Geochemical Characteristics of Non-volcanic Type Hot Spring Waters Related to Regional Tectonics in Japan

Abstract

Occurrences of non-volcanic hot and mineral spring waters, found in Niigata and the surrounding areas, as well as central to southern Kinki District, are documented in relation to the local tectonics to discuss on the importance of plate tectonics as sources of heat and dissolved chemical compositions in the deep groundwater/fluid cycle. Fossil seawater was altered at different temperatures, and remains as low-temperature mineral waters in Gunma Prefecture, and as oil and gas field brine and related hot springs in Niigata Prefecture and surrounding areas. One of the hot springs in Niigata, i.e., Matsunoyama Hot Spring, is known to contain geo-pressure hydrothermal water. The brines in Niigata Prefecture are heated via tectonics at the boundary between the Eurasian and North-American plates without contaminating modern local meteoric water. In the Kinki District, hot spring waters > 40°C appear only in three regions: coastal area along the Sea of Japan, Arima and surrounding area of Osaka Basin, and southern part of Kii Peninsula. In this area, mantle-derived fluids, such as He and CO2, are upwelling with slab-derived saline waters from the subducting Philippine Sea Plate. Non-volcanic hot spring waters occasionally give the important information on heat and energy cycles at the plate boundaries, as well as valuable information for understanding the mechanisms of inland earthquakes related to the deep-fluid movements.