Understanding matte and metallic melt mobility in mineralogically complex planetary interiors and their role in elemental cycling

• Applicants: Dr. Christopher Beyer; Professor Dr. Raúl Fonseca
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544290921

Fe-S melts (here defined as Fe-Ni-(Cu)-S melts with varying metal-to-sulfur ratios between the Fe-FeS eutectic and monosulfide solid solution) are an essential building block of planetary interiors. Although the relative volume of Fe-S liquids is small in the differentiated mantle, their distinct physical and chemical properties, such as density, viscosity, and electrical conductivity, turn them into an important component to study. During and after core formation, metallic liquids (high metal-to-sulfur ratio) play a central role in the chemical fractionation and stratification of siderophile and chalcophile elements in the differentiated planetary body. Because the process of core formation can vary dramatically due to differences in the availability of heat sources, solid matrices, and liquid compositions, to name a few, the segregation of Fe-S liquids is complex and demands further investigations. We identified three key aspects of Fe-S melt migration that have not been addressed yet and are the main objectives of this proposal. 1) The migration of Fe-S melts (metal-rich and sulfur-rich) through polymineralic matrices. Here, we put a focus on the effect of melt composition [non-ferrous metal content and light elements (S, C, and O)], mineral composition, crystal morphology and polymineralic interfaces on the mobility of Fe-S liquids at conditions relevant for Earth’s upper mantle and transition zone. 2) The upscaling of microscale observations on melt migration in typical lithologies of the Earth’s mantle to geological scales and modeling the consequences for siderophile and light element cycling, with special focus on the characterization of a melt’s metasomatic potential. 3) The effect of Fe-S melt composition and redox evolution on the formation and destruction of diamonds in the Earth’s lithospheric and sub-lithospheric mantle. We will investigate the conundrum of why S-rich sulfides are the dominant inclusions in diamonds, albeit these melts have a vanishingly low carbon solubility. We will use experimental methods to synthesize sulfide melts in crystalline matrices under controlled pressure, temperature, oxygen fugacity, and sulfur fugacity. The run products will be examined using 2-D and 3-D imaging methods to study the wetting properties and network morphology of sulfide melts.

• DFG Programme: Research Grants
• International Connection: Netherlands, United Kingdom
• Cooperation Partners: Dr. Katharina Marquardt; Professor Oliver Plümper, Ph.D.