The Graham and Terrible volcanic province (NW Sicilian Channel): gravimetric constraints for the magmatic manifestations

A few kilometres off the SW coast of Sicily lie the shallow banks of Graham, Terrible and Nerita. These morphological reliefs are affected by two lithospheric scale, N–S trending tectonic lineaments known as Capo Granitola to the west and Sciacca to the east. Within the Graham and Terrible banks, several volcanic edifices have been documented and mapped using high-resolution bathymetry and seismic profiles. Three groups of volcanic features can be distinguished: (i) a cluster of N–S aligned volcanic cones in the Graham Bank, generally developed along the Capo Granitola fault, (ii) a series of poorly developed volcanic constructs roughly positioned along the northern edge of the Terrible Bank, and (iii) a few isolated volcanic centres located north of the Terrible Bank, within an undeformed zone. Here we present a 2-D gravimetric model, constrained at shallow levels by an integrated seismic dataset, which we use to interpret the distribution of magmatic manifestations in this sector of the Sicilian Channel. At the Graham Bank, where there are no significant positive gravity anomalies, the magmatic material seem to migrate to the surface along the Capo Granitola lithospheric fault, without the presence of a shallow magma source. In the Terrible Bank, where there is a well-defined positive gravity anomaly, the model implies the presence of a shallow magma chamber from which sea-floor volcanic constructs are fed upwards along cracks. The origin for the volcanic cones located between the two fault systems is more problematic, as no significant structural discontinuities were identified in this area from the available seismic data. However, the presence of a potential wide sill complex suggests that it facilitated lateral magma flow from source to surface over lateral distances of tens of kilometres.