EMRP1.4
Posters on site: Wed, 26 Apr, 10:45–12:30 | Hall X2
Iron is considered to be the main component of the Earth's core. Substantial efforts have been made to understand its phase diagram and physical properties at extreme conditions. However, it remains debated about how the atoms in solid iron are arranged at Earth's core conditions, where possible candidates include hexagonal close-packed (hcp), body-centred cubic (bcc), and face-centred cubic (fcc) structures. As crystal structure and physical properties are closely related, there is also a significant uncertainty in the properties of Earth's core, such as elasticity, heat conductivity, and density, making the accurate interpretation of seismic observations difficult. Here we aim to study the phase stability of solid iron at Earth's core conditions. For this, a deep-learning interatomic potential was developed with ab initio accuracy but is more cost-effective. To further check the performance of such potential, we examine the elastic and plastic behaviour of hcp iron and the effects of structural defects at inner core conditions [1]. We then compute the Gibbs free energy of the bcc, fcc, hcp and liquid phases by performing large-scale molecular dynamics simulations. The calculated free energy allows for determining the phase stability of solid iron in Earth's core.
[1] Li, Z., & Scandolo, S. (2022). Elasticity and viscosity of hcp iron at Earth's inner core conditions from machine learning-based large-scale atomistic simulations. Geophysical Research Letters, 49, e2022GL101161.
How to cite: Li, Z. and Scandolo, S.: Phase diagram of pure iron in Earth's core from deep learning, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11982, https://doi.org/10.5194/egusphere-egu23-11982, 2023.
Pyroxene minerals are key to understand the structure and composition of Earth and rocky exoplanets interiors. Nevertheless, the full details of the MgSiO3 phase diagram still remain unclear, in particular in the high temperature region. Protoenstatite (PEn) is one of the HT polymorphs of MgSiO3 pyroxene, having stability range from ~1200 to 1800 K at ambient pressure. Its importance has been recognized by many authors, since PEn is regarded as a precursor phase of low-clinoenstatite (LP-CEn)/orthoenstatite (OEn) intergrowths in some cometary samples [1] and in calcium-aluminum-rich inclusions (CAIs) from CV3 chondrites [2]. Moreover, PEn is the liquidus phase of pyroxene in the MgO-SiO2 binary system and may have played a role in gas solar nebula condensation processes [3]. Very little is known about the thermodynamics and phase relations of protoenstatite. This is due for the most part to its unquenchable nature, meaning that even if PEn can be synthetized at high temperature conditions, it doesn’t preserve at ambient conditions since it very rapidly reverts either to OEn or LP-CEn. The difficulty to perform measurements on samples of PEn prevents to obtain complete information on its thermodynamic properties, which are in turn fundamental for the investigation of phase equilibria of this mineral. In that sense, ab initio calculations based on quantum-mechanical theory are one of the most reliable methods available to obtain information on thermodynamics and phase relations of minerals at HT conditions.
We present a DFT based ab initio B3LYP computational study on MgSiO3 PEn. All the relevant thermophysical and thermodynamic properties of PEn (e.g. heat capacity, vibrational entropy, thermal expansion, EoS) have been calculated in the framework of the quasi-harmonic approximation (QHA) by a full phonon dispersion calculation. This allowed to obtain original insights into protoenstatite thermodynamics and enabled to retrieve a complete set of physically consistent thermodynamic properties, that are in good agreement with the very few experimental data currently available [4]. The computed properties have been tested by predicting relevant phase equilibria involving PEn up to melting conditions, in particular the OEn – PEn phase transition. The P-T location of the phase boundary and its Clapeyron slope (dP/dT = 2.04 MPa/K) are consistent with previous pyston-cylinder experiments ([5],[6]). Theoretical modelling of the melting curve of MgSiO3 polymorphs reveals a change of the melting behavior from incongruent to congruent due to the onset of the OEn – PEn transition in the phase diagram.
[1] Schmitz, S., and Brenker, F.E (2008) Astrophys. J., 681, L105-L108.
[2] Che, S., and Brearley, A.J. (2021) Geochim. Cosmochim. Acta, 296, 131-151.
[3] Nagahara, H.. (2018) Rev. Mineral. Geochem., 84, 461-497.
[4] Thiéblot, L., Téqui, C., and Richet, P. (1999) Am. Mineral., 84, 848-855.
[5] Boyd, F. R., England, J. L., and Davis, B. T. (1964) J. Geophys. Res., 69, 2101-2109.
[6] Chen, C. H., and Presnall, D. C. (1975). Am. Mineral., 60, 398-406.
How to cite: La Fortezza, M. and Belmonte, D.: Ab initio thermodynamics and phase stability of MgSiO3 pyroxene polymorphs: new insights on protoenstatite, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12045, https://doi.org/10.5194/egusphere-egu23-12045, 2023.
Mars’ mantle dynamical history has certainly been dominated by a stagnant-lid regime, with limited mixing and homogenization. Accordingly, the chemical and mineralogical signatures of early processes, including the crystallization of a primitive magma ocean, are overall well preserved on Mars. The major geological structures visible at its surface are the remains of an intense ancient volcanism, not so dissimilar from the large igneous provinces found on Earth at very old ages (several million/billion years).
Current models used to determine the mantle thermal evolution and the crustal extraction heavily relies on melting properties of materials expected to form the Martian mantle, which, however are poorly known. In particular, the fact that the Martian mantle is probably richer in iron than the terrestrial mantle has a direct impact on the solidus and liquidus and on the chemistry of the magmas that can be produced at different pressures. Thus, the study of Martian volcanism and thermal history requires a precise understanding of the melting properties of the mantle (solidus, liquidus and extent of melting) as a function of pressure and temperature. Studies in literature are scant, mainly address the solidus, and are limited to analysis of recovered samples, missing in situ diagnostics.
To address this problem, we studied the solid-liquid melting relations and, more generally, the melting diagram for a mineralogical assemblage model of mantle composition, by high-pressure and high-temperature experiments in multi anvil press performed at the PSICHE beamline of the SOLEIL synchrotron. We determined the solidus and the liquidus of the investigated rock at pressures up to 12 GPa by complementary in-situ diagnostics (X-ray diffraction and falling sphere technic). The obtained solidus and liquidus are well lower (difference >200K), especially at the highest investigated pressures, compared to previous studies, with strong implications for the origin of volcanism and notably the crystallization of the magma ocean. Furthermore, our experiments provide important data to refine the extent of melting (Φ), modal proportion and the chemistry of all the different phases present between the solidus and the liquidus at different conditions (P, T, Φ).
Altogether, these new results are critical to constrain models of thermal evolution and crust extraction and formation, as well as to address the evolution of the magmatism and volcanism at the Mars surface since 3.5 Ga. Finally, depending on different parameters, such as the thickness of the crust or the concentration of radioactive elements, the estimated areotherm could cross the solidus and lead to partial melting of the mantle, especially close to the core-mantle boundary, where a high extent of melting could be reached.
How to cite: Pierru, R., Dominijanni, S., Parisiadis, P., Andriambariarijaona, L., Zhao, B., Blanchard, I., Guignot, N., King, A., Badro, J., and Antonangeli, D.: Melting properties and melting phase relations of the Martian mantle from in-situ measurements on iron-rich mineralogical assemblages, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12231, https://doi.org/10.5194/egusphere-egu23-12231, 2023.
The internal structure of Mercury holds key information regarding the planet’s formation and its peculiar magnetic field. Waiting for incoming observations by BepiColombo, current knowledge of the interior structure of Mercury relies primarily on geodetic and surface chemistry data collected by MESSENGER. Results from spectral and compositional analysis supplemented by cosmochemical evidence indicate that light elements such as S, and Si are most likely alloyed to Fe in Mercury’s core. This notion is further supported by the very reducing redox conditions (from -2.6 to -7.3 log units below Fe-FeO oxygen buffer) predicted to occur during the planet’s differentiation that argue for significant quantities of Si and S partitioned into metallic iron. Thus, it is of primary importance to determine the Fe-Si-S phase diagram and to understand the high pressure and high temperature properties and thermodynamic behavior of Fe-Si-S alloys at conditions directly relevant for Mercury’s core. Very recently the binary Fe-FeSi phase diagram has been established at Mercury’s core conditions, but phase and melting relations in the Fe-Si-S ternary system still are poorly constrained, in particular at the relatively low pressures and temperatures relevant for Mercury’s core.
To address this issue, we performed angular dispersive powder X-ray diffraction experiments in laser-heated diamond anvil cells on selected composition in the Fe-Si-S system (i.e., Fe-4S-6Si, Fe-16S-6Si, Fe-4S-12Si, and Fe-16S-12Si, all in wt. %) at the P02.2 Extreme Conditions beamline at DESY Synchrotron facility (Germany). For all compositions, eutectic melting and subsolidus phase relations were investigated up to about 45 GPa. Ex situ chemical analysis of the recovered run products were performed at the IMPMC laboratory on the extracted FIB thin sections cut throughout the heated spots.
Here we will present preliminary results on the eutectic melting and Fe-Si-S phase relations as a function of pressure, temperature and composition, with specific focus to the conditions expected within the core of Mercury.
How to cite: Dominijanni, S., Anzellini, S., Kurnosov, A., Morard, G., Boccato, S., Fedotenko, T., and Antonangeli, D.: Melting and subsolidus phase relations of Fe-Si-S alloys at Mercury’s core conditions , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13353, https://doi.org/10.5194/egusphere-egu23-13353, 2023.
Transient creep controls the behavior of Earth’s mantle at human timescales. Transient creep occurs during postseismic creep, glacial isostatic adjustment, and tidal deformation of planetary interiors experiencing large tidal stresses, such as Jupiter’s moon Io or various identified exoplanets. Unfortunately, laboratory data of transient creep of olivine, the most abundant mineral in Earth’s upper mantle, remain limited, and at present we lack the microphysical understanding of transient creep required to extrapolate experimental data to geological grain sizes and time scales. Several mechanisms for transient creep have been proposed, both intergranular mechanisms such as plastic anisotropy and elastically or diffusionally-assisted grain boundary sliding, and intragranular mechanisms including long-range dislocation interactions and various other dislocation damping mechanisms. Each mechanism produces distinct rheological behavior, presenting a hurdle for modeling geodynamic processes occurring on timescales of hours to years.
To distinguish among the various proposed microphysical mechanisms for transient creep, we performed compressional load-reduction experiments on cylindrical, isostatically hot-pressed aggregates of San Carlos olivine in a gas-medium Paterson apparatus at confining pressures of 300 MPa and temperatures of 1200°C. Samples were subjected to a constant differential stress of 200 MPa, which resulted in a steady-state strain rate of ~10-5 s-1. After steady state was achieved, the samples were subjected to a near-instantaneous load reduction of 10–70% of the original load.
For load reductions exceeding ~50%, the samples exhibited a period of transient anelastic relaxation with zero or negative strain rate before continuing to strain at a positive strain rate lower than the previous steady state. The duration of relaxation increased with the magnitude of the load reduction. Multiple load reductions from the same steady-state strain rate were performed during a single experiment to test for reproducibility.
We interpret our results to indicate that, at these conditions, the backstress stored in polycrystalline olivine is approximately half of the differential stress applied to the material. The magnitude of backstress is compatible with long-range dislocation interactions on the [100](010) and [100](001) or [001](100) slip systems previously observed for single crystals of olivine. If transient creep is controlled by such dislocation interactions then it may be inappropriate to apply the traditional Burgers rheology based exclusively on intergranular dissipation processes or power-law flow laws calibrated for steady-state creep to model transient creep and transient viscosity evolution in the upper mantle.
How to cite: Hein, D., Hansen, L., and Dillman, A.: Backstresses in polycrystalline olivine and implications for transient deformation of the mantle, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15457, https://doi.org/10.5194/egusphere-egu23-15457, 2023.
Our understanding on how opaque materials respond to extreme compression and high temperatures heavily relies on x-ray techniques. While X-ray diffraction is a powerful approach, some properties such as viscosity are experimentally not accessible with such approaches. Application of x-ray imaging has been widely applied in extreme pressure and temperature conditions using multi-anvil presses, but obtaining sufficient space and time resolution for similar experiments using diamond anvil cells, at commensurately higher pressure and temperature conditions, have been challenging. We present recent developments in synchrotron X-ray imaging at the ECB beamline at PETRA III, DESY used in combination with laser heated DAC. Simultaneous X-ray imaging and diffraction allows for deeper insight in properties of materials under high pressure as well as the direct correspondence of phase transition diagnostics. We present a case study of bismuth in the laser-heated diamond anvil cell showing detection of solid-solid and solid-liquid transitions and explore how X-ray imaging can be used to determine viscosity of molten bismuth under pressure.
How to cite: Massani, B., Husband, R., Campbell, D., Sneed, D., Jenei, Z., Liermann, H.-P., McWilliams, S., and O'Bannon, E.: Laser-melting Bismuth - A case study for X-ray imaging at high pressure and temperature, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-15584, https://doi.org/10.5194/egusphere-egu23-15584, 2023.
Large scale dynamics within the Earth are the result of cooling. Heat is transported towards the surface by large scale convection in the mantle and in the core, and by conduction across the thermal boundary layers at the core–mantle boundary and the lithosphere. There is a range of estimates for the thermal transport properties, e.g. thermal conductivity (k) in the lower mantle ranges between 4 and 16 W/m K, [i] resulting from a lack of consensus on how to represent the pressure (and temperature) dependence of k; different models yield very different extrapolations.[ii]
A three-pronged approach is here established to study thermal conductivity of deep earth minerals at CMB conditions.
(i) Generating high-pressure and high-temperature states of matter in a diamond anvil cell (DAC) and resolving crystallographic changes in the sample via powder XRD. HED at European XFEL is the only facility at present that has sufficiently high X-ray energy coupled with MHz pulse trains to perform time resolved measurements of heat flow in high pressure samples heated by XFEL pulse trains. The femtosecond FEL pulses generate a unique thermal disturbance in bulk matter at a definitive time point, providing an idealized starting point for thermal relaxation. The AGIPD detector at HED allows for easier determination of relaxation dynamics and heat flow.
(ii) Powder XRD analysis can be carried out by utilising the different timescales of XRD and X-ray absorption, whereby XRD is immediate and occurs before any subsequent unit-cell expansion due to X-ray absorption. The first X-ray pulse is used to collect a diffraction image of the unexcited state of the sample. The next X-ray pulse probes the heated state of the sample 222 ns after first excitation (at 4.5 MHz), before heating the sample again and the step is sequentially repeated.
(iii) Finite element modelling studies allow the determination of thermal parameters such as thermal conductivity and expansivity. Utilising volume change with temperature in a sample, which can be extracted from the diffraction data, a primary model can be made. Temperature dependent thermal conductivity is fitted to the data. Beam energetic data is integrated into the Finite element modelling to dynamically model the fluctuations in the intensity of energy pulses.
[i] (Goncharov et al., 2009, Lay et al., 2008, Hofmeister, 2007, Hofmeister, 1999, Brown, 1986, Kieffer, 1976)
[ii] Goncharov et al., 2009, Hofmeister, 2007, Brown, 1986).
How to cite: Younes, Z., Massai, B., Liermann, H., Konopkova, Z., Husband, R., Prescher, C., Sanchez, C., Jaisle, N., and McWilliams, S.: Thermal conductivity of deep earth minerals using high pressure-temperature time-resolved powder X-ray diffraction at European XFEL, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17152, https://doi.org/10.5194/egusphere-egu23-17152, 2023.
Posters virtual: Wed, 26 Apr, 10:45–12:30 | vHall TS/EMRP
Electrical resistivity measurements of Fe-5wt%Ni were made in-situ under pressures of 2-5 GPa and temperatures up to 2000 K in a cubic-anvil press. The thermal conductivity was calculated from the measured electrical resistivity data using the Wiedemann–Franz law. Comparison of these data with previous studies on pure Fe and Fe-10wt%Ni shows that a change in the Ni content within the range 0-10wt% Ni has no significant effect on electrical resistivity of Fe alloys.
The thermal conductivity values of Fe-5wt%Ni from this study, was used to calculate the adiabatic heat flux in Vesta’s core. Vesta is of interest because the remnant magnetism in eucrites dated at 3.69Ga, reveals it possessed an internally generated dynamo (Fu et al., 2012). Comparing the estimated adiabatic core heat flux of ~331 MW at the top of Vesta’s core to the range of estimated heat flux through the CMB of 1.5–78 GW, we infer that the mechanism stirring Vesta’s liquid outer core to generate its surface magnetic field tens of millions of years in its early history was thermal convection.
How to cite: Orole, O., Yong, W., and Secco, R.: Thermal Convection in Vesta’s Core from Experimentally-Based Conductive Heat Flow Estimates, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-479, https://doi.org/10.5194/egusphere-egu23-479, 2023.
ABSTRACT
In this talk, I will introduce the methods developed in my group, especially the machine learning and graph theory aided crystal structure prediction method (MAGUS) [1]. In addition, I will show some applications of these methods combined with first-principles calculations, for instance, the predictions of new possible compounds (helium-water, helium-ammonia, helium-methane, helium-silica, silica-water, etc) in the interior of giant planets or exoplanets, and their exotic new states under planetary high-pressure and high-temperature conditions (superionic state, plastic state, and their coexistence) [2-6]. These new compounds and their states may have some important implications for giant planets, including demixing, magnetic field, erosion of the rocky core, etc.
REFERENCE
- Kang Xia et al., “A novel superhard tungsten nitride predicted by machine-learning accelerated crystal structure search”, Sci. Bull. 63, 817 (2018).
- Cong Liu et al., “Mixed coordination silica at megabar pressure”, Phys. Rev. Lett. 126, 035701 (2021).
- Cong Liu et al., “Multiple superionic states in helium-water compounds”, Nature Physics 15, 1065 (2019).
- Cong Liu et al., “Plastic and Superionic Helium Ammonia Compounds under High Pressure and High Temperature”, Phys. Rev. X 10, 021007 (2020).
- Hao Gao et al., “Coexistence of plastic and partially diffusive phases in a helium-methane compound”, Natl. Sci. Rev. 7, 1540 (2020).
- Hao Gao et al., “Superionic Silica-Water and Silica-Hydrogen Compounds in the Deep Interiors of Uranus and Neptune”, Phys. Rev. Lett. 128, 035702 (2022).
How to cite: Sun, J.: Unexpected new compounds and their states in the interior of giant planets predicted from first-principles calculations, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3333, https://doi.org/10.5194/egusphere-egu23-3333, 2023.
Fostered by third-generation synchrotron sources, experimental studies of physical and chemical properties of liquids at high pressure and temperatures are constantly pushed towards more and more extreme conditions, with applications ranging from Earth and planetary science, to material science, to fundamental physics.
In the last 20 years, many efforts have been dedicated to the development of a method to obtain structural information from the X-ray diffuse scattering signal of a liquid [1], allowing, for instance, to improve our understanding of the structure and evolution of deep planetary interiors. However, while data collection protocols are by now quite advanced and overall comparable across beamlines worldwide, data analysis largely differs depending on user and employed codes. To answer to the need of a unified data analysis tool for liquids and amorphous systems, we developed Amorpheus [2].
Amorpheus is an open-source, versatile, free and easy-to-use software for the analysis of X-ray diffuse scattering signal, allowing to perform a customizable analysis of a large amount of data and to invert for the density. Available on GitHub [3] it is fully accessible by the community. This software has been tested on data collected with DAC and with large volume presses and it is well adapted for the analysis of liquid metals and alloys, as well as of amorphous systems. Here we will present and discuss selected examples of data analysis performed by Amorpheus in order to determine local structure and density of liquid iron binary and ternary alloys at planetary core conditions.
[1] Eggert JH, Weck G, Loubeyre P, Mezouar M. Quantitative structure factor and density measurements of high-pressure fluids in diamond anvil cells by x-ray diffraction: Argon and water. Phys Rev B. 2002;65(17):174105. doi:10.1103/PhysRevB.65.174105
[2] Boccato S, Garino Y, Morard G, et al. Amorpheus: a Python-based software for the treatment of X-ray scattering data of amorphous and liquid systems. High Press Res. 2022;42(1):69-93. doi:10.1080/08957959.2022.2032032
[3] https://github.com/CelluleProjet/Amorpheus
How to cite: Boccato, S., Morard, G., Garino, Y., Sanloup, C., Zhao, B., Morand, M., and Antonangeli, D.: Analysis of diffuse scattering from liquid and amorphous samples: protocols and software , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14735, https://doi.org/10.5194/egusphere-egu23-14735, 2023.
