【摘要】 位于西伯利亚板块东南缘的贝加尔裂谷是最典型的大陆裂谷之一,其形成的动力机制与演化过程一直是地学界争论的焦点.本研究使用一种改进的横波分裂测量方法———全局最小切向能量法,对研究区宽频带固定台站ULN和TLY记录的SKS震相和接收函数PmS震相进行分裂测量,得到了裂谷地区地壳和上地幔的各向异性属性.ULN台的SKS分裂测量结果表明,台站下方存在双层各向异性结构,其中,上层的快波偏振方向为N74°E,快、慢波分裂时差为0.80s,下层的快波偏振方向为N128°E,快、慢波分裂时差为0.80s;PmS震相分裂测量结果表明,台站下方地壳内存在单层各向异性结构,其快波偏振方向为N77°E,与SKS分裂测量的上层各向异性的快波偏振方向相近,快、慢波分裂时差为0.26s,这说明SKS分裂测量的上层各向异性同时包含了地壳和地幔岩石圈.对TLY台进行SKS分裂测量时发现,台站下方上地幔结构表现出横向非均匀性:当反方位角<90°时,快波偏振方向在N60°E左右,快、慢波分裂时差为1.27s;当反方位角>90°时,快波偏振方向约为N120°E,快、慢波分裂时差为1.40s;PmS震相分裂测量没有获得有效的结果,并且不同方位的PmS震相到时基本一致,说明TLY台下方地壳结构接近各向同性.根据分裂测量结果,结合贝加尔裂谷区的构造演化过程,得到以下结论:(1)ULN台双层各向异性的上层主要是岩石圈原始结构的反映,并且存在地壳与地幔岩石圈的一致性形变,而下层指示着现今软流圈地幔的流动;(2)由于刚性的西伯利亚克拉通的阻挡,地幔流动方向在克拉通南缘发生了偏转,在深部绕克拉通边缘流动,因此形成了TLY台下方上地幔结构的横向变化.更多还原

【Abstract】 The Baikal Rift lies at the southeast edge of Siberian Craton,and is one of the most representative continental rifts.The dynamic mechanism of its formation and evolution has always been the focus of argument.In this study,one improved analysis method of shear-wave splitting is used,which is called ’global minimum transverse energy’(GM),to process the seismic data from long-term-station ULN and TLY,and finally obtain the anisotropy attribute of crust and upper mantle.The SKS measurement at station ULN shows that,there are two anisotropic layers below station ULN: upper( means fast direction) =N74°E,δtupper(δt means delay time)=0.80 s,lower=N128°E,δtlower=0.80 s;while the measurement of phase PmS splitting reveals one anisotropic layer situated in crust: aver=N77°E,δtaver=0.26 s,with the  value near upper of the two-layer model,perhaps indicates that the upper layer includes both the crust and mantle lithosphere.On the other hand,the SKS measurement at station TLY shows that,the upper mantle structure displays strong lateral nonuniformity: when BAZ(back azimuth) <90°, is close to N60°E,δtaver=1.27 s;when BAZ>90°, is close to N120°E,δtaver=1.40 s.Besides,no effective PmS splitting measurement is obtained,and the arrival times of phase PmS from different azimuths are consistent with each other,both sustain an isotropic crust.After synthetic analysis we arrive at the following conclusions: 1) Below station ULN,the upper layer may be the frozen structure in lithosphere,and crust and mantle lithosphere have undergone conformable deformation,while the lower layer was formed due to the present flowing of asthenosphere mantle;2) Due to the block of the rigid Siberian Craton,the flow direction of mantle is deflected by the south edge of craton,that is,the deep mantle flows around the edge of craton,which further formed the lateral variation of upper mantle structure below station TLY.更多还原