The ophiolites from the Balagne area

The Balagne nappe, that crops out over some 100 km2 southeast of lie Rousse, is characterized by a Middle to Late Jurassic ophiolite sequence and Its Late Jurassic-Late Cretaceous sedimentary cover. This nappe represents a fragment of the Ligure-Piemontese oceanic basin escaped from high-pressure metamorphism, differently from mos! of the other units from Alpine Corsica derived from the same oceanic domain. The Balagne nappe shows a large-scale structure consisting of a pile of units deformed in a large, broad sinforniwiih N-S axis. To the west and to the south; the Balagne nappe is thrust over the Hercynian basement and its Eocene sedimentary cover (Nardi, 1968a: Nardi et al,, 1978; Dallan and Nardi, 1984; Durand-Delga, 1984; Rossi et al., 2001; Marroni and Pandolfi, 2003). Between the Hercynian basement and the Balagne nappe the Parautochtonous units, mainly represented by Palascaunit qccui To the east, the main NNW-SSE-striking Ostriconi Fault separates the nappe from the north-south trending Tenda antiform, where the Variscan basement is exposed. Both this basement and its cover underwent Alpine metamorphism and deformation, and plunge eastwards beneath the Schistes lustres complex. In the Balagne nappe three units have been identified referred, from top to the bottom, as Navaccia, Alturaja and Toccone units. In turn the Navaccia units can be subdivided in San Colombano slices, Novella and Punta Corbajola subunits (Marroni and Pandolfi, 2003). The succession of the Balagne nappe can be fully reconstructed in the Navaccia unit where a complete stratigraphic succession from Jurassic ophiolites up to the Late Cretaceous sedimentary cover has been recognized (Bosma, 1956; Lacazedieu, 1974; Nardi etal., 1978; Dallan and Nardi, 1984; Durand-Delga, 1984; Marroni et al., 2000). The ophiolite sequence consists of an oceanic basement represented by mantle Iherzolites and gabbroic complex, locally covered by ophiolitic breccias. Both the basement and the ophiolitic breccias are topped by a volcanic sequence, consisting of massive and pillow lava basalts cut by basaltic dykes with porphyric texture. According to Dal Piaz et al. (1977), Durand-Delga et al. (1997) and Saccani (2003), the geochemical features of the basalts reveal an affinity typical of a crust developed in the first stage of the oceanic spreading. In the volcanic sequence, levels of continental-derived debris with quartz and extrabasinal carbonate fragments have been described by Durand-Delga et al. (1997). The basalts are covered by cherts (Callovian-Early Kimmeridgian; Conti et al., 1985; De Wever et al., 1987) and Calpionella Limestone (Tithonian-Early Berriasian; Lacazedieu, 1974; Routhier, 1956; Nardi, 1968b). The latter are characterized by the occurrence of continental-derived debris as recognized in the basalts (Durand-Delga et al., 1997).