Transient mantle–crust interaction restores porphyry copper–molybdenum fertility during continental collision

Porphyry copper–molybdenum deposits are typically linked to subduction, yet some of the largest form during continental collision. Here, we investigate when mantle processes become effectively coupled to the crust to enable large-scale metal transfer. We combine seismic imaging with zircon and apatite mineral chemistry and whole-rock isotopes from southeastern Iran, where metal-poor and metal-rich magmas formed in the same crustal region. Despite similar mantle sources, fertile magmas show higher oxidation state (more oxidising conditions relative to a standard mineral buffer), higher melt sulphur contents (greater than 100 micrograms per gram), and signatures of deep, high-pressure differentiation (strontium to yttrium ratios above 40). These changes coincide with evidence for lateral inflow of hot mantle material. We interpret this as a transient transfer of heat and oxidising, volatile-rich components into the crust, destabilising sulphide minerals and releasing copper and molybdenum. Porphyry formation in collision zones, therefore, reflects short-lived thermochemical coupling rather than persistent mantle enrichment. Fertile porphyry systems formed when mantle heating increased magma oxidation, Sulphur and water, thereby mobilising lower crust metals without mantle enrichment, as shown by linking seismic images with zircon, apatite and whole rock geochemistry