No direct correlation of mantle flow beneath the North China Craton to the India-Eurasia collision: constraints from new SKS wave splitting measurements

The long-range effects of the ongoing India-Eurasia collision and their role in the Cenozoic tectonic evolution of eastern China are not well understood. Here, we investigate deformation beneath the North China Craton and the Qilian Mountain region between the Haiyuan and Kunlun faults, both of which are located immediately to the northeast of the Tibetan Plateau. We present teleseismic shear wave splitting parameters from 299 broad-band stations. These stations provided good spatial coverage in mapping upper-mantle deformation beneath the North China Craton and the Qilian Mountain. The backazimuth dependence of fast directions from stations located within the Qilian Mountain region indicates a complex anisotropy pattern. A multilayer anisotropy and/or anisotropy with a dipping symmetry axis may exist beneath the Qilian Mountain. The overlapping or underthrusting of material evident in anisotropy from this region may be a long-range effect of the India-Eurasia collision. The central North China Craton showed spatially coherent fast directions and the shear wave velocity anomalies within the upper mantle. These patterns suggest horizontal deflection of a regional mantle upwelling, possibly originating from the mantle transition zone. Anisotropy with large delay times was observed in the vicinity of Shanxi rift system. High partial derivative lnV(S)/partial derivative lnV(P) values for the upper mantle indicate that anisotropy in this area is enhanced by vertically aligned melt-filled fissures. Our results suggest that the dynamic processes beneath the central North China Craton are not directly related to the India-Eurasia collision.