【摘要】 北山造山带位于中亚造山带南缘中段，包含多个近东西向展布的古生代增生单元、洋壳俯冲残余以及大型韧性剪切带，是研究古亚洲洋闭合以及中亚造山带形成过程的关键部位.其中，南天山—索伦克缝合带在北山地区的位置厘定直接影响到对古亚洲洋最后闭合位置以及中亚造山带南缘边界的认识，但目前仍存在较大争议.本研究基于一条已有的经过青藏高原北部祁连山—北山南侧的近南北向的大地电磁剖面，沿剖面继续向北补充测点，形成横穿北山及邻区各构造单元的长剖面，利用大地电磁方法对横向电性变化敏感的特性来探测研究区内古缝合带的痕迹.采用多阶段的三维各向异性反演方法获取了沿剖面及邻近区域的地下电性结构，进而分析与造山带后期活动相关的韧性剪切带规模.研究发现北山自南向北存在三个规模依次减小的各向异性条带(DSZ1—DSZ3)，分别对应了地表的大型韧性剪切带.结合地质研究结果，我们认为这三个各向异性条带指示了早期古亚洲洋消减、微陆块缝合以及造山后期剪切变形的位置.其中，北山南缘的DSZ1条带规模最大，可能代表古亚洲洋在北山地区最后闭合的位置.更多还原

【Abstract】 The Beishan Orogenic Belt, located in the middle segment of the southern margin of the Central Asian Orogenic Belt(CAOB), contains several nearly east-west spreading Paleozoic accretionary units, oceanic crust subduction remnants and large ductile shear zones. It is a key place for studying the closure of the PaleoAsian Ocean(PAO) and the formation of the CAOB. Determination of the location of the Southern TianshanSolonker suture zone in Beishan directly affects the understanding of the final location of the PAO closure and the southern boundary of the CAOB, but it is still controversial at present. On the basis of an existing nearly north-south trending magnetotelluric(MT) profile starting from the Qilian Mountain, northern Tibetan Plateau to the south side of the Beishan, new MT sites were supplemented from south to north to form a long profile crossing Beishan and its adjacent tectonic units. As the MT method is sensitive to lateral variations in electrical resistivity, it can be used to detect traces of ancient suture zones in the study area. We used a multi-stage threedimensional anisotropic inversion method to obtain the subsurface electrical structure along the profile and its adjacent areas. Additionally, we further analyzed the scales of ductile shear zones related to the later evolution of orogenic belt.There are three anisotropic belts(DSZ1—DSZ3) with decreasing scale from south to north in Beishan,corresponding to the large ductile shear zones on the surface, respectively. Combined with geological results, we suggest that these three anisotropic belts may represent the positions of PAO subduction and micro-block suture in the early stage, and shear deformation in later orogeny. The largest anisotropic belt DSZ1, located in the southern margin of Beishan, probably indicates the final position of the PAO closure in Beishan.更多还原