ORIGINAL PAPER Precambrian crustal contribution to the Variscan accretionary prism of the Kaczawa Mountains (Sudetes, SW Poland): evidence from SHRIMP dating of detrital zircons Ryszard Kryza Æ Jan Zalasiewicz Æ Stanislaw Mazur Æ Pawel Aleksandrowski Æ Sergey Sergeev Æ Alexander Larionov Received: 22 March 2006 / Accepted: 17 November 2006 / Published online: 12 December 2006 Ó Springer-Verlag 2006 Abstract SHRIMP dating of detrital zircons from sandstones of the Gackowa Formation (Kaczawa Complex, Sudetes, SW Poland) indicates input from late (550–750 Ma) and early Proterozoic to Archaean sources (~2.0–3.4 Ga, the latter being the oldest re- corded age from the Sudetic region). These dates preclude within-terrane derivation from seemingly correlatory acid volcanic rocks of early Palaeozoic age. Rather, they indicate provenance from Cadomian and older rocks that currently form part of other, geo- graphically distant terranes; the most likely source identified to date is the Lusatian Block in the Saxo- thuringian Zone. Hence, the Gackowa Formation may be late Proterozoic rather than early Palaeozoic in depositional age, possibly coeval with the late Prote- rozoic (pre-Cadomian) greywackes of Lusatia, being subsequently tectonically interleaved with early Pal- aeozoic volcanic rocks into the Kaczawa accretionary prism during the Variscan orogeny. However, corre- lation with the lithologically similar early Ordovician Dubrau Quartzite of Saxothuringia, and so assignation to the early Paleozoic (post-Cadomian) rift succession deposited at the northern margin of Gondwana, cannot yet be precluded. Keywords SHRIMP Á Zircon Á Precambrian Á Sudetes Á Variscides Introduction The extensive Palaeozoic volcano-sedimentary succes- sions accreted within the Variscan belt were deposited in pre-orogenic, mostly extensional basins, initiated due to the break-up of the northern Gondwana margin (e.g., Pin and Marini 1993; Furnes et al. 1994; Floyd et al. 2000; Pin et al. 2007). The onset of sedimentation is currently thought to have taken place in late Cambrian to early Ordovician times and to be closely related to the incipient continental rifting of the Precambrian basement previously consolidated during the Cadomian orogeny (Linnemann et al. 2000, 2004). Shallow marine sedimentary and volcanic successions were deposited during the Ordovician on rifted continental margins of the early Palaeozoic terranes freshly separated from the Gondwana margin. These terranes, subsequently ac- creted within the European Variscides, included seg- ments of Precambrian crust capable of supplying detritus to the Palaeozoic sedimentary basins. Although such Precambrian crustal components are known from many localities across the Variscan belt (e.g., Edel and Weber 1995), the provenance of material supplied to early Palaeozoic sedimentary successions remains poorly constrained. This is because the Palaeozoic pre- orogenic successions of the Variscides are usually detached from their original basement, having been R. Kryza (&) Á S. Mazur Á P. Aleksandrowski Institute of Geological Sciences, Wroclaw University, ul. Cybulskiego 30, 50-205 Wroclaw, Poland e-mail: rkryza@ing.uni.wroc.pl J. Zalasiewicz Department of Geology, University of Leicester, University Road, Leicester LE1 7RH, UK S. Sergeev Á A. Larionov Center of Isotopic Research, A.P. Karpinsky All Russian Geological Research Institute (VSEGEI), 74 Sredny Pr, St Petersburg 199 106, Russia 123 Int J Earth Sci (Geol Rundsch) (2007) 96:1153–1162 DOI 10.1007/s00531-006-0147-x