On the Regional Properties of Hotsprings in Japan

2. Hotsprings other than those of Quaternary volcanic areas

Abstract

There are another kinds of hotsprings in Japan besides those of Quaternary volcanic areas which are accompanied with fumaroles. Most of them are distrbuted in Tertiary volcanic rock areas, Tertiary plutonic and hyperbyssal rock areas, pre-Tertiary granite areas, Teatiary oil-fields and non-igneous rock areas. Judging from the relation that Quaternary volcanic zones are parallel to those of Tertiary in Japan, hotsprings distributed in above-mentioned areas seem. to be related to Tertiary igneous activities, except a few related to pre-tertiary granite.
Chemical characters of hotsprings emitted from altered rock areas are as follows :
(1) hotsprings of younger altered rock areas central areas (A) acidic SO₄^--type (B) acidic Cl^--SO₄^--type outerside areas Cl^- type, Cl^--SO₄^-- type and HCO₃^- type
(2) hotsprings of older altered rock areas central area type and Cl^--HCO₃^- type outerside area HCO₃^- type
Among them, Cl^- type and Cl^--HCO₃^- type of group (2) are charcterized by high content of Cl^- 1.5g/1 above and HCO₃^- 1g/1 above. Through group (1) and (2), hotsproings of outside areas are diluted by ground water and characterized by HCO₃^- in general.
Refering to the genesis of igneous saline waters, hotsprings of Cl' type and Cr-HCO₃^- type seem to be related to hydrothermal solutions corresponding to hgihly concentrated magmatic waters which were formed below critical temperature under high pressure.
The ratio of Na⁺ to K⁺ and Br^- to Cl^-- is characteristic to reveal the regional properties of hotsprings. The ratio of Na + to K+ relates to pH, but there are some hot springs which indicate a wide range of ratio in spite of having constant pH value. The ratio of Br^- to Cl^- seems avairable to distinguish thermal waters of igneous origin from those of sea water or fossil water origin. Hot springs of volcanic origin are generally characterized by low value. However, some hot springs in igneous rock areas have so high value that it corresponds to that in those of Tertiary oil-fields. The ratio of halogens and alkali-metals in thermal waters may serve as the valuable key to study the regional properties of hotsprings.