| The South China continental margin is the most active continental margin for continental accretion and crustal growth on the southeastern margin of the Eurasian plate,and is an area with strong tectonic activity and strong exchange of crust-mantle material and energy.The South China continental margin is the main geothermal anomaly area in South China.The thermal material from the deep upwelling and the crust are mixed to form a lithological assemblage with mantle-derived attributes,and RHP(radioactive heat production)granite bodies with high heat generation rate are widely developed,especially the Fuzhou Basin and Zhangzhou Basin in the southeast coastal magma belt,with high terrestrial heat flow and abundant geothermal resources,with the storage potential of medium and high temperature geothermal.The predecessors have carried out a lot of research on the South China continental margin based on the methods of geophysics,geochemistry,geothermal geology and so on.The viewpoints of the heat sources in the South China continental margin mainly include: residual heat of magma,frictional heat generation between faults,partial melting in the crust,and heat generation by radioactive element decay.At the same time,predecessors have also found high-conductivity and low-velocity bodies at the crust-mantle scale in South China.The key to the main dispute is whether there is a unified deep heat source in the South China continental margin,what is the relationship between the deep high-conductivity anomaly and geothermal,and the existence of heat transfer modes What kind of difference.The magnetotelluric sounding method is an effective method to study the conductivity structure and rheological characteristics of the lithosphere,and can provide an important basis for the study of geothermal-related deep heat sources,heat channels,and thermal reservoirs.The use of magnetotelluric method to study the deep electrical structure of the South China continental margin,the formation mechanism of high conductors and the control of deep geothermal has important scientific significance and application value.This paper mainly uses 11 magnetotelluric profiles covering the South China continental margin belt(the Wuyi uplift belt to the west of the Zhenghe-Dapu fault zone,and the southeastern coastal magma belt to the east),and a total of 203 broadband magnetotelluric measuring points to obtain the lithospheric-scale conductivity.Model.Based on the decomposition of the magnetotelluric sounding phase tensor,the study area is dimensionally analyzed,which shows that the deep three-dimensionality of the southeastern coastal area of ??South China is strong;the effective detection depth of each measurement point is calculated,and the inversion depth is finally determined to be 100km;The full-band phase tensor decomposition calculation determines that the electrical main axis direction is NE direction 45°;considering the complexity of the geological structure of the South China continental margin,the three-dimensional inversion of the magnetotelluric in the The inversion data of the full impedance data of 18 frequencies are selected at intervals in the frequency range,and the study area is divided into two parts: south and north.The southern study area includes survey lines L1-L4,and the northern study area includes L5-L11.Sexual Structural Model.The results show that there is a thick high-resistivity layer in the upper crust of the South China continental margin,and there are high-conductivity blocks of different scales in the lower crust.Among them,there are high-conductors with low resistivity in the lithosphere of the Wuyi uplift belt at 70-80 km,and magma along the southeast coast.The lithosphere of the Fuzhou Basin and Zhangzhou Basin in the belt is extremely thick and highly conductive,and a number of low-resistance channels connecting the top of the upper mantle and the crust have been found.Based on the three-dimensional resistivity model,combined with the regional geological background and other geophysical,geochemical,geological and other data,the geothermal mechanism of the South China continental margin was comprehensively studied,and the deep geophysical characteristics and geothermal control process of the South China continental margin were revealed.It can be generally understood as follows:(1)The high-resistivity layer of the upper crust of the South China continental margin represents the granite bodies developed in the Mesozoic and Cenozoic,and the broken layers in the granite bodies provide space for the accumulation of radioactive elements;the high-conductivity of the lower crust is The partial melting of granite,the high conductor in the lithosphere of the Wuyi uplift belt is the coexistence of fluid and the partial melting of peridotite,and the high conductor in the lithosphere of the southeast coastal magma belt is formed by the undertransgression of basaltic magma;(2)the Wuyi uplift belt It has a different geothermal mechanism from the southeast coastal magma belt.The lithosphere of the Wuyi uplift belt is a thermal structure of "hot crust and cold mantle".The heat mainly comes from the decay of radioactive elements in the granite bodies in the upper crust and the partial melting of the lower crust granite;The lithosphere of the coastal magma belt is a thermal structure of "hot crust and hot mantle".The shallow granite bodies,the partial melting in the lower crust and the partial melting formed by the basalt undermining of the mantle all provide heat,and the high conductor in the mantle is the main source of heat.(3)The Wuyi uplift belt is consistent with the thermal channel of the magma belt in the southeast coast,and the deep and large fault zone controls the upwelling of deep thermal materials,providing a heat conduction carrier for the upward invasion of heat;(4)The Wuyi uplift belt and the The southeast coastal magma belt has experienced the same tectonic evolution process,but the Wuyi uplift belt has been subjected to more obvious tectonic compression,and the deep part of the southeast coastal magma belt has experienced more obvious extension,resulting in differences in the deep structure and the Wuyi uplift.Different geothermal control patterns in the uplift belt and the southeastern coastal magmatic belt. |
PDF Full Text Request