Lithospheric foundering and underthrusting imaged beneath Tibet

Abstract

Long-standing debates exist over the timing and mechanism of uplift of the Tibetan Plateau and, more specifically, over the connection between lithospheric evolution and surface expressions of plateau uplift and volcanism. Here we show a T-shaped high wave speed structure in our new tomographic model beneath South-Central Tibet, interpreted as an upper-mantle remnant from earlier lithospheric foundering. Its spatial correlation with ultrapotassic and adakitic magmatism supports the hypothesis of convective removal of thickened Tibetan lithosphere causing major uplift of Southern Tibet during the Oligocene. Lithospheric foundering induces an asthenospheric drag force, which drives continued underthrusting of the Indian continental lithosphere and shortening and thickening of the Northern Tibetan lithosphere. Surface uplift of Northern Tibet is subject to more recent asthenospheric upwelling and thermal erosion of thickened lithosphere, which is spatially consistent with recent potassic volcanism and an imaged narrow low wave speed zone in the uppermost mantle.

Mountain Building Orogeny in Precollision Hot Backarcs: North American Cordillera, India‐Tibet, and Grenville Province

“…Regional upper mantle velocities from surface wave tomography, receiver function, Pn velocities, and other seismic analyses in India and its extension beneath southern Tibet are fast, with speeds characteristic of cool stable cratons. The inferred cool cratonic temperatures extend at depth to as much as halfway under the Tibetan Plateau (Figure ; e.g., Burchfiel et al, ; M. Chen et al, ; C. Li et al, ; Nábělek et al, ; Priestley et al, ; Yu et al, ).…”

“…Some surface motion indicated by GPS data, but much of the motion is ductile lower crust channel flow. Estimates of the northern limit of underthrusting India range from “N” (Nábělek et al, ) to “C” (S. S. Chen et al, ; M. Chen et al, ). KF = Kunlun fault; TS = Tsangpo suture.…”

“…The India plate acts as a horizontal piston indenter into the Asian lower crust. The fate of the former subducting oceanic lithosphere that was attached to the Indian lithosphere is not yet clear, whether it has detached and foundered (e.g., DeCelles et al, ; Leech et al, ) or is still attached to the cratonic India lithosphere beneath Tibet (e.g., discussion by Shi et al, and M. Chen et al, ).…”

“…The uppermost Indian crust is weak (e.g., Figure ) so some rocks may have been scraped off at the collision suture zone as is inferred at the Himalayan front (e.g., Johnson, ; Le Pichon et al, ; Searle et al, ). There is evidence for quite high‐temperature metamorphism, indicating that some India crustal rocks were carried a substantial distance down the subduction channel before being exhumed (e.g., Leech et al, ), and seismic tomography data show a northward dipping high‐velocity zone (e.g., M. Chen et al, ). However, these rocks do not appear to comprise a significant part of the total underthrust Indian crust.…”

Linear Array Ambient Noise Adjoint Tomography Reveals Intense Crust‐Mantle Interactions in North China Craton

“…However, most of these studies employed the so-called traditional ambient noise tomography method based on ray theory, which does not consider complex wave propagation phenomena in heterogeneous media. Utilizing these seismic wave simulations, adjoint-state methods can efficiently incorporate the full nonlinearity of wave propagation in iterative seismic inversions (e.g., Bozdag et al, 2016;Chen et al, 2015Chen et al, , 2017Fichtner & Villaseñor, 2015;Fichtner et al, 2009Fichtner et al, , 2010Liu & Gu, 2012;Liu & Tromp, 2006Tape et al, 2009Tape et al, , 2010Tromp et al, 2005;Zhu et al, 2012;Zhu & Tromp, 2013, Zhu et al, 2015. Recent advances in numerical methods for the wave equation combined with developments in high-performance computation (HPC) have enabled routine simulation of seismic wave propagation in realistic 2-D and 3-D Earth models based on the spectral-element method (SEM) (Komatitsch et al, 2004;Komatitsch & Tromp, 2002a, 2002b.…”