牙形石(U-Th)/He热定年技术的研究进展  

Research Progress of Conodont(U-Th)/He Thermochronology

作　　者：蔡长娥 陈鸿 尚文亮 倪凤玲 Cai Chang'e;Chen Hong;Shang Wenliang;Ni Fengling(Chongqing Key Labrotary of Complex Oil and Gas Exploration and Development,Chongqing University of Science and Technology,Chongqing 401331,China;School of Petroleum Engineering,Chongqing University of Science and Technology,Chongqing 401331,China)

机构地区：[1]重庆科技学院复杂油气田勘探开发重庆市重点实验室,重庆401331 [2]重庆科技学院石油与天然气工程学院,重庆401331

出　　处：《地球科学进展》2020年第9期924-932,共9页Advances in Earth Science

基　　金：国家自然科学基金项目“自然演化碎屑锆石裂变径迹的初始径迹长度及径迹长度的影响因素探究”(编号:41802154);重庆市自然科学基金面上项目“沉积盆地碎屑锆石裂变径迹退火温度的研究”(编号:cstc2019jcyj-msxmX0764)资助。

摘　　要：海相碳酸盐岩地层缺乏有效的古温标恢复其复杂的热演化历史。研究认为广泛分布于古生界地层中的牙形石适用于碳酸盐岩地层热历史恢复。重点阐述了牙形石(U-Th)/He定年的基本原理、分析测试方法和牙形石He年龄的影响因素。热扩散实验揭示了牙形石He封闭温度为60~70℃。牙形石(U-Th)/He年龄与有效铀浓度呈明显负相关性,认为甲酸溶解过程中发生的母核元素U损失、成岩作用过程中U和Th元素的流动性、初始He过量、母核同位素非均匀分布等因素是导致牙形石(U-Th)/He开放系统行为的主要原因。分析得出牙形石色变指数越高,牙形石变得越脆,母核同位素损失的可能性增加,牙形石He年龄也越古老且分散性较大;牙形石的组织类型也会影响牙形石内部母核同位素分布和元素迁移,其显微结构变化会导致牙形石He年龄的分散。最后探讨了现阶段牙形石(U-Th)/He热定年体系研究中尚存在的问题,就未来研究发展方向做出展望,期望能有效推动牙形石(U-Th)/He热定年技术相关理论和技术的深入发展。Given the lacking of effective geothermometer,it is difficult to reconstruct the complex thermal evolution history of marine carbonate rocks. It is considered that conodonts widely distributed in Paleozoic strata are suitable for the reconstruction of thermal history of carbonate strata. In this study,we mainly discussed the basic principle and experimental test method of conodont(U-Th)/He thermochronology,and the influencing factors of conodont(U-Th)/He ages. The thermal diffusion experiment reveals that the closure temperature of conodont(U-Th)/He is 60°~70°. Conodont samples have strong inverse relationship between effective uranium concentration and(U-Th)/He data. The main reasons for the open-system behavior in conodont(U-Th)/He are possible U loss during dissolution procedure using formic acid,the fluidity of U and Th elements during diagenesis,excessive initial He,and the non-uniform parent isotope distributions,etc. The higher CAI values the conodonts have,the more brittle the conodonts will become;the possibility of parent isotope loss will increase,and consistently they have older(U-Th)/He dates and substantially more scattered individual dates.Conodont tissue type also affects the parent isotope distribution and element migration of conodonts,and the change of its microstructure leads to the dispersion of conodont(U-Th)/He dates. Finally,we explored the existing problems and put forward the future hot research and development direction of conodont(U-Th)/He thermal dating system,so as to promote the deep development of relative theory and technology of conodont(UTh)/He thermochronology.

关 键 词：牙形石 (U-Th)/He 封闭温度 开放系统 碳酸盐岩地层 

分 类 号：P597[天文地球—地球化学]