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

Some problems on the rock structure

George Kojima

1966 Volume 55 Issue 3 Pages 79-86
Published: March 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.55.79

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SIGNIFICANCE OF HORNBLENDE GABBROIC INCLUSIONS IN CALC-ALKALI ROCKS

TEIJI YAMAZAKI, HITOSHI ONUKI, TOKIKO TIBA

1966 Volume 55 Issue 3 Pages 87-103
Published: March 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.55.87

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Hornblende gabbroic inclusions are often observed in alkali olivine basalts together with preidottite inclusions at the continental margins. We recently found hornblende gabbroic inclusions in calc-alkali rocks in Central Japan. These inclusions in both kinds of Volcanic rock are mainly composed of tschermakitic hornblende and calcic plagioclase, and sometimes include minor aluminous clinopyroxene From the mineralogical view point, they cannot be explained to have been formed at ordinary plutonic conditions. It is suggested from the similarity of mineralogical features and the confined distribution between the hornblende gabbroic inclusions in the calc-alkali rocks and those from the alkali basalts that they are derived from the same position in the depth and they have considerable development under the continental margins. We cannot give a definite conclusion about the source of these hornblende gabbroic inclusions, because we have not sufficient data on the water content near the Mohorovicic discontinuity and the stability field of such mineral assemblage. It is likely that they are originated at considerable depty in the earth, however, as for example, the basement of the crust.

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Pumpellyite-bearing mineral ammemblages and type of metamorphism

Yotaro Seki

1966 Volume 55 Issue 3 Pages 104-112
Published: March 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.55.104

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On the basis of zonal distribution of some pumpellyite-bearing mineral associations, four types of metamorphism can be clearly recognized as shown in Figure 1. From petrochemical evidences it may be considered that the difference of the nature of zonal divisions between these four types of metamorphism is well explained assuming that solid pressure as well as water pressure decrease in order of Franciscan, Sanbagawa, New Zealand and Tanzawa type.

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On some cordierite-bearing rocks of the Meguro district in Hidaka Province, Hokkaido, with special reference to a large cordierite

Yono Tonosaki

1966 Volume 55 Issue 3 Pages 113-117
Published: March 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.55.113

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The Meguro district is situated in the the southern part of the Hidaka metamorphic belt in Hokkaido . The major rock types in the area are composed of the so-called migmatites and various metamorphic rocks. This paper presents a short description for the petrographic nature of the cordierite-bearing rocks found in the metamorphic rocks. The rocks are composed essentially of plagioclase, alkali-feldspar, quartz, biotite, muscovite, cordierite, sillimanite and many accessory or secondary minerals. A large cordierite listed in the sub-title of this paper have been examined optically, and by X-rays. The results of the examination are presented, and some problems are briefly discussed.

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[title in Japanese]

1966 Volume 55 Issue 3 Pages 121-132
Published: 1966
Released on J-STAGE: July 13, 2012

DOIhttps://doi.org/10.2465/ganko1941.55.121

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