山东昌乐新生代玄武岩中熔融包裹体研究：约束地幔源区与岩浆演化

Mantle source and melt evolution of basalts is one of the international hot issues, of which key points include compositions of parental magma and their evolutionary processes (e.g. fractional crystallization, crustal contamination). Traditionally, whole-rock samples or phenocrysts are employed for petrologic and geochemical investigation. However, these methods are unable to reveal the exact nature of the parental melts and also their temporal evolution in composition. This has been hindering a better understanding of the origins of those Cenozoic basalts in the North China Craton (NCC). In order to unravel this issue, we will study the chemical compositions of melt inclusions in the olivine and pyroxene phenocrysts of Cenozoic basalts and their xenoliths from Changle region in the southeastern NCC, together with the newly obtained whole-rock data. We will use the compositions of melt inclusions of different generations and their host phenocrysts, combined the whole-rock geochemistry, to: (1) evaluate crystallization and trapping conditions; (2) calculate the components of parental melts; (3) discuss the nature of the magma source and melt evolution; (4) constrain the evolution of lithospheric mantle beneath the southeastern NCC.

玄武岩源区性质和岩浆演化是岩石学领域研究热点之一，其重点是揭示玄武岩母岩浆的成分和刻画岩浆演化过程（包括分离结晶、同化混染等），以约束其地幔源区性质和演化。传统的研究方法是以岩石或矿物为尺度进行岩石学和地球化学分析，但很难精准地反映其源区性质，更无法展示母岩浆成分随时间的演化过程。针对以上研究瓶颈，本项目将以华北克拉通东南缘山东昌乐新生代玄武岩及其捕虏体为研究对象，从微区尺度出发，分析橄榄石、辉石等矿物中单个熔融包裹体的组分来进行突破。首先确定熔融包裹体类型及捕获期次，利用LA-ICPMS微区原位定量分析不同世代捕获的单个熔融包裹体的主微量成分，进而确定岩浆演化不同阶段的熔体成分。利用熔体、寄主矿物成分和显微测温结果，估算捕获温压条件，计算母岩浆成分，结合玄武岩全岩地球化学特征，最终揭示山东昌乐地区玄武岩源区性质并反演其岩浆演化过程，约束华北克拉通东南缘新生代岩石圈地幔性质与演化。