Enigmatic sedimentary–volcanic successions in the central European Variscides: a Cambrian/Early Ordovician age for the Wojcieszów Limestone (Kaczawa Mountains, SW Poland) indicated by SHRIMP dating of volcanic zircons

Abstract

AbstractMetamorphosed volcanic and sedimentary successions in the central European Variscides are, in many areas, poorly biostratigraphically constrained, making palaeotectonic interpretations uncertain. In such instances, geochronological data are crucial. Sensitive high resolution ion microprobe (SHRIMP) dating of volcanic zircons from a quartz–white mica schist (interpreted as deformed metavolcaniclastic/epiclastic rock) within the stratigraphically controversial Wojcieszów Limestone of the Kaczawa Mountains (Sudetes, SW Poland), near to the eastern termination of the European Variscides, has yielded an age of 498 ± 5 Ma (2σ error), corresponding to late Cambrian to early Ordovician magmatism in that area and constraining the depositional age of the limestones. The new SHRIMP data are not consistent with the recent revision of the age of the Wojcieszów Limestone based on Foraminifera findings that ascribed them to a Late Ordovician—Silurian or even younger interval. They are though, consistent with sparse macrofossil data and strongly support earlier interpretations of the lower part of the Kaczawa Mountains succession as a Cambrian–Early Ordovician extensional basin‐fill with associated initial rift volcanic rocks, likely emplaced during the breakup of Gondwana. Copyright © 2008 John Wiley & Sons, Ltd.