石榴石原位微区氧同位素的准确分析

The rapid advance of Earth Science research over the last decades has been closely related to the development of analytical technology. In situ micro-analysis, first of major elements and then of trace elements and isotopic ratios, has been one of the most productive new technologies. Information on micro-scale elemental and isotopic heterogeneity in rocks is widely used to track their sources, origins and evolution, and to understand how Earth works now and in the past. Garnet is a mineral of complex composition that occurs in both crustal and mantle rocks. Its tight lattice means that elements diffuse slowly in most geological environments; therefore, garnet compositions can record the temperature, pressure and chemical conditions during its growth and secondary modification. The micro-scale variability of the isotopic composition of oxygen in garnets therefore is a useful tracer of fluid processes in the crust and mantle. In this project, we will develop the methods required for high-precision, accurate in situ O-isotope analysis of garnet by SIMS (CAMERA-1280) to support geoscience research. We will collect natural garnet samples covering a wide range of composition, typical of both mantle and crustal rocks, and measure their micro-scale chemical and isotopic heterogeneity. The O-isotope ratios of the most homogeneous garnets will be measured by laser-fluorination methods, to provide standards and allow evaluation of SIMS matrix effects related to garnet composition. The outcomes will be a new methodology with wide applications, and high-profile publications in international journals.

分析技术的进步推动了地球科学的快速发展。天然样品的微观信息，特别是小尺度不均一性，被广泛用来示踪地质体的源区、来源及演化等地球动力学过程，研究地球运作机制。石榴石成分复杂，成因多样，广泛存在于地壳、地幔多种岩石中。由于晶格紧致，元素在石榴石中扩散速率很慢，记录了其生长、演化的温度、压力和化学条件。石榴石微区氧同位素组成更是示踪地壳、地幔流体的成分、源区、演化以及部分地幔物质来源的有效工具。目前国际上已有少数实验室可以利用SIMS对低Cr石榴石进行微区原位氧同位素分析，但国内尚未开展相关工作,阻碍了地质事业的发展。 本项目拟建立精准的高精度石榴石SIMS原位微区氧同位素分析方法，为研究各种地质过程提供技术支撑。我们将收集一系列不同成分天然石榴石样品，检查其微区化学成分及氧同位素的均一性，利用激光氟化法准确分析均一石榴石的氧同位素组成，校正石榴石成分引起的基质效应，从而建立准确的分析方法。

地球科学的发展，离不开分析技术的进步。原位微区分析技术的开展和进步为我们准确地理解地球的形成和演化提供了可能。石榴石，特征造岩矿物之一，广泛存在于地壳、地幔多种岩石中，能有效记录自身生长、演化的条件，从而制约区域地质过程的温度、压力、成分及时间等条件。地球物质的氧同位素组成，独立于时间，依赖于温度，对压力不敏感，能很好地示踪地质过程及物质源区。石榴石原位微区的氧同位素组成信息将是地质研究过程中非常有意义的工具。.该项目收集了不同成分的石榴石，利用SIMS （CAMECA 1280）分析并检验其氧同位素组成的均一性，对比相同样品激光氟化法的氧同位素结果，得出SIMS分析测量值与真实值之间的关系，从而校正石榴石成分引起的基质效应，建立准确的分析及校正方法。中国科学院地质与地球物理说离子探针实验室可以准确分析所有低Cr和部分高Cr石榴石的氧同位素组成。