Low-temperature thermochronology of the flanks of the southern Upper Rhine Graben

The Upper Rhine Graben (URG) is the most perceptible part of the European Cenozoic Rift System. Uplifted Variscan basement of the Black Forest and the Vosges forms the flanks of the southern part of the graben. Apatite and zircon fission-track (FT) analyses indicate a complex low-temperature thermal history of the basement that was deciphered by inverse modelling of FT parameters. The models were tested against the observed data and independent geological constraints. The zircon FT ages of 28 outcrop samples taken along an E-W trending transect across the Black Forest and the Vosges range from 136 to 312Ma, the apatite FT ages from 20 to 83Ma. The frequency distributions of confined track lengths are broad and often bimodal in shape indicating a complex thermal history. Cooling below 120°C in the Early Cretaceous to Palaeogene was followed by a discrete heating episode during the late Eocene and subsequent cooling to surface temperature. The modelled time-temperature (t-T) paths point to a total denudation of the flanks of URG in the range of 1.0-1.7km for a paleogeothermal gradient of 60°C/km, and 1.3-2.2km for a paleogeothermal gradient of 45°C/km since the late Eocen