Evaluating hydrothermal system evolution using geochronological dating and biological diversity analyses

To elucidate the evolution of hydrothermal activities, we conducted an interdisciplinary study including geochemistry and biology to develop a method of obtaining reliable age information. As geochemical dating techniques, two methods applicable for hydrothermal ore minerals were developed and improved: electron spin resonance method and uranium–thorium disequilibrium method. Cross checks between the two methods generally showed good agreement for the range of hundreds to thousands of years. As biological analysis, the biodiversity among faunal communities in the targeted areas was analyzed at the species and DNA levels. Species and genetic diversity of the local fauna were not always correlated to geochemical dating, either in the southern Mariana Trough region or in the Okinawa Trough region. Although the results are not simple, comparison of age information obtained from analyses of these two disciplines potentially provides important constraints for discussion of the history and evolution of hydrothermal activities.