3:00 PM - 3:15 PM
[SIT22-18] Light element isotope fractionation processes in the deep Earth
Keywords:Isotope fractionation, Deep Earth, Metallic melt-silicate fractionation
A review of the previous experimental studies in the Fe-C and Mg-Si-C-O systems suggest that large carbon isotope fractionation occur between graphite/diamond and iron carbide melt. The results indicate that the iron carbide melt will preferentially gather 12C than 13C, and has a strong temperature dependence. Factionation is also observed between graphite/diamond and carbonate melt at temperatures and pressures corresponding to upper mantle conditions. The pressure dependence on carbon isotope fractionation is also being tested at higher pressure conditions. Preliminary results indicate that carbon isotopes also fractionate at high pressures corresponding to the deep Earth. Recent results in the sulfur, nitorgen and hydrogen sytem are consistent with the carbon-bearing system, that lighter isotopes generally fractionate to the metallic melt and heavier isotopes to the silicate melt.
In order to understand the factionation process in detail, it is essential to have accurate measurement of isotopic composition for the run products at high-pressures. The difficulty arises from the smaller volume of samples, separation of phases and confirmation of equilibration between the phases. Ongoing studies on microvolume isotope measurements using laser ablation and curie point pyrolyser gave encouraging results with good accuracy.
It is anticipated that the combined high-pressure and high-temperature dependent fractionation of light element isotopes in the deep Earth is an effective mechanism that can create a “lighter core” with large scale differences in the distribution of the isotopes between the metallic core and bulk silicate Earth during the accretion and differentiation of early Earth. Our findings also have implications on the light element cycling at the core-mantle interface.