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Volume 76, Issue 9
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Jun-ichi Nishikawa1981 Volume 76 Issue 9 Pages 285-293
Published: September 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESS“Jyozankei quartz-porphyry” is one of the Tertiary granitoids which are developed in the Green-tuff region of southwestern Hokkaido.
It is classified into four rock types; granite-porphyry, granodiorite- porphyry I, granodiorite-porphyry II and dacite. Their SiO2 contents change gradually from 64 to 73wt.%. The variation of rock types seems to have been caused by fractionation of plagioclase and hornblends as inferred from their major- and minor-element chemistry.
Their initial 87Sr/86Sr ratios are almost identical (0.7046) for each rock type together with a quartz diorite inclusion. Judging from these rations, it is suggested that older crustal materials did not participate in the formation of this dody, and that the source material of the magma which produced this body had lower Rb/Sr ratio.View full abstractDownload PDF (686K) -
KOJI SATO, KAZUHIKO KASHIMA, ICHIRO SUNAGAWA1981 Volume 76 Issue 9 Pages 294-307
Published: September 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSIn all previous experimental studies on silicate systems, only nucleation densities and apparent growth rates were measured. Since growth of crystals in m, agma is regarded as solution growth, the nucleation density divided by time N/t and the apparent growth rate R* do not directly represent the nucleation rate I and the “real” growth rate R, respectively. In this study, a series of experiments of isothermal crystallization of plagioclase has been carried out to determine the nucleation and the “real” growth rates using a natural basalt collected at Maegatake in Adatara-yama, Japan. The results indicate that the curves of the nucleation and the “real” growth rates vs. ΔT are different from the curves of the nucleation density and the apparent growth rate vs. ΔT. Thus, care should be taken in interpreting textures of igneous rocks. Changes in morphology depending on ΔT are also illustrated and discussed.View full abstractDownload PDF (2349K) -
HARUO OHASHI1981 Volume 76 Issue 9 Pages 308-311
Published: September 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSThe dependence of the Si-O distances on the electronegativitq, the electronic structure and the size of the non-tetrahedral cations has been re-examined for NaM3+Si2O6 pyroxenes. In the Sc-V-Al series the difference, Δbr-Δmean, decreases with increasing the electronegativity and the diffeaence, Δnbr-Δmean, increases with increasing the electronegativity, where the dmean is the difference between the mean of the four Si-O distances inNaAISi2O6 pyroxene and teat in NaM3+Si2O6 pyroxene, and Δbr-Δmean is the difference between the mean of the Si-O (br) distances and the Δmean. In the Cr-ln-Fe series themean of the Si-O (nbr) distances increases with increasing the electronegativity and thedifference, Δbr-2Δmean, decreases with increasing the electronegativity.View full abstractDownload PDF (303K) -
ORTHOPYROXENE PORPHYROBLAST FOUND IN THE KAWAMI AMPHIBOLITE MASS IN YAWATAHAMA CITY, WESTERN SHIKOKUShigetoshi Noto1981 Volume 76 Issue 9 Pages 312-314
Published: September 05, 1981
Released on J-STAGE: August 07, 2008
JOURNAL FREE ACCESSOrthopyroxene porphyroblast (En75 Fs25) containing hornblende, olivine and ore as inclusions occur in the Kawamai amphibolite mass which suffered the two stages of metamorphism; the amphibolite (or epidote amphibolite) facies metamorphism and the Sanbagwaw metamorphism. It is estimated that the porphyroblasts would have been formed by a metamorphism that took place between the two stages of metamorphism.View full abstractDownload PDF (964K)
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