Luding Section of Luding Ductile Shear Zone and Its Engineering Effects
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摘要:
泸定韧性剪切带为南北向大渡河断裂中段，为川滇“Y”字构造重要组成部分.川藏铁路泸定特大桥在泸定县白日坝附近横跨泸定韧性剪切带，且左岸隧洞穿越⑤号糜棱岩带，该韧性剪切带组成及活动性直接影响重大基础工程建设.基于平硐、公路开挖剖面精细编录，配合薄片鉴定，对泸定韧性剪切带展布特征、组成特征及断裂活动性进行了研究，主要结论如下：（1）泸定韧性剪切带从西向东可区分为5个带，其中①、③、⑤为长英质糜棱岩带，②、④为糜棱岩化斜长角闪岩带，泸定韧性剪切带泸定段展布于桥位区河谷底部及左岸，总宽约1 000 m.①、③带由南向北横穿桥位区，产状N15°~20°E/NW∠55°~65°，带宽500 m，以灰色长英质糜棱岩、千糜棱岩为主，⑤带沿太阳沟-五里沟向东延伸，横穿左岸隧道，产状N43°E/NW∠54°，带宽500 m，糜棱岩为长英质糜棱岩、带状-小眼球状糜棱岩；（2）受断层带切割影响，河段构造节理密度大、组数多、期次多，岩体破碎、完整性较差；（3）泸定韧性剪切带晋宁期受韧性剪切变形影响，中生代以来受脆性破裂改造，但未形成大规模脆性破裂带，对泸定特大桥影响总体较小，工程效应主要表现为大渡河两岸隧洞进出口边坡稳定性较差及左岸洞内围岩完整性差.
Abstract:The Luding ductile shear zone is the middle section of the north-south Daduhe fault and is an important part of the "Y" structure in Sichuan and Yunnan. The Sichuan-Tibet Railway Luding bridge spans the Luding ductile shear zone near Bairiba, Luding County, and the tunnel on the left bank crosses the No.5 mylonite belt. The composition and activity of the ductile shear zone directly affect major foundation projects. Based on the fine cataloguing of excavation profiles of flat tunnels and highways, and the identification of thin sections, the distribution characteristics, composition characteristics and fault activity of the Luding ductile shear zone were studied. The main conclusions are as follows: (1) The Luding ductile shear zone can be divided into five zones from west to east, among which ①, ③ and ⑤ are felsic mylonite belts, and ② and ④ are mylonitized amphibolites. The Luding segment of the Luding ductile shear zone is distributed at the bottom of the valley and the left bank of the bridge area, with a total width of about 1 000 m. The belts ① and ③ traverse the bridge site from north to south, the fault occurrence is N15°-20°E/NW∠55°-65°, the fault width is 500 m, mainly gray felsic mylonite and thousand mylonite. The belt ⑤ extends along the Taiyanggou-Wuligou and crosses the tunnel on the left bank. The occurrence is N43°E/NW∠54°, and the fault width is 500 m. Mylonite is felsic mylonite, zonal-small eyeball mylonite. (2) Cut by the fault zone, the structural joint density of the river reach is high, the number of groups and stages are many, the rock mass is broken, and the integrity of the rock mass is poor. (3) The Luding ductile shear zone was deformed by ductile shear in Jinning Period, and was transformed by brittle fractures since the Mesozoic, but no large-scale brittle fracture zone was formed. The overall impact on the Luding bridge was small, and the engineering effect was mainly manifested in the tunnels on both sides of the Dadu river. The stability of the inlet and outlet slopes is poor and the integrity of the surrounding rock in the left bank cave is poor.
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图 2 ① 糜棱岩带实测剖面（沿公路实测）
1.动力变质千枚岩化斜长角闪岩；2.二长花岗岩脉；3.第四纪堆积体；4.第四纪；5. SCⅡ、SCⅢ、SCⅣ：分别为第二世代、第三世代、第四世代糜棱岩片理的代号；6.节理型脆性小断层及编号；7.长英质；8. a线理；9.节理密集带；10.千糜棱岩片理；11.第二世代糜棱岩片理；12.第三世代糜棱岩片理；13.早期轴面劈理；14.构造变形分带（由强到弱）：③条纹状长英质糜棱岩带，②眼球状长英质糜棱岩‒千糜棱岩带，①绿帘石化斜长角闪岩质千糜棱岩带；15.观察点号；16.平硐号
Fig. 2. ①Measured section of ductile shear zone (measured along the highway)
图 3 ⑤ 糜棱岩带实测剖面
1.斜长角闪质千糜棱岩；2.片麻状二长花岗岩；3.崩坡积物；4.长英质集合体或“σ”旋转斑；5. a线理；6.SCⅠ、SCⅣ：分别为第一世代、第四世代糜棱岩片理的代号；7.第一世代片麻理千糜棱岩片理（SCⅠ）；8.第二世代糜棱岩片理（SCⅡ）；9.第三世代糜棱岩片理（SCⅢ）；10.晚期脆性剪切面理或挤压带；11.变形强度分带：（1）眼球状千糜棱岩‒无根褶皱，长大拉伸线理；（2）小眼球‒条带状糜棱岩无根褶皱带；（3）强片理化‒条纹状长英质糜棱岩‒生长线理化带；12..断层及分支断层：⑤糜棱岩带，③糜棱岩带，①糜棱岩带；13.观察点号
Fig. 3. ⑤Measured section of ductile shear zone
图 4 泸定韧性剪切带典型照片
a.①糜棱岩带；b.③糜棱岩带；c.⑤糜棱岩带；d.④糜棱岩化斜长角闪岩
Fig. 4. Typical photos of the Luding ductile shear zone
图 5 糜棱岩显微特征
a.斜长石碎斑书斜构造；b.斜长石碎斑及相对位移的叶理
Fig. 5. Microscopical character of the mylonite
图 8 泸定河段长大结构面走向玫瑰花图
Fig. 8. The rose diagram of the long and large structural surface in the Luding river section
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