Journal of Volcanology and Geothermal Research, 53 (1992) 355-369 Elsevier Science Publishers B.V., Amsterdam 355 Structural setting of a typical alkali-potassic volcano: Roccamonfina, southern Italy Paolo Capuano, Rossella Continisio and Paolo Gasparini Dipartimento di Geofisica e Vulcanologia, UniversiM Federico II, Largo S. Marcellino 10, 80138 Naples, Italy (Received July 17, 1991; revised and accepted February 17, 1992) ABSTRACT Capuano, P., Continisio, R. and Gasparini, P., 1992. Structural setting of a typical alkali-potassic volcano: Roccamonfina, southern Italy. J. Volcanol. Geotherm. Res., 53: 355-369. The structural setting of Roccamonfina volcano is reconstructed using gravity and magnetotelluric plus time domain electromagnetic data. A 887 m deep bore-hole, drilled within the summit caldera, was utilized to constrain the inversion models. Roccamonfina volcano appears located at the intersection of two east-northeast- and north-trending narrow gra- bens. The location of historical seismic activity indicates that at least one of them (the north-trending) is still active. MT + TDEM apparent resistivity curves show the existence of a ubiquitous conductive layer which includes hydrother- mally altered volcanic rocks and flysch formations. The average thickness of the volcanic sequence is about 800-1000 m. No evidence was found for the presence of the intracrustal magrnatic reservoir which is required to justify the chemistry of magmas erupted during the second and final stage of activity of the volcano. Introduction Alkali-potassic volcanoes occur in two dif- ferent tectonic settings: continental rifts or grabens and island arc structures where they generally are found above the deepest earth- quake foci. Roccamonfina is a Quaternary volcano be- longing to the Roman comagmatic province. It is located at the northern edge of the Cam- pania plain (Fig. 1 ), which hosts also Mr. Ve- suvius, Campi Flegrei and Ischia. Barberi et at. ( 1973 ) suggested that these volcanoes are lo- zone, although no seismic evidence of a down- going lithospheric slab exists. The activity of the Roccamonfina volcano started with the eruption of high-K magmas (HKS) which built an about 1000 m high strato-volcano. The latest phases of activity were fed by low-K magmas (LKS), ranging in compositionfrom trachy-basalts to alkali- trachytes, which appear to form a differentia- tion series evolved inside a crustal magmatic reservoir (Ghiara and Lirer, 1976). This ac- tivity probably continued till shortly before the eruption of Campanian ignimbrite (about 30