Isotope Effects Accompanying Decarbonation at High PT Parameters: Experimental Data

The isotope effects that accompany the decarbonation process upon redox interaction of carbonate with metallic Fe and Ni at high PT parameters (1200°C, 6.3 GPa) are estimated. Carbonate under these conditions is decomposed with the formation of reduced carbon (ΣС: graphite, carbides, and carbon dissolved in metal) and metal oxides (wüstite and Mg-wüstite). The value of isotope shifts, which is calculated from models of bulk and Rayleigh decarbonation, varies from –1.2 to –0.5‰ for C isotopes in a ΣС–carbonate system and from –1.1 to –0.46‰ for O isotopes in the Mg-wüstite–carbonate system. Our estimations show that the C and O isotope shifts in residual carbonate during redox-induced decarbonation are directed toward its enrichment in heavy isotopes (18О and 13С). This direction of the isotope shift is opposite in sign to the isotope effects that accompany the low-pressure decarbonation with CO2 release.