青藏高原岩石圈低速结构的动力学模型

发布时间：2018-08-07 09:03

【摘要】：青藏高原是研究岩石圈形成演化,探讨地壳运动机制的理想区域。自新生代以来,青藏高原的隆升及其对周边地区气候与资源的深刻影响,一直为科学界所瞩目,成为国际上地球科学的研究热点。研究青藏高原的动力学机制,对揭示地球上生态演化规律和人类文明发展具有重要的科学意义。相比于其它现代大地测量技术,如GPS、InSAR和卫星重力技术,用地面重力数据研究青藏高原的动力学机制能够提供与其它大地测量技术互补的物质迁移信息,比如,能够探测到GPS和InSAR技术难以观测到的地球深部物质运动信号,与常用的GRACE卫星重力数据相比对地球局部浅层质量的形变迁移更加灵敏,能够捕获地震波层析成像技术难以捕捉到的深部物质的动态运动信号。岩石圈结构的(剪切波)低速结构通常被认为是强度较低的部分,因此在印度-欧亚板块的碰撞过程中更容易发生形变,理论上更容易产生显著的重力变化信号。本文的研究思路就是提取岩石圈低速结构在欧亚-印度板块碰撞过程中引起的地面重力信号,并建立利用提取到的重力变化信号研究深部物质迁移的理论和方法,将提取的重力信号与地震波层析成像模型(即青藏高原岩石圈结构)对比寻找两者的相关性,联合多种数据构造和分析青藏高原的动力学模型。以往缺乏类似的研究,本文提出系统的研究方法和理论,主要内容总结如下：(1)提出联合地面重力数据、地表位移观测数据和岩石圈速度结构模型研究青藏高原动力学机制的策略。研究了提取上地幔重力变化信号的方法,收集其它各类数据和模型,从总重力变化信号中改正和扣除各种不关心的重力变化信号分量。(2)在各种重力变化分量中,重点研究了估计地壳应变引起的重力变化,构建了相应的数学模型,利用地面GPS水平速度计算面应变,然后用面应变计算重力变化。(3)将青藏高原的地面重力测站划分为22个子区域,计算它们的上地幔重力变化、面应变和地表垂向位移,用于定量分析和辅助构建青藏高原的局部区域动力学模型。根据地表位移、岩石圈速度结构和提取的上地幔重力变化,本文提出相应的动力学模型,概括如下：(1)青藏高原北部存在一个大尺度的低速结构,这些低强度物质形成一个倒三角形状,很可能在印度-欧亚碰撞过程中上涌,在遇到地壳下表面以后沿莫霍面水平向扩散,由此形成青藏高原北部大范围的正重力变化信号。(2)青藏高原内陆的正重力变化在南部呈现一个突起,几何形态与地表拉张断层走向十分符合,表明与地表结构的形成具有密切的联系。本文倾向于认为是印度板块撕裂的结果。具体地,印度板块俯冲到欧亚板块下撕裂,板块裂隙被自北向南扩散的上地幔物质填充,引起正重力变化。(3)祁连山北部的低速结构对应一个明显的负重力变化信号,可能是由于低速结构受到南北向挤压下沉侵入地幔中形成。(4)青藏高原东南部岩石圈中存在多个低速结构,包括位于中-下地壳(26°N纬线以北)的两个低速带和位于上地幔(26°N纬线以南)的一个低速结构。本文认为26°N纬线以北的两个低速带是受到松潘-甘孜块体向南运动的挤压而增厚,形成正重力变化信号；26°N纬线以南的低速结构遵循Airy均衡调整的动力学模型,并释放青藏高原的重力势能。(5)青藏高原东南部的条带状低速结构延伸至龙门山断裂西南端,这里的中-下地壳低速构造受到挤压增厚,上地壳由于四川盆地的阻挡受到挤压和增厚,两者的共同作用导致龙门山断裂带西南端抬升。龙门山断裂带东北端的地壳受到挤压、缩短而堆积侵入地幔。因此,龙门山两端的重力势能差增大,并且方便两端之间的断层走滑运动,引发地震(如2008年汶川地震和2013年芦山地震)。
[Abstract]:The Qinghai Tibet Plateau is an ideal region to study the formation and evolution of the lithosphere and to explore the mechanism of the crustal movement. Since the Cenozoic, the uplift of the Qinghai Tibet Plateau and its profound influence on the climate and resources in the surrounding areas have been attracting the attention of the scientific community and becoming a hot spot in the international research of earth science. Compared with other modern geodetic techniques, such as GPS, InSAR and satellite gravity technology, the dynamic mechanism of the Qinghai Tibet Plateau can provide material migration information complementary to other geodetic techniques, such as the detection of GPS and InS, compared with other modern geodetic techniques. AR technology is difficult to observe the motion signal of the earth's deep material. Compared with the common GRACE satellite gravity data, it is more sensitive to the deformation and migration of the shallow layer of the earth, and can capture the dynamic motion signal of the deep material which is difficult to capture by the seismic wave tomography. The rock structure (shear wave) low velocity structure is usually recognized. As a part of the lower strength, it is easier to deform in the collision process of the India Eurasian plate, and it is easier to produce significant gravity change signals in theory. The force change signal studies the theory and method of the deep material migration, and compares the extracted gravity signal with the seismic wave tomography model (that is the lithosphere structure of the Qinghai Tibet Plateau) to find the correlation between the two, to combine various data to construct and analyze the dynamic model of the Qinghai Tibet Plateau. The main contents of the method and theory are summarized as follows: (1) the strategy of combining ground gravity data, ground displacement observation data and lithosphere velocity structure model to study the dynamic mechanism of the Qinghai Tibet Plateau is proposed. The method of extracting gravity change signals from upper mantle is studied, other kinds of data and models are collected and corrected and deducted from the total gravity change signals. Various signal components of gravity change that are not concerned. (2) in various gravity variation components, the gravity change caused by the estimation of the crustal strain is studied. A corresponding mathematical model is constructed. The surface strain is calculated by the horizontal velocity of the ground GPS, then the surface strain is used to calculate the gravity change. (3) the ground gravity station of the Qinghai Tibet Plateau is divided into 22 sub stations. The region, the gravity variation of the upper mantle, the surface strain and the vertical displacement of the surface are used for quantitative analysis and auxiliary construction of the local regional dynamic model of the Qinghai Tibet Plateau. Based on the surface displacement, the velocity structure of the lithosphere and the gravity change of the upper mantle, the corresponding dynamic models are proposed, which are summarized as follows: (1) the Northern Qinghai Tibet Plateau There is a large scale low velocity structure, which forms an inverted triangle shape. It is likely to surge up in the India Eurasia collision course and spread horizontally along the Moho surface after the surface of the earth's crust, thus forming a wide range of positive gravity change signals in the Northern Qinghai Tibet Plateau. (2) the positive gravity change in the inland of the Qinghai Tibet Plateau is The southern part presents a protruding, which is in close agreement with the direction of the surface stretching fault, indicating that it is closely related to the formation of the surface structure. This article tends to be considered the result of the tearing of the India plate. Specifically, the India plate subducts to the Eurasian plate and is torn under the Eurasian plate, and the plate fissure is filled with the upper mantle material spreading from north to south. (3) the low velocity structure in the northern part of Qilian Mountains corresponds to a significant negative gravity change signal, which may be due to the formation of the low velocity structure under the North-South extrusion and subsidence. (4) there are several low velocity structures in the lithosphere southeast of the Qinghai Tibet Plateau, including two low velocity zones and positions located in the middle lower crust (26 degree N weft North). It is a low velocity structure in the upper mantle (26 degree N weft South). This paper considers that two low speed belts north of the 26 N weft are thickened by the Songpan Ganzi block southward movement, forming a positive gravity change signal, and the low-speed structure in the south of the 26 degree N weft follows the dynamic mechanical model of the equilibrium adjustment of the Airy and releases the gravitational potential energy of the Qinghai Tibet Plateau. (5) the low-speed structure in the southeast of the Qinghai Tibet Plateau extends to the southern end of the Longmen mountain fault, where the low-speed structure of the middle and lower crust is squeezed and thickened, the upper crust is squeezed and thickened by the obstruction of the Sichuan basin. The joint action of the Sichuan basin leads to the uplift of the southwest end of the Longmen mountain fault zone. The crust in the northeast of the Longmen mountain fault zone is squeezed. The pressure, shortening and accumulation invades the mantle. Therefore, the gravitational potential difference between the two ends of the Longmen mountain increases, and facilitates the strike slip motion between the two ends, causing earthquakes (such as the Wenchuan earthquake of 2008 and the Lushan earthquake in 2013).
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：P542

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