Abstract

Granitoid gneisses as well as their migmatitic and anatectic derivates were investigated from theGóry Sowie (Owl Mts) Massif of SW Poland in the central West Sudetes. The gneisses and migmatites aretectonically interlayered with paragneisses, and experienced several consecutive tectono-metamorphicevents. Geochemically, the granitoid gneisses are calc-alkaline and similar to orogenic granite suites, whichtherefore lends support to a subduction-related origin.

Single zircon Pb–Pb evaporation ages suggest that the gneiss precursors were emplaced between 473 and488 Ma, and most samples analysed contain zircon xenocrysts with minimum ages between 1124 and2620 Ma. An early phase of high-grade metamorphism is documented by an age of c. 440 Ma for ananatectically derived granite. Two late Variscan granites have an age of c. 333 Ma. Nd isotope systematicssuggest variable involvement of crustal material in the generation of the granitoids.

We speculate that the Góry Sowie Massif was part of Avalonia in early Palaeozoic times, derived fromthe northwestern margin of Gondwana, probably northern South America. Granitoid emplacement in theOrdovician took place along a Japan-type active continental margin while Avalonia drifted towardsBaltica and the Tornquist Ocean was consumed. Collision with Baltica occurred in mid-Silurian times. Our data are compatible with an active magmatic arc extending from southern England to thesoutheastern Sudetes in Cambrian and Ordovician times.

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