Niobium, zirconium, titanium, and rare earth elements in alkaline silica-undersatured magmas: experimental determination of solubility, complexation and phase relations and implications for the formation of magmatic Nb-Zr-REE deposits

过碱性岩浆岩是地球上Zr、Nb、Ta和稀土元素（REE）富集量最大的岩浆岩。目前或在不久的将来特别重要的是或将是硅不饱和碱性岩石中的矿床（俄罗斯科拉半岛的希比尼和洛沃泽罗地块以及格陵兰南部加尔达尔省的矿床），其矿物学特征复杂。到目前为止，这些岩石的实验研究很少，因此缺乏这些元素的溶解度和络合性甚至相关系的基本数据。在这里提出的项目中，我们想要解决一些悬而未决的问题，并确定Nb， Zr， Ti和REE的溶解度，这些矿物在冷却时早期结晶（褐煤，钙钛矿，绿钛矿，二析出物，副钙钛矿，锆石，坏石）在碱性铝硅酸盐熔体中的溶解度，作为过碱度的函数，以及F， Cl， CO2和H2O的浓度)。这些实验也将提供有关相关系的信息。此外，我们计划研究Nb， Zr， Ti和REE在玻璃中的配位化学以及Nb在高温下的原位配位。

Peralkaline magmatic rocks host some the largest accumulations of Zr, Nb, Ta and rare earth elements (REE) on Earth. Of particular importance at present or in the near future are or will be deposits in silica-undersaturated alkaline rocks (Khibiny and Lovozero massifs, Kola Peninsula, Russia and deposits in the Gardar province, southern Greenland), which are characterized by a complex mineralogy. So far, these rocks are little studied experimentally, and thus fundamental data on solubility and complexation of these elements and even on phase relationships are missing. In the project proposed here, we would like to address some of the open questions and determine the solubility of Nb, Zr, Ti and REE from minerals that crystallize early upon cooling (lueshite, perovskite, loparite, eudialyte, parakeldyshite, zircon, baddeleyite) in alkali aluminosilicate melts as function of peralkalinity, and of the concentrations of F, Cl, CO2, and H2O). These experiments will also provide information on phase relationships. Moreover, we plan to study the coordination chemistry of Nb, Zr, Ti and REE in the produced glasses and the complexation of Nb in the melt in situ at high temperature.