We address the transition between the Paleozoic Variscan and Alpine Mesozoic–Cenozoic cycles using tectono-stratigraphy and thermochronology. This transition unfolds through a multi-phase rifting history. An initial rifting stage occurred in the early Permian, followed in the early–middle Permian by a phase of transcurrent tectonics. This was succeeded by a period of erosion/non-deposition in the middle Permian. Crustal stretching in the Middle Triassic marked the onset of the Alpine cycle.

The manuscript re-analyses seismic data from the UPPLAND profile in the Fennoscandian Shield, focusing on P- and S-wave velocity models. Significant differences between prior and present models emerge in the lower crust and mantle and in the Moho depth. The new model suggests ca. 7.1 km s^-1 in the lower crust and 8.05 km s^-1 in the upper mantle, with Moho at 43–50 km. Two tectonic interpretations are proposed to explain these findings, emphasising the complexities of seismic data interpretation.