西藏错那—沃卡裂谷带中段邛多江地堑晚新生代正断层作用

LATE CENOZOIC NORMAL FAULTING OF THE QUNGDO' GYANG GRABEN IN THE CENTRAL SEGMENT OF THE CONA-OIGA RIFT,SOUTHEASTERN TIBET

遥感解译和地表调查结果显示，位于西藏曲松县境内的邛多江盆地构成了藏南近南北向裂谷带最东端的错那一沃卡裂谷的中段。它是在该区近东西向逆冲构造带停止活动之后，上地壳沿N108～115°E方向发生引张作用所形成的第四纪半地堑式断陷盆地。控制晚第四纪盆地发育的主边界正断裂带位于盆地西缘，总体呈NNE走向，向东倾，长40km左右。断裂活动位移测量和年代学测试结果表明，该边界正断层带在5Ma左右就已开始活动，总累计垂直位移量至少为2．6～2．8km，最小长期平均垂直活动速率约0．5mm／a。末次冰期盛冰期以来，该断裂平均活动速率的最合理的估计值为1．2±0．6mm／a。

The Qungdo＇gyang graben in Qusum County, Tibet, belongs to the central segment of the NNE-trending Cona-Oiga （or Cona-Sangri） rift zone, which is the only rift located at the easternmost end of the nearly N-S-trending Yadong-Gulu rift zone in southern Tibet. It is a Quaternary semi-graben downfaulted basin formed by extension of the upper crust occurring in the N108-115°E direction after the nearly E-W-trending thrust zone in the study area ceased its activity. The main boundary normal fault controlling the development of the late Quaternary basin is located at the western margin of the basin. It generally strikes NNE and dips E with a length of - 40 km. Displacement measurements and isotopic dating indicate that： this boundary normal fault began activity at - 5 Ma BP; the total cumulative vertical displacement ranged from 2.6 to 2.8 km; and the minimum long-term average throw rate was -0.5 mm/a. The most rational estimate of the average throw rate since the last maximum glaciation （MIS2） of the fault is 1.2 ±0.6 mm/a.