MORPHOSTRUCTURAL FEATURES AND SOME PETROCHEMICAL DATA FROM THE SUBMERGED AREA AROUND ALICUDI AND FILICUDI VOLCANIC ISLANDS (AEOLIAN ARC, SOUTHERN TYRRHENIAN SEA)

During several oceanographic surveys of the submarine area surrounding the Aeolian islands, attention was focused on the western sector, which is occupied by the Alicudi and Filicudi volcanic complexes. Several kilometres of electroacoustical and high-resolution seismic reflection profiles and several submarine samples, collected by dredging or directly by diving, allowed us to draw the following conclusions on the morphostructural and volcanological evolution of the area: (1) the structural evolution of the volcanic complex of Alicudi, a regular subconical volcanic edifice with a stable feeding system, is not influenced by regional tectonics. A slight southeastward migration of the volcanic focus is evident in the activity of the subaerial summit of the complex, where remnants of the oldest submarine volcanic portions lie northeast of the more recent subaerial apparatus; (2) unlike Alicudi, the Filicudi complex is strongly influenced by NW-SE-oriented structural lineaments. The most important feature is represented by a volcanic belt which, starting from the subaerial volcanic centres of the island and passing northwest through the submarine centres of La Canna and Banco di Filicudi, continues down to the ''Alicudi North'' seamount for a total length of about 35 km. A submerged marine terrace (average depth of 100 m) surrounds ail the coast line of Filicudi and covers the top of the Banco di Filicudi indicating that almost all the volcanic activity was coeval, the only exception being represented by La Canna centre; (3) the structural evolution of the large area between the Filicudi and Salina islands is affected by two different structural systems, oriented NNE-SSW and NW-SE, respectively. The only volcanic manifestation of this area is represented by the NW-SE oriented ''Filicudi North'' seamount which, along with the ''Alicudi North'' seamount, must be considered to be among the oldest volcanic edifices in the whole area; (4):petrochemical data for two samples from the submarine portion of the oldest Alicudi edifices show calcalkaline character and compositions ranging from basalt to basaltic-andesite, which are similar to those of the subaerial rocks. The submarine samples of Filicudi have geochemical patterns indicating a good similarity with the calcalkaline trend of the Filicudi subaerial rocks; the only exception is represented by samples from La Canna, which show high-potassium calcalkaline features. The evolution trends are mainly controlled by crystal fractionation processes and subordinately by assimilation of crustal rocks.