No abstract

No abstract

No abstract

The crust shows large variations in Cu isotopic composition (δ 65 Cu relative to NIST 976) resulting from redox reactions and other supergene processes. The significant range of δ 65 Cu in mantle peridotites thus could be ascribed to recycled crustal materials and/or oxidative mantle metasomatism. However, the influence of normal magmatic fractionation processes on δ 65 Cu variations remains poorly understood, and it is unclear whether the magmatic processes also lead to large δ 65 Cu variations in mantle rocks. To address the issue, we present bulk-rock δ 65 Cu of fresh mantle pyroxenites from the Balmuccia peridotite massif, Northern Italy. These pyroxenites formed by melt-peridotite reaction and mineral accumulation from MORB-to OIB-like, sulfide-saturated basic magmas. Mass balance calculations show that sulfide phases host >98 wt % of the Cu budget of bulk rocks (87−484 μg/g). The pyroxenites show significant variations of δ 65 Cu from −0.66‰ to 0.66‰, which cover the range known for peridotites, including metasomatized ones. Three subsamples from the same pyroxenite layer display >0.3‰ decrease in δ 65 Cu with progressive differentiation. Nevertheless, δ 65 Cu does not display correlations with indicators of magmatic differentiation (e.g., Mg# and Cu/Pd) for all pyroxenites in this study. This might be attributed to variable extents of magmatic sulfide segregation for different samples and/or varying δ 65 Cu of the pyroxenite parent magmas, which were also affected by reactive migration through peridotites. The combined processes can change δ 65 Cu of evolving magmas and reacted peridotites and lead to Cu isotopic heterogeneity in the mantle, without involvement of oxidative metasomatism or recycled crustal materials.

No abstract