塔里木大火成岩省瓦吉里塔格镁铁–超镁铁质岩体富铁钛岩浆成因及地幔源区特征研究

The Fe–Ti–rich parental magma is a key factor that control abundant enrichment in Fe–Ti oxides and hence Fe-Ti oxide deposits in some large igneous province. Previous studies proposed that the formations of the Fe- and Ti-rich parental magma could plausibly result from a combination of the differentiation of a ferropicritic primary magma at depth and the characteristic of mantle source composition. However, the nature of mantle source composition remains unclear. This project chooses Wajilitag Fe–Ti oxide ore-bearing mafic–ultramafic intrusions in the northwestern Tarim large igneous province as the subject investigated. We will carry out in situ trace elemental composition analysis of clinopyroxene, and Mg–O isotopic analysis of both whole rocks and mineral separates. In combined with previous studies, the main purposes of the project are to document the trace elemental compositions of potential parental magma and the nature of estimated primary magma, and to identify recycled subducted oceanic crust materials in the source and to constrain the nature of possible mantle source compositions, which in turn aids in understanding potential link between deep geological process and Fe–Ti oxide metallogenesis, and providing important information about the genesis and potential for Fe–Ti mineralization in the Tarim large igneous province.

富铁钛母岩浆是控制大火成岩省中铁钛氧化物巨量富集的关键因素，已有的研究表明这类富铁钛岩浆的形成不仅与原生苦橄质岩浆在深部演化过程有关，而且与地幔源区特征密切相关，但具体的地幔源区物质组成尚不清楚。本项目拟以塔里木大火成岩省西北部瓦吉里塔格含铁钛氧化物矿石的镁铁–超镁铁质岩体为研究对象，基于之前的研究成果，通过对其主要组成矿物单斜辉石元素地球化学组成的微区原位分析以及全岩和单矿物的镁–氧同位素研究，恢复其富铁钛母岩浆的微量元素组成，以此对其原生岩浆的性质加以限定，阐明其地幔源区物质组成，识别源区物质是否有再循环俯冲洋壳物质的加入，揭示富铁钛岩浆与地幔源区可能的成因联系，为深入理解大火成岩省深部地质过程和铁钛氧化物成矿作用的内在联系提供新的科学依据，为塔里木大火成岩省铁钛氧化物矿床的成矿和找矿潜力评价奠定基础。

塔里木大火成岩省是我国继峨眉山大火成岩省之后又一个被国际地学界普遍承认的大火成岩省，该大火成岩省中发育有瓦吉里塔格等大型铁钛氧化物矿床，显示出其具有良好的铁钛氧化物成矿潜力。本论文选择位于塔里木大火成岩省西北部与岩浆矿床有关的镁铁-超镁铁质岩体为研究对象。岩相学特征和硅酸盐矿物化学组成表明该岩体是富铁钛母岩浆是同样具有高铁钛玄武质原始岩浆经历分离结晶和堆晶作用的产物。瓦吉里塔格镁铁-超镁铁质岩石具有较为均一的O同位素组成（δ18OV-SMOW=4.9–5.9‰）表明其母岩浆未发生显著地地壳混染。基于之前的研究成果，该岩体具有相对于正常地幔δ26Mg值（−0.25‰）更低的Mg同位素组成进一步指示其富铁钛母岩浆起源于受早-中古生代俯冲物质（如沉积碳酸盐岩）改变的大陆岩石圈地幔。该研究的开展为富铁钛母岩浆与受再循环俯冲物质加入的地幔源区潜在联系提供了重要信息。