石墨Re-Os同位素方法研究及其在山东南墅石墨矿成矿年代学中的应用

The research on Re-Os isotope in organic-rich samples has become a new hot spot within the isotope geochemistry field because of the organometallic nature of the elements. Re and Os can be enriched in graphite formed from sedimentary rocks by metamorphism, and the closure of Re-Os isotope system in graphite is well. However, because of the strong high-temperature resistance and chemical stability, the graphite samples are not easy dissolved using the routine method. A special closed dissolving device will be developed in this application to solution the problem and the method of Re-Os isotope analysis for graphite samples will be established. The sedimentary age and metamorphic age for different types and occurrences of graphite samples from Nanshu graphite deposit in Shandong province will be studied using the method, and metamorphic metallogenic geochronology for southeastern of North China will be researched. The regularity of graphite samples suitable for Re-Os isotope chronology will be studied according to the C isotope, major and trace elements data. The research not only can extend Re-Os isotopic system to the study of regional metamorphic event, but also can deepen the understanding of metamorphic metallogenic theory and provide geochronology data for the research of graphite metallogenic regularity in China.

由沉积岩中有机质变质而成的石墨，对Re、Os具有一定的富集能力。并且，其中Re-Os同位素体系封闭性较好，有望成为Re-Os同位素研究的理想对象之一，但由于石墨具有较强的耐高温性和化学稳定性，采用常规方法不易溶解，其Re-Os同位素鲜有研究。本申请拟通过研制专门的封闭溶样装置，解决石墨样品的难溶问题，进而建立石墨Re-Os同位素分析方法体系，并以此对山东南墅不同类型、不同产状的石墨矿样品进行Re-Os同位素研究，建立该石墨矿沉积-变质年代学格架，为研究华北地块东南缘区域变质成矿规律提供年代学依据。结合C同位素、主微量元素等数据，研究适合于Re-Os同位素年代学研究石墨样品的普遍规律性，本申请不仅能够拓展Re-Os同位素体系应用领域，还能够深化变质成矿理论的认识，为区域变质作用研究提供一种新的年代学研究技术手段。

本项目采用硝酸-硫酸-高氯酸组合解决石墨样品的难溶问题，进而建立了石墨Re-Os同位素分析方法，并以此对我国不同类型、不同产状的石墨矿样品进行Re-Os同位素研究。热接触变质型石墨矿床（湖南鲁塘）和岩浆热液型石墨矿床（新疆黄羊山）石墨Re-Os年龄与侵入岩锆石U-Pb年龄一致，Os同位素初始值揭示成矿物质来源于地层，表明岩浆的侵入造成沉积地层中有机质变质成石墨，沉积岩中有机质Re-Os体系在热接触变质的过程中发生重置，记录石墨成矿的时代；分别获得了山东南墅区域变质型石墨矿中石墨Re-Os等时线年龄为1935±47Ma，晚期磁黄铁矿Re-Os等时线年龄为1792±32Ma，结合含石墨片麻岩中碎屑锆石U-Pb年龄，揭示出荆山群片麻岩石墨矿原岩沉积时代晚于2100Ma，变质峰期时代为1900-1850Ma，退变质时代发生于1840-1820Ma。石墨和磁黄铁矿Re-Os年龄的获得，分别厘定了进变质作用和退变质作用发生时代，两者的时间差反映了整个胶东地区发生区域变质作用的持续时间大约为140Ma。厘定了山东石墨矿沉积-变质年代学格架，为研究华北地块东南缘区域变质成矿规律提供年代学依据。不仅拓展了Re-Os同位素体系应用领域，还能够深化变质成矿理论的认识，为区域变质作用研究提供了一种新的年代学研究技术手段。