Detrital zircon age data from the conglomerates in the Upper Silesian and Małopolska blocks, and their implications for the pre-Variscan tectonic evolution (S Poland)

Abstract

Detrital zircon age of the conglomerates from the Upper Silesian (USB) and Małopolska (MB) (S Poland) have been investigated to compare their deposition age  and possible provenience. The size and poor sorting of the lithoclasts reflect a short transportation, with deposition close to the sourceland. The Late Ediacaran conglomerate of the Potrójna IG 1 and Raciechowice 1 boreholes (USB) reveal a good match between the ages known from the local basement explored by boreholes. Detrital zircon clusters in a range of 579–585 Ma and 628–638 Ma and of 707 Ma are consistent with the distributions of Cadomian magmatism within the nearest orogenic belt or those identified elsewhere within the Brunovistulicum. In case of the conglomerate deposited in the Batowice 2 borehole (MB), the zircon clusters of 532, 551, 594 and 649 Ma, accompanied with a pre-Svecofennian group peaked at 2071 Ma, and the lack of Sveconorvegian population may document a tectono-sedimentary interaction between the Baltica’s southern margin and the Gondwanan Cadomian and Late Cadomian basement during Early Paleozoic time. This conglomerate bed was deposited later, after the Early Ordovician, then docking of Małopolska Block – Baltica was probably completed.