Geochemical constraints on core-mantle differentiation in Mercury and the aubrite parent body

摘要: Abstract Differentiation of Mercury and the aubrite parent body (AuPB) at extremely reducing conditions is implied from low FeO high S contents their mantles. Here, mantle abundances these elements as derived remote sensing (in case Mercury) meteorite analysis are used in conjunction with new experimentally determined metal-silicate partition coefficients presented Steenstra et al. (2020a) to quantify geochemical consequences core formation highly reduced planetary bodies. Plausible compositions AuPB assessed, distribution Si other during quantified. Combining results previous observations surface it found that its likely be Si-rich (>4.5–21 wt%). The estimated depend mostly on assumption C saturation Mercury's type bulk composition considered. Calculations for C-free also yield significant quantities (>6–20 wt%, depending redox state). amount greatly decreased if C-saturation assumed. experimental data related thermodynamic parameterization predicting graphite FeSi alloys (CCGS) shows was C-saturated following a core, allowing separation graphitic flotation crust. Due lower calculated under conditions, crust unlikely form smaller-sized asteroids such AuPB. nature C-undersaturated scenarios expected have resulted preferential partitioning majority volatile siderophile (VSE) into core. However, depletions most VSE cannot reconciled depletion only. Their aubrites require additional (I) segregating sulfide liquids differentiation and/or (II) compatible behavior mineral-melt fractionation (III) loss vapor phase after differentiation.