Fingerprinting Gondwana versus Baltica provenance: Nd and Sr isotopes in Lower Paleozoic clastic rocks of the Małopolska and Łysogóry terranes, southern Poland

Abstract

Neodymium and strontium isotope compositions of clastic material in Lower Paleozoic rocks, in addition to detrital zircon and mica geochronology and faunal data are used to constrain the geotectonic provenance of the Małopolska and Łysogóry terranes in southern Poland. Being characterized by markedly different geological histories during Early Paleozoic times, Małopolska and Łysogóry were most often interpreted as exotic terranes, but their identity, provenance and accretionary history are still being discussed. This study presents the first systematic Nd and Sr isotope survey of the Lower Paleozoic siliciclastic rocks. Cambrian clastic rocks of Małopolska differ in their Nd and Sr isotope compositions from those of Łysogóry. The former are characterized by a wide range of the εNd(505Ma) values, from −11.7 to −5.7, Sr isotope ratios from 0.712 to 0.767, and model ages (T2DM) predominantly younger than 1.9Ga, whereas the εNd(t) values of the latter vary within a fairly narrow range of the εNd(505Ma), from −11.0 to −8.3, Sr isotope ratios from 0.722 to 0.754, and model ages are older than 1.9Ga. New Nd data combined with detrital zircon ages provide evidence that Małopolska must have been supplied with clastic material from Amazonian sources during Cambrian times, being also progressively sourced from the Baltic Svecofennian crust in the Middle Cambrian. Detritus recognized in Łysogóry has mostly been derived from the Svecofennian basement of Fennoscandia, but it has also a small addition from Cadomian sources. All provenance and biogeographic data suggest that Małopolska was situated close to the Amazonian Craton near the western end of the Cadomian Belt during the Early Cambrian, and it was not until the late Middle Cambrian that Małopolska collided with the Baltica margin. During the Late Cambrian Łysogóry occupied a position between Baltica and the Cadomian Belt but it was probably not yet accreted to the Baltic crust at that time.