HIDDEN: Er jordens kjerne det skjulte reservoaret av edelgasser?

• Anzulovic, Ana; Davis, Anne Hope; Gaina, Carmen & Caracas, Razvan (2025). Buoyancy of volatile-rich kimberlite melts, magma ascent, and xenolith transport. Geology. ISSN 0091-7613. 53(11), s. 919–923. doi: 10.1130/g53387.1. Fulltekst i vitenarkiv Vis sammendrag

  Kimberlite melts are primary carriers of mantle-derived carbon and hydrogen, playing an important role in Earth’s deep carbon cycle and diamond transport. Their low densities, viscosities, and vapor exsolution enable fast ascent rates. Ascending from the upper mantle, kimberlite melts incorporate xenoliths and xenocrysts and exsolve volatiles. These processes alter their initial composition, increasing the discrepancy between the proto-kimberlite magma and the magma that reaches the surface. To explain kimberlite volcanism, we examine atomic diffusivities and densities of kimberlite melts with varying volatile contents. We show that water makes the melts more diffusive, which should also lower their viscosity. All our kimberlite melts are positively buoyant below the lower continental crust (the MOHO discontinuity). They require ∼8.2 wt% CO2 to cross and rise through the MOHO. Above the MOHO, the most volatile-rich kimberlite melts can carry up to ∼44% xenolithic fragments of depleted peridotite type.

• Saurety, Adrien & Caracas, Razvan (2025). Hydrous Chondrites under Shock. The Astrophysical Journal (ApJ). ISSN 0004-637X. 988(2). doi: 10.3847/1538-4357/ade87f. Fulltekst i vitenarkiv Vis sammendrag

  We examine the shock response of a chondrule-like multicomponent silicate melt enriched with 2 wt% H2O, representative of hydrous chondrites, using ab initio molecular dynamics. We calculate Hugoniot equations of state (HEOS) and evaluate how hydration affects transport, structural, and thermodynamic features under shock compression. Under the same initial conditions, our results show that water has a minimal direct effect on HEOS. However, the corresponding decrease in initial density significantly shifts the pressure–temperature trajectory. At constant shock pressures, hydration raises peak temperatures, altering volatile loss and melting behavior. The enhanced heating and melting caused by the presence of water implies that hydrated materials could have played a role in shaping the evolution of planetesimals. This challenges previous assumptions constructed on dry silicate models and suggests that volatile-rich bodies may have differentiated more efficiently. In shocked melts, the fast diffusion of hydrogen, compared to the cations, indicates its weak integration into the silicate network. Accordingly, we find that Si–H forms only transiently. Furthermore, analysis of the electron localization function supports the presence of bonded Si–H and Fe–H species along the HEOS, identified from a geometrical approach. The proportions of hydrides depend on the shock conditions and could affect the redox state of the melt, even when they are rare. Our results suggest that even a small amount of water in silicates influences the thermodynamics and chemical behavior during planetesimal impacts. These transformations should be considered in models of core formation and volatile depletion of early planetary bodies.

• Mohn, Chris Erik; Caracas, Razvan & Conrad, Clinton Phillips (2025). Lower mantle water distribution from ab initio proton diffusivity in bridgmanite. Earth and Planetary Science Letters. ISSN 0012-821X. 649. doi: 10.1016/j.epsl.2024.119095. Fulltekst i vitenarkiv Vis sammendrag

  Proton self diffusion coefficients for bridgmanite at lower mantle conditions are calculated from ab initio molecular dynamics simulations. We find that the proton self diffusion coefficient, is nearly constant ∼ 10−8 m2 s−1 along the lower mantle geotherm but increases by nearly one order of magnitude from ∼10−10 m2 s−1 to ∼ 10−9 m2 s−1 along a cold slab geotherm to about 1800 km depth. These rates imply that the proton diffusion length scale is less than 10 km in lower mantle peridotite in the 150-200 million years timescale for slab material to sink through the lower mantle. Cold wet slabs probably lose less than one percent of their total water content to the ambient mantle on their journey through the lower mantle, indicating that recycled water is far from homogeneously distributed since slab delivery is highly heterogeneous. We estimate that 0.1 to 0.3 ocean masses (<100 ppm wt%) of recycled water may be currently stored in slab remnant materials within the lower mantle. This water is likely not entrained by plumes but is instead captured by background mantle flow before returning to the mid-ocean ridges. By contrast, deep-rooted mantle plumes may entrain materials containing primordial-like water from the lowermost mantle or the core, and preserve these anomalies in fairly small-scale heterogeneities. Over the age of the Earth, the proton diffusion length scale is a few tens of km, which places constraints on the size of possible primordial water reservoirs isolated from convective mixing, and indicates little flux of water across the core-mantle boundary.

• Saurety, Adrien; Caracas, Razvan & Raymond, Sean N. (2025). Impact-induced Vaporization during Accretion of Planetary Bodies. Astrophysical Journal Letters. ISSN 2041-8205. 981(1). doi: 10.3847/2041-8213/adb30e. Fulltekst i vitenarkiv Vis sammendrag

  Giant impacts dominate the late stages of accretion of rocky planets. They contribute to the heating, melting, and sometimes vaporizing of the bodies involved in the impacts. Due to fractionation during melting and vaporization, planet-building impacts can significantly change the composition and geochemical signatures of rocky objects. Using first-principles molecular dynamics simulations, we analyze the shock behavior of complex realistic silicate systems, representative of both rocky bodies. We introduce a novel criterion for vapor formation that uses entropy calculations to determine the minimum impact velocity required to pass the threshold for vapor production. We derive impact velocity criteria for vapor formation—7.1 km s−1 for chondritic bodies—and show that this threshold is reached in 61% and 89% of impacts in dynamical simulations of the late stages of accretion with classical and annulus starting configuration (respectively) for analogs of Earth. These outcomes should be nuanced by factors such as the impact angle and the mass of the impacting bodies, which further influence the vaporization dynamics and the resultant material distribution. Our findings indicate that vaporization was common during accretion and likely played a crucial role in shaping the early environments and material properties of terrestrial planets.

• Caracas, Razvan (2024). The thermal equation of state of the magma Ocean. Earth and Planetary Science Letters. ISSN 0012-821X. 637. doi: 10.1016/j.epsl.2024.118724. Fulltekst i vitenarkiv
• Figowy, Sarah Margaux; Mohn, Chris Erik & Caracas, Razvan (2024). Noble gas migration in silica polymorphs at Earth's mantle conditions. Earth and Planetary Science Letters. ISSN 0012-821X. 633. doi: 10.1016/j.epsl.2024.118637. Fulltekst i vitenarkiv Vis sammendrag

  The diffusion of noble gases in SiO2 phases is studied using ab initio molecular dynamics based on the density functional theory, covering pressure and temperature conditions from the crust to the core. Our results show that the diffusion of noble gases in SiO2 minerals is not only controlled by external conditions such as temperature and pressure but is also highly sensitive to the structure of the host mineral as well as the size of the noble gas. We show that the diffusion coefficient of He in quartz at 1700 K is two orders of magnitude larger than that of He in seifertite at 5000 K. In quartz, the larger the noble gas, the slower the diffusion. Nudged elastic band (NEB) computations in quartz also give Ea(Ar) < Ea(Kr) < Ea(Xe). Interestingly, we predict that Ne diffuses faster than He in dense SiO2 phases at a given temperature, in apparent contradiction with the common assumption that heavier atoms diffuse slower. We explain this phenomenon in seifertite by greater repulsive interactions between Ne and its local environment than for He in the minimum energy configuration, triggering the rapid jumps of Ne toward the lower-coordinated transition site. In agreement with other studies, we predict He and to a lesser extent Ne are quickly released from the continental crust with limited storage in the deepest part of the mantle. However, Ar can be transported deeper than lighter noble gases, potentially trapped in stishovite, CaCl2-type and seifertite in the deep lower mantle. Given the abundance of these minerals in mantle basaltic compositions and the continental crust, their contribution to the volatile cycle of noble gases is far from negligible.

• Davis, Anne Hope & Caracas, Razvan (2024). Degassing of CO2 triggers large-scale loss of helium from magma oceans. Communications Earth & Environment. 5(1). doi: 10.1038/s43247-024-01509-1. Fulltekst i vitenarkiv Vis sammendrag

  The moon-forming impact caused widespread melting and vaporization of the proto-Earth, leading to the formation of a protolunar disk1,2. Volatile elements trapped in the inner parts of the disk condensed together with heavier elements into a global magma ocean3,4. By subsequent cooling and degassing, volatiles contributed to the formation of the Earth’s secondary atmosphere5. The thermodynamic conditions at the magma ocean-atmosphere interface profoundly impacted the degree of degassing that occurred. Today, our understanding of these conditions remains unclear. Here, we simulate the degassing of carbon and helium from a magma ocean with a bulk silicate Earth composition6 at presumed typical conditions for the early Earth5,7. We employ first-principles molecular dynamics calculations. We find that volatile loss is determined by pressure, temperature, and melt composition. Carbon and helium devolatilize more easily when both elements are present in the melt, leading to pronounced loss from the magma ocean. Our findings suggest that the early Earth atmosphere was carbon-rich, with a high fraction of helium and other noble gases, and thicker and hotter than previously thought. We evaluate the implications for Earth’s composition and thermal evolution, as well as other planets that may undergo similar processes with different chemistries.

• Saurety, Adrien; Ozgurel, Ozge; Mohn, Chris Erik & Caracas, Razvan (2024). Diffusion, chemical bonding, and kinetic fractionation of noble gases in the primordial magma ocean. Geochimica et Cosmochimica Acta. ISSN 0016-7037. 378, s. 144–152. doi: 10.1016/j.gca.2024.06.021. Fulltekst i vitenarkiv Vis sammendrag

  Noble gases record in their radiogenic/non-radiogenic isotope ratios the traces of accretion history and degassing events from the early Earth, including giant impacts and the magma ocean stage, to large-scale recent volcanism. The diffusional behavior of noble gases in silicate magmas is one of the essential parameters needed to correctly model devolatilization from the magma ocean and subsequent volcanic eruptions. Here, we study the diffusivity of He, Ne, Ar, Kr, and Xe in molten pyrolite using ab initio molecular dynamics. We find that the diffusivity of the noble gases decreases with increasing atomic size. The diffusion of Ar is comparable to that of Mg. We compute the partial molar volumes and find that at high pressure, He is almost one order of magnitude more compressible than the heavier noble gases. The analysis of the speciation of the noble gases in the melt indicates that the lifetime of the coordination polyhedra formed with O is not sensitive to the mass of the noble gases. Finally, we compute the electron localization function along the Xe–O interatomic vectors and show that there is no chemical bonding between the Xe and surrounding O atoms from the hosting silicate melt.

• Charnoz, Sébastien; Falco, Aurélien; Tremblin, Pascal; Sossi, Paolo; Caracas, Razvan & Lagage, Pierre-Olivier (2023). The effect of a small amount of hydrogen in the atmosphere of ultrahot magma-ocean planets: Atmospheric composition and escape. Astronomy and Astrophysics (A & A). ISSN 0004-6361. 674. doi: 10.1051/0004-6361/202245763. Fulltekst i vitenarkiv Vis sammendrag

  Context. Ultrahot (&gt;1500 K) rocky exoplanets may be covered by a magma ocean, resulting in the formation of a vapor rich in rocky components (e.g., Mg, Si, Fe) with a low total pressure and high molecular mass. However, exoplanets may have also captured a significant amount of hydrogen from the nebular gas during their formation. Ultrahot rocky exoplanets around the Fulton gap (~1.8 R ⊕ ) are sufficiently large to have retained some fraction of their primordial hydrogen atmosphere. Aims. Here, we investigate how small amounts of hydrogen (much smaller than the mass of the planet) above a magma ocean may modify the atmospheric chemistry and its tendency to thermally escape. Methods. We use a chemical model of a magma ocean coupled to a gas equilibrium code (that includes hydrogen) to compute the atmospheric composition at thermodynamical equilibrium for various H contents and temperatures. An energy-limited model is used to compute atmospheric escape and is scaled to consider H-rich and H-poor atmospheres. Results. The composition of the vapor above a magma ocean is drastically modified by hydrogen, even for very modest amounts of H (≪10 −6 planetary mass). Hydrogen consumes much of the O 2 (g), which, in turn, promotes the evaporation of metals and metal oxides (SiO, Mg, Na, K, Fe) from the magma ocean. Vast amounts of H 2 O are produced by the same process. At high hydrogen pressures, new hydrogenated species such as SiH 4 form in the atmosphere. In all cases, H, H 2 , and H 2 O are the dominant nonmetal-bearing volatile species. Sodium is the dominant atmospheric metal-bearing species at T &lt; 2000 K and low H content, whereas Fe is dominant at high H content and low temperature, while SiO predominates at T &gt; 3000 K. We find that the atmospheric Mg/Fe, Mg/Si, and Na/Si ratios deviate from those in the underlying planet and from the stellar composition. As such, their determination may constrain the planet’s mantle composition and H content. As the presence of hydrogen promotes the evaporation of silicate mantles, it is conceivable that some high-density, irradiated exoplanets may have started life as hydrogen-bearing planets and that part of their silicate mantle evaporated (up to a few 10% of Si, O, and Fe) and was subsequently lost owing to the reducing role of H. Conclusions. Even very small amounts of H can alter the atmospheric composition and promote the evaporation to space of heavy species derived from the molten silicate mantle of rocky planets. Through transit spectroscopy, the measurement of certain elemental ratios, along with the detection of atmospheric water or hydrogen, may help to determine the nature of a surface magma ocean.

• Farsang, Stefan; Caracas, Razvan; Adachi, Takuji B.M.; Schnyder, Cédric & Zajacz, Zoltán (2023). S ·<inf>3</inf>radicals and the S·²<inf>4</inf>polysulfide ion in lazurite, haöyne, and synthetic ultramarine blue revealed by resonance Raman spectroscopy. American Mineralogist. ISSN 0003-004X. 108(12), s. 2234–2243. doi: 10.2138/am-2022-8655. Fulltekst i vitenarkiv
• Ozgurel, Ozge & Caracas, Razvan (2023). The magma ocean was a huge helium reservoir in the early Earth. Geochemical Perspectives Letters. ISSN 2410-339X. 25, s. 46–50. doi: 10.7185/geochemlet.2314. Fulltekst i vitenarkiv Vis sammendrag

  Helium from mantle-derived rocks bears in its isotopic ratios the traces of Earth differentiation, degassing, and long term geodynamic evolution. The low 4He/3He ratio of rocks whose origins are in the deep mantle, like ocean island basalts (OIBs), reflect potentially concealed geochemical reservoirs rich in primordial 3He and isolated from the surface. Here we search for the geological repository of primordial He lasting from the core formation. For this, we determine the chemical behaviour of He in the magma ocean (MO) during core formation. We perform ab initio molecular dynamics simulations at temperatures and pressures along the MO adiabat. Our results show that primordial He was largely trapped in MO. At the top, under the hot dense early atmosphere, He remained mainly in the MO and degassed only later, at low atmospheric pressure. At the bottom, He partitions preferentially into the MO rather than the liquid core. The origin of the OIBs reflects a large contribution and contamination from mantle sources and no contribution from the top of the outer core, depleted in primordial He. We suggest the search for the He reservoirs should be done at the base of the solid mantle.

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• Caracas, Razvan; Mohn, Chris Erik & Zhi, Li (2023). Predicting HP-HT Earth and Planetary Materials. SpringerPlus. doi: 10.1007/978-3-031-28805-0_6. Fulltekst i vitenarkiv
• Anzulovic, Ana; Caracas, Razvan & Gaina, Carmen (2025). Volatile control on kimberlite melt structure, density, and viscosity: Atomistic study with implications for kimberlite volcanism. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The way a magma erupts is largely controlled by its volatile content, primarily carbon dioxide (CO₂) and water. This is particularly true for volatile-rich kimberlite magmas, which originate deep in the upper mantle beneath thick, cool continental lithosphere. Kimberlites are known for their rapid ascent and ability to transport mantle fragments to the surface; these characteristics make them the natural transport mechanism and primary host rocks of diamonds. As kimberlite magmas no longer erupt, our understanding of their volcanism relies on studying the altered rocks explosively emplaced in carrot-shaped volcanic pipes. To investigate the drivers of kimberlite volcanism, Ana Anzulović has developed an atomistic model of a kimberlite melt. The findings in the doctoral thesis work indicate that the deciding factor for a successful eruption is magma’s CO₂ content; at least 8.2 wt% is required for the melt to reach the surface. Simulting melt chemistry shows that carbon plays a dual role. At high pressure, it polymerizes the melt structure, but at lower pressure, it exsolves from the melt, driving vaporization. Both carbon and water lower the melt's density and viscosity, but water has a particularly strong depolymerizing effect, making the melt highly mobile.

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