Knowledge of the distribution of water in the Earth's mantle is key to understanding the mantle convection and geochemical evolution of the Earth. As wadsleyite and ringwoodite can incorporate large ...amounts of water in their crystal structures, proton conduction has been invoked to account for the widespread conductive anomalies observed in the mantle wedge, where descending slab stagnates at the transition zone. However, there is a lot of controversy on whether proton conduction by itself is able to explain such anomalies, because of large discrepancy in the extent of the water effect deduced from previous electrical conductivity measurements on hydrous polycrystalline wadsleyite and ringwoodite. Here we report the hydrogen self-diffusion coefficient obtained from H–D interdiffusion experiments in wadsleyite single-crystal couples. Our results demonstrate that the effect of water on the electrical conductivity of wadsleyite is limited and hydrous wadsleyite by itself is unable to explain conductive anomalies in the transition zone. In contrast, the expected hydrogen effective diffusion does not allow the wide propagation of water between the stagnant slab and surrounding mantle, probably leading to persistence of local water saturation and continuous release of supercritical fluids at the stagnant slab roof on geological time scales. This phenomenon provides an alternative explanation for both the high-conductivity and seismic-velocity anomalies observed in the mantle wedge at the transition-zone depth.
•The resulting H diffusivity demonstrates an overestimation of previous experimental results.•The resulting H diffusivity cannot explain alone the observed high conductivity anomalies in the deep Earth•Hydrogen solubility indicates a possible continuous generation of fluids in a stagnate slab.
Temari balls are traditional Japanese toys and artworks. The variety of their geometries and tessellations can be investigated formally and computationally with the means of combinatorics. As a ...further step, we also propose a musical application of the core idea of Temari balls. In fact, inspired by the classical idea of music of spheres and by the CubeHarmonic, a musical application of the Rubik’s cube, we present the concept of a new musical instrument, the SphereHarmonic. The mathematical (and musical) description of Temari balls lies in the wide background of interactions between art and combinatorics. Concerning the methods, we present the tools of permutations and tessellations we adopted here, and the core idea for the SphereHarmonic. As the results, we first describe a classification of structures according to the theory of groups. Then, we summarize the main passages implemented in our code, to make the SphereHarmonic play on a laptop. Our study explores an aspect of the deep connections between the mutually inspiring scientific and artistic thinking.
The induction of the germ cell lineage from pluripotent stem cells (in vitro gametogenesis) will help understand the mechanisms underlying germ cell differentiation and provide an alternative source ...of gametes for reproduction. This technology is especially important for cattle, which are among the most important livestock species for milk and meat production. Here, we developed a new method for robust induction of primordial germ cell-like cells (PGCLCs) from newly established bovine embryonic stem (bES) cells. First, we refined the pluripotent culture conditions for pre-implantation embryos and ES cells. Inhibition of RHO increased the number of epiblast cells in the pre-implantation embryos and dramatically improved the efficiency of ES cell establishment. We then determined suitable culture conditions for PGCLC differentiation using bES cells harboring BLIMP1-tdTomato and TFAP2C-mNeonGreen (BTTN) reporter constructs. After a 24-h culture with bone morphogenetic protein 4 (BMP4), followed by three-dimensional culture with BMP4 and a chemical agonist and WNT signaling chemical antagonist, bES cells became positive for the reporters. A set of primordial germ cells (PGC) marker genes, including PRDM1/BLIMP1, TFAP2C, SOX17, and NANOS3, were expressed in BTTN-positive cells. These bovine PGCLCs (bPGCLCs) were isolated as KIT/CD117-positive and CD44-negative cell populations. We anticipate that this method for the efficient establishment of bES cells and induction of PGCLCs will be useful for stem cell-based reproductive technologies in cattle.
We review the currently available results of laboratory experiments, geochemistry and MT observations and attempt to explain the conductivity structures in the oceanic asthenosphere by constructing ...mineral-physics models for the depleted mid-oceanic ridge basalt (MORB) mantle (DMM) and volatile-enriched plume mantle (EM) along the normal and plume geotherms. The hopping and ionic conductivity of olivine has a large temperature dependence, whereas the proton conductivity has a smaller dependence. The contribution of proton conduction is small in DMM. Melt conductivity is enhanced by the H2O and CO2 components. The effects of incipient melts with high volatile components on bulk conductivity are significant. The low solidus temperatures of the hydrous carbonated peridotite produce incipient melts in the asthenosphere, which strongly increase conductivity around 100km depth under older plates. DMM has a conductivity of 10−1.2~−1.5S/m at 100–300km depth, regardless of the plate age. Plume mantle should have much higher conductivity than normal mantle, due to its high volatile content and high temperatures. The MT observations of the oceanic asthenosphere show a relatively uniform conductivity at 200–300km depth, consistent with the mineral-physics model. On the other hand, the MT observations show large lateral variations in shallow parts of the asthenosphere despite similar tectonic settings and close locations. Such variations are difficult to explain with the mineral-physics model. High conductivity layers (HCL), which are associated with anisotropy in the direction of the plate motion, have only been observed in the asthenosphere under infant or young plates, but they are not ubiquitous in the oceanic asthenosphere. Although the general features of HCL imply their high-temperature melting origin, the mineral-physics model cannot explain them quantitatively. Much lower conductivity under hotspots, compared with the model plume-mantle conductivity suggests the extraction of volatiles from the plume mantle by the ocean island basalt (OIB) magmatism.
•Results of laboratory experiments, geochemistry and MT observations are reviewed.•High conductivity layers are limited under very young plates, which suggests their high-T origin.•Conductivity at 100–200km depth are well explained by the mineral-physics model.•Conductivity in shallower regions cannot be quantitatively explained.•Large lateral variations in shallow regions despite similar tectonic settings and close locations
Electrical impedance measurements were performed on two types of partial molten samples with basaltic and carbonatitic melts in a Kawai-type multi-anvil apparatus in order to investigate melt ...fraction–conductivity relationships and melt distribution of the partial molten mantle peridotite under high pressure. The silicate samples were composed of San Carlos olivine with various amounts of mid-ocean ridge basalt (MORB), and the carbonate samples were a mixture of San Carlos olivine with various amounts of carbonatite. High-pressure experiments on the silicate and carbonate systems were performed up to 1600
K at 1.5
GPa and up to at least 1650
K at 3
GPa, respectively. The sample conductivity increased with increasing melt fraction. Carbonatite-bearing samples show approximately one order of magnitude higher conductivity than basalt-bearing ones at the similar melt fraction. A linear relationship between log conductivity (
σ
bulk) and log melt fraction (
ϕ) can be expressed well by the Archie's law (Archie, 1942) (
σ
bulk/
σ
melt
=
Cϕ
n
) with parameters
C
=
0.68 and 0.97,
n
=
0.87 and 1.13 for silicate and carbonate systems, respectively. Comparison of the electrical conductivity data with theoretical predictions for melt distribution indicates that the model assuming that the grain boundary is completely wetted by melt is the most preferable melt geometry. The gradual change of conductivity with melt fraction suggests no permeability jump due to melt percolation at a certain melt fraction. The melt fraction of the partial molten region in the upper mantle can be estimated to be 1–3% and ∼
0.3% for basaltic melt and carbonatite melt, respectively.
Hydrogen lattice diffusion in Fe‐bearing ringwoodite was investigated through hydrogen and deuterium interdiffusing in a pair of synthesized single crystals at various temperatures (1000–1300 K) at ...21 GPa. Diffusion profiles were investigated by secondary ion mass spectrometer to determine the hydrogen self‐diffusivity in ringwoodite. Temperature dependences of hydrogen diffusion in ringwoodite were determined to be DH = 10− 7.29(±0.46) exp−101(±10)kJ mol− 1/RT m2/s in ringwoodite at 21 GPa. The proton conductivities of ringwoodite estimated from the present diffusion coefficients are similar to those of Yoshino et al. 2008 at the transition zone condition at low water content (<1000 ppm by weight (ppmw)) but lower at higher water content range (>1000 ppmw). If the proton‐vacancy mechanism is assumed to be a main controlling mechanism, contribution of water to the electrical conductivity of ringwoodite is insignificant due to large contribution of hopping conduction at the transition zone condition, and global average water concentration in the lower part of transition zone is less than 1000 ppmw.
Key Points
Hydrogen diffusivity in ringwoodite is determined by H‐D exchange method
EC from diffusivities are lower than former EC measure at high water content
This model suggests that average water content in transition zone is <1000 ppmw
We report here new experimental kinetic data on the structural evolution of carbonaceous material (CM) to graphite during heating at various temperatures (1000 to 1450°C) for various durations (10 ...min to 115 h) under a pressure of 1 GPa. Natural CMs extracted from sedimentary rocks in the Shimanto accretionary complex and the Hidaka metamorphic belt of Japan transformed in morphology and crystallinity with increasing temperature and annealing duration to become fully ordered graphite (d002 spacing ∼3.36 Å). Transmission electron microscopy showed that both samples have undergone microstructural evolution from amorphous carbon to platy graphitic carbon. These changes match the evolution of the samples' X-ray diffraction (XRD) patterns and micro-Raman spectra. The time-temperature relations of crystal parameters obtained by XRD and micro-Raman spectroscopy demonstrated a sigmoidal transformation curve from an amorphous to a graphitic structure, suggesting complexity of these successive and/or parallel chemical reactions are responsible for graphitization. To assess these complex chemical processes, we adopted three different approaches for formulating the graphitization kinetics using a power rate model, a Johnson-Mehl-Avrami (JMA) model and a superposition method. Irrespective of the models employed, the effective activation energies were estimated to lie between 259 and 339 kJ/mol, which are much lower than those reported previously for graphitization. Summarizing the previous studies and our results between 0.1 and 1000 MPa, we found that the effective activation energies systematically decrease as a function of pressure. Based on the experimental results in this study, the sigmoid functions obtained from the time-temperature relations can be extrapolated to low-temperature conditions at 1 GPa. Our kinetic model using unit-cell height c predicts that CM undergoing metamorphism for about 1 m.y. will begin to crystallize at ∼410°C, and will transform to fully ordered graphite at over ∼520°C. Thus, natural graphitization undergoes a much faster transformation than reported in previous studies at 1 atm and could be explored in laboratory experiments using natural precursor materials under pressure conditions and time spans that reflect natural conditions in the Earth's crust.
Hydrogen has been considered as an important candidate of light elements in the Earth's core. Because iron hydrides are unquenchable, hydrogen content is usually estimated from in situ X-ray ...diffraction measurements that assume the following linear relation: x = (VFeHx - VFe)/ΔVH, where x is the hydrogen content, ΔVH is the volume expansion caused by unit concentration of hydrogen, and VFeHx and VFe are volumes of FeHx and pure iron, respectively. To verify the linear relationship, we computed the equation of states of hexagonal iron with interstitial hydrogen by using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). The results indicate a discontinuous volume change at the magnetic transition and almost no compositional (x) dependence in the ferromagnetic phase at 20 GPa, whereas the linearity is confirmed in the non-magnetic phase. In addition to their effect on the density-composition relationship in the Fe-FeHx system, which is important for estimating the hydrogen incorporation in planetary cores, the magnetism and interstitial hydrogen also affect the electrical resistivity of FeHx. The thermal conductivity can be calculated from the electrical resistivity by using the Wiedemann-Franz law, which is a critical parameter for modeling the thermal evolution of the Earth. Assuming an Fe1-ySiyHx ternary outer core model (0.0 ≤ x ≤ 0.7), we calculated the thermal conductivity and the age of the inner core. The resultant thermal conductivity is ∼100 W/m/K and the maximum inner core age ranges from 0.49 to 0.86 Gyr.
•We report the electrical conductivity of partially molten peridotite under shear.•Shear-parallel conductivity values were one order higher than those normal to shear.•EC anisotropy was caused by the ...elongation of melt pockets in the shear direction.•Partial melt can explain conductivity anisotropy at the top of asthenosphere.•We discuss the mechanism of lubrication by partial melt at LAB.
The electrical conductivity of partially molten peridotite was measured during deformation in simple shear at 1 GPa in a DIA type apparatus with a uniaxial deformation facility. To detect development of electrical anisotropy during deformation of partially molten system, the electrical conductivity was measured simultaneously in two directions of three principal axes: parallel and normal to the shear direction on the shear plane, and perpendicular to the shear plane. Impedance spectroscopy measurement was performed at temperatures of 1523 K for Fe-bearing and 1723 K for Fe-free samples, respectively, in a frequency range from 0.1 Hz to 1 MHz. The electrical conductivity of partially molten peridotite parallel to shear direction increased to more than one order of magnitude higher than those normal to shear direction on the shear plane. This conductivity difference is consistent with the magnitude of the conductivity anisotropy observed in the oceanic asthenosphere near the Eastern Pacific Rise. On the other hand, conductivity perpendicular to the shear plane decreased gradually after the initiation of shear and finally achieved a value close to that of olivine. The magnitude and development style of conductivity anisotropy was almost the same for both Fe-bearing and Fe-free melt-bearing systems, and also independent of shear strain. However, such conductivity anisotropy was not developed in melt-free samples during shear deformation, suggesting that the conductivity anisotropy requires a presence of partial melting under shear stress. Microstructural observations of deformed partially molten peridotite samples demonstrated that conductivity anisotropy was attributed to the elongation of melt pockets parallel to the shear direction. Horizontal electrical conductivity anisotropy revealed by magnetotelluric surveys in the oceanic asthenosphere can be well explained by the realignment of partial melt induced by shear stress.
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