Heavyδ57Fe in ocean island basalts: A non-unique signature of processes and source lithologies in the mantle

Abstract

Lithological heterogeneity is a widely accepted feature of the Earth's mantle, with recycled crustal material accounting for a significant part of heterogeneity in ocean island basalt (OIB) geochemistry. Fe isotopes have been used to link geochemical heterogeneity in OIB sources to distinct mantle lithologies due to their mineral-specific equilibrium fractionation effects, or their composition, such as incorporation of kinetically-fractionated core liquids entrained from the core-mantle boundary.Here we present Fe isotope data for Samoan shield, and Azores volcanoes, together with a combined phase-equilibria and equilibrium mineral-melt isotope fractionation model. These OIB lavas allow us to study the roles of core-derived and recycled mantle components in

Linking Chemical Heterogeneity to Lithological Heterogeneity of the Samoan Mantle Plume With Fe‐Sr‐Nd‐Pb Isotopes

“…The Fe stable isotopic compositions of basalts are manifestations of both mantle source characteristics and magmatic processes (e.g., Soderman et al., 2021). In the following, we first evaluate potential effects of magma differentiation and mantle partial melting on the Fe isotopic compositions of the Samoan lavas, and then explore the lithological identities of the distinct geochemical components in the Samoan plume based on the diverse compositions of shield lavas.…”

An Early Garnet Redox‐Filter as an Additive Oxidizer in Lower Continental Arc Crust Traced Through Fe Isotopes

“…Rocks from the Tongde and DXY dikes have δ 57 Fe values ranging from −0.08 to +0.17‰ and −0.14 to +0.14‰, broadly within the range of modern CAB (−0.19 to +0.21‰; Foden et al., 2018), and notable with three samples lighter than the depleted mantle (δ 57 Fe = +0.04‰; Craddock et al., 2013). By comparison, rocks from the younger, post‐subduction Wudang dikes have variable but heavier δ 57 Fe values from +0.05 to +0.29‰, similar to MORB (+0.07 to +0.35‰) and OIB (+0.05 to +0.37‰) (S. Chen et al., 2019; Gleeson et al., 2020; Nebel et al., 2019; Soderman et al., 2021; P. Sun et al., 2020; Teng et al., 2013).…”

“… Plot of δ 57 Fe versus MgO for rocks from the Tongde, Dengxiangying (DXY) and Wudang dikes. Depleted mantle (DM; Craddock et al., 2013), mantle wedge (Nebel et al., 2013), mid‐ocean ridge basalts (MORB; Beard et al., 2003; S. Chen et al., 2019; Gleeson et al., 2020; P. Sun et al., 2020; Teng et al., 2013; Weyer & Ionov, 2007), back‐arc basin basalts (BABB; Nebel et al., 2013), continental arc basalts (CAB; Foden et al., 2018) and ocean island basalts (OIB; Nebel et al., 2019; Soderman et al., 2021; Teng et al., 2013) are shown for comparison. Rocks from the Tongde FC dikes follow the differentiation trend, those from the Wudang dikes follow the crustal contamination or source mixing trend, and those from the DXY dike show large variations in Fe isotopes.…”

Heavy iron in large gem diamonds traces deep subduction of serpentinized ocean floor

“…The presence of recycled heavy iron is generally supported by studies of oceanic basalts that identify a heavy iron end-member component in the mantle associated with pyroxenites ( 16 , 47 ), which represent the more fusible and incompatible element–rich constituents derived from subducted oceanic lithosphere. Similarly, heavy iron isotopic signatures in ocean island basalts from Azores, Pitcairn, and Samoa are proposed to be derived from a multiplicity of mechanisms including the incorporation of heavy iron from recycled oceanic lithosphere ( 17 ). Our identification of a very heavy iron component in the altered mantle of subducting slabs was not explicitly considered but nonetheless supports this model.…”

“…The measurements also have implications for mantle iron isotope systematics. Subduction recycling of heavy iron in the form of iron-rich and relatively fusible phases could help explain the longstanding problem of the variable and heavy iron isotopic signatures of oceanic basalts ( 56 Fe ≈ 0.1‰) relative to mantle peridotites and chondrites (both near 0.0‰) (12)(13)(14)(15) by adding to the effects of subduction-related recycling of pyroxenite (16,17).…”