U-Th-Pb副矿物的原地原位测年微束分析方法比较与微区晶体化学研究

Site-Directed and In-situ Dating Microbeam Techniques and Crystal Chemistry Microanalysis for U-Th-Pb Bearing Accesory Minerals

系统地对比分析了各种微束分析技术在原地原位测年中的优势和局限性,并对近年发展的微区原位化学测年技术(EPMA)和质子激发X射线微探针分析技术(μ-PIXE)进行了探讨。阐明了矿物微区晶体化学研究的各种方法及其对实现精确原地原位测年的重要性。介绍了北大别黄土岭麻粒岩锆石测定点的晶体化学特征,应用激光剥蚀微探针—感应耦合等离子体质谱(LAM-ICPMS)技术对其进行了锆石的U-Pb表面年龄的测定,结果表明该岩石的麻粒岩相变质发生在2.050Ga前,锆石来源为多源区。

The techniques of site-directed and in-situ dating should meet two requirements.It must accurately give age value and endow with definite geological meaning. The first one can be resolved by development of modern apparatus and testing methods.While the second drives people to attach importance to the study of crystal chemistry of minerals. This paper suggests the developing possibility of chemical dating technique of EPMA and/or μ-PIXE with high spatial resolution and the non-destructive character by comparison with all other microprobe techniques, and elucidates the methods of crystal chemical study of minerals and their important function for site-directed and in-situ dating on a micrometer-scale. Then it presents an example of implication for microbeam analytical results of apparent ages and crystal chemical features of zircon from Huangtuling granulite in North Dabie Mountains.It shows that zircon is of polygenetic due to complex geological events, and the granulite-facies metamorphism was reliably confirmed at 2.050 Ga.