热年代学基本原理、重要概念及地质应用  

The basics, essential concepts and geological applications of thermochronology

作　　者：田朋飞[1] 袁万明[1] 杨晓勇[2] TIAN Pengfei;YUAN Wanming;YANG Xiaoyong(Institute of Earth Sciences,China University of Geosciences,Beijing,100083;School of Earth and Space Sciences,University of Science and Technology of China,Hefei,230026)

机构地区：[1]中国地质大学科学研究院,北京100083 [2]中国科学技术大学地球和空间科学学院,合肥230026

出　　处：《地质论评》2020年第4期975-1004,共30页Geological Review

基　　金：国家重点基础研究发展规划项目(编号:2015CB452606);国家自然科学基金资助项目(编号:41730427)的成果。

摘　　要：岩石和矿物的同位素年龄从根本上取决于它们的综合热历史,而热年代学是一种能够分析其热历史的技术。岩石中一些矿物核衰变会生成子产物(同位素或矿物晶格的结构损伤),而热活化会使这些子产物逸失,热年代学主要分析子产物累积和逸失之间的相互关系。由于温度随地球岩石圈深度增加而升高,因此可以将温度信息转换为热年代学数据;应用热年代学可以分析岩石在给定时间内停留在地表以下的深度,从而获得地表到下地壳的多种地质过程的关键信息,其分析原理在于其同位素封闭系统。同位素系统在高温下均会表现为开放系统,即子产物通过扩散比核衰变逃逸更快;在低温下则表现为封闭系统,即子产物逃逸速率非常慢,以致在百万年为单位的地质时间都可以保留在原岩石和矿物中。从开放系统到封闭系统的切换不是瞬间完成,而是在离散的温度区间内进行的,这个区间称为部分保留区。封闭温度位于这个温度区间内,可以定义为热年代学系统中与其表观年龄相对应的温度。本文介绍了封闭温度≤350~400℃,(40)~Ar-(39)~Ar、裂变径迹和(U—Th)/He的测年原理、发展历史和样品选择;详细分析了封闭温度,部分退火区与部分保留区,裂变径迹年龄类型,滞后时间等重要概念;说明了岩体垂直运动、温度历史和其子产物积累之间所代表的年龄—海拔关系;进一步阐述了抬升、剥露和剥蚀定义,以及是否考虑均衡回弹情况下的关系。热年代学与其它年代学应用案例包括:约束地层和矿产年龄、隆升剥蚀、盆地演化、构造演化、矿床热历史演化与保存变化等方面。地球科学研究不断深化,综合热年代学有助于其更深入研究,可以带来更多丰硕成果。The isotopic ages of rocks and minerals are fundamentally determined by their integrated thermal history, and thermochronology is a technique that permits the extraction of information about the thermal history of rocks. It is based on the interplay between the accumulation of a daughter product produced through a nuclear decay reaction in the rock(whether this daughter product is an isotope or some sort of structural damage to the mineral lattice) and the removal of that daughter product by thermally activated diffusion. Because temperature increases with depth in the Earth ’ s lithosphere, this temperature information can be translated into thermochronological data thus contain a record of the depth below the surface at which rocks resided at a given time, providing key information on the various geological processes of the surface to the lower crust. Every isotopic system will behave as an open system at high temperatures, at which the daughter product is removed by diffusion more rapidly than it is produced by nuclear decay, and as a closed system at low temperatures, at which removal is so slow that all daughter product is retained within the host mineral over geological timescales. The switch from open-to closed-system behavior is not instantaneous, but rather takes place over a discrete temperature interval known as the partial-retention zone. Somewhere within this temperature range lies the closure temperature, formally defined as "temperature of a thermochronological system at the time corresponding to its apparent age". In this paper, we focus on low-to-intermediate-temperature systems, with closure temperatures ≤350 ~ 400 ° C, which including (40)~Ar-(39)~Ar、fission track and(U—Th)/He. We review basics of the three thermochronology and present detail interpretations such as closure temperature, partial annealing zone(PAZ) and partial retention zone(PRZ), fission track ages( mean age, pooled age, central age), and lag time are analyzed in detail. For the age—elevation relationship(AER), we il

关 键 词：中低温热年代学 40AR-39AR 裂变径迹 (U-Th)/He 封闭温度 部分保留区(PRZ) 隆升剥蚀 

分 类 号：P597.3[天文地球—地球化学]