低温热年代学方法及其在矿床学研究中的应用

Low-temperature Thermochronology and its Applications for Studying Ore Deposits

低温热年代学方法主要包括裂变径迹法和(U-Th)/He法,二者分别利用矿物中238U裂变产生径迹的积累和矿物中U、Th衰变产生4He的积累对矿物进行定年。由于低温热年代学方法的封闭温度低且对温度变化敏感,可用于定量确定地壳浅部所经历热事件和侵蚀事件的时间、幅度、速率及空间分布特征。目前低温热年代学方法在矿床学研究中的应用主要包括:间接或直接测定矿床的形成时代、恢复岩浆-热液成矿体系的热演化历史、约束成矿热液活动的持续时间、计算矿床的剥露速率和剥露量、估算矿床的形成深度、评价矿床的保存潜力、定量研究成矿后断层的位移、寻找古地热异常来指导找矿等。本文重点介绍这些应用的原理、方法和实例,并对部分应用的前提条件和注意事项作了说明。此外还指出低温热年代学方法还存在分析误差较大和成本较高等问题,分析技术的革新将进一步促进其在矿床学及其它领域中的应用。

Low-temperature thermochronology mainly includes the fission track and(U-Th)/He dating methods which are based on relationship between the time and accumulated tracks produced by 238U fission and the time and accumulated 4He contents produced by the U and Th decay in some minerals,respectively.Because the low-temperature thermochronology methods are characterized with low closure temperature and are sensitive to the temperature change,they can be used to quantitatively determine the time,amplitude,rate and spatial distribution of thermal events and erosion events occurred in the shallow level of crust.Currently,applications of low-temperature thermochronology in researches of ore deposits include to indirectly or directly determine mineralization age,to reconstruct the thermal evolution history of magmatic-hydrothermal metallogenic system,to constrain the duration of the metallogenic fluid activity,to calculate the exhumation rate and amount of orebodies in the ore deposit,to estimate the formation depth of orebodies in the ore deposit,to evaluate the preservation potential of ore deposit,to quantitatively determine the displacement distance of fault after the mineralization,and to identify paleogeothermal anomalies for guiding the ore prospecting.In this paper,the principles,methods,and examples of these applications have been mainly introduced,the preconditions and precautions for some of these applications have been especially instructed.At present,relatively large errors of analytical data and high analytical costs are still existed problems of the low-temperature thermochronology.The innovation of analytical technology will further promote the application of low-temperature thermochronology in researches of ore deposits and other fields.