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11 results on '"Nomura, Ryuichi"'

1. Reconciling Magma-Ocean Crystallization Models with the present-day Structure of the Earth's mantle

Author

Ballmer, Maxim D., Lourenço, Diogo L., Hirose, Kei, Caracas, Razvan, and Nomura, Ryuichi

Subjects
Astrophysics - Earth and Planetary Astrophysics
Abstract

Terrestrial planets are thought to experience episode(s) of large-scale melting early in their history. Fractionation during magma-ocean freezing leads to unstable stratification within the related cumulate layers due to progressive iron enrichment upward, but the effects of incremental cumulate overturns during MO crystallization remain to be explored. Here, we use geodynamic models with a moving-boundary approach to study convection and mixing within the growing cumulate layer, and thereafter within the fully crystallized mantle. For fractional crystallization, cumulates are efficiently stirred due to subsequent incremental overturns, except for strongly iron-enriched late-stage cumulates, which persist as a stably stratified layer at the base of the mantle for billions of years. Less extreme crystallization scenarios can lead to somewhat more subtle stratification. In any case, the long-term preservation of at least a thin layer of extremely enriched cumulates with Fe#>0.4, as predicted by all our models, is inconsistent with seismic constraints. Based on scaling relationships, however, we infer that final-stage Fe-rich magma-ocean cumulates originally formed near the surface should have overturned as small diapirs, and hence undergone melting and reaction with the host rock during sinking. The resulting moderately iron-enriched metasomatized/hybrid rock assemblages should have accumulated at the base of the mantle, potentially fed an intermittent basal magma ocean, and be preserved through the present-day. Such moderately iron-enriched rock assemblages can reconcile the physical properties of the large low shear-wave velocity provinces in the presentday lower mantle. Thus, we reveal Hadean melting and rock-reaction processes by integrating magmaocean crystallization models with the seismic-tomography snapshot.

Published
2018
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3. Data in Park et al., 2022, submitted to Geophysical Research Letters

Author

Park, Yohan, Azuma, Shintaro, Okazaki, Keishi, Uesugi, Kentaro, Yasutake, Masahiro, Nishihara, Yu, and Nomura, Ryuichi

Abstract

This is an archive of data in Yohan et al., 2022, submitted to GRL. The data includes all stress-strain curves shown in the manuscript. Files with a .tifextension are the XRD data (Debye-Scherrer rings) of the deformed MgO analyzed by the software package MAUD. PFs data of exp4 was used for calculation of the seismic wave velocities in Figure 4 using MTEX and Matlab.

Published
2022
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5. Spin crossover and iron-rich silicate melt in the Earth's deep mantle

Author

Nomura, Ryuichi, Ozawa, Haruka, Tateno, Shigehiko, Hirose, Kei, Hernlund, John, Muto, Shunsuke, Ishii, Hirofumi, and Hiraoka, Nozomu

Subjects
Analysis, Composition, Silicates -- Analysis -- Composition, Temperature control -- Analysis, Perovskite -- Analysis -- Composition
Abstract

Our melting experiments were performed on samples with bulk composition ([Mg.sub.0.89] [[Fe.sub.011]).sub.2] Si[O.sub.4] at pressures from 20 to 159 GPa in a laser-heated diamond-anvil cell (DAC; Supplementary Table 1). The [...], A melt has greater volume than a silicate solid of the same composition. But this difference diminishes at high pressure, and the possibility that a melt sufficiently enriched in the heavy element iron might then become more dense than solids at the pressures in the interior of the Earth (and other terrestrial bodies) has long been a source of considerable speculation (1,2). The occurrence of such dense silicate melts in the Earth's lowermost mantle would carry important consequences for its physical and chemical evolution and could provide a unifying model for explaining a variety of observed features in the core-mantle boundary region (3). Recent theoretical calculations (4) combined with estimates of iron partitioning between (Mg,Fe)Si[O.sub.3] perovskite and melt at shallower mantle conditions (5-7) suggest that melt is more dense than solids at pressures in the Earth's deepest mantle, consistent with analysis of shockwave experiments (8). Here we extend measurements of iron partitioning over the entire mantle pressure range, and find a precipitous change at pressures greater than ~76 GPa, resulting in strong iron enrichment in melts. Additional X-ray emission spectroscopy measurements on (M[g.sub.0.95] [Fe.sub.0.05])Si[O.sub.3] glass indicate a spin collapse around 70 GPa, suggesting that the observed change in iron partitioning could be explained by a spin crossover of iron (from high-spin to low-spin) in silicate melt. These results imply that (Mg,Fe)Si[O.sub.3] liquid becomes more dense than coexisting solid at ~1,800 km depth in the lower mantle. Soon after the Earth's formation, the heat dissipated by accretion and internal differentiation could have produced a dense melt layer up to ~1,000 km in thickness underneath the solid mantle. We also infer that (Mg,Fe)Si[O.sub.3] perovskite is on the liquidus at deep mantle conditions, and predict that fractional crystallization of dense magma would have evolved towards an iron-rich and silicon-poor composition, consistent with seismic inferences of structures in the core-mantle boundary region.

Published
2011
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8. Additional file 1: Figure S1. of Melting phase relations in the MgSiO3–CaSiO3 system at 24 GPa

Author

Nomura, Ryuichi, Youmo Zhou, and Irifune, Tetsuo

Abstract

Pressure calibrations at room temperature (RT) and high temperatures. Fo, Mg2SiO4, forsterite; Wd, Mg2SiO4 wadsleyite; Rw, Mg2SiO4 ringwoodite; Ak, MgSiO3 akimotoite; Bdg, MgSiO3 bridgmanite; Pc, MgO periclase. Pressures of the phase transitions at high temperatures were taken from Morishima et al. (1994), Suzuki et al. (2000), and Fei et al. (2004). The red point at 790 ton, 23 GPa, and 2273 K is 0.55 GPa away from the green curve of 1873 K, which is comparable to the standard deviation of the fitting curves, 0.4 GPa. Figure S2: Heating power-temperature relationships. Figure S3: Melting temperatures of MgO. The black line represents the melting temperatures calculated in this study, and the dashed gray line represents those by de Koker and Stixrude (2009). The melting temperatures determined by high-pressure experiments and ab initio calculations are also plotted: orange squares, Zerr and Boehler (1994); green triangles, Alfe (2005); blue circles, Zhang and Fei (2008); purple squares, Du and Lee (2014); and red squares, Kimura et al. (2017). Figure S4: Melting phase diagram in the MgO–MgSiO3 system at 24 GPa. The black line represents the phase boundary calculated in this study, and the gray line represents that by Liebske and Frost (2012). The experimental data by Liebske and Frost (2012) are also plotted, where the red circle represents the composition of liquid above liquidus, the green squares represent liquid coexisting with periclase (Pc), the orange squares represent liquid coexisting with bridgmanite (Bdg), and the diamonds represent subsolidus phases. Interaction parameter updated by Ohnishi et al. (2017) was used to calculate the phase relations. Figure S5: X-ray diffraction patterns of the run products. The black short bars beneath the curves denote the peak positions of bridgmanite (Bdg) and rhenium (Re). (PDF 1046 kb)

Published
2017
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