Imaging the Salinelle Mud Volcanoes (Sicily, Italy) using integrated geophysical and geochemical surveys

Abstract

Geochemical and geophysical prospecting methods (including measurements of soil heat flux and soil CO2 flux, gravimetry, self-potential and geomagnetism) are used to produce an integrated data set aimed at imaging the migration of fluids in the sub-surface at the Salinelle mud volcanoes, located on the lower southwestern flank of Mt Etna (Sicily, Italy). This area was affected by magmatic eruptions from local volcanic centers between about 48 and 27 ka. Today, only pseudo-volcanic phenomena due to over-pressured multiphase pore fluids there occur. Carbon dioxide of magmatic origin, mixed with biogenic hydrocarbons, warm hypersaline waters and mud, are constantly released at the surface through the main conduits of mud volcanoes, whose activity is characterized by alternation of mild gas bubbling periods and strong paroxysmal phases. The latter produce violent gas eruptions that eject warm water (T ≈ 50° C) to a height up to about 1 m. Surface distribution of the geophysical and geochemical parameters have been investigated to detect the main pathways through which fluids move toward the shallow crust. Integration of geochemical, geophysical and geological maps allowed for the tracing of the fluid flow in the shallowest (a few tens of meters below the surface) part of the local hydrothermal system. Our results showed that the rising of fluids from a deep reservoir is controlled by the main structural and geological features of the area and their temporal and spatial evolution depends on pressure conditions inside the hydrothermal system.