Magnetic Fabric-tectonic Research And The Characteristics Of The Stress Field Investigation In Southern Portion Of The Longmen Orogen Fault Zone

Longmen orogen, which presents an important boundary between the Sichuan block and Qinghai-Tibetan block, is a typical intra-continental orogenic belts. The tectonic evolution of Longmen orogen is controlled by which known as the three major faults. Based on previous research of the Shuangshi fault, Wulong fault and Longdong fault which are the south section of Longmen orogen. This paper is focused on Wulong fault and combine the methods of the magnetic fabric and tectonic research, outdoor-observation and indoor test analysis of the fracture geometry, kinematics, and on this basis to explore the characteristics of stress field, the possible formation age and tectonic reasons.The results show that, on the basis of the whole structure, the south section of Longmen orogen shows differences between the north and the south. In the south part, which contain Wulong, Tianquan etc, the fault zone occurrence have the tendency to West for structure and have the tendency to North-West(around310°) for magnetic fabric. However, those place such as Yanjing and Shuangshi which present the north part have the tendency to North-West for structure and to West (around270°) for for magnetic fabric.The kinematic characteristics which are reflected by the tectonic phenomenon,compressive stress is from North-West to South-East in the north part of the south section of Longmen orogen and West to East in the south. Kmax shows that E-W tensile stress in the North and NW-SE tensile stress in the south.According to the previous study on the kinematic characteristics of the three major faults during construction combined with the analysis of the data obtained by the study that, today the overall stress field characteristics of the the Southern Longmen orogen faults today represents the imprint of the Indosinian period tectonic deformation, including the combined effect of the extrusion from NW to SE and along the NE to SW trending sinistral slip. This reflects the stress field of the Indosinian period tectonic reasons, Longmen orogen oblique extrusion is mainly caused by the reverse push of North China plate, Yangtze plate and Songpan-Ganzi block’s collision and Bikou block extruse to the Southwest. The oblique compression stress derived forward push of the Longmen orogen and sinistral strike-slip. The former formate penetrative planar structures in the fault, the latter derived the tensile stress represented by Kmax.Both stress caused the positive flower structure.Today, the defference of the characteristics of the stress field between the north and the south are not native, but a transformation result of the stress field of the Indosinian period. This paper speculated that the structure of Southern Longmen orogen in the complex flattening relations, by its neighboring Sichuan and Yunnan north-south tectonic zone, leading to the southern structure tends to N-S. Meanwhile, the NW-SE left lateral strike-slip movement of Xianshuihe fault in the late Cenozoic cause here the Kmax shows the the NW-SE tensile characteristics.