摘要
直接测定热液矿物的同位素年龄乃是地质学家多年的梦想．矿床研究的关键问题之一就是成矿相对于围岩的时间关系．如果对一个矿床成矿时代的认识发生了改变，则与成矿过程相联系的地质事件和环境条件也就发生了改变，与此相关的成矿规律也会随之改变．本文试图对成矿流体活动的直接精确定年这一领域的研究现状、各种同位素定年方法目前存在的主要问题、以及今后的发展趋势进行综合评述．文章首先集中介绍目前研究程度最高的Ｒｂ－Ｓｒ等时线法，并以此为例讨论流体活动定年中一些带普遍性的问题，包括流体包裹体定年的适用性、实验技术难题、测年元素在热液矿物中的赋存形式等．并结合我们目前的工作提出自己的一些见解．由于原生包裹体之间的Ｒｂ／Ｓｒ比值差别太小，且很难排除次生包裹体的影响，流体包裹体等时线实际上应该摒弃，而代之以共生热液矿物组的等时线．然后对其它直接测定成矿年龄的同位素定年技术，包括Ｓｍ－Ｎｄ、Ｐｂ－Ｐｂ、Ｕ－Ｐｂ、Ｒｅ－Ｏｓ、Ｋ－Ａｒ。
For economic geologists,it′s crucial to know the true age of ore-forming processes,especially the time relation between ore and its host. By dating hydrothermal events precisely,we can get fundmental data to understand mechanisms of ore-forming and rock deformation processes,as well as to understand metallogeny and to help our exploration practice. But direct isotopic dating of hydrothermal ores is extremely difficult,much more difficult than rocks,mainly for the following reasons. (1)Hydrothermal fluids are in unceasing moving and interaction with different host-materials,that may result in isotopic and/or chemical dis-equilibrium of hydrothermal products. (2)The number of hydrothermal minerals with suitable parent/daughter element ratios and suitable concentration of target elements for precise geochronology is small. (3)Thereafter,it requirs technical improvements in blanks and mass spectrometry. (4)The exact host of target elements in hydrothermal minerals is not clear. In the present paper,recent approaches of Rb-Sr,Sm-Nd,Pb-Pb,U-Pb,Re-Os,K-Ar,Ar-Ar dating methods,regarding their appropriateness and possible amplication for dating hydrothermal events are reviewed. Rb-Sr isochron,the most commonly used method at the present time,was discussed in detail as a typical example. Dating fluid inclusions in hydrothermal minerals,a commonly accepted practice in the last decade,was regarded as disapproval,because small difference in Rb/Sr ratio between primary inclusions,and interference of secondary inclusions. It was strongly recommended to study isochron age of syngenetic hydrothermal minerals.
出处
《地球物理学进展》
CSCD
1998年第3期46-55,共10页
Progress in Geophysics
基金
国家攀登预选项目
关键词
热液成矿
同位素定年
共生热液矿物
等时线
Hydrothermal ore-forming
Isotopic dating
Isochron of syngenetic hydrothermal minerals
