Geochemical investigations applied to active fault detection in a volcanic area: The North-East Rift on Mt. Etna (Sicily, Italy)

Abstract

Geochemical investigations were performed on the Northeast Rift of Mt. Etna, a prominent volcanic structure of this volcano. Low-temperature fumaroles were found on the upper part of this area and the isotopic compositions of C(CO2) and He suggest a likely magmatic origin of the emitted gases. On the contrary, very low degassing was found in the lower part of the NE-Rift, with CO2 concentrations generally very close to those in air. This pattern is probably, due to sealing of the eruptive fissures by the repeated injections of magma solidified into dikes and by consequent shallow hydrothermal alteration of the fissured rocks due to residual magma degassing. High soil CO2 concentrations were also found in an elongated area parallel to the NE-Rift and located immediately to the east of it. The geometry of these anomalies suggests the existence of several hidden faults, sub-parallel to the NE-Rift and likely connected to the Pernicana fault system. This latter structure seems to merge with the NE-Rift at the altitude where the fumarole emissions are located. The hidden structures, together with the Pernicana system and the NE-Rift, represent the western and northern boundaries of a large eastward collapsing sector of Mt. Etna. Copyright 1999 by the American Geophysical Union.