About the age of the Neoproterozoic Lainici-Paius terrane (South Carpathians, Romania)

The pre-Alpine basement of the Danubian domain nappes from South Carpathians consists of high grade metamorphic groups and late Neoproterozoic plutons, underlying low grade metamorphosed Ordovician to early Carboniferous formations (e.g. Seghedi et al., 2005). Two types of pre-Ordovician metamorphic complexes with contrasting protoliths petrology, metamorphism and associated igneous activity, involved in a pre-Permian nappe structure are separated: Lainici-Paius group, dominated by HT-LP metasediments and Dragsan group, dominated by medium grade metabasites. Based on their distinct lithologic compositions, geologic histories and clear boundaries, we consider these two groups as parts of two different terranes (i.e. Lainici-Paius and Dragsan terranes). The southern part of Lainici-Paius terrane is intruded by elongated plutons up to 100 km long and 15 km wide. Based on the geochemical composition, the plutons are assigned to two distinct suites, (i) medium K, calc-alkaline, mostly granodioritic-tonalitic suite (i.e. Susita type) and (ii) very high K, calc-alkaline and mostly granitic (i.e. Tismana type). The first suite comprises Susita and Oltet granitoid bodies and the second suite consists of Tismana and Novaci granitic plutons. Previous age dating was carried out only on Tismana (567±3 Ma upper intercept, Liégeois et al., 1996) and Novaci (588±5 Ma, Grünenfelder et al., 1983 recalculated by Liégeois et al., 1996) granites. In situ zircon U/Pb LA-ICP-MS analyses performed on all four granitoid plutons yielded 596.3±5.7 Ma for Tismana granite, 592.0±5.1 Ma for Novaci granite, 591.0±3.5 Ma for Susita granite and 588.7±3 Ma for Oltet granite. The same method has been additionally applied for detrital zircons from a metasandstone sequence comprised by the Lainici-Paius complex. Fifty-five ages out of 78 dated grains are ranging between 690.1±5.5 Ma and 811.4±12,7 Ma. Therefore, considering the protolith ages of the four dated granites and the youngest age within the mentioned detrital age distribution we can constrain the formation of the sedimentary protoliths of the Lainici-Paius group to 690-600 Ma span.