Terra Nova, 24, 199–206, 2012 Abstract Three detrital zircon concentrates from the metasediments of the Orlica‐Śnieżnik dome, Bohemian Massif, have been dated using Sensitive High Resolution Ion Microprobe. They yielded Precambrian age spectra similar to those that are characteristic of the Cadomian terranes: (1) Archaean and Palaeoproterozoic zircons scattered between 3380 and 1860 Ma, and (2) abundant Neoproterozoic zircons dated at 770–560 Ma. Two of the analysed samples also contain Early Cambrian and Early‐Late Cambrian zircons. The estimated maximum sedimentation ages are: 563 ± 6 Ma for the Młynowiec paragneisses, 532 ± 6 Ma for the Stronie schist and 490 ± 9 Ma for the Goszów quartzite that are interpreted as three distinct metasedimentary successions. They represent a Neoproterozoic back‐arc basin, Early Cambrian incipient rift basin and a Lower Ordovician post‐rift succession respectively. These successions are the deformed and metamorphosed, allochthonous equivalent to the passive Saxo‐Thuringian margin. They were subducted during a Variscan collision and then exhumed in front of the rigid buttress of Brunia/East Avalonia.

The Carboniferous foreland basin of western Poland contains a coherent succession of late Viséan through Westphalian turbidites derived from a uniform group of sources located within a continental magmatic arc. Detrital zircon geochronology indicates that two main crustal components were present in the source area of Namurian A sediments. They represent Late Devonian and Early Carboniferous ages, respectively. The detritus from Westphalian D beds is much more diversified and contains admixture of Late Carboniferous zircons suggesting rapid unroofing of Variscan igneous intrusions in the hinterland between Namurian A and Westphalian D times. Tectonic repetitions of tens of metres thick fault-bounded stratigraphic intervals, recorded in several wells, provide evidence for compressional regime that occurred in the SW part of the Carboniferous basin not earlier than during the Westphalian C and produced NW-SE trending folds, concordant with the structural grain of the adjacent, NE part of the Bohemian Massif.

Seven granitoid gneisses from the contact zone between the eastern margin of the Variscan belt and the Brunian microcontinent in SW Poland have been dated by ion-microprobe and207Pb/206Pb single zircon evaporation methods. The zircons define two age groups for the gneiss protoliths: (1) late Neoproterozoicc.576–560 Ma and (2) early Palaeozoicc.488–503 Ma granites. The granitoid gneisses belonging to the basement of the Brunian microcontinent contain abundant Mesoproterozoic to latest Palaeoproterozoic inherited material in the range of 1200–1750 Ma. The gneisses of the Variscan crustal domain lack Mesoproterozoic inherited zircon cores. Trace element geochemistry of Proterozoic gneisses reveals features resembling either volcanic arc or post-collisional granites. The studied rocks are geochemically similar to other Proterozoic orthogneisses derived from the basement of the Brunian microcontinent. Gneisses with early Palaeozoic protolith ages are geochemically comparable to granitoid gneisses widespread in the adjacent Sudetic part of the Bohemian Massif and are considered characteristic of peri-Gondwanan crust. Our data prove the dissimilarity between the Brunia plate and the westerly terranes of the Variscan belt. The occurrence of granitic gneisses with late Neoproterozoic protolith ages and widespread Mesoproterozoic inheritance in our dated samples support an East Avalonian affinity for the Brunian microcontinent. In contrast, the abundance of gneisses derived from an early Palaeozoic granitic protolith and devoid of Mesoproterozoic zircon cores supports the Armorican affinity of the Variscan domain bordering on the Brunia plate from the west. Structural evidence shows that the eastern segment of the Variscan belt is juxtaposed against the Brunian microcontinent along a N–S-trending tectonic contact, possibly equivalent to the Rheic suture.