滇西怒江流域地质体剥露历史的低温热年代学研究

Thermochronology is a significant research tool to measure the timing and rates at which rocks approach the surface and cool as a result of exhumation. Scattered thermochronologic data within or surrounding Nujiang indicates its two features, the mismatch of value of ages and altitudes, the other is the difference in the evolution of thermal history of various sections. The reason and mechanism is unknown. Furthermore, the temporal and spatial patterns of exhumation history had not been systematically studied. This proposal intend to collect river-sand samples within main stem of Nujiang and its tributaries, and bed-rock samples from transects within the tributaries. Dating methods will concentrated in the apatite fission track, with few samples tested by apatite U-Th / He, and biotite 40Ar / 39Ar methods. The mathematical verification between the thermochrologic results will be used to ensure the adequacy of exhumation information derived from them. Ultimately achieve the temporal frame, erosion and amount of exhumation histories, provide crucial information for the uplift and exhumation of southeastern Tibetan Plateau since Cenozoic era and expand the application of thermochronology in exploring exhumation history and patterns of geological bodies.

热年代学方法是揭示地质体剥露历史的重要研究手段，怒江流域区内及周边零星分布的热年代数据显示该区热史年龄大小与海拔高度高低不匹配、不同区段热史演化存在差异，而以上两种特征的形成原因未得到解释，且区内岩体剥露历史的时空样式并没有系统的研究。申请项目拟分别对怒江两侧支流、主干河道进行河砂样品采集，并选择部分支流进行垂向剖面基岩样品的采集。测试手段以磷灰石裂变径迹测试为主，辅以部分河砂样品的磷灰石U-Th/He、黑云母40Ar/39Ar定年。并对热年代学数据结果进行多种方式和模型的数学验证，保证提取的剥露历史信息的准确可靠性，最终厘定滇西怒江流域地质体剥露历史的时间框架、剥露速率及剥露厚度的空间样式，为青藏高原东南缘新生来以来的隆升剥露特征提供重要依据，进一步拓展热年代学在地质体剥露历史研究中的应用。

本项目采集了怒江主干河道东西两侧共计5条支流河道河砂样品，进行磷灰石裂变径迹测试，结合已有的主干河道河砂年代学结果，分析得出13Ma以来怒江不同河段流域的地壳剥露过程存在差异性，贡山以北段以及六库以南段流域的地壳剥露速率要明显小于贡山至六库段流域。另外，项目测试了主干河道至片马镇的垂向剖面共计5个样品，反演模拟路线初步揭示，该地区在13Ma、7-8Ma有两次快速隆升历史，与河砂得出的结果基本一致。怒江南北向的剥露差异很可能是气候因素中的降雨量差异引起，降雨量大的地区使得含有更年轻冷却历史信息的岩体剥露至地表，造成现今的剥露样式，同时如此的空间差异可以很好地解释流域内不同级别变质岩以及不同深度构造层次的出露。