Highly siderophile element geochemistry of 187Os-enriched 2.8 Ga Kostomuksha komatiites, Baltic Shield

摘要: Abstract New analyses of highly siderophile elements (HSE; Re, Os, Ir, Ru, Pt, and Pd) obtained by Carius tube digestion isotope dilution inductively coupled plasma mass-spectrometry (ID-ICPMS) technique are reported for 187Os-enriched 2.8 Ga komatiites from the Kostomuksha greenstone belt. As a result significant improvement in yield over our previous digestions NiS fire-assay technique, these have now been shown to contain 22 25% more Pt 34% Ru. The emplaced komatiite lavas at thus had element abundances comparable those Abitibi discrepancies observed between two techniques interpreted be incomplete HSE carriers (particularly chromite) during procedure. Our results UB-N peridotite reference material agree well with high-pressure ashing ID-ICPMS literature. Two types distinguished this study based on IPGE (Os, Ru) behavior lava differentiation. type is unique characterized an incompatible IPGEs, bulk solid-liquid partition coefficients IPGEs being close olivine. Cumulate zones occupy 20% total thickness flows. calculated indicate that, as other Munro-type lavas, cumulate contained IPGE-rich minor phase(s) addition non-CI chondritic pattern source here similar that average depleted spinel lherzolite (ADSL) supports hypothesis composition Earth’s mantle. absolute demonstrated komatiites, even though contrast their Os isotopic compositions. This earlier if core-mantle interaction produced 187Os/188Os radiogenic signature source, it must occurred form exchange boundary. Other explanations similarly constrained conserve elemental abundance mantle komatiites.