The most likely pre-Permian position of the Sardinia-Corsica block is based on paleomagnetic data (Gattacceca, 2001), in addition to structural and gravity data (Gueguen, 1995). It involves an anticlockwise rotation of ~70° coeval for both Sardinia and Corsica. The resulting Variscan structures trend NNE-SSW and imply continuity of Sardinia-Corsica into the Maures-Tanneron-Estérel massifs. Gravimetric data also suggest continuation of these massifs to the Alpine External crystalline massifs (Masson et al., 2000). For this hypothesis to be confirmed and extended to others isolated massifs, correlations of lithology, structures, and metamorphism between the Maures massif and their surrounding Variscan areas are required. New detailed correlations are proposed here based on the presented lithological and structural data. They also take into account previous correlations (Chabrier and Mascle, 1974, 1975; Westphal et al., 1976; Arthaud and Matte, 1977; Tempier, 1978; Ricci and Sabatini, 1978; Tongiorgi, 1978; Bagnoli et al., 1979; Chabrier and Mascle, 1979; Orsini, 1979; Bourrouihl et al., 1980; Rau and Tongiorni, 1981; Seyler, 1986; Rey et al., 1997; Matte, 2001; Elter et al., 2004). Our correlations attempt to relate the Maures massif to a Sicilia-Calabria-Tuscany-Sardinia-Corsica-Alpine External massifs-Bohemia branch on one hand, and to a Massif Central-Pyrénées-South Brittany-Spain branch on the other hand.
The Cap Sicié Unit displays a range of similarities with the Upper Ordovician of the axial zone of Pyrénées (pers. observation), the Ordovician-Lowermost Silurian formations of southern Sardinia (Tempier, oral communication), and the Upper Ordovician-Lower Devonian Réaumur Group of Vendée (Wyns et al., 1989).
Middle Silurian graptolites of black schist located at the top of the Maurette Unit are similar to graptolites of the southern Gondwana margin, including Portugal, Morocco, western Pyrénées, Sardinia (Gueirard et al., 1970 and reference therein). Fenouillet and Maurette Units are similar to the Barousse units of Pyrénées (Waterlot, 1969; Capdepont, 1982), the Silurian of the southern Montagne Noire (e.g., Arthaud, 1970; Vidal, 1952; Engel et al., 1981; Feist et al., 1994), the Ordovician-Silurian of Catalanides (Bourrouihl et al., 1980;), the Goceano s.l. Group of North central Sardinia (Conti et al., 2001), the Upper Ordovician Galleria Group of Corsica (Naud, 1979), the Bocchegiano formation and the Bitu Group of Tuscany (Gianelli et al., 1978; Bagnoli et al., 1979; Seyler, 1986; Elter and Pandeli, 1990; Pandeli et al., 1994). More precisely, Fenouillet and Maurette Units are very similar to the Sarrabus and Gerrei Units (San Vito formation) of Central Sardinia, noted 62-63-64 on the 1/250 000 geological map (Carmignani et al., 2001).
The lower part of the Loli Unit, that includes carbonated nodules associated with phosphorous nodules, is very similar to the Tournaisian of the Castelnau-Durban, Alet, and Cierp formations of Pyrénées (Perret, 1988; Chernoff1 and Orris, 2002), the Mont Peyroux and Serre formations of the southern Montagne Noire (Gèze, 1949; Vidal, 1952; Maurel, 1956; Andrieu and Matte, 1966; Feist and Schoenlamb, 1973; Vachard, 1974; Vignard, 1976; Engel et al., 1981; Feist et al., 1994), the Lowermost Carboniferous of the Mouthoumet massif (Bourrouihl et al., 1980), and the lowermost Carboniferous of Catalanides (Fontbole and Julivert, 1954). It could also correspond to the culm-type flysch of the Riu Gruppa and Castello Madusa Unit of central Sardinia (Conti et al., 2001), noted 61 on the 1/250 000 geological map (Carmignani et al., 2001), and to some parts of the Bretignolles formation of southern Vendée that also includes phosphorous nodules (Combe et al., 1985). These similarities suggest a correlation of the Loli Unit with other synorogenic flysch-like deposits that took place in a southern foreland basin. Difference in nappes verging, WNW in the Maures massif and South in the Pyrénées and the Montagne Noire, may reflect the irregular shape for the northern Gondwana margin involved in the Early Carboniferous collision.
The Collobrières volcano-sedimentary Unit displays a range of similarities with the Lower Ordovician (Arenig: 485-470 Ma) of South Brittany (Chauvel, 1968; de Groulard, 1982), the Middle Ordovician volcano-sedimentary formation of the southern Montagne Noire (Robardet et al., 1994), the volcano-sedimentary Ordovician of the Pyrénées (André, 1985; Nicol, 1997 and references therein), the Arenig of the Barradian terrane of Bohemia (Matte et al., 1990), and the Barbagia Unit of Central Sardinia (Seyler, 1986; Conti et al., 2001), noted 60-59-58 on the 1/250 000 geological map (Carmignani et al., 2001).
The Bormes Unit seems to be similar to the Precambrian basement (550-580 Ma) of the Moravian terrane of southeastern Bohemia (Matte et al., 1990 and references therein), and to Cadomian Canignou-type granite of the Pyrénées (Laumonier et al., 2004).
The Cap Nègre Unit, of mica-schist and orthogneiss of probable Precambrian to Cambrian age, displays a range of similarities with the Allemont series of the Belledonne Alpine External massif (Ménot, 1988), the Medium grade metamorphic complex of Central Sardinia (Conti et al., 2001), noted 56 on the 1/250 000 geological map (Carmignani et al., 2001), and the Micaschist Group of Tuscany (Elter and Pandeli, 1990).
The Cavalaire Unit displays a range of similarities with serpentinites and gabbros of the Medium grade metamorphic complex of Central Sardinia (Ricci and Sabatini, 1978; Seyler, 1986), the Chamrousse-Séchilienne unit of the Aar-Tavetsch-Gotthard (von Raumer et al., 1999) and Belledonne Alpine External massifs (Ménot, 1988).
This Cavalières Unit displays a wide range of similarities with the Lower Gneiss Unit of the Massif Central (Burg and Matte, 1978; Ledru et al., 1994; Matte, 2001), with the Münchberg-Tepla terranes of Bohemian (Matte et al., 1990), the High grade metamorphic complex (the Gallura Group; Naud, 1979) of northeastern Sardinia (Conti et al., 2001), and the Belgodere gneiss of central Corsica (Palagi et al., 1985). In particulal, zircon U-Pb dating on fresh eclogites and retrogressed eclogites have yielded 460 5 Ma and 352 3 Ma, respectively interpreted as the age of emplacement for the mafic protolith and the age for amphibolites facies metamorphism. These two
The Petites Maures Unit displays a wide range of similarities with the Upper Gneiss Unit of the Massif Central (Burg and Matte, 1978; Ledru et al., 1994; Matte, 2001), the Sila area of Calabria (Atzori et al., 1984; Liotta et al., 2004), and central Corsica (Bourrouihl et al., 1980). Cavalières and Petites Maures Units are very similar to units of the Alpine External massifs (von Raumer et al., 2002) of Argentera/Mercantour (Bogdanoff, 1986), and Aiguilles Rouges/Mont Blanc (Dobmeier, 1996).
Upper Permian basins of Provence display a wide range of similarity in facies and paleoenvironments with those from Argentera (Vinchon and Toutin-Morin, 1987), although similar Permian volcanism is described in northwestern Corsica (Vellutini, 1977).
Overall, the Maures-Tanneron massif is likely to exposed three main contrasting zones as part of three zones of the Variscan belt (Figure 5).
The western Maures includes Cap Sicié, Fenouillet, Maurette, and Loli units. It corresponds to Ordovician-Early Carboniferous metasediments, low-metamorphosed and devoid of HP rocks. These units belong to an external zone of the Variscan belt including Pyrénées, Mouthoumet, southern Montagne Noire, Catalanides, south Sardinia, and Tuscany. They were formed at the north-Gondwana passive margin.
The central zone includes Collobrières, Bormes, Cap Nègre Unit, and Cavalaire units that correspond to Precambrian to Early Ordovician magmatic rocks having experienced HP metamorphism and polyphased regional metamorphism. These units belong to an intermediate zone of the Variscan belt including South Brittany, the Massif Central, central Sardinia, and Belledonne / Aar Alpine External massifs. They likely correspond to pieces of a Cambrian back-arc lithosphere involved in the Ordovician-Silurian continental subduction.
The eastern Maures-Tanneron, that includes Cavalières and Petites Maures units, is made of Cambrian-Ordovician metagranites and Ordovician metagabbros having experienced Silurian HP metamorphism and Upper Visean partial melting. These units belong to an internal zone of the Variscan belt including the Massif Central, northeast Bohemia (?), Argentera/Mercantour and Aiguilles Rouges/Mont Blanc Alpine External massifs, northeast Sardinia, Corsica, Tuscany, Sicilia, and Calabria. They likely correspond to pieces of an Ordovician back-arc oceanic basin developed from a Precambrian lithosphere, and involved in the Ordovician-Silurian continental subduction.
Figure 5. An attempt of reconstitution
An attempt of reconstitution for the southern Variscan belt based on lithological and structural correlations between Maures massif and other Variscan areas (modified after Matte, 2001). Abbrevations of Variscan outcrops: B = Bohemia, V = Vosges, R = Rhenish, S = Sardinia, C = Corsica, M = Maures, MC = Massif Central, SB = south Brittany. Abbrevations of Variscan faults: SHF = Sillon Houiller fault, BF = Bray fault, SASZ = South Armorica shear zone.
Early Carboniferous WNW-verging thrusts (D1) associated with IP metamorphism, that characterizes western and central Maures, have been found in the central and northern Massif Central (Bouchez and Jover, 1986; Faure et al., 1997; Roig and Faure, 2000; Bellot, 2001), western Bohemia (e.g., Matte et al., 1990), Alpine External massifs (Fernandez et al., 2002), and Sardinia (344 ± 7 Ma, whole rock Rb-Sr; Ferrara et al., 1978; Elter et al., 2000; Conti et al., 2001).
Lower Visean (~345 Ma) SE-verging thrusts (D2) associated with HT-IP metamorphism, that also characterizes the central Maures, have been described in the southern Massif Central (Gébelin, 2004), eastern Bohemia (Matte et al., 1990), and Alpine External massifs (Guillot and Ménot, 1999).
Upper Visean sinistral/top-to-the SSW shearing (D3), that followed or combined to SE-verging thrusts in the Maures massif, is also documented in northeastern Sardinia (Elter et al., 1999) where modern top-to-the SE shearing coeval with partial melting corresponds to top-to-the SSW in a pre-Permian position of Sardinia.
Namurian synorogenic extension (D4), that characterizes the central Maures, trends NW-SE in the Massif Central (Burg et al., 1994; Faure, 1995; Roig et al., 2002), Bohemia (e.g., Matte et al., 1990), Maures (Morillon et al., 2000; Bellot et al., 2000), and Sardinia (Elter et al., 2000; Carosi and Palmeri, 2002), but trends SW-NE in Alpine External massifs (Guillot and Ménot, 1999) and in the Vosges massif (Rey, 1992).
The late Carboniferous (~300 ± 10 Ma) emplacement of I-type granite associated with heat advection then cooling, strike-slip brittle faulting, and deposition of coal basins (D5) characterize the eastern Maures. Equivalent of this event may be, on one hand, domes of the axial zone of the eastern Massif Central (e.g., Faure, 1995), Montagne Noire (e.g., Soula et al., 2001), Pyrénées (Vissers et al., 1995), and Catalonia. On the other hand, the eastern Maures granite seems to belong to an orogen-parallel K-granite belt extending from the Alpine External massifs (Aiguilles Rouges-Mont Blanc, Aar-Tavetsch-Gotthard massifs) (von Raumer et al., 1999), to the Corsica-Sardinia batholith (Orsini, 1979; Rossi and Cocherie, 1991; Gattacceca et al., 2004), and Calabria (Schenk, 1990 Gräßner et al., 2000). This granite belt, associated with extensive LP-HT metamorphism and partial melting, therefore reflects the NNE-SSW trending postorogenic extension of the Variscan lithosphere (Carmignani et al., 1994; Gattacceca et al., 2004).