埼玉県秩父盆地第三系中の沸石

Abstract

In the Tertiary system of the Chichibu basin, Saiama Prefecture, analcime has been found in tuffaceous rocks and other sedimentary rocks of the lower part of the Tomita siltstone member, the Nenokami sandstone, the Miyato Formation and the upper part of the Nagura formation. Clinoptilolite occurs only at the limited lower and upper parts of the Nenokami sandstone. Assuming that the geothermal gradient and surface temperature in the basin were 2°C/100m and 10°C, respectively, the maximum burial depth of the Nenokami sandstone can be estimated to be about 4.3Km. Based on the thermodynamic calculations, analcimization of tuffaceous materials, reacted with interstitial water of the pH over 6.5, was possibly arried out within the dotted area of Fig. 4.