caracas

• Davis, Anne Hope; Solomatova, Natalia V. & Caracas, Razvan (2026). Dissociation of methane and formation of carbon clusters in a reducing pyrolitic magma ocean. Earth and Planetary Science Letters. ISSN 0012-821X. 692. doi: 10.1016/j.epsl.2026.120222. Fulltekst i vitenarkiv
• Wang, Tianhua; Badro, James; Caracas, Razvan; Gendre, Héloïse & Hébert, Cécile (2026). Formation of calcium silicate perovskite above the core-mantle boundary during solidification of Earth's magma ocean. Science Advances. 12(19). doi: 10.1126/sciadv.aea8372. Fulltekst i vitenarkiv
• Saurety, Adrien & Caracas, Razvan (2026). Carbonated Chondrites during Giant Impacts. The Planetary Science Journal (PSJ). 7(3). doi: 10.3847/PSJ/ae4488. Fulltekst i vitenarkiv
• Charnoz, Sébastien; Limare, Angela; Pereira, Eva De Araujo; Caracas, Razvan & Moynier, Frédéric (2025). Degasing of Phobos in a giant impact scenario: Implications for the MMX sample return mission. Icarus (New York, N.Y. 1962). ISSN 0019-1035. 434, s. 116462–116462. doi: 10.1016/j.icarus.2025.116462. Fulltekst i vitenarkiv Vis sammendrag

  The MMX mission, led by JAXA, is a sample return mission whose primary goal is to test whether the Martian moons, Phobos and Deimos, were formed during a giant impact or were captured. One of the main observations to test these scenarios will be whether Phobos and Deimos have lost volatile elements. If Phobos formed in a giant impact, simulations show that the impact was much less energetic than the Moon-forming impact, with peak temperatures as low as 2000 K. We present here a quantification of the volatile loss in anticipation of the MMX mission, assuming that Phobos’ building blocks were made of bulk silicate Mars material. We investigate the cooling of Phobos in two end-member scenarios : a convective case (relevant for an initially fully molten proto-Phobos) and a conductive case (relevant for an assemblage of 10 m building blocks). A homogeneous evaporation model is used for the convective case, and a diffusion-limited evaporation model is used for the conductive case. In both cases, we find that the cooling time is about 1–10 years in the absence of external heating sources (but the Sun). This leaves little time for evaporation: the most volatile elements, Na and K, may be depleted by 10% for the case of a fully molten and convective proto-Phobos. If Phobos is rather an assemblage of 10 m building blocks that cool conductively, the loss of Na and K would be limited to the first 10 cm below the blocks’ surface (by about 4%) representing about 0.1% loss in averaged bulk composition. If external sources of heating were present (such as a hot radiating Mars or a hot surrounding disk), and the body was kept at T 1400K (our assumed rheological transition temperature) for more than 10 years, a larger loss of Na and K is found. If degassing lasted more than 100 years with exterior temperature 1400K, then all Na and K may have been lost for the convective case, and more than 50% for the conductive case. Furthermore, a significant fraction of the refractory elements may also have been lost in both cases. K abundance will be measured from space by the MEGANE instrument onboard the MMX mission. If low K content is measured by the MEGANE instrument, this would favor the giant impact formation scenario and would imply either a long cooling time of the proto-Phobos (100 years), or degassing prior to the assembling of the proto-Phobos. If MEGANE does not measure K depletion, this could mean either that Phobos was not formed in a giant impact, or that it formed in a giant impact but experienced a short cooling time (10 years). In that case, laboratory analysis of the returned sample will be crucial in deciphering the origin of Phobos by focusing on various volatile elements and constraining their isotopic ratios.

• Anzulović, Ana; Davis, Anne Hope & Caracas, Razvan (2025). Chemical speciation and structure of kimberlite melts from ab initio molecular dynamics simulations. Geochimica et Cosmochimica Acta. ISSN 0016-7037. 410, s. 203–217. doi: 10.1016/j.gca.2025.10.016. Fulltekst i vitenarkiv Vis sammendrag

  Kimberlite magmas, known for their rapid ascent from the upper mantle, transport volatiles, deep-sourced xenocrysts, and xenoliths to the surface. Their ascent rates suggest highly mobile, low-viscosity fluids, with their velocities further accelerated by the exsolution of volatile-rich fluid and vapor phases. Despite their role in driving kimberlite ascent, the atomic-scale mechanisms by which melt composition and volatile content influence physical behavior remain elusive, in part due to the scarcity of direct experimental constraints under relevant conditions. Here, we use ab initio molecular dynamics to address this gap. We model kimberlite melts with varying amounts of CO2 (0-11 wt%) and H2O (0-9 wt%). Our simulations provide a quantitative basis for the distinct structural roles of the major cations. Silicon acts as a rigid network former, with the SiO4 tetrahedron being exceptionally stable (average lifetime 0.6 ps), while network-modifying cations (Mg, Ca, Fe) form highly transient coordination environments (lifetimes 0.1 ps), quantifying their role in promoting the melt’s characteristic mobility. The dominant speciation change with pressure is the conversion of molecular CO to carbonate ions (CO), a transition largely completed below 3 GPa. The carbonate ion is the most stable polyanionic complex in the entire system, with a lifetime exceeding 1.2 ps—more than double that of SiO4. This stability is more strongly controlled by the melt’s redox state than by its total carbon or water content. Hydrous kimberlite melts have the capacity to start degassing at significant mantle depths (90 km). This early and sustained degassing generates a buoyant, carbon-bearing vapor phase that provides a continuous driving force for the rapid ascent of kimberlite magmas.

• 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.

• Stoutenburg, Emma R.; Caracas, Razvan; Solomatova, Natalia V. & Campbell, Andrew J. (2024). Equation of State, Structure, and Transport Properties of Iron Hydride Melts at Planetary Interior Conditions. Journal of Geophysical Research (JGR): Planets. ISSN 2169-9097. 129(10). doi: 10.1029/2024JE008525. Fulltekst i vitenarkiv Vis sammendrag

  Iron hydrides are a potentially dominant component of the metallic cores of planets, primarily because of hydrogen's ubiquity in the universe and affinity for iron. Using ab initio molecular dynamics, we examine iron hydrides with 0.1, 0.33, 0.5, and 0.6 mol fraction hydrogen up to 100 GPa between 3,000 and 5,000 K to describe how hydrogen content affects the melt structure, hydrogen speciation, equation of state (EOS), atomic diffusivity, and melt viscosity. We find that the addition of hydrogen decreases the average Fe–Fe coordination number and lengthens Fe–Fe bonds, while Fe–H coordination number increases. The pair distribution function of hydrogen at low pressure indicates the presence of molecular hydrogen. By tracking chemical speciation, we show that the amount of molecular hydrogen increases and the number of iron in Hx≥1Fey≥0 clusters decreases as the hydrogen concentration increases. We parameterize a pressure, volume, temperature, and composition EOS and show that the molar volume and Grüneisen parameter of the melts decrease while the compressibility and thermal expansivity increase as a function of hydrogen concentration. We find that hydrogen acts as a lubricant in the melts as the iron and hydrogen become more diffusive and the melts become more inviscid as the hydrogen concentration increases. We estimate 2.7 wt% hydrogen in the Martian core and 0.49–1.1 wt% hydrogen in Earth's outer core based on comparisons to seismic models, with the assumption that the cores are pure liquid iron-hydrogen alloy, and we compare the small exoplanet population with mass-radius curves of iron hydride planets.

• 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.

• Caracas, Razvan & Stewart, Sarah T. (2023). No magma ocean surface after giant impacts between rocky planets. Earth and Planetary Science Letters. ISSN 0012-821X. 608. doi: 10.1016/j.epsl.2023.118014. Fulltekst i vitenarkiv
• 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
• Solomatova, Natalia V. & Caracas, Razvan (2023). Earth’s volatile depletion trend is consistent with a high-energy Moon-forming impact. Communications Earth & Environment. 4. doi: 10.1038/s43247-023-00694-9. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The abundance of volatile elements in the silicate Earth relative to primitive chondrites provides an important constraint on the thermochemical evolution of the planet. However, an overabundance of indium relative to elements with similar nebular condensation temperatures is a source of debate. Here we use ab initio molecular dynamics simulations to explore the vaporization behavior of indium from pyrolite melt at conditions of the early magma ocean just after the Moon-forming impact. We then compare this to the vaporization behavior of other minor elements. When considering the volatility of the elements from the magma ocean in the absence of the solar nebula gas, we find that there is no overabundance of indium. On the contrary, there is a slight deficit in the abundance of indium, which is consistent with its moderately siderophile nature. Thus, we propose that a high-energy Moon-forming impact may have had a more significant contribution to volatile depletion than previously believed.

• Davis, Anne Hope; Solomatova, Natalia; Caracas, Razvan & Campbell, Andrew (2023). Carbon storage in Earth's deep interior implied by carbonate-silicate-iron melt miscibility. Geochemistry Geophysics Geosystems. 24(8). doi: 10.1029/2023GC010896. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Carbonate melts have been proposed to exist in the lower mantle, but their interaction with other lower mantle melt compositions is poorly understood. To understand miscibility in the carbonate‐silicate‐metal melt system, we simulate endmember, binary, and ternary melt mixtures and study how their Gibbs free energies of mixing evolve with pressure. We find that carbonate‐metal and carbonate‐silicate melts have miscibility gaps that close with increasing pressure, while silicate‐metal melts are immiscible at all lower‐mantle pressures. Extending this analysis to the core‐mantle boundary, we suggest three miscible melt fields near the endmember carbonate, silicate, and iron melt compositions. Analysis of the densities of these miscible melt compositions indicates that some carbonate‐rich and some silicate‐rich melt compositions are gravitationally stable at the core‐mantle boundary and could be candidate compositions to explain ultra‐low velocity zones. Additionally, we evaluate the speciation of an example immiscible melt composition at various pressures throughout the mantle and identify reduced carbon species that would be expected to form in the melt. Our analysis reveals that a majority of Earth's carbon could have been transported to the core during core‐mantle differentiation and that much of Earth's carbon may be stored in the deep interior today.

• 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.

• Bögels, T.F.J. & Caracas, Razvan (2022). Critical point and supercritical regime of MgO. Physical review B (PRB). ISSN 2469-9950. 105(6). doi: 10.1103/PhysRevB.105.064105. Fulltekst i vitenarkiv Vis sammendrag

  The position of the critical point determines the top of the liquid-vapor coexistence dome, and it is a physical parameter of fundamental importance in the study of high-energy shocks, including those associated with large planetary impacts. For most major planetary materials, such as oxides and silicates, the estimated position of the critical point is below 1g/cm3 at temperatures above 5000 K. Here we compute the position of the critical point of one of the most ubiquitous materials: MgO. For this we perform first-principles molecular dynamics simulations. We find the critical density to be in the 0.45–0.6g/cm3 range and the critical temperature in the 6500–7000 K range. We investigate in detail the behavior of MgO in the subcritical and supercritical regimes, and we provide insight into the structure and chemical speciation. We see a change in Mg-O speciation toward lower degrees of coordination as the temperature is increased from 4000 to 10 000 K. This change in speciation is less pronounced at higher densities. We observe the liquid-gas separation in nucleating nanobubbles at densities below the liquid spinodal. The majority of the chemical species forming the incipient gas phase consists of isolated Mg and O atoms and some MgO and O2 molecules. We find that the ionization state of the atoms in the liquid phase is close to the nominal charge, but it almost vanishes close to the liquid-gas boundary and in the gas phase, which is consequently largely atomic.

• Solomatova, Natalia V.; Caracas, Razvan; Bindi, Luca & Asimow, Paul D. (2022). Ab initio study of the structure and relative stability of MgSiO<inf>4</inf>H<inf>2</inf>polymorphs at high pressures and temperatures. American Mineralogist. ISSN 0003-004X. 107(5), s. 781–789. doi: 10.2138/am-2021-7937. Fulltekst i vitenarkiv
• Hernandez, Jean-Alexis; Caracas, Razvan & Labrosse, Stéphane (2022). Stability of high-temperature salty ice suggests electrolyte permeability in water-rich exoplanet icy mantles. Nature Communications. 13. doi: 10.1038/s41467-022-30796-5. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Electrolytes play an important role in the internal structure and dynamics of water-rich satellites and potentially water-rich exoplanets. However, in planets, the presence of a large high-pressure ice mantle is thought to hinder the exchange and transport of electrolytes between various liquid and solid deep layers. Here we show, using first-principles simulations, that up to 2.5 wt% NaCl can be dissolved in dense water ice at interior conditions of water-rich super-Earths and mini-Neptunes. The salt impurities enhance the diffusion of H atoms, extending the stability field of recently discovered superionic ice, and push towards higher pressures the transition to the stiffer ice X phase. Scaling laws for thermo-compositional convection show that salts entering the high pressure ice layer can be readily transported across. These findings suggest that the high-pressure ice mantle of water-rich exoplanets is permeable to the convective transport of electrolytes between the inner rocky core and the outer liquid layer.

• Baziotis, Ioannis; Xydous, Stamatios; Papoutsa, Angeliki; Hu, Jinping; Ma, Chi & Klemme, Stephan [Vis alle 10 forfattere av denne artikkelen] (2022). Jadeite and related species in shocked meteorites: Limitations on inference of shock conditions. American Mineralogist. ISSN 0003-004X. 107(10), s. 1868–1877. doi: 10.2138/am-2022-8220. Fulltekst i vitenarkiv
• Davis, Anne; Solomatova, Natalia V.; Campbell, Andrew & Caracas, Razvan (2022). The speciation and coordination of a deep Earth carbonate-silicate-metal melt. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 127(3). doi: 10.1029/2021JB023314. Fulltekst i vitenarkiv Vis sammendrag

  Ab initio molecular dynamics calculations on a carbonate-silicate-metal melt were performed to study speciation and coordination changes as a function of pressure and temperature. We examine in detail the bond abundances of specific element pairs and the distribution of coordination environments over conditions spanning Earth’s present-day mantle. Average coordination numbers increase continuously from 4 to 8 for Fe and Mg, from 4 to 6 for Si, and from 2 to 4 for C from 1 to 148 GPa (4,000 K). Speciation across all pressure and temperature conditions is complex due to the unusual bonding of carbon. With the increasing pressure, C-C and C-Fe bonding increase significantly, resulting in the formation of carbon polymers, C-Fe clusters, and the loss of carbonate groups. The increased bonding of carbon with elements other than oxygen indicates that carbon begins to replace oxygen as an anion in the melt network. We evaluate our results in the context of diamond formation and of metal-silicate partitioning behavior of carbon. Our work has implications for properties of carbon and metal-bearing silicate melts, such as viscosity, electrical conductivity, and reactivity with surrounding phases.

• Caracas, Razvan; Kobsch, Anaïs; Solomatova, Natalia V.; Li, Zhi; Soubiran, Francois & Hernandez, Jean-Alexis Robert (2021). Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package. Journal of Visualized Experiments. 2021(175). doi: 10.3791/61534. Fulltekst i vitenarkiv
• Li, Zhi; Winisdoerffer, Christophe; Soubiran, Francois & Caracas, Razvan (2021). Ab initio Gibbs ensemble Monte Carlo simulations of the liquid–vapor equilibrium and the critical point of sodium. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 23(1), s. 311–319. doi: 10.1039/d0cp04158k. Fulltekst i vitenarkiv Vis sammendrag

  The ab initio (ai) Gibbs ensemble (GE) Monte Carlo (MC) method coupled with Kohn–Sham density functional theory is successful in predicting the liquid–vapour equilibrium of insulating systems. Here we show that the aiGEMC method can be used to study also metallic systems, where the excited electronic states play an important role and cannot be neglected. For this we include the electronic free energy in the formulation of the effective energy of the system to be used in the acceptance criteria for the MC moves. The application of this aiGEMC method to sodium yields a good agreement with available experimental data on the liquid–vapour equilibrium densities. We predict a critical point for sodium at 2338 ± 108 K and 0.24 ± 0.03 g cm−3. The liquid structure stemming from aiGEMC simulations is very similar to the one from ab initio molecular dynamics. Since this method can determine phase transition without computing the Gibbs free energy, it may offer a new possibility to study other materials with a reasonable computational cost.

• Li, Zhi & Caracas, Razvan (2021). Thermophysical properties of hot fluid iron in the protolunar disk. Physics of the Earth and Planetary Interiors. ISSN 0031-9201. 321. doi: 10.1016/j.pepi.2021.106806. Fulltekst i vitenarkiv Vis sammendrag

  We characterize the structural and transport properties of fluid iron at the low densities and high temperature conditions characteristic to the outer parts of protolunar disks, which form after giant impacts. We observe that decreasing the density and increasing the temperature decluster the fluid, which is eventually dominated by isolated atoms and dimers. In parallel, the electrical and thermal conductivities also decrease at a fast pace. The rapid diffusion enhances chemical equilibrium on large scales and the low viscosity favors turbulence in the disk.

• Solomatova, Natalia V. & Caracas, Razvan (2021). Genesis of a CO2-rich and H2O-depleted atmosphere from Earth’s early global Magma ocean. Science Advances. 7(41). doi: 10.1126/sciadv.abj0406. Fulltekst i vitenarkiv Vis sammendrag

  The magma ocean was a important reservoir for Earth’s primary volatiles. Understanding the volatile fluxes between the early atmosphere and the magma ocean is fundamental for quantifying the volatile budget of our planet. Here we investigate the vaporization of carbon and hydrogen at the boundary between the magma ocean and the thick, hot early atmosphere using first-principles molecular dynamics calculations. We find that carbon is rapidly devolatilized, while hydrogen mostly remains dissolved in the magma during the existence of a thick silicate-bearing atmosphere. In the early stages of the magma ocean, the atmosphere would have contained significantly more carbon than hydrogen, and the high concentrations of carbon dioxide would have prolonged the cooling time of early Earth.

• Kobsch, Anaïs & Caracas, Razvan (2020). The Critical Point and the Supercritical State of Alkali Feldspars: Implications for the Behavior of the Crust During Impacts. Journal of Geophysical Research (JGR): Space Physics. ISSN 2169-9380. 125(9). doi: 10.1029/2020JE006412. Fulltekst i vitenarkiv Vis sammendrag

  The position of the vapor‐liquid dome and of the critical point determine the evolution of the outermost parts of the protolunar disk during cooling and condensation after the Giant Impact. The parts of the disk in supercritical or liquid state evolve as a single thermodynamic phase; when the thermal trajectory of the disk reaches the liquid‐vapor dome, gas and melt separate leading to heterogeneous convection and phase separation due to friction. Different layers of the proto‐Earth behaved differently during the Giant Impact depending on their constituent materials and initial thermodynamic conditions. Here we use first‐principles molecular dynamics to determine the position of the critical point for NaAlSi3O8 and KAlSi3O8 feldspars, major minerals of the Earth and Moon crusts. The variations of the pressure calculated at various volumes along isotherms yield the position of the critical points: 0.5–0.8 g cm−3 and 5500–6000 K range for the Na‐feldspar, 0.5–0.9 g cm−3 and 5000–5500 K range for the K‐feldspar. The simulations suggest that the vaporization is incongruent, with a degassing of O2 starting at 4000 K and gas component made mostly of free Na and K cations, O2, SiO and SiO2 species for densities below 1.5 g cm−3. The Hugoniot equations of state imply that low‐velocity impactors (<8.3 km s−1) would at most melt a cold feldspathic crust, whereas large impacts in molten crust would see temperatures raise up to 30000 K.

• Li, Zhi; Caracas, Razvan & Soubiran, François (2020). Partial core vaporization during Giant Impacts inferred from the entropy and the critical point of iron. Earth and Planetary Science Letters. ISSN 0012-821X. 547. doi: 10.1016/j.epsl.2020.116463. Fulltekst i vitenarkiv Vis sammendrag

  Giant impacts are disruptive events occurring in the early stages of planetary evolution. They may result in the formation of a protolunar disk or of a synestia. A central planet and one or several moons condense upon cooling bearing the chemical signature of the silicate mantles of the initial bodies; the iron cores may partly vaporize, fragment and/or merge. Here we determine from ab initio simulations the critical point of iron in the temperature range of 9000-9350 K, and the density range of 1.85-2.40 g/cm3, corresponding to a pressure range of 4-7 kbars. This implies that the iron core of the proto-Earth may become supercritical after giant impacts and during the condensation and cooling of the protolunar disk. We show that the iron core of Theia partially vaporized during the Giant Impact. Part of this vapor may have remained in the disk, to eventually participate in the Moon's small core. Similarly, during the late veneer a large fraction of the planetesimals have their cores undergoing partial vaporization. This would help mixing the highly siderophile elements into magma ponds or oceans.

• Stewart, Sarah T.; Davies, Erik; Duncan, Megan & Caracas, Razvan (2020). The shock physics of giant impacts: Key requirements for the equations of state. AIP Conference Proceedings. ISSN 0094-243X. 2272(1). doi: 10.1063/12.0000946. Fulltekst i vitenarkiv
• Solomatova, Natalia & Caracas, Razvan (2020). Buoyancy and Structure of Volatile‐Rich Silicate Melts. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. doi: 10.1029/2020JB021045. Fulltekst i vitenarkiv
• Panero, Wendy & Caracas, Razvan (2020). Stability and Solid Solutions of Hydrous Alumino-Silicates in the Earth’s Mantle. Minerals. 10. doi: 10.3390/min10040330. Fulltekst i vitenarkiv Vis sammendrag

  The degree to which the Earth’s mantle stores and cycles water in excess of the storage capacity of nominally anhydrous minerals is dependent upon the stability of hydrous phases under mantle-relevant pressures, temperatures, and compositions. Two hydrous phases, phase D and phase H, are stable to the pressures and temperatures of the Earth’s lower mantle, suggesting that the Earth’s lower mantle may participate in the cycling of water. We build on our prior work of density functional theory calculations on phase H with the stability, structure, and bonding of hydrous phases D, and we predict the aluminum partitioning with H in the Al 2 O 3 -SiO 2 -MgO-H 2 O system. We address the solid solutions through a statistical sampling of site occupancy and calculation of the partition function from the grand canonical ensemble. We show that each phase has a wide solid solution series between MgSi 2 O 6 H 2 -Al 2 SiO 6 H 2 and MgSiO 4 H 2 -2 δ AlOOH + SiO 2 , in which phase H is more aluminum rich than phase D at a given bulk composition. We predict that the addition of Al to both phases D and H stabilizes each phase to higher temperatures through additional configurational entropy. While we have shown that phase H does not exhibit symmetric hydrogen bonding at high pressure, we report here that phase D undergoes a gradual increase in the number of symmetric H-bonds beginning at ∼30 GPa, and it is only ∼50% complete at 60 GPa.

• Solomatova, Natalia; Caracas, Razvan & Cohen, Ronald (2020). Carbon Speciation and Solubility in Silicate Melts. I Manning, Craig E.; Lin, Jung‐Fu & Mao, Wendy L. (Red.), Carbon in Earth's Interior. John Wiley & Sons. ISSN 9781119508229. s. 179–194. doi: 10.1002/9781119508229. Fulltekst i vitenarkiv Vis sammendrag

  To improve our understanding of the Earth's global carbon cycle, it is critical to characterize the distribution and storage mechanisms of carbon in silicate melts. Presently, the carbon budget of the deep Earth is not well constrained and is highly model‐dependent. In silicate melts of the uppermost mantle, carbon exists predominantly as molecular carbon dioxide and carbonate, whereas at greater depths, carbon forms complex polymerized species. The concentration and speciation of carbon in silicate melts is intimately linked to the melt's composition and affects its physical and dynamic properties. Here we review the results of experiments and calculations on the solubility and speciation of carbon in silicate melts as a function of pressure, temperature, composition, polymerization, water concentration, and oxygen fugacity.

• Caracas, Razvan; Hirose, Kei; Nomura, Ryuichi & Ballmer, Maxim D. (2019). Melt–crystal density crossover in a deep magma ocean. Earth and Planetary Science Letters. ISSN 0012-821X. 516, s. 202–211. doi: 10.1016/j.epsl.2019.03.031. Fulltekst i vitenarkiv Vis sammendrag

  The crystallization of a magma ocean (MO) early in Earth's history shaped the entire evolution of our planet. The buoyancy relations between the forming crystals and the residual melt is the most important but also the most unknown parameter affecting the large-scale structure and evolution of the MO. The accumulation of crystals, near the depth of neutral buoyancy between crystals and the coexisting melt, if happening at mid-depths, can separate convecting regions within the MO. Here we use jointly first-principles molecular-dynamics calculations and diamond-anvil cell experiments to obtain the density relations between the molten bulk silicate Earth and the bridgmanite crystals during the crystallization of the MO. The chemical evolutions of the liquid and the coexisting solid during progressive crystallization were constrained by experiments, and the relevant densities were calculated by molecular dynamics. We find that the first crystal of bridgmanite that is formed in a fully molten mantle is Fe-poor, and becomes neutrally buoyant at 110–120 GPa. Since the cooling of the deep MO is fast, and related convection is vigorous, however, first crystals remain entrained. As crystallization advances, the relative Fe content increases in the melt, and the pressure of neutral buoyancy decreases. At 50% solidification, close to the rheological transition, the pressure of the density crossover moves to ∼50 GPa. At this pressure, crystals form an interconnected network and block global convection currents, which in turn leads to the separation of the partly crystallized MO into a surficial MO and a basal MO through melt-solid segregation. Such a shallow segregation of a crystal mush at mid-mantle depth has important implications for the dynamics and timescales of early mantle differentiation. Moreover, the shallow segregation should have promoted the formation of a voluminous basal MO that evolves into a large geochemically enriched reservoir. Accordingly, the seismically observed residues of basal MO crystallization in the present-day mantle may host an unmixed reservoir for the missing budget of highly incompatible elements.

• Solomatova, NV; Caracas, Razvan & Manning, CE (2019). Carbon sequestration during core formation implied by complex carbon polymerization. Nature Communications. 10. doi: 10.1038/s41467-019-08742-9. Fulltekst i vitenarkiv
• Martin, A; Torrent, M & Caracas, Razvan (2019). Projector augmented-wave formulation of response to strain and electric-field perturbation within density functional perturbation theory. Phys. Rev. B 99, 094112. Physical review B (PRB). ISSN 2469-9950. 99(9). doi: 10.1103/PhysRevB.99.094112. Fulltekst i vitenarkiv
• Solomatova, NV & Caracas, Razvan (2019). Pressure‐induced coordination changes in a pyrolitic silicate melt from ab initio molecular dynamics simulations. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 124(11), s. 11232–11250. doi: 10.1029/2019JB018238. Fulltekst i vitenarkiv

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• Anzulović, Ana; Davis, Anne Hope & Caracas, Razvan (2025). Atomistic view on kimberlite eruptions. Fulltekst i vitenarkiv
• Anzulović, Ana & Caracas, Razvan (2024). Deciphering the Dynamics of Kimberlite Melts: Insights from FPMD Simulations. Fulltekst i vitenarkiv Vis sammendrag

  Kimberlite melts rapidly ascend, transporting a large amount of mantle cargo, indicating high buoyancy likely enabled by exsolution of a volatile-rich fluid phase [1]. Coming from mantle depths, there is a lot of ambiguity about their origin and conditions governing their ascent. Although composition determines density and viscosity of these melts, little is known about the influence of melt chemistry on the dynamic behavior of kimberlites, and the role volatiles play in this context. We want to calculate viscosity and bubble nucleation to better understand the fast ascent and explosive eruptions of kimberlite melts. We use first principles molecular dynamic (FPMD) simulations to model several compositions of kimberlite melts. We create a molecular scale kimberlite model and run it at different temperatures and pressures. FPMD are accurate but computationally expensive. To calculate temperature and pressure profile of the viscosity of these melts we need an array of pressure-temperature data points. Since achieving an acceptable statistical accuracy of the viscosity requires exceedingly long FPMD simulations [2] we have build a deep-learning based model of interatomic potential energy for kimberlites. To construct and train the deep-neural-network potential we use the DeePMD-kit [3]. This approach promises to enhance computational efficiency while preserving near-FPMD precision in capturing the intricate thermodynamic behavior of kimberlite melts.

• Anzulović, Ana & Caracas, Razvan (2024). The effect of volatiles on properties of kimberlite melts. doi: 10.29173/ikc4168. Fulltekst i vitenarkiv Vis sammendrag

  Introduction Kimberlite magmas derive from a carbon-rich parental melt [Wyllie 1980; Dalton and Presnall 1998] and ascent through narrow dykes at high speeds. Differences in emplacement styles are highly dependent on the primary melt compositions [Tovey et al. 2022]. CO2 and H2O are the main volatile component of kimberlite melts; they play a critical role in lowering the viscosity of the melt, promoting magma mixing, and enhancing bubble growth [Zhang and Gan 2022]. Kimberlites degas large quantities of CO2 as they erupt, forming diatremes and other more irregularly shaped bodies. While there has been significant research on kimberlite volcanism [Sparks et al. 2006; Sparks 2013; Giuliani 2023; Tovey et al. 2022], the lack of knowledge about the composition of the parental melt hampers our understanding of it. Kimberlite melts are generated with a low degree of partial melting of a carbonated peridotite when its solidus meets the cratonic geotherm [Wyllie 1980, Bailey 1980]. Melts formed this way would likely inherit high concentrations of carbon. Here, we use ab initio molecular dynamics simulations (AIMD) to determine the effect of the composition, and in particular, the role of carbon, on the dynamic behavior of kimberlite melts. We study the kimberlite melts across a pressure-temperature range characteristic to the upper mantle and the crust. We analyze the behavior of carbon in the kimberlite magmas in terms of diffusion, speciation, and melt structure. Methods The AIMD simulations were performed using the Vienna Ab initio Simulation Package [Kresse et al. 1996]. The electronic structure is calculated using the projector augmented wave method [Bloch 1994] within the Density Functional Theory [Kohn and Sham 1965]. We employ the general gradient approximation in Perdew–Burke–Ernzerhof [Perdew et al. 1996] formulation for the exchange-correlation function. The kinetic cutoff energy for the plane-wave expansion of the wave functions was set to 600 eV, the augmentation charge at 800 eV. The electronic wavefunctions were sampled at the Gamma point in the reciprocal space. With these parameters, the internal energy converged to better than 15 meV/atom. The simulations were performed within the canonical ensemble with constant volume, V and number of atoms, N; the temperature, T, was controlled using a Nose-Hoover thermostat [Hoover 1985, Nose 1984]. The timestep was 1 fs, after a thermalization period of 1 ps, the runs lasted between 2 and 8 picoseconds. The simulations were performed at temperatures of 1500, 2000, 2500, and 3000 K. We start our simulations using the Jericho kimberlite composition [Kopylova et al. 2007]. Starting with measurements of the whole-rock composition, we first build a ‘dry’ kimberlite melt, i.e., devoid of volatiles, with stoichiometry Mg52Si33Ca17Fe8Ti2Al1K1O151. For this dry kimberlite melt composition, we use a cubic cell containing 265 atoms. In a second set of simulations, we add 17 molecules of CO2 to the thermalized dry kimberlite melt to simulate the carbonated kimberlite composition. We use the UMD package [Caracas et al. 2021] to perform the post-processing of the AIMD results. First, we extract the thermodynamic parameters, like pressure, temperature, and energy. Then, we compute the mean squared displacements (MSD) of the atoms. The linear regression fit of the diffusive regime of the MSD curves yields the self-diffusion coefficients of each element. Then, we calculate the pair distribution function (PDF). The PDFs describe the relative geometric relations between the atoms. The first maximum of the PDF marks the most common interatomic distance, oftentimes considered as the average bond length. The first minimum of the PDF determines the radius of the first coordination sphere. We use the value of this radius to define whether or not two atoms are bonded. This also allows us to construct a connectivity matrix, to identify the different chemical species in the melt, and to separate the melt from the vapor phase. Results and discussion The average bond lengths between the atoms at 3000 K and 0.97 GPa, obtained from the analysis of the PDFs, are 1.83 Å for Fe-O, 1.63 Å for Si-O, 1.82 Å for Al-O, 1.97 Å for Mg-O, 1.83 Å for Ti-O, 2.28 Å for Ca-O, 2.7 Å for K-O and 1.27 Å for C-O. Over the 0 – 45 GPa pressure range, the bond distances between cations and oxygen decrease by less than 10%. In addition to oxygen, at certain temperatures and pressures, carbon also shows clear maxima and minima in the PDFs with Fe, C, and Si, with maxima at 1.9 Å, 1.5 Å, and 1.9 Å, respectively. The speciation of carbon in the melt is dominated by the carbonate ion CO32-. This is in full agreement with other observations, both theoretical and experimental, on carbonated silicate melts. CO and CO2 are the second most common species at lower pressures but CO4 steadily becomes more prominent as pressure increases. We observe that at higher temperatures, the pressure at which CO4 starts to be more abundant than CO and CO2 decreases. At low pressures, the formation of vapor starts with the nucleation of nanobubbles. We identify the nanobubbles from the bimodal distribution of the polymerization clusters in the melt. At high densities, all the atoms are bonded, resulting in a large infinite polymer. Upon decompression, as the bonds are continuously stretched, there is a density below which the metastability limit is breached. At densities lower than this value, a nanocavity separates spontaneously in the simulation cell, where small atomic clusters can freely fly. The cavity represents a nanobubble, and the clusters represent the gas phase. We obtain that the liquid and gas phases start to separate at 2.3 GPa and 3000 K, corresponding to a depth of about 60 kms. Considering that the depth of CO2 exsolution is a function of melt composition, primarily the SiO2 and H2O content of the melt, and the anhydrous nature of our system, water enabling a deeper exsolution of the CO2 phase, these results indicate a possibility of a deeper starting point of CO2 exsolution. This supports the ability of kimberlite magmas to transport xenoliths and xenocrysts from mantle depths. The self-diffusivity coefficients values are between 10−9 and 10−8, which are typical values for a liquid. The CO2 does not influence largely the diffusivity values of the atoms present in the anhydrous silicate melt. This consists of previous experiments [Watson 1991, Blank 1993, Sierralta et al. 2002] and theoretical [Zhang and Ni 2010, Davis et al. 2022, Solomatova and Caracas 2021] determinations.

• Anzulović, Ana; Davis, Anne Hope & Caracas, Razvan (2024). The effect of volatiles on properties of kimberlite melts. Fulltekst i vitenarkiv Vis sammendrag

  Kimberlites are an interesting case of transitional, silicic to carbonatitic melt compositions, due to their origin region beneath the thick cratonic lithosphere and processes occurring during their ascent to the surface (solid state upwelling, entrainment and interaction with mantle-cargo, volatile exsolution). Their carbon-rich compositions contribute to low density, high buoyancy and explosive eruptions. Near the surface, a drop in CO₂ solubility causes exsolution of a volatile-rich fluid phase. Although carbon, and volatiles in general play a crucial role in kimberlite volcanism, its behavior in the melts and broader impact on transporting carbon from Earth’s interior to the surface, remain poorly understood. Using ab initio molecular dynamics, we created an atomic-scale models of a kimberlite melt with varying volatile contents, and simulated their behavior across a wide pressure-temperature range. We calculated densities of these melts and compared them to the surrounding lithosphere. From the density contrast, we compared how much entrained cargo, melts with different volatile contents can carry while remaining positively buoyant. Our results indicate that adding CO2 and H2O increases melt’s transport capacity, with water having a more pronounced effect, especially at lower pressures. We analyzed carbon speciation and its effect on polymerization of the hydrous and anhydrous kimberlite melt. Most carbon exists as carbonate ions (CO3), bonded to network-disruptors, which de-polymerizes the melt. We determine a pressure point at which CO2 solubility drops, causing a formation of vapor phase formed of CO and CO2. We observe an increase in molecular CO2 around 2 GPa.

• Anzulović, Ana & Caracas, Razvan (2024). An atomistic view on kimberlite eruptions. Fulltekst i vitenarkiv
• Anzulović, Ana & Caracas, Razvan (2023). The effect of volatiles on the density of kimberlite melts. Fulltekst i vitenarkiv
• Anzulović, Ana & Caracas, Razvan (2023). The effect of volatiles on the density of kimberlite melts. Fulltekst i vitenarkiv
• Anzulović, Ana & Caracas, Razvan (2023). The effect of volatiles on the density of kimberlite melts. Fulltekst i vitenarkiv
• 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
• Mohn, Chris Erik & Caracas, Razvan (2023). Lower mantle rehydration and core-mantle water exchanges from ab initio proton diffusivity in bridgmanite and post-perovskite. Fulltekst i vitenarkiv
• Figowy, Sarah Margaux; Mohn, Chris Erik & Caracas, Razvan (2023). Diffusion of noble gases in silica polymorphs at Earth's mantle conditions. Fulltekst i vitenarkiv
• Anzulović, Ana & Caracas, Razvan (2022). The effect of volatiles on the mechanical properties of silicate melts. Fulltekst i vitenarkiv
• Caracas, Razvan; Solomatova, NV & Trønnes, Reidar G (2019). Buoyancy of dry and volatile-bearing silicate melts in the Earth’s mantle. AGU Fall Meeting Abstr.. 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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