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

The Lipari-Vulcano Volcanic Complex (LVVC, Aeolian Are, Southern Tyrrhenian Sea, Italy) develops along a strike-slip fault system that bisects the Aeo lian Are. The LVVC crustal structure is investigated by applying seismic me thods 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 l ateral discontinuities. The northern discontinuity bounds a low velocity ba sin-like structure including the La Fossa Caldera and Mt. Guardia Caldera d epressions. The southern discontinuity coincides with the southern boundary of a high-velocity diffractor located beneath the La Fossa Cone. Direct mo deling of DSS data define three crustal discontinuities showing a complex g eometry. The intra-crustal interfaces and the Moho discontinuity show an up heaval beneath the LVVC central sector. The estimated crustal velocities ar e lower than those generally reported for the continental crust. This featu re is due to the high heat flux and fluid circulation affecting the LVVC ar ea. The ratio between the thickness of the upper and lower crust and the pr esence of the Moho upheaval are consistent with that reported for continent al areas affected by extensional strain, The collected geophysical data, co mbined with volcanological and structural information, indicate that: (a) t he Mt. Guardia and La Fossa Caldera depressions represent the surface expre ssion of a single structure whose formation is mainly due to tectonic proce sses; (b) the LVVC crustal structure and the evolution of the volcanism are consistent with those recognized in zones of transition from are-related t o rift volcanism. In addition, results of a preliminary mechanical analysis based on the available structural data indicate low values of the ratio be tween magmatic overpressure and tectonic stress. This suggests a passive me chanism of mantle upwelling. The mantle upwelling is due the post-collision al normal strike-slip tectonics affecting the Aeolian Arc. (C) 1999 Elsevie r Science B.V. All rights reserved.