Dynamic model of the upper mantle beneath the northeastern Tibetan Plateau - constraints from the 410 km and 660 km discontinuities

Abstract

We determined the topography of the upper mantle 410 km and 660 km discontinuities (‘410’ and ‘660’) beneath the northeastern Tibetan Plateau and surrounding areas using a dense broadband seismic array. We binned the 95,474 teleseismic receiver functions into 0.5 × 0.5° grids; then the P410s and P660s arrival times were selected. Based on receiver function migration using three different regional tomographic models, the average ‘410’ and ‘660’ depths obtained are 413 ± 1 km and 672 ± 2 km, and the mantle transition zone (MTZ) thickness is ∼ 260 km. Combining these data with the velocity anomalies in the tomographic models, we find that the depressed ‘660’ beneath the northeastern Tibetan Plateau may be affected by cold anomalies delaminated from the thickened lithosphere. The depressed ‘410’ beneath the same area may be mainly affected by upwelling hot materials, which resulted from the delamination process and mixed with the eastward escape flow from the Tibetan Plateau. The slight uplift of ‘410’ is consistent with the extension of the high-velocity anomaly beneath the middle Ordos block. The thinning MTZ and depressed ‘410’ suggest that there are two branches of upwelling hot mantle beneath the northern and southern Ordos blocks. Considering the remote effects of both the subducted Indian Plate and Pacific Plate, we conclude that the dynamic model beneath the northeastern Tibetan Plateau and western North China craton (NCC) is controlled by two different large-scale subduction systems.