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Dislocation-related defects in minerals govern globally important rheological processes such as mantle convection in the deep Earth where dislocation creep is a common deformation mechanism of the constituent minerals. Understanding such processes requires the direct observation of individual dislocations in minerals and across their interfaces. Using electron channelling contrast imaging (ECCI) in a conventional field-emission scanning electron microscope (FE-SEM), we successfully observed individual dislocations in experimentally deformed polycrystalline ferropericlase as well as in natural olivine without special surface treatments to highlight dislocations such as oxidation decoration or chemical etching. Combining backscattered electron (BSE) imaging with electron backscatter diffraction (EBSD) techniques, we refined the two-beam condition of a Kikuchi band at the Bragg orientation to maximize the visibility of individual dislocations with a particular Burgers vector. The dislocation microstructures of progressive subgrain rotation as dominant recrystallization mechanism and the co-activation of two non-coplanar slip systems are demonstrated in ferropericlase and olivine, respectively. Inclined dislocations in olivine are also visualized in end-on view in ECCI. Orientation optimized ECCI in a FE-SEM may serve as an alternative to diffraction contrast imaging in transmission electron microscopy. ECCI shows promise as a non-destructive imaging of individual dislocations of rock-forming minerals.

The concentration of sulfur that can be dissolved in a silicate liquid is of fundamental importance because it is closely associated with several major Earth-related processes. Considerable effort has been made to understand the interplay between the effects of silicate melt composition and its capacity to retain sulfur, but the dependence on pressure and temperature is mostly based on experiments performed at pressures and temperatures below 6 GPa and 2073 K. Here we present a study of the effects of pressure and temperature on sulfur content at sulfide saturation of a peridotitic liquid. We performed 14 multi-anvil experiments using a peridotitic starting composition, and we produced 25 new measurements at conditions ranging from 7 to 23 GPa and 2173 to 2623 K. We analyzed the recovered samples using both electron microprobe and laser ablation ICP-MS. We compiled our data together with previously published data that were obtained at lower P-T conditions and with various silicate melt compositions. We present a new model based on this combined data set that encompasses the entire range of upper mantle pressure-temperature conditions, along with the effect of a wide range of silicate melt compositions. Our findings are consistent with earlier work based on extrapolation from lower-pressure and lower-temperature experiments and show a decrease of sulfur content at sulfide saturation (SCSS) with increasing pressure and an increase of SCSS with increasing temperature. We have extrapolated our results to pressure-temperature conditions of the Earth’s primitive magma ocean, and show that FeS will exsolve from the molten silicate and can effectively be extracted to the core by a process that has been termed the “Hadean Matte.” We also discuss briefly the implications of our results for the lunar magma ocean.

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