Looking Under the Orogenic Lid—Assessing the European Basement Beneath the Alpine Wedge by U‐Pb Zircon Geochronology

Following continental collision, the distal European margin was overridden by the Alpine wedge and is now largely concealed beneath the mostly intact orogenic lid. Consequently, the geological evolution and nature of the hidden basement domains remain poorly constrained. We address this gap using 2,137 new LA‐ICP‐MS U‐Pb zircon ages from 16 samples representing indirect archives of the hidden European basement: (a) drill cores reaching the basement of the Bohemian spur beneath the northern wedge; (b) exotic boulders derived from the distal southern European slope and preserved in Jurassic–Eocene sediments (Gresten Formation, Buntmergelseries); and (c) Gresten Formation sandstones hosting the boulders. The latter two were basally accreted to the overriding Alpine wedge, transported northward, and are now exposed in the Ultrahelvetic nappe system. We find that basement drill core samples correlate well with exposed units of the Bohemian Massif. Provenance of the Ultrahelvetic boulders and sandstones is less straightforward, as zircon ages record Ordovician (∼467 Ma), early Variscan (380–350 Ma), late Variscan (350–310 Ma), and post‐Variscan Permian (280–270 Ma) magmatic events. These data are interpreted in the context of Penninic Ocean opening and closure. In the eastern study area, sediment was primarily derived from the Bohemian basement spur, whereas its influence decreases westward and detritus from the Tauern Window marginal high, and subordinately from Austroalpine units, becomes increasingly important. Overall, these results refine reconstructions of the concealed European margin and demonstrate that exotic boulders preserved in sediments retain pre‐collisional records, effectively lifting the orogenic lid.