Insights on the Permian tuff beds from the Saint-Affrique Basin (Massif Central, France): an integrated geochemical and geochronological study

International audienceThe Permian marks the transition between the end of the accretion of the supercontinentPangea and the beginning of its dislocation. In the Eastern Pangea intertropical domain (i.e. thepresent-day Western Europe), the late-Paleozoic (i.e. uppermost Carboniferous–Permian) history remainspoorly constrained due to the lack of precise radiometric data. This is particularly true for Permianbasins from the southern part of the FrenchMassif Central, making it difficult to determine correlationsbetween basins and therefore robust timings and constraints on the environmental and climateevents described in these basins, and to compare them with the larger-scale settings. This articlefocuses on the Saint-Affrique Basin, via an integrated petrological, geochemical and geochronologicalstudy of eight of the volcanic-ash levels interbedded in the sedimentary succession. It highlightsthe existence of two different groups of felsic volcaniclastic rocks. The first group, located at thebase of the basin and attributed to the Stephanian continental stage, is related to a late-orogenic volcanicsetting and corresponds to calc-alkaline trachy-andesitic tuffites that could not be dated dueto the lack of volcanic zircon. The second group, located towards the top of the succession, is composedof calc-alkaline dacitic ash beds and tuffites yielding Kungurian ages, i.e. late early Permian(Cisuralian, 283.5§0.6 to 273.01§0.14 Ma), and are attributed to a post-orogenic deposition setting.These ages show that the sedimentary filling of the basin is younger than hitherto expected (i.e. Artinskian,290.1§0.26 to 283.5§0.6 Ma). The elemental geochemistry, the presence of inherited detritalzircons and the Hf signatures of the volcanic ones indicate the involvement of an old (Proterozoic and older) basement in the magma genesis; this crustal contribution becomes more prominent towardsthe top of the sedimentary succession