Electrochemical measurements and thermodynamic calculations of redox equilibria in pallasite meteorites: Implications for the eucrite parent body

The intrinsic oxygen fugacity (IOF) of olivine separates from the Salta, Springwater, and Eagle Station pallasites was measured between 850 and 1150[deg]C using oxygen-specific solid zirconia electrolytes at 105 Pa. The experimental apparatus consisted of a double-opposed electrolyte configuration with a CO-CO2 gas-mix bridging atmosphere. Four initial IOF measurements on Salta olivines revealed the effects of grain size and cell memory on experimental results; experiments with an IW cell memory and fine grain size (log fO2), contains Fa12.5 and Fe90.5Ni9.0; Springwater, of intermediate redox state (~IW), contains Fa18.0 and Fe87.5Ni12.1; Eagle Station, the most oxidized sample (IW + 0.5 logfO2), contains Fa20.5 and Fe85.0Ni14.6. Electron microbeam characterization of the starting materials and run products from these experiments have shown that olivine is the only phase present. Thermodynamic calculations of redox equilibria involving equilibrium pallasite assemblages are in good agreement with our experimental results and provide a lower limit to pallasite redox stability; others involving disequilibrium assemblages, suggest that pallasites experienced localized, late-stage oxidation and reduction effects. Consideration of the redox buffer metal-olivine-orthopyroxene utilizing calculated Eucrite Parent Body (EPB) mantle phase compositions indicates that small redox gradients may have existed in the EPB. Such gradients may have produced strong compositional variation within the EPB. In addition, there is apparently significant redox heterogeneity in the source area of Eagle Station Trio (EST) pallasites and Bocaiuva iron meteorites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28556/1/0000358.pd

A 'Mesosiderite' rock from northern Siberia, Russia: not a meteorite

A possible mesosiderite meteorite was found in the area of the Putorana Plateau, Noril'sk district, Siberia, Russia. Although this rock resembles a mesosiderite in its hand-sample aspect and in having Ni-bearing iron metal, it is not a meteorite. This inference is based on the lack of a fusion crust, the lack of cosmogenic nuclides, oxygen with terrestrial isotope ratios, and several mineral chemical criteria. Most likely, the rock is from the iron-metal-bearing basalts of the Siberian Trap basalt sequence, which are mined for their base and platinum-group metals. Mesosiderite imposters like this may be recognized by: (1) the presence of Cu metal in hand sample or as microscopic blebs in the low-Ni metal (kamacite), (2) the absence of high-Ni metal (taenite), and (3) the presence of iron carbide (cohenite) enclosing the kamacite. Even if these macroscopic tests are inconclusive, isotopic and mineral chemical tests will also distinguish rocks like this from mesosiderites

Chemistry of the Calcalong Creek lunar meteorite and its relationship to lunar terranes

The Calcalong Creek lunar meteorite is a polymict breccia that contains clasts of both highlands and mare affinity. Reported here is a compilation of major, minor, and trace element data for bulk, clast, and matrix samples determined by instrumental neutron activation analysis (INAA). Petrographic information and results of electron microprobe analyses are included. The relationship of Calcalong Creek to lunar terranes, especially the Procellarum KREEP Terrane and Feldspathic Highlands Terrane, is established by the abundance of thorium, incompatible elements and their KREEP-like CI chondrite normalized pattern, FeO, and TiO2. The highlands component is associated with Apollo 15 KREEP basalt but represents a variant of the KREEP-derived material widely found on the moon. Sources of Calcalong Creek's mare basalt components may be related to low-titanium (LT) and very low-titanium (VLT) basalts seen in other lunar meteorites but do not sample the same source. The content of some components of Calcalong Creek are found to display similarities to the composition of the South Pole-Aitken Terrane. What appear to be VLT relationships could represent new high aluminum, low titanium basalt types.The Meteoritics & Planetary Science archives are made available by the Meteoritical Society and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202