Experimental study of sulfur solubility in silico-carbonatitic melts at pressures of 6-10 GPa

虽然硫是地幔中的次要成分，但硫化物矿物的存在与否主要决定了亲硫元素(如铅、稀土和铂族元素)的微量元素特征和行为。此外，作为包裹体的硫化物在金刚石中的普遍存在，表明它们可能与金刚石的形成和生长过程密切相关。许多实验研究确定了硅酸盐熔体的S溶解度是压力、温度和氧逸度的函数。然而，关于碳酸盐熔体和硅碳酸盐熔体的S溶解度的信息却非常有限。尽管这种熔体可能是上地幔交代作用的重要因素，而且它们的S浓度可能超过类似条件下硅酸盐熔体的浓度。在这个项目中，我们的目标是在压力6-10 Gpa，温度1200-1500℃以及相对氧化和还原的条件下，测定硫化物饱和碳酸盐岩和硅碳酸盐熔体中的硫浓度。为此，我们将开发一种实验方法，将硫化物从含碳酸盐的熔体中物理分离出来，以避免在化学分析过程中受到S液滴的污染。使用橄榄石胶囊的测试实验为这个项目提供了一个有希望的起点。这些结果有助于理解S在上地幔碳酸盐岩熔体交代过程中的作用，以及亲磷元素在交代过程中的行为。

Although sulfur is a minor constituent of the Earths mantle, the presence or absence of sulfide minerals mainly determines the trace element signature and behavior of the chalcophile elements (e.g. Pb, Re and platinum group elements). In addition, the common occurrence of sulfides as inclusions in diamond suggests they may be intimately related to the process of diamond formation and growth. A number of experimental studies have determined the S-solubility of silicate melts as a function of pressure, temperature and oxygen fugacity. However, only very limited information is available on the S solubility of carbonatitic and silico-carbonatitic melts. This is in spite of the fact that such melts may be important agents for metasomatism in the upper mantle and that their S concentrations may exceed those of silicate melts at similar conditions. In this project, we aim to determine the sulfur concentration in sulfide-saturated carbonatitic and silico-carbonatitic melts at pressures of 6-10 GPa, temperatures of 1200-1500°C and at relatively oxidizing and reducing conditions. To do this we will develop an experimental approach that physically separates the sulfide from the carbonate-bearing melts in order to avoid contamination by S droplets during chemical analysis. Test experiments using olivine capsules provide a promising starting point for this project. These results have application to understanding the role of S during silico-carbonatitic melt metasomatism in the upper mantle and the behavior of chalcophile elements during such a process.