Late Cambrian/Ordovician magmatic arc type volcanism in the Southern Gemericum basement, Western Carpathians, Slovakia: U-Pb (SHRIMP) data from zircons

The low-grade crystalline basement of the Southern Gemeric Unit (Inner Western Carpathians) consists mainly of siliciclastic deep-water turbidite sequence associated with a huge mass of redeposited rhyolite/dacite volcanics and their volcaniclastics. In situ U-Pb SHRIMP zircon dating applied to metavolcanic rocks contributed to specification of the Southern Gemeric crystalline basement stratigraphy (the Gelnica Group). Zircon populations from ten samples of three lithostratigraphic units of the Gelnica Group rock complex have been analysed. The zircons presented significant magmatic zoning. Part of the magmatic zircons contained inherited older cores. The Vlachovo Formation gives the 494 +/- 1.6 Ma zircon average age. The Bystry potok Formation gives 465.8 +/- 1.5 Ma and the Drnava Formation 463.9 +/- 1.7 Ma average age. The geochemical data are compatible with an orogenic geodynamic setting. Dominant rhyolite-dacite volcanites belong to the peraluminous, calc-alkaline high-K magmatic series. The age data let us presume two phase longlasting magmatic activity, starting in the Late Cambrian and continuing to the Middle/Late Ordovician. Thus, the studied Late Cambrian volcanic sequence of the Gelnica Group reflects the active continental margin setting. The second Middle Ordovician volcanic phase documents an assumed rifting stage, accompanied by a strong volcanic activity with inherited features of the Late Cambrian magmatic arc. The inherited cores of magmatic zircons have Proterozoic (600-760, 1,000-1,400, 2,000-2,700 Ma) and Archean (3,099-3,164 Ma) ages.