西准噶尔岩石圈电各向异性研究

发布时间：2018-03-06 06:05

本文选题：大地电磁　切入点：电各向异性　出处：《中国地质大学》2016年博士论文　论文类型：学位论文

【摘要】：近年来随着地球物理观测技术和理论方法的发展,越来越多的研究表明地球介质具有明显的电各向异性特征。大地电磁法可以对整个岩石圈的电阻率进行成像,因而成为理解岩石圈的结构、组成以及演化的主要手段之一为了研究西准噶尔岩石圈的电性结构,完成了穿越北东-南西向的达尔布特断裂的三条大地电磁测深剖面。相位张量和感应矢量分析表明此区域地电结构是3D且可能存在各向异性。对阻抗张量和倾子矢量数据集分别进行3D各向同性反演,得到了两个极为不同的模型,说明没有一个简单的电各向同性模型可以同时解释所有的大地电磁响应函数。根据1D各向异性以及2D、3D各向同性的反演结果,建立了一个各向异性的3D电阻率模型,其中包含位于达尔布特与克一乌断裂之间、深度范围为5-40公里的方位电各向异性地壳层(最小电阻率方向为东西向)以及一个方位电各向异性的岩石圈地幔(最小电阻率方向为北东20°)。这一各向异性电阻率模型明显改善了反演中相位张量和感应矢量的拟合程度。推断方位电各向异性地壳层为玄武质海洋地壳在晚古生代对洋内达尔布特岛弧下俯冲的残余物,板块俯冲过程中发生脱水作用而产生大量的水,从而在板片和地幔楔内产生大量的蛇纹岩化岩石。该壳内电各向异性层的最小电阻率方向(近东西向)与海沟走向(-北东40°)的差异性可能是由于斜俯冲造成的。同时注意到,地壳各向异性层最小电阻率方向和海沟方向相对于岩石圈地幔最小电阻率方向(北东20°)分别有顺时针70°和200的偏离,表明该区地壳的运动与其下伏的上地幔是解耦的。
[Abstract]:In recent years, with the development of geophysical observation techniques and theoretical methods, more and more studies show that the earth media has obvious characteristics of electrical anisotropy. Magnetotelluric method can image the resistivity of the whole lithosphere. Therefore, it has become one of the main means of understanding the structure, composition and evolution of the lithosphere in order to study the electrical structure of the lithosphere in West Junggar. Three magnetotelluric sounding profiles have been completed across the Dabut fault in the NE-S direction. Phase Zhang Liang and induction vector analysis show that the geoelectric structure in this area is 3D and may have anisotropy. The vector data sets are respectively used for 3D isotropic inversion. Two very different models are obtained, which show that no simple electroisotropic model can interpret all magnetotelluric response functions at the same time. An anisotropic 3D resistivity model is developed, which is located between the Darbout and Keyawu faults. An azimuthal anisotropic crustal layer with a depth of 5-40 km (the minimum resistivity direction is east-west) and a azimuthal anisotropic lithospheric mantle (the minimum resistivity direction is 20 掳N E). This anisotropic resistivity is obtained. The model obviously improves the fitting degree of phase Zhang Liang and induction vector in inversion. It is inferred that the azimuth anisotropic crust is the residuals of Black Tortoise oceanic crust subducting under the arc of Darbout Island in the late Paleozoic. A lot of water is produced by dehydration during plate subduction. As a result, a large number of serpentinized rocks are produced in the plate and mantle wedge. The difference between the minimum resistivity direction (near east-west) of the anisotropic layer in the crust and the trench strike (40 掳NNE) may be caused by oblique subduction. The minimum resistivity direction and trench direction of the anisotropic layer of the crust deviate from the minimum resistivity direction of lithospheric mantle (20 掳N E) by 70 掳clockwise and 200 掳respectively, indicating that the crustal movement in this area is decoupled from the underlying upper mantle.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P631.3

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