海南岛前寒武纪石碌群和上覆石灰顶组的沉积-变质特征与对比

For this application, the key points to be clarified will be placed on the sedimentary and metamorphic petrological features, the provenances and depositional times or time-intervals, and the depositional settings and associated geodynamics of both the Precambrian Shilu Group and overlying Shihuiding Formation, which host the famous, Shilu large-scale Fe-Co-Cu polymetallic ore deposit in Hainan Province of South China. These emphases come from analsysis on the unsolved but still key scientific problems linked not only to the sedimentologic correlation of the Shihuiding Formation with the underlying Shilu Group but also to the genesis of the Shilu deposit. For the sake of our destinations, a detailed and systematic investigation, by means of field geology and thin-section observation, on the occurrences and spatial distributions, lithological types and assemblages, mineral types and parageneses, and textures and structures of as well as the possible fossils in both the Shilu Group and Shihuiding Formation in the Shilu district, will be firstly carried out to fully unravel their sedimentary and metamorphic characteristics. Then, an integrated U-Pb isotope with Lu-Hf isotope in situ analysis on detrital zircons using LA-ICP-MS or SHRIMP and LA-MC-ICPMS assisted by cathodoluminescence (CL) image as well as a combination of electron probe micro analyzer (EPMA) and rock probe using ICP-AES, ICP-MS and MC-ICPMS will applied largely to the metamorphosed clastic-sedimentary rocks and contained minerals from both the Shilu Group and Shihuiding Formation. All these utilized methods can confirm the origin (detrital, or metamorphic and/or hydrothermal, or magmatic, or composite, etc.) and P-T conditions of representative minerals including zircon, characterize the element geochemical and Sm-Nd isotopic compositions of the analysed rocks, and obtain the U-Pb age populations and Lu-Hf isotopic consitutes of detrital zircon. Finally, connected with the progresses on the Precambrian geology and associated metallogeny in the world, especially in South China, a comprehensive study on all the forementioned results as well as a comparison of the sedimentary-metamorphic characteristics are necessary to clarify the depositional relationship between the Shilu Group and the overlying Shihuiding Formation as well as to evaluate the associated geodynamic settings or implicit, important geological event(s) linked to the break-up(s) and assemblies of the Precambrin supercontinents such as Columbia, Rodinia and/or Gondwana, when both the studied successions were deposited. This study will provide important evidences for further elucidating the genesis of the Shilu deposit as well as the Precambrain tectonic histroies and associated geodynamic settings of South China including Hainan Island. Moreover, this study is of important implication not only for understanding the large-scale Fe-Mn-P metallogenesis during Precambrain but also for prospecting their mineral resources.

针对以往研究进展与存在的关键科学问题，项目以海南石碌铁-钴-铜多金属矿区的赋矿地层即前寒武纪石碌群和上覆石灰顶组为研究对象，在全面查清石碌群和石灰顶组的地质学特征的基础上，综合运用成因矿物学、元素地球化学和Sm-Nd同位素、以及碎屑锆石的原位化学和原位U-Pb与Hf同位素组成等测试技术，重点研究这些赋矿地层的①沉积岩石学和变质岩石学特征，②沉积物源区与沉积时代，和③沉积环境与地球动力学背景；开展沉积-变质特征的对比，并结合国内外、特别是华南前寒武纪地质构造与成矿事件研究进展，以①正确分析石碌群和石灰顶组的沉积序列与沉积演化关系，和②正确理解海南岛前寒武纪大地构造演化特征及与华南大陆和/或与前寒武纪超大陆的聚合和裂解关系。此研究，不仅可为进一步阐明石碌铁多金属矿床的成因提供依据，对深入揭示华南前寒武纪铁-锰-磷大规模成矿作用特征与地球动力学背景、开展找矿预测还具有重大理论和实际意义。

海南岛石碌群与其上覆石灰顶组为华南重要的前寒武地层之一，其构造演化历史为解决华南前寒武时期重大地质时间的窗口，但关于其地层特征、大地构造位置以及赋存其中的石碌铁矿的成因有着众多争议。本项目在全面清查石碌群与石灰顶组地质学特征的基础上，开展了石碌群和石灰顶组的沉积时代、源区、构造环境和变质变形演化过程，以及石碌矿床的富集机理研究，结果显示石灰顶组与石碌群具有相同的物质源区，一致的构造演化历史，因此可将石灰顶组归为石碌群第七层；石碌群和上覆石灰顶组形成与弧后前陆盆地；石碌矿床为多阶段地质作用改造富集后的产物，属于苏必利尔型BIF矿床，并提出了相应成矿模型。在此基础上，发现海南岛新生地壳主要增长时间与华夏板块不一致，提出海南岛在中元古代时期位于Laurentia大陆西部，并与华夏经历了不同的构造演化属性。