Metal transport in mantle-derived magmas: New insights from natural samples, numerical modeling and experimental data

Séminaire de Antoine Benard (Laboratoire Magmas et Volcans)

There is a complex interplay between physicochemical conditions, volatile elements and metal transport in mantle-derived magmas. Of particular interest is the key role played by redox conditions on controlling the stability and solubility of phases formed from multivalent chalcophile elements (e.g. sulfur), which ultimately trap metals. In this talk, I will first present new analytical results on arc and intraplate magmatic systems, using vaious whole-rock and in situ geochemical technique. The data show that there is a critical dearth in some platinum-group elements (PGEs) in arc magmas, which is inconsistent with their putative oxidized nature inferred from sub-arc mantle peridotites. This can only be explained by the formation of phases trapping PGEs at the early stages of arc magma evolution. In the intraplate context, rare alkaline magmas formed on the ocean floor can record those early stages of evolution. Notably, intra-oceanic magmas record the formation of high-temperature salts, which capture several critical metals from the magma, including PGEs. Finally, I will show the results of recent ex situ (piston-cylinder) and in situ (synchrotron) experiments investigating those processes. Experimental products reveal the complexation between oxidized species of multivalent volatiles in magmas, as well as rapid reaction and solubilization of metals in high-temperature salts. Taken together, the results of this research unravel new processes of metal transport in magmas, which will also help in targeting critical resources for the energy transition.