Fluxing of mantle carbon as a physical agent formetallogenic fertilization of the crust

Magmatic systems play a crucial role in enriching the crust with volatiles and elements thatreside primarily within the Earth’s mantle, including economically important metals like nickel,copper and platinum-group elements. However, transport of these metals within silicatemagmas primarily occurs within dense sulfide liquids, which tend to coalesce, settle and notbe efficiently transported in ascending magmas. Here we show textural observations, backedup with carbon and oxygen isotope data, which indicate an intimate association betweenmantle-derived carbonates and sulfides in some mafic-ultramafic magmatic systemsemplaced at the base of the continental crust. We propose that carbon, as a buoyantsupercritical CO2fluid, might be a covert agent aiding and promoting the physical transport ofsulfides across the mantle-crust transition. This may be a common but cryptic mechanismthat facilitates cycling of volatiles and metals from the mantle to the lower-to-mid continentalcrust, which leaves little footprint behind by the time magmas reach the Earth’s surface.