Hydrothermal activity indicated by oxygen and hydrogen isotopes of rocks and minerals from a paleogene cauldron, southwest Japan

Abstract

18O/16O, D/H and 34S/32S ratios were determined for whole-rock and mineral samples from the Hamada cauldron in southwest Japan, a complex of volcanic and shallow-intrusive rocks of Paleogene age. The low δ18O values for the whole-rock samples, ranging from -2.3 to +4.9‰ (relative to SMOW) for volcanic rocks, and from -1.8 to +7.0‰ for plutonic rocks, suggest isotopic exchange reaction with 18O-poor meteoric ground waters at elevated temperatures…