豫西 关中地区深部电性结构特征分析

Characteristics and interpretation of deep electrical structures inthe Western Henan-Guanzhong area

豫西关中地区地处秦岭造山带、华北克拉通和扬子克拉通接合部,盆山耦合、构造演化与壳幔结构关系极其复杂。在该区开展的深大地学断面综合解释及其成油、成藏关系研究中,深地震反射剖面法首先获取了高质量的地壳乃至上地幔的反射特征,解释出莫霍面内部滑脱面结构,对岩石圈内部结构有了全新的认识,对油气盆地结构及其演化研究具有重要指导作用。为扩大研究成果,佐证地震资料认识,以沿地震大剖面测量的宽频大地电磁勘探测线资料为依据,开展了深部电性构造特征研究。经过对横跨渭河盆地、三门峡盆地和洛阳盆地的东西向大剖面宽频带大地电磁资料的处理与反演,获得了深大断面的二维电阻率深度剖面,并结合地电模型、地质与地震资料进行分析研究。研究表明,表层电性特征与盆山结构对应良好,基底与盆山界限清晰;渭河盆地与三门峡盆地虽然都是在古、中生界基底上发育的新生代断陷盆地,但二者并非整体,而洛阳盆地与二者差异明显且盆山间存在清晰的断裂分界;研究区地壳电性结构纵向上可分为4层,由浅至深分别为低阻盖层、中低阻上地壳、中高阻下地壳以及高阻上地幔。研究区上、下地壳分界线(康氏面)清晰,地壳与上地幔之间的莫霍面基本连续。该区深层地电结构模型结果为新生代沉积盆地的识别和性质界定提供了重要依据,对油气和矿藏的生成关系研究有重要指导意义。

The Western Henan-Guanzhong area is located at the junction of the Qinling orogenic belt,North China craton and Yangtze craton,and the relationship between the basin-range coupling,tectonic evolution,and crust-mantle structure is extremely complex.In comprehensive interpretations of deep and large geological sections and in studies on the relationship between oil and reservoir formation in this area,the deep seismic reflection profiling method is first used to obtain high-quality reflection characteristics of the crust and upper mantle;following this,the structure of the internal detachment region of the Moho surface is interpreted,and a new understanding of the internal structure of the lithosphere,which plays an important guiding role in studies on the structure and evolution of oil and gas basins,is acquired.In this study,to expand the research results and support the understanding of seismic data,broadband magnetotelluric exploration and processing interpretation is performed along a large seismic profile.Additionally,a two-dimensional resistivity depth profile of the deep and large section is obtained through processing and inversion of four broadband magnetotelluric data along the deep seismic reflection profile,and analyses and research are conducted considering the geoelectric model and geological and seismic data.The results reveal that the surface electrical characteristics correspond well with the basin-mountain structure,and the boundary between the basement and basin-mountain is clear.Although both the Weihe and Sanmenxia basins are Cenozoic fault basins developed on the Paleozoic and Mesozoic basement,they are not integrated,a clear fault boundary exists between the basins and mountains,and their structure is significantly different from that of the Luoyang Basin.The electrical structure of the crust in the study area can be divided into four vertical layers with increasing depths:low resistivity cover and middle,low resistivity upper crust and middle,high resistivity lower crust,and high resistivity upper mantle.Additionally,the boundary between the upper and lower crust in the study area(Conrad s surface)is evident,and the Moho surface between the crust and upper mantle is basically continuous.These insights into the regional deep geoelectric structure model can be used as a reference for identifying and determining the nature of new sedimentary basins and for studies on the generation relationship between oil,gas,and ore deposits.