Rare-metal enrichment in carbonatite-bearing magmatic systems:Part A. Understanding magmatic evolution and enrichment processes in time by high-precision dating and inclusion studies

尽管使用多种地球科学方法和学科对碳酸岩和相关岩石（超基性岩、基性岩、碱性岩）进行了深入研究，但其成因和演化仍然相当难以捉摸。此外，对于导致金属活动化和富集以及矿床形成的关键先决条件和过程，仍然没有达成共识。在这里，我们提出了一项研究，结合岩石学，地球化学，地质年代学以及实验分析，以更好地了解最早的金属富集过程中的碳酸盐岩含岩浆岩（使用超基性基性岩的几个UACC的）。主要的重点将是寻找原始岩浆液体的组成和它们的演化之间的联系。这将在科拉碱性省的UACC的例子中实现，代表碳酸岩和相关矿床的经典和暴露良好的情况。特别是，我们将试图找到以下问题的答案：1） 在时间上的演变，i）在KAP内（可以是从高精度年龄构建的羽流的轨迹？），和ii）在选定的UACC（我们可以解决最早和最晚的融化之间的年龄差异？）。我们将通过高精度钙钛矿定年将地质年代学应用于最早期的岩石（如辉石岩），并通过高精度斜锆石和锆石定年将其应用于晚期熔体（碳酸岩/磷铁矿）。（二） 代表堆晶的最早期岩石的共轭熔体是什么？对橄榄岩、辉石岩、斜长角闪岩中早期形成的矿物（钙钛矿、橄榄石、辉石）的熔体包裹体的研究，可以提供这些熔体的化学成分和流体成分的信息。这些熔体的条件是什么（P，T，X，fO 2）？第三章 岩石及其矿物的地球化学演化：什么矿物（及其不同的世代）富集了REE、Nb和其他潜在的成矿金属？早期累积在分馏和富集过程中起什么作用？我们将应用薄片阴极发光技术来区分和表征不同的矿物世代，矿物地球化学（通过LA-ICP-MS），并对选定的矿物（如碳酸盐，磷灰石，钙钛矿）高精度地确定同位素组成（Sr，Nd，Pb）。最早的岩石（橄榄石，辉石）通常含有钙钛矿，通常被解释为堆积物。对这些岩石中矿物熔体包裹体的研究将提供共轭熔体的组成。有了这些信息，钙钛矿年龄将可靠地分配给这些早期熔体的形成时间。另一方面，对早期（橄榄岩、辉石岩、斜长角闪岩）和晚期岩石（磷块岩、碳酸岩）矿物的地球化学研究将阐明矿物分馏、熔体混合和不可渗透性在既定时间间隔内元素富集到矿石水平的作用。

Despite intensive investigations of carbonatites and related rocks (ultrabasic, basic, alkaline) using multiple geoscience methods and disciplines, their genesis and evolution remain quite elusive. Furthermore, there is still no consensus what are the critical prerequisites and processes leading to the mobilization and enrichment of metals and formation of ore deposits. Here we propose a study which combines petrological, geochemical, geochronological as well as experimental analyses to better understand the earliest metal enrichment processes in carbonatite-bearing magmatic rocks (using ultrabasic-basic rocks of several UACC´s). The main focus will be on searching the link between composition of primary magmatic liquids and their evolution in time. This will be achieved on the example of the UACC´s from the Kola Alkaline Province representing a classical and well-exposed case of carbonatites and related deposits. In particular, we will try to find the answers on the following questions:1) The evolution in time, i) within the KAP (can be a track of a plume constructed from high-precision ages?), and ii) within selected UACC (can we resolve an age difference between earliest and late melts?). We will apply geochronology to the earliest rocks (e.g. pyroxenites) by high-precision perovskite dating, and to late-stage melts (carbonatites/phoscorites) by high-precision dating of baddeleyite and zircon. 2) What were the conjugate melts of earliest rocks that represent cumulates? The study of melt inclusions of early formed minerals (perovskite, olivine, pyroxene) of olivinites, pyroxenites, amphibolites will provide information of the chemical composition of these melts and their fluid composition. What were the conditions of these melts (P, T, X, fO2)? 3) The geochemical evolution of rocks and their minerals: What minerals (and their distinct generations) concentrate REE, Nb and other potential ore metals? What role play early cumulates for fractionation and enrichment processes? We will apply cathodoluminescence of thin sections to distinguish and characterize different mineral generations, mineral geochemistry (by LA-ICP-MS), and determine the isotope composition (Sr, Nd, Pb) with high precision for selected minerals (e.g. carbonate, apatite, perovskite).The earliest rocks (olivinites, pyroxenites) often contain perovskite and are typically interpreted as cumulates. The study of melt inclusions of minerals from these rocks will provide the composition of conjugate melts. With this information obtained perovskite ages will be reliably assigned to the formation time of these early melts. Geochemical studies of minerals from dated early- (olivinites, pyroxenites, amphibolites) and late-stage rocks (phoscorites, carbonatites), on the other hand, will elucidate the role of mineral fractionation, melt mixing and immiscibility for element enrichment up to ore levels in the established time interval.