Isotopic dating of adularia-bearing epigenetic mineralizations: I. Saar-Nahe region/Southwest Germany
Mertz, Dieter F.; Lippolt, Hans J.; Müller, Gerhard
published: Mar 8, 1990
manuscript accepted: Oct 2, 1989
manuscript received: Feb 24, 1989
ArtNo. ESP147050201011, Price: 29.00 €
Abstract Isotopic age determinations (40Ar/39Ar, Rb/Sr) on hydrothermally formed K-feldspars (adularia) from epigenetic vein mineralizations in the Saar-Nahe region (SW Germany) yielded age values of 224 Ma and 219 Ma. This places mineralizing activities in this region in the Upper Triassic. The geological significance of the isotopic data is assured by age concordances between a) the Rb/Sr and K/Ar systems, b) petrographically different adularia types and c) adularia from different locations. According to chemical and X-ray structural investigations, the adularia are pure K-feldspars with Or contents > 98 mol.% with a relatively high degree of Al,Si disorder. Due to the paragenetic position of the adularia within the sequence of the Saar-Nahe mineralizations as well as to the corresponding experimentally determined time marks, a considerable number of these mineralizations can be attributed to a syn- to post-Triassic age. A genetic relationship to the Permian magmatism of the Saar-Nahe region does not exist for these mineralizations in the sense of a post-magmatic sequence. This conclusion is supported by the 87Sr/86Sr variation of paragenetic calcites of 0.7103 ± 0.0006 which is significantly higher than the Sr initial ratios of the Permian magmatic rocks. The mineralizing events confirm an Upper Triassic super-regional hydrothermal phase whose existence has already been established for Western and Southern Europe and can now be extended to Central Europe.