The complex history of the Permo-Carboniferous Graissessac-Lodève Basin (France) revealed by detrital zircon and apatite

The Graissessac-Lodève Basin (southern France) contains a thick and very well preserved record of Late Carboniferous to Permian continental sediments. These sediments are remnants of a complex erosional history of the Variscan orogen and post-orogenic extension, as well as a record of the local geotectonic history of southern France. The use of original isotopic detrital zircon and apatite data revealed the provenance of the siliciclastic strata. The detrital zircon age populations and sandstone compositions in the Permian strata, which reflect the rapid exhumation and unroofing of the Montagne Noire dome, are determined by the ages and compositions of units forming the Montagne Noire metamorphic core complex to the west of the basin. The Cambrian to Archean zircon ages are most likely recycled detritus derived from the Early Paleozoic sedimentary cover and Neoproterozoic to Early Cambrian shales that formerly covered the Montagne Noire dome. Ordovician detrital zircon ages may indicate orthogneiss units of the dome. The youngest detrital zircon suite, ranging in age from ca 285 to 320 Ma, reflects erosional products of Carboniferous to Permian granites of the Montagne Noire axial zone. The latter zircon population is absent from Carboniferous-aged strata, but was found throughout the studied Permian strata. These results suggest that the young granite suite was exposed during early Permian time, reflecting uplift of the southern Montagne Noire during post-orogenic extension. Detrital apatite data from the Permian strata show that the last thermal event in the hinterland of the Graissessac-Lodève basin occurred in the Upper Carboniferous.