Evidence of mantle derived fluid contributions to the thermal basins of Western Sicily: geotectonic and geodynamic implications

摘要

Geochemical investigations have been carried out over the seismic area of Western Sicily (Italy). The area, crossed by a major seismogenic structure, was severely damaged by the last destructive seismic sequence (Ml 6.4; January 1968). Three hydrothermal basins, located across this seismic belt, were investigated for the chemical and isotopic characteristics of natural waters and dissolved gases. The ~3He/~4He ratios ranging between 0.7 and 2.8Ra highlight variable contributions of "mantle-derived" He into the different basins, which increase southwards. Although the investigated thermal basins are located over a continental area characterized by thrust tectonics, both the anomalous He isotopic ratios and the estimated fluxes of mantle-derived He reveal the large-scale motion of mantle-derived fluids in the upper crust. The results allow a better understanding of the deep hydrothermal systems, and have improved the knowledge of the local geotectonic and geodynamic framework, which may lead to a deeper insight of the development of local seismogenic processes.