Geology and architecture of the Schistes Lustrés complex.
The Schistes Lustrés (SL) complex of Alpine Corsica occupies the eastern part of the belt and consists of a stack of variably metamorphosed units derived from the Western Tethys (e.g. Caron & Delcey, 1979; Jolivet et al., 1990; Lahondère, 1996) (Fig. 1.1a). The SL complex is juxtaposed to the continent-derived units of the Corsican margin (e.g. Tenda, Corte units), and is overlain by the very low-grade uppermost units (Fig 1.1a). Within the SL complex, four main homogeneous tectono-metamorphic units are defined on the basis of petrological data (e.g. Lahondère, 1996; Vitale Brovarone et al., submitted). They are folded together in a wide antiformal structure which post-dates their juxtaposition. Metamorphism ranges from the low-grade blueschist conditions (e.g. Lahondère, 1996; Levi et al., 2007; Vitale Brovarone et al., in prep) up to lawsonite eclogite conditions (Péquignot & Potdevin, 1984; Lahondère, 1996; Ravna et al., 2010; Vitale Brovarone et al., 2011a, b) (Fig. 1.1b). The lowermost structural position is occupied by the “Castagniccia” unit, which crops out in the axial culminations of the SL antiform in both the southern (i.e. the so-called Castagniccia region) and northern Alpine Corsica (i.e. the Cap Corse region). Notably, while all the metasediment-rich terranes of the southern and northern part of Alpine Corsica were traditionally ascribed to this unit (ref.), the definition of ‘Castagnoccia’ unit adopted here is somewhat restricted. This unit mostly consists of metasediments showing a temperature (T) of about 480°C in the southern Alpine Corsica and T of about 380°C in the Cap Corse region (Vitale Brovarone et al., submitted). As the Castagniccia unit mostly consists of monotonous metasediments, its paleogeographic origin is still under debate. The Castagniccia unit is overlain by the lawsonite-eclogite unit (Morteda-Farinole-Volpajola unit for the French authors) (Péquignot & Potdevin, 1984; Lahondèere, 1996; Vitale Brovarone et al., 2011a, b). This unit, which consists of metaophiolites, continental basement slivers and associated metasediments, originated from a Tethyan Ocean-Continent Transition zone (Vitale Brovarone et al., 2001b). This domain underwent Alpine metamorphism at ca.520°C and 2.3 GPa. The age of this HP event is debated, ranging from the Cretaceous (ca. 83 Ma; Lahondere & Guerrot., 2007, to the Eocene-Oligocene boundary (~ 35 Ma ; Brunet et al., 2000; Martin et al., 2011). The lawsonite-eclogite unit is overlain by a lawsonite-blueschist unit (Campitello-Morosaglia unit for the French authors) that, similarly to the underlying lawsonite-eclogite unit, consists of a complex lithological association referred to an inherited Ocean-Continent transition zone (Lahondère, 1996; Vitale Brovarone et al., 2011b). This unit equilibrated at T ~ 420°C (Vitale Brovarone et al., submitted) at P ~ 0.8 GPa (Lahondère, 1996). The uppermost structural position of the SL complex is occupied by a low-grade blueschist unit (Lento-Caseluna unit for the French authors). This unit is characterized by a typical distal oceanic sequence consisting of ophiolites and associated metasediments. The only continent-derived material found in this unit, whose origin is still under debate, is observed to the east of the Tenda massif, in the Santo Pietro di Tenda area (e.g. Caron & Delcey, 1979). Rocks from this unit equilibrated at around 350°C (Vitale Brovarone et al., in prep) and 0.6-0.8 GPa (Levi et al., 2007).
Figure 1.1. Simplified tectonic map of Alpine Corsica.
Modified after Miller et al., 2000. (b) Simplified tectono-metamorphic map of Alpine Corsica. Modified Vitale Brovarone (2011).