阿拉善地块南缘北大山断裂的晚第四纪构造活动证据  

EVIDENCE OF LATE QUATERNARY TECTONIC ACTIVITY OF THE BEIDA SHAN FAULT,SOUTHERN MARGIN OF THE ALASHAN BLOCK

作　　者：左玉琦 杨海波[1] 杨晓平[1] 詹艳[1] 李安[1] 孙翔宇[1] 胡宗凯 ZUO Yu-qi;YANG Hai-bo;YANG Xiao-ping;ZHAN Yan;LI An;SUN Xiang-yu;HU Zong-kai(State Key Laboratory of Earthquake Dynamic,Institute of Geology,China Earthquake Administration,Beijing 100029,China)

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029

出　　处：《地震地质》2023年第2期355-376,共22页Seismology and Geology

基　　金：地震动力学国家重点实验室自主研究课题(LED2021A01);国家自然科学基金(42102257,42072249)共同资助。

摘　　要：阿拉善地块南缘地处青藏高原东北缘地壳扩展前锋带的北侧,对该地区活动断裂晚第四纪的运动性质、滑动速率等开展研究,有助于理解阿拉善地块的晚第四纪构造变形特征及其对青藏高原向N扩展的响应。文中结合遥感影像解译与野外地质地貌考察,对阿拉善地块南缘的北大山断裂进行了分段和活动性研究。结果表明,北大山断裂左旋走滑断错晚第四纪洪积扇和阶地等地貌,形成显著的位错阶地坎、冲沟以及断层陡坎。通过对断错地貌线等标志的测量、复原、统计分析等,发现断裂的地貌位移值分布于3~20m,发育新鲜断层自由面的断层陡坎和左旋错动的纹沟指示了断层的最新一次活动。基于同期洪积扇年龄估算得到北大山断裂晚更新世以来的左旋滑动速率为0.3~0.6mm/a。北大山断裂的运动学特征与区域NE向应力场一致,可能受到了青藏高原NE向扩展的影响。The southern Alashan block is located at the crustal front of the northern Tibetan plateau.It was initially considered as a relatively stable area with weak tectonic activity.In recent years,an increasing number of studies have shown that the Alashan block has undergone significant tectonic deformation since the Cenozoic.Multiple active faults with a horse-tail distribution are developed in the southern margin of the Alashan block.However,there is still controversy over the tectonic deformation patterns of these active faults.One view is that the fault system in the southern margin of Alashan is the result of the eastward extension of the Altyn Tagh Fault and belongs to the tail structure of the strike-slip fault.Another view is that the fault system in the southern Alashan block is the result of the revival of the pre-existing fault caused by the northward compression and thrust of the Tibetan plateau.Therefore,deciphering fault’s kinematics and slip rates since the late Quaternary in the southern Alashan block is crucial to understand the tectonic deformation pattern of the block and its response to Tibet’s northward growth.In this paper,combined with interpretations of remote sensing images and field investigations,we documented the Quaternary activity of the Beida Shan Fault,one of the major faults in the southern Alashan block,along the segment developed in Quaternary alluvium.The Beida Shan Fault is a sinistral strike-slip fault with paralleled north and south branches that displaced the late Quaternary alluvial fans and terraces,forming offset gullies and fault scarps.According to the geometric distribution characteristics,activity and the landforms along the fault,we divided the fault into three segments:the Langwa Shan segment,the northern branch of the Jiapiquan Shan segment,and the southern branch of the Jiapiquan Shan segment.The fault is east-west trending,and the offset geomorphic features along the fault reveal that there are differences in the activity of different segments.The Langwa Shan seg

关 键 词：高原扩展 左旋走滑 晚第四纪活动 阿拉善南缘 北大山断裂 

分 类 号：P315.2[天文地球—地震学]