New age constraints for Early Palaeozoic volcanism and sedimentation of the Kaczawa Complex, the Sudetes (SW Poland)

In Variscan Europe, bimodal magmatism related to Early Palaeozoic thermal event in the northern part of Gondwana has been widely documented in rock successions extending from Spain to Poland (e.g. Franke et al. 2017). The Kaczawa Complex, the SW Poland, contains Early Palaeozoic felsic, intermediate to basic volcanic rocks, and Cambrian to Early Carboniferous sediments all involved in complex processes of the Variscan collision(s). This contribution provides new LA-ICPMS UP zircon data that specify the age and provenance of some important rocks occupying the lower part of the stratigraphic column of the Kaczawa Complex: 1) Osełka metarhyodacytes, 2) Lubrza metatrachytes, 3) Radzimowice slates and 4) Gackowa metasandstones.

The U-Pb dating of zircons coming from the Osełka metarhyodacites yields a crystallization age of 500±5 Ma, while the zircon dating of the Lubrza metatrachytes yields the Concordia age of 495±3 Ma. These data confirm the early Palaeozoic age of the volcanism of the Kaczawa Complex (e.g. Muszyński, 1994; Kryza et al. 2007), but they strongly suggest a single event of the bimodal volcanic activity. An inherited age component of c. 630 Ma is present in the Lubrza metatrachytes. The zircon dating of the accompanied metasedimentary rocks i.e. two samples of Radzimowice slates and one sample of the Gackowa metasandstones yields comparable detrital age spectra. The maximum depositional ages of these rocks are ca. 535 Ma. The Radzimowice and Gackowa metasedimentary rocks show the predominance of Neoproterozoic age zircons clustering around 580-605 Ma, 630-640 Ma and 730-770 Ma, which indicates that the sedimentary basins were mainly supplied by erosion of crystalline rocks of Ediacaran up to Tonian age. Paleoproterozoic and Archean components (1.7 Ga, 2.0-2.1 Ga and 2.9-3.0 Ga) are less common.

All these data show that rocks from the lower part of the lithostratigraphic column of the Kaczawa Complex represent the Late Cambrian metavolcano-sedimentary successions. The detrital zircon age spectra indicate that the source areas for the Kaczawa Complex metapelites may have been in the West Africa Craton of Gondwana.

The research was financed from the grant of the National Science Center, Poland No. 2018/29/B/ST10/01120.

 

References:

Franke, W., Cocks, L. R. M., Torsvik, T. H. 2017. The Palaeozoic Variscan oceans revisited. Gondwana Research 48, 257–284.

Kryza R., J.A. Zalasiewicz, S. Mazur, P. Aleksandrowski, S. Sergeev, S. Presnyakov, 2007. Early Palaeozoic initial-rift volcanism in the Central European Variscides (the Kaczawa Mountains, Sudetes, SW Poland): evidence from SIMS dating of zircons. Journal of the Geological Society, London 164, 207-1215

Muszyński A., 1994. Kwaśne skały metawukanogeniczne w środkowej części Gór Kaczawskich: studium petrologiczne. Wyd. Nauk. UAM., seria geologia, Nr 15: 144 pp