Publishing type：Research paper (scientific journal)  

This paper describes the formation mechanism of reversely zoned plagioclase, which has been observed frequently in lower crustal shear zones and is indicative of multistage fracturing and metamorphism in the lower crust, by studying the microstructural and chemical characteristics of plagioclase in sparsely fractured anorthosites and anorthositic mylonites from the Eidsfjord shear zone, Langoya, northern Norway. Based on the field relationship between sparsely fractured anorthosite and anorthositic mylonite, the fracturing of anorthosite occurred before the formation of mylonite. In sparsely fractured anorthosites, transgranular fractures are observed; hydration-reaction products, including Na-rich plagioclase, occur within cracks and fractures, suggesting that hydration reactions occurred during or after fracturing. The hydration reactions in sparsely fractured anorthosites are estimated to have occurred at higher-pressure (P) amphibolite-facies conditions (similar to 0.9-1.0 GPa and similar to 550-700 degrees C). In anorthositic mylonites, which are considered to have initiated by fracturing and subsequent hydration metamorphism at lower-P amphibolite-facies conditions (similar to 0.7 GPa and similar to 600 degrees C), recrystallized plagioclase grains often show compositional zoning with an Na-rich core and a Ca-rich rim. Because the compositions of metamorphic plagioclase grains in the sparsely fractured anorthosites and those of the Na-rich cores of the reversely zoned plagioclase in anorthositic mylonites are similar to each other, the Na-rich cores of the matrix plagioclase in the anorthositic mylonites have recrystallized under higher-P amphibolite-facies conditions and then been overgrown or replaced by the Ca-rich rims under lower-P conditions. Consequently, the reversely zoned plagioclase observed frequently in lower crustal shear zones is an indicator of multistage brittle fracturing and subsequent hydration metamorphism during exhumation, providing information relevant to understanding the deep rupture process caused by repeated seismicity alternating with aseismic creep below the seismogenic zone.

DOI： 10.2138/am-2020-7284

<p> Because deformation in the lower crust immediately below a seismogenic fault can accumulate stress on the fault, understanding the dominant deformation mechanism and the formation of ductile shear zones in the lower crust is crucial to reveal occurrences of intraplate earthquakes. Plagioclase-rich rocks (e.g., gabbro and gabbronorite) are major constituents of the lower crust. A change in the deformation mechanism from grain-size-insensitive creep to grain-size-sensitive creep would result in significant rheological weakening. The transition potentially increases the strain rate more than an order of magnitude at a constant stress, and the process of grain size reduction in plagioclase-rich rocks is particularly important. In addition to dynamic recrystallization, fracturing is another dominant mechanism of grain-size reduction at high temperatures. The most likely explanation for the occurrence of fracturing in the lower crust is the deeper penetration of large earthquakes, which nucleate in the seismogenic zone and propagate into the underlying ductile region at the stage of coseismic displacement. Zones with very fine grains that result from fracturing would be deformed by grain-size-sensitive creep. Fracturing also facilitates fluid flow due to the increased dilatancy and connectivity of pore spaces. An influx of fluid enhances hydration reactions, which form small, strain-free recrystallized grains. This process promotes grain-size-sensitive creep in narrow zones, and result in the development of ductile shear zones in the lower crust.</p>

DOI： 10.5026/jgeography.128.747

CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s00531-019-01749-z

Publishing type：Research paper (scientific journal)  

DOI： 10.1111/ter.12355

Publishing type：Research paper (scientific journal)  

Spatial growth patterns are natural recording media (NRMs) that preserve important historical information, which can be accessed and analyzed to reconstruct past environmental conditions and events. Here, we propose the Bayesian inversion method, which can reconstruct the evolution of target parameters from purely spatial data by extending data assimilation (DA), a method for integrating numerical simulations with time-series observations. Our method converts discrete spatial observation data to time-series data with the help of a law representing the NRM's time-evolution dynamics and Gaussian process regression, enabling us to directly compare the observations with a numerical simulation based on the DA framework. The method's effectiveness is demonstrated using a synthetic inversion problem, namely reconstructing the pressure-temperature-time (P-T-t) path of a metamorphic rock from chemical composition profiles of its zoned minerals. The proposed method is broadly applicable to a wide variety of NRMs.

DOI： 10.1103/PhysRevE.98.043311

Publishing type：Research paper (scientific journal)  

<p>We review research on the architecture of onshore fault zones. Drilling the Nojima Fault was a turning point in studies of shallow brittle faults, stimulating research on their hydrological and frictional properties. Investigations of the deep seismogenic zone of faults such as the Median Tectonic Line (MTL) have identified deformation mechanisms such as pressure solution, creep, and crystal plasticity of mica in foliated cataclasite. Cataclastic damage causes increased intracrystalline strain in surrounding rocks. Several studies of the Asuke shear zone and the MTL have estimated the stress and strain rate in the brittle–plastic transition zone. Some studies of the Hatagawa fault zone have revealed the processes involved in fracture nucleation and documented heterogeneous deformation on the scale of tens of kilometers. In the lower crust of the Hidaka metamorphic belt, evidence was found for plastic deformation of plagioclase and pyroxene by dislocation creep. It was also found that formation of fine-grained aggregates during deformation results in weakening by a change in deformation mechanism from dislocation creep to grain boundary sliding. Recently, evidence of fracturing has been found in deformed lower crustal rocks, possibly resulting from stress concentration at the down-dip termination of earthquake ruptures, although further studies are needed to confirm this inference.</p>

DOI： 10.5575/geosoc.2018.0004

CiNii Article

Publishing type：Research paper (scientific journal)  

Devolatilization reactions during prograde metamorphism are a key control on the fluid distribution within subduction zones. Garnets in Mn-rich quartz schist within the Sanbagawa metamorphic belt of Japan are characterized by skeletal structures containing abundant quartz inclusions. Each quartz inclusion was angular-shaped, and showed random crystallographic orientations, suggesting that these quartz inclusions were trapped via grain boundary cracking during garnet growth. Such skeletal garnet within the quartz schist formed related to decarbonation reactions with a positive total volume change (Delta V-t > 0), whereas the euhedral garnet within the pelitic schists formed as a result of dehydration reaction with negative Delta V-t values. Coupled hydrological-chemical-mechanical processes during metamorphic devolatilization reactions were investigated by a distinct element method (DEM) numerical simulation on a foliated rock that contained reactive minerals and non-reactive matrix minerals. Negative Delta V-t reactions cause a decrease in fluid pressure and do not produce fractures within the matrix. In contrast, a fluid pressure increase positive Delta V-t reactions results in hydrofracturing of the matrix. This fracturing preferentially occurs along grain boundaries and causes episodic fluid pulses associated with the development of the fracture network. The precipitation of garnet within grain boundary fractures could explain the formation of the skeletal garnet. Our DEM model also suggests a strong influence of reaction-induced fracturing on anisotropic fluid flow, meaning that dominant fluid flow directions could easily change in response to changes in stress configuration and the magnitude of differential stress during prograde metamorphism within a subduction zone.

DOI： 10.1007/s00410-017-1393-6

Publishing type：Research paper (scientific journal)  

To understand rheological weakening in the lower continental crust, we studied mylonites in the Paleoproterozoic Eidsfjord anorthosite, northern Norway. The zones of anorthositic mylonites range from a few millimeters to several meters thick, and include ultramylonites and protomylonites. They contain syn-kinematic metamorphic minerals, including Cl-bearing amphibole and scapolite. Thermodynamic analysis reveals that syn-deformational hydration reactions occurred at -600 degrees C and -700 MPa under CO2-bearing conditions. The protomylonites contain many fragmented plagioclase porphyroclasts. The fractures in porphyroclasts are filled with fine-grained plagioclase, suggesting that fracturing is a common mechanism of grain size reduction. The anorthite contents of fine-grained polygonal matrix plagioclase are different from those of porphyroclastic plagioclase, suggesting that the matrix grains nucleated and grew during syn-kinematic metamorphism. Plagioclase aggregates in the matrices of mylonites do not exhibit a distinct crystallographic preferred orientation, which implies that the dominant deformation mechanism was grain-size-sensitive creep. Consequently, in the lower crustal anorthositic mylonites, grain size reduction occurred via fracturing, rather than through dynamic. recrystallization, leading to grain-size-sensitive creep. The syn-kinematic recrystallization of minor phases at plagioclase grain boundaries may suppress the growth of plagioclase and contribute to the development of grain-size-sensitive creep. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2016.11.001

Publishing type：Research paper (scientific journal)  

To clarify the processes that occur in hydrous basaltic magma chambers, we have undertaken detailed petrological and geochemical analyses of mafic and intermediate rocks from the Ikoma gabbroic complex, southwest Japan. The complex consists mainly of hornblende gabbros, hornblende gabbronorites, and hornblende leucogabbros. The hornblende leucogabbros are characterized by low TiO2 and high CaO contents, whereas the hornblende gabbronorites have high TiO2 and low CaO contents. The initial Sr-87/Sr-86 ratios (Sr-I) of the hornblende gabbronorites and hornblende gabbros are higher than those of the hornblende leucogabbros and plagioclase, and they may have resulted from a higher degree of assimilation of metasediments. The geochemical features of the hornblende leucogabbros and hornblende gabbronorites can be explained by accumulation of plagioclase and ilmenite, respectively, in a hybrid magma that formed by chemical interaction between mafic magma and metasediment, whereas the hornblende gabbros were produced by a high degree of crustal assimilation and fractional crystallization of this hybrid magma. As a result of the density differences between crystals and melt, the Ikoma gabbroic rocks formed by the accumulation of plagioclase in the middle of the magma chamber and by the accumulation of ilmenite in the bottom of the chamber. Taking into account the subsequent assimilation and fractional crystallization, our observations suggest an enriched mantle (Sr-I = similar to 0.7071) as the source material for the Ikoma gabbros.

DOI： 10.1007/s00710-016-0423-9

Publishing type：Research paper (scientific journal)  

We report the results of field observations and microstructural analyses of meso-scale faults that cut Cretaceous granitoids along and near lineaments of the Ikoma active fault zone. Based on measurements of the slip direction on fault planes, a paleostress of N-S extension is determined using the multiple inverse method. This stress field differs from the present-day regional stress field of predominant E-W compression, inferred from the seismic data inversion and the multiple inverse method applied to the active faults. Illite crystals of various sizes collected from a fault gouge, give K-Ar ages of 45.2±1.0 Ma for the 0.2-0.4 µm fraction and 46.0±1.1 Ma for the 0.4-1.0 µm fraction. High- and low-temperature components of illite are quantified by decomposing X-ray diffraction patterns to extrapolate the authigenic and detrital end-members. The ratios of low-temperature illite (1M_d) to high-temperature illite (2M₁ and 1M) from a fault gouge are indistinguishable from one another. Based on the relative K-Ar ages of illite composites and of biotites from the host granitoid, the upper age limit of fault gouge formation is ca. 30 Ma. These results suggest that formation of the fault gouge occurred between ~45 and 30 Ma, indicating that the meso-scale faults in basement rocks formed by N-S extension during the late Eocene to early Oligocene, rather than active tectonics under E-W compression.

DOI： 10.5575/geosoc.2015.0039

CiNii Article

Publishing type：Research paper (scientific journal)  

We report newly obtained U-Pb SHRIMP ages of detrital zircons from metagreywackes in the Hiriyur Formation (Chitradurga Group, Dharwar Supergroup) from the central eastern part of the Chitradurga greenstone belt. U-Pb analyses yield three major Neoarchean age populations ranging from 2.70-2.54 Ga with some minor age population of Mesoarchean. The maximum age of deposition is constrained by the youngest detrital zircon population at 2546 Ma. This is the first report of the occurrence of supracrustal rocks less than 2.58 Ga in the central part of Chitradurga greenstone belt. Close evaluation of detrital ages with the published ages of surrounding igneous rocks suggest that the youngest detrital zircons might be derived from rocks of the Eastern Dharwar craton and the inferred docking of the western and eastern Dharwar cratons happened prior to the deposition of the Hiriyur Formation. The Chitradurga shear zone, dividing the Dharwar craton into western and eastern blocks, probably developed after the deposition. Furthermore, the lower intercept is interpreted as evidence for the Pan-African overprints in the study area.

DOI： 10.1007/s12594-016-0372-2

Publishing type：Research paper (scientific journal)  

Tephra beds intercalated in the Plio-Pleistocene sediments of the Osaka Group and the Takashima-oki core sediments in Lake Biwa were classified into eighteen types based on the volcanic glass morphology, mafic mineral composition and grain component. These tephra beds were further classified into five groups according to the tephra types in combination with the major element composition of the volcanic glass shards, which was measured by a Scanning Electron Microscopy + Energy Dispersive X-ray Spectrometry (SEM-EDS). We also examined these tephras with trace element compositions of the volcanic glass shards using as Y-Sr/Y, La/Y-Fe/(Fe+Mg) mol% and MgO-Ba diagrams, for which the trace elements measured by an Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Consequently, we classified the tephras into five groups; 1) Alkaline tephra group: characterized by high sodium and potassium contents which were derived from Ulreung-do Island; 2) High-K tephra group: characterized by relatively high MgO and Ba contents and are derived from the Aso caldera; 3) Medium-K tephra group: being composed of TACr (pumice type glass shard + amphibole dominant in heavy minerals+ vitric-crystal ash type) tephra type and Adakitic dacite tephra subtype; 4) Low-K tephra group: characterized by low La/Y ratio and low Ba content and were possibly derived from the Izu-Hakone regions; 5) High-silica and platy glass tephra group: characterized by high SiO_2 content with platy volcanic glass morphology. These petrological characteristics of the tephra types are useful for the first order identification of the sources.

CiNii Article

Publishing type：Research paper (scientific journal)  

The mechanism of shear zone formation in lower crustal, relatively dry rocks is still poorly understood. We have studied the high-temperature deformation of the Hasvik gabbro (northern Norway) which commences by fracturing. The 10-20 mu m wide fractures show little displacement. The fine-grained plagioclase and orthopyroxene in the fractures lack a crystallographic preferred orientation (CPO) or a systematic crystallographic orientation with respect to the host grains. Fractures grade into narrow shear zones, which are composed of fine (10-20 mu m), equant grains of recrystallized plagioclase, amphibole, and pyroxene. Recrystallized plagioclase and pyroxene have compositions different from the magmatic grains, suggesting that they have formed by nucleation and growth. Based on conventional plagioclase-amphibole thermobarometry, the shear zones have formed at temperatures and pressures of 700-750 degrees C and 0.5-0.6GPa. The observed primary minerals cut by fractures suggest high-temperature fracturing in the absence of high pore pressures, which implies a high strength of the lower crustal gabbros and high stresses at fracturing. The shear zones are characterized by the lack of CPO and a small grain size, suggesting that the mechanism of deformation of the fine-grained plagioclase and orthopyroxene has been grain boundary sliding accommodated by diffusive mass transfer. The amphibole grains have strong CPOs, which most likely result from oriented growth and/or rigid body rotations during deformation. The process that initiated the fracturing and subsequent viscous creep in the Hasvik gabbro may have resulted from a process of coseismic loading followed by creep during decaying stress in the lower crust.

DOI： 10.1002/2014JB011708

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

The chemical compositions of fly ash particles emitted in Northeast Asia were studied to better understand the long-range transportation of atmospheric pollutants. We examined the compositions of spheroidal carbonaceous particles (SCPs), a type of fly ash from several to similar to 20 mu m in diameter found in surface sediments in or near the main industrial cities of Japan, China, South Korea, and Taiwan. SCPs from different countries were found to vary; SCPs from Japan and South Korea were characterized by low Ti/Si and high S/Si ratios, whereas SCPs in China exhibited high Ti/Si and low S/Si ratios and particles from Taiwan showed high Ti/Si and S/Si ratios. We also examined the SCPs found in remote islands in the Sea of Japan, at least 100 km from any industrial city. On the basis of their chemical compositions, these SCPs were classified as Japan and Korea, China, and Taiwan types using discriminant analysis. The results indicated that 30-50% of the particles found in these islands were assigned to the China type, suggesting that most of these SCPs were probably transported from Chinese industrial regions to these islands. It implies that even large particulate pollutants of similar to 10 mu m, such as SCPs, could be transported long distances of similar to 1000 km. (C) 2014 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.atmosenv.2014.06.048

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Spheroidal carbonaceous particles (SCPs) are one of the types of fly ash particles produced by industrial fossil-fuel combustion. These SCPs are mainly composed of carbon, which enables them to be preserved in sediments for a long time; this preservation means that sedimentary SCPs have been used to study the distribution and history of environmental pollution. SCPs are used as a proxy for temporal and spatial atmospheric pollution, as a marker for sediment core dating, and as a proxy for the evaluation of transboundary pollution (i.e., the identification of the source of pollutants originating in one country but deposited in another country). The concentrations of sedimentary SCPs and their characteristics, such as morphology, size and chemical composition, provide useful information on past and present atmospheric pollution. This review provides a summary of the technique and its application, principally in Japan during the past decade.

DOI： 10.5575/geosoc.2014.0035

CiNii Article

Publishing type：Research paper (scientific journal)  

We report here on a study of three deformed granitoids: two mylonites and an ultramylonite from the inner ductile shear zone of the Ryoke metamorphic belt, SW Japan. Monophase layers composed of quartz, plagioclase or K-feldspar are present in all samples. The plagioclase-rich layers consist of grains 6-10 mu m in size, and sometimes include patchy K-feldspar and quartz, indicating solution-precipitation. In the mylonite, the fine-grained plagioclase is mainly An(23-25) and, the composition of plagioclase porphyroclast is An(21-39) without any significant maximum. The An compositions together with textural observations indicate that fine-grained plagioclase nucleated from solution with mass transfer during deformation. In the ultramylonite, fine-grained plagioclase is widely changed to be An(15-37), indicating that the grain-size-reduction process includes fracturing of original plagioclase porphyroclasts in addition to the solution-precipitation process, which results in the composition concentrated around An(30). In all samples, the crystallographic orientations of fine-grained plagioclases are almost random and do not correlate with neighbouring porphyroclasts. Grain-size-sensitive creep occurred during rock deformation subsequent to the process of solution-precipitation that involved mass transfer via fluids. (c) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2013.03.006

Publishing type：Research paper (scientific journal)  

To clarify the relationship between the transport distance of spheroidal carbonaceous particles (SCPs) and particle size, we investigated the spatial distribution of SCP sizes in swimming pool deposits in the central Osaka Plain, central Japan. Median particle size of SCPs generally decreases with distance (0 to similar to 20 km) downwind from the local coastal industrial area where SCP sources are distributed widely. This suggests that most SCPs found in the study area are derived from the industrial area. Samples with &gt;40 % of particles &gt;20 mu m were predominantly collected within 2 km of the industrial area, while samples with &gt;40 % of particles &lt;10 mu m were mostly collected over 10 km from the industrial area. Based on the results of our study and previous studies, we conclude that a higher proportion of particles of size &gt;20 mu m indicates that the origin of SCPs is within a few kilometres upwind of the sample site, whereas the presence of higher proportion of particles &lt;10 mu m indicates that their source is generally further than 10 km upwind. However, other factors may affect the size distribution of SCPs at a given location (e. g. fuel type, quality of the particle precipitator and topography of the terrain). Pool deposits provide more suitable samples than lake sediments for investigating atmospheric precipitation.

DOI： 10.1007/s11270-013-1580-7

Publishing type：Research paper (scientific journal)  

We evaluate a temperature-dependent coefficient for grain-boundary diffusion in quartz aggregates using grain size data from a contact aureole, based on the coupling of a numerical model for the temperature-time history of the contact aureole with a model for the kinetics of diffusion-controlled grain growth. The metachert samples were collected from the contact aureole of the Hanase-Bessho quartz diorite at Hanase Pass, Kyoto, Japan. The quartz grain sizes vary systematically with distance from the quartz diorite. We calculated the temperature-time history using a one-dimensional thermal model, validated by peak metamorphic temperature estimates that are based on the degree of graphitization of carbonaceous material in metapelites, as characterized by Raman microspectroscopy. To minimize the sum of the squares of the errors between the measured and calculated grain sizes, based on the normal grain growth law together with the temperature-time history, we estimated the activation energy and pre-exponential factor in the alpha-quartz field to be 208 kJ/mol and 1.1 x 10(-8) m(2)/s, respectively, assuming a grain-boundary width of 1 nm. The grain-boundary diffusion rates for temperatures in the greenschist and amphibolite facies are similar to those determined in natural or laboratory grain-coarsening experiments, but differ significantly from those determined in tracer diffusion experiments. During grain-size-sensitive deformation, "effective" grain-boundary diffusion rates may be intermediate between the rates of diffusion along and across the grain boundary, and would be higher than the grain-boundary diffusion rates estimated by grain-coarsening experiments, and lower than those by tracer diffusion experiments.

DOI： 10.2138/am.2013.4308

Publishing type：Research paper (scientific journal)  

Spheroidal carbonaceous particles (SCPs) are produced by the high-temperature combustion of fossil fuels and are emitted to the atmosphere. We examined the surface morphology and the chemical composition of SCPs in samples of surface sediment from five industrial cities each of Japan and China, using scanning electron microscopy with energy dispersive spectroscopy (EDS). There exists a relationship between surface morphology and the chemical composition of SCPs in China, but not for SCPs in Japan. The chemical compositions of SCPs differ between Japan and China: those in Japan are S-rich, whereas those in China are Ti-rich. The results suggest that EDS can be used to identify China-derived SCPs in East Asian countries such as Japan, South Korea, and Taiwan.

DOI： 10.1007/s11270-012-1232-3

Publishing type：Research paper (scientific journal)  

The electrical conductivity of fluid-bearing quartzite was determined as function of temperature and fluid fraction at 1 GPa in order to assess the origin of the high conductivity anomalies observed in the middle to lower crustal levels. Dihedral angles of quartz-fluid-quartz determined from recovered samples were below 60, suggesting that fluid forms an interconnected network through the quartz aggregate. The electrical conductivity of quartzite increases with increasing temperature, which can be approximately expressed by Arrhenius equation. The apparent activation enthalpy decreases from 0.70 to 0.25 eV with increasing fluid fraction in volume from 0.00043 to 0.32. The electrical conductivity (sigma) of the fluid-bearing quartzite increased with fluid fraction (phi) proportionally to a power law (sigma proportional to phi(0.56-0.71)) within the temperature range of 900-1000K. The electrical conductivity of the aqueous fluid-bearing quartzite with the maximum fluid fraction (0.32) was found to be about three orders of magnitude higher than that of dry quartzite at 1000 K. However, its electrical conductivity was definitely lower than the geophysically observed values of high-conductivity anomalies, even if the quartzite contained large fluid fractions (0.32). The present results suggest that fluid-bearing quartzite is unable to account for the high-conductivity anomalies in terms of fluid fraction. A significant amount of other ionic species, such as Na, Cl, and Al in aqueous fluid, in addition to silica phases dissolved in fluid, is required to increase conductivity. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.03.007

Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.tecto.2012.01.033

Publishing type：Research paper (scientific journal)  

Microstructural analyses of mylonites next to the Median Tectonic Line (MTL), SW Japan, reveal a transition in the dominant deformation mechanism of quartz from grain-size-insensitive dislocation creep to grain-size-sensitive grain-boundary sliding (GBS). The transition occurred under greenschist-facies conditions (similar to 300-400 degrees C) during grain-size reduction by dynamic recrystallization. The stereologically corrected grain size for the transition is approximately 4.3 mu m. At the boundary between the fields of dislocation creep and GBS, as calculated from creep constitutive relations, the differential stress and strain rate for this corrected grain size are estimated to be similar to 280 MPa and 1.2 x 10(-11) s(-1) for 300 degrees C, and similar to 110 MPa and 1.0 x 10(-10) s(-1) for 400 degrees C. The strain rates estimated for the mylonites next to the MTL are much higher than those estimated for the surrounding metamorphic rocks (similar to 10(-14) s(-1)), and the displacement rates calculated based on the thickness of high-strain mylonites and their strain rates are comparable with the average slip rates of the most active intraplate faults in Japan. These inferences suggest that the high-strain mylonite zones next to the MTL are the exhumed downward extension of a seismogenic fault in the ductile region. The zones were highly localized (&lt;10 m) and experienced very high strain rates (10(-11) to 10(-10) s(-1)).

DOI： 10.1029/2011JB008799

Publishing type：Research paper (scientific journal)  

Three basic minerals, biotite, chlorite and amphibole, were mineralogically and chemically examined to specify primary host phase(s) of As in the aquifer sediments and verify the formation mechanism of As contaminated groundwater of Sonareaon, Bangladesh, where the highest As contaminated groundwater appears in actively recharging zones. Among those minerals, only the chlorite included As by mu-XRF analysis. Fe-rich and tritoctahedral nature indicated this chlorite termed chatnosite. The chlorite was weathered to form eoethite on the cleavage, however, the eoethite did not host the As. Combining with the saturation of goethite in the groundwater (Itai et al., 2008), in situ chemical weathering of the chlorite promoted by accelerated aerobic water infiltration is suggested to be the first stage of formation of the As contaminated groundwater of the Holocene aquifer. This study implies the importance of aerobic aquifer condition to promote the As release via decomposition of As-bearing detrital mineral(s) as the formation mechanism of As contaminated groundwater in the Ganges-Bramaptra-Meghna river basin.

DOI： 10.2343/geochemj.2.0208

Publishing type：Research paper (scientific journal)  

Spheroidal carbonaceous particles (SCPs) are produced by the high-temperature combustion of fossil fuels and emitted in to the atmosphere. The distribution and concentration of SCPs in sediments have been used as a proxy for the distribution of pollutants emitted to the atmosphere. However, the effect on the distribution of SCPs due to industrial activity at nearby industrial cities is yet to be quantified. To clarify the origin of SCPs of similar to 20 mu m in size that are preserved in sediments, we evaluated the abundance, surface morphology, and chemical composition of SCPs in sediment core samples recovered from industrial cities in Japan (Tokyo, Osaka, and Nagasaki) and China (Beijing), with the cities being located at least similar to 500 km away from each other. Vertical profiles of SCP concentration in sediment cores from the Japanese cities and Beijing are different, reflecting the contrasting industrial histories of the two countries. The SCPs from different cities show contrasting morphological and chemical characteristics, suggesting that similar to 20 mu m SCPs in sediments from the industrial cities could represent the local combustion history in detail, as the influx of local SCPs is dominant at such sites.

DOI： 10.1007/s12665-011-0907-1

Publishing type：Research paper (scientific journal)  

 In the Ryoke belt formed at the eastern margin of East Asia during mid-Creataceous time, the most important geological record is that of felsic igneous activity, which may have been caused by the subduction of a young (hot) oceanic lithosphere. The mantle-derived arc magmas formed due to subduction of the hot lithosphere underplated the lower crust. Continuous underplating of the mantle-derived magmas resulted in partial melting of the lower crustal mafic to intermediate rocks to produce granite magmas. The granite magmas rose and were emplaced at a mid-crustal depth. They caused thermal perturbation around rocks of the Jurassic accretionary complex (Mino–Tamba belt) and formed the resultant low-pressure/high-temperature regional contact metamorphism (Ryoke metamorphism). At the time of Ryoke metamorphism, during subduction of a hot oceanic lithosphere with high obliquity, a low-angle detachment fault formed at the forearc region of the mid-Cretaceous SW Japan arc. Following this event, subduction of an inactive oceanic ridge or a very hot oceanic lithosphere with low obliquity occurred; a compressional stress regime occurred at the forearc region, forming granite mylonites and large-scale upright folds associated with crustal displacement along the detachment fault. After this event, the angle of subduction decreased gradually; the location of the felsic igneous activity moved toward the continent.

DOI： 10.5026/jgeography.120.452

CiNii Article

Publishing type：Research paper (scientific journal)  

To identify the dominant deformation mechanism in continental middle crust at an arc-trench system, we used an SEM-EBSD system to measure the lattice-preferred orientations of quartz grains in fine-grained metachert from the low-grade (chlorite and chlorite-biotite zones) part of the low-P/high-T Ryoke metamorphic belt, SW Japan. Quartz c-axis fabrics show no distinct patterns related to dislocation creep, although the strain magnitudes estimated based on deformed radiolarian fossils are high enough that a distinct fabric might be expected to have formed during deformation. Fabric intensities are very low, indicating a random distribution of quartz c-axes. Quartz grains are equant in shape and polygonal, and free of intracrystalline plasticity. These observations suggest that the dominant deformation mechanism in the metacherts was grain-size-sensitive flow (diffusion creep accompanied by grain-boundary sliding) rather than dislocation creep, possibly reflecting the relatively low strain rate or low flow stress compared with that in high-strain zones. The development of grain-size-sensitive flow in metamorphic tectonites at mid-crustal conditions would result in a significant decrease of the rocks strength of the continental middle crust. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2010.06.002

Publishing type：Research paper (scientific journal)  

Publishing type：Research paper (scientific journal)  

Spheroidal carbonaceous particles (SCPs) are produced by the high-temperature combustion of fossil fuels and are emitted to the atmosphere. Previous studies are divided regarding whether SCPs derived from the combustion of various fossil fuels can be identified based on their surface morphologies and chemical compositions. In this study, we examined the surface morphology and chemical composition of SCPs in sediment core samples collected from Osaka Bay, Japan, with the aim of evaluating the usefulness of SCPs morphology in identifying their origin. Scanning electron microscope (SEM) observations reveal three distinct surface morphologies: (1) smooth, (2) rough and irregular, and (3) convoluted and layered. According to a morphological classification scheme proposed previously, the former two morphologies correspond to coal-derived carbon particles, whereas the latter corresponds to oil-derived carbon particles. In terms of the chemical compositions of the particles with different morphologies, as analyzed by energy-dispersive spectroscopy, linear discriminant analysis reveals that the two fuel types can be distinguished. An overall success rate of &gt;90% of reference of morphologically classified material correctly assigned to two groups that are chemically different each other, indicating a relationship between surface morphology and chemical composition. This result suggests that morphological characterization based on conventional SEM observations is useful in identifying the source fuel of SCPs.

DOI： 10.1007/s12665-009-0154-x

Publishing type：Research paper (scientific journal)  

The strain geometry of a Cretaceous low-P/high-T metamorphosed accretionary complex in SW Japan is one of the key geological constraints in understanding the Cretaceous tectonics of the forearc region at the eastern margin of Eurasia. We studied the strain geometry of upper greenschist to lower amphibolite facies metamorphic rocks from the mid-Cretaceous low-P/high-T Ryoke metamorphic belt, which during the mid-Cretaceous were located at mid-crustal depths close to the volcanic front. Strain analysis focused on deformed radiolarian fossils in metachert and sandstone/chert clasts within metapelite. The maximum stretching direction (X-direction) of the strain ellipsoid of the schistosity-forming deformation at the peak metamorphism is oriented E-W, and the XY-plane of the strain ellipsoid developed parallel to schistosity. The metachert and metapelite exhibit plane strain to general flattening strain that probably largely resulted from the schistosity-forming deformation. Based on the results of the previous strain analyses and this study, it reveals that the schistosity-forming deformation occurred under bedding-normal shortening, resulting in general flattening strain throughout the Ryoke metamorphic belt. The X-direction of the strain ellipsoid of the schistosity-forming deformation is oriented parallel to the length of the Ryoke metamorphic belt throughout the SW Japan arc. The schistosity formed parallel to bedding planes that developed horizontally in non-metamorphosed accretionary complexes of SW Japan, indicating horizontal XY-plane of the strain ellipsoid. These observations indicate the occurrence of horizontal shear deformation within the middle crust (similar to 15 km depth) at the time of the low-P/high-T metamorphism. The deep-seated horizontal shear zone and the shallower incipient Median Tectonic Line (MTL) fault system could result in a crustal-scale detachment fault in the forearc region of the mid-Cretaceous SW Japan arc. After the formation of the detachment, the left-lateral pull-apart forearc basins, Onogawalzumi Group distributed on the north side of the MTL and the southern marginal mylonite zone might be formed by the sinistral movement along the detachment fault. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jseaes.2008.11.015

DOI： 10.1016/j.apgeochem.2008.12.034

Mineralogy and oxygen isotope ratios of <0.1μm authigenic clay minerals were determined for the nine volcanic ash layers in the sediment column from 580 to 1255 meters below sea floor at ODP Site 808 in the Nankai Trough. Seven of 9 samples comprise of monomineralic smectite, and 2 samples from 922.2 and 998.6 mbsf comprise of R=1 illite-smectite mixed-layered clay minerals. Assuming that oxygen isotope compositions of the clay minerals are equilibrated with those of the coexisting porewater, of which composition is the same as that of sea water, formation temperature of the clay minerals was estimated to be ca 50℃ regardless of burial depth. It means that the smectite was formed most actively when the temperature of sediments rose at ca 50℃ during burial, and no distinctive change of oxygen isotope composition occurred after its formation. Three samples from 775.6, 812.3 and 1253.8 mbsf gave the high formation temperature of ca 75℃, probably due to the simultaneous formation of clinoptilolite and/or analcime. R = 1 illite-smectite mixed-layered clay minerals may be formed at the same temperature as smectite but under different condition(s) of water/rock ratio and/or porewater chemistry.

DOI： 10.14934/chikyukagaku.43.1

CiNii Article

DOI： 10.5575/geosoc.114.s75

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CiNii Article

Publishing type：Research paper (scientific journal)  

DOI： 10.5575/geosoc.114.S75

CiNii Article

Publishing type：Research paper (scientific journal)  

To clarify the deformation history of rocks formed within an arc-trench system, we studied the strain geometry and strain path of upper greenschist to lower amphibolite facies metamorphic rocks of contrasting lithologies (i.e., metapelite and metachert) from a metamorphosed accretionary complex (the Cretaceous low-pressure/high-temperature Ryoke metamorphic belt, SW Japan). Strain analysis focused on deformed radiolarian fossils in the metachert and pebbles in the metapelite. The metachert records flattening strain, whereas the samples of metapelite record flattening (non-folded samples) and constrictional strains (folded samples). The samples that plot in the flattening field may record strain related mainly to the schistosity-forming deformation, whereas the samples that plot in the constriction field may record the total tectonic strain of both the schistosity-forming deformation and late-stage upright folding. The fold structures observed in the layered metachert are distinct from those in the metapelite; it is likely that they mainly formed during accretion. The preservation of primary fold structures in the metachert may reflect lower strain than that in the metapelites for the period during and after the main metamorphism event. The present results demonstrate that the geometries and strain paths of different lithologies differ over a small area; consequently, in using strain analysis to constrain tectonic models, strain analysis must be undertaken in conjunction with a clear distinction of the deformation phases recorded in different lithologies. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2007.09.008

Publishing type：Research paper (scientific journal)  

The Kibaran Supergroup, a &gt;= 13000-km-long belt of metasedimentary and igneous rocks in the southeastern Congo, is in a critical location between the Congo Craton (sensu stricto) and the Tanzania-Bangweulu Block. Understanding its tectonic evolution will shed much-needed light on the amalgamation history of sub-Saharan Africa. This study presents U-Pb SHRIMP age data for 150 detrital zircons from four metasedimentary formations of the Nzilo Group, the middle lithostratigraphic unit within the Kibaran Supergroup in Katanga Province. These samples yielded dates between 3214 +/- 7 and 1329 +/- 32 Ma. Prismatic Mesoproterozoic detrital zircons (dated at 1499 +/- 49 to 1329 +/- 32 Ma, with a peak at 1380 Ma) occur in all samples and are inferred to be derived from the Mitwaba orthogneisses, which intrude the Kiaora Group, the oldest lithostratigraphic unit of the Kibaran Supergroup. More than three-quarters of the zircon population is composed of recycled grains, yielding dates between and Ma, with 2434 +/- 5 1696 +/- 18 peaks at 2050 and 1850 Ma. These peaks overlap with the timing of geological events in the adjacent Paleoproterozoic Bangweulu Block, including the Ubendian-Usagaran belts. Archean zircons were not found in the oldest Nzilo units and are restricted to the youngest Nzilo rocks, where they form only a minor component (&lt;6%) of the zircons recovered. The Archean zircons are inferred to be derived from the unroofing of successively older crust in the East African lithosphere. U-Pb data support field observations and indicate that the Nzilo Group sediments postdate the similar to 1.38-Ga Kibaran syn-D-1 igneous rocks and received some detritus from them. The lithostratigraphic and geochronological data, coupled with the regional geology, indicate that a substantial portion of the Nzilo Group detritus came from interbasinal reworking of the underlying Kiaora Group and its associated 1.38-Ga orthogneisses, with a significant contribution from the Tanzania-Bangweulu Block. The data support a previously proposed subductional model for the Kibaran belt and constrain the paleotectonic environment during the deposition of the Nzilo Group.

DOI： 10.1086/509270

Publishing type：Research paper (scientific journal)  

Granitic mylonites from an upper greenschist facies mylonite zone in the Ryoke metamorphic belt, SW Japan show three types of microstructure with increasing mylonitization: (1) mylonite, (2) banded mylonite and (3) banded ultramylonite. The banded mylonites and ultramylonites include bands of quartz, biotite, K-feldspar, plagioclase &gt; K-feldspar (&gt;quartz + biotite) and K-feldspar &gt; plagioclase &gt; quartz. The inequality sign indicates abundance in modal proportion within a band. Microstructural and textural investigations by cathodoluminescence (CL), scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD) show that the microstructural changes from mylonites to banded ultramylonites have occurred through fracturing of plagioclase porphyroclasts, K-feldspar replacement by myrmekite, K-feldspar precipitation in fractures and tails and dislocation creep of quartz and K-feldspar. Development of the banded structure was promoted by high mobility via solution transfer of K-feldspar. Clear spatial distribution of constituent minerals in polyphase feldspar-rich bands, instead of homogeneous mixing of them, indicates that the grain boundary sliding was not the dominant deformation process. (c) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jsg.2007.02.008

Hatsuse plutonic complex in the Ryoke metamorphic belt, central Kinki Province, SW Japan, is composed mainly of the Cretaceous gneissose biotite granodiorite and hornblende gabbros. The biotite granodiorite is a syn-kinematic pluton during the deformation forming upright folds and the hornblende gabbros are syn-plutonic dykes intruded subparallel to the gneissosity of the surrounding granodiorite. The trends of the gneissose structure in the granodiorite and of the lithological boundaries between the granodiorite and gabbros exhibit basin structure possibly divided into major E-W trending synform and minor N-S trending synform. The gneissose structure in the granodiorite is defined mainly by the alignment of the long-axis of the biotite clots. Based on the microstructural analyses, the gneissose structure was formed by the magmatic to submagmatic flow during the emplacement of the granodiorite magma. Based on the amphibole chemistry, emplacement depth of the granodiorite magma was estimated to be 450-600 MPa that corresponds to crustal depth of about 20 km. In the granodiorite, since high-temperature plastic deformation conditions determined by the c-axis fabric of quartz grains (<i>X</i>-maximum and type-II crossed girdle patterns) are observed in the quartz grains and the maximum elongation directions between the magmatic/submagmatic flow and the high-temperature plastic deformation structures are consistent with each other, the deformation related to the emplacement of the granodiorite magma lasted just after the solidification of the magmas. The basin axis of the major E-W trending synform is parallel to the regional upright folds observed elsewhere in the Ryoke metamorphic belt ; the emplacement of the plutonic complex may be governed by the regional stress fields to form the upright folds in the Ryoke metamorphic belt.<br>

DOI： 10.5575/geosoc.113.249

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Publishing type：Research paper (scientific journal)  

The Cretaceous low-pressure/high-temperature Ryoke Metamorphic Belt contains abundant Ryoke and San-yo Granitoids that intruded to various crustal depths during or after formation of the belt. To clarify the tectono-metamorphic history of the belt, it is necessary to evaluate the thermal effects of the intrusion of the different types of granitoids. The geology of Kasado-jima Island, SW Japan, consists of metasedimentary rocks, massive biotite granite, and migmatitic biotite tonalite. The granite and tonalite occur in the central and southern areas of the island, respectively. Within the central area, granite intrudes metasedimentary rocks and cuts across bedding-parallel schistosity within the metapelites; this indicates that intrusion of the granite postdates Ryoke metamorphism. In contrast, tonalite in the southern area was emplaced parallel to the schistosity. On the basis of the field occurrences and petrographic characteristics of these granitoids, we correlate the biotite tonalite and biotite granite with the Older Ryoke and San-yo Granitoids, respectively. Based on the paragenesis of schistosity-forming minerals within metapelites, we identify two mineral zones in the island: the biotite and cordierite zones. The biotite zone is characterized by a mineral assemblage of muscovite + biotite ± garnet, and the cordierite zone is characterized by the assemblage muscovite + biotite + K-feldspar + cordierite or garnet. On the basis of mineral chemistry, we estimate peak metamorphic conditions for the biotite and cordierite zones to be ∼ 470 °C (reference pressure: 200 MPa) and ∼ 550 °C at 250 MPa, respectively. In the central part of the island, a contact aureole adjacent to the biotite granite is identified by the occurrence of randomly oriented muscovite and very large dendritic cordierite porphyroblasts. These randomly oriented porphyroblasts may have formed under a high degree of supersaturation associated with the thermal perturbation of the shallow intrusion of the biotite granite into cooler crust. In the southern area, most metamorphic minerals are of similar size, and their long axes are aligned to form a schistosity; this indicates a small degree of thermal perturbation and/or a high strain rate. These observations indicate that the biotite tonalite on Kasado-jima Island, as a deep-seated granitoid, was related to regional low-pressure/high-temperature metamorphism.

DOI： 10.2465/jmps.101.240

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Publishing type：Research paper (scientific journal)  

Nahcolite (NaHCO₃) has been found in fluid inclusions in quartz veins hosted by the Ryoke metamorphic rocks in Kasado-Jima (Island), Yamaguchi Prefecture, Japan. The inclusions are classified into three types: type 1 containing vapor +/− liquid of the H₂O-NaCl-CO₂-CH₄ system, type 2 of H₂O-NaCl fluids and type 3 with nahcolite solid. Salinities of the nahcolite-bearing fluids are lower than 4 wt% NaCl eq. Extremely large volume fractions of nahcolite solids, occupying more than 50% of total inclusion volume, and various fluid compositions are indicative of their origin as accidentally trapped ones while the fluids were immiscible below the nahcolite melting temperature (270 °C). A thermodynamic calculation of the nahcolite stability and a phase analysis of the fluids show log<i>a</i>_Na⁺ = 7.4 − pH as the minimum activity at P = 100 MPa and T = 270 °C where the neutral pH = 5.6. Hence, it can be concluded that the original (prior to immiscible state) liquids might have contained high Na⁺ and low Cl⁻ yielded by an interaction of a low-salinity fluid and Na-bearing minerals such as plagioclase in the host metamorphic rocks below the fractures now occupied by quartz if nahcolite precipitated from boiling fluids.

DOI： 10.2465/jmps.101.254

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Publishing type：Research paper (scientific journal)  

Five representative key regions from the NE-SW-trending Mesoproterozoic Kibaride belt of SE Congo are described. Although the present database is still insufficient for a definitive reconstruction of the tectonic setting, available data suggest that the investigated areas experienced a similar geological history. The Kibaran Supergroup comprises four major lithostratigraphic units in SE Congo. The Kiaora Group is the oldest unit. It starts with a basal conglomerate which is overlain by siliciclastic rocks deposited in fluviatile and possibly lacustrine environments. The conglomerate is overlain by abundant metapelites (predominantly black schist) with calc-silicate, volcano-sedimentary rocks and minor metachert deposited in shallow marine environments. These units are cut by 1.38 Ga granitoids. The overlying Nzilo Group is composed of coarse-grained, siliciclastic metasedimentary rocks including metaconglomerates, quartzites and minor metapelites and metamorphosed ironstones. Frequent herringbone and wavy ripples suggest tidal flat deposition. The maximum depositional age of this group is given by the 1.38 Ga granitoids on which it rests disconformably and by detrital zircons from a quartzite which yields a concordant age of 1360 +/- 27 Ma. The above two groups are separated by a disconformity along with the matrix-supported Kataba Conglomerate occurs at the base of the Nzilo Group. Higher in the succession, the Hakansson Group is essentially pelitic with minor quartzites. At the top of the succession, the Lubudi Group is made of (stromatolitic) carbonates, black schists and minor black quartzites and is inferred to record shallow marine deposition. All these metasedimentary rocks were deposited before the emplacement of ca. 1.0-0.95 Ga tin granites and are older than 1.08 Ga, which is the age of the climax of Kibaran deformation in the Mitwaba area.
Two major deformational events have been recognized in the study areas. The earliest (D(1)) is characterized by ENE-trending asymmetric folds and thrusts showing N to NNW transport directions. These structures occur in the Kiaora Group and predate the deposition of the Nzilo, Hakansson and Lubudi Groups. The second deformation (D(2)) marks the climax of the Kibaran orogeny and affects all sedimentary units. It is defined by NW-verging mesoscopic and macroscopic isoclinal folds (F(2)) and reverse faults parallel to D(2) planar fabrics. M(2) metamorphism is characterized by medium-pressure/medium-temperature (MP/MT) mineral parageneses, with preliminary data indicating peak P-T conditions between 740-780 degrees C and 6-6.5 Kb. U-Pb dating of metamorphic zircon in older orthogneisses in the Mitwaba region tentatively constrains the timing of M(2) metamorphism at 1079 +/- 14 Ma.
The Kiaora Group was intruded by widespread arc-related gabbro-diorite and ca. 1.38 Ga syn-D(1) calcalkaline and strongly peraluminous granitic plutons similar to those documented in the Lachlan and Hercynian belts. Late to post-kinematic granites and related pegmatites and greisens hosting tin-group ore deposits were emplaced at similar to 1.0-0.95 Ga and exhibit geochemical similarities with SE Asian collisional granites. The Kibaran orogenic system was active between similar to 1.4-1.38 (accretionary stage) and similar to 1.0-0.95 Ga (continental collision and post-orogenic exhumation), but the Kiaora Group sedimentary rocks were deposited prior to 1.4-1.38 Ga, which is the igneous crystallization age for the syn-D(1) Kibaran orthogneisses intruding them. Sedimentological data broadly indicate that the Kiaora Group was deposited in shallow marine environments, during the rift-drift stage of the evolving Kibaran basin while the post-D(1) Nzilo Group was deposited in an intra-arc environment, although more modern data are required before a definite conclusion can be reached. Available structural, sedimentological, geochronological and petrological data support a convergent margin setting for the Kibaride belt and are inconsistent with an intracontinental, rift model. (c) 2006 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jafrearsci.2006.01.017

Publishing type：Research paper (scientific journal)  

Mesoproterozoic supracrustal rocks in the Kibaride belt (southeast Congo) were intruded by mafic-intermediate plutonic rocks. These igneous rocks were affected by greenschist- to amphibolite-facies metamorphism during the Mesoproterozoic Kibaran orogenesis. U-Pb single zircon dating of the Mitwaba mafic-intermediate plutonic rocks yields an emplacement age of 1.38 Ga. The compositions of the Mitwaba mafic-intermediate plutonic rocks range from gabbro to diorite and show the following elemental concentrations: SiO2: 49-58 wt %, TiO2: 0.53-0.92 wt %, Al2O3: 13.1-18.68 wt %, Zr: 45-142 ppm, Y: 13-43 ppm. Mg no. 40-66 indicates variable degrees of fractionation of the magmas. The rocks are marked by high and variable Th/Ta (3-14), La/Nb (2-5) and low Ce/Pb (0.3-12.8) and Ti/V (10-19). Chondrite-normalized REE patterns exhibit enrichment in LREE relative to HREE ((La/Yb)(N) = 2.9-5.8). Primordial mantle-normalized spider diagrams show negative slopes with gradual decrease from LIL to HFS elements and are marked by Nb and Ti negative anomalies. Immobile trace-element contents indicate a continental arc setting for these mafic-intermediate igneous rocks. They are inferred to have originated from a mantle wedge enriched by fluid from a subducting slab, with possibly an additional contribution from subducted sediments. Low, sub-chondritic Nb/Ta ratios in these mafic rocks support this interpretation. A model involving underplating of mafic-intermediate arc magma into the crust, triggering partial melting of Mitwaba group metasedimentary rocks during the accretionary stage of the Kibaran orogeny, is proposed to explain the coeval emplacement of mafic-intermediate arc magmas and peraluminous S-type granitoids in the Kibaride belt of central Africa.

DOI： 10.1017/S0016756804009951

Publishing type：Research paper (scientific journal)  

In the Ryoke metamorphic belt in the Asuka area, Kinki Province, SW Japan, many mafic rocks are found as sheet-shaped xenoliths in the Older Ryoke granitoids. They show a strong to weak foliation defined by preferential alignment of long axis of plagioclase and amphibole grains. The grains of plagioclase and amphibole exhibit hypidiomorphic to xenomorphic shapes, and show no chemical zonings. Almost all plagioclases and amphiboles have unique chemical compositions of An_40-45 and magnesiohornblende-ferrotschermakite, respectively. Using a conventional thermometer, equilibrium temperatures of plagioclase and amphibole rims are estimated to be 500-600°C that is too low to obliterate the pre-existing zoning profiles due to low diffusivity in plagioclase and amphibole under such mid-crustal conditions. These observations suggest that the mafic rocks were amphibolite-facies metamorphic rocks. In some outcrops, there are obliquities between the trend of foliation of the mafic rocks and that of their contact planes to the Older granitoids. In many cases, the trend of foliation of the mafic rocks is oblique to that of the Older granitoids. The foliation of the Older granitoids is defined by preferential alignment of long axis of euhedral plagioclases and biotites, and may result from the magmatic-submagmatic deformation during their ascending and emplacement. Because there is a discordant relationship between foliation of the mafic rocks and that of the Older granitoids, the formation of foliation of the mafic rocks may predate the magmatic-submagmatic deformation of the Older granitoids. Consequently, the amphibolite-facies metamorphism of the mafic rocks occurred before their involving to the Older granitoids ascending/emplacing to the upper crust.<br>

DOI： 10.5575/geosoc.111.141

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Publishing type：Research paper (bulletin of university, research institution)   Kind of work：Single Work  

Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

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Publishing type：Research paper (scientific journal)   Kind of work：Single Work  

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Publishing type：Research paper (bulletin of university, research institution)  

Publishing type：Research paper (bulletin of university, research institution)   Kind of work：Single Work  

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Book type：Scholarly book

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Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

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Presentation type：Oral presentation (general)  

Venue：千葉  

Presentation type：Oral presentation (general)  

Venue：千葉  

Presentation type：Oral presentation (general)  

Venue：日本  

Presentation type：Oral presentation (general)  

Venue：Japan  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Venue：東京  

DOI： 10.14863/geosocabst.2022.0_50

<p>During plastic deformation of quartz under the upper crustal conditions, <<i>a</i>> slip systems are predominantly active, which has been considered to be temperature-dependent (Law 2014). However, based on a detailed textural analysis of CPOs of experimentally and naturally deformed quartz samples, Kilian and Heilbronner (2017) argued that the basal <<i>a</i>> slip system is not the dominant slip system under the upper crustal conditions. To clarify the relative importance of slip systems in quartz, based on optical and EBSD observations, we analyze quartz phenocrysts in deformed granite porphyry samples of different strains reported by Kano and Takagi (2013). The quartz phenocrysts exhibit undulate extinction, commonly elongate and lenticular with different aspect ratios (ARs) (i.e., strain) ranging from 1.2 to 6.3 to identify the dominant active slip system based on misorientation analyses via EBSD data (Lloyd et al. 1997). The misorientation axis of almost all concentrated subparallel to the <i>Y</i>-axis (i.e., rotation axis) of the sample coordinates. Only the phenocryst with AR=1.8 has concentrated in the periphery near the <i>Z</i>-axis of the sample coordinates and also parallel to the [<i>c</i>] axis; the high density distributed around the [<i>c</i>] axis in the crystal coordinates may be twist boundary. Phenocrysts with ARs of 6.3 and 3.7, the misorientation density shows a maximum around the [<i>c</i>] axis, indicative of the activity of prism <<i>a</i>>. Phenocryst with AR of 3.1, the highest density concentration is close to the {<i>m</i>} and perpendicular to the [<i>c</i>] axis, indicative of the activity of basal <<i>a</i>> (+ prism [<i>c</i>]). The phenocryst with AR of 1.6 has distributed two concentrations around the [<i>c</i>] and <<i>a</i>> axes, indicative of twist boundary (basal +basal ) and the activity of prism [c]. Consequently, the dominant slip systems in the quartz phenocrysts are prism <<i>a</i>> and basal <<i>a</i>> (+ prism [<i>c</i>]). The values of the AR of quartz phenocrysts indicative of the activity of prism <<i>a</i>> slip system are higher than those with basal <<i>a</i>> slip system, implying that the CRSS for the former is lower than that for the latter. References: Kano and Takagi (2013) J Geol Soc Japan 119:776. Lloyd et al. (1997) Tectonicphysics 279:55. Kilian and Heilbronner (2017) Solid Earth 8:1095. Law (2014) J Struct Geol 66:129.</p>

DOI： 10.14863/geosocabst.2022.0_310

<p>Introduction:Cathodoluminescence (CL) is sensitive to defects and/or impurities in crystals. CL images have been used to observe microstructures within grains to understand mineral growth and diagenetic processes (Götze 2009). It has also been used in structural geology to observe patterns of healed fractures, subgrain boundaries (SGBs), and twins (Shimamoto et al 1991; Hamers et al 2017). We observed deformed quartz phenocrysts with different degrees in mylonitized granite porphyries reported by Kano and Takagi (2013). In CL images of the deformed quartz phenocrysts, some planar deformation features (PDFs) can be observed. In this study, we analyzed the CL images and EBSD maps of the weakly deformed quartz phenocryst to clarify the formation processes of PDFs observed in CL images. In addition, we will evaluate impurity distribution within quartz phenocrysts by EPMA compositional maps and FT-IR H₂O concentration maps.</p><p>Results and Discussion:Quartz phenocrysts exhibit an undulose extinction indicative of internal plasticity under the optical microscope. Kernel Average Misorientation (KAM) maps and orientation difference profile normal to the extension direction of an undulose extinction show misorientation angles between two adjacent pixels are less than 2°. SGBs with a misorientation angle of no less than 0.4° can be assigned to almost all the PDFs. In pole figures, the crystallographic axes and planes of quartz are rotated around the <i>c</i>-axis, and the misorientation axes distribute parallel to the <i>c</i>-axis, indicating a dominant prism <<i>a</i>> slip system. Our observations suggest that SGBs under the optical and EBSD observations can be comparable with the PDFs in CL images, implying that the PDFs in CL images can be derived from the accumulation of defects to SGBs. Furthermore, we estimated the stress applied to quartz phenocryst based on the subgrain size piezometer of Goddard et al (2020). Given the misorientation angle of 1°, the subgrain size is 29 µm, and the estimated stress is 14 MPa.</p><p>References<b>: </b>Goddard et al (2020) Geophys Res Lett 47:e2020GL090056; Götze (2009) Mineral Mag 73:645–671; Hamers et al (2017) Phys Chem Mineral 44:263–275; Kano and Takagi (2013) Geol Soc Japan 119:776–793; Shimamoto et al (1991) J Struct Geol 13:967–973.</p>

DOI： 10.14863/geosocabst.2022.0_309

DOI： 10.14863/geosocabst.2021.0_276

DOI： 10.14863/geosocabst.2019.0_548

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DOI： 10.14863/geosocabst.2019.0_496

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DOI： 10.14863/geosocabst.2019.0_531

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[Program canceled for a disaster] Program canceled for the 2018 Hokkaido Eastern Iburi earthquake. However, This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2018.0_221

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[Program canceled for a disaster] Program canceled for the 2018 Hokkaido Eastern Iburi earthquake. However, This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2018.0_228

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<b> [Program canceled for typhoon]</b>
Program canceled for typhoon. However, This abstract is quotable and viewable on PDF.

DOI： 10.14863/geosocabst.2017.0_339

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DOI： 10.14863/geosocabst.2017.0_471

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DOI： 10.14863/geosocabst.2016.0_147

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DOI： 10.14863/geosocabst.2016.0_145

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DOI： 10.14863/geosocabst.2015.0_395

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DOI： 10.14863/geosocabst.2014.0_568

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DOI： 10.14863/geosocabst.2014.0_547

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DOI： 10.14863/geosocabst.2013.0_421

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DOI： 10.14863/geosocabst.2013.0_536

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We have re-assessed the geologic relationship and metamorphism of the gneiss-schist belts in Archaean Dharwa Craton, southern India.

DOI： 10.14824/jakoka.2013.0_205

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DOI： 10.14863/geosocabst.2012.0_421

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DOI： 10.14863/geosocabst.2012.0_253

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DOI： 10.14863/geosocabst.2012.0_533

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DOI： 10.14863/geosocabst.2012.0_22

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DOI： 10.14863/geosocabst.2011.0.202.0

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DOI： 10.14863/geosocabst.2011.0.403.0

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DOI： 10.14863/geosocabst.2011.0.163.0

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DOI： 10.14863/geosocabst.2010.0.488.0

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DOI： 10.14863/geosocabst.2010.0.517.0

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DOI： 10.14863/geosocabst.2010.0.446.0

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In order to document the source of arsenic of the arsenic contaminated groundwater in the Ganges-Bramaptra Plains, detrital biotite and chlorite were analyzed by microbeam XRF in SPring-8. Although the biotite rarely included detectable arsenic, the chlorite included arsenic ubiquitously in the crystal. The arsenic concentration of chlorite could be quantified, a few tens to hundreds ppm was estimated from the X-ray intensities in comparison with arsenic bearing minerals such as realgar and arsenocpyrite. The chlorite included submicron-order size goethite, assured by X-ray diffraction using Gandorfi camera and TEM observation. However, the goethite was not a product of chemical weathering in situ, judged from the well crystallized nature. Unlike the widely accepted hypothesis, in which the adsorbed arsenic onto Fe-hydroxides via chemical weathering of arsenic bearing sulfide minerals in Himalayas was released into groundwater in association with microbial reduction-dissolution of the Fe-hydroxides, the arsenic was released from the chlorite in the aquifer.

DOI： 10.14862/geochemproc.56.0.98.0

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DOI： 10.14863/geosocabst.2008.0.434.0

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DOI： 10.14863/geosocabst.2008.0.151.0

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DOI： 10.14863/geosocabst.2008.0.512.0

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DOI： 10.14863/geosocabst.2007.0.581.0

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DOI： 10.14863/geosocabst.2007.0.246.0

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DOI： 10.14863/geosocabst.2006.0_208_2

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DOI： 10.14863/geosocabst.2005.0_121_2

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DOI： 10.14863/geosocabst.2005.0_156_1

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Type：Peer review 

Type：Peer review 

Type：Peer review 

Type：Peer review 

Type：Peer review 

Type：Peer review 

Type：Peer review 

Type：Peer review