Search results for "chondrite"
showing 10 items of 25 documents
Aluminium distribution in an Earth's non–primitive lower mantle
2020
The aluminium incorporation mechanism of perovskite was explored by means of quantum mechanics in combination with equilibrium/off-equilibrium thermodynamics under the pressure-temperature conditions of the Earth's lower mantle (from 24 to 80 GPa). Earth's lower mantle was modelled as a geochemically non-primitive object because of an enrichment by 3 wt% of recycled crustal material (MORB component). The compositional modelling takes into account both chondrite and pyrolite reference models. The capacity of perovskite to host Al was modelled through an Al2O3 exchange process in an unconstrained Mg-perovskite + Mg-Al-perovskite + free-Al2O3(corundum) system. Aluminium is globally incorporate…
Formation of refractory metal nuggets and their link to the history of CAIs
2015
Abstract Ca, Al-rich inclusions (CAIs) often contain numerous refractory metal nuggets (RMNs), consisting of elements like Os, Ir, Mo, Pt and Ru. The nuggets are usually thought to have formed by equilibrium condensation from a gas of solar composition, simultaneously with or prior to oxide and silicate minerals. However, the exact mechanisms responsible for their extremely variable compositions, small sizes and associations with CAI minerals remain puzzling. Expanding on previous work on chemically separated RMNs, we have studied a large number of RMNs within their host CAIs from three different meteorite types, i.e., the highly primitive chondrite Acfer 094 (C2-ungrouped), Allende (CV3 ox…
Composition and clues to the origin of refractory metal nuggets extracted from chondritic meteorites
2014
Refractory metal nuggets (RMNs) contain elements, such as Os, Ir, Mo, and Ru, which are predicted to condense from a cooling gas of solar composition simultaneously with CAI-minerals. Berg et al. (2009) identified a large number of RMNs in acid-resistant residues of the Murchison meteorite and suggested that they are pristine condensates. In extending the work of these authors, we have improved the chemical extraction process to enrich the concentration of RMNs in the residue sample and prepared three additional RMN-rich residues from the chondritic meteorites Murchison, Allende, and Leoville. The results show that, while their origin is clearly solar, the compositions in detail of RMNs fro…
The Evolution of Individuality at the Molecular and Protocellular Levels
1984
The most important bioelements (= organoelements) hydrogen, carbon, oxygen and nitrogen, are also the most abundant elements throughout the Universe besides helium, neon, and silicon (Fig, 1). In the Universe carbon is about four times as abundant as silicon. Certainly, the abundance of elements in various celestial bodies may vary greatly depending on the history of these celestial bodies.
Evidence for fractional condensation and reprocessing at high temperatures in CH chondrites
2003
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…
Constraints on Earth accretion deduced from noble metals in the oceanic mantle
1998
If the Earth's mantle were in equilibrium with its core, the mantle would contain three orders of magnitude less of the noble metals (platinum-group elements Pt, Os, Ir, Ru, Pd and Rh, plus Au and Re) than are observed. An explanation put forward to account for this disparity has been that the last 1% of the Earth's accretion occurred after the iron-rich core had separated from the mantle1,2. Recent debate has accordingly centred on which meteorite class or classes made up this ‘late veneer’ of accretion3. Here we present analyses of noble-metal concentrations in oceanic peridotites (plutonic rocks which are thought to represent samples of the Earth's upper mantle). We find that the average…
Are highly siderophile elements (PGE, Re and Au) fractionated in the upper mantle of the earth? New results on peridotites from Zabargad
2000
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
2000
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…
Chemical abundances determined from meteor spectra II. Evidence for enlarged sodium abundances in meteoroids
2004
9 pages, 5 figures.-- Printed version published Mar 2004.
DIRECT EVIDENCE FOR CONDENSATION IN THE EARLY SOLAR SYSTEM AND IMPLICATIONS FOR NEBULAR COOLING RATES
2009
We have identified in an acid resistant residue of the carbonaceous chondrite Murchison a large number (458) of highly refractory metal nuggets (RMNs) that once were most likely hosted by Ca,Al-rich inclusions (CAIs). While osmium isotopic ratios of two randomly selected particles rule out a presolar origin, the bulk chemistry of 88 particles with sizes in the submicron range determined by energy dispersive X-ray (EDX) spectroscopy shows striking agreement with predictions of single-phase equilibrium condensation calculations. Both chemical composition and morphology strongly favor a condensation origin. Particularly important is the presence of structurally incompatible elements in particl…