Groundwater circulation at Mt. Etna: evidences from ~(18)O, ~2H and ~3H contents

摘要

Groundwaters from Mt Etna and the local meteoric recharge were analyzed for their δD and δ~(18)O and tritium contents. δD and δ~(18)O values of groundwaters define the local meteoric water line (δD=86~(18)O+18). Rainwaters show a wide range for both δD (-84 to -12 per thousand) and δ~(18)O (-12.8 to -3.0 per thousand) with the more negative values measured in colder periods and at higher altitudes. Isotopic data confirm that the differences in chemical composition existing between the SW and the E flanks of the volcano are mostly related to their peculiar hydrology. Waters collected in the eastern hydrogeological basin have mean recharge altitude significantly lower (410 m) than those of the northern (850 m) and south-western (1000 m) ones. Moreover the higher tritium contents indicate that the eastern basin has generally shorter and higher-gradient circuits. The longer residence times of the south-western basin allow the groundwaters to reach very high magmatic CO_2 and He contents.