Abstract:

The study of paleotectonic stress field and division of tectonic stages in the Southeastern Sichuan, is one of the key research object for the analysis of the evolution of the Sichuan basin in recent years. It is of great significance to clarifying the relationship between tectonic evolution and paleo-stress field, and to further studying the stress evolution of the margin of Sichuan basin and guiding oil and gas exploration in the later period. Based on the analysis of the 452 group joints observed in the Xujiahe Formation of the Jiudianya-sangmuchang structure, using the structural geometrical analysis method and the apatite fission track and the acoustic emission experiment combined with the relevant regional tectonic evolution history, the phases and the tectonic stress field in the study area were analyzed. The results show that there are two sets of structure joints in this area, which are the joints formed by the two main tectonic stresses of nearly NW-SE direction and near NE-SW direction. This region has at least two or more tectonic movements which have a great influence on the area since the Triassic: the first phase is the middle and late period of the Yanshan Movement. The direction of the maximum principal axes of stresses is 133°, mainly forming tectonic system with a large scale in NE and NNE directions. The fracture is relatively developed. The second stage is the late stage of the Yanshan Movement-early Himalayan Movement. The direction of the principal axes of stresses is 51°, mainly forming structural system in NW direction with a small scale, but the fracture is still relatively developed.

Key words: Jiudianya-sangmuchang structure, Xujiahe Formation, joint, development characteristics, structural stress field, fracture structural analysis