The Study On The Tectonic Division Based On Gravity And Magnetic Data In Madagascar And Its Adjacent

Madagascar is located in the southeast of Africa,the mineral resources are abundant,but the research results of tectonic division are quite different,and geological data of oil and gas are scarce.In order to clarify the geological and geophysical characteristics of the study area and provide the exploration direction of oil and gas and mineral resources,the geophysical data(gravity and magnetic)are processed and interpreted,finally,the structural zoning characteristics such as faults,igneous rocks and basins are obtained.By using topographic data,satellite altimetry gravity anomaly,magnetic anomaly and geological data,the satellite altimetry gravity anomaly is calculated,after the elimination of the influence of seawater value obtain bouguer gravity anomaly,and then after processing of bouguer gravity anomaly,obtain the normalized vertical derivative of the total horizontal derivative(NVDR-THDR),the location of faults plane distribution is identified by using its maximum and maximum staggered position,and the faults depth information is calculated by using the depth inversion method of curvature attribute;the regress to residual gravity anomaly is obtained by dealing with bouguer gravity anomaly,the regional gravity anomaly of sedimentary and the residual gravity anomaly of sedimentary are calculated by using the minimum curvature technique for potential field data separation,and the thickness of sedimentary is obtained by inversion calculation,and then the basin boundary and internal uplift and depression structural framework were divided;through the processing and transformation of magnetic anomaly,the reduction to the pole magnetic anomaly and residual reduction to the pole magnetic anomaly are obtained,and the distribution of igneous rocks is explained by gravity and magnetic correspondence analysis.the geological and geophysical characteristics of the main faults are analyzed,and the fault characteristics,basin distribution and sedimentary thickness in the study area are determined.Through the study of faults,igneous rocks and basins,the tectonic division of the study area is clarified.Through this study,combined with geological data and geophysical data,we have a systematic understanding of the faults in the study area,and analyzed the causes of the faults and their control on the distribution of igneous rocks and the basin boundary(Majunga,Murundava,Tamtaff),to determine the fracture characteristics of the study area and basin and igneous rock distribution,and defined the tectonic division of the Madagascar and adjacent areas.The study shows that the northern fault of Madagascar and adjacent areas is affected by the tensile fracture between Madagascar and Somali,the strike direction is NE,the boundary of Majunga basin is controlled,the western fault is affected by the drift of Madagascar Island,the strike is near NS direction,control Morandava basin,the eastern fault toward is NNE,affected by the Indian plate and the Madagascar tensile fracture;combined with fault distribution and previous research status,the boundary and internal uplift tectonic framework of Madagascar island Tamtaff basin,Morandava basin and Majunga basin are reclassified,and new recognition the Mozambique Channel basin,the boundary of basin is controlled the first class fault,the second class fault controlled the uplift and depression of basin,the basin shows belt distribution of "two depressions and one uplift";and the unexposed igneous rocks in the island have been identified,which are mainly distributed at the fault position and the boundary of the basin.The research results of this paper can provide geophysical basis for oil and gas and mineral resources exploration in Madagascar and its adjacent areas.