Upper-Miocene Submarine Volcanism in the Strait of Sicily (Banco senza Nome) L. BECCALUVA P. COLANTONI P. DI GIROLAMO C. SAVELLI Istituto di Petrografia dell'Universitc~, Parma, Italy CNR - Ist. di Geologia Marina, Bologna, Italy Istituto di Mineralogia dell'Universit&, Napoli, Italy CNR - Ist. di Geologia Marina, Bologna, Italy ABSTRACT Two basaltic fragments dredged from a volcanic seamount in the Sicilian continental slope of the Strait of Sicily show petrochemical features typical of within plate alkalibasaltic lavas and IZ4Arage of about 10 m.y. The data represent the first volcanic evidence of Upper Miocene tensional tectonics in this sector of the African plate. INTRODUCTION Widespread Quaternary volcanic activity is known to have occurred in the Strait of Sicily continuing up to historical time (WASHINGTON, 1909;, RITTMAN et al., 1967; ROMANO, 1968; BARBERI et al., 1969; ZARUDZKI, 1972; COLANTONI et al., 1975; CARaPEZZA et al., 197,8). This activ- ity during Pleistocene times built up the Islands of Linosa and Pantelleria (BAR- BERI et aI., 1969; BIGAZZI et al., 1971) where the volcanic products are well exposed. In this paper we present K/Ar and petrochemical data on two basaltic fragments dredged, during the 1975 cruise of the R/V Bannok from a seamount near the Banco Senza Nome, in the northern part of the Strait of Sicily. These data represent the first evidence of an Upper Miocene volcanism in the area. GEOLOGICAL SETTING The strait of Sicily is a shallow water sea (mean depth: about 350 m), belonging Bull. Volcanol., Vol. 44-3, 1981 to the northern part of the African plate, floored by continental-type crust and its Mesozoic/Cainozoic sedimentary cover. The depth of the Moho discontinuity is 18-20 km in the ~Yi~l zone of the Sicily channel s.s., whereas it increases towards Africa and Sicily, reaching 3040 km under this latter (COLOMBI et al., 1973; GIESE and MORELLI, 1973). From the physiographic point of view about 35% of the area belongs to the continental shelf, 60% to the continental slope and 5% to deeper basins (up to 1700 m in depth) along graben structures (e.g., the Pantelleria rift), mainly in the axial zone of the Strait (BoRSETT1 et al., 1974; COLANTONI, 1975). Tensional or shear faults trending NW- SE are prec~ominant, which, together with the NE-SW conjugated system, have brought about a generalized horst-and- graben mosaic pattern in the area (COLAN- TONI and ZARUDZKI, 1973). Volcanic islands and seamounts, occupy- ing only < 1% of the area, are mainly aligned along these tectonic trends. The basaltic fragments studied in the present work were dredged from the NE slope of a volcanic seamount located east- ward of the Banco Senza Nome (Fig, 1), together with limestones of Eocene age which probably represent the sedimentary basement of the volcano (BORSETTI et al., 1974; COLANTONI, 1975). The dredgehaul started at 36 ° 51.7'N, 13° 07.0' E and ended at 36 ° 51.4' N, 130 06.9' E~ in waterdepths from 510 to 420 m.