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Abstract

Isotope and chemical analyses of zircon from the Po lish Lowland provide information on magma sources and processes of magma evolution during the period of intense magmatism that affected Central Europe at the Carboniferous/Permian boundary. Since zircon reflects 18 O/16 O of the magma from which it crystallized, we have measured the 18 O/ 16 O in zircon to establish the fraction of the rhyolite precursors that was derived from juvenile magmas and also to reconstruct magma evolution during the zircon crystallization. Zircon isotope ratio determinations were conducted at the GFZ-Potsdam using the Cameca 1280-HR SIMS instrument. The reference zircon 91500 (Wiedenbeck et al. 2004) was analyzed 39 times as part of this project, yielding a repeatability of ± 0.2 ‰ (1SD). We studied zircon grains from four localities Pniewy, Wysoka, Daszewo and Chrzypsko. Altogether more than 100 magmatic grains were measured. The highest δ 18 O values were measured in Daszewo and the lowest in Wysoka suggesting that magmas from different localities represent different sources. Each locality have zircon with the range of δ 18 O values exceeding the error, which is consistent with zircon crystallizing in an evolving magma or in separate magma batches. The latter seems to be more probable as zircon is not zoned in δ 18 O from the core to the rim. As the whole, zircons from the Polish Lowland have the greatest variability in δ 18 O observed so far amongst all of the localities studied from the Central European basin large igneous province (Piet ranik et al. 2013). The results extend from low values typical for derivation of the magmas from the sources altered by hydrothermal activity up to results consistent with a important sedimentary input into the system. So far the localities from the Polish Lowland are the first ones studied within the CEB-LIP, which show δ 18 O lower than the mantle values (δ 18 O <5.3 ‰).