DETRITAL ZIRCON DATA FROM UPPER CARBONIFEROUS-PERMIAN STRATA OF THE LODÈVE BASIN, FRANCE: A PROVENANCE STUDY

The Lodeve Basin (southern France) preserves a thick and exceptionally complete record of sedimentation spanning Late Carboniferous through Permian time, and records tectonic and climatic events in low-latitude eastern Pangea. This study presents results of detrital zircon U-Pb geochronology data that address the provenance of Upper Carboniferous-Permian siliciclastic strata of the Lodeve Basin. Seven samples were collected from a variety of lithofacies, which include (in stratigraphic order): Pennsylvanian conglomerate of the Croix de Mounis Formation, Pennsylvanian deltaic and fluvial conglomerate and sandstone of the Pabau and Houilliere Formations, Lower Permian fluvial sandstone and mudstone of the Usclas, Loiras, Viala, and Rabajec Formations, and Middle-Upper Permian, oxidized, mud/siltstone redbeds of the Salagou Formation, previously interpreted as lacustrine strata.

New detrital zircon 207Pb/206Pb ages were obtained with the LA-MC-ICPMS at the University of Arizona Laserchron Facility. Detrital zircons (n=95) in seven samples yielded concordant ages including significant populations that correspond with the ages of regional tectonic events: 342-290 Ma (Variscan arc-continent collision and post-orogenic extension), 483-451 Ma (Variscan magmatism related to rifting and back-arc extension prior to the Hercynian collision), and a broader peak at 662-544 Ma (reworked basement terranes such as metasediments of the Montagne Noire Dome, or granites in the Armorican Massif). The relative proportions of these peaks shift through time, implying significant temporal changes in provenance from the Late Carboniferous through the Permian. For example, whereas Neoproterozoic ages (542-1000 Ma) predominate (82%) in the Pennsylvanian Croix de Mounis conglomerate, this population diminishes up-section in the Houilliere (21%) and Rabajec (24%) formations, then increases through the Permian Salagou Formation (24- 49%).

In combination with lithofacies observations, framework composition analysis, and geochemisty, these data will contribute to a more comprehensive understanding of provenance, and thus paleodispersal and paleogeographic patterns in this part of eastern tropical Pangea.