利用低温热年代学数据计算剥露速率的基本方法

Basic Methods to Inverse Exhumation Rates Using Low-Temperature Thermochronological Data

利用低温热年代学数据定量反演岩体的剥露速率及其演化历史已经在地质学相关领域内得到了广泛应用。本文系统介绍了低温热年代学技术记录岩石冷却年龄和反演热史的原理方法,概述了区域地温场函数及其在热年龄解释和剥露速率反演过程中的重要作用,阐述了多种常用的剥露速率计算方法,包括:①利用矿物的冷却年龄和其所对应封闭温度关系的年龄-封闭温度法;②基于径迹退火或元素热扩散机制的热史模拟方法;③使用多种不同封闭温度的测年体系分析同一样品的矿物对法;④应用在近垂直采样剖面获得的样品年龄值和高程关系计算剥露速率的年龄-高程法。在阐述以上基本方法的原理和应用的基础上,提出了应用低温热年学技术反演岩体剥露作用的主要挑战和发展方向。

Low-temperature thermochronology not only is a geochronological tool to date a rock but also can provide valuable information about its thermal evolution. Accordingly, this technique has been widely used to solve the geological problems including surface processes, rock exhumation, or faulting in shallow crust, topographic relief evolution etc. This paper first briefly reviews the principles of low- temperature thermochronometries such as （U-Th）/He and fission track analysis, focusing on its geological interpretations on tectono-thermal history. Then the physical conditions of regional geothermal field and its influences on the interpretation of low-temperature thermocbmnometers are discussed. The main part of this paper discusses the basic methods to constrain the exhumation rate based on low- temperature thermochronological data, including （1） the age-closure temperature method using the relationship between the cooling age and the closure temperature; （2） the thermal history modeling method based on the annealing or diffusion models; （3） the mineral-pair method dating a same sample by multiple thermochronometers with different closure temperatures; and （4） the age-elevation relationship method extracting exhumation rate by the linear relationship of the ages and elevation data of a series of samples collected from a near-vertical profile. Although the above methods prove to be powerful in estimating the rock exhumation rate, there are some uncertainties in age measurements, modeling and geothermal field, which pose challenges for a more accurate quantification of exhumation rate.