Composite Melt–Rock Interactions in the Lowermost Continental Crust: Insights from a Dunite–Pyroxenite–Gabbronorite Association of the Mafic Complex from the Ivrea–Verbano Zone (Italian Alps).

This article focuses on the petrological and geochemical study of the Monte Mazzucco dunite–pyroxenite–gabbronorite association within the Permian Mafic Complex of the Ivrea–Verbano Zone, Italian Alps, to elucidate magmatic underplating processes in deep continental crust. The study reveals that the ~60 m thick dunite lens underwent pervasive reactive melt percolation and two major melt–rock interaction events: (1) focused reactive infiltration of hydrous mantle-derived melts forming magmatic veins (hornblende lherzolite, olivine hornblendite, and hornblende websterite) within the dunites, and (2) development of a websterite ring around the dunite lens through reaction with an invading, evolved, H2O-poor melt that had experienced plagioclase fractionation and likely crustal contamination. The enclosing gabbronorites and associated contact zone rocks represent crystallization products of chemically evolved melts that sealed the magmatic evolution of the sequence. These findings highlight the importance of melt–rock reactions and dynamic deformation in the lithological differentiation of underplated continental crust in extensional tectonic settings.