GNGTS 2014 - Atti del 33° Convegno Nazionale

14 GNGTS 2014 S essione 3.1 buried volcanic structures and overlying Quaternary deposits of the south-eastern offshore of the Ischia Island have been discussed to highlight their implications on the marine geophysics and volcanology. The Ischia Bank is a large and flat relic volcanic edifice with steep slopes, merging on the continental shelf. The age of this monogenic volcano is unknown, lacking a direct datation of its basement. It represents the eruptive center of the pyroclastic fall cropping out onshore in the eastern sectors of the island, ranging in age from 8 to 6 ky B.P. In the eastern Ischia offshore relict volcanic edifices, mostly formed by hialoclastites, have been investigated through high- resolution seismics. They represent remnants of hydro-magmatic volcanic vents and suggest a subaqueous emplacement. Regional seismic sections in the south-eastern Ischia offshore, across buried volcanic structures, have been presented and discussed (Aiello et al. , 2012). In the case of Ischia island, the occurrence of isolated volcanic bodies, such as intrusions, domes, volcanic necks and tabular, acoustically transparent seismic units, makes the sequence stratigraphic approach particularly complex for the geological interpretation of seismic profiles. In the Ischia offshore the volcanic bodies, such as the lava flows, the domes and the intrusions, cannot be investigated in their inner part through the reflection seismics, because they are acoustically transparent. On the contrary, the seismic facies of the pyroclastic edifices and/or the buried pyroclastic deposits may be detected, due to their internal stratification. The marine sedimentation includes both the contribution of alluvial and marine sediments and the input of volcanites and volcaniclastic deposits originated from the eruptions of Ischia and Procida volcanic complexes. Deep sea depositional systems in Ischia island are well developed in correspondence to the Southern Ischia canyon system (Aiello and Marsella, 2014). The canyon system engraves a narrow continental shelf from Punta Imperatore to Punta San Pancrazio, being limited southwestwards from the relict volcanic edifice of the Ischia bank. While the eastern boundary of the canyon system is controlled by extensional tectonics, being limited from a NE-SW trending (counter-Apenninic) normal fault, its western boundary is controlled by volcanism, due to the growth of the Ischia volcanic bank. Submarine gravitational instabilities also acted in relationships to the canyon system, allowing for the individuation of large scale creeping at the sea bottom and hummocky deposits already interpreted as debris avalanche deposits. High resolution seismic data (Subbottom Chirp) coupled to high resolution Multibeam bathymetry collected in the frame of the Stromboli geophysical experiment aimed at recording seismic active data and tomography of the Stromboli island are here presented. The Stromboli geophysical experiment has been already carried out based on onshore and offshore data acquisition in order to investigate the deep structure and the location of the magma chambers of the Stromboli volcano. A new detailed swath bathymetry of Stromboli islands is here shown and discussed to reconstruct an up-to-date morpho-bathymetry and marine geology of the area, compared to the volcanologic setting of the Aeolian Arc volcanic complex (Aiello et al. , 2014). Due to its high resolution the newDTMof the Stromboli island has given interesting information about the submerged structure of the volcano, particularly about the volcano-tectonic and gravitational processes involving the submarine flanks of the edifice. Several seismic units have been identified based on the geologic interpretation of SubbottomChirp profiles recorded around the volcanic edifice and interpreted as volcanic acoustic basement pertaining to the volcano and overlying slide chaotic bodies emplaced during its complex volcano-tectonic evolution (Fig. 1). They are related to the eruptive activity of Stromboli, mainly poliphasic and to regional geological processes involving the geology of the Aeolian Arc (Aiello et al. , 2014). Some new insights about the morphobathymetry, marine geology and seismic stratigraphy of the Stromboli submarine area are discussed through Multibeam and seismic data. New bathymetric maps coupled with seismic interpretation provide new data on the submarine structure of the volcanic edifice of the Stromboli island. Eight subaerial volcanic edifices are located in correspondence to the Aeolian Arc. While the most part of these volcanoes are supplied by fluid magmas genetically related to the Ionian lithospheric slab, other ones