Plate interactions, crustal deformation and magmatism along the eastern margins of the Tibetan Plateau
Abstract In order to investigate the deep structure and dynamics of the triangular colliding system of the eastern Tibetan Plateau (TP) as well as the Yangtze Platform and the Qinling Dabie Fold Belt, a large number of P and S wave arrival times from both local and teleseismic earthquakes were used to generate high resolution tomographic images beneath the eastern margins of TP. The results of this study show that the western margin of the Minjiang fault is characterized by low velocity (low V) anomalies in sharp contrast to the high velocity (high V) anomalies that are derived from the eastern part. This means that the Minshan uplift zone is imaged as high V and acts as a barrier to the eastward escape crustal flow, which leads to obvious segmentation of the Longmenshan fault (LMSF) zone between velocity belts that are concatenated into the Minjiang fault. Because high V anomalies are clearly imaged in this study to extended depths of ca. 450 km, we consider the Yangtze Platform (containing the Sichuan Basin) to comprise craton like lithosphere. This study reveals the presence of a low V belt extending to a depth of ca. 250 km between the Sichuan basin and the Ordos Block which probably represents the migration pathway of upwelling asthenosphere materials from Tibet. At the same time, low V zone with a downdip depth of ca. 500 km accompanied by an approximately 400 km rectangular high V body is imaged under the Tengchong volcano. We interpret the high V body and the low V zone as evidence for the subducted Indian plate and the volcanic magma source, respectively. The results of this study reveal a number of new features of structural heterogeneities relative to deep coupling between the Tibet and the Yangtze platform, as well as the relationship between the Sichuan Basin and the Ordos Block, and the original source of the Tengchong volcano. The results presented here enable us a better understanding of the plate interaction, crustal deformation, and magmatism of the Tengchong volcano along the eastern margins of TP.