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11.
12.
Abstract A recent K–Ar study elucidated that eruptive style in the eastern Izu peninsula changed from polygenetic to monogenetic volcano at 0.3–0.2 Ma. To narrow down the time of change, we determined 10 K–Ar ages on Togasayama Andesite of Amagi volcano, the youngest polygenetic volcano in the area, and Togasayama Monogenetic Volcano, one of the oldest monogenetic volcanoes in the area, which overlies a part of the Togasayama Andesite. Dating results showed that the Togasayama Andesite effused at least from 0.34 to 0.20 Ma, whereas the Togasayama Monogenetic Volcano erupted at 0.26–0.29 Ma, suggesting that the northern part of the Togasayama Andesite effused after the eruption of the Togasayama Monogenetic Volcano. Considering previous data, it is therefore inferred that change of eruptive style in the eastern Izu area occurred during the period 0.29–0.20 Ma, with considerable overlap of both polygenetic and monogenetic volcanism. 相似文献
13.
14.
Shin-Ichi Machida Hisako Hirai Taro Kawamura Yoshitaka Yamamoto Takehiko Yagi 《Physics and Chemistry of Minerals》2007,34(1):31-35
High-pressure Raman studies of methane hydrate were performed using a diamond anvil cell in the pressure range of 0.1–86 GPa
at room temperature. Raman spectra of the methane molecules revealed that new softened intramolecular vibration mode of ν
1 appeared at 17 GPa and that the splitting of vibration mode of ν
3 occurred at 15 GPa. The appearance of these two modes indicates that an intermolecular attractive interaction increases between
the methane molecules and the host water molecules and between the neighboring methane molecules. These interactions might
result in the exceptional stability of a high-pressure structure, a filled ice Ih structure (FIIhS) for methane hydrate, up
to 40 GPa. At 40 GPa, a clear change in the slope of the Raman shift versus pressure occurred, and above 40 GPa the Raman
shift of the vibration modes increased monotonously up to 86 GPa. A previous XRD study showed that the FIIhS transformed into
another new high-pressure structure at 40 GPa. The change in the Raman spectra at 40 GPa may be induced by the transition
of the structure. 相似文献
15.
Tadashi Kondo Hiroshi Sawamoto Akira Yoneda Manabu Kato Akihito Matsumuro Takehiko Yagi Takumi Kikegawa 《Pure and Applied Geophysics》1993,141(2-4):601-611
A new multi-anvil type high-presure apparatus has been developed using sintered diamond anvils to generate pressures over 30 GPa and temperatures up to about 2000°C. A maximum sample volume of about 1 mm3 is available in this system. The pressure was confirmed by dissociation of forsterite into Mg-perovskite and periclase. The basic techniques and problems in utilizing sintered diamond in the MA8 type high-pressure apparatus are discussed with an emphasis on the future prospect of incorporating simultancous X-ray diffraction observation. 相似文献
16.
Kosmochlor (NaCrSi2O6) was synthesized by the flux method from melts along the join Na2O·2 SiO2-Na2O·Cr2O3·4 SiO2 at 1000° C in air, and isolated by dissolving the glassy matrix with hydrofluoric and perchloric acids. The join CaMgSi2O6-NaCrSi2O6 was studied at 1 atmosphere in air by the quenching technique at temperatures between 900° and 1450° C, using mixtures of kosmochlor and diopside crystals or diopside glass as starting materials. The phases are diopside solid solution, kosmochlor, spinel (Mg-chromite), eskolaite (Cr2O3) and glass. The maximum solubility of kosmochlor in diopside is 24 wt percent at 1140° C, while diopside is not soluble at all in kosmochlor, resulting in the existence of a wide range of immiscibility. Petrologic significance of the results is discussed. 相似文献
17.
K. Yagi 《Bulletin of Volcanology》1969,33(4):1101-1117
Many sheets of alkalic dolerites found in the Cretaceous formations in the Nemuro peninsula can be divided into the following two types. Differentiated sheets, more than 100 m in thickness. Gravitational differentiationin situ is distinguished, producing rock types such as picritic dolerite, dolerite, monzonite and syenite. Undifferentiated sheets, less than 30 m in thickness. Differentiationin situ is not observed, and dolerite is the only rock type. Distinguished pillow structures are commonly observed. Petrochemistry of these rocks indicates that K.O contents are high, especially in the middle and later stages, predominating over Na2O and that MgO content is rather high as compared with iron oxides. These features place the suite in a characteristic position clearly distinguished from the other alkalic rock suites in Japan. Fourteen trace elements were determined spectroscopically and their distribution during the differentiation is discussed. The parent magma of the Nemuro rocks is estimated to be shonkinitic in composition, rather rich in potash. Its possible genesis by the partial melting of the phlogopite-peridotite in the upper mantle under the continent is discussed. 相似文献
18.
The system CaMgSi2O6CaAl2SiO6CaFeAlSiO6 has been studied in air at 1 atm. The phase assemblage at subsolidus temperatures in the CaMgSi2O6-rich portion is Cpx + An + Mel and that in the CaMgSi2O6-poor portion Cpx + An + Mel + Sp. At subsolidus temperatures the sigle-phase field of clinopyroxene increases with an increase in the CaFeAlSiO6 component of the system. The Al2O3 content of clinopyroxene, however, continues to increase beyond the single-phase field and attains at least 16.04 wt.% Al2O3 with 3.9 wt.% Fe2O3. The stability field of fassaite in the system over a range of pressures and oxygen fugacities has been estimated from data in the literature as well as the present data. The CaFeAlSiO6 content of fassaite is dependent on oxygen fugacity, but is not influenced by pressure. The stability field is strongly influenced by oxygen fugacity at low and high pressure, and decreases with decreasing oxygen fugacity. Clinopyroxenes in both volcanic and metamorphic rocks from various localities, when plotted on the CaMgSi2O6CaAl2SiO6CaFeAlSiO6 triangle, show that there is no compositional gap between diopside and fassaitic pyroxene in metamorphic rocks, and that the fassaitic pyroxene in alkalic rocks becomes richer in both CaAl2SiO6 and CaFeAlSiO5 components as crystallization proceeds. These results agree with those obtained in the experimental study. 相似文献
19.
Bulletin of Volcanology - The possibility of formation of nephelinite magma from picrite magma by separation of eclogitic fraction is discussed from experimental results on some picritic rocks.... 相似文献
20.
Takehiko Yagi Yoshiaki Ida Yosiko Sato Syun-Iti Akimoto 《Physics of the Earth and Planetary Interiors》1975,10(4):348-354
The pressure dependence of the three lattice parameters and unit cell volume of fayalite (Fe2SiO4 olivine) was determined by X-ray diffraction under hydrostatic pressures up to 70 kbar. In order to eliminate stress inhomogeneity within a composite material consisting of a specimen mixed with an internal-pressure standard, a liquid (1 : 1 mixture of ethanol and methanol) was used as a pressure-transmitting medium. The isothermal bulk modulus calculated on the basis of the second-order Birch-Murnaghan equation of state gives the values K0 = 1.19 ± 0.10 Mbar and K0′ = 7 ± 4, and if we assume K0′ = 5: K0 = 1.24 ± 0.02 Mbar. Three axes of fayalite were found to be compressible in the following order, b >c >a. Comparisons with the results obtained under non-hydrostatic compression are made. 相似文献