Experimental investigation of sulfide-sulfate equilibria in silicate melts

硫化物在很大程度上控制着S地幔和地壳中亲硫和亲铁元素的地球化学。因此，了解影响硫化物稳定性的因素对于理解硫、亲硫化合物和亲铁元素的行为是至关重要的。在岩浆系统中，硫被认为主要以硫化物的形式存在。然而，一些岩浆含有硫酸盐，或者作为结晶相(例如硬石膏、鼻石、海因、磷灰石、硅灰石)，或者作为熔体中的溶解物质。到目前为止，评估岩浆过程中硫化物氧化程度的数据很少。在充分氧化的岩浆源中，在部分熔融过程中可能不存在硫化物。此外，理论模型表明，二氧化硅活性和熔体碱度可能会影响硫化物-硫酸盐的平衡，从而在较低的fO2下稳定硫酸盐。这个项目将产生实验数据来约束这些模型。在此背景下，该项目的主要目标是：(1)限制硅酸盐熔体中硫化物-硫酸盐的平衡作为fO2和熔体组成的函数，(2)确定是否存在硫化物和硫酸盐物种共存的fO2范围，(3)确定是否存在其他硫物种(例如亚硫酸盐)。这些结果将为利用亲铁元素示踪岩浆过程、高硫火山脱气的原因以及岩浆-热液矿床的成因提供相关信息。

Sulfides largely control the geochemistry of chalcophile and siderophile elements in the Earth¿s mantle and crust. Therefore, understanding the factors affecting sulfide stability is essential to the understanding of the behavior of sulfur and chalcophile and siderophile elements. In magmatic systems sulfur is thought to be present dominantly as sulfide species. However, some magmas contain sulfates, either as crystalline phases (e.g., anhydrite, nosean, hauyne, apatite, silvialite) or as dissolved species in the melt. To date there are very few data to evaluate the extent of sulfide oxidation in magmatic processes. In sufficiently oxidized magma sources, sulfides may not be present during partial melting. In addition, theoretical models indicate that silica activity and melt alkalinity may affect sulfide-sulfate equilibria, stabilizing sulfates at lower fO2. This project will generate experimental data to constrain these models. In this context the main goals of this project are: (1) To constrain sulfide-sulfate equilibria in silicate melts as a function of fO2 and melt composition, (2) To determine if there is a fO2 range in which both sulfide and sulfate species coexist, (3) To establish whether other sulfur species (e.g., sulfite) are present. The results will provide information relevant to the use of siderophile elements as tracers of magmatic processes, the causes of high-sulfur volcanic degassing, and the genesis of magmatic-hydrothermal ore deposit.