Séminaire ISTeP - Muriel Laubier

(LMV)

Linking the redox state of magmas to that of their mantle source

Arc magmas are more oxidized than mid-ocean ridge magmas, likely because the mantle source region of arc magmas has been modified by a release of oxidized and volatile-rich fluids from the subducting slab. In particular, the migration of Fe-bearing fluids released during serpentine devolatilization to the mantle wedge is likely to result in the oxidation of mantle Fe²⁺ to Fe³⁺. However, it is still up to debate whether the variations in Fe³⁺/ΣFe of magmas from various environments arise due to differences in mantle fO₂ or to differentiation processes in the arc crust such as partial crystallization and degassing. Here our aim is to combine different fO₂ proxies in order to carefully reconstruct mantle source fO₂ from the compositions of melt inclusions and erupted glasses from mid-ocean ridge, hot spot and arc settings. These fO₂ proxies include Fe³⁺/ΣFe measured by micro-X-ray absorption near edge structure (µ-XANES) spectroscopy and trace element proxies that were calibrated experimentally such as V/Sc and V/Yb ratios, Cu, Zn/Fe*.