Old orogen – young topography: Linking rift evolution, thermal overprinting, and apatite (U-Th)/He thermochronology in the Black Forest and Vosges Mountains

Investigating the thermal evolution of continental rifts is essential for understanding how lithospheric extension, surface uplift, and exhumation are recorded in the shallow crust. However, interpreting low-temperature thermochronological data in rift settings remains challenging, particularly where exhumation magnitudes are small and geothermal gradients are elevated and spatially heterogeneous. In such environments, cooling ages may reflect a combination of regional tectonic processes and localized thermal overprints, complicating the reconstruction of rift-related exhumation histories. Here, we present new apatite (U-Th)/He ages from the Black Forest and Vosges Mountains, integrated with published apatite fission-track data, to reconstruct the Cenozoic thermal evolution of the Upper Rhine Graben rift flanks. Sampling along multiple transects perpendicular to the rift axis provides the spatial resolution required to distinguish regional cooling trends from localized thermal perturbations. The data and time-temperature modeling indicate that maximum temperatures were reached during the Late Cretaceous to Paleocene, approaching but generally not exceeding the apatite partial retention and annealing zones (PRZ/PAZ). Cooling occurred in three main phases during the Late Cretaceous, Eocene, and Oligocene, resulting in pronounced single-grain apatite (U-Th)/He age dispersion. A regionally pervasive Miocene reheating event is not required to explain the observed age patterns. Instead, the data are best explained by a combination of incomplete resetting, radiation damage effects, and localized hydrothermal influences in the vicinity of normal faults. These results highlight the importance of integrating multiple low-temperature thermochronometers with high spatial sampling density to disentangle tectonically driven cooling from localized thermal overprinting in intracontinental rift systems.