Haruka Ozawa

Tokyo Institute of Technology, Edo, Tōkyō, Japan

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Publications (21)116.29 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The continental crust is a unique reservoir of light elements in the solid Earth; it possesses an intermediate composition and is believed to have been created principally along volcanic arcs, which are major sites of terrestrial andesitic magmatism. Mantle-derived arc magmas are, however, generally mafic or basaltic. A simple mechanism to overcome this apparent dilemma and generate andesitic melts in such a setting is through the partial remelting of an initial mafic arc crust by heat supplied from underplating basaltic magmas. An antithesis to the formation of continental crust in this way should be the production of refractory melting residue, here referred to as ‘anti-continent’. This anti-continent is likely to detach from arc crust as a result of a density inversion and descend into the upper mantle. High-pressure experiments demonstrate that sinking anti-continent is, in contrast to the subducting oceanic crust, always denser than the surrounding mantle, suggesting that it penetrates through the upper-lower mantle boundary, without stagnation, and accumulates at the base of the mantle to form a 200–400 km thick mass known as the D″ layer. Geochemical modeling provides further evidence that this accumulating anti-continent contributes to a deep-seated hotspot source. Therefore, through complementary processes, Earth creates buoyant continents and dense anti-continents at the top and the base of the mantle, respectively, and has recycled portions of anti-continent in mantle plumes.
    Geochimica et Cosmochimica Acta 10/2014; 143:23–33. · 4.25 Impact Factor
  • American Mineralogist 07/2014; 99(7):1270-1276. · 2.06 Impact Factor
  • American Mineralogist 11/2013; 98(11-12):2053-2062. · 2.06 Impact Factor
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    ABSTRACT: stability of the K-rich new aluminous (NAL) phase was examined on the join Na1.00Mg2.00Al4.80Si1.15O12-K1.00Mg2.00Al4.80Si1.15O12 (Na100-K100) up to 144 GPa by X-ray diffraction in a laser-heated diamond anvil cell. Single-phase K100 and Na50K50 NAL were formed up to the lower mantle conditions, and the NAL phase coexisted with the calcium ferrite-type (CF) phase at 120 GPa and 2300 K for the Na75K25 bulk composition. This is a striking contrast to the K-free (Na100) NAL that becomes unstable above 27 GPa at 1850 K, which suggests that potassium stabilizes NAL at significantly higher pressures. K-rich NAL may host potassium in the lower mantle that contains K2O more than 0.09 wt %. In addition, the NAL phase likely formed owing to partial melting in the ultralow-velocity zone or because of a basal magma ocean. Future seismological observations may clarify whether NAL is a radiogenic heat source above the core-mantle boundary.
    Geophysical Research Letters 10/2013; 40(19):5085-5088. · 4.46 Impact Factor
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    ABSTRACT: [1] We have determined subsolidus phase relations in the Fe–FeS system up to 271 GPa using laser-heated diamond-anvil cell techniques. In situ synchrotron X-ray diffraction (XRD) measurements performed at high pressure and high temperature demonstrate the coexistence of hexagonal close-packed (hcp) Fe and tetragonal Fe3S up to 241 GPa and 2510 K. In contrast, the XRD data obtained above 250 GPa show that the hcp phase coexists with the CsCl (B2)-type phase for three different Fe–S bulk compositions (10, 16, and 20 atm% S). Furthermore, chemical analyses using a scanning transmission electron microscope on a retrieved sample indicate that Fe3S sample decomposes into two phases at 271 GPa and 2530 K, consistent with the XRD data. Theory predicts the presence of extensive solid solution between Fe and FeS at inner core conditions, whereas our results suggest that the Fe–FeS system remains eutectic at least to 271 GPa.
    Geophysical Research Letters. 09/2013; 40(18).
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    ABSTRACT: The sound velocities of two aluminum-rich phases in the lower mantle, hexagonal new Al-rich phase (NAL) and its corresponding high-pressure polymorph orthorhombic Ca-ferrite-type phase (CF), were determined with the Brillouin scattering method in a pressure range from 9 to 73 GPa at room temperature. Both NAL and CF samples have identical chemical composition of Na0.4Mg0.6Al1.6Si0.4O4 (40 % NaAlSiO4–60 % MgAl2O4). Infrared laser annealing in the diamond anvil cell was performed to minimize the stress state of the sample and obtain the high-quality Brillouin spectra. The results show shear modulus at zero pressure G 0 = 121.960 ± 0.087 GPa and its pressure derivative G’ = 1.961 ± 0.009 for the NAL phase, and G 0 = 129.653 ± 0.059 GPa and G’ = 2.340 ± 0.004 for the CF phase. The zero-pressure shear velocities of the NAL and CF phases are obtained to be 5.601 ± 0.005 km/sec and 5.741 ± 0.001 km/sec, respectively. We also found that shear velocity increases by 2.5 % upon phase transition from NAL to CF at around 40 GPa.
    Physics and Chemistry of Minerals 03/2013; 40(3). · 1.40 Impact Factor
  • American Mineralogist 02/2013; 98(2-3):335-339. · 2.06 Impact Factor
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    ABSTRACT: We report the measurements of aggregate shear velocity (VS) of CaSiO3 perovskite (CaPv) at high pressure (P) between 32 and 133 GPa and room temperature (T) on the basis of Brillouin spectroscopy. The sample had a tetragonal perovskite structure throughout the experiments. The measured P–VS data show the shear modulus and its pressure derivative at ambient condition to be G0=115.8 GPa and G'=1.20, respectively. The zero-pressure shear velocity is determined to be VS0=5.23 km/s, in good agreement with the previous estimate inferred from the ultrasonic measurements on Ca(Si,Ti)O3 perovskite at 1 bar. Our experimental results are broadly consistent with the earlier calculations on tetragonal CaPv but exhibit lower velocity at equivalent pressure. Such tetragonal CaPv is present in cold subducting slabs and possibly in wide areas of the lowermost mantle. While primitive mantle includes certain amount of CaPv, a depleted peridotite (former harzburgite) layer in subducted oceanic lithosphere is deficient in CaPv and enriched in ferropericlase in the lower mantle. Such harzburgite exhibits 0.9% faster VS and 0.7% slower bulk sound velocity (VΦ) at the lowermost mantle P–T conditions if CaPv is present in the tetragonal form in the surrounding mantle. The observed fast VS and slow VΦ anomalies in the D” layer underneath the circum-Pacific region might be attributed in large part in the presence of subducted harzburgitic materials.
    Earth and Planetary Science Letters 10/2012; s 349–350:1–7. · 4.72 Impact Factor
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    ABSTRACT: The crystal structure of Fe-10%Ni was investigated up to 340 GPa and 4700 K, corresponding to the Earth's inner core conditions by synchrotron X-ray diffraction measurements in-situ at ultrahigh pressure and temperature in a laser-heated diamond-anvil cell. The results show that hexagonal closed-packed (hcp) structure is stable throughout the experimental conditions investigated with no evidence for a phase transition to body-centered cubic (bcc) or face-centered cubic (fcc) phases. The axial c/a ratio of the hcp crystal obtained around 330 GPa has a small temperature dependence similar to the axial ratio of pure Fe. Iron alloy with less than 10% Ni crystallizes to an hcp structure with c/a ratio of ˜1.61 at inner core conditions, although the effect of small amount of light elements remains to be examined by experiments.
    Geophysical Research Letters 06/2012; 39(12):12305-. · 4.46 Impact Factor
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    ABSTRACT: Stishovite is considered to be an important constituent of subducted oceanic basalts and sediments in the Earth's deep interior. It has the tetragonal rutile structure and transforms to an orthorhombic CaCl2 structure at around 60 GPa in the pure SiO2 system. According to theoretical models, the phase transition is trigged by the lattice instability of a soft transverse acoustic mode associated with the shear elastic constant and it has been suggested that this elastic softening could relate to several distinctive seismic structures in the Earth's lower mantle (e.g., [1], [2]). This possibility was denied by the phase study of pure SiO2 at high pressure and high temperature [3], however, natural stishovite in subducted basalts and sediments may contain several impurities, such as Al, Mg, and Na. Therefore, the effect of impurities on the phase transition and elastic properties of stishovite should be clarified. In this study, we investigated elastic properties of sodium contained stishovite by simultaneous measurements of acoustic velocity and X-ray diffraction across the post-stishovite phase transition at room temperature and a pressure range of 0-70 GPa.The phase transition from rutile-structure to CaCl2-structure was observed at around 25GPa with X-ray diffraction and a dipping of transversal velocity was also observed at the transition pressure. [1]Karki et al. (1997) GRL 24, 3269-3272. [2]Kaneshima & Helfrich (1999) Science 283, 1888-1891 [3] Ono et al. (2002) EPSL 197, 187-192.
    AGU Fall Meeting Abstracts. 12/2011;
  • R. Caracas, H. Ozawa, K. Hirose
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    ABSTRACT: The Earth's lower mantle, which is the largest part by volume of our planet, is mainly formed of Fe- and Al- bearing MgSiO3 perovskite (pv). The Fe-component exhibits a spin transition under pressure whose nature and outcome is still a matter of debate. Here we are using lattice dynamical calculations based on density functional perturbation theory to disentangle a part of its complex phase diagram and the spin behavior. To do this we investigate the dynamic stability of Pbnm FeSiO3 pv and show the existence of unstable phonon modes. We track the eigendisplacements of the phonons modes to find low-spin and intermediate spin states. On solid-state physical basis we explore a set of hypothetical structures with various spin configurations and considerably lower enthalpy than the parent orthorhombic Pbnm structure. We show that the spin evolves along a high-spin to mixed high- and intermediate spin to low-spin transition sequence. Based on numerical results from first-principles calculations, we show that the spin transitions can be observed experimentally in X-ray diffraction and Raman measurements. New diffraction peaks form during the spin transition, which are explained by the associated symmetry breaking. Certain observable Raman peaks exhibit a shift at the transition; the Grüneisen parameters of certain few modes are also affected by the transition. Finally we discuss some of the implications of the spin transition on the physical properties of pv. We show that the elastic moduli and the bulk seismic wave velocities are weakly affected by the spin transition at all pressures. However, the intrinsic differences in seismic anisotropy between the high-spin and low-spin phases of Fe-bearing pv coupled with lattice preferred orientation that can develop during mantle flow lead to distinct seismic signatures between the top and the bottom of the lower mantle [1]. These signatures are detectable by seismic observations and they need to be taken into account in tomographic studies of the Earth's lower mantle. We find that the electronic gap widens during crossover to the low-spin phase. This has a direct influence on the electrical conductivity and agrees qualitatively with in situ measurements [2]. [1] Caracas, Mainprice, and Thomas (2010) Geophys. Res. Lett. 37, L13309. [2] K. Ohta, et al. (2008) Science 320, 89.
    AGU Fall Meeting Abstracts. 12/2011;
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    ABSTRACT: Light elements such as oxygen in Earth's core influence the physical properties of the iron alloys that exist in this region. Describing the high-pressure behavior of these materials at core conditions constrains models of core structure and dynamics. From x-ray diffraction measurements of iron monoxide (FeO) at high pressure and temperature, we show that sodium chloride (NaCl)-type (B1) FeO transforms to a cesium chloride (CsCl)-type (B2) phase above 240 gigapascals at 4000 kelvin with 2% density increase. The oxygen-bearing liquid in the middle of the outer core therefore has a modified Fe-O bonding environment that, according to our numerical simulations, suppresses convection. The phase-induced stratification is seismologically invisible but strongly affects the geodynamo.
    Science 11/2011; 334(6057):792-4. · 31.48 Impact Factor
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    ABSTRACT: We report high-spin to low-spin crossover of iron in NiAs (B8)-type Fe 0.96 O (FeO hereafter) at high pressure by a combination of in-situ x-ray emission spectroscopy (XES) and x-ray diffraction (XRD) measurements. The XES spectra show a loss of spin in B8-type FeO approximately above 119 GPa at 300 K, consistent with the ∼2.5% volume reduction around 120 GPa. The high-temperature XRD study also demonstrates a similar volume decrease at 1560–1780 K under the same pressure condition. While the crystal structure of FeO remains to be B8 type across such volume reduction, the atomic arrangements of Fe and O change from inverse to normal NiAs form with considerable decrease in c/a axial ratio. With recent electrical resistance measurements, these suggest that iron spin crossover, inverse-normal structural change, and insulator-metal transition occur concurrently in B8 FeO around 120 GPa.
    Physical Review B 10/2011; 84:134417. · 3.66 Impact Factor
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    ABSTRACT: 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. 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. Recent theoretical calculations combined with estimates of iron partitioning between (Mg,Fe)SiO(3) perovskite and melt at shallower mantle conditions suggest that melt is more dense than solids at pressures in the Earth's deepest mantle, consistent with analysis of shockwave experiments. 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 (Mg(0.95)Fe(0.05))SiO(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)SiO(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)SiO(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.
    Nature 05/2011; 473(7346):199-202. · 42.35 Impact Factor
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    ABSTRACT: FeO is definitely an important component in the Earth's core because of high oxygen solubility into liquid iron at high pressure. High-pressure behavior of FeO is, therefore, of our great interest to geophysics. However, phase relationships in FeO at high pressure and high temperature still remain controversial, which is mainly due to lack of information on magnetic state of iron. The spin state of iron in FeO has been experimentally investigated by Mössbauer spectroscopy and X-ray emission spectroscopy (XES) to Mbar pressures [Pasternak et al., 1997 PRL; Badro et al., 1999 PRL]. However, there is a discrepancy between these studies probably because of sluggish structural transition at room temperature from rhombohedral to NiAs-type (B8) in FeO. Here we examined the spin state of iron and the crystal structure in FeO with combination of XES and X-ray diffraction (XRD) measurements at SPring-8. Starting material was commercially available Fe0.95O powder. The high-pressure phases of FeO were synthesized at high pressure and high temperature using a laser-heated diamond-anvil cell and examined by in-situ XRD measurements. XES spectra of the Fe Kbeta fluorescence lines were collected up to 146 GPa. At 36 GPa, FeO with rhombohedral structure shows high-spin state, which is consistent with the previous studies. The satellite peak Kbeta' of iron in B8 phase completely disappeared at 146 GPa, indicating the loss of the 3d magnetic moment. We further collected XES spectra at 119 and 103 GPa with decreasing pressure. The presence of the Kbeta' peak of iron in B8 phase was clearly observed at 103 GPa whereas it was absent at 119 GPa, which suggests that the spin collapse occurred between these pressures. Furthermore, the volume measurements of B8 phase were conducted at P=77-132 GPa and 88-139 GPa at T=300 K and 1500-1700 K, respectively, using in-situ XRD. Sharp density discontinuity was observed at around 120 GPa at both 300 K and 1500-1700 K, which is most likely explained by the spin transition of iron. These results consistent with the present XES study demonstrate that high-spin to low-spin transition occurs within the stability field of B8 phase. The relative intensities of the diffraction peaks of B8 FeO above 120 GPa are consistent with those of the normal B8 structure. Since the normal B8 FeO can be metallic according to the previous first-principle study [Fang et al., 1999 PRB], B8 FeO above 120 GPa would be a Pauli paramagnetic phase.
    AGU Fall Meeting Abstracts. 12/2010;
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    ABSTRACT: Mt. Narryer and Jack Hills meta-sedimentary rocks in the Narryer Gneiss Complex of the Yilgarn Craton, Western Australia are of particular importance because they yield Hadean detrital zircons. To better understand the tectonothermal history and provenance of these ancient sediments, we have integrated backscattered scanning electron images, in situ U–Pb isotopic and geochemical data for monazites from the meta-sediments. The data indicate multiple periods of metamorphic monazite growth in the Mt. Narryer meta-sediments during tectonothermal events, including metamorphism at~3.3–3.2 and 2.7–2.6Ga. These results set a new minimum age of 3.2Ga for deposition of the Mt. Narryer sediments, previously constrained between 3.28 and~2.7Ga. Despite the significant metamorphic monazite growth, a relatively high proportion of detrital monazite survives in a Fe- and Mn-rich sample. This is likely because the high Fe and Mn bulk composition resulted in the efficient shielding of early formed monazite by garnet. In the Jack Hills meta-sediments, metamorphic monazite growth was minor, suggesting the absence of high-grade metamorphism in the sequence. The detrital monazites provide evidence for the derivation of Mt. Narryer sediments from ca. 3.6 and 3.3Ga granites, likely corresponding to Meeberrie and Dugel granitic gneisses in the Narryer Gneiss Complex. No monazites older than 3.65Ga have been identified, implying either that the source rocks of>3.65Ga detrital zircons in the sediments contained little monazite, or that>3.65Ga detrital minerals had experienced significant metamorphic events or prolonged sedimentary recycling, resulting in the complete dissolution or recrystallization of monazite. KeywordsMonazite-Ancient zircon-Hadean-LA-ICPMS-U–Pb-Early crustal evolution
    Contributions to Mineralogy and Petrology 12/2010; 160(6):803-823. · 3.02 Impact Factor
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    ABSTRACT: We have determined the phase transition boundary between NaCl-type (B1) and NiAs-type (B8) structures of FeO up to 208 GPa and 3800 K on the basis of synchrotron X-ray diffraction (XRD) measurements in situ at high pressure and temperature using a laser-heated diamond-anvil cell (DAC). The boundary is located at 200 GPa and 3200 K with positive Clapeyron slope. These results show that B1 phase of FeO is stable along the whole mantle geotherm, whereas B8 phase is stabilized at the inner core condition. Additionally, FeO coexisted with metallic Fe in the present experiments. We found that hexagonal close-packed (hcp) iron is stable over the entire present experimental conditions. Moreover, the direct chemical analyses of the recovered sample demonstrated that solid iron did not contain any detectable oxygen. While extensive solid solution between Fe and FeO has been speculated above 60–80 GPa, the present results strongly suggest that the system Fe–FeO is simple eutectic at least to 200 GPa pressure range.
    Physics of The Earth and Planetary Interiors 04/2010; · 2.40 Impact Factor
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    ABSTRACT: We have determined the phase transition boundary between NaCl-type (B1) and NiAs-type (B8) structures of FeO up to 208 GPa and 3800 K on the basis of synchrotron X-ray diffraction measurements in-situ at high pressure and temperature using a laser-heated diamond-anvil cell. The boundary was determined by both forward and backward experiments to be located at 200 GPa and 3200 K with considerably high positive Clapeyron slope. These results show that B1 phase of FeO is stable along the whole mantle geotherm, whereas B8 phase is stabilized at the inner core condition. Additionally, FeO coexisted with metallic Fe in the present experiments. We found that hexagonal close-packed iron is stable over the entire present experimental conditions. The chemical compositions were analyzed for recovered samples with the field-emission-type electron probe microanalyzer, demonstrating that solid iron did not contain any detectable oxygen. Moreover, the intermediate compounds such as Fe3O and Fe4O were not observed in either X-ray diffraction measurements or chemical analyses of the recovered samples. While extensive solid solution between Fe and FeO has been speculated above 60-80 GPa, the present results strongly suggest that the system Fe-FeO is simple eutectic at least to 200 GPa pressure range.
    AGU Fall Meeting Abstracts. 12/2009;
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    ABSTRACT: Partitioning of oxygen and silicon between molten iron and (Mg,Fe)SiO3 perovskite was investigated by a combination of laser-heated diamond-anvil cell (LHDAC) and analytical transmission electron microscope (TEM) to 146GPa and 3,500K. The chemical compositions of co-existing quenched molten iron and perovskite were determined quantitatively with energy-dispersive X-ray spectrometry (EDS) and electron energy loss spectroscopy (EELS). The results demonstrate that the quenched liquid iron in contact with perovskite contained substantial amounts of oxygen and silicon at such high pressure and temperature (P–T). The chemical equilibrium between perovskite, ferropericlase, and molten iron at the P–T conditions of the core–mantle boundary (CMB) was calculated in Mg–Fe–Si–O system from these experimental results and previous data on partitioning of oxygen between molten iron and ferropericlase. We found that molten iron should include oxygen and silicon more than required to account for the core density deficit (<10%) when co-existing with both perovskite and ferropericlase at the CMB. This suggests that the very bottom of the mantle may consist of either one of perovskite or ferropericlase. Alternatively, it is also possible that the bulk outer core liquid is not in direct contact with the mantle. Seismological observations of a small P-wave velocity reduction in the topmost core suggest the presence of chemically-distinct buoyant liquid layer. Such layer physically separates the mantle from the bulk outer core liquid, hindering the chemical reaction between them.
    Physics and Chemistry of Minerals 06/2009; 36(6):355-363. · 1.40 Impact Factor
  • American Mineralogist 11/2008; 93:1899-1902. · 2.06 Impact Factor

Publication Stats

158 Citations
116.29 Total Impact Points

Institutions

  • 2008–2014
    • Tokyo Institute of Technology
      • Earth and Planetary Sciences Department
      Edo, Tōkyō, Japan
  • 2011–2013
    • Japan Agency for Marine-Earth Science Technology
      • Institute for Research on Earth Evolution
      Йокосука, Kanagawa, Japan