Geological Structure Characteristics and Genetic Mechanism of Baige Landslide Slope in Changdu, Tibet
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摘要: 在西藏昌都市江达县波罗乡发生的两次高位大型滑坡，形成堰塞体阻断金沙江，其溃决洪水对下游造成了巨大损失.本文基于野外地质调查与工程验证、遥感影像、倾斜摄影测量、岩体微观特征，结合区域地质资料进行分析研究.结果表明：(1)白格滑坡发育于金沙江构造混杂岩带，坡体属于河谷型构造破碎松散体；(2)坡体物质主要由弱变形构造透镜体岩块和强变形错动带(糜棱岩带、碎裂岩带、断层泥)组成，镜下岩石结构破坏严重，岩石强度显著降低；(3)断层破碎带控制滑坡体两侧及后缘边界，为滑坡提供了侧向及后缘的切割面；(4)不连续错动带为白格滑坡的滑动层，在重力卸荷作用下发生贯通，导致坡体发生多期次崩滑；(5)综合坡体失稳启动分析，白格滑坡为"推移式+牵引式"混合型滑坡；(6)白格滑坡是在内动力和外动力耦合作用相互交替下促进形成，加之金沙江对坡脚掏蚀，松散体在重力卸荷作用下剪切破坏致使滑坡发生.白格滑坡事件可为研究金沙江构造混杂岩带中大型滑坡形成机制提供依据，同时也为该区域防灾减灾研究提供理论指导.Abstract: The Baige landslide, which involved two large-scale high-elevation landslides, occurred in Boluo Township, Jiangda County, Changdu, Tibet. This catastrophic landslide blocked Jinsha River and formed a landslide-dammed lake. The consequent outburst flood caused downstream damage. The geomorphological and geological characteristics of the Baige landslide, which were defined by field surveys, engineering verification, remote sensing images, oblique photogrammetry and microscopic analysis of rocks, were investigated in combination with previous geological information. The results suggest that: (1) The Baige landslide was located on a valley-type structurally broken and loosened rock, which was developed along the Jinsha River tectonic mélange belt; (2) the slope is mainly composed of rock blocks with slightly deformed tectonic lens and intensely deformed dislocation zones (mylonite, cataclasite, and fault gouge), and it has been observed under microscope that rock structures have been greatly damaged, which reduced the rock strength; (3) both sides and the main scarp of the landslide were controlled by the fault fracture zone, which acted as the lateral and trailing cutting planes for the landslide; (4) the sliding layer of the Baige landslide was composed of the discontinuous dislocation zones, which were connected under the gravity unloading, and resulted in a multiple landslides of the slope in stages; (5) comprehensive start-up analysis of slope instability suggests the Baige landslide was a complex landslide with modes of moving and traction; (6) the Baige landslide occurred as a consequence of coupling of internal and external dynamics. In addition, the continuous eroding on slope toe by the Jinsha River, and the loose rock mass damaged under the gravity unloading also contributed to the Baige landslide. The Baige landslide event can not only provide information for studying the formation mechanism of large-scale landslides in the Jinsha River tectonic mélange belt, but also provide theoretical guidance for hazard prevention and mitigation in the region.
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图 1 滑坡区域地质构造图
1. 三叠系上统阿堵拉组；2. 三叠系上统波里拉组；3. 三叠系上统甲丕拉组；4. 三叠系上统洞卡组；5. 三叠系中统瓦拉寺组；6. 三叠系下统色容寺组；7. 三叠系下统普水桥组；8. 二叠系‒三叠系岗托岩组；9. 三叠系上统图姆沟组；10. 辉绿岩脉；11. 花岗闪长岩脉；12. 花岗闪长岩；13. 二长花岗岩；14. 志留纪碳酸盐岩块；15. 断层；16. 金沙江；17. 滑体边界及滑动方向；18. 金沙江构造混杂岩带
Fig. 1. Regional geological structure of landslide area
图 3 白格斜坡地质结构
1.片岩岩块；2. 钠长透闪岩岩块；3. 蛇纹岩岩块；4. 千枚岩岩块；5. 大理岩岩块；6. 千枚状板岩岩块；7. 花岗闪长斑岩岩脉；8. 糜棱岩；9. 第四纪；10. 构造角砾岩带；11. 大理岩；12. 断层；13. 金沙江；14. 滑体边界及滑动方向；15. 高程；16. 剖面线
Fig. 3. Geologic structure of the Baige slope
图 5 白格斜坡破碎岩体结构特征
Fig. 5. Structural characteristics of fractured rock mass in the Baige slope
图 6 错动带岩体宏观与微观特征
Fig. 6. Macroscopic and microscopic characteristics of rock mass in dislocation zone
图 7 白格斜坡不同岩石类型破碎微观结构
Fig. 7. Microstructure of different fractured rock types in Baige slope
图 10 白格滑坡前Google Earth影像(a)；滑坡后缘及中部正射影像(b)；滑坡后缘音频大地电磁测深图(c)
Fig. 10. Pre-sliding Google Earth image of the Baige landslide (a); orthograph image of main scarp and middle of landslide (b); audio-frequency magnetotelluric sounding of main scarp of landslide (c)
图 12 监测孔滑动层破碎岩体特征(a)及深部位移曲线图(b)
Fig. 12. Characteristics of fractured rock mass in sliding layer of monitoring hole (a) and deep displacement curve (b)
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