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Journal of the Geological Society

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Early Palaeozoic initial-rift volcanism in the Central European Variscides (the Kaczawa Mountains, Sudetes, SW Poland): evidence from SIMS dating of zircons

^{1 1}Wrocaw University, Institute of Geological Sciences, ul. Cybulskiego 30, 50-205 Wrocaw, Poland (e-mail: rkryza{at}ing.uni.wroc.pl)
^{2 2}University of Leicester, Department of Geology, University Road, Leicester LE1 7RH, UK
^{3 3}Centre of Isotopic Research, A. P. Karpinsky All Russian Geological Research Institute (VSEGEI), 74 Sredny Pr, St. Petersburg, 199 106, Russia

Early Palaeozoic volcanic suites are widespread throughout the Variscan Belt, and have commonly been ascribed to incipient rifting along the northern periphery of Gondwana in Cambrian to Ordovician times. Their distribution across Europe defines the present-day extent of Gondwana-derived terranes and constrains the timing of their separation from the Gondwanan margin. The Kaczawa Mountains in the West Sudetes, at the eastern termination of the Variscan Belt, include bimodal rift-related rocks, but their protolith age and, hence, their significance have been highly uncertain. We have applied secondary ionization mass spectrometry zircon geochronology to a metarhyodacite and a metatrachyte from this suite, yielding ages of 502.4 ± 2.6 Ma and 485.7 ± 1.6 Ma, respectively. This constrains the initial rift magmatism to c. 500–485 Ma in this part of the European Variscides. The rift-related Early Palaeozoic volcanism thus seems to have been broadly synchronous throughout the peri-Gondwanan terranes of Europe.