Structural And AFT Constraints On The Meso-Cenozoic Uplift-Subsidence Between Northern Nanpanjiang And Southern Sichuan Basins

The study area crosses three different tectonic units from south to north - northern Nanpanjiang Basin, Qianzhong Uplift and its surrounding tectonic region and southern Sichuan Basin. The basin– mountain tectonic pattern composed by the three units makes the structural deformation and uplift- subsidence of the region complex. However, the study on the uplift process and the uplift relationships of the three is relatively little. Therefore, this paper focused on the major profile between northern Nanpanjiang and southern Sichuan basins, divided the structural deformation stages and analyse the characteristics of the various stages through geology investigation and statistical analysis on the structural foliation and lineation, then, selected rock samples in the study area to do apatite fission track simulation analysis using detrital grain themroehronology theory, finally, explained the uplift stages, time and rate of the study area in Meso-Cenozoic. The conclusions are as follows:1. From the uplift starting time and the deformation intensity, the uplift of the study area in late Indo-Chinese was constantly advanced from south to north.2. From the beginning of the uplift to about 20Ma, there has some difference in the uplift trend and rate of the three tectonic units, and from 20Ma to the present, the uplift characteristics show consistency. From the beginning of the uplift to about 60Ma, the average uplift rates of the three have gradually become larger, particularly of the southern margin of Sichuan Basin; 60 ~ 20Ma, the average rates have become smaller, the rate of the Qianzhong Uplift and its surrounding tectonic region suddenly drops to about 0.002Km/Ma from 0.03Km/Ma earlier, which shows the influence of the early Himalayan movement to the study area is smaller than Yanshan movement, and is almost none to the Qianzhong Uplift. 20~0Ma, three tectonic units uplift fast, with an average uplift rate above 0.07Km/Ma. 3. The fission track simulation results and the stages based on field geological structure have a good response mechanism, the uplift stages and the characteristics of every stages of the study area in Meso-Cenozoic are as follows: 220 ~ 190Ma, develop steep thrust faults, structural lineation vertically to strike of the faults and overturned fold with closed upper plate; 180 ~ 60Ma, characterized by dextral strike-slip and thrust; 60 ~ 40Ma, characterized by counterclockwise rotation deformation of small-scale block; 20~0Ma, characterized by the tectonics combination of Paleogene intermountain fault basin and the normal fault.