Crustal structure of the tibetan plateau and its surroundings from receiver function studies

The Tibetan Plateau is the highest and largest plateau in the world, generated by the collision of India and Eurasia. Details of this continent-continent collision and the uplift mechanism of the plateau are still hotly debated. In this study, I collected a large amount of seismic waveform data recorded by more than 300 stations in Tibet and its northern neighbor Tien Shan. I processed the data using teleseismic receiver function techniques to image crustal structures beneath the Himalayas, the southern Tibet plateau, and Tien Shan.;The results of receiver function studies show gentle northward dipping Moho beneath the Himalayas and increase of the dip of subduction near the Yarlung-Zangbo Suture, the boundary between the India plate and Tibet. This suggests that the Indian continental lithosphere is subducting underneath Tibet and the front of the Indian slab in the uppermost mantle is near the Yarlung-Zangbo suture. I also found that the crustal Vp/Vs ratios (Ratios between seismic P wave velocity and S wave velocity) are consistently low in the Himalayas and are mixed with high and low Vp/Vs ratios in the Tibetan Plateau. This suggests that only limited and localized partial melting exists in the mid and lower crust in the southern and central Tibetan Plateau.;I determined crustal structures in and around the Yadong-Gulu rift, the largest north-south-trending rift in southern Tibet, using receiver function techniques and joint-inversion technique with surface wave dispersion data. The results show a narrow zone beneath the rift here the crustal structure is different from outside the rift. This indicates that the east-west extension deformation of the Tibetan Plateau is localized in several narrow vertical zones through the entire crust.;The Tien Shan in central Asia is the largest and most active intra-continental orogen in the world. This mountain range is located nearly 2000~km north of the Indian and Asian collision front. I also used a receiver function techniques to study this region. The results show no dipping Moho beneath its southern edge with the Tarim basin. However, a southward dipping interface can be seen beneath its northern edge with the Kazakh Shield. The Moho becomes shallower beneath the Naryn Basin in the interior of Tien Shan. The results suggest that the uplift of Tien Shan is due to a combination of horizontal shortening from the India-Tibet collision and mantle upwelling from below.