Razvan Caracas

The bonding potential of noble gases in high-pressure silica-bearing solids and melts remains debated, yet it is a central question for understanding their retention behavior and evaluating the role of silicate-bearing phases in the transport and storage of noble gases originally present in the atmosphere. Here, we assess the chemical behavior of noble gases in three silicates: quartz, seifertite, and perovskite. Using the electron localization function and Bader charge analysis, we find no evidence of stable covalent or ionicbonding. The very slow intracrystalline diffusion of heavy noble gases governs their trapping in silicates during crystal growth. Noble gases are more likely to reside in melts or grain boundaries than in silicate crystal lattices.

Calcium silicate perovskite (CaPv) is the host for many trace elements in the lower mantle. Whether, when, and where it forms during the solidification of the magma ocean is fundamental to understanding the geochemical and geodynamical evolution of the early Earth. We performed first-principles molecular dynamics simulations to investigate the partitioning of Ca (alongside Sr and Ba) between bridgmanite and molten pyrolite and laser-heated diamond anvil cell experiments to replicate the crystallization of pyrolitic melt. Results show that Ca is incompatible in bridgmanite at all relevant crystallization conditions in the lower mantle, indicating a progressive enrichment of Ca in the magma ocean as it solidifies. This leads to the crystallization of CaPv during the final stages of solidification in the deep mantle. Coupled with the low bridgmanite-melt partition coefficients for Sr and Ba, our findings infer that both large ion lithophile elements and their host, CaPv, will be concentrated in the deep mantle at the end of magma ocean solidification.

The solubility of various volatiles in magma oceans plays a significant role in the formation and evolution of planetary atmospheres. Using ab initio molecular dynamics simulations, we investigate the dissolution of various volatiles in a magma ocean with bulk silicate Earth composition under conditions relevant to both early Earth and exoplanetary systems.We find that hydrogen is highly soluble in silicate magma oceans, and its solubility increases dramatically with pressure and temperature. In particular for exoplanets, like sub-Neptunes, this solubility influences the structure and functioning of the entire planet. It significantly alters the redox state of the system and causes a massive outflux of oxygen. The results are large-scale formation of water vapor and the release of other complex chemical species. This process profoundly impacts the thermal and chemical evolution of exoplanets, particularly sub-Neptunes, whose atmospheres may show observable spectral signatures linked to magma ocean interactions. At conditions characteristic to the beginning of the Hadean, the Earth’s magma ocean could have easily dissolved large amounts of hydrogen. As a result, the amount of water present in the early atmosphere was determined by a fine balance between water degassing and hydrogen solubility. Changes in the redox state of the magma at shallow conditions would further influence this balance.With regard to noble gases and CO/CO2, our simulations show that they are profoundly incompatible in silicate melts. They easily degas under lower pressure conditions, particularly when they are present jointly in the melt. The partial pressures of either of these gases need to reach at least a couple GPa to prevent degassing. These results suggest that the magma ocean contributed to the CO2-reach atmosphere of the Hadean, by both limited ingassing in the aftermath of the giant impact, and by massive outgassing, once the magma ocean was put in place.

Iron meteorites preserve key records of early planetary differentiation and core formation processes. However, the combined effects of metal–silicate separation, core crystallization, and subsequent impact modification have produced complex and variable geochemical signatures, complicating efforts to reconstruct their parent-body origins and evolutionary histories. To address this challenge, we compiled a comprehensive geochemical dataset of iron meteorites and developed a process-oriented statistical framework that characterizes iron meteorite geochemistry through element covariation patterns and compares their internal chemical structures across different meteorite groups. The results reveal distinct and internally consistent geochemical structures among major magmatic iron meteorite groups. IIAB and IIIAB irons show strong positive correlations among HSEs and systematic anticorrelations with Ni, consistent with well-developed metal crystallization trends and relatively continuous core differentiation histories. In contrast, IVA and IVB irons exhibit weaker coupling between HSEs and other elements, together with subdued or decoupled Ga–Ge behavior, suggesting more complex or non-equilibrium differentiation pathways. The IID group displays intermediate and less coherent correlation structures, indicating greater heterogeneity in internal processes or parent-body conditions. This process-oriented framework provides a quantitative basis for comparing the internal geochemical architectures of iron meteorite groups and offers new perspectives on the diversity of differentiation histories recorded by metallic planetary cores.

Pyrite is one of the most abundant sulfide minerals in the Earth’s crust and can host a wide range of transition metals. However, due to their higher electron counts and atomic sizes different from that of Fe, these substitutions often destabilize the lattice, and the mechanisms controlling their incorporation remain poorly understood. Here we use ab initio simulations to systematically investigate transition-metal substitution in pyrite, using Au-As coupling as a representative example within a broader set of transition-metal systems. We analyze defect formation energies, lattice distortions, and electronic structures for single and double substitutional configurations. Isolated substitutions are generally thermodynamically unfavorable, whereas joint substitutions are more likely to take place. In particular, anion-site dopants with fewer valence electrons than sulfur, such as arsenic, facilitate the incorporation of large-radius transition metals by promoting locally constrained coordination environments and alleviating lattice strain. Electronic structure analyses show that impurity stability is governed by band filling and Fermi-level positioning. Double substitution enables electronic compensation, eliminates mid-gap states, and lowers defect formation energies across multiple transition-metal systems. These results establish electronic compensation as a fundamental control on transition-metal enrichment in pyrite, with implications for pyrite-hosted ore deposits and trace-metal capture across the pyrite life cycle.

Impurities and mineral or fluid inclusions in natural diamonds can provide valuable insights into the evolution of mantle conditions through geologic time (Stachel et al., 2015). In particular, information on the isotopic composition of the early mantle can be inferred by studying helium and hydrogen impurities in diamond, which are usually trapped either as fluid inclusions or as interstitial defects in the diamond lattice. However, a critical aspect to consider is whether or not the isotopic information carried by diamonds is still representative of the original diamond-forming fluid. Processes such as diffusion might occur during prolonged residence time in the Earth’s mantle at high temperature conditions, leading to the re-equilibration of He and/or H with the surrounding mantle, either by loss or gain of He and H themselves. Here we compute the diffusion of He and H in diamond using ab initio molecular dynamics and machine learning molecular dynamics simulations, as implemented in the Vienna Ab Initio Simulation Package (VASP); postprocessing was realized using the UMD package (Caracas et al.,2021). All simulations were performed on a broad range of high pressure and high temperature conditions, compatible with those expected in the Earth’s mantle where diamonds are formed. We determine the diffusion coefficients as a function of both pressure (0, 5 and 10 GPa) and temperature (300 – 3000 K) for He and H. We show that diamonds at greater depths may act as closed systems throughout geological time.MLF, MCD, FI, and MGP acknowledge funding from the European Union (ERC, INHERIT, Starting Grant No. 101041620) Caracas, R., Kobsch, A., Solomatova, N. V., Li, Z., Soubiran, F., & Hernandez, J. A. (2021). Analyzing melts and fluids from ab initio molecular dynamics simulations with the UMD package. JoVE, e61534. doi:10.3791/61534Cherniak, D. J., Watson, E. B., Meunier, V., & Kharche, N. (2018). Diffusion of helium, hydrogen and deuterium in diamond: Experiment, theory and geochemical applications. Geochimica et Cosmochimica Acta, 232, 206-224. https://doi.org/10.1016/j.gca.2018.04.029Stachel, T., & Luth, R. W. (2015). Diamond formation—Where, when and how? Lithos, 220, 200-220. https://doi.org/10.1016/j.lithos.2015.01.028

Early planetary accretion and giant impacts likely generated a global magma ocean on the proto-Earth, enabling extensive dissolution of primordial volatiles from the solar nebula into silicate melts. During subsequent core-mantle differentiation, the partitioning of noble gases between pyrolitic silicate melts and iron-sulfur (Fe-S) melts would have controlled their redistribution and long-term preservation in Earth’s deep interior. The contrasting noble gas signatures observed in mid-ocean ridge basalts and mantle plume sources, particularly in He/Ne ratios, motivated the existence of a deep primitive reservoir potentially linked to early core-mantle differentiation. Here, we use ab initio molecular dynamics simulations combined with thermodynamic integration to quantify the partition coefficients of He, Ne, Ar, Kr, and Xe between pyrolitic silicate melts and Fe-S melts. We further assess the effects of melt composition by comparing pyrolite with MgSiO3 melts and Fe-S with metallic iron melts. Our results reveal systematic variations in noble gas partitioning with atomic size and melt chemistry. Based on these partitioning coefficients, we estimate the potential noble gas inventories preserved in the mantle and core. These results provide new quantitative constraints on the fate of primordial noble gases and the origin of deep-mantle volatile reservoirs.