Origin of associated metaophiolites and continental basement slivers.
Continent-derived rocks are commonly found within the HP units of the Schistes Lustrés of Alpine Corsica, (e.g. Caron et al., 1981; Caron & Delcey, 1979; Malavieille, 1983; Sedan, 1983; Péquignot & Potdevin, 1984; Lahondère, 1996; Vitale Brovarone et al., 2011b). The origin of this particular lithological association of ophiolitic and continental basement rocks, also extensively documented in the Western Alps (e.g. Dal Piaz, 1999; Beltrando et al., 2010, geology), has been matter of debate since a long time in both orogenic belts. In Alpine Corsica, during the last forty years, two main interpretations have been proposed: i) they originated as tectonic mixes during Alpine subduction (e.g., Sauvage-Rosemberg, 1977; Durand-Delga, 1978; Faure & Malavieille, 1981; Mattauer et al., 1981; Cohen et al., 1981; Malavieille, 1983; Durand-Delga, 1984; Péquignot & Potdevin, 1984), or ii) they correspond to the more distal part of thinned continental margins primarily associated or close to ophiolitic rocks (e.g. Lahondère et al., 1992; Lahondère, 1996; Lahondère and Guerrot, 1997). However, the strong metamorphic overprint and the lack of a detailed knowledge of passive margins left this debate open, with a general tendency to favour an orogent-related juxtaposition. Following a significant number of studies on present-day (e.g., Boillot et al., 1980, 1987; Péron-Pinvidic and Manatschal, 2009) and fossil Ocean-Continent Transition (OCT) zones (e.g., Florineth and Froitzheim, 1994; Froitzheim and Manatschal, 1996; Hermann and Müntener, 1996; Manatschal et al., 2006; Mohn et al., 2010), the second interpretation has been recently reconsidered in the HP units of both the Western Alps and Alpine Corsica (Beltrando et al., 2010; Vitale Brovarone et al., 2011b), pointing to the presence of preserved OCT zones. The term “OCT” refers to portions of rifted margins where “typical” continental and oceanic lithosphere are separated by regions of exhumed mantle rocks locally overlain by slivers of continental basement, which are known as ‘continental extensional allochthons’ (e.g., Manatschal et al., 2004) (Fig. 1.2). This juxtaposition is related to rift-related lithospheric thinning (e.g. Florineth and Froitzheim, 1994; Froitzheim and Manatschal, 1996; Hermann and Muntener, 1996; Manatschal et al., 2006; Péron-Pinvidic and Manatschal, 2009). Drilling along the Iberia/Newfoundland margins, and reflection and refraction seismic studies suggest that these domains may extend over >50% of the present-day rifted margins (Péron-Pinvidic and Manatschal, 2009).
Figure 1.2. Schematic representation of magma-poor rifted margin and Ocean-Continent Transition (OCT) zones.
