Low‐Degree Melt Metasomatic Origin of Global Upper Mantle Fe Isotope Fractionation

Abstract

Abstract The upper mantle is heterogeneous in Fe isotope compositions, but the origin of the heterogeneity needs understanding. Recent studies on oceanic basalts demonstrate that the upper mantle Fe isotope heterogeneity results from low‐degree melt metasomatism. However, whether this hypothesis is of global significance needs testing in continental settings. Here we present an Fe isotopic study on intraplate continental alkali basalts from continental China, which are shown to have derived from upper mantle containing more metasomatized lithologies. The results show first‐order positive correlations of δ56Fe with indices of low‐degree melt metasomatism (e.g., [La/Sm]N), which, together with the so‐far published mid‐ocean ridge basalts data, define global trends, substantiating the global significance of low‐degree melt metasomatism in causing upper mantle Fe isotope variation. We, thus, suggest that low‐degree melt metasomatism is a globally effective process to preferentially concentrate heavy Fe isotopes in metasomatic lithologies at upper mantle conditions both today and in Earth's history.

Keywords

• mantle metasomatism
• upper mantle
• Fe isotope fractionation
• continental alkali basalt