The influence of the Variscan belt collapse on the onset of the Paris Basin

Abstract

At the scale of the European peri–Tethyan basins, the Paris Basin is one of the largest intracratonic sedimentary repositories within the collapsing post-Variscan continental crust. However, the limited availability of petrochronological constraints on its late Carboniferous detritus has hindered the development of an accurate model for the timing and tectonic evolution of the Paris Basin’s early subsidence stages. We present a new set of U–Pb ages and trace-element data for ∼1000 detrital zircons and apatites from four late Carboniferous and early Permian sedimentary units collected in two sub–basins of the Saxo–Thuringian and Armorican zones of the Paris Basin. The new U–Pb and geochemical datasets provide evidence for the diachronous nature of subsidence throughout the base of the Paris Basin from ∼320–315 Ma in the Saint–Die sub–basin (Saxo–Thuringia Zone), to ∼300 Ma in the Brecy sub–basin (central Armorican Zone / Moldanubian Zone). The detritus of the Saint–Die sub–basin yields petrochronological signals typical of the Saxo–Thuringian zone and shows a stable provenance record through the late Carboniferous and early Permian. By contrast, the detritus of the Brecy sub–basin shows an up–sequence increase in complexity. The early Permian sandstone of the Brecy basin yields evidence of a large influx of high– and low–grade metamorphic grains, together with a mixed mafic–felsic igneous detritus, which is consistent with a large–scale unroofing and reworking of the northern Armorican and Central French Massif at ∼310–300 Ma, and seems to correspond to the petrochronological record of the collapse of the Variscan belt. Hence, we argue that the previously postulated intracratonic nature of the Paris Basin does not fully describe the tectonic events that led to its formation. In this contribution we have observed that a geological model describing the onset of the Paris Basin as controlled by late Carboniferous Variscan lithospheric instability in French Variscides is in broader agreement with the new petrochronological data.