Acta Petrologica et Mineralogica

The immiscibility between silicate melt and sulfate melt widely exists in the nature, which is closely related to the enrichment of metalic elements and mineralization. Currently, the experimental study on the immiscibility process between basic silicate and sulfate melt is still weak, as well as the partition behavior of elements in such process. In this study, we designed a geochemical simulation experiment, which is kept normal pressure and 1 200℃ for 12 hours, and then cooled to room temperature within 5 minutes. Cooled samples were analyzed in detail by micrography, EPMA and in-situ LA-ICP-MS. The results show that sulfate can be miscible with basic silicate melt in a certain proportion at 1 200℃, and cooling will cause immiscibility between them. After cooling, the sample forms two distinct layers. The upper layer is mainly sulfate phase and contains magnesioferrite and forsterite crystals. The lower layer is mainly silicate glass phase, and contains sulfate globes and mineral crystals such as magnesioferrite, hauyne and hematite. The crystallization separation of hauyne caused by cooling and the immiscibility between sulfate melt and silicate melt may be the reason for the low S content and relative reduction of sulfur rich and relatively oxidized mantle derived basic shallow intrusive and volcanic rocks. The analysis results of major and trace elements show that Na, Ca, K and REEs tend to enter the sulfate melt in the immiscibility process. The content of rare earth elements in early immiscible sulfate melt is not high, which has little effect on the content of rare earth elements in silicate melt. However, the content of rare earth elements in the immiscible sulfate melt formed in the late stage and low relative temperature is significantly higher than that in the early exsolved sulfate melt and residual silicate melt. The partition behavior of metalic elements in sulfate melt has a certain correlation with electronegativity, and the partition coefficient increases with the decrease of electronegativity. The partition behavior of rare earth elements shows that sulfate melt plays an important role in the enrichment of rare earth elements, but it can not cause the strong differentiation of light and heavy rare earth elements.

basic silicate; sulfate; melt immiscibility; hauyne; REEs enrichment