大金刚石(MCDs)是记录古岩石圈地幔演化过程及深部碳循环独特的"探针"。已开展的预研究发现，湖南沅水流域大金刚石不同生长层碳同位素组成及氮含量变化、包裹体矿物组合、矿物组成及化学成分等显示金刚石形成过程中可能有古老地壳物质的参与。本项目拟通过激光定向切片，采用阴极发光、FTIR(Mapping)等方法，结合电子探针，LA-(MC)-ICPMS及SIMS等微区微束分析技术，对沅水流域大金刚石内部不同生长层碳同位素组成，氮和氢杂质元素含量与分布，包裹体矿物组成（特别是E型包裹体）和化学组成，同位素组成等开展原位 (in-situ)分析，进一步示踪沅水流域大金刚石生长过程中地幔深部物质组成特征及演化，限定金刚石生长过程温度、压力和氧逸度等物理化学参数的变化，进而探讨沅水流域金刚石形成与扬子克拉通地幔深部地质过程及壳-幔碳循环事件的内在成因联系，为湖南寻找原生金刚石矿提供科学依据。

Macrocrystalline diamonds (MCDs) are exclusive probes from deep mantle for studying the evolution of ancient lithospheric mantle and recycling of carbon. Our previous researche shows that MCDs from the Ruan river basin, Hunan are characterized by distinct carbon isotopes, nitrogen abundances, proportions of peridotite/ecologite parageneses of inclusions, and compositions of inclusion minerals such as the occurrence of kyanite, obviously different from those of MCDs from the North China craton, indicating some features related to ancient crustal substances, and hence implying there probably occurred subduction of ancient ocean crust slab into lithospheric mantle beneath the Yangtze craton and resulted in the formation of ecologite mantle and recycling of crustal carbon into lithospheric mantle. This project plans to perform analyses upon directionally-cut diamond plates on carbon isotopes, nitrogen and hydrogen abundances of diamonds along various growth layers from core to rim, as well as the inclusion mineral assemblages and their major & minor element composition, by using in-situ analyzing techniques such as cathodoluminescence microscopy, FTIR(Mapping), LA-(MC)-ICPMS and SIMS, etc.. The results will be applied to approach to the mantle environment and physics-chemistry conditions for diamonds' forming such as sources and their variation of carbon and nitrogen, the temperature and pressure and the oxygen fugacity, and finally to explore the relationship between diamonds' formation and the evolution of deep lithospheric mantle beneath the Yangtze craton, and the carbon cycling event between the surface and mantle. Furthermore, we hope to provide some geochemistry clues for prospecting primary mine for Hunan alluvial diamonds.