Abstracts of Papers Presented at the Annual Meeting of The Japanese Association of Mineralogists, Petrologists and Economic Geologists
2003 Annual Meeting
Displaying 1-50 of 91 articles from this issue
G1
G2:
  • Tomohiro Usui, Eizo Nakamura, Herwart Helmstaedt
    Session ID: G2-01
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Junichi Masuda, Makoto Arima
    Session ID: G2-02
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Nobutaka Tsuchiya
    Session ID: G2-03
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Island arc magmatism along convergent plate margins is one of the major processes of continental crust generation. The net flux from mantle to crust at convergent plate margins is considered to be basaltic (Ellam and Hawkesworth, 1988), since a basaltic parental magma is preferred for island arc magmatism (Ringwood, 1974; Arculus, 1981; Gill, 1981). It is inconsistent with the estimation of andesitic average composition of continental crust (e.g. Taylor and McLennan, 1985). This inconsistency can be explained by the hypothesis of partial melting of subducted oceanic crust (slab melting model: Martin, 1986; Drummond and Defant, 1990), however, silicic slab melts may reacted with mantle peridotite. High Mg andesites (HMA) may be produced by reaction between ascending silicic melts and mantle peridotite (Kelemen et al., 1993; Yogodzinski et al., 1995; Uematsu et al., 1995; Shimoda et al., 1998), and give us an important information on the ascending silicic melt through mantle.
    The Eocene HMA in Kitakami carries phenocrystic olivine with remarkable high NiO contents (maximum 0.58 wt%), and are plotted beyond the olivine mantle array after Takahashi (1986). These Ni-rich olivine phenocrysts are consisitent with Fe-Mg exchange partitioning between olivine and the bulk rock. Moreover, since equilibrium crystallization trend for olivine phenocrysts obtained from MELTS calculations (Ghiorso and Sack, 1995) is consistent with the observed chemical compositions of olivine, high-Ni contents in olivine phenocrysts result from high-Ni contents in melt.
    The petrochemical features of the HMA in Kitakami can be explained by the modelling calculation of mantle AFC, indicating derivation from slab melt/mantle reaction. When a slab melt is reacted with mantle peridotite, it produces orthopyroxene-rich rocks as a reaction of olivine + SiO2 (in liquid) = Opx. Then, Ni content in melts increases as a result of olivine dissolution, because Ni is enriched in olivine relative to orthopyroxene. Therefore, particularly Ni-rich nature of olivine phenocrysts in the Kitakami HMA may be an evidence for slab melt/mantle reaction.
  • Batkhishig Bayaraa, Greg Bugnall, Noriyoshi Tsuchiya
    Session ID: G2-04
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    The Shuteen Cu-Au prospect, ca. 450km SSE of Ulaanbaatar (South Mongolia) is associated with Carboniferous subduction-related magmatic activity. We initiated a detailed geochemical study to decipher the genetic relationship between subduction-related volcano-plutonic rocks hosting the intrusion-related mineralization.
    In the Paleozoic, south Mongolia experienced island arc accretion and Andean-type magmatism. Extensive rifting and formation of the South Mongolian paleo-ocean (SMPO) characterize Ordovician to Silurian times, with migration of the South Mongolian microcontinent in the Devonian closing the SMPO. The 321 Ma Shuteen Pluton and Dusiin Ovoo Volcanic Formation comprise the 200km2 Shuteen Complex, which represents the root of a magmatic arc associated with subduction of SMPO beneath the South Mongolian microcontinent.
    Major/trace element data indicate the Shuteen Complex comprises well-differentiated, high-K series rocks, with high Al2O3 compositions and <1 ASI molar ratios, whilst Na2O contents and occurrence of accessory titanite indicate plutonic rocks to be "I-type". The Shuteen Complex has chemical characteristics typical of (calc-alkaline series) volcanic arc rocks. Most Shuteen Complex rocks have high Sr/Y and La/Yb ratios, and low Y concentrations indicative of (Archean) high-Al TTD type (high Al2O 3 trondhjmite-tonalite-dacite) magma, whilst low Sr samples are typical of island arc ADR type (andesite-dacite-rhyolite) magmas. Isotopic data indicate fractional crystallization and partial melting of altered MORB produced Shuteen Complex magma and residual eclogite facies. N-MORB normalized plots of Shuteen andesite and granitoids reveal subparallel enriched LREE, depleted HREE patterns. Initial 87Sr/86 Sr and 143 Nd/144 Nd isotope ratios for Shuteen plutonic rocks indicate a N-MORB source.
    High pressure partial melting of subducted slab, including oceanic sediment, produced residual eclogite and source magma for the Shuteen Complex, although our model also requires contamination by crustal material. During its ascent through the mantle wedge, slab-derived magma can assimilate mantle material - however, Shuteen rocks have a Cr:Ni ratio of 2:1, and average Mg-number ∼34, which indicate magma genesis involved negligible mantle contribution. Melting of lower crust was unlikely to produce adakitic-type rocks at Shuteen, as the crust beneath South Mongolia in the Trans-Altai suture zone
    Preliminary fractional crystallization modeling, involving hornblende and plagioclase crystallization, and 30% fractional crystallization of a magma with 10% contaminated crustal material, is consistent with geochemical characteristics in plutonic rocks exposed in the Shuteen area.
  • Akihiko Fujinawa, Mitsuharu Kamata
    Session ID: G2-05
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Eruptions of calc-alkaline magma developed the main body of the Adatara volcano in recent 250,000 years. Geology and stratigraphy are reexamined to distinguish 37 eruptives. Based on geological affinity, the eruptives are grouped into 7 volcanic units; eastern side No1 and No2 ( ES1, ES2), Minowasan (MI), summit area (SA), northern and southern rims of Numanotaira (NN, SN), and Numajiri (NU) units, respectively. Chronological data revealed that the ES1 and MI units and SA unit were developed 0.25-0.20Ma and around 0.12Ma, respectively. Bulk chemically, these are classified into 4groups: Group 1 ( stage 3-1a; ES1, ES2 ) ejecta are rich in TiO2 and FeO*, poor in MgO and K2O, and FeO*/MgO = 2.2-2.7. Also, they show low Rb, Ba and Zr, high Sc, V and Co contents. Rb/Ba, Nb/Zr and Rb/Zr are consistently around 0.12, 0.04 and 0.25-0.3, respectively. Group 2 (stage 3-1b; MI) is rich in Al2O3, poor in CaO and K2O. These show similar Rb/Ba, Nb/Zr and Rb/Zr to those of the group1, but display distinctive trends for Sr, Nb, Sc and V. Composition of the group 3 (stage 3-2; SA) is scattered, showing no distinct trend. Group 4 (stage 3-3; NN, SN, NU) shows contrastive chemical characteristics to the group 1. Also, Rb/Ba, Nb/Zr and Rb/Zr (0.14, 0.035, 0.3-0.4, respectively) are distinctive. If the compositional difference between the groups 1 and 4 reflects the transition of the plumbing system, the scattering in the group 3 may represent various products from different systems. Within a single pyroclastic fall deposit, three essential materials (pumice, scoria 1 and scoria 2) are recognized. None of the three types can be derived from other types, having been isolated prior to the eruption. Further, correlations of geochemistry and stratigraphy indicate that the low-Mg andesitic magma has been replaced by more mafic magma during the eruption. There are observations that support that the abrupt replacement from the scoria 1 to the scoria 2 reflects the major change of the plumbing system in recent 250,000 years. Compositions of the scoria 1 correspond to those of the primitive members of ES1, and those of scoria 2 come close to the low SiO2 extension of the trends for the SN. Also, these correlations accord with their relevant chemical characteristics such as Rb/Ba, Nb/Zr and Rb/Zr. Change of the magma plumbing system is assumed as follows: About 0.25 to 0.2 Ma, magma system 1 (stage 3-1a + scoria 1) and the system 2 (stage 3-1b) had been developed. During 80,000 years of dormancy, primitive magma had been preserved only in the system 1. Around 0.12 Ma, magma system 3 (stage 3-3 + scoria 2) came under the system 1. At the beginning of the eruption, felsic and two andesitic magmas co-existed, but system 1 exhausted before coming to the end of eruption. The magma system 3 has been preserved and active after the 0.12 Ma eruption.
  • Eiji Ohtani
    Session ID: G2-06
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Water plays an important role in slab dynamics near the 660 km discontinuity. We have determined the phase boundary of the post-garnet transformation by high pressure and temperature in situ X-ray diffraction experiment and the conventional quenching experiment using the Kawai anvil apparatus. We observed that the phase boundary in wet MORB is lower by about 2 GPa than that in the dry MORB, and MORB and peridotite has an equal density at 24.6 GPa and 1200 °C under the wet condition. Change of the post-garnet transformation boundary in wet conditions indicates that along the geotherm of the cold subducting slab, basalt is denser than periodotite and there is no density crossover between basalt and surrounding peridotite. The bottom of the transition zone and the uppermost lower mantle are supposed to be a zone of dehydration of the down going slabs due to decomposition of hydrous ringwoodite and/or superhydrous phase B in peridotite. Thus, hydrated basaltic crust, in which water for hydration can be readily provided from the peridotite layer below, can penetrate effectively into the lower mantle. The former oceanic crust is buoyant and can be trapped at the depth of 660 km discontinuity under relatively dry conditions. Whereas, under the wet conditions the subducting basaltic crust continuously sinks into the lower mantle without separation from the underlying peridotite along the lower temperature geotherm corresponding to the cold subduction
G3:
  • Konstantin Litasov, Eiji Ohtani
    Session ID: G3-01
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Water plays very important role in the geodynamics of the Earth's interior. It can dramatically affect physical properties, melting temperatures and melt compositions. Recently, Litasov and Ohtani (2002) reported phase relations at 10-25 GPa for the starting composition of CaO-MgO-Al2O3-SiO2-pyrolite+2wt% H2O and found significant decrease of intensive melting temperature (defined as an apparent solidus) at the pressures of 13-16GPa near olivine/wadsleyite boundary. This observation can be connected with differences in water storage capacity in wadsleyite and olivine. It is also play very important role for possibility of hydrous origin of the volcanics rocks (like komatiites) in Archean, when temperature of mantle plumes could be enough for very deep melting. Possible release of water from hydrous wadsleyite to the melt or fluid may cause intensive melting in the bottom of the upper mantle. The possibility of hydrous origin of some Archean komatiite magmas was recently demonstrated by different studies. However, 2wt% of H2O should be very high for the natural systems. Therefore, here we tested hypothesis of hydrous melting at the bottom of the upper mantle in the pyrolite with 0.5wt% of H2O. Phase relations and melt compositions have been determined at 13.5-17.0GPa and temperatures from 1600 to 2100°C. Garnet is the first liquidus phase in the pressure range of 13.5-17GPa followed by olivine at 13-16GPa and anhydrous phase B at 16-17GPa. Clinopyroxene appears only in experiment at 13.5GPa and 1600°C. Experimental products at 13.5GPa and 1600-1900°C do not contain any quench crystals. Quench crystals of the partial melt were detected at 13.5GPa and 1950°C. Similarly, at 16-17GPa quench crystals were detected only at 2100°C, whereas they are absent at lower temperatures. Therefore, the apparent solidus temperature at pressures above 16GPa is close to that of dry solidus, however it is lower than dry solidus at 13.5GPa (1900°C and 2050°C respectively). We do not detect drastic decrease of solidus temperature along phase boundary between olivine and adsleyite in the pyrolite with 0.5wt% H2O. The solidus temperature decreases gradually. Compositions of small fraction melts of pyrolite+0.5wt% H2O fall in the range of those obtained in dry pyrolite and pyrolite+2.0wt% H2O (Litasov and Ohtani, 2002). Partial melt at 13.5 GPa has high CaO (13.8wt%). The CaO content decreases significantly with increasing pressure from 13.5 to 17GPa. The SiO2 contents of partial melts at 16-17 GPa is high (50-52wt%) relative to that at 13.5GPa (48.2wt%) due to formation of anhydrous phase B.The present results for pyrolite with 0.5 wt% H2O still support a model for hydrous origin of some ancient komatiites by dehydration melting of rising wet plumes at the base of the upper mantle. Hydrous melting of mantle plume can be started at every pressure below 15-16GPa (olivine/wadsleyite transition). The water affects on composition of the partial melts indirectly, changing melting temperature and degree of partial melting.
G4:
  • Harrison Gedikile, Munetomo Nedachi
    Session ID: G4-01
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    The Hishikari low-sulfidation Epithermal gold deposit, Southern Kyushu, Japan is one of the biggest gold veins with extremely high grade. The Hishikari gold deposit comprises of Honko, Sanjin and Yamada deposits. Rock samples from several veins and the adjacent host rocks from Hishikari epithermal Au deposit were analyzed for their sulfur isotopic compositions to establish the source of the hydrothermal fluids. The sulfur isotopic ratio varies from zero to +2 permil for the Kurozonsan and Shishimano dacites, and mostly from -3 to +16 permil for the hydrothermal sulfide minerals obtained from the veins and the adjacent host rocks. The heavier values of +11 to +16 permil were obtained from the pyrites in the latest druze of the Yamada and Sanjin deposits. Most of the values are in the range of -3 to +4 permil, which are similar to those of the magmatic sulfide in the Kurozonsan and Shishimano dacites. These data suggest that the sulfur in the hydrothermal fluid is originated in magma. The heavier values are probably from sulfate. The hydrothermal reduced species of sulfur might be oxidized in the overlaid volcanic rock of magnetite series and/or by mixing with oxic meteoric water to form sulfate ions. The isotopic ratio of sulfate should be heavier. If these ions descend into the Shimanto super group, the sulfate might be reduced to HS or H2S. If the reduction would be completed, the isotopic ratio of H2S and the derived pyrite might be also heavy. The evidence that the heavier values of the sulfide formed at the later stage supports this idea.
  • Junko Hara, Noriyoshi Tsuchiya
    Session ID: G4-02
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    1.Introduction Various types of alteration zone characterizing chemically geothermal phenomena have been formed in geothermal area. Alteration type is specified by characteristic chemical composition and temperature conditions of geothermal fluid, which was generated by hydrothermal fluid-rock interactions in geothermal area. However, it has not been clear how to generate the geothermal fluid enriched for selected elements and how to form the secondary minerals. These phenomena could not be explained by equilibrium relationship of rock-hydrothermal water composition. We need to consider hydrothermal water composition in the system changed by time and space. Purpose of this research is estimation of the formation mechanism of alteration zone based on experimental approaches attracting dynamics of reaction.
    2.Methodology We conducted two types of hydrothermal experiments. One is batch type experiment to estimate apparent dissolution and precipitation rate and dissolution behavior, and the other is flow type experiment to examine the mass transport phenomena on hydrothermal water/rock interface. Hydrothermal experiments for pyroclastic rocks were conducted under saturated vapor pressures at given temperatures which are appropriate for ordinary geothermal environments in Japan.
    3.Kinetics of water/rock interaction The pyroclastic rock did not proceed stoichiometrically with respect to chemical composition of rock forming minerals and whole rock, because dissolution rates were different for each element. The chemical composition of reacted solution is characterized by thus difference of dissolution rate and the composition of secondary minerals. Particularly, alkali and alkali earth elements are well matched with its solution chemistry. Dissolution and precipitation rate model also consisted with experimental results.
    4.Mass transport coefficients Mass transport coefficients at interface between fluid and rocks in reaction term were also different for each element and an outstanding factor, for determination of the mass transport coefficient is change of temperature, flow velocity condition and the distance from water input. Specifically, &delta;Na is greater at lower temperature conditions and δCa is greater at higher temperature conditions. The relationship between major elements depends on temperature conditions, but δvalues most strongly depend on flow rate condition. Bulk solution chemistry of reacted solution generated hydrothermal water/rock interactions could be possible to interpret using diffusion-advection-reaction rate equation introducing kinetic and mass transport parameter, which was estimated quantitatively in this experiment.
    5.Summary Leaching and enrichment processes of selected elements was controlled by kinetic and mass transport processes, which is an important part in formation process of alteration zone. Dynamic approach described in this study is effective to understand coupled hydrothermal-chemical processes of geothermal alteration.
  • Masanori Kurosawa, Sadayoshi Shimano, Satoshi Ishii, Kunihiro Shima, T ...
    Session ID: G4-03
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Trace metal compositions of single fluid inclusions in quartz from pegmatites and hydrothermal veins were analyzed by micro-PIXE to elucidate the compositional change of granite-derived fluids during a pegmatite and hydrothermal stages. Quartz samples were collected from a pegmatite at Kurobera, a hydrothermal vein at Suisyo-toge, and a hydrothermal vein near Fe-Cu ore deposit at Kawahage, central Japan. Three veins are genetically related to a Miocene granite body. The quartz sample from Kurobera includes two-phase fluid inclusions, and the Suisyo-toge sample and the Kawahage sample include two-phase inclusions and polyphase inclusions including halite crystals. Salinity (NaCl eq %) of the polyphase inclusions are ~30% for the Suisyo-toge sample and 30-38% for the Kawahage sample. Determined concentrations are as follows: 200 ppm for Fe, 150-500 ppm Cu, 150-250 ppm Ge, 20-100 ppm for Br, Rb, and Pb from Kurobera; 900 ppm for Fe, 2300 ppm for Mn, 250-400 ppm Cu, 120 ppm Ge, 10-350 ppm for Br, Rb, Sr, Zn, and Pb from Suisyo-toge; 2000-90000 ppm for Ca and Fe, 300-8000 ppm for Mn and Zn, 40-3000 ppm for Cu, 100-4000 ppm for Br, Rb, Sr, and Pb, less than 100 ppm for Ge, from Kawahage. The contents of Mn, Fe, Cu, Pb, Zn, Rb, Sr, and Br increase from the pegmatite to the hydrothermal veins, whereas the Ge contents decrease. Since the salinity of the inclusions also increases in the hydrothermal vein, the base-metal enrichment could relate to a formation of hyper saline water and a metal separation by boiling of fluids after the pegmatite stage.
  • Ken-ichiro Hayashi, Tomoko Shinden
    Session ID: G4-04
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
G5:
G6:
  • Yong Ui Kim, Takuya Kimura, Tomoyuki Kannno
    Session ID: G6-01
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Seishi Kawanami, Yasuhito Osanai, Masaaki Owada, Jun Yada, Yuka Hiraha ...
    Session ID: G6-02
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Akira Ishikawa, Eizo Nakamura
    Session ID: G6-03
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    The 34 Ma alnoite from Malaita, Solomon Islands, contains a wide variety of mantle xenoliths regarded as fragments of the lithosphere beneath the Ontong Java Plateau. Most such xenoliths are spinel-bearing peridotites and classified into garnet-spinel lherzolite, spinel lherzolite and spinel harzburgite with low-equilibrated temperature (750-1100°C). This indicates that the xenoliths were composed of the shallower lithospheric mantle. Trace element compositions of clinopyroxene show good agreement for spot analyses of thin sections by SIMS, and bulk mineral analyses by ICP-MS and ID-TIMS, suggesting the chemical homogeneity of clinopyroxene within a single xenolith. In contrast, chondrite-normalized REE patterns of individual xenoliths differ extremely ranging from smooth LREE depleted, enriched LREE with inflection, to convex-upward REE patterns. The chemical diversity can be explained by the integration of following processes; (1) partial melting of an initially fertile and homogeneous peridotite, (2) subsequent metasomatic enrichment caused by a mobile melt/fluid, and (3) continuous inter-mineral redistributions accompanied by metamorphic recrystallization until host eruption.In order to constrain the origin of the source peridotite, we focused on Sr and Nd isotopic systematics of less-metasomatised samples (eight spinel lherzolites and one garnet-spinel lherzolite). Clinopyroxenes of these xenoliths show smooth LREE depleted patterns (except for La) and systematic depletion of Sr, Sm and Nd abundances. They have relatively depleted Sr-Nd isotopic compositions (present-day values: 87Sr/86Sr = 0.70237-0.70311 and 143Nd/144Nd = 0.51311-0.51331). Although no correlation can be found between two isotopic ratios, 143Nd/144Nd ratios are positively correlated with 147Sm/144Nd ratios, suggesting that these samples preserve the information about depletion age and initial 143Nd/144Nd ratio. By using mass-balance calculation, we evaluated bulk compositions of these two ratios for individual xenoliths with assumptions of isotopic equilibrium within single xenoliths at the time of host eruption, and negligible effect of metasomatism. Reconstructed bulk isochron yields a depletion age of 168±38 Ma with an intercept of εNd = 7.1. These values significantly deviate from those of overlying crust originated from the Ontong Java Plateau (121-125 Ma with εNd = 3.7-6.0), indicating that the peridotites are not genetically related with the Ontong Java Plateau basalts. We interpret that the peridotites were originated from residual to melt extraction of the Pacific MORB crust, which possibly exists beneath large volume of the Ontong Java Plateau basalts. The estimated age is consistent with those of neighboring crusts inferred from the magnetic reversal patterns (approximately 120-160 Ma). From these observations, we conclude that the shallow mantle beneath the Ontong Java Plateau was previously constructed at the mid-oceanic ridge, followed by subsequent emplacement of the Ontong Java Plateau at the off-ridge location.
  • Tomoaki Morishita, Jin-ichiro Maeda, Sumio Miyashita, Takeshi Matsumot ...
    Session ID: G6-04
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Srilankite (Ti2ZrO6), a mineral rich in the high field strength elements (HFSE), was originally described in pebbles found in the washing concentrate of a gemstone mine in Rakwana in the province of Sabaragamuva, Sri Lanka (Willgallis et al., 1983). It was also reported as an inclusion in garnets from the Yagodka lamprophyre pipe in Tobuk-Khatystyr field (Kostrovitskiy et al., 1993) and from Colorado Plateau ultramafic diatremes in the Navajo Volcanic Field (Wang et al., 1999). Recently, Bingen et al. (2001) reported srilankite from crustal mafic granulite and interpreted that it was a reaction product between baddeleyite and ilmenite controlled by very local conditions where no free silica was available. Thus occurrence of srilankite is an indicator of the high HFSE/SiO2 conditions in its formation. Here we first report srilankite from the ocean floor.
    The studied sample was directly collected from an outcrop at 2605m depth exposed on the eastern rift valley wall of the Atlantis II Fracture Zone, the Southwest Indian Ridge (SWIR), during Dive #643 of the ABCDE cruise using submersible SHINKAI 6500 of the Japan Marine Science Technology Center (JAMSTEC). The SWIR is an ultraslow spreading ridge with a 14 mm/year full spreading rate (Hosford et al., 2003). The Atlantis II Fracture Zone is a 199-km offset of the SWIR with a 6-km deep transform-valley. Srilankite occurs as small patches, < 30 micron meter, always coexisting with ilmenite and rutile. Zircon, apatite and phlogopite also occur as accessory minerals in the vein. A Zr/Ti ratio of the srilankite is close to a stoichiometric value of one-half. Based on petrography, the srilankite appears to be directory crystallized with ilmenite and rutile from melts rather than metamorphic recrystallization. Mineral assemblages and mineral compositions in the vein indicate that melts which produced the vein have high concentrations of compatible elements (MgO and Cr2O3) as well as incompatible elements (high-filed strength elements, K2O and H2O). On the other hand, TiO2-enrichment of minerals in the peridoitite host on the periphery of the gabbroic vein may result from the interaction with the melts. Geochemical interactions between peridotite and melt in the upper mantle may lead to effectively concentrate the incompatible elements in a modified melt, which in the extremely case is able to precipitate srilankite directly. Physical conditions under slow-spreading ridges, characterized by a highly attenuated magma supply and high rock/melt ratio, are favorable for the peridotite-melt interactions.
  • Hiroyuki Takeshita, Chitaro Gouzu, Tetsumaru Itaya
    Session ID: G6-05
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Anomalously large chemical variations in muscovite-paragonite and muscovite-celadonite systems are observed in white micas from the Piemonte calcschists in the Chisone valley area, internal western Alps. The petrographical and chemical observations on white mica strongly suggest that most mica crystals with high Na/K ratio in the chlorite zone are of detrital origins and were derived from the pre-Alpine high-temperature metamorphic sequence such the Caledonian and/or Variscan. The continuous compositional variations from 0.00 to 0.78 in Na/(Na+K) ratio are due to that the part having various mixtures of submicroscopic muscovite and paragonite crystal aggregates were analyzed by EPMA. In the rutile zone, the paragonite content of white micas are less than 20%, suggesting that the white micas have been homogenized in the Alpine metamorphism even if the detrital white micas existed. Metamorphic mica is still very heterogeneous. The total range in Si content becomes wider with increasing of metamorphic grade: 3.22-3.39 pfu for the chlorite zone, 3.07-3.45 pfu for the chloritoid zone and 3.06-3.59 pfu for the rutile zone. This clearly indicates that some mica grains have disequilibrium chemistry with other metamorphic primary phases, suggesting that the micas have experienced significant retrogressive chemical reactions in cooling and exhumations of the host schists.
  • Yoshikuni Hiroi, Mihoko Suzuki, Simon Wallis
    Session ID: G6-06
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    One of the fundamental problems concerning the ultrahigh pressure metamorphic rocks worldwide is the mechanism of uplift. In addition, it is important to clarify whether the rocks experienced partial melting at the peak-pressure or subsequent decompression stages, because sufficiently high temperatures have been estimated for most of them to melt partially in the presence of water. We examined plagioclase which occurs with or without epidote and muscovite around kyanite next to quartz in some ultrahigh pressure metamorphic rocks from the Sulu-Dabie belt, eastern China, in some detail. It is plausible that the plagioclase formed by partial melting of host rocks and subsequent crystallization of the produced melt during uplift.
  • Akira Ishiwatari, Yutaka Shimizu
    Session ID: G6-07
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Paleozoic high-pressure metamorphic rocks of the Joetsu belt appear only as sporadic small outcrops on top of the Mt. Tanigawa-dake and as boulders in the Miocene Awazawa Formation. Shimizu et al. (2000, Geol. Soc. Japan 107th Meeting Abst. 289; 2001, GSJ 108th Meeting Abst. 160) reported petrologic nature of those basic and pelitic schists. Combining these petrographic and mineral chemical data, we discuss nature of the Joetsu high-pressure metamorphis, and compare it with those of the Renge, Sambagawa and Kamuikotan high-pressure metamorphic belts.
  • Zaw Win Ko , Masaki Enami, Mutsuki Aoya
    Session ID: G6-08
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Nobuhiko Nakano, Yasuhito Osanai, Masaaki Owada, Tsuyoshi Toyoshima, T ...
    Session ID: G6-09
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Si content in Cpx is considered as an important indicator of UHP metamorphic condition. Typical UHP a mineral such as Coe or micro-Dim coexists with supersilicic Cpx within Zrn grains. Cpx in the matrix also forms Qtz-exsolution lamellae during retrograde metamorphism. Then it is suggested that formation of Qtz-lamellae in Cpx would be suggesting UHP conditions (e.g. Liou et al., 1998). During the detailed observation, we found the Grt-Opx-Cpx granulite from the Kontum massif, which contains Cpx with Qtz-exsolution lamellae.
    The granulite is normally found as blocks or lenses enclosed within mylonitic felsic gneisses. These granulite blocks are considered to be originally high-temperature eclogites. However, various retrograde minerals have also been formed during isothermal decompression through the following reactions;
    Grt+ Si, Na-rich Cpx1 (CaEs10-13) + Qtz (UHT-UHP condition)
    Grt+Cpx1+ Qtz= Al-poor Opx1+ Na-rich Pl1+ Si, Na-poor Cpx2 (UHT-HP condition)
    Grt= Al-rich Opx2+ Na-poor Pl2+ Spl (HT/ HP condition)
    Cpx1= Qtz+ Na-rich Cpx3
    Cpx1= Na-rich Pl3+ Cpx4
    Cpx2= Opx3+ Hbl+ Pl4+ Cpx5
    We assume that the peak metamorphic condition of these granulites would have been up to UHT-UHP condition due to the presence of supersilicic Cpx and estimated P-T condition. After the peak metamorphism, a near isothermal decompression had taken place with forming the Grt breakdown assemblage.
  • Yoshikuni Hiroi, Yoichi Motoyoshi
    Session ID: G6-10
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Khondalite is a graphitic garnet-sillimanite-alkali feldspar-quartz granulite commonly associated with quartzites and dolomitic marbles in the Highland Complex of Sri Lanka.Symplectitic intergrowth of corundum and alkali feldspar (or K-feldspar and sodic plagioclase) is newly found to replace sillimanite partially in the vicinity of quartz in some khondalites, in which both sillimanite and garnet are irregularly replaced by symplectitic intergrowths of hercynite + sodic plagioclase most probably caused by fluid infiltration. Partial melting is inferred to have taken place in the rock when the fluid infiltration occurred, because such a local steep gradient of chemical potential of silica can be formed not by the presence of fluid but by partial melting of coarse-grained dissimilar minerals (e.g., quartz and feldspar) as revealed by experiments.
  • Yasuhito Osanai, Krishnan Sajeev, Wilbert Kehelpannala, Bernard Prame
    Session ID: G6-11
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Satoko Suzuki, Kazuyuki Shiraishi, Hiroo Kagami, Makoto Arima
    Session ID: G6-12
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Yukiyasu TSUTSUMI, Kazumi YOKOYAMA, Kentaro TERADA, Hiroshi HIDAKA
    Session ID: G6-13
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Shinji Tujimoto, Isao Kusachi, Yasuhito Osanai
    Session ID: G6-14
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    Almost all the geologic basement of Sri Lanka is underlain by Precambrian high-grade metamorphic rocks, which have been subdivided into four lithological units as follows: the Wanni Complex, the Highland Complex, the Kadugannawa Complex and the Vijayan Complex (e.g. Hiroi et al., 1990; Kroner et al., 1991) based on the difference of Nd-model ages. At Gintota near Galle, calc-silicate rock occurs as layers into charnockite belonging to the Highland Complex. The calc-silicate rocks composed mainly of clinopyroxene (Cpx) Scapolite (Scp) -bearing layers, and minor of Scp and Alkali-feldspar (Afs) layers, and wollastonite (Wo) layers. Judging from its mode of occurrence in the field, the calc-silicate rock probably formed during high-grade regional metamorphism of the calcic sediments originally. Simultaneously, the layers of the calc-silicate rocks cut by the veins up to 50 cm composed mainly of platy Wo. Cpx and Scp of coarse grain size are locally formed near the Wo vein intruding discordantly to the calc-silicate rock. Associated minerals are plagioclase (Pl), apatite, titanite (Spn), calcite (Cal), quartz (Qtz), graphite and pyrrhotite, except for Cpx, Scp, Wo and Afs. In the present study, we deal its mode of occurrence and mineralogical properties, and discuss the geneses of the calc-silicate minerals at this locality. Description of main minerals: Cpx occurs as aggregates of euhedral to anhedral crystals up to 15 cm. The mineral is dark-green in hand specimen. XMg value of the mineral is 0.53-0.60. The cell parameters are a=9.767(8), b=8.957, c=5.258(4) Å, β=105.58(4). Wo occurs as platy crystals characteristically in the vein. The mineral is white to pale yellow in color. It is monoclinic with the following cell parameters; a=15.409(4), b=7.311, c=7.066(2) Å, β=95.36(2). Scp found as a constituent mineral of the layer. The mineral occurs as aggregates of subhedral to anhedral crystals. It is gray in color and colorless in thin section. The chemical composition is uniform. The meionite content varies from 72 to 87 mole %. The cell parameters calculated from the powder data are a=12.165(3), c=7.567(3) Å. Afs found as melt pots and a constituent mineral of the layer. The mineral occurs as anhedral crystals. The chemical composition of the mineral is Or85-100. Genesis: THERMOCALC v.3.2 (Powell and Holland, 1988) and the thermodynamics data set (Holland and Powell, 2002) were used to construct activity-corrected partial petrogenetic grids. In the CASV model system, the formation of minerals such as Wo and Scp, and the metamorphic history were considered. Since the Scp is in equilibrium with Cpx, Afs, and Spn, the peak metamorphic temperature is estimated to be above 800°C. It is possible that aCO2 was to be greater 0.2 and less than about 0.5, judging from the absence of grossular. The breakdown reactions of Scp and Woe are respectively indicators for cooling. The increase in aCO2 is presumed from the presence of symplectite textures such as Cal+Qtz, Pl+Qtz, and Scp+Qtz that may be of retrograde origin.
  • Masaru Taga, Mamoru Murata, Isao Kusachi
    Session ID: G6-15
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Mamoru Murata, Michio Kiji, Hiroaki Ozawa, Hiroshi Nishimura
    Session ID: G6-16
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Kazuki Tanimoto, michio Tagiri
    Session ID: G6-17
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    We evaluated the accuracy of the degree of graphitization on the basis of the repeated experiments on pelitic schist, and of the analysis on ten pelitic schists collected from an out crop. The experimental accuracy of the degree of graphitization is ±1 in both experiments at GD=31 and GD=26. This evaluation strongly suggests that the difference over GD=6 between closely neighboring two samples is derived from a discontinuous metamorphic condition. Based on the samplings in 20 cm and in 25 cm interval along the direction normal to the strike, we found this difference at two places, at a stream of the Sanbagawa-river and at an out crop of the Arakawa-river, Kanto Mts. Miyashiro(1994) called its geologic relation the shuffled-cards structure. In the first case, serpentinitic greenschist forms the boundary between the shuffled-cards. In the second case, the thrust plane in pelitic schists divides the shuffled-cards. However, a continuous pile also exists in the Sanbagawa metamorphic terrain such as the Kamabuse-yama boringcore of 280m depths.
  • Yasutaka Yoshimura, Tomoharu Miyamoto, Yoichi Motoyoshi
    Session ID: G6-18
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
G7:
  • Yuka Hirahara, Kenji Shuto
    Session ID: G7-01
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Kazuki Nakamura, Hiromitsu Taniguchi
    Session ID: G7-02
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    The diversity of ejecta produced by explosive eruption depends mainly on the difference of phenomena during magma ascends in the conduit. It seems that the morphology and structure of pumice records the phenomena, so the analysis of pumice should be useful to obtain the knowledge on the phenomena. In a history time, Usu-Volcano erupted five times that accompanied an eruption column. The eruptions produced various types of pumices. In this study, the Plinian products of 1977 eruption, especially the Big. I (Katsui et al., 1978), will be characterized. Special attention will be given to the lithofacies of the deposit, proportion of particles, morphology and the texture of pumice. In 1977, four large eruptions that produced eruption column occurred, i.e., Big. I, II, III and IV (Katsui et al., 1978). According to Niida et al. (1982), the Big. I column grew up step by step, and then became weak rapidly. The sediment of this column consists of 4 fall units with a clear boundary. They should correspond to earlier gradual growth and later rapid decrease. The 1977 eruption has various types of pumice in morphology and in color. Some of them are elongated form with a fibrous texture, and the other almost pumice are spherical or ovoid form. Based on color, they are classified into 3 types, i.e., white, bright-gray and dark-gray pumice. Although there are some types of pumice in morphology and color, the bulk chemical compositions of them were almost identical to each other. This suggests that the difference of color was not caused by the difference of bulk chemistry and that they were produced using the same magma. Compared with white, bright-gray and dark-gray pumice, it was found that the proportion of crystals in the groundmass of white pumice was lower and the porosity was larger. Because the texture of groundmass should reflect the cooling rate of magma, i.e., ascending rate in the conduit, white pumice should be produced by the magma that ascended rapidly. The fact that gray pumice has lower porosity may suggest the presence of obstruction by the crystals in the groundmass. Based on the analysis of types of rock fragment in the Big. I deposit, it was found that much white pumice, elongated pumice and much accessory products characterized the deposit of climax stage. This may suggest that the increase of eruption rate induced the increases of accessory products, elongated pumice and white pumice.
  • Mitsuhiro Yasui, Masatsugu Yamamoto, Nao Ito, Eiji Hisaeda, Tetsuya Ya ...
    Session ID: G7-03
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Ryoichi Yamada, Takeyoshi Yoshida
    Session ID: G7-04
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Tomohiro Takahashi, Yoshitaka Nagahashi, Yukio Yanagisawa, Takeyoshi Y ...
    Session ID: G7-05
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
  • Masao Ban, Yuzo Tanaka, Hiyori Sagawa
    Session ID: G7-06
    Published: 2003
    Released on J-STAGE: December 31, 2004
    CONFERENCE PROCEEDINGS FREE ACCESS
    A small cone Goshikidake situates in inner part of a horse shoe shaped Umanose caldera (1.7 km in diameter), which is located in the central part of the Zao volcano. Crater Lake Okama (350m in diameter) is in the western part of the cone and pre-Okama crater (210m in diameter) is just southeastward of Okama. The past ca. 30-ky eruptive products of the Zao volcano are divided into the Komakusadaira agglutinate and the Goshikidake pyroclastic rock. At about 30ka, Umanose caldera was formed by explosive eruptions. The Komakusadaira agglutinate, which are spattered over along the top of the caldera wall, probably formed this period. Bulk silica contents of juvenile fragments of the agglutinate are 55.1-56.2%. Phenocrystic assemblage is cpx, opx, pl, and mt. The groundmass is mainly composed of glass with various amounts of vesicles. Afterwards (~ca.1ka), Goshikidake (2.2km3), which was composed of the Goshikidake pyroclastic rock, was built in inner part of the caldera. The pyroclastic rock can be divided into five units by angular unconformities. Unit 3 products were the final products from pre-Okama crater and units 4 and 5 products were erupted from Crater Okama. Most of unit 5 products were erupted in AD1895. The vents of units 1 and 2 are unclear. The cone products are composed of numerous pyroclastic layers and most of the constituents are dark gray to reddened colored pyroclastic surge deposits. Climbing duneform, planner bedded deposits with penecontemporaneous slumping, and bomb sags are commonly observed. These deposits thin rapidly away from the vent. Some exceptions can be seen. The lower part of unit 1 is mainly composed of vulcanian fall deposits, and also, the lower part of unit 4 and whole of unit 5 are composed of white to gray colored tuff breccias caused by phreatic eruptions. Phenocrystic assemblage (ol+-, cpx, opx, pl, and mt) and the groundmass (mainly composed of glass with vesicles) of juvenile fragments from the cone are similar among the units. Bulk silica contents of these are 56.2-58.1%, which is higher than those of Komakusadaira agglutinate. In some co-variant diagrams, chemical compositions of the agglutinate are not plotted on the silica poorer extrapolated lines of the trends drawn by the cone products, which is suggesting renewal of magma feeding system under the volcano. Although most of the major elements of the cone products are plotted on the same trends, K2O and some incompatible trace elements show higher values in unit 4 products than in the other units at same silica contents, which may be related to a differentiation of magma under the volcano.
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