【作者】 常利军；

【导师】 丁志峰； 王椿镛；

【作者基本信息】 中国地震局地球物理研究所 ， 固体地球物理学， 2014， 博士

【摘要】 中国大陆及邻区位于欧亚大陆东南部,四个重要的板块强烈交互作用,东部受到太平洋板块和菲律宾海板块的俯冲作用,西部受到印度板块的碰撞作用,形成了诸多俯冲带、造山带及数千公里的大陆离散变形带。因此,中国大陆及邻区是开展地球动力学研究的天然实验室。提高岩石圈和软流圈的变形特征认识对理解中国大陆及邻区的动力学含义具有重要的意义。本研究将通过联合地表变形场和地幔变形场来分析中国大陆及邻区的岩石圈壳幔耦合程度和软流圈的地幔流特征。本研究收集了位于中国大陆及邻区的宽频带固定和流动地震台(共1800个台)记录的)CKS (SKS, SKKS, PKS)波形资料,采用最小切向能量的网格搜索和叠加分析方法测量了每个台站的各向异性参数,即快波偏振方向和快、慢波时间延迟,并利用他人在区域内993个宽频带地震台站得到的横波分裂参数,一起组成表征地幔变形场的数据集；并利用发表的～3600个GPS和断裂第四纪滑动速率测量数据,采用连续样条函数方法求取了中国大陆及邻区的地表连续变形场(速度场和应变率场)。根据应变率分布和岩石圈构造特征,按照高应变率和厚岩石圈区域采取岩石圈变形模式分析,定量求取和确定每个测点的岩石圈变形类型(左旋简单剪切、右旋简单剪切和纯剪切变形),通过预测的横波分裂参数与实测参数的对比来确定岩石圈壳幔力学耦合的程度。研究结果表明,大部分地区符合垂直连贯变形模式,属于壳幔耦合特征,如青藏高原、天山造山带、阿尔泰造山带、台湾造山带、琉球岛弧等构造单元,但在印度板块和欧亚板块陆-陆碰撞带—喜马拉雅碰撞带、日本和稳定的四川盆地、塔里木盆地等区域,可能由于板块的俯冲导致的复杂构造变形或一种古老的“化石”各向异性并不符合垂直连贯变形模式。在低应变率和薄岩石圈区域采用简单软流圈变形模式分析,假设各向异性是由于岩石圈底部和软流圈之间的运动速度差异引起的。基于预测的地幔流和地表速度场模拟的快波方向与XKS波分裂快波方向之间的比较,通过迭代反演确定了最佳地幔流。研究结果显示,长白山火山活动区将中国东部下面软流圈地幔流分成两部分,北部顺时针旋转的地幔流向东运动,指向东方向太平洋俯冲带,而南部顺时针旋转的地幔流自北向南由向南运动到向西南运动的变化,指向西南的缅甸俯冲带和巽达俯冲带。长白山火山活动区下的热地幔上涌使得中国东部软流圈地幔流分成流动方向相反的两部分,北部的顺时针旋转的地幔流向东运动,而南部的顺时针旋转的地幔流自北向南,由向南运动到向西南运动。而在蒙古地区拟合的最佳软流圈地幔流为顺时针旋转的地幔涡流,其形成可能与太平洋板片俯冲、后撤／回转,以及巨厚岩石圈的西伯利亚克拉通的几何形态相关。东亚地区的太平洋板片、巽达板片和缅甸板片的俯冲作用和后撤／回转作用导致了中国大陆及邻区顺时针旋转的软流圈地幔流,使得与岩石圈底部产生了一个水平差异运动,在软流圈中产生一个与简单剪切一致的变形结构,进而形成了研究区所观测各向异性。更多还原

【Abstract】 China’s mainland and its adjacent regions are located in the southeastern part of the Eurasian plate where four major plates are interacting with each other, i.e., the subduction of the Pacific and Philippine oceanic plates in the east and the collision with the Indian plate in the west, and form subduction zones, active orogens and broad continental diffusion that spreads thousands of kilometers. Thus, China’s mainland and its adjacent regions provide a natural laboratory for studying the geodynamics. An improved knowledge of the deformation characteristics of lithosphere and asthenosphere is very important for a better understanding of the geodynamics in China’s mainland and its adjacent regions. The present thesis focuses on determining the extent of crust-mantle coupling in lithosphere and mantle flow in asthenosphere beneath China’s mainland and its adjacent regions through the joint analysis of surface and mantle deformation fields.In order to infer the mantle deformation field, we determine the XKS (SKS, SKKS PKS) fast polarization directions and delay time between the fast and slow waves for1800permanent and temporary broadband seismic stations where the fast polarization and delay time for each arrival were determined following the grid searching method of the minimum tangential energy and stacking procedure, and also, we use993previously published results in China’s mainland and its adjacent regions. For the continuous surface deformation field, we determine a model strain-rate and velocity field using continuous spline functions to interpolate between observed surface strain rate data inferred from-3600GPS observations and Quaternary fault slip rates.According to the magnitude of strain rate and lithosphere thickness, we divide the study area into two parts, one is high strain rates and thick lithosphere, and another is low strain rates and thin lithosphere. In high strain rates and thick lithosphere area, we measure the deformation pattern (left-lateral simple shear, right-lateral simple shear or pure shear) at each station based on lithosphere deformation model. We can constrain the extent of crust-mantle coupling through comparing the predicted anisotropy orientations with the observed anisotropy. For most parts of the high strain rates and thick lithosphere area, such as the Tibetan plateau, Tianshan orogen, Altay orogen, Taiwan orogen, Ryukyu Island Arc, the comparison showing the crust and lithospheric mantle are deforming coherently, thus arguing for crust-mantle mechanical coupling of lithosphere. However, in the convergence belt of Himalayan orogen, the Japan trech, the Sichuan basin and Tarim basin, vertical coherence in the deformation is no longer present, the crust-mantle decouping within these areas most likely due to the subduction of plate or fossil from past geologic processes.In low strain rates and thin lithosphere area, we can assume the anisotropy is generated by the differential flow between the lithosphere and asthenosphere. The best fit mantle flow is determined in an iterative inversion by comparing the predicted anisotropy, based differential velocities between predicted mantle flow and the velocity field at the surface, with orientations with the observed anisotropy. The studies showing that the asthenospheric mantle flow beneath the East China is split two parts in Changbaishan volcanic region, one is an eastward-directed clockwise rotation of the asthenospheric mantle directed toward the Pacific subduction in the north, and another is a clockwise rotation of the asthenospheric mantle from southward to southwestward in the south, and directed toward the Burma/Sunda slabs. We think that the asthenospheric mantle flow beneath the North China and South China is generated by the subduction and rollback/retreat of Burma/Sunda slabs, and the mantle flow beneath the Northeast China is generated by the subduction and rollback/retreat of Pacific slab, meanwhile, the mantle upwelling beneath Changbaishan volcanic region split the asthenospheric mantle flow beneath the East China into two flows in the opposite direction. The asthenospheric mantle flow beneath Mongolia is a vortex with clockwise rotation which possibly related to the subduction and rollback/retreat of Pacific slab and the geometry of stable Siberia craton with thick lithosphere.更多还原