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The Sicilian accretionary prism shows a large, southward imbricated system of thrust sheets. The frontal part of the belt has been tectonically emplaced in Plio-Pleistocene times. Major decollement surfaces and sole thrusts at the base of and inside the prism consist of melanges with a “blocks in matrix” fabric. In the frontal part, two superposed decollement levels are recognized, the upper one located at the base of the Paleogene-Neogene sedimentary series, and the basal one at the base of duplexes (Triassic-Miocene sedimentary series). Syntectonic dewatering of the sedimentary sections occurred along decollements and thrust faults, involving hydrofracture and mineralized vein development. Inside the deep sole thrusts (rooted in the basal decollement); hydrofractured blocks show different generations of syntectonic quartz and calcite extensional veins, while in the upper decollement only calcite veins have been observed. Both quartz and calcite veins show aqueous primary fluid inclusions of low salinity, with low trapping temperature for fluids in the upper decollement ( If we assume that, at the time of deformation, the main heat source was the regional conductive geothermal gradient, the trapping temperatures of the fluids inside veins of the deep sole thrusts are higher than those predicted by the Pilo-Pleistocene gradient for this subduction zone and correspond to a thermal anomaly. We suggest that the frontal Sicilian prism supported localized transient fluid flow of deep freshwater sourced from two different origins: a shallow one for fluids now trapped in the upper decollement, and a deep internal origin (6–10 km minimum depth) for the hot fluids channelized along the basal decollement and now trapped inside the sole thrust of the Mt. Scalpello duplex area. |
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