海拉尔盆地中-上地壳电性结构特征研究

本文通过对横穿海拉尔盆地的一条长约222km的北西—南东向大地电磁测深剖面数据的定性分析及二维定量反演解释,首次获得了海拉尔盆地高精度大范围的电性结构图.海拉尔盆地中-上地壳电性结构纵向上具有典型的分层特性,总体可分为四层,即低阻层-高阻层-低阻层-高阻层,而横向上又具有分块特点.海拉尔盆地边缘及内部分布的众多断裂将盆地划分为隆起与坳陷相间的格局,并发现盆地内部坳陷区也存在有小规模凸起,每一构造单元内部电性结构各具特点.海拉尔盆地中-上地壳低阻层底面最深达28km,通常在6~16km之间,但厚度变化不大,在4~10km之间,且隆起区与坳陷区底面埋深差别较大.据电性结构模型推测出两条新断裂F8和F9,且断裂F9规模较大,为基底断裂.中-上地壳的低阻层可能在一定程度上控制着海拉尔盆地内油气田的分布格局.

Study of the central-upper crust electrical structure of Hailar Basin

In order to study the central-upper crust electrical structure and tectonic features of Hailar Basin, and discuss metallogenic geological srtucture background characteristics and metallogenic environments of Hailar Basin,this paper selected 66 magnetotelluric sounding points in Hailar Basin which is acquired in 2011 of "Comprehensive geophysical survey in the eastern part of China-Mongolia border region" project for line 4 to treatment and research. The magnetotelluric sounding methord via studying the propagation characteristics of natural electromagnetic field in the earth to detect the underground geological structure. The model of lithosphere scale electrical conductivity can be obtained by magnetotelluric sounding methord, and provides a physical basis for the study of deep geological structure.#br#Through analysis and interpretation of 2D inversion results based on magentotelluric sounding profile, knowing that the deep geological structure of the study area is NE-SW trending, and large scale electrical resistivity structures were revealed for the first time. The electrical structure of the middle-upper crust of Hailar Basin is clearly stratified and can generally be divided into four layers, namely the high conductivity layer—high resistivity layer—high conductive layer—high resistivity layer, while the transverse could also be divided into several blocks horizontally. The numerous distributed faults in Hailar Basin's edge and interior divide the Basin itself into alternating structures of uplifts and depressions. It's also found that there are small scale bulges in depression parts, and the electrical structure of each tectonic unit is of distinct features. The lower boundary of high conductivity layer in middle-upper crust of Hailar Basin is generally between 6 and 16 km, which can reach 28 km at the deepest part with little change in thickness, which is about 4~10 km. The lower boundary in uplift and depression areas are largely different. According to the electrical structure model, two new faults of F8 and F9 are inferred, and the fault F9 is of larger scale that cut the basement. The high conductivity layer in middle-upper crust may to some extent control the distribution of oil and gas deposits within the Hailar Basin. It is speculated that the high conductivity layer uplifts is a favorable area for oil and gas exploration.