U-Pb-ages of detrital zircon and apatite from recent river sands of the eastern Erzgebirge

This talk presents radiometric ages and mineral sizes of detrital zircons and apatites representing six sediment samples from three different recent rivers of the eastern Erzgebirge: The Wilde Weißeritz, the Freiberger Mulde and the Müglitz. We took one sample from the upper and one from the lower reaches of each river.

The objectives were, (1) to find evidence for thermal, magmatic events in the apatites, (2) to record the U-Pb-spectrum of zircons for each sample, and (3) to improve insight into the transport behaviour and sediment composition of the studied rivers.

The apatites showed thermal overprinting of their U-Pb ages, which varied between ca. 306 Ma and ca. 328 Ma. Therefore, small, local thermal events seem to be more likely than one large event affecting the entire study area. The older ages are interpreted to represent the end of the Variscan Orogeny and the beginning of the post-Variscan magmatism. The younger ages are interpreted as later thermal overprinting by local magmatic events, possibly caused by heating events along the margins of the Erzgebirge Block at the beginning of the Permian magmatism.

The U-Pb-ages of the zircons represent the rocks of the hinterland of the specific rivers and show mainly Cadomian ages derived from the gneisses combined with (post-)Variscan ages from the igneous rocks. Therefore, the spectrum of zircons found at the sampling sites is dominated by the local rocks.

Interestingly, the detrital minerals analysed do not allow interpretation of very long sedimentary fluvial transport.