The Moldanubian Thrust Zone — A terrane boundary in the Central European Variscides refined based on lithostratigraphy and U–Pb zircon geochronology

Abstract

The zircon age populations of metavolcano-sedimentary successions in the Orlica–Śnieżnik Dome (OSD), Staré Město Belt (SMB) and Velké Vrbno Dome, the Sudetes (Poland and Czech Republic), have been used to refine the location of the Moldanubian Thrust Zone (MTZ), which is a boundary between the Saxothuringian Terrane of Gondwana descent and the Brunovistulian Terrane being a promontory of Laurussia. In the northern continuation of the MTZ, a set of multiply activated, regional-scale thrusts developed and brought into contact rocks of different ages and geological histories. Metarhyolites in the Orlica–Śnieżnik Dome and the Staré Město Belt have similar geochemistry and U–Pb isotopic zircon records, which is taken in favour of their coeval formation and common Saxothuringian affinity. Felsic metavolcanic rocks from the OSD and from the thrust-bounded upper and lower units of the SMB yielded protolith ages of 500±3Ma and 493±4Ma to 498±5Ma, respectively, which indicates that metavolcano-sedimentary successions in the OSD and SMB were deposited in Late Cambrian times. Structurally below these rocks, there are the highly sheared Brousek quartzites with detrital zircons that yielded a maximum depositional age of ~530Ma. The mylonitic quartzites accommodate deformation induced by tectonic transport on the East Nýznerov Thrust, which is interpreted as the easternmost margin of Saxothuringia. This fault separates Palaeozoic rocks of the Saxothuringian Terrane from Neoproterozoic bimodal volcanogenic succession in the Velké Vrbno Dome of Brunovistulia, dated at ~558Ma. The late-Variscan thermal events in the Early Carboniferous left imprints in the form of U-rich rims around the zircons of the metavolcanic rocks from the Staré Město Belt and only a very minor overprint in the zircons from the Velké Vrbno Dome and Orlica–Śnieżnik Dome.