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Mantle plumes are oxidised

DOI: 10.1016/j.epsl.2019.115798 DOI Help

Authors: Yves Moussallam (University of Cambridge) , Marc-antoine Longpré (Queens College, City University of New York) , Catherine Mccammon (Bayerisches Geoinstitut, University of Bayreuth) , Alejandra Gomez-ulla (Université Clermont Auvergne, CNRS) , Estelle F. Rose-koga (Université Clermont Auvergne, CNRS) , Bruno Scaillet (Université d'Orléans-CNRS-BRGM) , Nial Peters (University of Cambridge) , Emanuela Gennaro (stituto Nazionale di Geofisica e Vulcanologia) , Raphael Paris (Université Clermont Auvergne, CNRS) , Clive Oppenheimer (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Earth And Planetary Science Letters , VOL 527

State: Published (Approved)
Published: December 2019
Diamond Proposal Number(s): 17250

Abstract: From oxic atmosphere to metallic core, the Earth's components are broadly stratified with respect to oxygen fugacity. A simple picture of reducing oxygen fugacity with depth may be disrupted by the accumulation of oxidised crustal material in the deep lower mantle, entrained there as a result of subduction. While hotspot volcanoes are fed by regions of the mantle likely to have incorporated such recycled material, the oxygen fugacity of erupted hotspot basalts had long been considered comparable to or slightly more oxidised than that of mid-ocean ridge basalt (MORB) and more reduced than subduction zone basalts. Here we report measurements of the redox state of glassy crystal-hosted melt inclusions from tephra and quenched lava samples from the Canary and Cape Verde Islands, that we can independently show were entrapped prior to extensive sulphur degassing. We find high ferric iron to total iron ratios (Fe3+/∑Fe) of up to 0.27–0.30, indicating that mantle plume primary melts are significantly more oxidised than those associated with mid-ocean ridges and even subduction zone. These results, together with previous investigations from the Erebus, Hawaiian and Icelandic hotspots, confirm that mantle upwelling provides a return flow from the deep Earth for components of oxidised subducted lithosphere and suggest that highly oxidised material accumulates or is generated in the lower mantle. The oxidation state of the Earth's interior must therefore be highly heterogeneous and potentially locally inversely stratified.

Journal Keywords: oxygen fugacity; degassing; XANES; melt inclusions; mantle plumes

Subject Areas: Earth Science

Instruments: I18-Microfocus Spectroscopy