GNGTS 2013 - Atti del 32° Convegno Nazionale

activity ranges from the “Pomici di Base” (18 ky) and the “Pomici Verdoline” plinian eruptions, enabling the collapse of the Somma edifice and the consequent calderization. Three main plinian eruptions (“Mercato”, “Avellino” and “Pompei”) followed among 7900 B.C. and 79 A.D. The total magnetic field map of the Somma-Vesuvius volcano (Fig. 1) shows interpretative elements that have an indicated value for the trend of volcanites in the volcanic complex’s peripheral areas (Cassano and La Torre, 1987). A main sub-circular anomaly is centred on the volcano; two positive appendages diverge towards SE and SW. They might correspond to a great thickness of lava products, possibly in pre-existing depressions of the sedimentary basement of the graben of the Campania Plain. These products should have enhanced the occurrence of an elongated magnetized body, which tends to move towards the Naples Bay from the Vesuvius volcano towards Torre del Greco; an alternative explanation would be the presence of a strip of eruptive vents, settled on a system of NE-SW normal faults (Bernabini et al. , 1971; Finetti and Morelli, 1973). A new aeromagnetic map of the Vesuvius area has been produced (Paoletti et al. , 2005). It is dominated by a large dipolar anomaly related to the volcano, showing a southwards trending elliptical shape. A narrow anomaly is located on the western flank of the edifice and small anomalies are located on the south-eastern slope of the volcano. High frequency anomalies occur in the area surrounding the edifice, related to the high cultural noise of this densely inhabitated area. The Phlegrean Fields are a volcanic district surrounding the western part of the Gulf of Naples, where volcanism has been active since at least 50 kyr (Rosi and Sbrana, 1987), corresponding to a resurgent caldera having a diameter of 12 km and erupting the Campanian Ignimbrite (37 ky B.P.) and the Neapolitan Yellow Tuff (12 ky B.P.) deposits. A volcano- tectonic uplift of the caldera center is indicated by coastal sediments ranging in age from 10 to 5.3 ky B.P., cropping out in correspondence to the marine terrace of La Starza (Gulf of Pozzuoli). Gravimetric and magnetometric informations available for the Phlegrean Fields have been summarized (Cassano and La Torre, 1987), focussing on volcanological and structural reconstruction of the area. From north to south, the most important gravimetric elements are the positive anomalyrelatedtothecarbonatichorst of the Massico Mount, the negative anomaly of the Volturno graben, the positive gravimetric anomalies of Villa Literno and Parete. The total magnetic field map (Cassano and La Torre, 1987; Fig. 1) has evidenced a strong positive anomaly in the area of Monte di Procida, related to the weaker anomalies of the Procida Channel, Procida and Ischia. It may be related to considerable volumes of lavas, confirmed by the presence of trachybasaltic and latitic eruptive centres at Procida. Another large Fig. 1 – Total magnetic field map of the Somma-Vesuvius volcanic complex with sketch structural interpretation (modified after Cassano and La Torre, 1987). 87 GNGTS 2013 S essione 3.2