基于U-Th年代学的三峡库区黄土坡滑坡期次及其对古气候变化的响应

Landslide has become one of the highest frequency and largest loss of various types of geological disasters. The formation of the giant landslides and their developments are closely related to the stages of tectonic movements and paleoclimate changes．The relationships between giant landslides and paleoclimate changes have attracted scientists all around the world and become one of the hottest issues in the research on landslide disasters. Dating their ages and reproducing their sequences in quaternary period are foundation of confirming the history and relationships and forecasting the development trend in the future. The Three-Gorge reservoir area is the urgent and ideal place for developing research about relationships of giant landslides and paleoclimate changes. However, the fit chronology methods are the bottleneck of further knowing the relationships. This project plans to select Huangtupo paeleolandslide in the Three-Gorge reservoir area with high frequency of landslides and sensitive and complex climate as example. Based on comprehensive data collections and detailed systemic field investigations and sample collections, we will date on calcite crystal from the Huangtupo paeleolandslide zone and calcrete nodules from the "Wushan loess" section by U-Th methods, analyze the time and periods of landslides movements, reconstruct the sequences of paleoclimate evolutions, and grope for the responses process and mechanism of landslides to paleoclimate evolution in Three-Gorges reservoir area. The results of this project can improve the theory background of forecast of landslides and provide the important insight into the fundamental issues concerning landslide disasters prevention in Three-Gorges reservoir area.

大型滑坡灾害已成为各类地质灾害中频度最高、危害最大的灾害类型，滑坡灾害的成因、预测、预警受到高度重视。构造和气候是滑坡的两大主控因子，随着全球变暖话题的热议，滑坡对气候变化的响应成了地质灾害学研究的热点。开展地质事件年代学研究，重建事件发生的时间序列，是认识当今重大地质事件过程、现状及预测其发展趋势的基础。黄土坡滑坡是三峡库区最危险的滑坡，是结构组成复杂的大型复合古滑坡体，其成因机制、演化规律和稳定现状还尚不明晰。本项目拟对黄土坡滑坡滑带方解石、“巫山黄土”古气候剖面进行系统采样，运用U-Th不平衡测量法对滑坡滑带方解石晶体、“巫山黄土”钙结核定年，探讨黄土坡滑坡的年代及期次，选取微生物类脂分子GDGTs重建古气候变化序列；选用典型相关分析法和投影追踪主成分法，探索黄土坡滑坡年代期次对气候变化的响应。研究成果可提高滑坡预测理论，为黄土坡滑坡及区域滑坡灾害预防提供年代学与气候学方面的依据。

大型滑坡灾害已成为各类地质灾害中频度最高、危害最大的灾害类型，滑坡灾害的成因、预测、预警受到高度重视。构造和气候是滑坡的两大主控因子，随着全球变暖话题的热议，滑坡对气候变化的响应成了地质灾害学研究的热点。开展地质事件年代学研究，重建事件发生的时间序列，是认识当今重大地质事件过程、现状及预测其发展趋势的基础。黄土坡滑坡是三峡库区最危险的滑坡，是结构组成复杂的大型复合古滑坡体，其成因机制、演化规律和稳定现状还尚不明晰。开展地质历史时期滑坡的年代学研究，是正确认识重大滑坡灾害历史发育过程、现状、与未来发展趋势的重要基础之一。项目以三峡库区巴东县黄土坡滑坡为研究对象，在资料收集和野外调查基础上，在黄土坡1号临江滑坡体3号支洞滑坡带上采集4个方解石晶体样品，并开展了MC-lCPMS 230Th年代学分析。4个样品碎屑Th校正230Th年龄分别为155.2±18.6、134.6±5.6、70.9±8.5和103.3±18.2ka B.P.。年代结果表明，三峡黄土坡1号临江滑坡体的滑动时代在70.9-155.2Ka之间。这些年龄虽然具有较大的误差，但存在明显差异，可能反映了不同滑坡期次，印证了黄土坡滑坡滑坡体的多期次性，是一个发生频率高、多个崩滑堆积体和滑坡组成的特大型复合滑坡。最后，将黄土坡滑坡年代期次与长江三峡及邻区新构造动动、地貌过程、气候变化和其它滑坡活动期进行对比分析，发现三峡库区黄土坡滑坡在新构造快速抬升时期广泛发育，并与暖湿多雨期相对应，表明黄土坡滑坡的发育演化受到新构造运动和气候变化耦合作用的控制。