Detrital zircon populations in quartzites of the Krkonose-Jizera Massif: implications for pre-collisional history of the Saxothuringian Domain in the Bohemian Massif
Abstrakt
Age spectra of detrital zircons from metamorphosed quartzites of the Krkonose-Jizera Massif in the northeastern part of the Saxothuringian Domain were obtained by U-Pb laser ablation inductively coupled plasma mass spectrometry dating. The zircon ages cluster in the intervals of 450-530 Ma and 550-670 Ma, and show individual data between 1.6 and 3.1 Ga.
Zircons in the analysed samples are predominantly of Cambrian-Ordovician and Neoproterozoic age, and the marked peak at c. 525-500 Ma suggests a late Cambrian maximum age for the sedimentary protolith. Detritus of the quartzites probably originated from the erosion of Cambrian-Ordovician granitoids and their Neoproterozoic (meta) sedimentary or magmatic country rocks.
The lack of Neoproterozoic (meta) sedimentary rocks in the central and eastern part of the Krkonose-Jizera Massif suggests that the country rocks to voluminous Cambrian-Ordovician magmatic bodies were largely eroded during the formation of early Palaeozoic rift basins along the southeast passive margin of the Saxothuringian Domain. The detrital zircon age spectra confirm the previous interpretation that the exposed basement, dominated by Neoproterozoic to Cambrian-Ordovician granitoids, was overthrust during Devonian-Carboniferous subduction-collision processes by nappes composed of metamorphosed equivalents of the uppermost Cambrian-Devonian passive margin sedimentary formations.
Only a negligible number of Mesoproterozoic ages, typically from the Grenvillian event, supports the interpretation that the Saxothuringian Neoproterozoic basement has an affinity to the West African Craton of the northwestern margin of Gondwana.