青藏高原东南缘上地壳晚新生代构造变形综述

Review of Structural Deformation in the Upper Crust of the Southeastern Margin of the Tibetan Plateau since the Late Cenozoic

青藏高原东南缘是检验青藏高原演化模型的理想实验场,也是全球地震活动最为频繁的地区之一.综述了青藏高原东南缘主要活动断裂十年和万年尺度的滑动习性研究和百年时间尺度区域地震活动分布,结合前人总结的百万年时间尺度的年代学研究,认为自中新世中晚期以来,青藏高原内部物质逐渐向东流出,受四川盆地阻挡,转而向东南缘地区作顺时针旋转运动,至晚第四纪时期,东南缘地区上地壳变形已由原本集中分布在大型走滑边界断裂和逆冲褶皱带转变为弥散式分布至区内次级断裂,形成了以鲜水河-小江断裂带和实皆断裂带为边界,围绕喜马拉雅东构造结作顺时针旋转的运动学特征.据此青藏高原东南缘变形可划分为两阶段,中新世早期及以前变形集中在大型边界断裂,符合刚性块体变形,至晚第四纪时期转为弥散式连续变形.基于水平滑动速率和地震活动性对比,青藏高原东南缘活动断裂可大致分为三级.一级断裂为边界断裂鲜水河-小江断裂带和实皆断裂带,水平滑动速率均≥10 mm/a,曾发生8级及以上地震和连续的7~7.9级强震,是东南缘地区晚第四纪以来一级构造格架;二级断裂往往控制东南缘地区强活动构造单元,水平滑动速率为~3~6 mm/a,通常发生过7~7.9级地震;三级断裂水平滑动速率一般≤2 mm/a,通常发生过7级以下地震,一般规模较小,但数量较多.此外,川滇地块晚第四纪变形特征发生转变,构造运动由原本的沿大型边界走滑断裂运动转变为鲜水河-小江断裂带周缘次级活动地块的旋转、平移和差异隆升.

The southeastern margin of the Tibetan Plateau is an ideal experimental field to test the evolutionary model of the Tibetan Plateau and one of the most seismically active regions in the world.In this paper,we review the decadal and 10,000-yearscale slip habits of the major active faults on the southeastern margin of the Tibetan Plateau and the 100-year-scale regional seismic activity,combined with the million-year time-scale chronology studies,we think the internal material of the Tibetan Plateau gradually flowed out to the east and was blocked by the Sichuan Basin,turning to the southeastern margin area for clockwise rotational movement since the middle and late Miocene.In the Late Quaternary,the upper crustal deformation in the southeastern margin has changed from being concentrated in large strike-slip boundary faults and thrust fold belts to being diffusely distributed to secondary faults in the region,forming the kinematic characteristics of clockwise rotation around the eastern Himalayan syntaxis with the Xianshuihe-Xiaojiang Fault Zone and the Sagaing Fault Zone as boundaries.Accordingly,the deformation of the southeastern margin of the Tibetan Plateau can be divided into two stages.The deformation of the early Miocene period was concentrated in large boundary faults,which conforms to the deformation of rigid blocks,and turned into diffuse continuous deformation in the late Quaternary.Based on the comparison of horizontal slip rate,seismogenic capacity and seismic activity,the active faults on the southeast edge of the Tibetan Plateau can be roughly divided into three levels.The first-tier faults are the boundary fault Xianshuihe-Xiaojiang fault zone and Sagaing fault zone,with horizontal slip rates≥10 mm/a,capable of occurring earthquakes of M 8 and above alone,and can continuously generate strong earthquakes of M 7-7.9,which are the first-tier tectonic frame since the Late Quaternary in the southeastern margin;the second-tier faults can control the strongly active tectonic units in the southeast margin,with horizontal slip rates~3-6 mm/a,generally capable of occurring earthquakes of M 7-7.9,and can continuously generate earthquakes of M 6-6.9;the horizontal slip rate of Level 3 faults is generally≤2 mm/a,they are only capable to generating earthquakes less to M 7,and are generally smaller in scale but more numerous.In addition,the Late Quaternary deformation characteristics of the Chuandian Block have changed from the original slip movement along the large boundary faults to the rotation,translation and differential uplift of the secondary active blocks around the Xianshuihe-Xiaojiang Fault Zone.