U–Pb zircon ages from Permian volcanic rocks and tonalite of the Northern Veporicum (Western Carpathians) (original) (raw)

Original Paper

U–Pb zircon ages from Permian volcanic rocks and tonalite of the Northern Veporicum (Western Carpathians)

Journal of Geosciences, volume 61 (2016), issue 3, 221 - 237

U-Pb dating (SHRIMP) of magmatic zircons from the Northern Veporicum Permian volcanics of the Ľubietová Group yielded concordia ages of 273 ± 6 Ma and 279 ± 4 Ma. Both zircon ages correspond to the Cisuralian Epoch in the time span of Kungurian Stage. The 272 ± 4 Ma U-Pb zircon age, determined on the volcanic dyke cutting the neighbouring crystalline basement, belongs to the same stratigraphic range.
The acquired age data support a contemporaneous origin of the Permian sedimentary basin with the volcanic event and the dyke formation in the crystalline basement. Based on the whole-rock geochemical composition, the studied volcanic rocks correspond to weakly alkaline suite (trachyandesite to rhyolite/dacite). They exhibit light rare earth elements enrichment (LaN/YbN = 9.5-17.7) and small negative or absent Eu anomalies (Eu/Eu* = 0.95 and 1.05 for the Permian volcanites and 0.73 for the volcanic dyke). Characteristic of these volcanites is the enrichment in Cs, Rb, Th, U, K and Pb and the depletion in Nb, Ta, Sr and Ti if compared with average primitive mantle composition. All the studied volcanic rocks have low Nb/Ta (0.29-0.38) and Nb/U (4.07 to 5.87) ratios, implying a crustal magmatic source. Based on the incompatible trace elements Ta, Th and Yb, the Permian volcanics as well as the volcanic dyke cutting the crystalline basement fall close to the boundary between active continental margin the within-plate fields.
The 358 ± 4 Ma magmatic zircon concordia age confirmed the Early Mississippian (Tournaisian) intrusion of the metatonalites in the Volchovo Valley, later blastomylonitized and covered by Permian siliciclastics.