Apatite Fission Track Dating of the Central European Basement. Postvariscan Thermo-Tectonic Evolution

Abstract

Apatite fission track (FT) dating reveals the thermotectonic evolution of rocks below 140°C. It is applied to 75 samples from the Central European crystalline basement in the Oberpfalz, Schwarzwald, and Vosges regions. Most intensively studied are the areas around the potential target locations for the deep continental drilling project KTB near Erbendorf/Oberpfalz and Haslach/Schwarzwald. The measured apatite FT ages range from 30 to 200 Ma. For nearly all samples, except for a few samples in the Oberpfalz, confined track length measurements indicate steady cooling below 140°C. The measured apatite FT ages date the cooling to ca. 100°C. In addition, projected track length measurements allow one to calculate the cooling age to ca. 60°C. Consequently, for each sample the temperature vs time path can be reconstructed. Since for most of the areas the cooling is due to tectonic uplift, uplift rates between 0.02 and 0.08 km Ma⁻¹ can be inferred. Block faulting prevails in the Schwarzwald. In some cases elevated palaeo-thermogradients must be assumed in order to reconcile the apatite FT data. Notably, the Steinwald Höhenzug, in the southwestern extension of the Eger-Graben, and the Haslach area were likely geothermally active during the Tertiary. The selected KTB location near Windisch-Eschenbach/ Oberpfalz seems to have experienced uniform uplift (0.05 km Ma⁻¹) without significant thermal disturbance during the last 60 Ma.