SIMS study of self-consisted fractionation of iron and titanium isotopes in ilmenites

Abstract

A set of terrestrial geological samples with varying compositions of Fe 2O 3+MeO·TiO 2 (Me=Fe, Mg, Mn, etc.), distinguished by their Fe 2O 3 content (<25%), was studied using SIMS. The dependence of isotope fractionation upon the oxide phase content as well as the degree of iron oxidation was determined. It is shown that heavy isotopes fractionation is directly proportional to Fe 2O 3 content and the percentage of higher oxides in the sample. It is also shown that the fugacity of oxygen is a good general integral measure of these physical and chemical changes. It is concluded that the migration, redistribution, and accumulation of the iron group isotopes are controlled by the oxidation–reduction processes. Of particular note is the redistribution of oxygen between the local atomic environment of titanium and iron. The role of the ion-beam induced effects during isotopic SIMS analysis of these specimens is discussed.