东昆仑活动断裂带秀沟盆地段晚第四纪构造变形与地貌特征研究

秀沟盆地是发育在东昆仑走滑断裂带上的一级拉分盆地,位于该断裂带西大滩-东大滩段与托索湖段的左阶连接部位。本研究通过解译分析高分辨率遥感影像和数字高程模型(DEM)数据,并结合野外高精度实时差分GPS(RTK-GPS)测量数据,对秀沟盆地第四纪构造活动及其地貌特征进行了研究。研究结果表明,沿东昆仑活动断裂带秀沟盆地段发育了晚第四纪地表地震破裂带、次级走滑拉分盆地、错断阶地陡坎、错断冲积扇等典型走滑构造地貌特征。其中秀沟盆地东北部发现约50km长,而且保存完好的地表地震破裂带,很可能是1902年秀沟盆地东北部M7.0级的地震地表破裂带。在破裂带的长度上,它与1963年发生在其东部阿拉克湖段的M7.0所产生的40km长的地震地表破裂带相近。高分辨率遥感影像的解译结果表明,冲积扇上发育的河流T3阶地与T4阶地之间发生了90m左右的水平断错累积位移,根据同一海拔高度沉积物的宇宙成因核素暴露年代测定资料得出的T3和T4阶地的形成年龄分别是 6276±262a和 8126±346a,估算出东昆仑活动断裂带秀沟盆地段全新世以来的平均走滑速率为12.9±2.9mm/a。此外,遥感影像解析和野外测量指示晚第四纪冲积扇发生的累积错断距离为2970±30m,根据这些推测冲积扇形成年代约为 297±19kaB.P.,由此估算出秀沟盆地段晚更新世以来的长期平均走滑速率为10.1±0.8mm/a。两者结果接近,表明东昆仑活动断裂带秀沟盆地段晚第四纪以来有比较一致的走滑速率。

LATE QUATERNARY STRUCTURAL DEFORMATION AND TECTONO-GEOMORPHIC FEATURES ALONG THE XIUGOU BASIN SEGMENT,EASTERN KUNLUN FAULT ZONE

Eastern Kunlun Active Fault Zone is one of the largest strike-slip faults in the northern Tibetan Plateau,which was considered to accommodate the eastward extrusion of Tibet.The almond-shaped Xiugou Basin,75km long and 15km wide,is the first order pull-apart basin associated with the long-term strike-slip movement of the Kunlun fault zone.Geometrically,this pull-apart basin is just located on the releasing step-over between the Xidatan-Dongdatan and Tuosuo Lake segments.On the basis of our field geologic investigations,DGPS(Differential Global Positioning System)geomorphic measurement and tectono-geomorphic interpretation of satellite remote sensing images along the Xiugou Basin,our goal of this study is to document the Late Quaternary structural deformation and geomorphic features along the Xiugou Basin segment.Geomorphic features such as sag-ponds,varied pull-apart basins and displaced fluvial fans,terrace risers are found to well develop around the Xiugou Basin segment.These well-preserved geomorphic features are related to long-term geomorphic growth of the Kunlun fault zone.We identified a ca.50-km-long surface rupture zone produced by the most recent large seismic event(M7.0),which most likely occurred in the northeast part of the Xiugou Basin in 1902.The length of this surface rupture zone is almost same order with the 40km-long surface rupture zone produced by the 1963 Alake Lake M7.0 Alake Lake earthquake.A long-term slip rate of 12.9±2.9mm/a was estimated based on lateral offsets of terrace riser,it is close to the result estimated from the displaced fluvial fans(10.1±0.8mm/a)in the west part of Xiugou Basin.Our estimated slip rate along the Xiugou Basin segment is in the same range measured by GPS.