Conference Agenda

In the ELMO laboratory we explore processes from the condensation in the protoplanetary disk, to magma ocean worlds, and volcanism on atmosphereless rocky planets such as Mercury. We study kinetics and equilibrium conditions of evaporation processes of volatile and moderately volatile elements, as well as refractory phases at temperatures up to 2000 °C, and under high vacuum conditions, using state of the art in-situ experiments. In this presentation I will introduce the laboratory techniques and present two case studies with preliminary data.

In the first case study we measured the evaporation kinetics of the refractory CaS-MgS system (oldhamite and niningerite). These sulfides occur at highly reducing conditions in enstatite chondrites, and have been proposed as phases on the surface of Mercury. On Mercury, the decomposition of CaS in particular has been suggested to play a key role in the formation of the enigmatic hollows, active, irregular depressions, suggesting loss of volatiles. However, our new results exclude oldhamite as an important phase in hollow formation.

Second, we present the first in-situ measurements of activation energies for the evaporation of enstatite and forsterite in vacuum, with coupled measurements of the evaporated gas phase of these silicates.

Magma oceans represent a key stage in the early evolution of rocky planets, particularly for the formation and evolution of primordial atmospheres. Under these extreme conditions, moderately volatile elements such as Cu can partition into the gas phase, making them useful tracers of outgassing processes. However, the chemical composition of ancient magma oceans in our Solar System remains inaccessible to direct observation. Therefore, experimental studies are essential to understand magma ocean-atmosphere interactions. Here, we investigate the evaporation behavior of Cu-bearing systems using a novel high-temperature system combining scanning thermal analysis and mass spectrometry (NETZSCH STA 449 F3 Jupiter), allowing simultaneous quantification of evaporative mass loss and identification of gas-phase species. This enables the determination of kinetic parameters, such as activation energies, for simple chemical systems including Cu metal, Cu oxides, and Cu sulfides, as well as for more complex systems such as Cu-bearing silicate melts. Investigations of these simple systems already reveal significant differences in Cu volatility and gas-phase speciation depending on the starting material. In particular, Cu-bearing sulfides release Cu into the gas phase at temperatures as low as 600 °C, Cu oxides at around 900 °C, whereas Cu metal shows significant evaporation only at temperatures above 1250 °C. These results indicate that the presence of specific elements exerts a strong control on Cu volatility. In subsequent experiments, this effect is investigated in silicate melts, with a particular focus on the role of ligands such as S and Cl.

Lithium is known to diffuse very fast in silicates, often by two simultaneous mechanisms (e.g., in olivine, plagioclase and clinopyroxene). However, there is still a lack of experimental data for Li diffusion in orthopyroxene. This is surprising given its potential as a geochrometer for late-stage volcanic processes (even in the range of seconds to minutes) and its importance when interpreting Li isotopic signatures diagnostic of diffusive isotopic fractionation. Additionally, some attention has been given to Li as a tracer of the petrogenesis of planetary materials, including martian meteorites. For these reasons, a robust understanding of Li diffusion coefficients (D) in orthopyroxene is needed.

We measured diffusion coefficients for Li in orthopyroxene (X_Fe=0.1 and ca. 14 μg/g Li), using San Carlos olivine powder (ca. 1 μg/g Li) as a sink, so that Li diffused out of the orthopyroxene crystal. The experiments were conducted in vertical gas mixing furnace at controlled oxygen fugacity and temperatures between 950 ºC and 1100 ºC. Trace element and isotope depth profiles were measured using a femtosecond laser ablation system coupled with a sector field-ICP-MS and a MC-ICP-MS, respectively. We observed complex diffusion profiles with uphill gradients for Li, which could be simulated by a two species diffusion model considering Li diffusing via an interstitial and a vacancy mechanism, the latter being ca. 4 log units slower than the first. We observed a consistent dependence of the vacancy diffusion mechanism on the crystallographic direction, with D // [001] > D // [010] > D // [001].

Moderately volatile elements (MVEs), particularly those with siderophile tendencies, are key tracers of planetary accretion and differentiation, recording both nebular condensation and metal-silicate segregation. Light elements (i.e., sulfur) induce strong non-ideal interactions in metallic liquids, leading to overestimation of Fe activity coefficients at high S contents (>10 wt.%). Oxygen fugacity varies significantly among terrestrial planets, as reflected by differences in their mantle’s FeO contents and in the compositions of their metallic cores, all of which influence the metal-silicate partitioning behavior in these planetary bodies. In this study, we investigate how the molar fraction of S in liquid Fe-rich metal affects metal-silicate partitioning. To achieve this, we equilibrated a high-MgO synthetic picrite with Fe-Ni-S metal compositions containing 2 to 30 wt.% S. Experiments were conducted in the piston-cylinder at 1.5 GPa and ~1500 °C, determining metal-silicate partitioning coefficients for Co, Cd, Sc, Tl, Bi, Zn, As, Mo, Ga, Ge, Sn, In, and Sb. Although only the S content in the metal is varied, associated changes in Fe content, oxygen fugacity, and silicate melt composition render these parameters interdependent and difficult to isolate. By integrating our results with existing datasets, we systematically evaluate their combined effects. We show that S produces element-specific preferences in MVE partitioning, increasing siderophile behavior in Cd and Bi, decreasing it in Ga, Ge, and Sn, while others remain insensitive within the studied parameter space. This contribution seeks to constrain the effects of the S content on the metal-silicate partitioning of MVEs, with implications for planetary accretion and differentiation.