Fe Oxidation State and Oxygen Isotope Composition of Diverse Metasomatized Peridotite Rocks

ABSTRACT Metasomatic fluids are thought to be oxidising agents that react with the surrounding mantle rocks, causing changes in the bulk Fe 3+ /∑Fe, their redox state, and affecting the partitioning of trace elements and the fractionation of O isotopes. Worldwide distributed metasomatized peridotites represent the ideal case study to investigate the role that crystal chemistry has on the O‐isotope fractionation. We present mineral‐chemical data of mantle peridotites from Tallante (Spain) such as major and trace elements, oxygen fugacity, and O‐isotope data. Our results show that the O‐isotope composition of volumetrically minor spinel in the residual mantle can be significantly affected by the oxidising metasomatic melts or fluids, likely implying that the oxidation of Fe 2+ to Fe 3+ favours 18 O uptake in spinel structure with respect to 16 O.