青函トンネルの粘土鉱物 (第3報) : 海峡中央部の概略と粘土化に関する基礎的検討

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Mineralogical composition of representative rock samples from the pilot tunnel at the central part of the straits were investigated by means of X-ray diffraction technique, giving the result that they contained only a little amount of dioctahedral smectite as clay mineral. Furthermore, in order to study the genesis of clay minerals occurring in the undersea portion of the straits experimentary, (1) obsidian from Tokachi district, Hokkaido, and (2) typical clay minerals obtained from exploratory horizontal borings were treated with artificial seawater under hydrothermal conditions. The materials and solutions after treatment were examined by means of X-ray diffraction technique and atomic absorption spectroscopy, respectively. As a result, the following alteration processes were observed. (1) obsidian → smectite (2) dioctahedral and trioctahedral smectite → randomly interstratified chlorite/smectite → chlorite (3) ordered interstratified chlorite/smectite → chlorite And the above alteration processes were found to be always accompanied by the decrease of Mg^<2+> in artificial seawater. From the results obtained above, formation mechanism of clay minerals in the undersea portion of the straits could be considered as below ; in the first stage, volcanic glass in the matrix of the rocks is changed to smectite, then the smectite is altered to chlorite through interstratified chlorite/smectite by forming brucite layer at its interlayer.
日本粘土学会の論文
1984-09-01

青函トンネルの粘土鉱物 (第3報) : 海峡中央部の概略と粘土化に関する基礎的検討

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