有馬地域の温泉,鉱泉の水素と酸素の同位体比について

Saline waters of thermal and mineral springs in Arima area, at Takarazuka, and in Ishibotoke area of Kawachinagano City indicate wide ranges of δD and δ(18)O values (Table 1). Excellent linearity exists between the δD and δ(18)O values (Fig. 1) and between the δ(18)O value and the chloride concentration (Fig. 2). These facts as well as the chemical evidence of the previous investigators strongly support the view that Arima springs are admixtures of a single deep brine and local ground water (TSURUMAKI, 1964). The deep brine may have the δ(18)O value of +8.0～+8.5‰, the δD value of -25～-30‰, and the chloride concentration of 1.20～1.25 eq/l, which were estimated from the water of the maximum salinity so far reported. Because the thermal and mineral springs in Arima area closely associate with the upper Cretaceous granitic rocks, and the estimated δ(18)O value of the deep brine is similar to a value of water in isotopic equilibrium with those granitic rocks at 500～600℃, the deep brine of Arima might have been the magmatic water of those granitic rocks. The mineral springs at Takarazuka and in Ishibotoke area also show the similar linearity among Cl(-), δ(18)O and δD to those in Arima area. Therefore it is assumed that the mineral springs at Takarazuka may be of the same origin as that in Arima area, and the mineral springs in Ishibotoke area might have been the fluid associated with Ryoke metamorphic rocks. Alternatively, the deep brine in Arima area may be isotopically and chemically similar to the saline formation waters in Illinois basin (GRAF et al., 1966). The high δD values and salinities of those formation waters were attributed to the isotopic and chemical fractionation during the passage of water through sediments. The deep brine in Arima area may be genetically similar to those saline formation waters. If such a saline water could have formed in Osaka basin, it is not surprising to find out the similar brines at Arima and Ishibotoke which are the northwestern and southeastern rims of the basin, respectively. At the present, it cannot be answered which of these two models is more probable. Further studies on other saline springs fluid inclusions of Cretaceous granitic rocks may be useful in order to solve this problem.

原著論文 (Original Papers)