The continental crust (CC) with an intermediate composition has been created along volcanic arcs. Mantle-derived arc magmas are, however, generally basaltic. A consequence of CC formation thus should be the corresponding production of refractory residue, referred to as 'anti-continent (AC)'. AC is likely to detach from arc crust by density inversion and descend into the upper mantle. High-pressure experiments demonstrate that sinking AC is, in contrast to the subducting oceanic crust, always denser than the surrounding mantle, suggesting that AC founders headlong and accumulates at the base of the mantle to form a 250km-thick mass known as the D" layer. Geochemical modeling further suggests the contribution of the accreted AC to deep-seated hotspot sources (EM1). In complementary processes, Earth creates buoyant CC and dense AC at the top and the base of the mantle, respectively, and has recycled portions of AC in mantle plumes.

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In northeast China, intra-continental magmatism is active, and some studies suggest the relations with subducted Pacific slab which is stagnant at the mantle transition zone beneath NE China. High pressure experiments and electrical conductivity studies indicate the existence of wet mantle above the stagnant slab, but the amount of water has not been estimated yet. In this study, the water content of mantle beneath NE China has been estimated by elucidating the conditions of melting. Temperature and depth of magma generation are estimated from thermodynamic constraints and REE compositions to be 1300 - 1310 degree C, 75 - 100 km depth. With hydrous mantle solidus calculation by Adiabat_1ph software, 220 - 600 ppm of water is required for generating partial melt beneath NE China.

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New of the mechanisms by which magma reaches the Earth's surface is ascent along brittle fractures that develop where plates flex due to subduction and/or loading by seamounts, thereby forming a swarm of small knolls termed "petit-spots". The widespread occurrence of this process is supported by the reinterpretation of the origin of alkaline basalts found within accretionary prisms.

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Three prominent tectonically indexed stages of volcanic activity are recognized in the NE Honshu arc, Japan. These are, continental margin, back-arc basin, and island-arc stage. Recent geological and petrological studies are reviewed and synthesized to present the tectonic and magmatic evolution of the late Cenozoic NE Honshu arc, and the resulted crustal structure of the NE Honshu arc.

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Late Cenozoic magmatism in Kyushu shows the complex temporal, spatial and geochemical patterns. For example, the Hisatsu volcanic province is a northwor curved belt of about 100km in length from northwest to southwest and 25km wide in southern Kyushu. The Hisatsu volcanic rocks are divided into three stages. In the first stage(7.6-2.5Ma), the low-K andesites occurred in the west side and the high-K andesites in the east side of the province. In the second stage(2.5-2Ma), the high-K andesites widely erupted throughout the area(flood andesite). In the third stage(2-0.4Ma), the loe-K andesites erupted in the west side again, and the high-K andesites in the east saide. These volcanic activities have some characteristics differing from those of subduction zone magmatism, so it is assumed that the Hisatsu volcanic rocks originated from an ascending heterogeneous mantle. Recently, Shimono et al.(2006) reported that the late Miocene to Pleistocene magmatism in southern Kyushu are not associated with plate subduction on the basis of boron contents in volcanic rocks.

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We discussed the chemical compositions of rhyolites from three distinct tectonic settings: the continental rift from Ethiopia; the early Miocene continental arc of Japan; and the Izu oceanic island arc. The comparison revealed distinct chemical differences between continental rift and oceanic island arc, but rhyolites from Miocene continental arc heralding the Japan Sea opening resemble those from Ethiopia except for some subduction-zone signatures. This implies that fractional crystallization processes were dominant in the rift-related rhyolites both from continental rift and continental arc regardless of the nature of underlying crust, whereas the oceanic island arc rhyolites may form through partial melting of young, mafic crust.

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We determined the major and trace element and Sr, Nd and Pb isotopic compositions of Quaternary magma from Futagoyama volcano, northeastern Kyushu, Japan. From the results, the most silisic magma keeps primary magma character, which is adakite generated by slab melting, and the less silisic magmas affected a contribution of crustal materials.

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Investigation of slab component is of particular importance to understanding igneous activity of subduction environments. This paper describes the petrochemical features of adakitic rocks in the Kitakami Mountains and late intrusive rocks in the Oman ophiolite. Petrochemical investigation indicates that the high-Sr andesite and high-Mg andesite magma can be resulted from interaction of slab derived adakitic melt with overlying wedge mantle. On the other hand, late intrusive rocks in the Oman ophiolite are considered to be derived from slab melting under the shallow-pressure conditions.

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Olivine-hosted melt inclusions from arc volcanoes in northeast-central Japan commonly contain sulfide precipitates, and suggest that sulfur in primary mafic-magmas are fractionated by sulfide precipitation. The most mafic melt inclusions formed by early melt entrapment are expected to record the primary sulfur concentration (> 3000 ppm).

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Recent geochemical studies on melt inclusions proposed that crustal magmas often suffer CO2 fluxing, a process in which a mantle-derived CO2-rich fluid flows through, and interacts with, an H2O-rich shallow-stored magma. However, the mechanisms of CO2-rich fluxing are scarcely understood. In order to explore fundamental properties of CO2 fluxing, we constructed a reactive transport model and examined how the volatile composition in the melt and fluid evolve temporally and spatially. The results allowed us to infer the velocity of the CO2-rich fluid flow. For example, in the case of the Etna's magma, in which CO2 fluxing is expected to have occur, we estimated the fluid velocity to be 10-4 m/s.

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It has been widely believed that a large scale, caldera-forming eruption was derived from a zoned magma chamber, which was composed of large, homogeneous silicic magma and injected mafic magma. In this study, we show two examples from Hokkaido, japan, in which several silicic magmas coexisted in addition to mafic magma. During caldera-forming eruptions, voluminous rhyolitic magma erupted accompanied with distinct two or three dacitic magmas. These silicic magma was not related with the mafic magma of the volcano. The felsic magma during caldera-forming eruptions of these volcanoes was composed of several distict types. These silicic magmas can be distinguished by Sr isotope ratios, suggesting that one of these silicic magma is not the product of fractional crystallization of the other magma. If the silicic magmas were produced by crustal melting, partial melting of heterogeneous crustal materials might occur to produce several distinct silicic melts. It should be noted that the simultaneous generation of several types of felsic magma would be common especially in the case of large scale silicic magmatism such as caldera-forming eruptions.

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Our geologic and petrologic study revealed detailed sequence of the largest caldera-forming eruption (KpIV: 110ka) of Kutcharo volcano. The eruption started by pumice-fall from an unstable column, immediately followed by large volume pumice flows from distinct two (NW and SE side) vent systems. Pumice flow deposit from NW-side vent contains a small amount of scoria, which is not recognized in SE-side. After the pumice flows, scoria flow issued only NNE direction from NW-side vent.

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We investigated trace element and isotopic compositions of the post-caldera volcanic products from Aso volcano in order to constrain their compositional diversity and the genetic relationship with the caldera-forming magma. The results indicate that the compositional diversity of post-caldera volcanic products was probably generated from at least two different magma sources. Although the trace element compositions of the post-caldera products are similar to those of the caldera-forming pyroclastic products, the isotopic compositions of the former are quite difference from those of the latter. These observations imply that the post-caldera magma is not the remnant of the caldera-forming magma, but the newly generated magma after the caldera formation.

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Late-Pliocene to Quaternary volcanic rock in Aso area in SW Japan, were determined to reveal temporal changes of the magma characteristics and a mechanism of magmatic system. Isotopic ratios of volcanic products at each stage distributed in 87/86 Sr-143/144 Nd diagram are as follows. 1) early pre-caldera stage: separately distributed in two areas (component A: around (0.7040, 0.51285), component B: around (0.7044, 0.51270), 2) late pre-caldera stage: distributed between component A and B along mantle array, 3) caldera forming stages: distributed in an area surrounded by component A, a point (0.7040, 0.51270) and a point (0.7042, 0.51270), showing that component of low Nd ratio affecting component A, 4) inter-caldera stage: distributed within the area of caldera forming stage (excepting for ratios of Neko-dake), 5) post caldera stage: distributed between component A and B like that of late pre-caldera stage.

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I investigated the stratigraphic relations between the tephra sequence and geologic evidence of ground shaking events during the 7.3 cal ka BP eruption of the Kikai caldera. The important points for the caldera-forming eruption are: the long dormant period is not an essential factor for the eruption, and some magmas of different compositions existed prior to the eruption. On the bases of the magma plumbing model of the Kikai caldera, the magma reservoir of the Aira caldera is storing silicic magma, whereas andesitic magma is passing nearby the main magma reservoir without any mixing. Ground deformation data around the Aira caldera suggest that the silicic magma has been stored since the latest eruption of ca. 30 ka, and that several tens km3 of silicic magma has already accumulated in it.

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The open-system degassing from silicic arc magmas controls the explosivity of volcanic eruptions. The timescale of buoyant movement of bubbles in silicic magmas is much longer than that of magma ascent through the shallow crust. Hence, the permeable gas transport through connected bubbles and through brittle fractures is thought to be a possible mechanism for the degassing. We have experimentally determined the rate of the permeable gas transport (i.e., gas permeability) in crystal-bearing and -free rhyolite to evaluate the degassing rate and to explore factors controlling the explosivity of volcanic eruptions. The experimental results show that the gas permeability is controlled by total shear strain and water contents, and that the degassing at the shallow part (several hundred meters in depth) is influenced by the formation of brittle fractures in magmas. Consequently, the explosivity of volcanic eruptions is inferred to be controlled by the depth of a magma chamber and the width of a volcanic conduit in the crust, which dominate the shear strain and water contents.

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We note an example of eruption processes of basaltic magmas generated in a subduction factory. The Younger Fuji volcano (ca. 11ka to present) produced mostly basaltic ejecta. Some are explosive (A.D.1707 Hoei, ca. 3000ybp Omuroyama etc), and others are effusive (A.D.864 Aokigahara lava flow, Omuroyama lava flow, Mishima lava flow, Saruhashi lava flow etc). All the basaltic eruption products are mildly evolved (FeO*/MgO=2.0-2.8). Some of the explosive eruption products are sparsely-phyric with calcic plagioclase and olivine, and most of the effusive eruption products are porphyritic with 15-30 vol% plagioclase and associated olivine, augite, and orthopyroxene. Sodic compositions of abundant plagioclase phenocrysts suggest they crystallized by degassing of water at shallow depth.

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To constrain the timing and conditions of syneruptive magma ascent that are responsible for shifting eruption intensity, we have investigated a basaltic sub-Plinian eruption that produced Yufune-2 scoria in Fuji volcano 2200 years ago. We deduced magmatic decompression conditions from groundmass microlite textures, including decompression path (i.e. evolution in decompression rate) and approximate decompression rate, in order to relate them to eruption intensity. The overall decompression rate in each eruptive unit (from a to e) has a positive correlation with eruption intensity. The variation in decompression rate was enlarged in the final units, due to 1) variation in flow velocity across conduit and 2) part of the erupted magma in unit d experienced remarkably slow decompression resulting from decreased overpressure in the reservoir following the major eruption of unit b. Two factors had a major impact on eruption intensity. First, magma decompression rate determined the degree of gas-phase separation from ascending magma. The second factor is the conduit radius that, in combination with magma ascent rate, controlled the magma discharge rate.

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We developed an automatic ash sampling system for active volcanoes. We also examined several petrological analyses of magmatic ejecta to achieve daily monitoring and forecast of eruptions. We found that the amount of microlite-rich/poor particle can be one of activity indices at Suwanosejima volcano, and that two different but very similar magmas are mixing and erupting at Sakurajima volcano.

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Previous studies on the Tholeiitic (TH) and calc-alkaline (CA) magma series at Adatara volcano showed that the two series were derived from distinct parent magmas with independent evolutionary processes. The TH and CA magmas erupted concurrently about 0.35 Ma were investigated in detail, to reveal their temporal compositional variations. Petrological features for a series of TH magmas which erupted successively from a common vent are basically reconciled with the idea that the TH series were related through fractional crystallization, with minor supply of primitive magma or local heterogeneity within the reservoir. Petrology of the cognate inclusions and heterogeneous CA lavas indicates that a magma mixing acted a crucial role in the compositional variation of the CA series.

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Scoriae of Z-To5 tephra in Zao volcano, NE Japan were formed by the mixing of three magmas: basalt with high-Mg (Fo〜81) olv and An-rich plg; basaltic andesite with Mg-rich opx (〜78, Mg#) and cpx (〜78, Mg#), lower-Mg olv (Fo〜78), and An〜85 plg; and andesite with Mg-poor opx (61-66, Mg#) and cpx (64-68, Mg#), and An-poor plg. The basaltic magma was formed by fractionation of Fo〜85 olv from a less differentiated magma during fast ascent from depth. The andesitic shallow magma chamber was heated by underplating of the basaltic magma, and then, the basaltic andesite magma was formed by mixing of the basaltic and andesitic magmas in the chamber. Textural and chemical evidence for the rapid growth of phenocrysts in the basaltic andesite magma suggests that the magma residence time was short.

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Fine lithic fragments erupted recently from the Sakurajima volcano show microstructures characterized by (1) High degree of decompression-induced rapid crystallization at very low pressure and high temperature, (2) high porosity and irregular pores due to crystallization and dehydration, (3) exsolution, oxidation and reaction textures of phenocrysts (4) vapor phase minerals condensed from the hot volcanic gas flew through the pores (5) Minerals growth from low-temperature volcanic gas or in hydrothermal environments, accompanied by accretionary lapilli-like products. These microstructures may provide insights into the conduit conditions including high permeability.

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We calculated the seismic velocities of rocks in the Oman ophiolite and compared with those of Oceanic crust. The calculated P-wave velocities of pillow lavas and dolerites are comparable to those of the layer-2 to layer-3 of oceanic crust. The calculated P-wave velocities of gabbros are comparable to those of layer-3 of oceanic crust. The velocity structure of layer-2 likely reflects the distribution of porosity in the upper oceanic crust. On the other hand, the velocity structure of layer-3 likely reflects the modal proportion of main mineral constituents in the rocks of lower oceanic crust.

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Niijima is one of the rhyolite dominant Quaternary volcano located in northern part of Izu volcanic arc. Rhyolites in Niijima are classified into four types based on mafic phenocrystic minerals: hypersthene-(hornblende)-bearing (Hyp-Hb-type), cummingtonite-bearing (Cum-type), cummingtonite-biotite bearing (Cum-Bt-type), and biotite-bearing (Bt-type) rhyolites. Petrographical observation, mineral chemistries and whole rock chemical compositions show that Cum-type and Bt-type rhyolites were generated from different parental magmas and fractionated, each other, and that Cum-Bt rhyolites were produced by magma mixing between Cum- type and Bt-type rhyolites. Sr isotope ratios of basalts (and basaltic inclusions) are slightly higher than those of rhyolites, proving different origin of magmas. Also, newly examined xenoliths of granite and gabbro and tonalite will be discussed with host rhyolites and basalt.

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Petrological and geochemical studies were carried out for the Nanzaki Basanite in the southern most part of the Izu Peninsula, which is close to the volcanic front of Izu-Bonin volcanic arc. Nanzaki Basanite (0.43Ma) is consist of massive lava, layered lava and scoria. Whole rock chemical composition suggests primary magma for its origin. Variation in Sr, Ba, Ti and Zr contents indicates difference in degree of partial melting. Incompatible element, REE patterns and mineral assemblage (Ol+Cpx) may represent that matasomatised mantle by carbonatite magma was the source material.

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There is a caldera cluster around southern base of Kurikoma volcano, and their eruptive products are exposed there. Most of them have been regarded as members of the neogene Onoda Formation. This study shows the stratgraphy, petrology and K-Ar data of two new samples in the Onoda Formation. Onoda Formation contains four tuff members, Yubama, Chijimisawa, Modume, Toshoji tuffs, in stratgraphic order. These four tuffs are composed mainly of pyroclastic flow deposits, and Modume Tuff is accompanied by the lower fall-out deposit. Whole-rock chemical analysis revealed that Toshojisawa Tuff belongs to dacite, and other tuffs belong to rhyolite, according to IUCS classification. K-Ar ages are 1.00±0.06 Ma and 0.87±0.21 Ma for Chijimisawa and Toshoji tuffs, respectively.

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Iron hydroxides are nanoparitcles found in verious environment, which affects greatly the environmental behavior of trace elements due to its reactive nature and large surface area. There are a number of researches on the interaction between trace elements and iron hydroxides. In this presentation, some new aspects of the interction is given such as isotopic fractionation of trace elements during their adsorption on iron hyrdoxides and also microbial effect on the adsrotpion. For Mo isotopic fractionation, it was found that lighter isotope is enriched in manganese oxdies, but not in ferrihydrite. These differences can be explained by their different adsorbed species on the two minerals: inner-sphere complex on manganese oxides, but outer-sphere complex on ferrihdyrite.

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Selenium-79 in high-level radioactive waste needs to be safely disposed in geological repository. However, Se has low affinity against various sorbents due to the common anion species. On the other hand, apatite was proposed as an efficient sorbent for anion species. In order to understand the mechanism of Se sequestration by apatite and pyromorphite in the Se-Pb-P-O system, we have conducted selenite immobilization experiments by hydroxyapatite and hydroxypyromorphite. In the experiment using hydroxypyromorphite, the secondary Pb-selenite, molybdomenite, precipitates. In the experiment of selenite sequestration during hydroxypyromorphite formation, selenite coprecipitates with hydroxypyromorphite.

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In this study, the nano- to atomic scale condition of Pb in synthetic Pb-doped zircon is reported. We have investigated divalent Pb-doped zircon that were synthesized under a range of conditions: (i) dry at 1430 ^oC w/o P₂O₅; (ii) wet at 800 ^oC at 1.0 GPa w/o P₂O₅; (iii) wet at 900 ^oC at 1.5 GPa in the presence of P₂O₅, utilizing transmission electron microscopy (TEM). TEM results reveal four types of Pb occurrences. Type I: Pb-rich particles in 50 - 200 nm of diameter, identified as Pb oxide hydrate. Type II: Amorphous Pb-rich phase concentrated at grain boundary. Type III: spherical Pb particles identified as Pb phosphate. Type IV: Pb is diluted into the matrix zircon locating at the lattice. In the P-free system, Pb occurs as particles which are classified as type I without detectable Pb in the matrix zircon. In the P-rich condition, Pb is present not only as type I but also as various forms from type II to type IV.

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We have performed surface x-ray scattering method using the crystal truncation rods (CTR) technique and classical molecular dynamics (MD) simulations to understand the structure of muscovite (001) surface/0.5 M NaCl solution interfaces. The electronic density oscillation was observed up to 15 A apart from the surface. The density oscillation corresponds to the hydrated sodium ions and the ordered water molecules.

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We will report a relation between rounding etch pits on a calcite cleavage surface and a determining step in the dissolution kinetics.

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Silica dissolution was simulated using Gaussian 03 software at B3LYP/3-21G* and the B3LYP/6-311G(2d, p) levels, applied to a modeled silica Si4O6(OH)4 in the presence of an NaOH molecule and up to five water molecules. The atomic positions of the sodium hydroxide, the water molecules and the surface SiO3(OH) moiety were varied to mimick the surface reaction whereas the positions of the remaining Si3O3(OH)3 atoms were frozen throughout the geometry optimization. The energy barrier was 88 kJ/mol (85 kJ/mol after the zero-point correction), which is still in the range of experimental activation energies of 46 - 96 kJ/mol. The sodium plays a role in stabilizing the surface silicon in five-fold coordination, which induces the elongation of Si-O distances and the weakening of the bonded interactions. This makes the Si-O rupture easier and faster, which is a clue to how presence of alkali enhances silica dissolution.

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We here describe a kinetic theory of the crystallization of nanoparticles, where nanoparticles are dissolving and crystals are forming in solution. The theory assumes that a crystal nucleates only on a nanoparticle, the crystal stops growing at a certain size, and the concentration of metal ion in solution is close to the solubility of the nanoparticles. On the basis of these assumptions, we have derived integral equations for R(t) (crystal ratio as a function of time). We have solved the integral equations with a successive approximation mehod. When time t is less than time at the inflection point (=r/G, r: maximum radius of crystal, G: growth rate of crystal), R(t) is close to fourth power of time; when t is larger than tinflec, R(t) is close to an exponential-type function. The kinetic theory has been applied successfully to the transformation of ferrihydrite nanoparticles to goethite or hematite crystals, and the crystallization of TiO2 . The theory shows that the nucleation rate of crystal essentially determines the crystallization rate, and that induction period is observed when the growth of crystal is slow.

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On the surface of present Earth, iron in aqueous solutions exists as Fe(II) or Fe(III) ions. Fe(II) is unstable, oxidizes into Fe(III), and rapidly Fe(III) precipitates as (hydr)oxides. The oxidation rate of Fe(II) is represented as following equation:-d[Fe(II)]/dt=k[Fe(II)][O₂][OH^-]². This equation has been confirmed in the range of 5<pH<9,pO₂=0.107-0.195atm,0.308-0.903atm. On the other hand, oxygen evolution in the Paleoproterozoic could be estimated by using the oxidation rate and measuring ratio of remained Fe(II) against Fe(III) of pareosols formed during such period. Oxygen considered to have risen from <10^-6atm to >10^-3atm through 2.5 to 2.0 billion years before, the equation above is not proper for the application to this period which was under the conditions of such pO₂. In this study, we redefined the equation for the oxidation rate as -d[Fe(II)]/dt=k[Fe(II)][O₂]^x[OH^-]^y and evaluated x under the conditions of pO₂=10^-3,10^-4atm.

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Mn nodule was examined by TEM and simulation about their forms and textures.Their characteristics were described and the genesis was estimated.

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In natural environments the interaction between existing dissimilar colloids can affect the metal adsorption on the colloids and result in the deviation from the additivity of the adsorption models for single colloid. This effect was studied with goethite and humic acid (HA) as sorbents and H⁺, Cu²⁺ and UO₂²⁺ as adsorbing ions. Due to the interaction of HA and goethite (i.e. the adsorption of HA on goethite), H⁺ was released from adsorbed HA molecules and negative charges were induced on HA at relatively low pH. On the other hand, at relatively high pH, H⁺ coadsorbed on the goethite surface with HA and net positive charges were induced. As for Cu²⁺ and UO₂²⁺, the adsorption of the former was enhanced in the ternary system possibly because of the aforementioned charge regulation between HA and goethite, and the latter diminished by the direct competition between HA and UO₂²⁺ for the surface sites of goethite.

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In order to understand the physical and chemical state of Fe in the aeolian dust occurred in March 2010, a combination of bulk and nano scale analytical techniques was employed to characterize the aerosol samples collected simultaneously in Fukuoka, Japan and Hefei, China during the dust storm event on March 21-23, 2010. The major mineral assemblage is similar in both samples: quartz, muscovite, calcite, gypsum and chlorite. X-ray absorption near-edge structure analysis and electron microscopy reveal that Fe-bearing phase in the sample >4 micro meter is mainly aluminosilicate and Fe-oxide containing ~20 % of Fe(II), whereas Fe is predominantly present as maghemite, gamma-Fe₂O₃, submicron-sized particle in the sample <4 micro meter.

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The present study has demonstrated the multi-scale investigation of Fe species in urban particulate matter (PM). The PM samples were collected by a cascade impactor and high volume air sampler at Fukuoka, Japan. According to XANES analysis Fe is present mainly as Fe(III). SEM-EDX point analysis has shown that >1 µm particles containing Fe have high concentrations of Si and Al, and <1 µm particles containing high S and low Si concentrations. TEM analysis reveals that Fe-bearing particles <1 µm are spherical maghemite nanocrystallites, which implies the presence of abundant active site for reaction on the surface. A presence of various concentrations of Mn in the maghemite is anticipated to promote oxidizing reaction of co-existing heavy metals such as chromium, resulting in higher toxicity.

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In the nuclear waste disposal, a barrier material, bentonite, is predicted to lose its barrier function by reaction under hyper alkaline conditions. In this study, compacted bentonite with Fe plate has been reacted with Ca(OH)₂ saturated solutions of groundwater and 5.0 mol/L sodium nitrate solution at 60°C for 7-21 days. A variety of analytical techniques including SEM, TEM and XAFS have been utilized. Iron-bearing minerals and Fe nanoparticles occur in bentonite reacted after 7 days. In addition, bentonite was intensively altered and porous needle-like materials formed. The occurrence of Fe nanoparticles and alteration of bentonite can be key factors to facilitate the mobility of radionuclides under certain condition similar to the present study.

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Phosphate is nutrients for organism. Therefore, chemical fertilizer containing phosphate can significantly increases food productions. However, dissolved phosphate due to the fertilizer leads to eutrophication in hydrosphere environment and has much effect on ecological system in lakes. For that reason, it is necessity to remove the dissolved phosphate to avoid lake eutrophication.Recovery of phosphates and reusing them as chemical fertilizer attracts attention in the world, because they can become brake-through for both the resource and environment problems (Kuroda .2005). Monohydrocalcite (CaCO3•H2O; MHC) has been known as a metastable phase of calcium carbonate minerals. It is rare mineral and has been found in saline lakes or seawater environment. It has been known that metastable phase has larger specific surface area and more reactive than stable phase (Fukushi and Sato, 2005). Because MHC is a metastable phase, it is expected that MHC is more efficiency for dissolved species uptake than calcite and aragonite. The object of this study is to investigate the uptake behavior of phosphate by MHC.

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In this study, we investigated local structures of Sb species in synthetic Sb(V)-coprecipitated and -adsorbed ferrihydrite and goethite, which are common Fe(III) oxyhydroxides in environment, at various Sb/Fe molar ratios by extended X-ray absorption fine structure (EXAFS) analyses. In the EXAFS spectra of the coprecipitated ferrihydrite and goethite, some features of the spectra significantly differed from those in the adsorbed samples. The EXAFS simulation indicated that the difference is due to the larger coordination number of Fe to Sb atom in the coprecipitation samples, indicating a structural incorporation (heterovalent substitution) of Sb(V) into ferrihydrite and goethite. This study directly provided the first evidence for the structural incorporation of Sb(V) into the Fe(III) oxide structure.

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Adsorption of elements on the surface of mineral is important process with respect to the concentration and migration in soils and aquatic environments. Understanding of surface speciation is needed to evaluate the long-term behavior of dissolved elements. Ferrihydrite, nano-mineral widely distributed in the surface envirnoment is an effective anion adsorbent because of its positively-charged surface in natural water. It is reported that sulfate affects the coexistence inorganic anion, trace metals and organic acid adsorption. The present study aims to reveal the surface speciation of sulfate at the electrolyte solution-ferrihydrite interface under various pH and ionic strength conditions by means of in-situ IR spectroscopy.

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Molybdenum is an essential trace element for plants and animals. Its deficiency causes serious health problems. The behavior of molybdenum varies with redox conditions. The molybdenum isotopic composition is thought to be a unique geochemical tool for indicator of paleoredox conditions. Although the biogeochemical behavior of molybdenum in the surface conditions is important, the elementary reactions affecting the behavior are currently lucking. The concentration and mobility of trace elements at surface condition is governed by adsorption reactions on mineral surfaces. In present study, we analyzed the published adsorption data of molybdate on oxides by means of surface complexation modeling to understand the elementary reactions of molybdenum adsorption behavior.

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Chiton tooth cusps are known to be one of the biominerals forming the amorphous precursor phases, though the biomineralization process and mechanism are not really understood. In order to promote further understanding of the biomineralization process, the immature to mature tooth cusps in two chiton species, Acantopleura japonica and Acantochitona achates, were investigated by various analytical techniques, micro-XRD, synchrotron-XRD, micro-XANES, and FIB-TEM.

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Bacterial formation of framboidal pyrite was successfully achieved. The results will vbe shown.

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In order to understand the behavior of rare earth elements during modearn weathering of granites, the textures and chemistries of RE minerals of granite in Inada and its weathered soil were investigated. The values of Ce anomaly (Ce/Ce*) of observed rhabdophane in weathered soils were highly dispersed probably because of kinetics of low oxidation rate of Ce3+. Therefore, the minimum values of Ce anomaly of rhabdophane are useful for the estimation of atmospheric oxgen evolution.

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Ultrafiltration through 100, 25, and 5nm filters besides conventional filtration of 450nm was performed to examine the effects of nanominerals on chemical analyses of river waters. In our previous study at the Lampa river, Santiago, Chile, sudden decrease of pH and increase of Eh and SO₄^2- followed by variations of trace metal concentrations were observed at one part of the river (Rocco, 2008). The increase of ions implies dissolution of sulfates and the decrease of trace metals suggests that they were carried by secondary formed Fe nanominerals. Ultrafiltration was intended to remove the effects of nanominerals on chemical analyses. Filtered waters of 5nm filters showed different concentrations from those of larger pored filters. These tendencies of concentrations varied among trace metals and Fe that form nanominerals.

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Atmospheric oxygen increased greatly in Paleoproterozoic, and changed surface environment dramatically. In this study, I focused on the behaviors of trace elements during weathering, because they reflected the surface environment. Considering element profiles, element retentions, and thermodynamics, I discussed the change of atmospheric oxygen and ocean chemistry. The samples were paleosols which formed ~2.76-1.85Ga. They were measured the concentration of trace elements by ICP-AES/-MS, and those of major elements by XRF. I obtained element profiles and element retentions. It was conceivable that trace element distributions were heterogeneous in parent rocks, but in many cases, heterogeneity did not matter. The results are as follows. Before ~2.2-2.4 Ga, Ni, Co, and Zn flowed from the continent, and retained since then. Before ~2.4-2.4 Ga, Cu, V, Cr, Mo retained in the continent, and flowed since then. W flowed from the continent throughout Paleoproterozoic. These results suggest that atmospheric oxygen rose gradually. In addition, the behavior of trace elements can be proxies for the ocean chemistry, and continental weathering probably contributed to the ocean chemistry.

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There are various reactions between nanoparticles and biological tissues, which strongly depend on the speciation and form of constituent elements. We have focused on the speciation of metals particularly on fine fraction of PM to elucidate the toxicity of those particles. Research targets were urban PM from Detroit, Fukuoka, Hefei, and a NIST standard (SRM1649a). Advanced electron microscopy and synchrotron-based X-ray absorption fine structure have been utilized. The results obtained from these samples reveal the complex mixing state of toxic metals and the size-dependent phase heterogeneity bearing the elements of interest. This presentation summarizes the results obtained from our recent projects focusing on the speciation of metals: Fe, Pb, Cr, and Mn.

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226Ra is radioactive nuclide (half life of 1600 year) released to the environment via uranium mining and water pumping from deep thermal groundwater. Because of positive correlations between 226Ra and salt concentrations in groundwater, inhibition effects of salts on 226Ra sorption have been suggested. Clay minerals are ubiquitous geological minerals with high cation exchange capacity (CEC) and specific surface area. They are expected to regulate 226Ra concentration in groundwater as a function of salt concentrations. However, 226Ra sorption mechanisms by clay minerals are not simple ion-exchange, making 226Ra behavior in groundwater difficult to evaluate. In this context, we investigated the mechanisms of salt concentrations to affect sorbed amount of 226Ra by clay minerals. The effects of clay contents and their types on the salt concentration dependency were also discussed.

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