Constraining the distribution and budgets of life-essential volatile elements, such as carbon and nitrogen, on terrestrial planets holds the key to understanding planetary formation, evolution, dynamics, and habitability. For example, over Earth’s history, the surface inventory of carbon has been maintained by the cycling of materials between the surface and interior via outgassing and ingassing mechanisms induced by plate tectonics, which stabilizes the long-term moderation of the climate. However, the global carbon flux to the convecting lower mantle and the stable format of carbon at mantle conditions remain largely uncertain, mainly due to limited understanding of the fate of carbonates through subduction. In this talk, I will present experimental constraints on the fate of carbonates coexisting with the mantle silicates along mantle geotherm. The results show CaCO3, instead of MgCO3, remains stable as the host for oxidized carbon in Earth’s deep lowermost mantle, which has implications for interpreting ultradeep diamond inclusions and geochemical evidence for exchange between the core-mantle boundary and Earth’s surface. On the other hand, during the early planetary history, the distribution of carbon and nitrogen between the core-forming metallic melt, silicate melt, and atmosphere is controlled by partitioning between metal and silicate, and solubility in silicate melt in equilibrium with the overlying atmosphere. I will then discuss the motivation, plan, and implications for establishing partitioning and solubility models of carbon and nitrogen from both experimental and theoretical perspectives.
(Hosts: Tom Duffy & Jie Deng)
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