东喜马拉雅构造结墨脱断裂晚第四纪活动地质证据的发现

GEOLOGICAL EVIDENCES OF LATE QUATERNARY ACTIVITY OF MOTUO FAULT IN EASTERN HIMALAYAN SYNTAXIS

墨脱断裂位于东喜马拉雅构造结南迦巴瓦峰的东侧。在遥感信息解译的基础上,结合前人的研究成果,通过详细的野外调查,获得了墨脱断裂在中国境内的空间展布、运动性质和断错晚第四纪以来地层的证据。在雅鲁藏布江大峡谷内的墨脱村和地东村开挖的探槽均揭示出墨脱断裂断错了晚第四纪地层,其中墨脱村探槽地质剖面上显示出断裂最新活动具有逆冲性质,地东村探槽剖面上表现出的最新活动则为正断性质。结合断裂沿线典型的断错地貌分析,认为墨脱断裂晚第四纪以来以左旋走滑运动为主,不同段表现出逆断或正断的倾滑分量。地东村探槽揭示断裂断错的最新地层14C年代约为(2 780±30)aBP,表明墨脱断裂全新世晚期发生过断错地表的事件。墨脱断裂的左旋走滑运动与阿萨姆构造结的向N推挤相关。

Motuo Fault locates at the east of Namjagbarwa Peak in eastern Himalayan syntaxis. Based on the remote sensing interpretation,the previous work,and with the field investigation,this paper obtains the spatial distribution and movement characteristics of Motuo Fault in China, and geological evidences of late Quaternary activity. Two trenches in Motuo village and Dongdi village located in Yalung Zangbo Grand Canyon reveal that the Motuo Fault dislocates the late Quternary stratum and behaves as a reverse fault in Motuo village and normal fault in Dongdi village. Motuo Fault is dominated by left- lateral strike-slip associated with the faulted landforms, with different characteristics of the tilting movement in different segments. The trench at Didong village reveals the latest stratum dislocated is ~ 2780± 30aBP according to radiocarbon dating,implying that Motuo Fault has ruptured the ground surface since late Holocene. The movement of left-lateral strike-slip of Motuo Fault is related to the northward movement process of Indian pate.