Variscan and pre-Variscan basement units in the central Tauern Window (Austria): constraints from single zircon U-Pb geochronology

Variscan and pre-Variscan basement units of the Tauern Window (TW) were strongly over-printed by Alpine orogeny; and, hence, delimiting the basement assemblages into their respective components remains to be challenging. Although considerable knowledge is accumulated from previous geological and geochronological investigations on the TW basement units; distinction between the pre-Variscan and Variscan components of the basement rocks is far from comple-tion and, therefore, necessitates systematic approaches. Here we present new single-grain and within-grain zircon U-Pb ages (±2s) of selected lithotectonic units (Basi-samphibolit, Biotitporphyroblastenschiefer and equivalent lithologies, Zwolferzug, Habach Phyllite, and Zentralgneis) of the central TW basement sequence. The new and published previous age data are combined to place constrains on outstanding geologic problems such as the relationship of the Basisamphibo-lit to the Zwolferzug garnet amphibolite, the strati-graphic position as well as the maximum sedimentation age of the Biotitporphyroblastenschiefer and Zwolferzug leucocratic gneisses, and the distinction of the lower and upper magmatic sequences of the Habach Formation referred to here as LMS and UMS [1, 2].