Distribution of gold, palladium, platinum, rhodium, ruthenium, and iridium in Leg 115 hotspot basalts: implications for magmatic processes

Abstract

A comparison of 50 basalts recovered at Sites 706, 707, 713, and 715 along the Reunion hotspot trace shows that seafloor alteration had little effect on noble metal concentrations (Au, Pd, Pt, Rh, Ru, and Ir), determined by inductively coupled plasma-mass spectrometry (ICP-MS), which generally tend to decrease with magma evolution. Their compatible-element behavior may be related to the precipitation of Ir-Os-based alloys, chromite, sulfides, and/or olivine and clinopyroxene in some combination. The simplest explanation indicates silicate control of concentrations during differentiation. Basalts from the different sites show varying degrees of alkalinity. Noble metal abundances tend to increase with decreasing basalt alkalinity (i.e., with increasing percentages of mantle melting), indicating that the metals behave as compatible elements during mantle melting compared with basalts from some other ocean basins, may reflect fundamental primary variations in upper-mantle noble metal abundances. -from Authors