The plate boundary fault between Philippine Sea plate and Honshu plate is the source of the Kanto earthquake of 1923 in the central Japan. It is important to identify the geometry of the plate boundary. In this study, a N-S trending tear of the seismogenic zone was identified beneath the Tanzawa Mountain with three dimensional GIS analysis for earthquake data. This is a slab tear of the subducted lower crust of the Izu arc which is the uppermost layer of Philippine Sea slab. The Philippine Sea slab beneath the western half of the Tanzawa Mountain is much deeper than the slab depth beneath the eastern half of the Tanzawa Mountain. The position of the slab tear shows a spatial link to the predicted western margin of the earthquake source fault of the Kanto earthquake of 1923. The identified complex geometry of the plate boundary can be used to predict hazardous earthquakes of the Tokyo metropolitan region.

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Series of high P-T melting experiments of amphibolite were carried out at 900-1200°C and 0.3-0.7GPa to understand the origin of felsic plutonic rocks in the northern Mariana Trough. The present data suggest that andesitic melts chemically similar to the Mariana Trough felsic plutonic rocks can be produced by anatexis of hydrous basaltic materials at ∼0.15 GPa and ∼1000°C. We develop the petrogenetic model for the plutonic rocks in the northern Mariana Trough.

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P-wave velocity (Vp) and S-wave velocity (Vs) of Ichino-megata mafic xenoliths, northeast (NE) Japan, were measured simultaneously under the subsolidus conditions. We obtain non-linea r velocity-temperature correlation for all rock studied. Significant Vp and Vs decreases at higher temperatures are probably attributed to thermal cracking and/or phase transition of plagioclas e and/or amphibole.

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A series of direct observation of complete miscibility between H2O fluids and island arc andesite/rhyolite magmas has been conducted using Bassett's type externally heated diamond anvil cell. The supercritical behaviors are observed between H2O fluids and Fuji 1707 magmas with chemical compositions from andesite (62 weight % SiO2) to rhyolite (69 % SiO2). Such a supercritical behavior between H2O fluids and magmas equilibrated with mantle peridotite system remains uncertain. This study is the first observation of a supercritical behavior of natural andesite and rhyolite with H2O fluids, suggesting a possibility of a second critical point between magmas and aqueous fluids in the depths of the Earth.

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Judging from existing data, we could speculate that silicate melt and aqueous fluid in the Earth's interior became indistinguishable from each other beyond the second critical endpoint with pressure. Here we report the determination of the second critical endpoint in peridotite-H2O system using high-pressure X-ray radiography technique. We found the second critical endpoint occurs at around 3.8 GPa and 1050 C (corresponding to depth of c.a. 110 km) in the Earth's hydrous upper mantle. This position of the second critical endpoint could play an important role in magmatism and chemical evolution of the Earth's interior. Our new technique can be applied to the direct observations of various kinds of 2-fluid coexisting under deep mantle conditions.

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Hydrogen diffusivity in synthesized polycrystalline wadsleyite and ringwoodite, the major constituent minerals in the mantle transition zone, was measured by Fourier Transform Infra-Red (FTIR) Spectroscopy. Hydrogen diffusion rate in wadsleyite is roughly comparable to the average diffusion rate of hydrogen in olivine. The hydrogen diffusivity in ringwoodite is also measured and found that it is comparable to that of wadsleyite. Water transported to the transition zone by hydrous phases is dehydrated at the top of the lower mantle. The dehydrated water moves upwards and is reacted and absorved by the overlying ringwoodite phase in the slab of the transition zone depth. Superhydrous phase B can be formed as the reaction product. This mechanism is effective to concentrate water in the slab at the transition zone depths; even if the amount of water transported by the slab (with the subducting speed of 10 cm /year) is very small around 0.05 wt.%, absorption of the dehydrated water by overlying ringwoodite crystals can build the hydrous zone containing 1 wt.% water with a thickness of 250 km in the slab at the transition zone depths by continuous subduction during 50 Ma. The transition zone surrounding the slab may also be hydrated but the region may be limited to less than 1 km in width due to a relatively slow diffusion of hydrogen in wadsleyite and ringwoodite.

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An internally-consistent thermodynamic data set for phase A, clinohumite, and chondrodite has been derived by mathematical programming analysis of phase equilibrium and thermophysical data. The derived thermodynamic data are in excellent agreement with measured volumes and most experimental phase equilibrium data. Calculated phase diagram suggests that, at pressures higher than ca. 8 GPa, clinohumite and/or chondrodite are stable in the average mantle composition. This suggests that, at the conditions, these phases may play an important role for hydration of mantle wedge peridotite.

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In this study, we compare the P-wave velocity (Vp) and S-wave velocity (Vs) crustal model of the NE Honshu arc by Nakajima (unpublished) with the laboratory measurements of Vp and Vs values by Nishimoto et al. (this meeting), and interprete petrological/ seismic crustal structure. The Vp and Vs of lower crustal layer beneath the back-arc side are comparable to the measured Vp and Vs values of Ichino-megata mafic xenoliths (hb. (px.) gabbro and/or amphibolite) at solidus conditions (600-700 deg.C).

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Percolation threshold is an important issue for consideration of a primary magma. The fractional melting and the equilibrium batch melting are important endmember models for the generation of primary magmas. The old concept of the percolation threshold is a static one, whereas Obata and Takazawa (2004) proposed a new concept of the dynamic percolation threshold. They proposed a possibility of a dynamic batch melting in an ascending mantle, in which percolation threshold varies according to the pressure balance between the solid and the fluid and thereby induced microstructural transformation of the partially molten region.

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Anomalously young volcanoes, of approximately 6, 4 and 1 Ma in age, for the 130-135 Ma Pacific Plate were discovered form the toe of the oceanward slope of the northern Japan Trench [1] and the abyssal plain on the Northwestern Pacific Basin. The new bathymetric, geological and petrological data indicate two types of eruptive style, different in the degree of vesicularity and major element composition; one is very vesicular lava forming knolls, another is dense lava forming sheet flows. The distributions of these volcanoes clearly have the trend of WNW to ESE, which are perpendicular to the hinge line of the flexural lithosphere (outer-rise) due to plate-subduction. The lavas are trapped some xenoliths of basalts, gabbros and peridotites, which are likely oceanic crust and lithospheric mantle in origin. Two types of olivine are also present in these lavas, xenocrysts with reaction rims and magmatic. The forsterite (Fo) (#91-92) values and NiO contents (0.3-0.5 wt%) of the xenocrysts are similar in composition to those of the depleted mantle peridotite. Chromian spinel inclusions in the xenocrysts also show the depleted composition in the range of abyssal peridotite. These data indicate that the xenocrysts originate from MORB-depleted mantle [2]. The calculated primitive magma, on the other hand, follows a low degree of partial melting along the 2.5 to 3 GPa cotectic lines, which would corresponds the depth of asthenosphere. The ascending magma from asthenosphere, therefore, would trap some xenoliths and xenocrysts originating in the conduit wall, possibly when brittle fractures occurs in the upper lithosphere due to the concave flexure of the plate in front of the convex bowing of outer-rise. The eruption occurred along some fissures being bent before subduction, in parallel to the maximum horizontal compression due to the down-warping of the Pacific plate motion for sub-crustal magma injection.

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The upper Paleozoic Yakuno ophiolite in the Asago body, southwest Japan exposes a 3.0 km-thick middle to lower crustal section of intra-oceanic island arc, which is composed of metabasites (metagabbro and schistose amphibolite) of MORB-like affinity and granitoid intrusives of island arc affinity (Hayasaka, 1990; Suda, 2004). Mafic migmatite develops in the lower crustal section, whereas the granitoid intrusives forming plutons and dykes develop in the middle crustal section. Mmorphological change of the migmatite with increasing structural level suggests the melt segregation process. Small-scale primary melt formed at the lowermost horizon (metatexite migmatite), which moved upward, accompanied by increasing degree of melt segregation (melt-enriched migmatite), and finally led to the formation of plutons.

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[in Japanese]

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An advanced heating stage has been developed in order to carry out in-situ observation of the bubble growth in silicate melt. A new attempt for the measurement of physical properties of silicate melt using equilibrium shape of bubble is proposed.

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Recent advances in seismic tomography enable visualization of the crust-mantle structures beneath the NE Honshu arc. Combined with geology and petrology, the seismic images have become valuable tools for revealing the mantle-crust thermal structures of the arc. The thermal structure of the present mantle wedge inferred from geological and petrological data correlates well with the mantle seismic structures. Intra-crustal thermal structures would have been affected by intensive magma intrusions to form large magma storages beneath the late Miocene to Pliocene calderas. The remnants of these thermal disturbances are still detectable by seismology. The mantle-crust thermal structures of the NE Honshu arc appear to have developed in relation to the development of the igneous arc.

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The mechanism of development of shallow magma chambers and their relationships with caldera collapse are poorly known. Here we review the studies of pluton emplacement and caldera collapse, proposing a model linking the two processes. Magma ascending through diapirs or dikes is mostly halted at middle crustal levels. In the upper crust, the further rise of magma occurs by diking and the emplacement occurs along major anisotropies. Many plutons are emplaced at subhorizontal discontinuities, consisting of tabular, sill-like intrusions. Their growth will eventually induce doming of the overburden, forming laccoliths. Various evidence for shallow felsic and mafic laccoliths have been provided, suggesting that laccoliths are the most common mechanism to store magma in the upper crust, especially when the magmatic rates exceed the tectonic ones.

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Analytical data of Nio meteorite sherules (Yamaguchi, Japan), PTB spherule (Meishan, China), and impact-related breccias indicate that 1) FeNi minerals are separated after high temperature reaction to Ni-rich spherules or particles, 2) new tweedy and lamellar texture of spherules are formed with Fe-Ni and Al-Si chondritic elements, and 3) Ni-rich deposit of Sudbury are related with formation of Ni-rich materials from FeNi minerals.

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Sulaibikhat bay is a subsystem of Kuwait bay where intertidal mudflats are extended. It receives variety of discharges from land use activities. Significant changes in the sediment characteristics of the northern territorial waters of Kuwait exist; the construction of the Third River and the effect of draining of the Iraqi marshes. the scope of this study is to evaluate the effects of the previous incidents and investigate the secular variation of the heavy metals in the intertidal sediments of Sulibikhat bay. Geochemical characteristics of these sediments provide us last 50 years environmental change in northern parts of Kuwait. Eight cores were collected from intertidal zone sediments and geochemical analyses were carried out. XRF and ICP-MASS were used to measure the major and the trace elements of the sediments. Initially the longest core was analyzed by XRF and XRD, and the data with depth shows clear secular chemical variation.

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As a consequence of atmospheric pollution and related strong acid deposition, soil acidification has been considered to be a major environmental problem in the forest regions adjacent to densely populated cities. In this study, we assess acid neutralization potential of two types of soil; soils derived from granite parent material (tonalitic soils) and soils derived from volcanic ash (loam soils), in Tanzawa mountain area. The Tanzawa Mountains is located about 50 km west of the Metropolitan Tokyo and has received significant amounts of pollutants through atmospheric deposition. In addition, this area has received considerably amounts of SO2 emitted from Mt. Miyake volcano since August 2000. The study area is located in the southern part of Oomuroyama watershed (~25 km2) and covered by mixed hardwood forest (elevation 525-1600 m). The bedrock of the study area is Miocene granitic (tonalitic) rock with minor amounts of gabbro. The area is partly blanketed by the Kanto loam. We conducted the fieldwork in every one month (from Apr 2003 to Nov 2004), and collected tonalitic soil and loam soil samples (Ao, A, AB, BC, C, and R horizon; 30 to 300 cm total thicknesses) from 77 sampling points. Average pH in the soil solutions in the A horizon is 5.96 in the tonalitic soils and 5.04 in the loam soils. The loam soils have lower pH values compared with the tonalitic soil. In the B-horizon, the soil solutions of loam soil exhibit a wide range of pH variation ranging from 5.61 to 7.39 (average 6.57). This average value is slightly higher than that in the tonalitic soil (6.18), suggesting that higher potentiality of acid neutralization in the loam soil.The tonalitic soils show a wide range of chemical variation from C to Ao horizon. From bottom to up, SiO2, Al2O3, CaO, K2O, Na2O systematically decrease, while TiO2, P2O5, total C (TC) and total N (TN) markedly increase. The concentrations of analyzed elements are normalized to the Ti content in the same sample to evaluate quantity of elemental lost during weathering. We take the chemical composition of the bottom horizon (C) as the initial composition of parent material. The data suggest that the tonalitic soils have need extensively weathered and considerable mounts of elements leached out from the parent material. The present results indicate that 25 wt.% SiO2 in the parental material has leached out. The estimated amounts of other elements lost from the parent material are: 5wt.% Al2O3, 0.8wt.% Fe2O3, 0.4wt.% MgO, 1.6%wt.% CaO, 1.2wt.% Na2O:, and 0.3wt.% K2O. SiO2 exhibit well defined correlation with Al2O3, Na2O, K2O, CaO, and Fe2O3 in the tonalitic soil. Al2O3 has good correlation with CaO and Fe2O3. The present observation suggests that chemical changes in the soil are associated with chemical weathering of plagioclase, hornblende and biotite, and formation of clay minerals. The loam soils exhibit narrow stratigraphic variation.These show comparable composition from the top to the bottom horizon. The present data indicate that the loam soils were not extensively modified by weathering and have higher potential in acid neutralization than the tonalitic soil.

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This study is devoted to the monitoring solute concentrations in river water (from May 2001 to January 2005) in the Tanzawa Mountain. As a consequence of atmospheric pollution and related strong acid deposition, surface water and soil acidification has been considered to be a major environmental problem in the forest regions adjacent to densely populated cities. The Tanzawa Mountains is located about 50 km west of the Great Metropolitan Tokyo and an area receiving higher amounts of pollutants through atmospheric deposition than the Kofu Mountains. In addition, the areas have received considerably high SO2 deposition emitted from Mt. Miyake volcano since August 2000. All water samples were filtered (0.45 mm pore diameter membrane filter) and concentrations of SiO2, Ca2+, Mg2+, Al3+, PO34- were analyzed by ICP, Na+ and K+ by AA, and Cl-, NO2-, NO3-, SO42- by IC. HCO3- was determined by the 0.1N-H2SO4-titillation method.

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Orogenic peridotites typically contain abundant mafic layers or lenses of basaltic to picritic compositions. A popular hypothesis for the origin of such mafic layers is that they represent crystal precipitates from mafic magmas flowing in the upper mantle in various depths (Suen and Frey, 1987). Some mafic rocks have been suggested to be of gabbroic origin from their geochemical and mineralogical signature such as positive Eu anomaly and the presence of corundum (e.g., Kornprobst at al, 1990) By examining the whole rock compositions of these rocks and associated rocks, the author proposes a new criterion of identifying mafic layers of gabbroic. According to the new criterion, mafic layers of gabbroic origin appear to be more pervasive than previously thought in mantle derived peridotites.

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[in Japanese]

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[in Japanese]

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Chromian diopside with high K content up to 0.56 wt% was discovered from the Osayama serpentinite melange, SW Japan (Tsujimori and Liou, 2005). K-bearing clinopyroxene (K-Cpx) fills hydrothermal micro-veins together with uvarovite within albite vein of a tremolite rock. K-Cpx consists mainly of kosmochlor + augite (92-98%; Ko19-38Aug56-76) components and minor amounts of jadeite (0-6%), aegirine (0-5%), Ca-Tschermak (0-3%), and K-kosmochlor (0-2%). K correlates with Na and Cr, indicating a simultaneous enrichment of K for Na and Cr during pyroxene growth. The incorporation of K into the kosmochlor_-_diopside series solid solution with at least 0.2 Cr cation p.f.u. is possible even at low P conditions.

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Mechanism of Ni incorporation into dunite has been studied in order to simulate the compatible elements behavior in fluid-bearing rocks. Fe-free dunites were synthesized from gel powders using a piston cylinder apparatus. The gel powders were put into Pt-lined Ni capsules with water. As the run proceeded, Ni penetrated Pt liner all the way through and infiltrated into dunite in which forsterite grains were continuously growing. The sweeping of the grain boundaries that are enriched in Ni by grain boundary diffusion and surface equilibration should be responsible for more effective Ni - Mg exchange flux between fluid and olivine than by inter-diffusion from the stationary grain boundaries.

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[in Japanese]

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The Kodaikanal region of Madurai Block in southern India exposes a vast segment of high-grade metamorphic rocks dominated by Al-rich migmatite suite, designated herein as the Kodaikanal Metapelite Belt (KMB). The peak metamorphic assemblage is considered to be garnet-spinel-cordierite-quartz, which indicates possible pressure-temperature conditions of 900 °C at 7-8 kbar based on petrogenetic grid considerations. We show that the evidence for extreme crustal metamorphism at ultrahigh-temperature (UHT) conditions in granulite facies rocks can be extracted even if they lack typical UHT mineral assemblages due to bulk chemical constraints.

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To reveal exhumation history of UHPM rocks, isochron ages in K-Ar system are examined with phengite and paragonite in the eclogitic rocks from the Tso Morari complex (TMC), western Himalaya, India. TMC is composed of pelitic gneisses and schists including mafic rock lenses (eclogites and basic schists). Eclogite has coesite pseudomorph in garnet and/or quartz rods in omphacite, suggesting UHPM. Pelitic schist gives an isochron age of 91±13 Ma using K-Ar analyses of paragonite and phengite. Phengite and paragonite in eclogite were analyzed by Ar/Ar method. Step-heating analyses using single phengite crystal showed 132 Ma plateau ages. The inverse isochron age by spot analyses of paragonite and phengite is 130±39 Ma.

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The Lesser Himalaya in central Nepal exposes an inverted metamorphic sequence. The metabasites in the sequence occur as sheet-like bodies of a meter to tens of meters thickness. All the samples studied have the mineral assemblage Amp+Ab+Ep+Qtz+Titanite±Magnetite. Amphiboles occur as (1) sheared and elongated porphyroclasts with asymmetric pressure shadows and overgrown rims, (2) acicular and bladed aggregates parallel to the foliation and (3) inclusions in plagioclase. Amphibole chemistry suggests that (i) the peak metamorphism was attained during shearing related to the MCT movement and (ii) the peak thermal structure is inverted in the MCT shear zone.

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I would like to report the corundum-quartz coexistence obtained from melting experiments of a mudstone.

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Metatrondhemite from Cape Hinode, Lutzow-Holm Complex, East Antarctica, has yielded 1017 Ma SHRIMP zircon U-Pb dating. Additional EMP monazite datings on metapelitic rocks yielded 935~1007 Ma which are consistent with the SHRIMP result. It is worth noting that no 500 Ma were detected by both methods. Petrographical investigations suggest that metamorphic rocks from Cape Hinode belong to granulite-facies conditions. These lines of evidence imply that Cape Hinode is exotic within the Lutzow-Holm Complex with respect to geochronology and metamorphic grade, and possibly correlatable with the neighboring Rayner Complex.

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We examined petrological characteristics of the metapelites from the Androyen system, which occupies the eastern part of the terrain. It is composed of charnockite, leptynites, pyroxenite, granite and metapelites. This terrain is bounded by two major shear zones: to the north by the SW-SE trending Bongolava-Ranotsara shear zone and to the west by NS Betroka shear zone. In this study we mapped Spl-Qtz occurrences in the metapelites in strikingly wide areas extending over ∼200km. Spl-Qtz rocks are distributed along the two shear zones (Bongolava Ranotsara shear zone and Betroka shear zone). The Spl-Qtz metapelites probably represent the roots of the continental crust uplifted during the Pan African collision event.

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The Ntem Complex is situated at the north-western border of the Congo Craton in the south of Cameroon. It makes up the Archean basement and extends over its contact with the North Equatorial Mobile Belt represented by the Yaounde group. This group overthrusted the Ntem Complex during the Pan-African orogeny (650-500 Ma) and is affected by high pressure syn-tectonic metamorphism. The Sangmelima region belongs to the Ntem Complex made up of three main lithologic groups: the intrusive complex (TTG, Granodiorites and Granites), the banded series and greenstone belts or iron trenches, so has undergone several magmatic episodes. The first is linked with the beginning of the major deformation phase (D1) faced by the region, associated with a granulite facies metamorphism. It corresponds to the successive diapiric emplacement of charnockitic rocks (TTG suite) during Meso to Neoarchean (2.9-2.8 Ga). The intense migmatization of TTG and the emplacement of Potassic Granitoids which marked the second magmatic episode, correspond to the period between 2.6-2.5 Ga. TTG and Orthogneisses are of Trondhjemitic affinity whereas Potassic Granitoids are high-K acid rocks of typical Calc-alkaline differentiation series. This Archean-Proterozoic transition granitic magmatism (2.6-2.5 Ga) is one of the important stages in the evolution of the Ntem Complex (Congo Craton) since it marks a crustal reworking event.

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