Geochemistry and U-Pb detrital zircon ages of metasedimentary rocks of the Lower Unit,Western Tatra Mountains (Slovakia)

Abstract

Acombined geochemical, isotopic and detrital zircon dating study has been carried out on metasedimentary rocks of the Lower Unit from the Western Tatra Mountains (Slovakia) forming an eastern border of European Variscides. Geochemical data suggest derivation of the protolith – magmatogenic greywackes and claystones from the recycled continental island arc source. ⁸⁷Sr/⁸⁶Sr₍₃₅₀₎  isotopic ratios between 0.713 and 0.723 together with low ε_Nd(350) values of –9.5 to –11.1 and/or Pb isotope composition indicate a crustal origin of the investigated rocks. Detrital zircons from the metasediments often display homogeneous magmatic zoning with ²⁰⁷Pb/²⁰⁶Pb ages from 660 to 515Ma and/or inherited components, with old cores displaying ages from ca. 1980 to 1800Ma. These late Paleoproterozoic detrital source ages are similar to the Nd model ages of the studied metasedimentary rocks with t_(DM2st) ca 1960 ~ 1830 Ma. The Late Cambrian (ca 500 Ma) age represents the last magmatic activity of the precursor rocks and/or it defines the maximum age for sedimentation of the present day metasediments. A possible source for the clastic material of the Lower Unit from theWestern TatraMountains was the peri-Gondwanan continental margin alike the eastern border of the Bohemian Massif – Moravo-Silesian zone or Sudetic block.