Study On Three-dimensional Electrical Structure In The Middle Section Of Gan-hang Tectonic Belt

The Gan-hang tectonic belt(GB)is an important uranium polymetallic metallogenic belt in the South China continent,which is formed by the extrusion and collision between the Yangtze plate and the Cathaysian plate.Here are many controversies about the geodynamic background of the magmatic eruption and intrusion caused by a series of intermediate acid volcanic intrusive complexes.The research on the deep structure and state of the Gan-hang belt is still insufficient.The geophysical exploration is sparse and the deep situation is unknown,which seriously restricts the understanding and solution of regional geological problems and basic scientific problems in the Gan-hang belt.Due to the lack of deep geophysical data for the uranium metallogenic belts,the study degree of deep structure in the study area is relatively low,which seriously restricts the study of tectono-magmatic evolution and its dynamic process in the Gan-hang belt.Therefore,it is of great significance for the study of tectonic-magmatic evolution in the study area to obtain the deep electrical structure of the study area and find out the deep structure,and the spatial distribution characteristics of major deep faults in the Gan-hang belt by magnetotelluric method.Based on several projects,magnetotelluric data were collected by MTU-5 broadband magnetotelluric instrument in the study area.The analysis of field data by phase tensor and induction vector decomposition show that the underground three-dimensional characteristics of the study area are quite remarkable.Therefore,the three-dimensional magnetotelluric forward and inversion software MT3 DINV compiled by the research group was used to compare and calculate various inversion parameters,and the three-dimensional electrical structure at the lithospheric scale in the study area was obtained.Combined with other geophysical data,the dynamic mechanism of magmatic activity in the study area is expounded.The results show that the three-dimensional electrical structure of the lithosphere in the study area presents the characteristics of transverse discontinuous distribution and longitudinal stratification.The electrical structure in the western shell has high resistance generally.Its feature reflects the relatively stable Precambrian basement.The electrical structure in the middle of the fault is mainly characterized by banded high-conductivity dipping to the southeast,which indicates the distribution characteristics of Jiangshao fault in the deep.The high resistivity electrical distribution in the eastern upper crust corresponds to the widespread distribution of Cretaceous magmatic rocks,while some high-conductivity layers in the lower crust are probably caused by water-bearing fluids in the crust.The Shallow volcano-intrusive complex belt in the study area is connected with the deep highconductivity layer under the Wuyi uplift belt through the highly conducting Jiangshao fault.It reveals that the intermediate acid magma activity in this area is probably the result of the uplift and intrusion along the regional deep faults under the extension of the Late Mesozoic lithosphere.This back-arc extensional tectonic environment may be related to the subduction and retreat of the paleo-Pacific plate during the same period.