Petrochemistry of Volcanic Rocks in the Hishikari Mining Area of Southern Japan, with Implications for the Relative Contribution of Lower Crust and Mantle-derived Basalt     

Takahiro Hosono  Takanori Nakano 《Resource Geology》2003,53(4):239-259

Abstract. This study presents the petrographical, mineralogical, and geochemical characteristics of Late Pliocene‐Pleistocene volcanic rocks distributed in the Hishikari gold mining area of southern Kyushu, Japan, and discusses their origin and evolution. The Hishikari volcanic rocks (HVR), on the basis of age and chemical compositions, are divided into the Kurosonsan (2.4–1.0 Ma) and Shishimano (1.7–0.5 Ma) Groups, which occur in the northern and southern part of the area, respectively. Each group is composed of three andesites and one rhyodacite. HVR are characterized by high concentrations of incompatible elements compared with other volcanic rocks in southern Kyushu, and have low Sr/Nd and high Th/U, Th/Pb, and U/Pb ratios compared with typical subduction‐related arc volcanic rocks. Modal and whole‐rock compositions of the HVR change systematically with the age of the rocks. Mafic mineral and augite/hypersthene ratios of the andesites decrease with decreasing age in the Kurosonsan Group, whereas in the Shishimano Group, these ratios are higher in the youngest andesite. Similarly, major and trace element compositions of the younger andesites in the former group are enriched in felsic components, whereas in the latter group the youngest andesite is more mafic than older andesites. Moreover, the crystallization temperature of phenocryst minerals decreases with younger age in the former group, whereas the opposite trend is seen in the latter group. Another significant feature is that rhyodacite in the Shishimano Group is enriched in felsic minerals and incompatible elements, and exhibits higher crystallization temperatures of phenocryst minerals than the rhyodacite of the Kurosonsan Group. Geochemical attributes of the HVR and other volcanic rocks in southern Kyushu indicate that a lower subcontinental crust, characterized by so‐called EMI‐type Sr‐Nd and DUPAL anomaly‐like Pb isotopic compositions, is distributed beneath the upper to middle crust of the Shimanto Supergroup. The HVR would be more enriched in felsic materials derived from the lower crust by high‐alumina basaltic magma from the mantle than volcanic rocks in other areas of southern Kyushu. The Kurosonsan Group advanced the degree of the lower crust contribution with decreasing age from 51 %, through 61 and 66 % to 77 %. In the Shishimano Group, the younger rhyodacite and andesite are derived from hotter magmas with smaller amounts of lower crust component (58 and 57 %) than the older two andesites (65 % and 68 %). We suggest that the Shishimano rhyodacite, which is considered to be responsible for gold mineralization, was formed by large degree of fractional crystallization of hot basaltic andesite magma with less lower crustal component.  相似文献   

Petrological study of Nasu-Chausudake Volcano (ca. 16 ka to Present), northeastern Japan     

Masao Ban  Takahiro Yamamoto 《Bulletin of Volcanology》2002,64(2):100-116

Chausudake Volcano is representative of the active volcanoes in northeastern Japan, and has a record of many historical eruptions. Because its 16-ky eruptive history is well documented, Chausudake is well-suited for examining the temporal change of magma chamber processes and for assessing potential hazards. The activity of the Chausudake Volcano can be divided into six magmatic units (CH1-CH6). Most of its products have similar characteristics, but those from unit CH1 show wider variation. Most rocks are andesite and have plagioclase, clinopyroxene, orthopyroxene, and Fe-Ti oxides as phenocrysts, with or without olivine or quartz. Mafic inclusions, which are observed in most products, are basaltic andesites that have various combinations of the same phenocryst species. Petrographic features observed in host rocks and mafic inclusions, such as disequilibrium phenocrysts and resorbed textures, suggest magma mixing/co-mingling. Whole rock compositions of both host rocks and mafic inclusions show linear trends in variation diagrams, which suggest that the rocks are derived from the mixing/co-mingling between mafic and felsic end members. Bulk silica content of the mafic end-member magma is estimated to be ca. 52%, and contains Mg-rich olivine and An-rich plagioclase. The temperature of this end member is estimated to have been higher than 1,100 °C. Bulk silica content of the felsic end-member magma is estimated to be ~66%, and contains Mg-poor pyroxenes, An-poor plagioclase, and quartz phenocrysts, with a temperature of between 800 and 900 °C. Trace element compositions show that the end members have different origins, but have changed little over the entire 16-ky of activity. The mafic end-member magmas might come from a lower-crustal homogeneous, large magma chamber, whereas the felsic end-member magmas may be partial melts of crustal materials produced by the heat of the mafic end member. Felsic end-member magma may have accumulated in the middle crust before CH1 activity. The mixing ratio of the felsic to mafic end members was 0.5:0.5 to 0.4:0.6 for the CH1 unit, and ca. 0.4:0.6 for the other units. Considering that ca. 75% of the total volume of the eruptive products form the first unit, its wider compositional variation is attributed to more heterogeneous mixing ratios.  相似文献   

Sedimentary Steryl Chlorin Esters (SCEs) and Other Photosynthetic Pigments as Indicators of Paleolimnological Change Over the Last 28,000 Years from the Buguldeika Saddle of Lake Baikal     

Yuko Soma  Yukinori Tani  Mitsuyuki Soma  Hideo Mitake  Ryo Kurihara  Shinya Hashomoto  Takahiro Watanabe  Toshio Nakamura 《Journal of Paleolimnology》2007,37(2):163-175

Detailed depth profiles of photosynthetic pigments in a sediment core (G-12) collected at the BDP93 site, the Buguldeika saddle, of south Lake Baikal, along with depth profiles of total organic carbon (TOC) and biogenic silica, were studied to elucidate the temporal changes of phytoplankton assemblages in the lake during the past 28 kyr. In addition to the quantification of carotenoids by high-performance liquid chromatography with photodiode-array detection (HPLC-PDA), steryl chlorin esters (SCEs) were analyzed by HPLC-PDA, HPLC-mass spectrometry (LC-MS) and sterols in SCEs by gas chromatography–mass spectrometry (GC–MS) to enrich the taxonomical information on the phytoplankton composition. Allochthonous input of organic matter from the Selenga River resulted in the higher TOC contents in core G-12 than in a previously reported core (G-6) collected at another site from the southern basin. The poorer correlation in core G-12 than in G-6 between TOC and chlorophyll-a-originating pigments, which are indicative of autochthonous production, also indicated a significant allochthonous input at the site. The abundance of lutein among the carotenoids detected, and the good correlation of total chlorophyll a and b shows that green algae represented a significant portion of the phytoplankton, accompanying the diatoms at the G-12 site, after the last glacial period. The presence of cryptomonads and cyanobacteria were confirmed from marker carotenoids in the sediment core. GC–MS analysis of sterols in SCEs detected marker sterols of diatoms, green algae, chrysophytes and dinoflagellates. The depth profiles of the measured indicators gave consistent features for temporal changes in phytoplankton assemblage at the G-12 site of Lake Baikal after the last glacial maximum. Notably, the profile of a chrysophyte-specific sterol in SCEs was consistent with the reported distribution of chrysophyte cysts during the Holocene. The presence of phytoplankton, such as green algae, diatoms and chrysophytes, in Lake Baikal during the late last glacial period was indicated by the analysis of sterols in SCEs. Sedimentary carotenoids and sterols in SCEs were found to give complementary information about phytoplankton composition. These molecular indicators allow us to reconstruct past lake phytoplankton assemblages responding to environmental changes with a time resolution as high as age–depth relationship in sediments attainable at present.  相似文献   

A Global Model of MHD Wave Support of a Stratified Molecular Cloud     

Takahiro Kudoh  Shantanu Basu 《Astrophysics and Space Science》2004,292(1-4):161-166

We perform numerical simulations of nonlinear MHD waves in a gravitationally stratified molecular cloud that is bounded by a hot and tenuous external medium, within a 1.5-dimensional approximation. Under the influence of a driving source of Alfvénic disturbances, the cloud is lifted up by the pressure of MHD waves and reaches a steady state characterized by oscillations about a new time-averaged equilibrium state. The nonlinear effect results in the generation of longitudinal motions and many shock waves. Models of an ensemble of clouds show that, for various strengths of the input energy, the velocity dispersion in the cloud σ ∝ Z ^0.5, where Z is a characteristic size of the cloud. Furthermore, σ is always comparable to the mean Alfvén velocity of the cloud, consistent with observational results.  相似文献   

Extinction map of the Galactic centre: OGLE-II Galactic bulge fields     

Takahiro Sumi 《Monthly notices of the Royal Astronomical Society》2004,349(1):193-204

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Estimates of the turbulent kinetic energy budget in the oceanic convective boundary layer     

Takahiro Endoh  Takeshi Matsuno  Yutaka Yoshikawa  Eisuke Tsutsumi 《Journal of Oceanography》2014,70(1):81-90

The terms of the steady-state turbulent kinetic energy (TKE) budget in the oceanic convective boundary layer (CBL) are estimated by use of microstructure data obtained over the continental shelf of the East China Sea. The dissipation term is calculated from the micro-scale vertical shear of horizontal velocity measured directly using a freely-falling microstructure profiler, whereas the buoyancy flux and shear production terms are estimated indirectly by integrating vertically the one-dimensional conservation equation of density and by applying similarity theory, respectively. The transport term, calculated as the residual of the other three terms, vertically redistributes the TKE from the upper half of the CBL to the lower half, consistent with the TKE budgets in the atmospheric CBL and in shear-free and slightly-sheared CBLs simulated by large eddy-simulation models. The relatively large contribution of the transport term to the TKE budget shows that a local equilibrium form of the TKE equation is not appropriate for the TKE budget in the oceanic CBL.  相似文献   

Seasonal barotropic sea surface height fluctuation in relation to regional ocean mass variation     

Tsurane Kuragano  Yosuke Fujii  Takahiro Toyoda  Norihisa Usui  Koji Ogawa  Masafumi Kamachi 《Journal of Oceanography》2014,70(1):45-62

A consistency between seasonal fluctuation of actual sea surface height (SSH) and those caused by mass and density variations in gyre-scale regions is examined. The SSH obtained from satellite altimetry (altimetric SSH) is adopted as the actual SSH. SSH caused by mass variation (mass-related SSH) is simulated using a barotropic global ocean model forced by water flux, wind stress and surface pressure. SSH caused by density variation (steric SSH) is calculated from water density profile, i.e. temperature and salinity profiles. The model SSH well represents mass-related SSH for gyre-scale regional means, and seasonal fluctuation of the altimetric SSH corrected for the model SSH is similar to that of steric SSH above a pressure level larger than 300 dbar. The results indicate that the mass-related SSH does not much respond to the baroclinic adjustment to the seasonally varying wind stress curl. The mass-related SSH forced by wind stress and surface pressure should be accounted for regional evaluation, though it is not necessary for global mean evaluation. Detection of steric SSH from altimetric SSH would be useful for assimilation approaches in which the altimetric SSH is treated as the variable reflecting subsurface temperature and salinity.  相似文献   

Estimation of nearshore groundwater discharge and its potential effects on a fringing coral reef     

Blanco AC  Watanabe A  Nadaoka K  Motooka S  Herrera EC  Yamamoto T 《Marine pollution bulletin》2011,62(4):770-785

Radon (²²²Rn) measurements were conducted in Shiraho Reef (Okinawa, Japan) to investigate nearshore submarine groundwater discharge (SGD_nearshore) dynamics. Estimated average groundwater flux was 2-3 cm/h (maximum 7-8 cm/h). End-member radon concentration and gas transfer coefficient were identified as major factors influencing flux estimation accuracy. For the 7-km long reef, SGD_nearshore was 0.39-0.58 m³/s, less than 30% of Todoroki River’s baseflow discharge. SGD_nearshore was spatially and temporally variable, reflecting the strong influence of subsurface geology, tidal pumping, groundwater recharge, and hydraulic gradient. SGD_nearshore elevated nearshore nitrate concentrations (0.8-2.2 mg/l) to half of Todoroki River’s baseflow -N (2-4 mg/L). This increased nearshore Chl-a from 0.5-2 μg/l compared to the typically low Chl-a (<0.1-0.4 μg/l) in the moat. Diatoms and cyanobacteria concentrations exhibited an increasing trend. However, the percentage contributions of diatoms and cyanobacteria significantly decreased and increased, respectively. SGD may significantly induce the proliferation of cyanobacteria in nearshore reef areas.  相似文献   

Propagating tsunami wave and subsequent resonant response signals detected by HF radar in the Kii Channel,Japan     

Hirofumi Hinata  Satoshi Fujii  Keita Furukawa  Tomoya Kataoka  Masafumi Miyata  Takashi Kobayashi  Masahiro Mizutani  Takahiro Kokai  Nobuyoshi Kanatsu 《Estuarine, Coastal and Shelf Science》2011

Signals from the tsunami waves induced by the March 11, 2011 moment magnitude (M_w) 9.0 Tohoku-Oki earthquake and from subsequent resonances were detected as radial velocity variability by a high-frequency ocean surface radar (HF radar) installed on the eastern coast of the Kii Channel, at a range of about 1000 km from the epicenter along the eastern to southern coasts of Honshu Island. A time–distance diagram of band-passed (9–200 min) radial velocity along the beam reveals that the tsunami waves propagated from the continental shelf slope to the inner channel as progressive waves for the first three waves, and then natural oscillations were excited by the waves; and that the direction of the tsunami wave propagation and the axis of the natural oscillations differed from that of the radar beam. In addition, spectral analyses of the radial velocities and sea surface heights obtained in the channel and on the continental shelf slope suggest complex natural oscillation modes excited by the tsunami waves.  相似文献   

Mineralogy of new Antarctic achondrites with affinity to Lodran and a model of their evolution in an asteroid     

Hiroshi Takeda  Hiroshi Mori  Takahiro Hiroi  Jun Saito 《Meteoritics & planetary science》1994,29(6):830-842

Abstract— We studied five new Antarctic achondrites, MacAlpine Hills (MAC) 88177, Yamato (Y)74357, Y75274, Y791491 and Elephant Moraine (EET)84302 by mineralogical techniques to gain a better understanding of the mineral assemblages of a group of meteorites with an affinity to Lodran (stony-iron meteorite) and their formation processes. This group is being called lodranites. These meteorites contain major coarse-grained orthopyroxene (Opx) and olivine as in Lodran and variable amounts of FeNi metal and troilite etc. MAC88177 has more augite and less FeNi than Lodran; Y74357 has more olivine and contains minor augite; Y791491 contains in addition plagioclase. EET84302 has an Acapulco-like chondritic mineral assembladge and is enriched in FeNi metal and plagioclase, but one part is enriched in Opx and chromite. The EET84302 and MAC88177 Opx crystals have dusty cores as in Acapulco. EET84302 and Y75274 are more Mg-rich than other members of the lodranite group, and Y74357 is intermediate. Since these meteorites all have coarse-grained textures, similar major mineral assemblages, variable amounts of augite, plagioclase, FeNi metal, chromite and olivine, we suggest that they are related and are linked to a parent body with modified chondritic compositions. The variability of the abundances of these minerals are in line with a proposed model of the surface mineral assemblages of the S asteroids. The mineral assemblages can best be explained by differing degrees of loss or movements of lower temperature partial melts and recrystallization, and reduction. A portion of EET84302 rich in metal and plagioclase may represent a type of component removed from the lodranite group meteorites. Y791058 and Caddo County, which were studied for comparison, are plagioclase-rich silicate inclusions in IAB iron meteorites and may have been derived by a similar process but in a different body.  相似文献