激光探针分析在氧同位素地球化学研究中的应用

APPLICATIONS OF LASERPROBE METHOD TO OXYGEN ISOTOPE GEOCHEMISTRY

简要介绍了氧同位素分析的最新方法———激光探针法的主要特点，并详细评述了激光探针分析在氧同位素地球化学研究中的应用。某些矿物内部存在氧同位素组成的变化，构成氧同位素环带。与其他化学成分环带一样，矿物氧同位素环带也可以分为生长环带（包括次生加大的环带）和扩散环带两种。变质岩中石榴石经常保存有明显的生长环带，而矽卡岩中石榴石、变质花岗质岩石中锆石和蚀变花岗岩中石英等矿物均可以记录岩石形成早期的某些氧同位素特征。由于这种差异与岩石的形成环境有关，因此通过对矿物氧同位素组成的微区分析可揭示岩石的某些成因信息。在缓慢冷却的变质岩中，磁铁矿的氧同位素环带常是扩散作用形成的，由此可以确定岩石的冷却速率。通过对脉石英的激光探针分析，可以研究流体的流动机理。变质岩的氧同位素微区分析为ｐＴｔｆ轨迹研究提供了有力的武器，而氧同位素示踪可用来解决流体在变质岩形成过程中的作用问题。

Some main advantages of the laser probe method, a new method of oxygen isotope analysis, have been briefly introduced, and its applications to oxygen isotope geochemistry are reviewed. There are variations in the oxygen isotope compositions of intra minerals, e.g., oxygen isotope zoning which can be classified into two types, i.e., growth zoning and diffusion zoning. Garnets in metamorphic rocks have often preserved the significant growth zone of oxygen isotopes, but garnet in skarn, zircon in meta granitic rock, and quartz in altered granite can record some signatures of oxygen isotope compositions at the time of rock formation. The study of oxygen isotope zoning in magnetite from slowly cooled metamorphic rock will help to determine the cooling rate of the rocks. Analysis of oxygen isotope ratios for vein quartz by laser probe will enable to discover the mechanisms of fluid flow. In addition, oxygen isotope microanalysis provides a powerful tool to investigate the p T t f path of metamorphic rocks, and to effectively study the geochemical role of fluid during metamorphsim.