Oxidation of La Reunion lavas with MORB-like fO2 by assimilation

Oxygen fugacity (fO(2)) is poorly constrained in mantle reservoirs, especially those sampled by ocean island basalts (OIBs). This is partly due to complications from secondary processes acting on fO(2) in OIB parental magmas. To investigate these issues insitu trace element data of olivine in lavas from the island of La Reunion are reported. La Reunion lavas are useful for examining post-melting modification due to their limited range in isotopic signatures, indicating a largely homogenous mantle source.Vanadium abundances in olivine were used to constrain the lava fO(2) to between +0.2 and +1.5 Delta FMQ, intermediate between that of mid-ocean ridge basalts (MORBs) and other OIBs. The variable fO(2) of Reunion lavas results from assimilation processes within the volcanic edifice, and not source heterogeneity. The Reunion mantle plume likely has fO(2) similar to that of MORB, despite isotopic evidence for the plume sampling an early-formed isolated mantle reservoir. Assimilation processes can have a pronounced effect on lava fO(2) and should always be accounted for when constraining mantle redox.

Automated summary

The oxygen fugacity (fO(2)) in mantle reservoirs is poorly constrained, and this study focuses on the investigation of fO(2) in ocean island basalts (OIBs). By analyzing trace elements in olivine of lavas from La Reunion island, it is found that the variable fO(2) in Reunion lavas is a result of assimilation processes within the volcanic edifice rather than source heterogeneity. It suggests that the Reunion mantle plume likely has fO(2) similar to that of mid-ocean ridge basalts (MORBs), despite isotopic evidence for the plume sampling an early-formed isolated mantle reservoir.