Prone Sliding Geo-Structure and High-Position Initiating Mechanism of Duolasi Landslide in Nu River Tectonic Mélange Belt
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摘要: 多拉寺滑坡是位于怒江构造混杂岩带的特大型古滑坡，具有典型的地质构造与特殊岩性联合控制的特点.采用现场调查和地球物理勘查、无人机测绘、岩土力学和年代学测试等技术手段，揭示了多拉寺滑坡的易滑地质结构、多期次发育特征及高位启滑机制.结果表明：（1）厚层大理岩与蛇纹岩交互堆叠及黏土化蚀变带是多拉寺滑坡重要的易滑地质结构，蚀变黏土是影响滑坡高速远程运移的重要因素.（2）多拉寺滑坡具有多期活动特征，可划分出主滑体区、次级滑体区和现代崩积区，主滑体的形成时代为距今19.4±2.8 ka，次级滑体为距今4.24±0.35 ka.（3）主滑坡体的高位启滑过程与陡峻的斜坡地貌、岩溶多重渗透结构、蚀变黏土的软弱基座效应、地震动力促发作用等因素密切相关.（4）主滑坡体呈现上部粗大块石与下部细粒物质分层堆积的伪地层模式，说明滑坡整体以剪切运动为主，滑坡上部物质比下部物质运动得更快.上述认识可为青藏高原东缘构造混杂岩带大型滑坡形成机制研究和风险防控提供参考依据.Abstract: The Duolasi landslide is a super-large scale ancient landslide located in the Nu River tectonic mélange belt, which is characterized by the combination control of typical geological structure and special lithology. In this paper, several technical means, such as field investigation, geophysical exploration, unmanned aerial vehicle mapping, geo-mechanics and chronological testing, were applied to reveal the prone sliding geological structure, multi-stage development characteristics and high-position initiating mechanism of the Duolasi landslide. The results show follows: (1) The thick-bedded marble and ophiolite are stacked alternately and the corresponding clay-altered zone is an important prone-sliding geological structure of the Duolasi landslide. The altered clay is an important factor to the high-speed and long run-out of the landslide. (2) The Duolasi landslide has the characteristics of multi-stage activity, and can be divided into the main sliding body area, the secondary sliding body area and the modern colluvial area. The formation age of the main sliding body is 19.4±2.8 ka, and that of the secondary sliding bodies is 4.24±0.35 ka. (3) The high-position initiating process of the main landslide is closely related to factors such as steep slope landform, multi-permeable karst structure, weak base effect of altered clay, and seismic dynamic triggering. (4) The main landslide presents a pseudo-stratigraphic pattern of layered accumulation, i.e., coarse boulders in the upper part and fine-grained materials in the lower part, indicating that the overall landslide is mainly shear motion, and the material in the upper part of the landslide moves faster than the material in the lower part. The above understanding can provide a reference for the formation mechanism research and risk control of large scale landslides in the tectonic mélange belt on the east Tibetan plateau.
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图 1 八宿县大地构造位置及区域地质图
a.青藏高原地貌特征；b.西南三江构造混杂岩带分布图；c.八宿县城一带地质图；1.全新统冲积物；2.古近系宗白群；3.下白垩统多尼组；4.下白垩统朱村组；5.中侏罗统马里组；6.中侏罗统桑卡拉佣组；7.上三叠-下侏罗统瓦达岩组；8.上三叠统目本组；9.上古生界瞎绒曲岩组；10.上古生界怒江岩组；11.蛇纹岩；12.断层；13.大型滑坡
Fig. 1. Geotectonic location and regional geology of Basu county
图 2 多拉寺斜坡地质特征
1.主滑坡边界；2.滑坡后壁；3.次级滑坡边界；4.构造混杂岩带范围；5.断裂；6.工程地质剖面；7.物探剖面；数值单位：m
Fig. 2. Geological characteristics of the Duolasi slope
图 3 多拉寺滑坡平面分区(a)及滑坡湖特征(b)
Ⅰ.主滑体，Ⅱ.次级滑体，Ⅲ.现代崩积区，S01.取样点编号
Fig. 3. Plane zonation of the Duolasi landslide (a) and the view of landslide-lake (b)
图 4 多拉寺滑坡地质剖面图
1.构造混杂岩；2.中侏罗统马里组；3.古近系宗白群；4.大理岩；5.蛇纹岩；6.石灰岩；7.砂岩泥岩互层；8.岩溶管道和洞穴；9.蚀变黏土；10.河流阶地；11.滑坡体；12.断层
Fig. 4. Geological profile of the Duolasi landslide
图 5 多拉寺滑坡高密度电法探测剖面图
Fig. 5. High-density resistivity geophysical profile of the Duolasi landslide
图 6 多拉寺滑坡堆积体特征
a.滑坡体表面巨型大理岩块石（镜向NW）；b.滑坡体内部细粒堆积物（镜向W）；c.滑坡前缘多层交错堆积特征（镜向S）；d.滑坡前缘堆积层序特征.①大理岩块石、碎石；②棕红色砂砾石；③蚀变黏土；④紫红色砂砾；⑤蚀变黏土；⑥砂砾石
Fig. 6. Characteristics of the Duolasi landslide accumulation
图 7 多拉寺滑坡典型易滑地质结构特征
a.岩溶角砾灰岩与蚀变蛇纹岩互层（镜向S）；b.蛇纹岩和大理岩接触关系（镜向SW）；c.蚀变软岩中发育的剪切面（镜向SE）；d.蚀变软岩中发育的剪切带（镜向SE）
Fig. 7. Typical characteristics of the prone sliding geo-structure of the Duolasi landslide
图 8 黏土化蚀变岩<5 μm黏粒XRD定量测试结果
Fig. 8. Oriented X-ray diffractograms of <5 μm clay fraction in clayey altered rocks
图 9 滑体中采集的蚀变黏土样品(a)及浸水崩解现象(b)
Fig. 9. Characteristics of altered clay from the sliding body (a) and its disintegration phenomenon in water (b)
图 11 不同含水率蚀变黏土的抗剪强度包线
Fig. 11. Shear strength curve of altered clay with different water contents
图 12 多拉寺滑坡高位启动-运移-堆积过程示意图
Fig. 12. Schematic diagram of high-position startup, migration and accumulation process of the Duolasi landslide
图 13 伪地层堆积模式图(据Strom, 1994)
Fig. 13. Pseudo-stratified pattern of layered accumulation (after Strom, 1994)
表 1 多拉寺滑坡黏土化蚀变岩的粒度分析结果
Table 1. Grain-size analysis results of clayey altered rock in the Duolasi landslide
样品编号 地点 岩性 颗粒组成(mm•%) > 2.0 0.075~2.0 0.005~0.075 < 0.005 < 0.002 S01-1 滑坡前缘滑带 灰绿色蚀变黏土 4.6 18.9 37.4 28.9 10.2 S02-1 滑坡中前部东侧边缘 黄褐色蚀变黏土 13.5 32.9 32.7 20.9 11.2 S03-3 滑坡中部冲沟东侧 黄褐色蚀变软岩 33.3 27.9 24.9 13.9 7.3 S09-2 滑坡前缘滑带 黄褐色蚀变黏土 0.4 21.0 46.7 31.9 10.4 S09-3 滑坡前缘滑带 黄褐色夹灰绿色蚀变黏土 0.9 26.3 41.4 31.4 23.1 
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表 2 多拉寺滑坡黏土化蚀变岩的黏土矿物定量测试结果
Table 2. Quantitative test results of clay mineral composition of clayey altered rock in the Dolasi landslide
样品编号 黏土矿物成分(%) S I/S I K C I/S混层比(% S) S01-1 100 - - - - - S02-1 100 - - - - - S03-3 100 - - - - - S09-2 40 28 32 - - 65 S09-3 29 30 41 - - 65 注：S.蒙脱石；I/S.伊/蒙混层；I.伊利石；K.高岭石；C.绿泥石.
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