长江三峡坝区断层泥的裂变径迹法年龄

FISSION TRACK AGE OF FAULT GOUGE IN THE YANGTZE THREE-GORGE DAM SITE

仙女山断裂带和九湾溪断裂带是位距三峡工程坝址最近的两条主断裂。本文对断裂带中断层泥、断裂壁岩和断裂带围岩内选出的磷灰石进行了裂变径迹断代学的研究 ,并对径迹长度的频率分布进行统计测量。研究证实 ,仙女山断裂带与九湾溪断裂带发生的时期分别为 0 .60± 0 .0 5Ma B.P.和 0 .2 9± 0 .0 4 Ma B.P.,与它周边的围岩经受的主要构造 -热事件年龄 (2 2 .30± 1 .8Ma)截然不同。与其它方法年龄测定结果对比分析 ,均未见到全新世以来有明显的活动迹象 ,以此确认三斗坪坝址属稳定地壳区。

The Xiannufeng and Jiuwanxi fault zones are tow major fault zones which are most adjacent to the Yangtze Three Gorge Dam Site. To assess the danger of reservoir engineering project induced strong earthquake and the stability of the regional crust, a fission track geochronological study of apatite separated from fault gouge and cliff rock and country rock in the fault zones was conducted in this paper . In addition, statistical measurement of the fission track length frequency distribution was also made. The study indicated that the Xiannufeng and Jiuwanxi fault zones were formed at 0.60±0.05 Ma B.P. and 0.29±0.04 Ma B.P. respectively, in sharp contrast with the main tectono thermal age (22.30±1.8 Ma B.P. ) in their peripheral country rocks . By comparing the result with other age data obtained by other dating methods, it is evidenced that there has been no sign of fault activity since the Holocene. Therefore, it is concluded that the Sandouping Dam Site is located in a regionally stable crust.