The mantle source of basalts from Reunion Island is not more oxidized than the MORB source mantle

Edward Stolper,John Eiler,Maryjo Brounce

doi:10.1007/s00410-021-01870-w

Abstract

Glasses quenched from relatively undegassed ocean island magmas erupted from volcanoes at Iceland, Hawaii, the Canary Islands, and Erebus have elevated Fe3+/∑Fe ratios compared to glasses quenched from mid-ocean ridge basalts. This has been ascribed to elevated fO2 of their mantle sources, plausibly due to subducted, oxidized near-surface-derived components in their mantle sources. The basaltic magmas from Reunion Island in the Indian ocean have Sr–Nd-Hf-Pb-Os isotopic compositions suggesting that their mantle sources contain little or no subducted near-surface materials and contain the C/FOZO/PREMA mantle component. To constrain the fO2 of the C/FOZO/PREMA mantle component and test the link between oxidized OIB and recycled surface-derived materials in their sources, we measured major and volatile element abundances and Fe3+/∑Fe ratios of naturally glassy, olivine-hosted melt inclusions from Piton de La Fournaise volcano, La Reunion. We conclude that the fO2 of the mantle source of these Reunion lavas is lower than of the mantle sources of primitive, undegassed magmas from Hawaii, Iceland, the Canary Islands, and Mt. Erebus, and indistinguishable from that of the Indian-ocean upper mantle. This finding is consistent with previous suggestions that the source of Reunion lavas (and the C/FOZO/PREMA mantle component) contains little or no recycled materials and with the suggestion that recycled oxidized materials contribute to the high fO2 of some other OIBs, especially those from incompatible-element-enriched mantle sources. Simple mixing models between oxidized melts of EM1 and HIMU components and relatively reduced melts of DMM can explain the isotopic compositions and Fe3+/∑Fe ratios of lavas from Hawaii, Iceland, the Canary Islands, and Mount Erebus; this model can be tested by study of additional OIB magmas, including those rich in the EM2 component.

Highlights

As discussed above, many factors can influence the fO2 levels of the mantle sources of basaltic magmas, in this final section, we extend the modeling by Jackson et al (2020) of source mixing to include their Fe3+/ΣFe ratios
MORB, in contrast to the recent suggestion that all ocean island basaltic magmas are more oxidized than MORB (e.g., Moussallam et al 2019)
The least degassed inclusions are used to reconstruct the fO2 of the primary magmas from which they were derived, at the mantle conditions under which they likely equilibrated with their mantle sources; this reconstruction suggests that the mantle sources of the 2005 Piton de la Fournaise eruption had fO2 levels corresponding to ΔQFM0.1 ± 0.1

Summary

Introduction

Exceed those of subduction zone magmas (Fig. 1a; e.g., arc basalts ~ 0.28; Brounce et al 2014) This range in OIBs is sometimes recorded in samples from the same volcano, from the same island, and/or island group (Brounce et al 2017; Moussallam et al 2014; Shorttle et al 2015; Novella et al 2020), and even from the same eruption (Hartley et al 2017; Helz et al 2017). The higher fO2s of relatively undegassed glasses from ocean island basalts (OIBs) relative to MORB glasses have been interpreted as having been inherited from their mantle sources and attributed to the presence of recycled surface-derived and oxidized materials in their mantle sources (Brounce et al 2017; Hartley et al 2017; Helz et al 2017; Moussallam et al 2014, 2016, 2019; Shorttle et al 2015; Novella et al 2020)

Methods

Results

Conclusion