Iron Isotope Behavior During Melt‐Peridotite Interaction in Supra‐subduction Zone Ophiolite From Northern Tibet

Abstract

AbstractMelt‐peridotite interaction has the ability to modify the δ56Fe of peridotite. However, iron isotopic fractionation during melt‐peridotite interaction is not well understood at present. In this study, we present high‐precision iron isotopic data for serpentinized and carbonated peridotite from the Yushigou supra‐subduction zone ophiolite in the North Qilian orogen of northern Tibet, to provide insights into iron isotope behavior during melt‐peridotite interaction in the mantle wedge. High‐Cr and high‐Al dunites coexist with harzburgite in the Yushigou ophiolite. The high‐Cr and high‐Al dunites were produced by interaction of peridotite with boninitic melt and tholeiitic melt, respectively. Serpentinization and carbonation have negligible influence on δ56Fe of the peridotite. The harzburgite mostly has δ56Fe ranging from −0.055 ± 0.029‰ to 0.056 ± 0.030‰, which overlaps with δ56Fe of abyssal peridotite. The high‐Al dunite is enriched in FeO, but it has δ56Fe (0.004 ± 0.034‰–0.083 ± 0.064‰) similar to the harzburgite. In contrast, the high‐Cr dunite displays a large range in δ56Fe from −0.173 ± 0.017‰ to 0.173 ± 0.057‰. Moreover, δ56Fe of the high‐Cr dunite is negatively correlated with its FeO content, which is ascribed to kinetic iron isotopic fractionation during melt‐peridotite interaction. Surprisingly, distinct iron isotope behavior during melt‐peridotite interaction recorded by the Yushigou peridotite can well explain the large variation of FeO and δ56Fe in abyssal peridotite and mantle wedge peridotite on a global scale.