Phlogopite and K-richterite constitute important carrier phases for H and F in Earth's lithosphere and mantle. The relative importance depends on their stabilities at high pressure and temperature, which in turn depends on bulk composition. Most previous experimental studies focused on the thermal stability of phlogopite and K-richterite were conducted using simplified chemical compositions. Here, partial melting experiments on metasomatized and carbonated, OH ± F-bearing near-natural peridotite were performed at high pressures (2 and 5 GPa) and temperatures (1,100–1,350°C) to assess the thermal stability of F-free versus F-bearing phlogopite and K-richterite. Experimental results demonstrate that the thermal stability of F-bearing phlogopite is increased by >55°C/wt.% F, relative to F-free phlogopite, whereas K-richterite is absent in all experiments with significant degrees of melting (>2%). The thermal stability of phlogopite containing several wt.% F exceeds continental and oceanic geotherms within the upper 150 km. Fluorine-rich phlogopite would therefore be stable in virtually all of the continental lithosphere, only to be decomposed during large, regional melting events such as continental break-up, thereby acting as a major long-term sink for F and/or H. This could even be the case for the oceanic asthenosphere, depending on the oceanic geotherm of the area of interest.

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The processes responsible for the isotopic compositions and abundances of volatile elements in the early solar system remain highly debated. Orders of magnitude variation of (highly) volatile elements exist between different magmatic iron meteorite groups, but it is unclear to what extent their depletions can be explained by evaporation from metal melts during parent body accretion and/or subsequent break up. To this end, we present 86 new evaporation experiments with the aim of constraining the volatility of most volatile metals from metallic melts. The results confirm the previously proposed important effects of S in metal melt on the volatility of the elements of interest governed by their S-loving or S-phobic behavior. Nominally S-loving elements In, Sn, Te, Pb and Bi are significantly more volatile in Fe melt relative to FeS liquid, whereas nominally S-avoiding elements Ga and Sb are more volatile in FeS liquid relative to Fe melt, at a given pressure and temperature. The newly derived volatility sequences for S-free/poor and S-rich metallic melts were also compared with commonly used volatility models based on condensation temperatures. The results indicate significant differences between the latter, including the much more volatile behavior of Te, relative to Se, in both explored bulk compositions, which are traditionally assumed to be equally volatile. The (minimum) degree of volatile element depletion due to evaporation was quantified using the new experimental results and models. A comparison between the volatile element depletions in magmatic iron meteorites and the predicted depletions appropriate for evaporation from Fe melts shows that the latter depletions can be easily reconciled with (an) evaporation event(s). Altogether, the new data and models will provide an important framework when more accurate and precise estimates of magmatic iron meteorite bulk volatile element contents are available.@en

The formation of the Moon is thought to be the result of a giant impact between a Mercury-to-proto-Earth-sized body and the proto-Earth. However, the initial thermal state of the Moon following its accretion is not well constrained by geochemical data. Here, we provide geochemical evidence that supports a high-temperature origin of the Moon by performing high-temperature (1973–2873 K) metal-silicate partitioning experiments, simulating core formation in the newly-formed Moon. Results indicate that the observed lunar mantle depletions of Ni and Co record extreme temperatures (>2600–3700 K depending on assumptions about the composition of the lunar core) during lunar core formation. This temperature range is within range of the modeled silicate evaporation buffer in a synestia-type environment. Our results provide independent geochemical support for a giant-impact origin of the Moon and show that lunar thermal models should start with a fully molten Moon. Our results also provide quantitative constraints on the effects of high-temperature lunar differentiation on the lunar mantle geochemistry of volatile, and potentially siderophile elements Cu, Zn, Ga, Ge, Se, Sn, Cd, In, Te and Pb. At the extreme temperatures recorded by Ni and Co, many of these elements behave insufficiently siderophile to explain their depletions by core formation only, consistent with the inferred volatility-related loss of Cr, Cu, Zn, Ga and Sn during the Moon-forming event and/or subsequent magma-ocean degassing.@en