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

Petrology of the Tertiary basalts of Hamamasu, Hokkaido

Yoshio Oba, Shigeru Tagami

1966 Volume 56 Issue 6 Pages 235-245
Published: December 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.56.235

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Various kind of basalts of the Pliocene age are developed in the western extremity of the so-called “Kabato mountainland” in central Hokkaido.
In this area, voluminous andesitic lavas and pyroclastic rocks are predominant in Miocene to Pliocene age, and normal sedimentary rocks are very limited in distribution.
The basalts occur as lava flows, covering the Miocene and Pliocene formations, or as dikes, cutting them.
The basalts can be divided into the following three types on the basis of the petrographic characters;
A type: Olivine basalt (IIIb, IIIb→c)
Augite-olivine basalt (IVb, IVb→c)
B type: Olivine basalt (IIIc)
Augite-olivine basalt (IVc)
Augite basalt (Xc)
Olivine-augite basaltic andesite (IVc)
C type: Olivine basalt (IIIa→d, IIId)
Olivine-augite basalt (IVa→d, IVd)
Among them, C type basalts noteworthy include holocrystalline xenoliths and xenocrysts of plagioclase, quartz and hornblende.
The present study clarified that the basalts of this area are presumably generated from the alkali basalt magma; A and B type basalts are derived solely by the fractional crystallization, whereas C type basalts which compose the majority of the basalts, are produced under the influences of contamination of the magma with salic rocks of the basement.

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Mg-Fe⁺²DISTRIBUTION BETWEEN COEXISTING HORNBLENDE AND CA-RICH PYROXENE

HITOSHI ONUKI

1966 Volume 56 Issue 6 Pages 246-255
Published: December 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.56.246

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Some theoretical considerations made on the distribution coefficient. Mg-Fe⁺² distribution in coexisting hornblende and Ca-rich pyroxene from many kinds of rocks including igneous and metamorphic rocks are examined. The distribution coefficient of Mg-Fe⁺² between these two minerals varies with temperatures at which they were formed, and is useful as a geothermometer. An approximate variation of the distribution coefficient with temperature is proposed.

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On the granitic rocks and their collapse at Kamo District, Shimane Prefecture

Kiyoshi Miura

1966 Volume 56 Issue 6 Pages 256-283
Published: December 05, 1966
Released on J-STAGE: August 07, 2008

DOIhttps://doi.org/10.2465/ganko1941.56.256

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The geology, petrographic characters of the granites, and the types of collapses of the rocks caused by heavy rain fall in the Kamo District, Shimane Prefecture, are described to clarify the relation between rock types and collapsing phenomena in the granite mountain area.
The granitic rocks comprise granodiorite and biotite granite, and both are weathered remarkably in most parts. From the genetic point of view, the collapses are classified into six types.
1) Collapse, closely related to the joint structure of the rocks; they occur characteristically at the foot of slopes in the region of weathered granodiorite.
2) Collapse of the weathered zone (uppermost layer covered with vegetation) of slopes, caused by difference of physical properties to the ground water between the weathered zone and the basement rocks.
3) Collapse with characters of (1) and (2).
4) Collapse closely related with dikes in granite.
5) Collapse accompanying landslide in fault breccia zones.
6) Collapse or resliding of the talus deposit, made by an older land slide of the adjoining rock masses.
The majority of the collapses in this district belong to types (1), (2) and (3). Types (1) and (2) predominate in granodiorite and (3) in biotite granite.

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