Abstract
The Polish Lowlands, located southwest of the Teisseyre–Tornquist Zone, within Trans-European Suture Zone, were affected by bimodal, but dominantly rhyolitic, magmatism during the Late Paleozoic. Thanks to the inherited zircon they contain, these rhyolitic rocks provide a direct source of information about the pre-Permian rocks underlying the Polish Lowland. This paper presents zircon U–Pb geochronology and Hf and O isotopic results from five drill core samples representing four rhyolites and one granite. Based on the ratio of inherited vs. autocrystic zircon, the rhyolites can be divided into two groups: northern rhyolites, where autocrystic zircon is more abundant and southern rhyolites, where inherited zircon dominates. We suggest that the magma sources and the processes responsible for generating high silica magmas differ between the northern and southern rhyolites. Isotopically distinct sources were available during formation of northern rhyolites, as the Hf and O isotopes in magmatic zircon differ between the two analysed localities of northern rhyolites. A mixing between magmas formed from Baltica-derived mudstone–siltstone sediments and Avalonian basement or mantle can explain the diversity between the zircon compositions from the northern localities Daszewo and Wysoka Kamieńska. Conversely, the southern rhyolites from our two localities contain zircon with similar compositions, and these units can be further correlated with results from the North East German Basin, suggesting uniform source rocks over this larger region. Based on the ages of inherited zircon and the isotopic composition of magmatic ones, we suggest that the dominant source of the southern rhyolites is Variscan foreland sediments mixed with Baltica/Avalonia-derived sediments.
Highlights
The Central European Basin was affected by extensive magmatism with the emplacement of c. 80,000 km3 of magma during the Late Carboniferous to Early Permian (Paulick and Breitkreuz 2005)
Based on the inherited to magmatic zircon proportions and zircon inherited ages, we suggest that the southern rhyolites were derived predominately from the Carboniferous turbidites with admixture of Baltica and/or Avalonia component, whereas northern rhyolites were derived from fine-grained sediments, poor in zircon, such as thick Ordovician–Sylurian sampled present in the Koszalin–Chojnice zone (Modliński and Podhalańska 2010)
Late Paleozoic rhyolites from the Polish Lowlands offer insight into the composition and structure of the crust which makes up the Trans-European Suture Zone in Poland
Summary
The Central European Basin was affected by extensive magmatism with the emplacement of c. 80,000 km of magma during the Late Carboniferous to Early Permian (Paulick and Breitkreuz 2005). 80,000 km of magma during the Late Carboniferous to Early Permian (Paulick and Breitkreuz 2005) This resulted in a bimodal volcanism which is observed across central Europe (Benek et al 1996; Breitkreuz and Kennedy 1999; Geißler et al 2008; Hoffmann et al 2012; Kryza and Awdankiewicz 2012; Awdankiewicz et al 2013; Turniak et al 2014; Fig. 1a). The resulting Permo-Carboniferous volcanic rocks are today covered by younger sediments with thickness varying from approximately 1000 m in the Fore-Sudetic Monocline to over 5000 m close to the Teisseyre–Tornquist Zone (TTZ; Fig. 1); (Jackowicz 1994; Maliszewska et al 2003; Dadlez 2006). The volcanic rocks constitute less than 12% of the material in the drill cores (Breitkreuz et al 2007), but in many places, they provide crucial information about the underlying pre-Permian basement. The pre-Permian basement is probably composed of several Precambrian-to-lower Paleozoic units that have been interpreted as having formed through a juxtaposition of several fragments of continental crust along the margin of Baltica prior to being overlain by sedimentary and low-grade metasedimentary cover (Mazur et al 2010, 2015; Żelaźniewicz et al 2016)
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