三峡库首区仙女山等断裂活动性同位素测年研究

Isotope age determination study on activity of Xiannushan Fault etc in the Primary Three Gorges Reservoir area

在仙女山、九湾溪两断层形变监测洞室中,通过对断裂带进行地质编录和对构造岩进行微观分析,挑选出断层泥与方解石两类样品进行热释光(TL)测年。同时对洞外披覆跨仙女山断层上的第四纪河流冲积物、断层一侧周坪河谷底上第四纪湖相纹泥夹碳化木及披覆跨九湾溪断层上的第四纪崩滑堆积体中滑带土进行测年。综合分析表明,仙女山断层与九湾溪断层新活动年龄与三峡地区区域断层基本一致,为距今22～23万年左右。最新活动年龄仙女山断层为16～19万年、九湾溪断层为14万年左右。最新活动年龄的下限值仙女山断层为14～16万年、九湾溪断层为13万年左右。晚更新世以来,两断层均没有活动迹象。九湾溪断层上的滑坡为外动力作用所致,并非该断层活动作用的结果。

Through the geologic drawing of fault zone and microscopic analysis of tectonic rook in the deformation monitoring caves of the Xiannushan fault and the Jiuwanxi fault, the samples of fault mud and calcite were selected and dated age by thermoluminescent (TL). At the same time, the age determination of the Quaternary alluvial deposits on the Xiannushan fault, the Quaternary lake facies sediment lamina and carbonized wood on the bottomland of the Zhouping river on the side of the fault and the clay of landslide zone of the Quaternary as well as the information collection of isotope age date in the past years indicate that the new activity ages of the Xiannushan fault and Jiuwanxi fault accord with the ones of the faults in the Three Gorges Project area, which were about 0.22～0.23Ma as yet. The newest activity age of the Xiannushan fault was about 0.16～0.19 Ma and the Jiuwanxi fault was about 0.14 Ma. The lower limit of the newest activity ages of the Xiannushan fault is 0.14～0.16Ma and the Jiuwanxi fault is 0.13 Ma or so. Since the late Pleistocene, the two faults haven't been active. So the landslide on the Jiuwanxi fault was caused by external force rather than the fault activity.