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Mei Feng, Institute of Geomechanics (China)
Meijian An, Institute of Geomechanics (China)
Suzan Van der Lee, Department of Earth and Planetary Sciences (United States)
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The Chinese part of the Asian continent, including some of its stable cratons, has been strongly deformed since the late Mesozoic. Geodynamical processes, such as continental collision to the southwest and deep oceanic subduction to the east, left their imprint on the upper mantle beneath China. Imaging upper mantle seismic velocity structure can help discover and understand the tectonic evolution of the continent. By collecting and analyzing surface wave data from a large number of seismic stations in and around China, we obtained an updated 3-D S-velocity model down to ∼200 km depth with a newly developed efficient surface wave dispersion tomography, and down to 400 km depth with a joint inversion technique of surface waveforms and surface wave dispersions.
Previous studies have reported a thinned lithosphere beneath the North China platform, but the mechanism causing the lithospheric thinning is still under debate. Our new S-velocity model shows a shallow plume-like low velocity anomaly beneath the North China platform, above the graveyard of the stagnant subducting slab in the upper/lower mantle transition zone of the eastern Chinese continent imaged by recent body-wave tomographic studies. The coincidence between the plume-like low-velocity anomaly and the slab graveyard may support the lithospheric thinning mechanism of thermal and/or compositional bottom-up erosion/transformation.
Western China, including the Qinghai-Tibetan Plateau and Tarim craton, has collided with the Indian subcontinent and had been previously subducted by the Tethys Ocean. The Qinghai-Tibetan Plateau has been strongly influenced by the collision. Thick lithosphere in the plateau has been widely observed, possibly indicating lithosphere doubling from shallow subduction of the Indian subcontinent. Comparatively, the Tarim craton has been less affected, but according to seismic velocity images, its lithosphere seems to be slightly thinned.
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