冈底斯中段岩石圈电性结构研究

发布时间：2018-06-24 09:30

本文选题：大地电磁测深 + 深部电性结构　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：青藏高原自形成以来,由南至北形成了喜马拉雅地体,雅鲁藏布江缝合带,拉萨-冈底斯地体,班公—怒江缝合带,羌塘地体等地质单元及界线。印度板块和亚欧板块两大板块的碰撞对于缝合带的形成和地体的演化有着重要的意义。本文依托项目“冈底斯大地电磁剖面调查与岩石圈电性结构研究”,选择主要研究区域为雅鲁藏布江缝合带以北、班公-怒江缝合以南的冈底斯地体。设计一条穿过雅鲁藏布江缝合带和班公-怒江缝合带的大地电磁测深剖面,对采集的大地电磁数据采用先进的处理方法,分析数据点的二维偏离度,磁感应矢量和相位张量分解等流程后,进行区域内的二维反演和三维反演,获得了冈底斯地体可靠的深部电性结构模型。该模型表现出剖面整体具有的特征为:垂直分层,水平分块。研究区电性结构模型由浅到深可分为三个电性层:第一层以不连续的高阻体为主,平均埋深约20km-30km。第二层为在中下地壳由雅鲁藏布江缝合带开始存在规模较大的北倾高导层,由南至北厚度逐渐增大,班公-怒江缝合带南侧高导体有延伸至上地幔的趋势。第三层下地壳至上地幔则主要为高阻体。根据电性结构模型电性梯度带和高导层的特征,结合地质资料划分了地质单元。通过电性结构模型的特征对喜马拉雅地体、冈底斯地体和羌塘地体的深部结构特征进行了分析与说明。将500线和剖面的三维反演结果进行拼合得出结论:班公-怒江缝合带南侧东西向的电性结构相一致,说明在冈底斯地体,高阻体和高导层具有东西向的连通性。冈底斯上地壳出现的高阻层,可能是冈底斯大规模浅层火成岩的表现,与前期大规模的岩浆运动有关。在班公-怒江缝合带南侧存在下沿深度较深的高阻体,推测可能是在发生岩浆活动后的冷却作用形成大规模的岩体。高阻体下存在连续高导层,可能是水流体和熔融体的共同作用的结果。由于羌塘地体高导层减薄且电阻率值减小,对于动力学模型探讨,推测印度-亚欧板块相向“双向俯冲”,俯冲前缘位置在班公怒江缝合带以南。
[Abstract]:Since the Qinghai-Tibet Plateau was formed, the Himalayan terrane, Yalu Zangbo River suture zone, Lhasa Gangdis terrane, Bangong-Nujiang suture zone, Qiangtang terrane and so on have been formed from the south to the north. The collision between the Indian plate and the Eurasian plate plays an important role in the formation of suture zone and the evolution of terrane. Based on the project "investigation of magnetotelluric profile and electrical structure of lithosphere", this paper selects the Gangdis terrane north of the Yarlung Zangbo River suture belt and south of the Bangong-Nujiang River suture. A magnetotelluric sounding profile passing through the Yalu Zangbo suture zone and the Bangong- Nujiang suture zone is designed. The advanced processing method is used to analyze the two-dimensional deviation of the data points. After the flow of magnetic induction vector and phase Zhang Liang decomposition, 2D and 3D inversion in the region are carried out, and a reliable deep electrical structure model of Gangdis terrane is obtained. The characteristics of the model are vertical stratification and horizontal partitioning. The electrical structure model of the study area can be divided into three layers from shallow to deep. The first layer is composed of discontinuous high resistive bodies with an average buried depth of about 20km-30km. In the second layer, there is a large northerly high conductivity layer in the middle and lower crust from the Yalu Zangbo River suture belt, and the thickness from south to north increases gradually, and the high conductors in the southern side of the Bangong-Nujiang suture belt tend to extend to the upper mantle. The third lower crust and upper mantle are mainly high resistivity bodies. According to the characteristics of the electrical gradient zone and the high conductivity layer of the electrical structure model, the geological units are divided according to the geological data. The deep structural characteristics of Himalayan, Gangdis and Qiangtang terrains are analyzed and explained by the characteristics of electrical structural models. Combining the three dimensional inversion results of 500 lines and sections, it is concluded that the electric structure of the south and west direction of Bangong- Nujiang suture belt is consistent, which indicates that the high resistivity body and the high conductance layer have east-west connectivity in the Gangdis terrane. The high resistivity layer in the upper crust of Gangdis may be the manifestation of the large scale shallow igneous rocks in Gangdis, which is related to the large-scale magmatic movement in the early stage. In the south of Bangong- Nujiang suture belt, there are deep and high resistivity bodies along the lower side of the suture zone, which suggests that the cooling process after magmatic activity may form a large scale rock mass. The existence of a continuous high conductivity layer under high resistivity may be the result of the interaction between water fluid and molten body. Due to the thinning of the height conductance and the decrease of resistivity in Qiangtang, it is inferred that the India-Eurasian plate faces "bidirectional subduction" and the leading position of the subduction is south of the Bangong Nujiang suture zone.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P631.325

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