Late Pliocene-Early Pleistocene igneous rocks of Yoneyama Formation from the northern Fossa Magna region, central Japan, consist of basaltic to andesitic rocks and small intrusive rocks; they contain frequently hornblende (Hbl) gabbroic xenoliths and Hbl xenocrysts. Based on field data, together with petrographic, geochemical, and geochlonological descriptions, the volcanism comprised 5 stages. The rocks at the Ogamidake, the 1st and 3rd stages are tholeiitic rock series (TH), whereas calc-alkalic rock series (CA) are dominated at the 2nd and 4th stages. All rocks are characterized by high-K content and contain pargasitic Hbl phenocrysts in both rock series. Estimation using Ca-amphibole geobarometer suggests that Hbls have crystallized at depths of lower crust. Existence of Hbl and high An content of plagioclase (～ An90) in both rock series imply that both magmas are rich in H2O. Estimated H2O contents are ～ 5 wt％ for both TH and CA magmas. Based on mineral texture, P-T estimation and major-trace elements modeling, we infer that cryptic fractionation of Hbl can produce the TH magma trend. Our model is incompatible with general model that TH magma originate from anhydrous or low H2O content magma.
I have researched on the Earth's mantle constituent minerals and their analogue materials using thermodynamic approaches and crystal structure analyses. In this article, the following my representative studies are introduced: (1) Rietveld analyses of Al-bearing MgSiO3 bridgmanites to show some crystal structural evidences for the aluminum substitution with oxygen vacancies, (2) crystal structure determinations for newly found high-pressure phases of SrSi2O5, Mg2Al2O5, CaRuO3, and CaRhO3, (3) development of thermal expansion and heat capacity estimation methods for calcium ferrite-type MgAl2O4 using the Grüneisen relation equation, high-pressure micro-Raman spectroscopy and Kieffer model calculation of heat capacity, (4) re-determination of the post-spinel phase transition enthalpy in Mg2SiO4 by drop-solution enthalpy measurements of MgSiO3 bridgmanite, MgO and Mg2SiO4 ringwoodite, (5) re-measurement of high-temperature heat capacity of Mg2SiO4 ringwoodite, and (6) thermodynamic calculation of the post-spinel transition boundary in Mg2SiO4 by adopting the new phase transition enthalpy and heat capacity of Mg2SiO4 ringwoodite, independent of those determined by high-pressure high-temperature experiments. The developed estimation methods for thermal expansion and heat capacity are useful to assess internally-consistent thermodynamic data sets of mantle minerals.
High-pressure and high-temperature experiments are vital tools for knowing the structure and evolutions of the Earth's deep interior. In this paper, I will introduce recent progress on the studies of the crystal structure, physical properties, and electronic state of iron and the phase relationships of minerals at lower mantle conditions. It was found that the partitioning and valence state of iron between minerals dramatically changes upon reaching the post-perovskite phase transition at the lowermost mantle. This may explain very sharp D″ discontinuity observed above core-mantle boundary. This research was achieved by a combination of the diamond anvil cell and transmission electron microscope techniques. Multiple analytical methods were combined to discover a new iron-oxide phase that might exist in the lower mantle. Relics of this phase may be found as inclusions in diamonds formed in the deep mantle. In situ high-pressure/high-temperature electrical conductivity measuring system was developed to experimentally investigate further Earth's internal structure. In addition to electrical conductivity, I have investigated the valence state, substitution site, and spin state of iron in lower mantle minerals by means of single crystal X-ray diffraction and Mössbauer spectroscopy. Results showed that the pyrolitic chemical model is consistent with the electrical conductivity of the ‘average’ lower mantle. New resistive heating techniques are now developed for use in diamond anvil cells that will, hopefully, guarantee homogeneous and stable heating.
Layered double hydroxides (LDHs) have attracted considerable attention because of their extremely high anion-exchange capacities and diversity of composition. In this paper, we described the following research topics related to applications of LDHs. (1) We focused on surface complexation reactions on the synthetic LDH surfaces, and the effects of complexation reactions on the solid state properties of LDH were also evaluated. The results indicated that oxyanions with low ionic potential, such as AsO4 and PO4, had a tendency to form inner-sphere complexes with the LDH surfaces. The formation of inner-sphere complexes shifted the isoelectric point and the surface charge of the LDH. Furthermore, the solubility of the LDH was reduced by the inner-sphere complexes with PO4 and AsO4. (2) The synthesis of Zn-FeIII LDH was attempted, employing different pathways using either FeII or FeIII species together with Zn as the initial reagents. The product derived from the synthesis employing FeII was found to transition to a Zn-FeIII LDH phase following oxidation process. In contrast, the product obtained with FeIII did not contain a LDH phase. And the syntheses of Mg-FeIII LDH with different compositions at varied temperature were also attempted. The well-crystallized and white colored LDH were obtained. The synthesized Mg-FeIII LDH was treated with melted sugar alcohol in order to reduce FeIII. The Mg-Fe LDH resulting from a sugar alcohol treatment showed the reduction property in an aqueous solution. (3) The behavior of synthetic Zn-Al LDH in photo-induced degradation of an anionic dye was evaluated by determining the ultraviolet-visible absorption spectra under ultraviolet light irradiation. Zn-Al LDH showed photocatalytic activity toward various anionic dyes, and degradations of anionic dyes were accelerated without stabilization under ultraviolet irradiation. Zn-Al LDH should be useful as efficient photocatalysts for harmful organic anions.