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Volume 81, Issue 8
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Toshimitsu Iwaya, Hajime Kurasawa1986 Volume 81 Issue 8 Pages 291-301
Published: August 05, 1986
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSHime-shima volcanic rocks in the the Hime-shima Island, southwest Japan are composed of five bodies: Daruma-yama lava (garnet-bearing biotite-hornblende dacite), Shiro-yama lava (garnet-bearing rhyolite), Yahazu-dake lava (biotite-bearing hornblende dacite-rhyolite), Morose lava (biotite-bearing hornblende dacite) and Hashiraga-dake lava (garnet-bearing biotite-hornblende rhyolite).
These rocks can be divided into two types: garnet-bearing and garnet-free types. The lavas of garnet-bearing type are subdivided into hornblende-bearing and hornblende-free subtypes. The lavas of garnet-free type are distributed in cenrtal parts of the Hime-shima Island, while those of garnet-bearing type are in the eastern and western ends of the Hime-shima Island.
Hime-shima volcanic rocks range in composition from dacite (morose lava; SiO2=68.81%) to rhyolite (Shiro-yama lava; SiO2=74.88%). The lavas of garnet bearing type tend to be more felsic than those of garnet free type. The Hime-shima volcanic rocks may represent a later stage of magmatic differentiation, but it seems difficult to decide whether these volcanic rocks are derived from an original basaltic magma or they are remelting products of deeper part of the crust.View full abstractDownload PDF (1500K) -
YOSHIMASU KURODA, YOSHIHARU KIDA, KOJI WATANABE, TAKESHI OBA, SADAO MA ...1986 Volume 81 Issue 8 Pages 302-311
Published: August 05, 1986
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThere is no difference between the δD values of the water extracted from coexisting Mgchlorite and sericite in the Iwami Kuroko deposit. The average δD values of the minerals agree with each other in the range from - 49 to - 52‰. This indicates that there is no D/H fractiona-tion between Mg-chlorite and sericite under the hydrothermal condition. The δD value of the hydrothermal solution participated in the formation of these minerals is estimated to be - 10‰according to the fractionation factor determined by O'Neil and Kharaka (1976), or - 23 to - 26‰ according to that estimated from natural samples by Marumo et al. (1980). The value is completely different from that of the contemporary meteoric water in the mining district (average, - 51‰).
The δD value of the water extracted from fluid inclusions in quartz from the ore-veins is - 58 to - 59‰, which is different from those estimated for the hydrothermal solution during the formation of chlorite and sericite. This may indicate that there was a time difference between formation of chlorite-sericite clay and quartz.
δD values of waters released from chlorite-smectite mixed layer mineral, smectite, clinoptilolite and gypsum have also been measured. The δD values of the mixed layer minerals are rather reliable for estimating the δD value of hydrothermal solution, but those of smectite are not useful. The fractionation factors between clinoptilolite-water and gypsum-water are also estimated.View full abstractDownload PDF (599K) -
Kenji Shuto, Teiko Ichinose, Toshiaki Takimoto, Ryuichi Yashima1986 Volume 81 Issue 8 Pages 312-323
Published: August 05, 1986
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSHigh-magnesian tholeiitic basalts of early Miocene age are distributed on Nodegamiyama which is located in the eastern part of Fukushima Prefecture, Northeast Japan. These basalts (Nodegamiyama basalts) occur as a dome, with a diameter of about 300 meters, which intrude into Cretaceous granitic rocks occupying in Abukuma mountainland.
Nodegamiyama basalts are sparsely phyric (phenocrysts of olivine with chrome-spinel inclusions, clinopyroxene, orthopyroxene and plagioclase 10 vol%>). These basalts are characterized by relatively high SiO2 (52.0-52.7 wt%), high MgO (8.0-9.3 wt%), relatively low CaO (8.7-9.1 wt%), high Ni (167-220ppm) and high Cr (540-690ppm). The clinopyroxene phenocrysts contain considerable amounts of Al2O3 (3.8-8.0 wt%), and the calculated Ca-Tschermak's component ranges from 7.5 to 13.6 mol per cent, which suggest that these clinopyroxene phenocrysts are thought to have crystallized from the basalt magma at a depth of about 30km in the lower crust in this region.
Differences in bulk chemical compositions between Nodegamiyama basalts and Ryozen basalts may be ascribed to differences in the degree of partial melting between these two primary magmas and also in water content in the source mantle peridotites of these two primary magmas.View full abstractDownload PDF (680K) -
Masahiro Daishi, Masao Hayashi, Yuzo Kato1986 Volume 81 Issue 8 Pages 324-332
Published: August 05, 1986
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe fission track ages of zircon have been measured in nine acidic intrusive rocks from the Ryukyu Islands by the arranged fix-area population method and the external-surface external-detecter grain-by-grain method. The ages are as follows: Kuchinoerabujima xenolith (granodiorite), 15.0±1.2Ma; Okinoerabujima granodiorite, 32.9±2.7 Ma; Okinawajima tonalite, 30.0±4.7Ma; Okinawajima quartzporphyry, 15.7±1.3Ma, 15.3±1.5Ma, and 15.8±1.7Ma; Ishigakijima Omoto granite, 28.7±0.9Ma, 29.9±0.9Ma and 29.9±1.1Ma. These fission track ages indicate that the acidic intrusive rocks were emplaced in late Oligocene and early to middle Miocene times.View full abstractDownload PDF (594K) -
HARUO OHASHI1986 Volume 81 Issue 8 Pages 333-339
Published: August 05, 1986
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe heats of formation of halides (HfX4 ZrX4, TiX4SiX4CX4), -ΔH°298, are empirically expressed in terms of electronegativities (xC and xA) of cation and anion (halogen ion):
-ΔH°298/(4e2/rC)=axA+b/xC-c+dxA+e,
where a, b, c, d, and e are empirical constants; factor 4, e, and rC represent the valence number of cation, the charge on the electron, and cation-radius, respectively. The value of 4e2/rC corresponds to electrostatic energy between effective nuclear charge of the M4+ ion (4e) and an electron at a distance from its nucleus equal to its ionic radius rC. Although physical meaning is not clear, this empirical equation is useful in predicting electronegativity and/or ionic radius from the heat of formation, and vice versa. The electronegativity of Hf4+ is revised to be 1.4 in Pauling's scale and the ionic radius of Th4+ in tetrahedral site is estimated to be 0.77Å. The heats of formation of GeX4, SnX4 and PbX4 (X: halogen) are related to both cation radius (rC) and anion radius (rA):
-ΔH°298{(-e2/rA)/(-100kcalthmol-1)}1/2/(4e2/rC)=axA+b.
From this empirical equation the heat of formation of SnF4, (g) is estimated to be 235 kcalthmol-1.View full abstractDownload PDF (350K)
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