Constraints on the Abundances of Carbon and Silicon in Mercury's Core From Experiments in the Fe-Si-C System
Abstract
The composition of a planet's core has important implications for the thermal and magmatic evolution of that planet. Here, we conducted carbon (C) solubility experiments on iron-silicon (Fe-Si) metal mixtures (up to 35 wt% [~52 atom%] Si) at 1 GPa and 800-1800°C to determine the carbon concentration at graphite saturation (CCGS) in metallic melt and crystalline metal with varying proportions of Fe and Si to constrain the C content of Mercury's core. Our results, combined with those in the literature, show that composition is the major controlling factor for carbon solubility in Fe-rich metal with minimal effects from temperature and pressure. Moreover, there is a strong anticorrelation between the abundances of carbon and silicon in iron-rich metallic systems. Based on the previous estimates of <1-25 wt% Si in Mercury's core, our results indicate that a carbon-saturated Mercurian core has 0.5-6.4 wt% C, with 6.4 wt% C corresponding to an Si-free, Fe core and 0.5 wt% C corresponding to an Fe-rich core with 25 wt% Si. The upper end of estimated FeO abundances in the mantle (up to 2.2 wt%) are consistent with a core that has <1 wt% Si and up to 6.4 wt% C, which would imply that bulk Mercury has a superchondritic Fe/Si ratio. However, the lower end of estimated FeO (≤0.05 wt%) supports CB chondrite-like bulk compositions of Mercury with core Si abundances in the range of 5-18.5 wt% and C abundances in the range of 0.8-4.0 wt%.
- Publication:
-
Journal of Geophysical Research (Planets)
- Pub Date:
- May 2020
- DOI:
- 10.1029/2019JE006239
- Bibcode:
- 2020JGRE..12506239V