Deep Electrical Structure Of Chuxiong Basin In Southwest Of China

Yunnan is located in the southeastern edge of Tibetan plateau,where tectonic activity is intense.Its topography and landform are controlled by the uplift and tilt of the Tibetan Plateau,and its deep dynamics is very complex.Chuxiong basin,located in the central Yunnan block,is the joint site of the meso-cenozoic tethys tectonic dynamic system and the littoral-pacific tectonic force system.The basin has undergone multiple stages of complex tectonic movement,with different tectonic evolution,its deep structure and dynamics are still poorly understood.Therefore,it is of great significance to study deep electric structure of Chuxiong basin and understand its deep structural characteristics,so as to reveal the relationship between the region and the adjacent structure and the dynamic mechanism.In this paper,the power spectrum re-editing processing,dimensional analysis,impedance tensor decomposition,phase tensor analysis and other data processing and analysis of MT data of 1188 measuring points of 14 measuring lines were carried out.WinGLink software was used to carry out the 2D inversion of the data of each line,and the results were preliminarily interpreted.The 3D inversion software based on GPU workstation developed by the laboratory was applied to carry out the 3D inversion of the topography of MT data belt in the work area,and the regional 3D geoelectric structure model with high confidence was obtained.Based on the geological and other geophysical data of the study area and the adjacent area,the electrical structural characteristics of Chuxiong basin are preliminarily analyzed and interpreted.The research results show that :(1)The 3D inversion results are confirmed to be credible and the algorithm is effective by comparing with others' inversion results in the adjacent region.(2)The electrical structure of the work area has the characteristics of transverse block and longitudinal layer.According to electrical property,it can be roughly divided into three blocks: the Western foreland thrust zone,the central foreland uplift zone and the eastern foreland fault depression zone.The Western foreland thrust area and the central foreland uplift area are mainly high resistivity at 2-24 km depth,while the eastern foreland fault depression area is mainly low resistivity.Longitudinally,the electrical structure of the Western foreland thrust area is relatively complex.Most of the electrical structure is high resistance-low resistance.The central foreland uplift area and the eastern foreland fault depression area are characterized by high resistance in shallow part and low resistance in middle and deep part.(3)The low resistivity layer beneath the Yupaojiang fault is butterfly shaped by the compression of the underlying basement.It is presumed that the reason is that the Western terrain of the basin was pushed upward during the Himalayan period due to the continuous eastward compression of the Indian plate and the downward thrust of the Simao-Indosinian block on the Yangtze plate.(4)It is confirmed that there are low resistivity layers in the crust of this region,and they are different in different locations,scales and burial depths.The low resistivity bodies correspond basically to the model of crustal flow proposed by Bai et al.in shape and burial depth,which can be preliminarily interpreted as the southward extension of the crustal flow in the Tibetan Plateau.(5)The preliminary geotectonic dynamics analysis of the Sanjiang fold belt and its adjacent areas shows that the Fault fold in the front of thrust margin and Sanjie fault fold belt in the study area were formed in Yanshanian period due to the left strike-slip movement of the Red river fault blocked by the Simao-Indosinian block.The dynamic state of the area today is the result of the adjustment and absorption of the Red river fault and so on.