Redox and temperature conditions governing chemical and isotopic equilibration of CO2 and CH4 in volcanic-hydrothermal environments

点击翻译按钮获取中文摘要

Contrary to what has been previously assumed, recent investigations on Nisyros volcano, Greece, and Vesuvio, Italy, imply that chemical and isotopic equilibration between CH4 and CO2 is possible down to temperatures as low as 320°C. Overall equilibrium is attained in solution and secondary re-equilibration of both gases after vapor separation seems to be only of minor importance. This possibly makes the CH4-C02 geothermometers suitable candidates to monitor temperature variations of aquifers overlying rising magma bodies and, hence, to reflect the state of volcanic activity. Furthermore, they could help to identify and characterize aquifers for the purpose of geothermal energy exploration. However, more combined data (compositional and isotopic) on volcanic-hydrothermal systems is needed to identify the prerequisites for CH4-C02 equilibration, its relative occurrence in nature and, hence, its significance for volcanic risk evaluation. We, therefore, intend to investigate the chemical and isotopic composition of fumarolic gases emitted from three tectonically distinct volcanic settings in Italy.