ABSTRACT

Minerals formed in high-temperature environments are distributed along faults on Yonaguni Island. Volcanic activity is thought to be a possible heat source. In this study, samples from the carbonate veins distributed around the basement rocks and faults of Yonaguni Island were melted in vacuum, and the concentrations and isotope ratios of the noble gases in the furnace were investigated. The observed isotope ratios suggest that the noble gases were dominated by crustal helium, with little influence from mantle helium. These results suggest that there was some kind of non-volcanic heat supply at Yonaguni Island (e.g., eruption of non-volcanic hot springs).