The Zircon-Bearing Chromitites of the Phlogopite Peridotite of Finero (Ivrea Zone, Southern Alps): Evidence and Geochronology of a Metasomatized Mantle Slab

The phlogopite peridotite unit of the Finero Complex is a restitic harzburgite that records two metasomatic events. The first event is related to the intrusion of basaltic magma, which reacted with the pyroxene of the host harzburgite to produce chromitite pods with dunite haloes. It also produced secondary clinopyroxene and amphibole in the harzburgite and enriched harzburgite in Na and the light rare earth elements. The second metasomatic event is related to the later intrusion of clinopyroxenitic dykes. During this event, water-rich vapour penetrated the harzburgite along fractures and reacted with it to form phlogopite, thus enriching the rock in K. Chromitites host zircons that yield an age for the first metasomatic event of 207·9 + 1·7/−1·3 Ma, during which time extensional tectonics prevailed in the Southern Alps.