基于航磁资料的中国蛇绿岩带研究OA北大核心CSTPCD

The aeromagnetic survey has almost covered the Chinese continent after the work has lasted for nearly 60 years,which provides detailed geophysical data for the study of regional geological structures.Aeromagnetic anomalies mainly reflect the distribution of magnetic materials in the lithosphere,especially the obvious magnetic anomalies produced by tectonic-magmatic activities,which lays a foundation for the prediction of concealed magmatic rocks.Mafic-ultramafic rocks usually have strong magnetic susceptibility and can be identified by aeromagnetic anomalies.Based on 1∶1000,000 aeromagnetic anomaly data and its inferred lithology and structure results in China,this paper systematically describes the identification and delineation methods of mafic-ultramafic rocks,and analyzes the relationship between inferred mafic-ultramafic rocks and ophiolite belts.The results show that the ophiolite belts usually have the characteristics of narrow width,high intensity,linear or bead-like magnetic anomaly with regular shape,which are mainly related to the preservation of the ophiolite.The ophiolite belts are usually splices of different plates,showing the boundaries of regional magnetic anomaly,and representing the differences in basement properties of different continental blocks.However,some ophiolitic belts,such as those formed by back-arc basins,usually do not divide the regional magnetic field because of the similar basement properties of the two sides of the block.Based on the inferred distribution of mafic-ultramafic rocks,22 ophiolitic mafic-ultramafic rock belts are divided in China,and the characteristics of these belts are described in detail.For example,the Yarlung Zangbo ophiolite belt shows double magnetic anomaly zones,the northern zone is large in scale and extends over a long distance,which indicates concealed mafic-ultramafic rocks probably exist in the deep.The southern zone is small in scale and only distributed continuously in Shigatse,while the rest are beaded magnetic anomalies and do not divide regional magnetic fields.Through 3D inversion of magnetic anomalies,the deep structural characteristics of the Yarlung Zangbo ophiolite belt are constructed.Through qualitative and quantitative analysis of magnetic anomalies,this paper aims to provide more information for the study of ophiolite belts,especially the concealed ophiolites,to guide chromite prospecting.At present,aeromagnetic survey is mainly carried out on small and medium scale,which is insufficient for ophiolite belt research and chromite exploration,and 1∶50000 or larger scale aeromagnetic data are needed for detailed analysis and deep structure modeling.