Fossilized lithospheric deformation revealed by teleseismic shear wave splitting in eastern China
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Global mantle convection significantly impacts the processes at Earth’s surface and has been used to gain insights on plate driving forces, lithospheric deformation, and the thermal and compositional structure of the mantle. Upper-mantle seismic anisotropy has been widely employed to study both present and past deformation processes at lithospheric and asthenospheric depths. The eastern China region was affected by extreme mantle perturbation and crust-mantle interaction during the Mesozoic, leading to large-scale destruction of the cratonic lithosphere, accompanied by widespread magmatism and metallogeny. Here we use teleseismic shear wave splitting measurements to evaluate the lithosphere and upper mantle deformation beneath this region. Our results from some of the individual and station averages show WNW-ESE- to NW-SE–trending fast polarization direction, similar to those observed in eastern Asia in some previous studies, consistent with the direction of Pacific plate subduction during the Cenozoic. This feature suggests that the asthenospheric flow beneath the eastern China region is influenced by the subduction of the western Pacific or Philippine plate. However, most of our data show E-W- or ENE-WSW–trending fast polarization direction, which is inconsistent with subduction from the east. The seismic stations in this study are located near the Qinling-Dabie-Sulu orogenic belt, which formed through the collision between the North and South China blocks during the Late Paleozoic–Triassic, and the anisotropy with an E-W- or ENE-WSW–trending fast polarization direction parallel to the southern edge of the North China block suggests lithospheric compressional deformation due to the collision between the North and South China blocks. Although the deep root of the craton was largely destroyed by cratonic reactivation in the late Mesozoic, our results suggest that the “fossilized” anisotropic signature is still preserved in the remnant lithosphere beneath eastern China.
Manuscript received 19 Apr. 2013; accepted 7 June 2014.