The Ardenne

This overview paper focuses on the Ardenne region in its broadest sense, encompassing both the Ardenne Allochthon and the Brabant Massif. The first part delves into the Lower Paleozoic Caledonian cycle, while the second part focuses on the Upper Paleozoic Variscan cycle. The Ardenne boasts a diverse array of sedimentary rocks, with many well-described and easily accessible sections or quarries preserving these formations. Several of these sections are globally renowned for their stratigraphic or sedimentological significance. Situated west of the Rhenish Massif and south of the northern Variscan front, the Ardenne Allochthon comprises Lower Paleozoic inliers (Stavelot-Venn, Rocroi, Givonne, Serpont) belonging to the Avalonia microplate, likely influenced by both the Caledonian and Variscan
orogenies. In contrast, the Cambro-Silurian Brabant Massif, also part of Avalonia, lies north of the Variscan front and remains unaffected by Variscan orogeny. Stratigraphic and paleoenvironmental analyses suggest that the Brabant Massif and Ardenne inliers once constituted a single sedimentary basin. Divergent subsidence patterns, particularly evident during the Cambrian, imply distinct basement types: rift and rift shoulder. The Brabant-Ardenne basement records four well-dated episodes of magmatism. Geochemical analysis indicates post-collisional or intracontinental orogenic potassic
magmatism sourced from ancient lithospheric crust for felsic episodes, while mafic tholeiitic episodes suggest predominantly asthenospheric mantle origin. A Large Igneous Province (LIP) association is proposed for the bimodal magmatism across the Ardenne and is supported by zircon evidence from Ardennian unconformity conglomerates, correlating with mafic/felsic rocks of the Southern Taunus and Harz in the eastern Rhenish Massif. Geophysical data reveal that the basements of southwest Brabant, Ardenne, and Rhenish Massif extend southeastward from the Midlands microcraton. It is hypothesized that the southern rim of Avalonia comprises a metacratonic Gondwana basement separated from the West African craton during the opening of the Rheic Ocean. Finally, a geodynamic model is proposed, integrating these findings to contextualize the Brabant-Ardenne within the broader Rheno-Hercynian
realm. The Variscan sedimentary-tectonic cycle took place in the northern sector of the Rheic Ocean during the Upper Paleozoic. Beginning in the Early Devonian with renewed sedimentation on the southern periphery of the Old Red Sandstone Continent, it ended in the Late Carboniferous with the Variscan orogeny, contributing to the formation of the Pangea supercontinent. This chapter provides a comprehensive overview of Devonian and Carboniferous stratigraphic units, delineating their formations, interrelations, and paleoenvironments. Lastly, it addresses the Variscan orogeny, which molded the Lower Paleozoic basement inliers and their Devonian to Carboniferous cover into a fold-and-thrust belt geometry.