Deformational features of the Ustica volcanic island in the Southern Tyrrhenian Sea (Italy)

Macro- and meso-structural analyses of the Ustica rock formations lead to an interpretation of most of the deformational features that define the structural framework of the island. A regime of sinistral transtension seems to be the best explanation for the most significant fault associations. This regime is consistent with the kinematic model for the Tyrrhenian back-arc-accretionary wedge system proposed by Doglioni (1991). A caldera collapse in the northern part of the island provides the major source of volcanotectonic deformation while cracks, open or filled by clastic and/or volcanic material, were formed by downslope block sliding mostly along the southern coastline. Joints in indurated surge deposits were generated by brittle deformations induced by gravity after deposition, rather than by tectonism.