U-Pb ages of magmatic and detrital zircon of the Döhlen Basin: geological history of a Permian strike-slip basin in the Elbe Zone (Germany)

摘要

The post-orogenic evolution of Variscan Central Europe is characterized by the formation of numerous basins. The early Permian Dohlen Basin is located in the Elbe Zone (Germany) and is bordered by metamorphic rocks of the Erzgebirge and numerous Variscan magmatic complexes. The NW-SE-oriented basin is evidence for a major rearrangement of stress fields during the post-Variscan reactivation of fault zones in Central Europe. Eleven samples of magmatic rocks and sediments have been analyzed with respect to their U-Th-Pb isotope ratios and geochemical composition. Of three magmatic samples (two tuffs, one trachyandesite), we analyzed 170 zircon grains. The Unkersdorf Tuff of the Unkersdorf Formation gave an age of 294 +/- 3 Ma (Upper Asselian to Sakmarian), whereas a trachyandesite of the same formation was dated at 293 +/- 5 Ma (Lower Artinskian to Lower Asselian). The Wachtelberg Ignimbrite (Upper Bannewitz Formation) showed an age of 286 +/- 4 Ma (Artinskian to Lower Kungurian). As the first study, we also analyzed 984 detrital zircon grains of nine Late Paleozoic Central European sandstone and conglomerate samples of the Niederhaslich Formation and the Bannewitz Formation with respect to their U-Pb age composition. All sediments but two yielded two distinct age groups between 295 and 340 Ma and 530-750 Ma, as well as a minor amount of Precambrian zircon ages. Geochemical data points to an active margin setting with developing strike-slip basins. The data suggests a c. 10 Ma lasting basin formation during the second culmination of volcano-tectonic activity with basic to intermediate melts. The second youngest formation (Niederhaslich Formation) consists predominantly of pre-Permian basement material, which implies only minor volcanic activity and erosion from adjacent basement blocks. On the contrary, the uppermost and youngest Bannewitz Formation features strong evidence for volcanic activity in the neighboring area of the basin. The present study strongly suggests a rapid basin development and further shows how the evolution of the Dohlen Basin is proof for several post-Variscan tectonic reactivation phases in Sakmarian and Lower Kungurian of Central Europe. Finally, our results exemplarily show how basin evolution may be characterized by radiometric data of detrital zircon grains.