Platinum-group elements are useful for better understanding of deep Earth processes including silicate and metal phases. However, the behavior of platinum-group elements in the mantle has not been well understood, because the distribution and origin of the host phases for platinum-group elements are not known. We discovered tiny platinum-group minerals from mantle peridotites with synchrotron radiation micro-XRF, and found that sulfur-bearing fluids play significant roles in formation of platinum-group minerals.

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Plešovice peridotite occurs as a lenticular body in the high-P type Gföhl granulite derived from crustal materials in the Bohemian Massif, Czech Republic. Plešovice peridotite was originally harzburgite and then suffered metasomatic enrichments resulting in the presence of phlogopite, apatite, monazite, U-Th oxide, ThSiO4, dolomite, and zircon. These metasomatic minerals occur not only as isolated phases in the matrix, but also as multiphase solid (MS) inclusions with negative crystal shapes in the chromian spinel. Ferrando et al. (2005) have proposed that such MS inclusions may be the frozen remnant of supercritical fluids or silicate melts. Thus it is plausible that MS inclusions in our study are fossils of metasomatic agents that have invaded into the Plešovice peridotites at the root zone of Variscan Orogen. We would like to introduce the nature of MS inclusions and the timing of the incorporation of metasomatic agents in the presentation.

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We examined a compositionally layered diamondiferous eclogite, which yields a diamond grade of approximately 8400 carats per metric ton, discovered in a new collection from the Roberts Victor Mine, South Africa, with the aim of further constraining eclogitic diamond genesis. This high concentration of diamond, the relatively large size of the xenolith host (15 x 12 x 8 cm) together with its compositional layering shown by modal variations of garnet, clinopyroxene and diamond, provide a rare opportunity to test whether the diamond formation was contemporaneous with or post-dated the formation of the host eclogite. We will address this issue based on the results of (1) 3D mapping of the rock using the HRXCT technique, (2) major element analyses of garnet and clinopyroxene across the layering, (3) FTIR analysis of the nitrogen content and aggregation state of the diamonds, and (4) Carbon isotope analyses of the diamonds.

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Although U-Pb isotopic analysis of zircon is well established for constraining the timing of high-temperature geological events, chronological data are often open to multiple interpretations. However, dating is not the only tool in the microbeam analyst's kit; such methods have the unique ability to measure a variety of other elements (e.g. Ti, Hf and REEs), on a sub-30 micron scale, in polished sections that preserve paragenetic mineral relationships. Three unusual examples demonstrate the diagnostic value of such information. Microbeam analysis of zircon with diagnostic chemical and textural relationships to host lithologies makes the assignation of age data to geological events far from arbitrary.

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U-Th-Pb analysis for microdomain of zircon and monazite crystals using SIMS/SHRIMP, LA-ICP-MS and EMP/EPMA is one of convincing age determination techniques to unravel the multiple thermal events recorded in the rocks having experienced high temperature (HT) and ultra high temperature (UHT) metamorphism. Chemical features (Th/U ratio, rare earth elements (REE), Ti, Zr and P etc.) combined with the morphology and internal structure of zircon and monazite crystals can tie the obtained ages to the pressure, temperature and other information recorded in the coexisting metamorphic minerals.

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Accessory minerals play an important role as a sink mineral of trace elements in the continental crust. Above all, the accessory mineral whose trace element concentration governed by stoichiometry is important, as it may buffer the trace element concentration in other coexisting minerals. Following may be considered as end member cases of trace element redistribution when the sink mineral breaks down. (i) New accessory mineral works as a sink of the trace element concerned. (ii) No new sink mineral is formed, and the trace element concerned is redistributed among major rock-forming minerals. (iii) The trace element concerned is redistributed among melt and fluid only. Accessory minerals enable us to observe new geological phenomenon, and is important in future petrological studies.

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High temperature metamorphic rocks which compose lower continental crust have been reported from various orogenic belts. Their presence is important to define the past plate convergence zone and to understand the history of crustal thickening or subduction processes. However, in most cases evidence of its early burial history has been obliterated by extensive hydration, and replaced by low pressure mineral assemblages during a late amphibolite/granulite facies overprint that is related to exhumation. Micro-inclusions and chemical zoning in coarse-grained garnet also occasionally give useful information on the early stage P-T conditions of the host rock.

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Metasedimentary rocks with ca. 3.0 Ga depositional ages exposed at Mt. Narryer, Western Australia contain Hadean (>4.0 Ga) detrital zircons. Previous studies have demonstrated that detrital zircons from the metasedimentary rocks define two distinctive age groups, an older group from 4.28-4.00 Ga and a younger group from 3.75-3.25 Ga. We have studied the age of monazites from the metasedimentary rocks relative to zircon U-Pb ages to constrain their provenance as well as post-depositional thermal history. About 450 monazite grains were separated from five rock samples and their U-(Th-)Pb isotopes were measured by LA-ICPMS. All monazite populations show a prominent peak at 2.70-2.65 Ga in the 207Pb/206Pb age histograms, indicating monazite recrystallization and/or growth during the metamorphism at that time. The older pre-depositional monazite population shows a small peak at 3.6 Ga and more dominant peaks at 3.30-3.25 Ga, approximately corresponding to the minimum age of the younger zircon group. Interestingly, no Hadean monazites have been found here: the oldest monazites identified have a maximum age of ca. 3.6 Ga. The lack of Hadean monazite can be interpreted as indicating that the source rocks experienced a sequence of metamorphic events from ca. 3.6, or alternatively, the source rocks might be mafic-intermediate in composition, rather than felsic, and hence did not contain igneous monazite.

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Zircons from granitic rocks, Japan, were divided into two types: an HREE-U-Th-poor type from granites and an HREE-U-Th-rich type from granitic pegmatites. Zircons of an HREE-U-Th-poor type from granites are formed at high temperature (>700 °C), whereas those of an HREE-U-Th-rich type from granitic pegmatites at low temperature (<500 °C) (Hoshino et al., 2007). Hoskin & Schaltegger (2003) suggested that zircon contain less than 1 wt% ΣREE + Y and analyses containing significantly higher abundances almost certainly represent altered zircon or accidental analysis of inclusions. This aims of this study are (1) to determine accurate chemical compositions and crystal structure of zircon from Takenouchi granitic pegmatite, Japan and (2) to confirm occurrence of zircon formed at low temperature in an igneous process.

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Rock permeability was examined by fluid flow through single fracture in granite under confining pressure up to 100 MPa. Permeability of rocks below near surface is around 10^-6 to 10^-11 (log k [m2]), and it changed to ca. 10^-13 [m2] under 40 MPa (confining pressure). However, it was almost constant up to 100 MPa. These facts suggest that fracture is main field for fluid flow and crustal permeability is determined by density and properties of rock fracture even in the lower crust conditions.

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The Taiwan Chelungpu-Fault Drilling Project was undertaken in 2002 to investigate the faulting mechanism of the 1999 Mw 7.6 Taiwan Chi-Chi earthquake. Hole B penetrated the Chelungpu fault, and core samples were recovered from between 948.42- and 1352.60-m depth. Three major zones, designated FZB1136 (fault zone at 1136-m depth in hole B), FZB1194, and FZB1243, were recognized in the core samples as active fault zones within the Chelungpu fault. Nondestructive continuous physical property measurements and various kind of the chemical analyses were conducted on all core samples. In this presentation, we introduce the main result from this project.

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We have investigated microchemical analyses of syn-tectonic veins along the Nobeoka thrust, the Shimanto belt, Kyushu. Fault fill veins are composed of Fe-carbonate with positive Europium anomaly, suggesting extremely anoxic environment during their deposition. This anoxic environment can be explained by mecanochemical Hydrogen generation caused by comminution processes during earthquake.

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We conducted hydrothermal flow-through experiments to observe silica precipitation on granite substrates so as to understand the controls and mechanism of textural development of quartz veins. The precipitation conditions were 400-430 degreeC and 31 MPa, at which quartz solubility, CSi, ,qtz,eq is 80-100 ppm. The various Si-saturated solutions were initially created by dissolution of sands of quartz, amorphous silica and granite at 350-370 degreeC. It is revealed that the precipitated silica species (quartz, cristobalite and amorphous silica) and their textures generally vary depending on Si concentration in the solution and precipitation sites, indicating that the texture of natural quartz veins is suggestive of chemical compositions of the solutions during vein formation.

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The isotope exchange between minerals and fluids is enhanced in the area swept by the migrating grain boundaries (GBs; Nakamura et al., 2005; McCaig et al., 2006). This "GB sweeping" mechanism may control the rate processes of chemical transport in the mantle metasomatism and partially molten rocks. To investigate the effect of GB migration on the compatible element exchange between rocks and fluids, we have carried out piston-cylinder experiments in the dunite-Ni system at the uppermost mantle condition. The volume swept by the GBs is at most 50%, and the maximum average concentration of NiO is 4 times as high as that calculated in a static GB diffusion model. In this paper, the experimental results will be presented with their analysis based on the 2-dimensional diffusion model.

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We found dark brownish rock veins and bodies in the oceanic crust of the northern Oman ophiolite. The outcrop belongs to the isotropic gabbro member located slightly below the lower boundary of the sheeted dyke complex along Wadi Bani Umar. This rock was formed by strong alteration of gabbro and dolerite altered by hydrothermal fluids and almost all minerals have been changed to chlorite. So we call this rock <chlorite rock.> In the wall rock gabbro and dolerite, Cpx is partially replaced by amphibole, and Opx, by aggregate of amphibole and chlorite. We analyzed wall rocks and chlorite rocks for mahor to trace elements to reveal genesis of the chlorite rocks and related chemical budget in the context of hydrothermal circulation in oceanic lithosphere.

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The chemical equilibrium for calcite, anhydrite and quartz of HDR geothermal fluid is calculated using SOLVEQ-CHILLER. In early stage of circulation, the equilibrium temperature of calcite was about 100°C and those of anhydrite and quartz were about 250°C in production well, HDR-2a. However, after thermal breakthrough occurred, the equilibrium temperature of anhydrite and quartz decreased and the log(Q/K) of calcite at 80°C increased rapidly. This is corresponds to the calcite precipitation in surface installations and the temperature fell down in well HDR-2a. And calcite precipitated with CO₂ gas release in pipeline.

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Alteration of the pyroxene-amphibole andesite of Garan-dake volcano, Oita, occurs by the acidic hydrothermal fluid to form cristobalite. Hand specimens with unaltered/weakly altered core and cristobalite crust show various sequences of intermediately altered layers including alunite, pyrite, kaolinite, goethite and hematite. These alteration products suggest that the hydrothermal fluids change their geochemical conditions temporally and spatially. Especially, sulfur and/or iron-bearing mineral species are influenced by the fluctuations of the redox conditions in the hydrothermal fluids.

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For the long-term assessment of CO2 geological sequestration, the dissolution rate of feldspar was measured under various degrees of undersaturation based on observations of the time-course change of dissolved crystal surfaces on a nanoscale. We identified that the dependence of solution saturation state on anorthite dissolution rate follows to a sigmoidal curve function, rather than to a linear function. Compared with a linear assumption, such a nonlinear form provides a much lower estimate of dissolution rate. This implies that the difference of rate formula can cause meaningful errors in the timescale evaluation of various geochemical processes. In this study, therefore, the effect of the function form of dissolution rate was also checked using the geochemical simulation code to analyze CO2 geological sequestration.

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Water chemistry and mineral occurrences in mineral/hot springs associated with calcareous depositions were investigated. The waters have high Na and Cl concentrations, and depositions are composed mainly of Fe-bearing oxyhydroxide, calcite and aragonite. The result of this study might be available for CO2 capture and storage as a natural analogue, and provide useful information for carbonate scaling issues in hot springs and geothermal exploitation.

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Geological CO2 storage,especially open aquifer storage,is attracting attension as immediately applicable measure in the reduction of atomspheric CO2. The injected CO2 deep into the underground strata is ecpected to react with reservoir rocks and groundwater to produce new carbonate mineral(s) stable at the conditions of the reservoir. We have conducted geochemical modeling, both equilibrium amodeling nd reactive transport modeling, to investigate geochemical changes that would take place in the CO2 reservoir, setting the Tokyo Bay area as a model field.

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Hydrothermal alteration mineral assemblages were determined by X-ray diffraction pattern of samples from two deep boreholes, which were drilled at Nebukawa and Miyashita, southeast flank of the Hakone volcano. Both boreholes reached the basement (Hayakawa tuff breccias and Yugashima formation) thorough Hakone volcanic rocks. Characteristic mineral assemblages are smectite, swelling chlorite, chlorite, chlorite + epidote + wairakite in descending order in the Nebukawa borehole. In the Miyashita borehole, they are smectite, chlorite, and chlorite + epidote, in descending order. Basically, these changes in mineral assemblages are results of temperature gradient in neutral to basic hydrothermal activity. The difference in two boreholes probably comes from the difference in chemistry of hydrothermal fluid, in particular, CO2 concentration.

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Frequent impacts of extraterrestrial objects melted the embryonic Earth, forming an inorganic body with a CO2 and N2-rich atmosphere. How and when abundant organic molecules appeared in such an inorganic world are fundamental inquiries into the origin of life. Here we report a facile impact synthesis of some biomolecules and their precursors from solid carbon (13C), iron, nickel, water, and nitrogen all of which would have been available during impact events on Earth's early oceans. Biomolecules and their precursors identified in the present shock recovery experiments are carboxylic acids, amines, and an amino acid. Therefore impacts of extraterrestrial objects on Hadean oceans might have prepared organic molecules in necessary abundance, variety, and complexity for life's origin.

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Shock-recovery experiments were performed in order to water-rock interaction during the meteorite ocean impact events. Rapid formation of serpentine and generation of ammonia from atmospheric nitrogen were found in the present study. Those results imply that the late heavy bombardment was controlling elemental cycles on the Earth during the late Hadean age.

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Hakkoda-Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the Northeast Japan arc. Our recent studies have revealed the detailed volcanic and magmatic history of HTCC. There was a long volcanic hiatus of several million years before the activity of HTCC. The HTCC volcanism started at 3.5 Ma in the back-arc side. Subsequently, the area of volcanism has migrated gradually toward the volcanic front side with time. Those variations are probably explained by the small-scale convection model of mantle wedge shown by Honda and Yoshida (2005).

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We examined the genesis of felsic magmas of three post large-caldera volcanoes; Aoso, Takamatsu, and Gassan from front to rear arc side, NE Japan. These volcanoes are mainly composed of andesites which were formed by mixing between mafic and felsic end-members. The following data suggest the two end-member magmas are cogenetic. (1) Increasing potassium contents in felsic end-members from front to back arc side can be observed, as well as in mafic ones. (2) Sr isotopic data of each volcano are rather constant in all range of silica contents. Fractional crystallization process of phenocrystic minerals from the mafic end-member can not explain the whole rock compositions of the felsic one. An alternative process to produce the felsic end-members is partial remelting of solidified mafic ones. The trace element composition shows that the felsic end-member can be formed by remelting, leaving hornblende gabbroic residues.

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Volcanic evolution of the Akakura caldera can be divided into the four stages. (1)Precaldera tumescence stage: regional uplift of basement due to upward movement and accumulation of felsic magma in a large, shallow chamber. (2)Caldera-forming pyroclastic eruption stage: eruption of voluminous pyroclastic flows and piston-cylinder-like subsidence of basement rocks along ring faults. (3)Postcaldera volcanism stage: eruption of andesitic magma via a feeder dykes in a subaqueous setting and quench fragmentation in contact with water to produce the hyaloclastites. (4)Resurgent uplift stage: uplift of central resurgent dome accompanying a significant deformation of the caldera fill with a half-circular reverse fault.

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The Shirakawa ignimbrites were generated by large-caldera-forming eruptions in Fukushima Prefecture, NE Japan, during Early Pleistocene. The ignimbrites consist of the Kumado (1.4 Ma) from Ono caldera, Ashino (1.3 Ma) and Nagurasawa (1.2 Ma) from Tonohetsuri caldera, Nishigo (1.1 Ma) from Narioka caldera and Ten-ei (1.0 Ma) from unknown-concealed caldera. These calderas overlap each other within 20-by-20 km area on the backbone range of the arc. Tonohetsuri (14 km in diameter) is the largest caldera of them and accompanied with a typical post-caldera resurgent dome. The Shirakawa ignimbrites are crystal rich and lack vertical chemical zoning. Pumices of Kumado, Ashino, Nagurasawa, Nishigo and Ten-ei are 68-70 wt%, 67-70 wt%, 68-69 wt%, 72-74 wt% and 69-70 wt% in SiO2 contents, respectively. They are plotted within medium-K field, but make different trends for other major-elements in same range of SiO2. So, these pumices are not generated by simple crystal fractionation from a parental magma. On the contrary, these are similar in trace-elements pattern having Nb, Ta and Ti negative anomalies, high LREE and flat HREE. Although their pattrens can be explained by partial melting from similar K-rich basaltic sources, their Zr/Nb, Ba/Th and K/La ratios are apparently different. Also, these pumices independently differ in isotopic ratios, which vary from 0.7044 to 0.7047 in 87Sr/86Sr and from 0.51271 to 0.51278 in 143Nd/144Nd, although they repeatedly erupted from overlapped calderas. These results suggest that the ignimbrite sources were made up of similar basaltic rocks, but renewed at every caldera-forming eruption. In general, it is increasingly evident that some silisic magma is generated in the lower crust and erupts without spending a significant time in the upper crust. To explain renewal of the Shirakawa ignimbrite magmas, melted materials vanished from deep crustal hot zone due to upward migration and similar crustal materials subsequently subsided into the hot zone as source materials for the next eruption.

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The 1.75 Ma Chayano-Ebisutoge Pyroclastic Deposits (PD) is a large(300 km3 volume) eruptive unit consisting of ignimbrite, coignimbrite ash fall and pumice fall located in the central portion of the North Japanese Alps. The Chayano-Ebisutoge PD covered all central Japan, including the Osaka, Kyoto, Nagoya, Tokyo, and Niigata areas, distributed over a radius of >300 km. The tephra was erupted after a dacitic ignimbrite Nyukawa Pyroclastic Flow Deposit (PFD) at 1.76 Ma, and is regarded as the effusive phase of the Takidani Granodiorite, which is now exposed at the surface due to extremely rapid uplift in the area. The Chayano-Ebisutoge rhyolitic tephras have high K2O characteristics, and feature iron enrichment relative to magnesium, combined with low oxygen fugacity. The major element composition of the Chayano-Ebisutoge PD is similar to silicate melts produced experimentally from pelitic gneiss and granites at upper crustal pressures, suggesting a crustal melt origin. Neodymium and Sr isotopic compositions of the Chayano-Ebisutoge PD match those of the basement granitoids and gneiss. Assimilation-fractional crystallization of contemporaneous Ueno Basalts magma in the same area cannot account for the compositions of the Chayano-Ebisutoge PD. However, mixing between Chayano-Ebisutoge rhyolite magma and evolved Ueno basalt can generate the dacitic magma responsible for the Nyukawa Pyroclastic PFD and the Takidani Granodiorite, judging from major, trace, and isotope compositions. All the geochemical evidence above strongly supports a crustal melt origin for the Chayano-Ebisutoge PD. Accumulation of a voluminous basalt magma caused extensive melting of the crust, thus producing the huge volume of the Chayano-Ebisutoge PD.

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Mamga genesis of silicic and mafic magmas in three large pyroclasitic eruption cycles at Aso volcano between 150 ka and 90 ka has been investigated on the basis of geochemical data. In each large eruption cycle, the silicic and mafic magmas have identical isotope ratios of Sr so that they were generated from the same source material, whereas they do not have parent-daughter relationships by simple fractionation. Petrogenesis of these two magmas can be explained by partial melting of mafic lower crust due to injection of hot, mantle-derived magma. The mafic magma was produced by fractionation of partial melt with higher degree of lower mafic crust. The silicic magma is partial melt with lower degree of the lower mafic magma. Generation of these two magmas occurred in every large pyroclastic eruption cycle at Aso volcano.

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Stratigraphy, component, and lithology of the pyroclastic deposits in the 7.3 ka eruption of the Kikai caldera were analyzed in order to reconstruct the eruption. The duration of the plinian stage is estimated to be more than 28 h, based on the thickness and clast-size data of the fallout deposits. The sedimentary characteristics resulted from the plinian column collapse indicate that high temperature density currents were generated. In the final phase, multiple pyroclastic density currents were followed by the main sustained current. In total the estimated magma volume in the system was 70-80 km³ in DRE, with compositional range of andesite to rhyolite spanning with the climactic phase. The caldera collapse duration was estimated to be less than 6 hours, based on tsunami numerical simulation combined with simple caldera collapse model, magma chamber condition, and coastal geological data.

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Miocene felsic volcanic field at the Kii Peninsula (MFVK) in southwest Japan allows us to reveal temporal and spatial change of a large felsic volcanic system in response to changes in the local and regional stress field. Approximately 1,500 km³ of magma were erupted from the MFVK. An area normalized eruption rate is ranked as one of the larger rates of LFVF worldwide. The large eruption rate is due to a large magma supply in combination with local and regional stress conditions, promoting magma accumulation for a large silicic magma chamber. We suggest that such a large magma chamber can generate excess pressure inside the chamber itself that results in a local tumescence and counteracts the tectonic compressional stress field, allowing magma to reach the surface.

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The Nohi Rhyolite (> 5000-7500 km³) and its related granitoids (hypabyssal stocks and the Naegi-Agematsu batholith) constituted one of the large silicic magma systems (LSMS) in the Eurasian continental margin during the Late Cretaceous (ca. 85-68 Ma). This LSMS is characterized as (1) a very large-scale system, which was built over time scales of 10⁶ years, (2) monotonous silicic composition, which consists of high-K, I-type, ilmenite-series dacitic to rhyolitic rocks without mafic ones, and (3) crystal-rich eruptive products (fiammes of ash-flow tuffs have 30-45 vol. % phenocrysts), which suggests that the magmas were able to erupt when they became mushy and water-saturated. Some further studies on the Nohi igneous province can contribute to the LSMS themes, e.g. high-precision dating to reveal rates of magmatism of the very large-scale system.

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There are many Cretaceous-Paleogene granitoid masses distribute in the Shirakami and Taiheizan. Each emplasement ages are 86-92 Ma with the Shirakami granitoids and 85-97 Ma Taihei granitoids by Rb-Sr whole rock isochron and K-Ar mineral method. The Kitakami granitoids indicate same radiometric ages 100-135 Ma by each method, but the Abukuma granitoids show 125-100 Ma Rb-Sr to 120-110, 105-95 Ma hornblende K-Ar and 95-90 Ma biotite K-Ar ages. On the initial ratio about the Sr, Nd isotopes, the Shirakami and the Taihei granitoids space in the North-zone (Kagami et al., 2000) and correlatable to the Abukuma granitoids.

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Adakitic plutons dominate the Early Cretaceous igneous suite of the Kitakami Mountains of northeast Japan. The zoned plutons typically consist of adakitic granite in their centers (central facies) surrounded by adakitic to non-adakitic granites in their margins (marginal facies). The central facies granites are characterized by low Y and high Sr concentrations and fractionated LREE/HREE patterns, characteristics common to Archean TTG and modern adakite. Chemical compositions of the central facies granites can be explained by the ``slab melting'' model. The marginal facies granites are characterized by slightly lower Sr/Y ratios, less fractionated REE patterns, and weak negative Eu anomalies. The marginal facies magma is considered to be derived from the reaction of slab melts with mantle peridotite and lower crustal amphibolite.

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The Fosdick Mountains of Marie Byrd Land, West Antarctica host subordinate migmatitic gneisses corresponding to the middle-to-lower crust (∼6-10 Kbar) and dominant granites. Based on petrography and geochemistry the granites are divided into silimanite-bearing low-Sr and silimanite-free high-Sr types. U-Pb geochronology on magmatic zircon from the granites reveals two periods of emplacement during Carboniferous and Cretaceous, consistent with a polyorogenic evolution of the region during Devonian-Carboniferous continental arc activity and Cretaceous continental rifting. The Cretaceous high-Sr granites, with U-Pb zircon ages and Sr-Nd isotope compositions comparable to the Cretaceous Byrd Coast Granite suite, are interpreted as a feeder zone for the shallow-level intrusions.

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Pyroxene temperatures of the Aoso-Osore, Sekiryo, Moriyoshi, and Chokai volcanic zones are 1050°C, 1090±35°C, 1050±35°C, and 1080±35°C(1σ), respectively. Estimated water contents and the pressures were as following: 4.6wt.%H₂O and 1.9kbar(An64-74) for Aoso, 4.5wt.%H₂O and 1.5kbar(An75-78) for Kurikoma, 4.8wt.%H₂O and 1.9kbar(An76-80) for Zao, 5.6wt.%H₂O and 2.6kbar(An65-70) for Akitakomagatake, 5.5wt.%H₂O and 2.6kbar(An50-55) for Iwaki, and 4.9wt.%H₂O and 2.0kbar(An69-76) for Chokai. These high water contents imply near water-saturation conditions at the pressures. Plagioclase phenocrysts were possibly crystallized by decompression dehydration crystallization.

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Hakusan volcanic rocks younger than a dormant period (ca 0.3-0.1 Ma) are adakitic, while older ones have geochemical affinity with common island arc andesites and dacites. Type of magma genesis is likely to have changed during the dormant period from that triggered by the dehydration of Pacific plate to that by the partial melting of Philippine Sea plate beneath the area.

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We analyzed the major and trace element and isotopic compositions of the volcanic rocks from the Kofu Basin, and investigated the temporal geochemical variations. As a result, these volcanics show the typical island arc magma. From the Sr/Y ratios, the magma genesis of this area is caused by slab dehydration of Pacific plate at Tertiary, and by slab melting of Philippine Sea plate at Quaternary. The isotopic compositions of Sr, Nd and Pb suggest that the materials derived from Philippine Sea plate contributed former magma genesis. From these observations, it can be concluded that the Philippine Sea plate was reached near below the studied area at Tertiary, and reached just below this area at Quaternary.

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The Izu-Bonin arc to back-arc system gives us the chance to examine magmatism in the period following back-arc spreading but with on-going subduction. This stage in arc evolution is characterised by widespread across arc volcanism and the occurrence of two contrasting and contemporaneous magmas.

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NW Rota-1 volcano is an active submarine volcano in the Southern Seamount Province of the Mariana arc. Using JAMSTEC's ROV, a total of 42 rock samples were collected from the summit region (531-1080 mbsl) and near the base (1474-2260 mbsl) of the volcano. These lavas are medium-K basalts and andesites with 51.5-58.2 wt% SiO2. We note, that lavas ranging from 54-57 wt% SiO2 are conspicuously absent and that most lavas tend to cluster at 52 and 57 wt% SiO2. In constrast, melt inclusions trapped within olivine grains from the same lavas span a much wider range (48.7 to 56.9 wt% SiO2) and show a continuous range (i.e., no gaps). Here we explore why this difference is observed and evaluate whether melt inclusions record primary andesite melt compositions.

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Anorthite megacrysts occur in many of volcanic products in Japanese volcanic arcs. They are recognized as disequilibrium minerals in host basalt and andesite in each volcano. This study focused on the mineral chemistry and Sr isotope composition of anorthite megacrysts in volcanic rocks in the Kyushu-Ryukyu volcanic arc where tholeiitic and calc-alkaline rocks coexist. The lattice constant of anorthite megacrysts are identified to be C=7A type, and their An mol. % are around 92 %. Measured Sr isotope ratios show that the ratios are slightly different between megacryst and host basalt and andesite, but that the ratios of megacrysts and host rocks parallelly increase from north to south (Aso volcano to Akusekijima volcano). We will try to compare the ratios in the Aso and Aira volcanoes where Sr isotope data of various volcanic rocks with long time span are already reported.

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In a cooling magma chamber, magmatic differentiation can proceed both by fractionation of crystals from the main molten part of the magma body (homogeneous fractionation) and by mixing of the main magma with fractionated melt derived from the low-temperature mush zones (boundary layer fractionation). In this study, the relative role of these two fractionation processes in chemical differentiation of magmas have been examined, using a thermodynamics-based mass balance model. Model calculations show that, in magma chambers located at relatively shallow levels, the magmas evolve principally by homogeneous fractionation. On the other hand, in basaltic magma chambers located at relatively deep levels, boundary layer fractionation can occur effectively depending on the melt water contents.

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Distribution of incomaptible elements in mantle xenoliths are examined.

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X-ray radiography in SPring-8 indicates that fluids derived from the downgoing slab can be in supercritical conditions underneath volcanic arcs. Such supercritical fluids separate into aqueous fluid and silicate melt during their ascents. Elemental partitioning between them is key information.

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Carbon and chlorine are circulated elements among three states of gas-liquid-solid as own and com-pounds of micro- and nano- particles of solid –states which are found by electron microscopy in ter-restrial materials Formation of carbon-bearing solid materials which are found in (ore) minerals and rocks as natural resources are considered to be control solids for terrestrial environments, though chlorine-bearing ma-terials are largely found in sea-water to control circulation process of chlorine. Therefore, micro-particles and fine materials are considered to be rapid and effective material changes in circulation process of terrestrial environment.

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There are two plausible mechanism of magmatic differentiation in a crustal magma chamber. One is uniform differentiation, which features crystal nucleation, growth, and gravitational crystal separation in the main magma body, and the other is boundary layer differentiation with compositional convection driven by the formation of lighter or denser melt along the chamber wall. In order to clarify which mechanism becomes effective in a given conditions of magma chamber, Aosawa dolerite sill (Fujii, 1974) 100m in thickness and intruded into Miocene mudstone was studied by exploiting the merits of a simple cooling history of a medium-sized sheet-like magma body.

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The garnet group minerals are among some of the most important minerals, occuring under a wide range of metamorphic conditions. Because garnet in high-P/T type metamorphism shows compositional zoning controlled by the metamorphic history, much work has been carried out to deduce metamorphic conditions and P-T path from the analysis of such zoned garnet. This study concerns other information from garnet that is critical to evaluate the formation conditions of metamorphic rocks. The relative growth rate of crystallographic faces depends on not only the atomic structure but also the interfacial energy with surrounding environment(chemical potential gradient and dihedral angle). Thus, morphological research can become a powerful tool not only to analyze mineral growth processes, but also to determine growth conditions, as the growth habit reflects the growth environment. If grain shape can be expressed quantitatively, it may provide useful insight into the petrogenesis of rocks. A garnet grain of the epidote-amphibolite rock was picked up to analyze the three-dimensional morphology, following thermal extraction method(Kretz,1973). The grain is about 10 mm in size and expresses an elongated shape maintained by the {110} growth surface. The aspect ratio is 1.83, which could not be produced by an isotropic growth. Applying the relation between the maximum aspect ratio and the ratio between the growth rates, it is indicated that the elongated garnet may be formed as a result of different growth rates with the ratio of 1.29 in symmetry both-sides model. We also calculated cross-sections assuming isotropic growth zoning. Examples are shown in Fig. 8-a, which reveals that "pseudo-anisotropic growth" caused by the variation in the apparent growth breadth. By dividing the cross section into regions so that each region is configured by parallel growth surfaces, the "hkl division map" is drawn. On the other hand, in the single region, the zoning width is constant and their sides are parallel. Thus the chemical profile should be measured in the single hkl region to obtain the accurate growth increment.

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The Horoman peridotite complex of Japan is one of the freshest orogenic peridotite complexes in the world. Dunite channels occur both as large scale (several 10 meters width) concordant layers and as small scale (< several meters width) discordant layers. The small scale dunite channels incorporate two-pyroxenes + spinel segregations. We present the Rb-Sr isotopic compositions of olivine, orthopyroxene and clinopyroxene both from a dunite dyke swarm (Sample Nos. SPR4 and 6) and from a wall harzburgite (Sample Nos. SPR14). Obtained data and previous reported data indicate that melt through the dunite channel was derived from source of their wall harzburgite metasomatized by melt and fluid derived from slab. This event could occur around 50 Ma, coevaled with peak metamorphism of surrounding Hidaka metamorphic rock.

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The Murotomisaki Gabbroic Intrusion is a sill-like layered gabbro emplaced in sedimentary strata of Tertiary age in Shikoku, Japan. We studied the zoning (including resorption structures) and the compositional variations of plagioclase from throughout the intrusion and found out that the zoning pattern may be classified into four types, A, B, B' and C, which may well correlated with the hosting rock types, the mode of occurrences and their stratigraphic positions in the intrusion. We successfully decoded the plagioclase zoning and deduced a sequences of events that took place during the magmatic differentiation and further interpreted them in the context of a stratified basal boundary layer slowly ascending in a solidifying magma body. It was revealed that various layered structures - modal layering, podiform gabbroic pegmatites and anorthositic layers - observed in the Murotomisaki Gabbro were formed within the moving basal boundary layer with the aid of flushing of water-enriched silicate melts from below but within the basal boundary layer. It was proposed that hydrous immiscible melt droplets that were generated near the base of the basal boundary layer had played an important role in displacing water upward, creating the water-enriched horizon within the basal boundary layer. Anorthositic plumes also generated in this horizon and ascended through the basal boundary layer and probably reached the main magma body lying above.

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Song Ma suture zone is a metamorphic complex developed between the South China and the Indochina Blocks, and composed of greenschist to amphibolite facies metamorphic rocks. Analytical results of whole rock compositions of amphibolites are reported for considering the origin of metamorphic rocks in the suture. The amphibolite show basaltic compositions with slightly enriched incompatible elements, especially HFS elements as Y and Zr from the primitive mantle composition. Almost amphibolites show nearly flat REE patterns with restored high Nd isotopic compositions. Such compositional characters of HFSE and REE are equivalent to those of basalt originated from depleted mantle. On the other hand, an amphibolite with LREE-enriched composition was also found. This has comparatively much LILE. Protolith of the amphibolite was possibly originated from enriched mantle. Based on such compositional evidence, amphibolites in the Song-Ma suture zone were probably metamorphosed mid-ocean ridge basalt with a few ocean island basalts.

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