Late Quaternary Movement Characteristics of Lilong Fault at the West Side of Namcha Barwa Syntaxis
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摘要: 本文通过卫星影像解译、地质地貌调查、地质探槽开挖、断错地貌测量和样品年代学测试，对南迦巴瓦构造结西侧的里龙断裂晚第四纪活动特征进行了分析和研究，结果表明：里龙断裂是一条以右旋走滑活动为主、兼有挤压逆冲的北北西向断裂，其最新活动时代为全新世；该断裂晚第四纪以来的平均水平滑动速率为3-4mm/a，平均垂直滑动速率为0.10-0.15mm/a。研究还表明，南迦巴瓦构造结晚第四纪以来的向北俯冲运动已经停止，喜马拉雅东构造结地区的构造变形主要受阿萨姆构造结的俯冲影响。Abstract: Based on the interpretation of satellite images, quantitative geomorphological deformation measurement, trench excavation and dating of young terrace deposits, this paper obtains some new results as follows:Lilong fault, at the west side of Namcha Barwa syntaxis, is a Holocene dextral strike-slip fault with a thrust slip component, its strike is NNW. The terrace T3 of Yarlung Zangbo rive, composed mainly of alluvial deposits formed during 22-32ka BP, was offset by Lilong fault, with right-lateral and vertical displacements of 120m and 3-5m, respectively. The landslide body on the terrace T2 of Yarlung Zangbo rive was dislocated with right-lateral and vertical displacement respectively of about 20m and 1m. The landslide body on the terrace T2 of Yarlung Zangbo rive was dislocated with right-lateral and vertical displacement respectively of about 20m and 1m. The displacement of small ditch at the right bank of Lilong gully was dislocated with a right-lateral displacement of 15m. The strike-slip rate of Lilong fault is 3-4mm/a and the vertical slip rate is 0.10-0.15mm/a since late Quaternary, which is well consistent with GPS measurement. Those indicate that the tectonic deformation around the Eastern Himalaya Syntaxis is mainly affected by the subduction of the Assam Syntaxis.
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图 2 堆米村里龙断裂位错雅鲁藏布江和滑坡体影像（据Google Earth）
Figure 2. Satellite image of dislocation of the Yarlung Zangbo river and landslide at Duimi village (from Google Earth)
图 4 里龙乡探槽和断层露头位置示意图（据Google Earth）
Figure 4. Diagram of trench & fault outcrop at Lilong village(from Google Earth)
图 5 南侧探槽北壁地质剖面
① 浅灰黄色砾石层夹粗砂，粒度1—20cm不等，分选差，磨圆好，没有胶结，采碳样TC-1-Ⅰ；② 灰黑色粉砂层，具层理，胶结硬；③ 褐黄色砾石层与灰黑色砂层互层，分选和磨圆都较好，被多次错断；④ 灰黑色粉砂层；⑤ 灰黄色粗砂与黄色砾石层互层；⑥ 灰黄色粉细砂层，具水平层理，采释光样LLTC-1-1、2；⑦ 砾石层，磨圆好，分选差，粒度1—20cm不等；⑧ 灰黑色粉砂夹砾石层，采释光样LLTC-1-3、4；⑨ 灰黄色风成砂
Figure 5. Geological section on the northern wall of south trench
图 6 北侧探槽北壁地质剖面
① 灰黄色风成砂；② 灰黑色中粗砂夹砾石层，分选、磨圆中等，成分主要为石英、花岗岩等；③ 灰黑色粉砂夹砾石层，磨圆好，砾径5—10cm；④ 灰黑色粗砂夹砾石层，砾径2—3cm，磨圆好，分选差；⑤ 砾石层，分选差，磨圆好；⑥ 灰黑色粉细砂层，采释光样LLTC-3-1、2；⑦ 灰黑色粗砂夹砾石；⑧—⑨ 灰黑色粉砂质粘土与灰黄色细砂互层，采释光样LLTC-3-3、4；⑩—⑮ 黄色砾石层与灰黑粗粒砂砾石互层，局部被错断；⑯ 灰黄色砾石层夹粗砂，粒度为1—20cm不等，分选差，磨圆好，未胶结；⑰ 灰黑色粉砂层，层理发育，胶结硬
Figure 6. Geological section on the northern wall of north trench
图 7 南侧探槽延长段南壁地质剖面
① 灰黄色风成砂与砂砾石，底部有一陶罐，采碳样L02；② 灰色中粗砂夹砾石层；③ 灰黑色砾石层，粒径1—3cm，磨圆好，分选差；④ 灰黑色砾石层，粒径2—5cm，磨圆好，分选差；⑤ 灰色中细砂夹砾石层；⑥ 灰黑色砾石层，粒径2—10cm，磨圆好，分选差；⑦ 灰黑色砾石层，粒径5—50cm，磨圆好，分选差，成分主要为石英、花岗岩等，采碳样L01；⑧ 灰黑色粉砂与灰黄色细砂互层，夹砾石层；⑨ 灰黑色砾石层，粒径1—5cm，磨圆好
Figure 7. Geological section on the southern wall of expanded south trench
图 8 里龙沟探槽北壁地质剖面
① 河湖相粉细砂与粗砂互层，有火焰状沉积构造或者沙土液化，采样LLG-1、2；② 灰色砂砾石层；③ 细粒砂砾石层；④ 粗粒砂砾石层；⑤ 灰黑色砂砾石层，粒度0.1—2cm，磨圆好，成分主要为石英、花岗岩等；⑥ 灰黑色粉砂层，具层理，采样LLG-3、4；⑦ 灰黑色粗砂层；⑧ 灰色砾石层，粒度1—4cm，分选磨圆好；⑨ 粗砂层，粒度在1cm之内；⑩ 浅黄色粉细砂层；⑪ 浅黄色细砂夹大砾石，为砂土液化所致
Figure 8. Geological section on the northern wall of trench in Lilong gully
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