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

Petrological studies of the Cenozoic basaltic rocks from the western San-in district (1)

Basaltic rocks from Mishima Island, Yamaguchi Pref.

Yoshio Oji

1960 Volume 44 Issue 2 Pages 73-82
Published: April 01, 1960
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.44.73

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Mishima Island is composed mostly of the basaltic rocks of the alkali rock series and partly of the tholeiitic basalt, which were erupted in the Miocene or Pliocene to Pleistocene. Eleven lavas of different periods which are chemically analysed, are classified into the tholeiitic basalt, picrite-basalt, trachybasalt and trachyandesite. These rocks are generally rich in MgO, and particularly its content is as high as 14.2% in the picrite-basalt. This is the first occurrence of picrite-basalt in Japan. It is a distinct character of the rocks of this island that they devoid entirely hypersthene either as phenocryst of groundmass, though they contain abundant xenocrysts and xenolithes. Thus these rocks belong not to the calc-alkali rock series, but to the alkali rock series. This is a remarkable diference from the rocks of Iki Island, Where many calc-alkalirocks are derived from the contamination of the alkali rock series, as pointed out by Dr. Aoki. This fact is interesting from the genetic consideration on the magmatic differentiatin in this island, and will be discussed later.

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Noritization and hyperitization accompanied with biotite migmatite, at the mid-stream of Horoman river in southern Hidaka metamorphic terrain (I)

Hiroshi Asai

1960 Volume 44 Issue 2 Pages 83-89
Published: April 01, 1960
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.44.83

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At the contact between hornblende tonalite and its xenolith, biotite nortite was formed, while at that of biotite migmatite and amphibolite, biotite hyperite was produced. From the careful observation in the field and microscope the writer attained the conclusion that the norite or hyperite is not originated from gabbroic magma and the inclusion is not ascribed to the forerunner of magma, nor to the amphibolite. Feature of mechanical movement in norite or hyperite is considered to have taken place at the time of formation of biotite migmatite or amphibolite. Metamorphic aspect in biotite migmatite is a kind of “metablastesis”. Dispersion of biotite into matrix, and recrystallization of biotite into pyroxene or hornblende are the general behaviors in this district.

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Zonal structures of the porphyritic plagioclases in the dacitic contaminated rocks from Shiroishi, with special reference to their origin

Keidi Oide

1960 Volume 44 Issue 2 Pages 90-101
Published: April 01, 1960
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.44.90

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The zonal structures of porphyritic plagioclases in the dacitic rocks from Shiroishi, Miyagi Prefecture, can be divided according to the ranges in size into the three types as follows:
(1) 0.5-4.0mm in size; they are made of anorthite core and mantle of intermediate composition, the later forming even oscillatory zoning,
(2) 0.5mm± in size; they have an even oscillatory type of zoning as a whole, ranging from An₆₅ to An₄₂ in composition,
(3) microphenocryst; they have the simplest zoning, for example, An_{48_??_44}, An_42-54, An_{55_??_44}, etc.
The first type is most interesting from genetic point of view. From its volumetric relation and the charcter of zoning, the crystallizing stage of the mantle of this type is inferred to correspond to that of the second type. The author believes that the anorthite core should have crystallized out from the basaltic magma, which changed its composition to dacitic as a result of contamination of granitic materials in the country rocks, and that this process have resulted in abrupt change of composition in the mantle of the larger phenocrysts.
The zonal structures of second and third types can be simply explained as the result of the fractional crystallization in the contaminated dacitic magmas.
Some geological and petrological significance of these zoned plagioclases is dicussed in detail.

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Distribution of organic constituents in the shelf sediments off Yamagata Prefecture

Studies on the organic constituents of Recent sediments (3rd report)

Ikuro Shimada

1960 Volume 44 Issue 2 Pages 102-110
Published: 1960
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.44.102

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Distribution of extractable organic matters, hydrocarbon content and some other organic compounds in the bottom sediments which were collected from the continental shelf off kamo and Fukura, Yamagata Prefecture, has been studied with reference to the distance from the coast, and the lithologic features of the sediments.
The small quantities of lipoid substances were obtained from all the selected 67 bottom samples. they are generally subject to the distribution of sediments which can be divided into three zones such as near-shore fine sand to the depth of nerly 40m (average value 0.04%), off-shore coarse sand between 40 to 70 m (0.06%), and silt and clay below 100m depth (0.08%). The high extractable contents are concentrated in the submarine basin in the east side of Tobishima Island, and in the narrow trough running in NNE direction in the south of this basin (0.07 to 0.18% of the samples). In these places, there are also relatively high hydrocarbons and asphaltene contents of the column chromatographic fractions. Besides, the high contents are partly extracted in sapropelic mud contained in the off-shore coarse sand zone off Kamo, but the rate of chromatographic fractions is not always high. Free sulfur was obtained from the samples of the regions above mentioned. It seems that the free sulfur is contained within the bottom samples characterized by high extractable fractions. the column chromatographic fractions of these lipoid substances show the high hydrocarbons and asphaltenes in composition, and the high paraffinic in hydrocarbon proportions are more than that of the lagoon sediments from the Hachiro-gata.

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On the talc crystals obtained from a talc pneumoconiosis lung.

Kenzo Yagi, Kiyoshi Konno

1960 Volume 44 Issue 2 Pages 111-117
Published: April 01, 1960
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.44.111

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This is the first case of a talc pneumoconiosis not associated with tuberclosis or other diseases in Japan. The talc crystals were separated from the dried lung tissue after the Sundius and Bygdoen method, amounting over 10% in weight of the lung tissue. The crystals are prismatic or scaly in shape, and 0.004-0.016mm in length. Colorless and distinct cleavages. Refractive indices α=1.540, γ=1.585. X-ray diffraction pattern shows several peaks characteristic to talc. The chemical composition of this talc is shown in Table 3, and is compared with talcs from different localities in Table 4. The chemical formula of this talc is calculated as H_1.70 Mg_3.14 Si_4.00 O_12.00.

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Mineralogical problems on silicosis

Kunihiko Koga

1960 Volume 44 Issue 2 Pages 118-120
Published: April 01, 1960
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.44.118

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