TOMO-ETNA marine geophysical data highlight the crustal structure offshore Etna volcano

The polyphasic emplacement of Etna volcano and its relation with the complex geodynamic setting of southern Italy is still object of debate, largely due to the lack of adequate resolution data for imaging the mid-shallow crustal seismo-stratigraphic and structural pattern of the area. The huge amount of geophysical data acquired during the “TOMO-ETNA” experiment of the FP7 Project “MED-SUV”, furnishes a unique opportunity to better constrain the geological knowledge of such a highly populated area, affected by high seismic and volcanic risks. We adopted a multidisciplinary geophysical approach for studying the crustal characteristics of the morphological high recognized offshore Mt. Etna, between the towns of Aci Trezza and Acireale, interpreted as the underwater portion of a shield volcano (Chiocci et al., 2011), pertaining to the Acireale Synthem (ca 220 - 130 ka) of Etna volcano (Branca et al., 2011). This area represents a pivotal point for understanding the evolution of the volcano since it marks the changing between a roughly WNW-ESE scattered tholeiitic (Aci Trezza Synthem, ca 500 ka) to a NNW-SSE oriented transitional to Na-alkaline magmatism (Acireale Synthem). This abrupt change could be related to large scale rearrangement of tectonic stress affecting this area. The geological complexity of the area required a remarkable effort for processing several multi-channel seismic reflection profiles, to highlight both shallow and deep primary reflections. The structural pattern of the area is well imaged, allowing us to define different phases and stiles of tectonic deformation. Gravity and magnetic data processing focuses on providing information about density and magnetic susceptivity of the bodies previously identified on the seismic profiles, strengthening the geological interpretation. Several high density wide bodies rising up below this area were detected, likely pertaining to the above mentioned eruptive phases. Besides, the presence of volcanics in correspondence and few tens of meters below the seafloor has been detected as well, related to shallow intrusions and lava flows of the shield volcano and locally, to the most recent eruptive phases. By comparing our seismic reflection profiles, which clearly image the geometry of the fault systems, with the wide literature concerning the tectonic pattern of the area, we clearly identify the coexistence of both compressive and extensive structures possibly related to dominant dextral transtensive tectonics and large-scale gravitational instability (Chiocci et al., 2011). Transtensive related structures may represent the possible way for magma rising at Etna volcano. Branca S., Coltelli M., Groppelli G., Lentini F. (2011) Geological map of Etna volcano, 1:50,000 scale. Ital. J. Geosci., 130 (3), 265-291, DOI: 10.3301/IJG.2011.15. Chiocci, F. L., Coltelli, M., Bosman, A., Cavallaro, D., 2011. Continental margin large-scale instability controlling the flank sliding of Etna volcano. Earth and Planetary Science Letters 305, 57–64. DOI:10.1016/j.epsl.2011.02.040.