峨眉山大火成岩省幔源岩浆氧化还原状态：对岩浆矿床成矿的制约

Redox state are closely related with numerous processes such as the behavior and fate of metallic elements involved in magmatism, the depth of partial melting and associated mantle wakening，the differentiation trend of magma, the crystallization of Fe-Ti oxide, and the sulfide saturation. The oxygen fugacity of the mantle-derived magma is not only controlled by the geodynamic setting, but also closely related with the depth of mantle melting, mantle metasomatism and degree of partial melting and influence by crystallization differentiation, magma degassing and crustal contamination. Recent studies on the Emeishan large igneous province and associated magmatic deposits achieved some progress, but its redox state has not been well studied. This project focuses on the picrites, basalts and associated magmatic Fe-Ti-V oxide deposit and Ni-Cu-PGE sulfide deposit in the Emeishan large igneous province. Using the LA-ICP-MS and X-ray Absorption near edge structure spectral (XANES) in situ microanalysis technique, combined with the existing calculation method of oxygen fugacity based on the experimental petrology, systematic study on the redox state and its variation in the mantle source area and during magma evolution of the Emeishan a large igneous province. Investigate the controlling of oxygen fugacity on the ore-forming processes of the magmatic Fe-Ti-V oxide deposit and Ni-Cu-PGE sulfide deposit. This will provide constraints on the understanding the genesis of the magma deposit.

氧化还原状态与金属元素在岩浆过程中的行为和命运、部分熔融深度及地幔弱化、岩浆分异演化趋势、Fe-Ti氧化物结晶、硫化物饱和等过程密切相关。幔源岩浆的氧逸度不仅受到地球动力学背景的控制，还与地幔熔融深度、交代作用、部分熔融程度有着密切联系，并受到结晶分异、岩浆去气、同化混染等过程的影响。近来对峨眉山大火成岩省及相关岩浆矿床的研究取得了许多进展，但关于其氧化还原状态还未深入研究。本项目拟选取峨眉山大火成岩省中苦橄岩、玄武岩及相关钒钛磁铁矿矿床与Ni-Cu-(PGE)硫化物矿床为研究对象，运用LA-ICP-MS及X射线吸收近边结构谱原位微区分析技术，结合已有基于实验岩石学的氧逸度计算方法，系统的研究峨眉山大火成岩省地幔源区及其岩浆演化过程中的氧化还原状态及其变化规律，探讨氧逸度对岩浆Fe-Ti-V氧化物矿床与Ni-Cu-PGE硫化物矿床成矿过程的控制作用，从而为理解岩浆矿床的成因提供制约。

幔源岩浆的氧化还原状态与岩浆的分异演化过程关系密切，是控制钒钛磁铁矿矿床和铜镍硫化物矿床成矿的关键因素之一。在峨眉山大火成岩省中形成了数个超大型钒钛磁铁矿矿床和铜镍硫化物矿床，但关于其氧化还原状态及其对成矿的控制还未深入研究。本项目以峨眉山大火成岩省中苦橄岩、玄武岩及相关的钒钛磁铁矿矿床与Ni-Cu-(PGE)硫化物矿床为研究对象，在详细的野外地质研究的基础上，开展了系统的岩石学、矿物学、铂族元素地球化学、元素及同位素地球化学研究，主要取得了以下重要进展：（1）发现了峨眉山大火成岩省地幔源区存在氧逸度的不均一性，钒钛磁铁矿成矿母岩浆的高氧逸度继承自氧化的地幔源区,从而导致了磁铁矿的早期结晶。（2）揭示地幔柱-古特提斯洋俯冲板片相互作用对峨眉山大火成岩省地球化学及氧逸度不均一性的重要贡献。（3）建立了超大型钒钛磁铁矿矿床的岩浆通道成矿模式，揭示了形成巨厚块状钒钛磁铁矿矿层的动力学机制。（4）揭示了峨眉山钒钛磁铁矿含矿岩体母岩浆的硫化物饱和历史与铜镍硫化物成矿潜力。（5）发现弧岩浆经历了早期的硫化物饱和，揭示了早期饱和硫化物的溶解对形成斑岩–浅成低温热液铜金矿床的贡献。相关研究已发表SCI论文6篇。项目负责人入选中科院青促会，并获得基金委优秀青年基金资助。