which may be inferred as related to the dehydration of the downgoing slab. (2) Sections depicting gravitational potential energy suggest that the subducted lithosphere is less dense than the ambient rocks, and thus, being buoyant, it cannot be driven by gravitational slab pull. The subduction process can be inferred by the faster SW-ward motion of Eurasia relative to India as indicated by the plate motions relative to the mantle. An opposite NE-ward mantle flow can be inferred beneath the Himalaya system, deviating E and SE-ward toward China along the tectonic equator. (3) The variation in the thickness of the metasomatic mantle wedge suggests that the leading edge of the subducting Indian slab reaches the Bangoin-Nujiang suture (BNS), and the metasomatic mantle wedge overlaps with a region with poor Sn-wave propagation in north Tibet. The metasomatic layer, north of the BNS, deforms in the E-W direction to accommodate lithosphere shortening in south Tibet.
A fragmented Indian slab and no south-verging subduction
Earth and Planetary Science Letters
Due to the non-uniform seismic station coverage in Tibet, critically important questions remain about the existence of southward continental subduction of Eurasia beneath northern Tibet from north, and the nature of the underthrusting Indian lithosphere underneath southern Tibet from south. Using differential P-and S-wave travel-times measured from 301 stations of all the temporary experiments deployed throughout Tibet, we constructed a comprehensive tomographic model. The upper mantle of northern Tibet consists of a rather homogeneous low velocity zone with no evidence of southward Asian continental subduction. In contrast the upper mantle from the Himalayas to central Tibet exhibits laterally variable P-and S-wave velocities. Significant low velocity zones are observed that are elongated in a north-south direction and extending to at least 150 km depth, which we interpret as evidences for fragmentation of the underthrusting Indian continental lithosphere.