Research On Three-dimensional Electrical Structure And Dynamics Of Lithosphere In South China

The South China Block is located in southern China and is composed of the Yangtze Block in the northwest,the Cathay Block in the southeast,and the Jiangnan Orogenic Belt,which is in contact with the two.In order to divide the northern-middle boundary of the Jiangnan orogenic belt from the perspective of magnetotelluric sounding and to explore the impact of the Pacific plate subduction on the South China block,this study used the magnetomagnetic array observations and the crustal electrical structure survey of the Qinhang junction zone and adjacent areas 2016 ?MT points collected in 2017,MT points collected in the second project of the second project of “Deep Detection Technology and Experimental Research”(No.:Sino Probe-02-04),And the MT points collected from the oil and gas chambers of the I nstitute of Geophysical and Geochemical Exploration,A total of 877 Chinese Academy of Geological Sciences magnetotelluric sounding dat a,this set of data includes the northeast of the Yangtze block,the north middle section of the Jiangnan orogenic belt,and most of the China block.The results of the electrical principal axis analysis show that the electrical principal axis of the Huaxia block in the study area is roughly 30 °-45 ° northeast,and the direction of the electrical principal axis in some parts of the middle part of the southern Jiangnan orogenic belt is chaotic.There are no rules to follow,indicating that deep The electrical structure is more complex and has strong three-dimensional features.The results of phase tensor analysis in the study area show that the study area has good one-dimensionality in the shallow layer.At the deep level,except for the eastern part of the study area,which shows less obvious two-dimensionality,the study area shows obvious three-dimensionality in the central and western parts of the study area.The three-dimensional inversion of MT data in the study area was carried out.The inversion results showed that the east of the Yangtze block showed high conductivity,the Cathay block showed high resistance,and the eastern boundary of the Jiangnan orogenic belt showed obvious low resistance.,Forming an obvious resistivity gradient zone with the east-high-resistance Huaxia lithosphere,indicatingthe deep position of the eastern boundary of the Jiangnan orogenic belt;the western boundary of the Jiangnan orogenic belt is opposite,showing a high-resistance Jiangnan orogenic belt The boundary with the relatively low resistance Yangtze block.In other words,the western side of the Jiangnan Orogenic Belt exhibits a very high high resistance,which may indicate that the basement has not undergone post-transformation;while its eastern side exhibits a relatively low resistance,possibly due to the late subduction of the Pacific Plate on its eastern side Remodel.The study found that the high-resistance lithosphere of the Cathaysia block was invaded and destroyed by magma,and there were strips spreading from the lower crust to the upper mantle along the northeast direction of Tunxi-Yingtan-Anyuan and Shangyu-Dapu-Zhenghe fault Band-shaped low-resistance and high-resistance interphase anomalies,such band-shaped anomalies indicate that the subducted Pacific Ocean has retreated under the drag of gravity,resulting in the extension of the Cathaysian environment,and the deep matter along the Northeast fault in the Cathaysian block Upwelling,forming a low resistance strip corresponding to the fracture location.There is an obvious east-west resistivity gradient zone on the north side of the study area,which may be related to the collision and compression between South China and North China.The south side of the study area also has a large range of low resistance,which may be related to the collision and compression of the Indosinian block.