橄榄石微量元素在示踪东北富钾火山岩成因中的应用

This project will analyze element concentrations in olivines hosted in potassic volcanic rocks from Northeast China (Erkeshan, Wudalianchi, Keluo and Xiaogulihe area) with the aim to decipher genetic connections between lithospheric mantle and potassic volcanic rocks, and thus to better constrain their petrogenesis. The main attention will be paid on the characteristics of magma source, magmatic processes and metasomatic characteristics. The highlight of this project is applying minor and trace elements in olivines as probes into early igneous and mantle melting processes, basing on the LA-ICP-MS analysis and trace element mapping. It provides a new perspective for exploring objective laws of element distribution, migration and evolution in source region and further characterize the formation process of potassic volcanic rocks. The research goals include: obtaining the high precision elements distribution characteristics of different types of olivine; tracing the petrogenesis by trace elements information of early and late olivine phenocrysts, xenocrysts, reaction rim and composition zoning; investigating the relationship between the trace element variation in olivine and the mantle metasomatism, and identifying the indicator element for the specific metasomatic agents (such as silicate melt and carbonate melt); establishing the methodology for tracing petrogenesis and providing reference information for similar researches.

本项目以东北富钾火山岩（二克山-五大连池-科洛-小古里河及周边地区）中橄榄石为主要研究对象，通过矿物学、岩石学和地球化学研究，约束岩浆源区性质、岩浆过程及交代特征，限定岩石圈地幔与富钾火山岩的成因联系，从而完善富钾火山岩成因机制。项目创新性在于利用近年来新兴的橄榄石微量元素岩石成因示踪手段，对橄榄石进行系统LA-ICP-MS原位微量元素分析和元素面扫描（Mapping），从更精细直观的视角来认识研究区岩浆源区元素配分、迁移、演化规律，进一步刻画富钾火山岩形成过程。预期取得以下进展：获得研究区不同种类橄榄石高精度元素含量分布特征；利用橄榄石早期斑晶、晚期斑晶、捕虏晶、反应边及环带微量元素信息示踪岩石成因；判别橄榄石微量元素含量变化特征与不同地幔交代作用的关系，识别橄榄石指针元素对特定交代端元（如硅酸盐熔体、碳酸岩熔体）的响应及指示意义，并力争建立相应的示踪体系为同类型富钾火山岩地区提供借鉴。