华南武夷-云开造山带混合岩成因机制及意义

The partial melting of crustal rocks in the deep crust during orogeny is the most important mechanism for the generation of granite and has significant implications for crustal differentiation and orogenic evolution. The crustal anataxis processes can be recorded by migmatite, which can provide evidences, in their mineralogy, textures and chemical compositions, of the melting reactions and physical processes involved in the generation and segregation of granitic magmas. The Early Paleozoic Wuyi-Yunkai orogeny resulted in development of large scale felsic magmatism in South China, indicating significant crustal mobilization. There are different types of migmatites outcropped in the orogen, which witnessed complicated crustal anataxis processes. In this study, we will conduct detailed petrographic observation and in situ analysis for major, trace elemental and isotopic compositions on the minerals from different types of migmatites in the orogen to decipher the melting reactions and the corresponding temperature and pressure during the crustal anataxis processes. These results will be integrated with the whole-rock geochemical and Sr-Nd-Hf isotopic compositions for tiny lenticular leucosomes (<0.5 cm) and the surrounding melanosome, which are sampled through micro drilling, to illustrate the influence of the melting process on the melt compositions. This study will provide new insights for understanding the petrogenesis of granite in the Wuyi-Yunkai orogen and for constraining the temporal and spatial evolution of the orogen.

造山运动中，地壳岩石在地壳深部发生深熔，是花岗岩最主要的形成机制之一，对大陆地壳分异及造山带演化具有重要意义。混合岩记录了地壳深熔过程，对其进行详细的研究是全面认识造山带地壳深熔过程最重要的途径。华南武夷-云开造山带出露了不同类型的混合岩，记录了不同类型变沉积岩复杂的熔融过程，为研究造山带地壳深熔作用提供了良好的条件。本次研究拟利用显微镜、电子探针和扫描电镜对混合岩的矿物结构进行详细的岩相学观察，结合矿物主、微量元素和同位素分析，解析熔融过程中反应矿物和残留矿物组合和比例，揭示熔融反应类型及其温压条件，为理解武夷-云开造山带地壳深熔过程及其演化机制提供重要的科学依据。此外，利用微钻技术，对混合岩中的细小透镜状淡色体（<0.5 cm）及其周围暗色体进行原位采样和主、微量元素含量和Sr-Nd-Hf同位素组成分析，阐明熔融反应对熔体化学成分的控制作用，为理解造山带花岗岩成因机制提供新的认识。

本项目分别对华南早古生代武夷-云开造山带中的辉长岩、高镁闪长岩和花岗岩及三叠纪混合岩进行了系统的年代学、岩石学与地球化学研究。对早古生代高镁闪长岩的研究揭示地壳岩浆演化过程对该类岩石高Ba-Sr特征的重要贡献。综合华南早古生代不同类型岩浆岩的成因及时空演化过程，阐明华南早古生代武夷-云开造山作用的构造演化机制，指出该造山带可能为碰撞-陆内复合型造山带，提出古老构造薄弱带在陆内造山带地壳生长与演化的重要意义。在对华南三叠纪混合岩研究中发现源区熔融及熔体迁移过程中复杂的矿物反应类型及其对熔体成分的控制作用，揭示副矿物对花岗岩稀土元素及Nd同位素的重要控制作用，为深入认识花岗岩成因提供重要科学依据。上述成果已发表国际SCI文章6篇。