The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists

PETROGRAPHY AND PETROCHEMISTRY OF KIRIGAMINE VOLCANO, CENTRAL JAPAN (I)

TEIJI YAMAZAKI

1965 Volume 54 Issue 2 Pages 39-54
Published: August 05, 1965
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.54.39

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The rocks from the Kirigamine volcano are andesites and dacites, which are in the cale-alkalic rock series (hypersthenic rock series) in mineralogy. The rocks which belong to alkalic or tholeiitic rock series have not been erupted. From the characters of alakali-lime indices, K₂O enrichment at the later stage and others, the parental magma of this volcano may not have relation with tholeiitic magma. The phenocrystal hornblende has crystallized at middle stage of fractionation at this volcano. There is no chemical discontinuity between the hornblende free and the hornblende bearing rocks. The contamination is negligible at this volcano. Having no connection with the presence or the absence of phenocrystal hornblende, the differentiated veinlets are often present with groundmass hornblende. From the mineralogical and chemical differences between the host rock and the veinlets, these veinlets may be produced by gas transformation. The enrichment of volatile components are very effective to the crystallization of hornblende.

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Petrological studies of the alkali basalts from eastern San-in, Japan (3)

Basalts of Tsuyama basin

Kyoko Oji, Yoshio Oji

1965 Volume 54 Issue 2 Pages 55-61
Published: August 05, 1965
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.54.55

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The alkali basalts of Tsuyatna basin are dikes or lava-flows which were erupted in Pleistocene age. They are composed of abundant olivine and titanaugite, with a little plagioclase and magnetite. Intersertal crystals of zeolite are of usual occurrence and an isotropic mineral found in them may be one of the feldspathoids. Chemically the rocks are characterized by containing, with a low silica-percentage, a considerable quantity of magnesia and lime. Thus they resemble some of the trachybasalts of Kibi plateau, and seem to be limburgite, some of which being of a similar kind. The small dikes of andesites belong to the calc-alkali rock series and have no relationship at all with the alkali basalts in both mineral and chemical compositions.

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On the Himekami granitic body, Kitakami mountainland

Koichi Masuda, Hitoshi Onuki, Tokiko Tiba

1965 Volume 54 Issue 2 Pages 62-75
Published: August 05, 1965
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.54.62

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The Himekami granitic mass, Kitakami mountainland, consists of various rock facies. From the field and microscopic observations, this body is divided into five rock types, namely the Himekami A, B, C and the Ohira A and B. The Himekami types are more leucocratic than the Ohira types and the boundary between the Himekami and the Ohira types is rather sharp and is easily recognized in the field. The results of modal analyses on twenty-three rocks of these five types are given. If they are derived from a common magma, these data indicate that the Himekami and the Ohira types have slightly different cooling histories. In thedistribution area of the Ohira types, characteristic alkali gabbros and biotite clinopyroxenites are encountered at small outcrops. Chemical compositions of seven representative rocks and two micas are given. The several features of the Himekami granitic body resemble those of the Ichinohe plutonic complex, though some differences are also found between these two bodies.

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