The influence of FeO on the solubilities of cobalt and nickel in silicate melts

摘要: Abstract The effect of iron on the solubilities Co and Ni in silicate melts was determined at a wide range oxygen fugacities (from 10 −8.1 to −12.6 atm) temperatures ranging from 1305–1600°C. Four different systems were studied. In system A an FeO-free anorthite diopside eutectic composition equilibrated with pure Co- or Ni-metal. B same starting material FeCoNi-alloys. C D, FeO-containing silicates (basaltic komatiite) metal (system C) FeCo- FeNi-alloys D). Experiments below 1450°C performed by equilibrating loops silicates; higher temperature well mixed powder alumina crucibles. Concentrations some alloys neutron activation analysis; most alloy compositions analyzed electron microprobe. At constant (1400°C) but variable fugacities, Co, Ni, Fe metal/silicate partition coefficients calculated increase decreasing fugacities. extent suggests that all three metals are dissolved as oxides (CoO, NiO, FeO) melt. No evidence for presence metallic major species melt found within fugacity covered experiments, even log units Fe-FeO equilibrium (IW-3). minor fraction (below 20%) may be present reducing experiments. difference solubility silicates. Depending decrease slightly increasing along appropriate core formation, 2.3 (IW-2.3). experiments confirm relatively high present-day upper mantle concentrations particular chondritic Ni/Co ratio cannot explained between coreforming Earth's low pressure environment 4000°C, thus supporting models inhomogeneous accretion Earth. Accumulation differentiated planetesimals, i.e., cores, building blocks Earth can also excluded. these bodies metal-silicate equilibration would have occurred pressures cores accreting planetesimals is unlikely. Homogeneous only possible if lower minerals liquid forming during differentiation Earth, relevant sufficiently high. Mg-wustite Mg-perovskite not known.