Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties
Huang, Y., Nakatani, T., Nakamura, M., & McCammon, C. (2019). Saline aqueous fluid circulation in mantle wedge inferred from olivine wetting properties. Nature Communications, 10(1), 1–10. https://doi.org/10.1038/s41467-019-13513-7
Recently, high electrical conductors have been detected beneath some fore-arcs and are believed to store voluminous slab-derived fluids. This implies that the for-arc mantle wedge is permeable for aqueous fluids. Here, we precisely determine the dihedral (wetting) angle in an olivine–NaCl–H2O system at fore-arc mantle conditions to assess the effect of salinity of subduction-zone fluids on the fluid connectivity. We find that NaCl significantly decreases the dihedral angle to below 60° in all investigated conditions at concentrations above 5 wt% and, importantly, even at 1 wt% at 2 GPa. Our results show that slab-released fluid forms an interconnected network at relatively shallow depths of ~80 km and can partly reach the fore-arc crust without causing wet-melting and serpentinization of the mantle. Fluid transport through this permeable window of mantle wedge accounts for the location of the high electrical conductivity anomalies detected in fore-arc regions.
Schematic model for migration of saline aqueous fluids. a Overview of subduction fluid migration. b Enlargement of the black rectangle in a. Slab-derived saline fluids can form an interconnected network in the mantle wedge at depths of ~80 km, and can percolate partly through the overriding mantle without causing melting or serpentinization to form a fluid reservoir in the forearc crust (blue thick open arrow). At depths <~80 km, where antigorite is still stable, slab-derived fluids can enter the cold corner of mantle wedge as a channelized flow along cracks. At depths >~80 km, saline fluid continuously infiltrates the mantle wedge with temperatures above ~1050 °C, which triggers the partial melting of peridotite67 (blue thick solid arrows). It should be noted that this hydrous peridotite solidus was constrained in a fertile peridotite system; the solidus temperature in a relatively depleted peridotite should be higher than that shown here. Magma ascent results in the formation of arc volcanoes (red arrows), although the location of the volcanic front is not directly related to the dihedral angle threshold for saline fluid. The geothermal structure is after Wada et al.80; the stability of antigorite is after Bromiley and Pawley78 and Evans et al.79; and the stability of chlorite is after Till et al.11. Atg antigorite, Chl chlorite. □
Synthesis of magnesium-nitrogen salts of polynitrogen anions
Laniel, D., Winkler, B., Koemets, E., Fedotenko, T., Bykov, M., Bykova, E., Dubrovinsky, L., & Dubrovinskaia, N. (2019). Synthesis of magnesium-nitrogen salts of polynitrogen anions. Nature Communications, 10(1). https://doi.org/10.1038/s41467-019-12530-w
The synthesis of polynitrogen compounds is of fundamental importance due to their potential as environmentally-friendly high energy density materials. Attesting to the intrinsic difficulties related to their formation, only three polynitrogen ions, bulk stabilized as salts, are known. Here, magnesium and molecular nitrogen are compressed to about 50 GPa and laser-heated, producing two chemically simple salts of polynitrogen anions, MgN4 and Mg2N4. Single-crystal X-ray diffraction reveals infinite anionic polythiazyl-like 1D N-N chains in the crystal structure of MgN4 and cis-tetranitrogen N44− units in the two isosymmetric polymorphs of Mg2N4. The cis-tetranitrogen units are found to be recoverable at atmospheric pressure. Our results respond to the quest for polynitrogen entities stable at ambient conditions, reveal the potential of employing high pressures in their synthesis and enrich the nitrogen chemistry through the discovery of other nitrogen species, which provides further possibilities to design improved polynitrogen arrangements.
The crystal structure of the MgN4 and β-Mg2N4 salts at 58.5 GPa. a The unit cell of MgN4 (the light blue, dark blue and orange spheres represent the N1, N2 and Mg atoms, respectively); b a projection of the MgN4 structure along the c-axis, emphasising 1D chains of nitrogen atoms aligned along the a-axis; c a repeating N42− subunit of a chain with the N-N distances and angles indicated; d the unit cell of β-Mg2N4 (the light green and dark green spheres represent the four distinct nitrogen atoms forming the a-N44− and b-N44− units, respectively, the orange spheres represent Mg atoms); e a projection of the β-Mg2N4 structure along the b-axis allowing to see the alternating layers of isolated a-N44− and b-N44− units, intercalated with Mg2+ ions. f The a-N44− (left) and b-N44− (right) entities with bond lengths and angles indicated. □
Novel experiments at BGI explain the sharpness of the 660-km discontinuity
Ishii, T., Huang, R., Myhill, R., Fei, H., Koemets, I., Liu, Z., Maeda, F., Yuan, L., Wang, L., Druzhbin, D., Yamamoto, T., Bhat, S., Farla, R., Kawazoe, T., Tsujino, N., Kulik, E., Higo, Y., Tange, Y., & Katsura, T. (2019). Sharp 660-km discontinuity controlled by extremely narrow binary post-spinel transition. Nature Geoscience, 12(10), 869–872. https://doi.org/10.1038/s41561-019-0452-1
The Earth’s mantle shows an abrupt increase of seismic velocities at a depth of 660 km, referred to as the 660-km discontinuity. Mineral physics data suggest that ringwoodite decomposes to bridgmanite plus ferropericlase around a pressure corresponding to the depth of 660 km. It has therefore been considered that the 660-km discontinuity is caused by this “post-spinel transition”.
One of the prominent features of the 660-km discontinuity is that it occurs over an interval of less than 2 km, corresponding to 0.1 GPa variation in pressure. This extreme sharpness could not be duplicated by any laboratory experiment. One reason is that the pressure resolution in previous studies was limited to 0.2~0.5 GPa. Another reason may be that during previous experiments, sample pressures dropped more than 2 GPa even at constant temperature and press load. We developed high-precision pressure measurements with an accuracy of 0.05 GPa by in situ X-ray diffraction, and attempted to keep sample pressures constant by finely controlling press load. By combining such state-of-the-art high-pressure experiments with thermochemical calculation, we were able to demonstrate that the pressure interval of the post-spinel transition is only 0.01 GPa, corresponding to a thickness of the discontinuity of 250 m.
These results are more than sufficient to explain the sharpness of the discontinuity, and provide new support for whole mantle convection in a chemically homogeneous pyrolitic mantle. The present work also proposes a new method to detect flow between the upper and lower mantle based on discontinuity sharpness, because the interval should increase by a rapid flow across the 660-km discontinuity.
Phase relations in the system Mg2SiO4-Fe2SiO4 at a temperature of 1700 K. Brg: bridgmanite, fPc: ferropericlase, Rw: ringwoodite, St: stishovite. At mantle composition, the width of the Rw + Brg + fPc loop is only 0.01 GPa in pressure, corresponding to 250 m in depth. This width becomes even smaller for a mantle temperature of 2000 K. The horizontal axis is the fraction of Mg2SiO4 component. □
Deep magma ocean changes Earth’s atmosphere
Armstrong, K., Frost, D. J., McCammon, C. A., Rubie, D. C., & Ballaran, T. B. (2019). Deep magma ocean formation set the oxidation state of Earth’s mantle. Science, 365(6456), 903–906. https://doi.org/10.1126/science.aax8376
New results show that ferrous iron in a deep magma ocean will disproportionate to ferric iron plus metallic iron at high pressures. The redox state of the mantle became more oxidising at some stage after Earth’s core started to form, but up to now there has been no clear indication of how this occurred. These new results imply that the separation of metallic iron to the core would have raised the oxidation state of the upper mantle, changing the chemistry of volatiles that formed the atmosphere to more oxidised species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved carbon dioxide from the atmosphere to precipitate as diamond at depth. This explains Earth’s carbon-rich interior and suggests that redox evolution during accretion was an important variable in determining the composition of the terrestrial atmosphere.
The ferric iron content of silicate melt changes with pressure. At low pressure iron becomes more reduced, but at higher pressure it oxidises, likely through disproportionation of ferrous iron to ferric iron plus metallic iron. The same reaction occurs at both high oxygen fugacity (red region) and low oxygen fugacity (grey region). Modified from Armstrong et al. (2019) □
First Observation of Hydrogen-Hydrogen Interactions in Metal Hydrides at Multi-Megabar Pressures
Thomas Meier, Florian Trybel, Saiana Khandarkhaeva, Gerd Steinle-Neumann, Stella Chariton, Timofey Fedotenko, Sylvain Petitgirard, Michael Hanfland, Konstantin Glazyrin, Natalia Dubrovinskaia & Leonid Dubrovinsky (2019). Pressure-Induced Hydrogen-Hydrogen Interaction in Metallic FeH Revealed by NMR. Physical Review X, 9(3), 031008. https://doi.org/10.1103/PhysRevX.9.031008
Hydrogen is the most abundant element in our universe; it comprises one of the most fundamental building blocks of stars and gaseous planets. Also on Earth, element number one is ubiquitous: in organic material such as the human body, in synthetic materials as well as everywhere in Nature.
The elusive properties of Hydrogen under extreme conditions is a research field engaged by condensed matter scientists since almost 80 years. For Hydrogen, one of the seemingly simplest chemical substances, is believed to yield to the key to superconductivity at room temperature. This superconductive state of H2 however has never been experimentally found in high pressure laboratories. A promising alternative constitute hydrogen rich metal hydrides. Over the course of the last years several research groups succeeded in subjecting certain metal hydrides, e.g. H3S and LaH10, to pressures above 100 GPa and detect evidence for superconductivity at refrigerator temperatures (-23°C). The microscopic physical effects leading to such high transition temperatures could, however, not be experimentally investigated.
In this new work, a group from the Bavarian Geoinstitute, Bayreuth University, the European Synchrotron Radiation Facility as well as the German Electron Synchrotron have been able to synthesize metal hydrides, i.e. FeH, in diamond anvil cell experiments and subject it to pressures as high as 200 GPa while investigating its electronic properties using Nuclear Magnetic Resonance spectroscopy. These experiments showed that hydrogen atoms in metal hydrides form a sublattice connected by conduction electrons, a requisite for superconductivity, which has only been predicted before but never observed.
This study leads the way to novel methods verifying theoretical predictions and might lead to predictions and the discovery of novel high temperature superconducting materials at ambient conditions.
Left: Computed electron localization function maps at about 10 GPa and 200 GPa, green areas denote regions of free electron gas, i.e. enhanced conduction electron density. Right: comparison of experimental data, i.e. electron-nuclear hyper-fine interaction, and density of states data from ab-initio calculations. □
High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re2(N2)(N)2 stable at ambient conditions
Bykov, M., Chariton, S., Fei, H., Fedotenko, T., Aprilis, G., Ponomareva, A. V., Tasnádi, F., Abrikosov, I. A., Merle, B., Feldner, P., Vogel, S., Schnick, W., Prakapenka, V. B., Greenberg, E., Hanfland, M., Pakhomova, A., Liermann, H. P., Katsura, T., Dubrovinskaia, N., & Dubrovinsky, L. (2019). High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re2(N2)(N)2 stable at ambient conditions. Nature Communications, 10(1), 1–8. https://doi.org/10.1038/s41467-019-10995-3
High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re2(N2)(N)2. Unlike known transition metals pernitrides Re2(N2)(N)2 contains both pernitride N24− and discrete N3− anions, which explains its exceptional properties. Re2(N2)(N)2 can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re2(N2)(N)2 turned to be at a threshold for superhard materials.
Although LHDAC is an efficient method to study high-pressure chemical reactions, it is challenging to scale up the synthesis. The search for suitable synthetic strategies, which would enable an appropriate reaction to be realized in a large volume press (LVP) instead of a LHDAC, is an important challenge for high-pressure chemistry and materials sciences. In this study, focusing on the high-pressure synthesis of nitrogen-rich phases in the Re-N system and the development of new synthetic strategies, we resolved this problem for a rhenium nitride ReN2 with unusual crystal chemistry and unique properties.
Phonon and electronic structure calculations for ReN2. Calculated phonon dispersion relations (a), charge density map (b), densities of states (c), and electron localization function (d) for ReN2 at ambient conditions. □
Magnetism in subduction zones
Kupenko, I., Aprilis, G., Vasiukov, D. M., McCammon, C., Chariton, S., Cerantola, V., Kantor, I., Chumakov, A. I., Rüffer, R., Dubrovinsky, L., & Sanchez-Valle, C. (2019). Magnetism in cold subducting slabs at mantle transition zone depths. Nature, 570(7759), 102–106. https://doi.org/10.1038/s41586-019-1254-8
Materials constituting Earth's mantle are traditionally considered to be non-magnetic due to pressures and temperatures being too high to preserve magnetic order. However, satellite and aeromagnetic data provide evidence for magnetic anomalies in the mantle, particularly around cooler areas such as subduction zones. The reasons and sources of the anomalies remain largely unknown, but iron-bearing oxides are a potential source due to their postulated high critical temperatures. Of these, hematite (Fe2O3) could be one of the most abundant iron oxides in oxidised subducting slabs.
A new methodology that combines a Synchrotron Mössbauer Source to probe magnetism and double-sided laser heating in diamond anvil cells (DACs) to generate pressures and temperatures characteristic for Earth's mantle was developed at BGI and at ID18 at ESRF. This methodology was applied to study the behaviour of Fe2O3 at pressures up to 90 GPa and temperatures over 1300 K. The surprisingly result is that different phases of Fe2O3 retain magnetic order at conditions in cold subducting slabs that penetrate (or stagnate) in the transition zone. Thus, it has been demonstrated that materials in Earth's mantle are not always “magnetically dead” and can be a source of deep magnetic anomalies.
Graphical illustration of Earth's interior and the experiment. Blue lines with arrows show Earth's magnetic field. Samples of iron oxide (hematite as starting material) were compressed and laser-heated in DACs (right) to simulate the extreme conditions in Earth's mantle. The key observation is the existence of magnetically ordered Fe2O3 phases at these conditions. Courtesy of Timofey Fedotenko. □
The surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy
Kitazato, K., Milliken, R. E., Iwata, T., Abe, M., Ohtake, M., Matsuura, S., Arai, T., Nakauchi, Y., Nakamura, T., Matsuoka, M., Senshu, H., Hirata, N., Hiroi, T., Pilorget, C., Brunetto, R., Poulet, F., Riu, L., Bibring, J. P., Takir, D., … Tsuda, Y. (2019). The surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy. Science, 364(6437), 272–275. https://doi.org/10.1126/science.aav7432
The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu’s surface acquired with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)–bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body. □
Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu-A spinning top-shaped rubble pile
Watanabe, S., Hirabayashi, M., Hirata, N., Hirata, N., Noguchi, R., Shimaki, Y., Ikeda, H., Tatsumi, E., Yoshikawa, M., Kikuchi, S., Yabuta, H., Nakamura, T., Tachibana, S., Ishihara, Y., Morota, T., Kitazato, K., Sakatani, N., Matsumoto, K., Wada, K., … Tsuda, Y. (2019). Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu-A spinning top-shaped rubble pile. Science, 364(6437), 268–272. https://doi.org/10.1126/science.aav8032
The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu’s shape, mass, and geomorphology. Ryugu has an oblate “spinning top” shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu’s shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge. □
The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes
Sugita, S., Honda, R., Morota, T., Kameda, S., Sawada, H., Tatsumi, E., Yamada, M., Honda, C., Yokota, Y., Kouyama, T., Sakatani, N., Ogawa, K., Suzuki, H., Okada, T., Namiki, N., Tanaka, S., Iijima, Y., Yoshioka, K., Hayakawa, M., … Nakamura, T., … Tsuda, Y. (2019). The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes. Science, 364(6437). https://doi.org/10.1126/science.aaw0422
The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multicolor images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of ≲106 years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu’s surface supports partial dehydration due to internal heating of the asteroid’s parent body. □
Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains
Bykov, M., Bykova, E., Aprilis, G., Glazyrin, K., Koemets, E., Chuvashova, I., Kupenko, I., McCammon, C., Mezouar, M., Prakapenka, V., Liermann, H. P., Tasnádi, F., Ponomareva, A. V., Abrikosov, I. A., Dubrovinskaia, N., & Dubrovinsky, L. (2018). Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains. Nature Communications, 9(1). https://doi.org/10.1038/s41467-018-05143-2
Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N–N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure. Here, through a direct reaction between Fe and N2 in a laser-heated diamond anvil cell, we synthesize three iron nitrogen compounds Fe3N2, FeN2 and FeN4. Their crystal structures are revealed by single-crystal synchrotron X-ray diffraction. Fe3N2, synthesized at 50 GPa, is isostructural to chromium carbide Cr3C2. FeN2 has a marcasite structure type and features covalently bonded dinitrogen units in its crystal structure. FeN4, synthesized at 106 GPa, features polymeric nitrogen chains of [N42−]n units. Based on results of structural studies and theoretical analysis, [N42−]n units in this compound reveal catena-poly[tetraz-1-ene-1,4-diyl] anions.
Fragments of the crystal structure of FeN4 at 135 GPa. a A fragment of the crystal structure parallel to the (1-10) lattice plane featuring polymeric zigzag N–N chains. Out-off –plane atoms are not shown. b The same fragment shown in a different projection. c A fragment of the crystal structure showing the coordination geometry of the nitrogen atoms. d The charge density map with zig-zag N–N chains in FeN4 structure. e A scheme of poly[tetraz-1-ene-1,4-diyl] anion. f A scheme of coordination of iron atoms by poly[tetraz-1-ene-1,4-diyl] anions. □
Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity
A. Kurnosov, H. Marquardt, D. J. Frost, T. Boffa Ballaran & L. Ziberna (2017). Evidence for a Fe3+-rich pyrolitic lower mantle from (Al,Fe)-bearing bridgmanite elasticity data. Nature 543(7646), 543–546. https://doi.org/10.1038/nature21390
Scientists from BGI Bayreuth measured the high-pressure seismic properties of (Al,Fe)-bearing bridgmanite, Earth’s most abundant mineral, in the laboratory. To facilitate these measurements, advanced FIB sample preparation techniques were combined with a worldwide unique Brillouin spectroscopy and x-ray diffraction laboratory system operating at BGI Bayreuth. It has been found that the seismic velocities of (Al,Fe)-bearing bridgmanite are markedly different from those previously reported for the Mg-endmember of bridgmanite.
Based on the novel measurements, synthetic seismic profiles for the Earth’s lower mantle have been calculated in order to test mineralogical models directly against seismic observations. It is found that velocities predicted for a lower mantle with a pyrolitic model composition are in excellent agreement with seismic observables if the newly determined effects of Fe/Al-incorporation on the seismic properties of bridgmanite are taken into account. Furthermore, it is found that the modelled velocities are in increasingly poor agreement with those of the lower mantle at depths >1200 km, indicating either a change in bridgmanite cation ordering or a decrease in the ferric iron content of the lower mantle. This finding calls for follow-up studies designed to understand possible effects on the physical and chemical properties of the lower mantle.
Pressure-dependence of the here-derived average acoustic velocities of Al-Fe-bearing bridgmanite (red circles). The blue dotted line indicates the pressure-trend of Mg-endmember bridgmanite inferred from previous work. The inset shows a view into the pressure chamber of a diamond-anvil cell loaded with two half-circular samples of single-crystal Al-Fe-bearing bridgmanite with different crystallographic orientations. □
Flux of volcanic CO2 estimated from melt inclusions
and a model of fluid transport in volcanic activity
Yoshimura S. & Nakamura M. (2013) EPSL
Origin of Earth’s Volatiles
Hayabusa and Hayabusa-II missions -
The Hayabusa spacecraft
PI of Sample recovery from asteroid 25143 Itokawa
Nakamura, T. et al, (2010) Science
Impact-induced devolatilization of hydrous C-type asteroid
Nakamura T. (2006) EPSL
Volatile induced melts
Discovery of Petit spot volcanism, a new type of submarine volcanism in oceanic lithosphere
Hirano et al. (2006) Science
IRTG cooperation – Water bearing minerals
Water in the mantle
Ohtani E. (2005) Elements
Density, viscosity, and structure of magmas
Ponded melt at the boundary between the lithosphere and asthenosphere
Sakamaki T, Suzuki A, et al. (2013) Nature Geoscience