川西杂谷脑“冰碛物”中软沉积物变形构造的成因  

ORIGIN OF DEFORMATIONAL STRUCTURES OF SOFT SEDIMENTS IN MORAINES OF THE ZAGUNAO AREA,WESTERN SICHUAN

作　　者：王萍[1] 邱维理[2] 张斌[1,3] 

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 [2]北京师范大学地理学与遥感科学学院,北京100875 [3]中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《第四纪研究》2009年第3期484-493,共10页Quaternary Sciences

基　　金：中国地震局地震动力学国家重点实验室自主课题(批准号:LED2008A02);国家自然科学基金项目(批准号:40472090)资助

摘　　要：对四川理县杂谷脑"冰碛物"的地层结构进行了观察,对河湖相地层中的软沉积物变形构造进行了分析。综合研究表明,所谓杂谷脑晚更新世"冰碛物"是由泥石流、崩滑塌堆积物、堰塞湖沉积和河流相砂砾石层构成的多成因"混杂"堆积,湖相地层中发育的强烈褶皱和断裂是河岸陡壁岩石崩塌滑落导致古堰塞湖沉积物发生软沉积变形的结果。软沉积变形构造包括卷曲构造、液化泥块、阶梯状微断裂、球枕构造、火焰构造、落石沉陷构造、环状构造、同生断层和大型褶曲等。一次崩滑塌事件的典型沉积层序由崩塌体、不规则接触面和下伏的河湖相变形地层所组成。沿杂谷脑河上游发现的一系列大型崩塌褶曲构造以及伴生的多种典型的液化变形构造,指示可能是地震活动触发了群发性的崩塌、滑坡灾害事件。The existence of Pleistocene glaciers at altitudes lower than 3000m in the East Tibetan Plateau is still a matter of debate and requires further studies based on sedimentary features. In the Zagunao area,unconsolidated sediments mainly composed of boulder clay and laminated layers were firstly reported in 1964 as moraines of the last glaciations, and intense folds and faults in the sediments were believed to be deformation caused by glacial processes. However, the same sediments were also recognized as a mixture of debris flows, glacial varved clay, fluvial deposits,and colluviums. The Zagunao River,the largest tributary in the upper reaches of the Min River,is originated from the east lope of the Qionglai Mountains and runs into the main stream at Wenehuan,the center of the Ms8.0 earthquake occurred on May 12, 2008. This area belongs to the Western Sichuan and is located at the east edge of the Tibetan Plateau in an active earthquake region, known as the Longmenshan Fracture Zone. The representative section of the sediments is located at about 1 km upstream from the Lixian County, the Zagunao Town with an elevation of 1909m at the highest point. Based on careful observation of the sedimentary textures and structures of the so-called moraines, the components of the section are identified as a complex assemblage of different facies including debris flows, colluvial deposits, fine grained lacustrine sediments of dammed paleolakes and fluvial sand and gravel layers. The deformational structures of different scales are discovered mainly in the lacustrine layers and can be sorted as hydroplastic deformation, liquefied mud, fault grading, ball-and-pillow structure, flame structures, dropstone structure, loop beddings, synsedimentary faults and folds, etc., which are typical deformational structures in seismites. The lacustrine layers in the Zagunao section are overlaid by massive colluviums which were formed by large landslips or collapses from the bank cliff. Adjoining the uneven contact beneath the colluviums are big

关 键 词：堰塞湖 软沉积物变形 崩塌体 震积岩 杂谷脑河 

分 类 号：P931[天文地球—自然地理学] P315.2