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

• Published in: Journal of the Geological Society Vol. 164; no. 6; pp. 1207 - 1215
• Main Authors: Kryza, R, Zalasiewicz, J. A, Mazur, S, Aleksandrowski, P, Sergeev, S, Presnyakov, S
• Format: Journal Article
• Language: English
• Published: London Geological Society of London 01-12-2007; The Geological Society of London; Geological Society; Geological Society Publishing House
• Subjects: Central Europe; Europe; Gondwana; igneous and metamorphic rocks; igneous rocks; ion probe data; Kaczawa Mountains; lower Paleozoic; magmatism; mass spectra; metaigneous rocks; metamorphic rocks; nesosilicates; orogeny; orthosilicates; Paleozoic; Petrology; Poland; protoliths; rhyodacites; rifting; SHRIMP data; silicates; spectra; Structural geology; Sudeten Mountains; tectonics; trachytes; Variscan Orogeny; Variscides; volcanic rocks; volcanism; zircon; zircon group
• ISSN: 0016-7649; 2041-479X
• DOI: 10.1144/0016-76492006-137

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.