Experimental investigation of sulfide-sulfate equilibria in silicate melts

硫化物在很大程度上控制着地幔和地壳中亲铜和亲铁元素的地球化学特征。因此，了解影响硫化物稳定性的因素对于理解硫、亲铜和亲铁元素的行为至关重要。在岩浆系统中，硫被认为主要以硫化物形式存在。然而，有些岩浆含有硫酸盐，或者是作为结晶相（如硬石膏、硅石、铝石、磷灰石、银云石），或者是作为熔融物中的溶解物。迄今为止，评价岩浆过程中硫化物氧化程度的资料很少。在充分氧化的岩浆源中，硫化物在部分熔融时可能不存在。此外，理论模型表明，二氧化硅活性和熔融碱度可能影响硫化物-硫酸盐平衡，在低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。在这种情况下，本项目的主要目标是：(1)约束硅酸盐熔体中硫化物-硫酸盐平衡作为fO2和熔体成分的函数，(2)确定是否存在硫化物和硫酸盐共存的fO2范围，(3)确定是否存在其他硫化物（例如亚硫酸盐）。这些结果将为利用亲铁元素作为岩浆过程的示踪剂、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.