Generation of metal-rich felsic magmas during crustal anatexis

Abstract

We show that partial melting of a preexisting mineral deposit during regional anatexis is likely to lead to incorporation of sulfide melt into silicate melt. Simple dissolution of metals in silicate melt during anatexis leads to minor metal addition to escaping magma, but physical entrainment of sulfide melt can lead to extreme enrichment and higher total metal incorporation. Metal enrichment is enhanced if melt segregation is structurally driven; only dissolved metal is incorporated if initial segregation is driven by buoyancy alone. However, once encapsulated within a larger volume of silicate melt, immiscible globules of sulfide melt are physically carried by buoyantly rising magma. Gradual dissolution of entrained sulfide melt globules is expected as the silicate magma migrates from the lower crust. This process may lead to significant variations in metal contents of silicate magmas above regions that underwent anatexis.