青藏高原东北缘马衔山断裂带构造属性的综合研究

左旋走滑的马衔山断裂带位于青藏高原东北缘陇中盆地内部，呈北西-南东向伸展.宽约8~10 km，长约115 km.马衔山断裂带表面虽然局部已被黄土覆盖，但并不代表它的活动性不强.1125年的兰州M_S7.0地震就发生在马衔山断裂带北缘的西侧.前人对马衔山断裂带的研究基本上多依靠于地表地质和地球化学数据分析进行一般性讨论，而缺少对马衔山断裂带深部构造伸展的清晰认识.本文中，我们主要依靠一条横跨马衔山断裂带的深地震反射剖面数据资料进行地壳尺度的构造解释.在此基础之上，对研究区所获得的重力数据进行相应的处理分析.最后辅助于马衔山断裂带两侧野外地表形变的观察和前人研究所获得的地球化学数据分析，我们的研究认为马衔山断裂带为一不同块体间的边界断裂带.它可能形成于早古生代祁连造山带东缘北部马里亚纳式岛弧和南部日本式岛弧的相互拼贴作用.该边界断裂带在随后的青藏高原东北缘物质逃逸过程中被激活，并且目前仍处于构造活动活跃期.

Integrated analysis on the tectonic features of the Maxian Shan fault zone in the northeastern Tibetan plateau

The sinistral strike-slip Maxian Shan fault zone is located within the interior of the north-easternmost Tibetan Plateau. It extends in northwest-southeast direction over a distance more than 115 km with widths 8~10 km. Although this fault zone is partly covered by widespread Quaternary losses, its tectonic activity is not necessarily low. One piece of evidence that the 1125 M_S7.0 Lanzhou earthquake took place just at the west of the north edge of the Maxian Shan fault zone. Previous studies are mostly concentrated on the surface expression of this fault zone and geochemical analysis of the plutons on its both sides to delineate its traces, lacking the information on its extension at depth. In this work, we employed a NE-SW striking 310 km-long deep seismic reflection profile that crosses the Maxian Shan fault zone to reveal its deep structure. In combination with processing and analysis of the available gravity anomalies and previous geochemical studies, we suggest that the Maxian Shan fault zone is a block boundary that separates two different paleo-volcanic arcs of the Qilian orogenic belt. It formed during the amalgamation of these two paleo-volcanic arcs in Early Paleozoic. The Maxian Shan fault zone was later reactivated during northeastward extrusion of the Tibetan Plateau and remains tectonically active now.