Relationships among crustal structure, volcanism and strike–slip tectonics in the Lipari–Vulcano Volcanic Complex (Aeolian Islands, Southern Tyrrhenian Sea, Italy)

Abstract

The Lipari–Vulcano Volcanic Complex (LVVC, Aeolian Arc, Southern Tyrrhenian Sea, Italy) develops along a strike–slip fault system that bisects the Aeolian Arc. The LVVC crustal structure is investigated by applying seismic methods to two data sets: P-wavefronts generated by local and distant events constrain the shallow velocity structure; DSS data provide shape and depth of the main crustal discontinuities. The obtained velocity model shows that the LVVC shallow structure is characterized by the presence of two sharp lateral discontinuities. The northern discontinuity bounds a low velocity basin-like structure including the La Fossa Caldera and Mt. Guardia Caldera depressions. The southern discontinuity coincides with the southern boundary of a high-velocity diffractor located beneath the La Fossa Cone. Direct modeling of DSS data define three crustal discontinuities showing a complex geometry. The intra-crustal interfaces and the Moho discontinuity show an upheaval beneath the LVVC central sector. The estimated crustal velocities are lower than those generally reported for the continental crust. This feature is due to the high heat flux and fluid circulation affecting the LVVC area. The ratio between the thickness of the upper and lower crust and the presence of the Moho upheaval are consistent with that reported for continental areas affected by extensional strain. The collected geophysical data, combined with volcanological and structural information, indicate that: (a) the Mt. Guardia and La Fossa Caldera depressions represent the surface expression of a single structure whose formation is mainly due to tectonic processes; (b) the LVVC crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from arc-related to rift volcanism. In addition, results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio between magmatic overpressure and tectonic stress. This suggests a passive mechanism of mantle upwelling. The mantle upwelling is due the post-collisional normal strike–slip tectonics affecting the Aeolian Arc.