0000000000205073
AUTHOR
Herbert Palme
Evidence for fractional condensation and reprocessing at high temperatures in CH chondrites
We performed a detailed study of silica-rich components (SRC) in the paired CH chondrites Acfer 182 and 207. These SRCs appear either as chondrules or fragments, and they contribute <0.1 vol% to the bulk meteorite. They usually contain a silica and a silicate portion. Both portions are, in most cases, cryptocrystalline and have bulk SiO2-concentrations between 65 and 85 wt%. The silicate generally has a pyroxene normative composition. The silica often appears as blebs within the silicate matrix or vice versa. If there are no blebs, silica and silicate still form rounded interfaces. The SRCs are depleted in refractory elements like Ca, Al, and Ti relative to CI. A few SRC- like objects are e…
Are highly siderophile elements (PGE, Re and Au) fractionated in the upper mantle of the earth? New results on peridotites from Zabargad
Abstract Seven peridotite samples from Zabargad Island (Red Sea) were analyzed for highly siderophile elements (HSE), including five platinum-group elements (PGE: Os, Ir, Ru, Rh, Pd) and Re and Au. Petrography and chemical composition of the samples had been published earlier [Kurat, G., Palme, h., Embey-Isztin, A., Touret, J., Ntaflos, T., Spettel, B., Brandstatter, F., Palme, C., Dreibus, G., Prinz, m., 1993. Petrology and geochemistry of peridotites and associated vein rocks of Zabargad Island, Red Sea, Egypt. Mineralogy and Petrology 48, 309–341]. Five samples with chemical compositions typical of upper mantle rocks, from fertile to increasingly depleted mantle (CaO: 3.39 to 0.21%), hav…
Highly siderophile element geochemistry of the Earth's mantle: new data for the Lanzo (Italy) and Ronda (Spain) orogenic peridotite bodies
Abstract Nine plagioclase/spinel lherzolites from the Lanzo (Italy) and Ronda (Spain) peridotite bodies were analysed for Re, Os, Ir, Ru, Rh, Pd, and Au using a high-precision instrumental neutron activation (INA) procedure after NiS fire assay. Our data conform with previous observations that orogenic lherzolite massifs sampled domains of the subcontinental lithospheric mantle (SCLM) displaying a characteristic enrichment of Ru, Rh and Pd (i.e. the light platinum group elements; PGEs) over Os and Ir. The Pd/Ir, Rh/Ir and Ru/Ir ratios are superchondritic and very similar in both suites (2.46±0.32 vs. 2.42±0.21; 0.46±0.07 vs. 0.45±0.10; 1.99±0.14 vs. 2.25±0.25, respectively). Rhenium and gol…
Highly siderophile elements (PGE, Re and Au) in mantle xenoliths from the West Eifel volcanic field (Germany)
Abstract Mantle peridotite xenoliths ranging in modal composition between fertile lherzolites and modally metasomatized harzburgites, and magmatic pyroxenite xenoliths from the West Eifel and Vogelsberg volcanic fields (Germany) have been analyzed for their whole rock major and minor elements, six platinum-group elements PGE (PGE: Os, Ir, Pt, Ru, Rh, Pd), Re and Au, rare earth elements (REE), and several other trace elements (e.g., As, Ta). The bulk rock Ir concentrations range from 0.23 to 9.07 ng/g (total PGE contents range between 43.2 ng/g), exceeding the range previously found in mantle rocks. Two pyroxenite samples show large variabilities in their PGE concentrations, with Ir contents…
Highly siderophile elements (Re, Os, Ir, Ru, Rh, Pd, Au) in impact melts from three European impact craters (Sääksjärvi, Mien, and Dellen): Clues to the nature of the impacting bodies
Twenty-two large (10 g) impact melt samples from three Scandinavian craters (i.e., Saaksjarvi, Finland; and Mien and Dellen, Sweden) were analyzed for highly siderophile elements (HSE: platinum group elements, Rh, and Au) by the nickel sulfide technique in combination with neutron activation. The ten impact melt samples from Saaksjarvi are enriched in Ir and other highly siderophile elements (Ir = 2.48 ± 0.73 ng/g) relative to average upper crust concentrations (0.03 ± 0.02 ng/g Ir). The twelve Dellen and Mien samples are marginally enriched in Ir (0.48 ± 0.23 ng/g for Dellen, and 0.37 ± 0.23 ng/g for Mien). The amount of meteoritic component corresponds to 0.5% of a nominal CI component fo…
Origin of SiO2-rich components in ordinary chondrites
Abstract Silica-rich objects are common minor components in ordinary chondrites (OC), occurring as fragments and as chondrules. Their typical paragenesis is orthopyroxene + SiO 2 (with bulk SiO 2 >65 wt%) and occasionally with additional olivine and/or spinel. Individual silica-rich components (SRC) have previously been studied in various types of OCs, although there is only one comprehensive study of these objects by Brigham et al. [Brigham, C.A., Murrell, M.T., Yabuki, H., Ouyang, Z., El Goresy, A., 1986. Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta 50, 1655–1666]. Several different explanations of how SRCs formed have been published. The main ques…