青藏高原西部岩石圈电性结构与动力学研究

发布时间：2018-05-26 19:22

本文选题：大地电磁测深 + 青藏高原西部　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：青藏高原作为欧亚大陆最醒目的地貌单元,是印度大陆与亚洲大陆碰撞的产物;由于印度洋中脊持续扩张使印度板块岩石圈向北楔入到亚洲大陆之下,挤压增厚形成了青藏高原,它具有复杂而独特的巨厚地壳和岩石圈结构。青藏高原西部地区是印度洋向北扩张挤压的应力集聚带,是陆-陆碰撞造山带的典型地区之一,它拥有更为复杂的地质构造与物质组成,对此区域进行详细的研究对于从整体上认识青藏高原的一系列地学问题起着关键的作用,因此,青藏高原西部地区近些年来已经成为地学研究者关注的热点区域。论文以“深部探测技术与实验研究”专项(SinoProbe,2008-2012)子课题“大陆电磁学参数标准网实验研究(SinoProbe-01)”在青藏高原西部地区沿80° E、81°E、82° E三条经线采集得到的14个“标准点”,共计148个大地电磁测深点作为原始数据资料,对数据进行了处理、分析及反演;最终得到了研究区的二维及三维电性结构模型。二维反演模型和三维反演切片对应良好,说明得到的电性结构模型可信度较高。电性结构模型显示,研究区上地壳以高阻为主,在缝合带及断裂带处,有垂向延伸的低阻带切割高阻层;中、下地壳内有大规模高导层,雅鲁藏布江缝合带处高导层厚度小、埋深浅,拉萨-冈底斯地体内高导层的厚度和底界面深度向北增大,在班公湖-怒江缝合带附近下方高导层厚度最大,底界面已经达到上地幔深度,羌塘地体高导层厚度整体较大;高导层之下为高阻层,但受剖面的有效深度限制,并不能判定该层的厚度。研究认为,印度板块岩石圈向青藏高原下方俯冲产生的热效应,使俯冲接触面上的岩石发生了部分熔融,熔融的岩石电阻率降低;另外,熔融的岩石会析出水分,水分在压力作用下会向上方运移;因此在部分熔融和含水流体的共同作用下导致了研究区内喜马拉雅地体和拉萨-冈底斯地体下方高导层的出现。羌塘地体内的高导层的成因主要是因为幔源物质上涌,导致壳内岩石发生部分熔融,形成了高导层。研究认为,印度岩石圈已经俯冲进入青藏高原之下,在青藏高原西部,其俯冲前缘没有越过班公湖-怒江缝合带,俯冲的印度岩石圈在班公湖-怒江缝合带下方下插进入上地幔。
[Abstract]:The Qinghai-Xizang Plateau, as the most prominent geomorphological unit in Eurasia, is the result of the collision between the Indian continent and the Asian continent. Due to the continuous expansion of the mid-Indian Ocean ridge, the lithosphere of the Indian plate wedge north into the Asian continent. The compression thickening forms the Qinghai-Xizang Plateau, which has a complex and unique structure of the extremely thick crust and lithosphere. The western part of the Qinghai-Xizang Plateau is a typical region of the continental and continental collision orogenic belt, which is characterized by a more complicated geological structure and material composition. The detailed study of this region plays a key role in understanding a series of geoscience problems in the Tibetan Plateau as a whole. Therefore, the western region of the Tibetan Plateau has become a hot spot of geoscience researchers in recent years. In this paper, 14 "standard points" have been collected in the western part of the Qinghai-Xizang Plateau along three longitude lines of 80 掳E ~ (81 掳) and 82 掳E, based on "Sino Probe-01", a sub-project of "SinoProbe-2008-2012", a subproject of "Sino Probe-01", which is a special project of "deep exploration technology and experimental research" ("Sino Probe-01"). A total of 148 magnetotelluric sounding points were used as raw data to process, analyze and inverse the data. Finally, the two-dimensional and three-dimensional electrical structure models of the study area were obtained. Two dimensional inversion model and three dimensional inversion slice correspond well, which indicates that the obtained electrical structure model has high reliability. The electrical structural model shows that the upper crust of the study area is dominated by high resistivity, and there is a vertical extension of low resistivity zone in the suture zone and fault zone to cut the high resistivity layer, and in the middle and lower crust there is a large scale high conductivity layer, and the thickness of the high conductivity layer in the Yalu Zangbo suture zone is small. The depth of the buried layer is shallow, the thickness of the high conductivity layer and the depth of the bottom interface of the Lhasa-Gangdis area increase northward, and the thickness of the high conductivity layer near the Bangong Lake-Nujiang suture zone is the largest, and the bottom interface has reached the depth of the upper mantle. The thickness of the high conductivity layer in Qiangtang is relatively large, but the thickness of the high conductivity layer is limited by the effective depth of the section. It is believed that the thermal effect of the subduction of the Indian plate lithosphere beneath the Qinghai-Xizang Plateau has partially melted the rocks on the subduction contact surface and reduced the resistivity of the melted rocks. In addition, the molten rocks will precipitate water. Water will move upward under pressure, so the combination of partial melting and water-bearing fluids leads to the appearance of high conductivities beneath the Himalayan terrane and Lhasa Gangdis terrane in the study area. The formation of the high conductivity layer in Qiangtang is mainly due to the upwelling of mantle material, which leads to partial melting of the rocks in the crust and the formation of the high conductivity layer. The study shows that the Indian lithosphere has already subducted into the Tibetan Plateau, and in the western part of the Tibetan Plateau, the leading subduction front has not crossed the Bangonghu Lake-Nujiang suture zone. The subducted Indian lithosphere enters the upper mantle below the Bangong Lake-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】：P631.3;P313

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