The origin of ultrahigh pressure peridotites from Western Gneiss Region, Norway inferred from highly siderophile element chemistry

Abstract

The elemental abundance of the primitive mantle is important for uncovering the origin and evolution of the Earth, but the estimates are based entirely on analysis of mantle peridotites from lithosphere formed no earlier than Proterozoic and whether it is representative for early Earth's mantle remains uncertain. In our study, we carried out bulk-rock major, minor, and highly siderophile element concentrations, and Os isotope analyses comprehensively on newly collected peridotite samples from Western Gneiss Region, Norway, where some peridotites show Archean model age and have relict of majoritic garnet. The least mobile elements such as Al and Yb show positive correlations. In addition, some samples show Archean Re depletion model age, and Os isotope ratio positively correlates with Pd/Os. These facts suggest that the samples experienced a common melting event in the Archean and that relatively fertile samples possess the elemental abundance of source mantle. In our presentation, combining these facts with the partitioning behavior of lithophile elements such as Sc and the elemental abundance of S and Cu, which are intimately related to highly siderophile elements, we are going to discuss the depth of the melting and the elemental abundance of source mantle.