南迦巴瓦构造结西侧里龙断裂晚第四纪活动特征

Late Quaternary Movement Characteristics of Lilong Fault at the West Side of Namcha Barwa Syntaxis

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。

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 five, composed mainly of alluvial deposits formed during 22--32ka BP, was offset by Lilong fault, with fight-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 lm. The landslide body on the terrace T2 of Yarlung Zangbo rive was dislocated with right-lateral and vertical displacement respectively of about 20m and lm. The displacement of small ditch at the right bank of Lilong gully was dislocated with a fight- 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.