Rhenium systematics in submarine MORB and back-arc basin glasses: laser ablation ICP-MS results

Abstract

Rhenium and other trace elements, including the moderately chalcophile elements Mo and Cu, were determined for 37 submarine basaltic glasses from the Lau and Coriolis Troughs (CT) back-arc basins and Woodlark marginal basin, as well as 30 mid-ocean ridge basalt (MORB) glasses from the Pacific and Atlantic Oceans, using laser ablation ICP-MS. Rhenium is strongly positively correlated with Yb for all these submarine basaltic glasses. Enriched (E-) and normal (N-) MORB as well as King's Triple Junction samples show similar correlations with constant Yb/Re ratios, indicating that Re and Yb exhibit similar compatibility during melt evolution [Chem. Geol. 139 (1997) 185]. In contrast, samples from the East and Central Lau Spreading Centers have much higher ratios compared with MORB samples and form steeper arrays on Re–Yb variation diagrams, similar to komatiites. More incompatible element-depleted samples including those from the Lau and Woodlark Basin spreading centers and the more depleted (D-) MORB samples are also distinguished from E- and N-MORB and samples from King's Triple Junction and Coriolis Troughs Basin on the basis of their higher Cu/Re ratios. These observed elemental systematics are interpreted to reflect progressive melting of depleted mantle, where previous melting events result in the elimination of sulfides in the source regions of the depleted samples. Using the determined Yb/Re and Ce/Mo ratios and assuming that the abundances of Yb and Ce are 10% and 40% reduced in the DMM compared to the primitive mantle (PM), average concentrations of 0.12 ppb for Re and 34 ppb for Mo are estimated for the DMM. The partition coefficients of the analysed moderately incompatible elements are in the order of Mo<Ce<Re<Yb for the depleted samples (no residual sulfide), while for those that were derived from sources with residual sulfide, the order is Mo=Ce<Yb=Re.