西藏东南部嘉黎断裂新知

QUATERNARY FAULTING OF JIALI FAULT, SOUTHEAST TIBETAN PLATEAU

野外调查表明 ,西藏东南部的嘉黎断裂带从那曲到嘉黎由三段呈雁行排列 ,大致沿N60°W方向延伸 ,其东南段在波密附近向南转折 ,沿贡日嘎布曲向南南东过上察隅和下察隅后转为近南北向延入缅甸境内与什阶断裂相连。嘉黎断层全新世以来活动性不强 ,其第四纪以来的平均滑动速率约为 4mm/a。一个有趣的现象是 ,虽然总体上嘉黎断裂的新活动不强 ,但在局部与张性盆地相邻的地段表现出较强的活动性 ,在这些段上沿断裂发育晚第四纪地表破裂 ,横跨断层的冲沟和河流被错断 ,其晚第四纪以来的平均滑动速率达到 15mm/a。但是这种现象的存在只局限在盆地中 ,盆地以外则截然终止 ,不复存在。从上述事实看 ,嘉黎断裂的走滑活动似乎是伴随张性活动而产生的 ,在断层几何和活动特征上类似于横切大洋中脊的转换断层。

The Jiali fault is one of the major faults in the southeastern Tibetan Plateau. A field investigation of this fault has been made recently. From Naqu to Jiali the fault extends roughly in N60°W direction and consists of three segments arranged in an en echelon way. From Luoermano to Esukongma (about 40km) where the fault is the northern boundary of the Sangdi basin that extends north south, late Quaternary surface ruptures have been found. Within this segment the creeks and gullies that cross the fault were offset and the displacements range from several meters to about 5km. The average slip rate during late Quaternary is about 15mm/a for this segment. An interesting phenomenon is that the large displacement can only be found at those places where the fault is related to the basins that extend north south. Outside the basins, no convincing evidence has been found for late Quaternary surface ruptures and the average slip rate for the whole fault is only about 4mm/a during Quaternary. It seems that these strike slip faults behave like a transform fault and the strike slip motion along them are a consequence of east west extension that creates the north south graben systems rather than the vice versa.