The Palaeozoic evolution of the Maures massif (France) and its potential correlation with others areas of the Variscan belt: a review

J-P. Bellot

A simplified Palaeozoic history for the Maures-Tanneron massif is proposed by using a review of lithology, tectonics, metamorphism and radiometric ages, and by making a comparison with its surrounding Variscan outcrops, mainly the Massif Central, the Pyrénées, Bohemian, the Alpine crystalline massifs, Sardinia, Corsica, and Italian massifs (Toscany, Catabria, and Silicia).

The Maures-Tanneron massif is formed of three zones. The western Maures includes Cap Sicié, Fenouillet, Maurette, and Loli units that correspond to Ordovician-Early Carboniferous low-metamorphosed metasediments devoid of HP rocks. These units belong to the southern external zone of the Variscan belt including Pyrénées, Mouthoumet, southern Montagne Noire, Catalanides, south Sardinia, and Tuscany. They were formed at the north-Gondwana margin. The central Maures includes Collobrières, Bormes, Cap Nègre Unit, and Cavalaire units that correspond to portions of a Precambrian to Early Ordovician supra-subduction zone lithosphere involved in continental subduction of probable Ordovician-Silurian age. These units belong to an intermediate zone of the Variscan belt including South Brittany, the Massif Central, central Sardinia, and Belledonne Alpine External massif. The eastern Maures-Tanneron, that includes Cavalières and Petites Maures units, corresponds to portions of an Ordovician back-arc lithosphere involved in the Silurian continental subduction. These units belong to an internal zone of the Variscan belt including the Massif Central, northeast Bohemia (?),Alpine External massifs, northeast Sardinia, Corsica, Tuscany, Sicilia, and Calabria.

These zones have possibly suffered early specific tectonics, but a common Carboniferous polyphased tectonics is inferred from superimposed metamorphic fabrics, composite foliations and various lineations. During the Tournaisian (350-340 Ma), WNW-verging thrusting (S1-L1) is responsible for stacking of units and a first regional IP/HP metamorphism. This event is well preserved in the western Maures. During the Middle-Upper Visean (340-330 Ma), SE-verging back-thrusts (S2-L2) reworked the nappes pile at the climax of the regional metamorphism. This event is well preserved in the central Maures. SE-verging thrusting evolved into, or combined with, a main orogen-parallel transcurrent tectonics (S3-L3) that produces upright folding and left-lateral shearing of the nappes pile (S0-1-2 foliation). During the Namurian (325-315 Ma), synorogenic extension thins the nappes pile by combining orogen-parallel, top-to-the NNW flat-lying shearing and dextral shearing (S4-L4), leading to exhumation of the central Maures. During the Upper Westphalian-Lower Stephanian (310-300 Ma), postorogenic extension produces a thermal overprint in the eastern Maures associated with orogen-parallel sinistral transcurrent tectonics, development of coal basins, granite emplacement, and rapid exhumation of eastern Maures. The orogenic evolution is achieved with deposition of Permian volcano-sedimentary deposits. All along the orogenic process, the Grimaud fault, that separates central and eastern Maures, plays a major role in the partitioning of deformation and seems to be the root of WNW-verging nappes.

The Paleozoic history of the Maures massif is interpreted as the formation of continental/oceanic rifts at the north-Gondwana margin during the Cambrian-Ordovician, their subduction at mantle depths during the Ordovician-Silurian, and their exhumation coeval with their thrusting during the Carboniferous collision between Gondwana and Baltica-Laurentia. Similarities of lithology and differences in tectonics between Maures and its surrounding Variscan areas may reflect the irregular shape of the north-Gondwana margin involved all along the orogenic process.