Platinum-group elements in the Icelandic rift system: melting processes and mantle sources beneath Iceland

摘要: Abstract Thirty new platinum-group element (PGE) analyses of various basalt types from Iceland are presented in this study. The analysed samples divided into three groups based on their Mg-contents, high-Mg tholeiites (10–14 wt.% MgO), composed primitive olivine and picrites, evolved (7–10 MgO) basalts (4–7 consisting FeTi basalts, quartz alkaline basalts. have a range compositions between relatively Cu-rich Pd-poor (120 ppm Cu 6 ppb Pd) end-member Cu-poor Pd-rich (74 17 end-member. There is positive correlation the highly siderophile elements, whereas Pd correlate negatively tholeiite picrite Negative PGEs cannot be reconciled model where two end-members form by varying degrees partial melting common source. sub-primitive mantle Cu/Pd ratio (∼4300) could indicate strongly depleted source, was efficiently retained sulphide, relative to Cu, during previous melt extraction episodes. In models here, composition can approximated 25% source that previously lost normal MORB component (F∼15%). (Cu/Pd∼19000) assuming derivation separate one slightly Cu-enriched undergoing beneath rift. Based variations, majority interpreted mixtures melts derived enriched sources, which consistent with studies Sr–Nd isotopic variations. similar ratios infer latter parental liquids under S-undersaturated conditions. Relatively high low Ir concentrations (∼7 indicate, too, these magmas underwent fractionation accumulated incorporated fractionating assemblage. This contrast group less than 7 MgO PGE contents suggest experienced S-saturation. We propose scenario for generation Icelandic rift zone, picritic magma generated mantle, forms as well It proposed domains were exhausted at depth since products absent most uppermost part central region. around 11–12% triangular regime zone. reflect efficient collection deepest distal parts triangle. contrast, represent degree (F∼25%) without incorporation batches