Subaerial-submarine evidence of structures feeding magma to Stromboli Volcano, Italy, and relations with edifice flank failure and creep

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Structural field data, including parameters of 109 sheets (strike: mostly N10-55°E, average dip angle: mostly 70–90°; average thickness: two peaks at 1.2 m and 4.2 m), and of 14 eruptive fissures and vents, as well as bathymetric and numerical data, suggest that Stromboli experienced the development of a volcanic rift zone across the cone summit, with a tendency to widen towards the lower submarine flanks, during the last 100 ka. Inside this rift zone, intrusive sheets mostly strike NE and become more abundant, more steeply dipping and thicker on approaching the rift axis. This rift persistence reflects the edifice's state of stress, with a NW–SE horizontal least principal stress, on the magma intrusion paths. After 13 ka ago, sheets mainly intruded with a horseshoe-shaped geometry in plan view along the boundaries of the northwestern unstable volcano flank, where four main lateral collapses occurred; during the last 13 ka they also intruded with a NE-strike across the volcano summit and the northeastern volcano flank. The horseshoe-shaped geometry is influenced by the lateral creep of the volcano flank, which provides space for intrusion along the transtensional boundaries of the unstable sector where thinner sheets were emplaced. When the collapse depression was filled up by new deposits, NE-striking thicker dykes emplaced across the northwestern volcano flank indicating a rapid re-establishment of regional tectonic forces across the cone. Unbuttressing due to the present Sciara del Fuoco depression, and ongoing flank creeping, can account for intrusions also inside the Sciara del Fuoco (the latter in 2007).