科研之友
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摘要
The electrical structure of western Yunnan is revealed by a NW-SE trending Mouding-Shangri-La magnetotelluric (MT) sounding profile. It shows a huge sub-horizontal high conductivity layer (HCL) in crust beneath northwestern Yunnan. This high conductivity layer extends from Shangri-La to east of the Yongsheng basin for at least 200 km with thickness more than 40 to 50 km and a depth of the bottom about 80 to 90 km. The HCL can be divided into 2 sections. The west section extends from Shangri-La to the east of the Lijiang basin, steeping upward in east Lijiang with depth less than 10 km from the earth surface. The east section extends from the east Lijiang basin to the Yongsheng basin and steepens upward near the Yongsheng basin. The two HCL sections form a composite shape in the profile like two bananas linked each other. The two high resistivity bodies (HRB) on the top of the HCL look like two HRB bowls. A comprehensive analysis of the tectonics is made based on 2-D inversion of MT data in combination with geology and relocation of small earthquakes. The tectonic pattern of the study area is characterized by a system of imbricate thrust nappes, which slip up and down stretching at least a total length more than 250 km. The first main nappe stretches more than 150 km, and rises up in the east of Lijiang close to the surface. Of this nappe, the Xiaojinhe fault is the main fault which extends to the surface. The second main nappe is more than 120 km long, extending nearly to the earth surface in the east of Yongsheng after crossing the Chenghai fault. According to the reverse low resistance images, we infer the existence of back thrusting structure that forms pop-ups in two regions. One lies at the east margin of Jade Dragon Mountain to the east of Lijiang, while the other is at the western margin of the Yongsheng basin to the Pingchuan basin. Listric faults in the profile reveal a gentle-steep-gentle-steep shaped ladder-like structure.
- 出版日期2016-1
- 单位中国地震局地震预测研究所
