Partial re-equilibration of highly siderophile elements and the chalcogens in the mantle: A case study on the Baldissero and Balmuccia peridotite massifs (Ivrea Zone, Italian Alps)

Replacive dunites at Balmuccia have low abundances of Re, Au, Pd and chalcogens, but variable and higher abundances of Os, Ir and Ru, high S/Se and Se/Te, yet 187Os/188Os similar to BM lherzolites. The residual HSE and chalcogen compositions differ from those in dunites of subduction-related ophiolites. The composition and contact relations of the BM dunites with the host rocks likely reflect focused flow of sulfur-undersaturated melt after open system melting and re-equilibration of the lherzolites. The compositional record of the Balmuccia massif thus reflects the composition of different types of melts and their interaction with the peridotites at different P-T conditions.