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Jiangnan Uplift located in the collision zone between Yangtze and Cathaysia block is the key to interpret the tectonic evolution of Smith China block. The Cenozoic thermal history and the uplift processe of Mufushan pluton are constrained by the combination of analysis of apatite fission track and (U-Th-Sm)/He ages with modeling of fission track length distribution. Based on analysis of thermochronological dating, the authors probed into the relationship between the thermochronological evolution and the tectonic development combining with regional tectonic settings. The exhumation of plutons arrived at about 4800 m since 80 Ma, and the uplift processes were not uniform in space, and different plutons had somewhat different uplift processes. Thermal history modeling of the AFT data shows, that the Mufushan pluton experienced three episodes of cooling event, two of which exhumed rapidly happened in Upper Cretaceous-Paleocene (about 80 similar to 50 Ma) and Upper Miocene (since 10 Ma). There is a period of relative thermal stability at 50 similar to 10 Ma and exit the PAZ. The first stage of rapid uplifting during 80 similar to 50 Ma in this region is coeval with extension episode of Mid-Lower Yangtze during Himalayan which resulted in the formation of fault basin and exhumation of shoulder block; the Upper Miocene rapid cooling since 10 Ma is attributed to the westward movement and subduction of Pacific plate. The uplift and exhumation of Mufushan pluton since Late Yanshanian led to a good deposition response in basins and the cooling events of three phases just coincided with the regional tectonic settings of study area.

To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of South China Sea with data such as whole crustal thickness, depth of Cenozoic sedimentary basement and the horizontal displacement of faults. An isometric line drawing on whole crustal stretching factor is then obtained. Along the seismic Line 1530 in Baiyun sag, we also calculated the stretching factors of the upper and lower crust. The results suggest that the whole crustal thickness decreases seaward while the whole crustal stretching factor increases from shelf to slope. The Moho upwells highest beneath where the crust is thinned most. The value of the whole crustal stretching factor ranges from 1.5 to 6. Two areas were thinned intensely: the center of Yinggehai Basin, and the Baiyun sag in the Pearl River Mouth Basin. The calculation of the upper and lower crustal stretching factors from DSP1530 in Baiyun sag shows that the original crust of Baiyun sag should be thinned before deformation. Its pre-Cenozoic evolution as well as tectonic position during Cenozoic might be responsible for that.

The low-velocity layer (LVL), closely related with tectonic activities and dynamic settings, has always been a hot topic in the deep crustal structure studies. The deep seismic (OBS/OBH) and onshore-offshore experiments have been extensively implemented in the northern South China Sea (SCS) since the 1990s. Six seismic profiles were finished on the northern margin of SCS by domestic and international cooperations. The features of crustal structures were revealed and five velocity-inversion layers were discovered. Among them three LVLs with 3.0-3.5 km.s(-1) velocity are located in the sedimentary structure (2.0-6.0 km in depth and 2.0-4.6 km in thickness) of the Yinggehai Basin and Pearl River Mouth Basin. They were identified by the reflective and refractive phases for their shallow depth. The other two LVLs with 5.5-6.0 km.s(-1) velocity generally existed in the middle crust (7.0-18.0 km in depth) with an about 2.5-6.0 km thickness in the transitional crustal structure of the northeastern and northwestern SCS. They were detected by the refractive phase from their overlain and underlying layers. We explored the possible tectonic formation mechanisms combining with previously reported results, which provided evidence for the formation and evolution of SCS.