Seamount-Volcanic Island Transition and Evolution From Fissural to Central Activity Inferred by the Magnetic Modeling of Salina Island (Tyrrhenian Sea)

Volcanic islands represent the later stage of an early submarine volcanic activity and show different morphologies reflecting the geometry of shallow plumbing systems, magma output rate, gravitational instability, and erosive phases. Two end-member morphologies may be recognized: (a) rift-like elongated edifices and ‘stellate’ volcanoes and (b) cone-shaped, central-type volcanoes. While the evolution from early conical shapes to stellate shapes is relatively well known, the reverse is less constrained, commonly lacking geophysical and geological data to support it. We present magnetic forward and 3-D inverse models of the volcanic island of Salina (244-15 ka; Aeolian Arc, Southern Tyrrhenian Sea) to characterize its shallow plumbing system. The detected magnetic sources are interpreted as the crystallized portions of dykes and vertical conduits. The dykes mainly characterize the offshore of Salina Island, whereas subcircular conduits are located onshore. The results show that the early, mainly submarine phases of Salina concentrated along dykes following weakness zones of tectonic significance. As the volcanism proceeded, the subaerial activity focused on two main cone-shaped stratovolcanoes (Monte Fossa delle Felci and Monte dei Porri). The intersections among dykes and the progressive loading of volcanic products during the early growth of Salina are responsible for the transition from an early fissural basaltic activity to a later, basaltic to a last, more evolved central-type volcanism. We conclude that intrusions along pre-existing tectonic structures, dyke intersections, and loading processes related to the formation of a volcanic pile regulate the morphology and structural evolution of volcanic islands from the early, submarine phase to the later subaerial activity.