Aeromagnetic anomalies reveal hidden tectonic and volcanic structures in the Aeolian Islands, southern Tyrrhenian Sea, Italy

摘要

The structures of the Southern Tyrrhenian Sea active volcanoes have been successfully investigated through theuse of the magnetic data. Particularly, several high resolution aeromagnetic campaigns have been carried out onthe Aeolian Archipelago and its western limit by the Airborne Geophysics Science Team of Istituto Nazionaledi Geofisica e Vulcanologia of Roma. The results indicate that the volcanism is controlled by tectonic structuresboth at local and regional scale. The emplacement of magnetized bodies (e.g. volcanic conduits, dikes swarms,intrusions) is along or strictly correlated with this tectonic framework. The consolidation of highly magnetizedmaterial inside the volcanic conduits determines contrast with surrounding less magnetized material producingintense magnetic anomalies. Therefore, modeling of these sources is suggestive of the position and deep extentof eruptive vents, especially in the offshore area, where we do not know where future submarine activity maytake place (De Ritis et al., 2005). We present here a case study were the magnetic tool resolved a geologicalinterpretative problem that was not settled earlier. In fact, in the Calabria mainland, widespread, dacitic to rhyoliticpumices with calc-alkaline affinity of Pleistocene age (1-0.7 Ma) are exposed. The tephra falls are related toexplosive activity and show thickness decreasing from the Capo Vaticano area southeastward. The lithics indicatea source located not far from Capo Vaticano. The interpretation of the magnetic anomaly field together with theother geological and geophysical data has allowed to discover the presence of a previously unknown volcanicstructure (De Ritis et al., 2010), very close to the Calabria Western coast (Capo Vaticano). Aeromagnetic datacollected between the Panarea island and the Calabria arc highlight a WNW-ESE elongated positive magneticanomaly centered on the Capo Vaticano morphological ridge. Forward and inverse modeling show a magnetizedbody extending from the bathymetric surface to about 3 km of depth. The magnetic properties of such a body areconsistent with those of the medium to highly evolved volcanic rocks of the Aeolian Arc, i.e. dacites and rhyolites.The combined interpretation of the magnetic and available geological data reveal that (1) the Capo Vaticano WNW-ESE elongated positive magnetic anomaly is due to the occurrence of a WNW-ESE elongated sill; (2) such a sillrepresents the remnant of the plumbing system of a Pleistocene volcano that erupted explosively producing thepumice tephra exposed in Calabria; and (3) the volcanism is consistent with the Aeolian products, in terms ofage, magnetic signature, and geochemical affinity of the erupted products. The results indicate that such volcanismdeveloped along seismically active faults transversal to the general trend of the Aeolian Arc and Calabria block, inan area where uplift is maximized (4 mm/yr). Such uplift could also be responsible for fragmentation of the uppercrust and formation of transversal faults along which seismic activity and volcanism occur.