Oxidising agents in sub-arc mantle melts link slab devolatilisation and arc magmas

Antoine Benard (1) , Kevin Klimm (2) , Alan B. Woodland (2) , Richard J. Arculus (3) , Max Wilke (4) , Roman E. Botcharnikov (5) , Nobumichi Shimizu (6) , Oliver Nebel (7) , Camille Rivard (8) , Dmitri Ionov (9)

1 Institute of Earth Sciences, Lausanne
2 Institut für Geowissenschaften [Frankfurt am Main]
3 ANU - Australian National University
4 University of Potsdam = Universität Potsdam
5 Leibniz Universität Hannover=Leibniz University Hannover
6 WHOI - Woods Hole Oceanographic Institution
7 Monash University, Clayton
8 SSOLEIL - Synchrotron SOLEIL
9 Géosciences Montpellier

Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42− in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/∑Fe in spinel record a S6+–Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and δ34S (+ 7 to + 11‰), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas.

Domaines: Géochimie; Milieux et Changements globaux

Antoine Benard, Kevin Klimm, Alan B. Woodland, Richard J. Arculus, Max Wilke, et al.. Oxidising agents in sub-arc mantle melts link slab devolatilisation and arc magmas. Nature Communications, 2018, 9, pp.3500. ⟨10.1038/s41467-018-05804-2⟩. ⟨hal-01992903⟩