Middle/Late Cambrian intracontinental rifting in the central West Sudetes,NE Bohemian Massif (Czech Republic): geochemistry and petrogenesis of the bimodal metavolcanic rocks

The Early Palaeozoic East Krkonoše Complex (EKC) situated in the central West Sudetes, NE Bohemian Massif, is a volcano‐sedimentary suite containing abundant mafic and felsic volcanics metamorphosed to greenschist facies. The trace element distribution patterns and Nd isotope signatures (E_Nd500 = + 3.1 to + 6.6) of the metabasites (metabasalts) indicate that they may be related to a rising mantle diapir associated with intracontinental rifting. At the early stage, limited melting of an upwelling asthenosphere produced alkali basalts and enriched tholeiites which compositionally resemble oceanic island basalts. A later stage of rifting with larger degrees of melting at shallower depths generated tholeiitic basalts with E‐MORB to N‐MORB characteristics. The values of (⁸⁷Sr/⁸⁶Sr)_i = 0.706 and E_Nd500 = − 5 ±1 of the porphyroids (metarhyolites) as well as the lack of rocks with intermediate compositions suggest that the felsic rocks were formed by a partial melting event of continental crust triggered by mantle melts. The geochemistry of the EKC bimodal metavolcanics and their association with abundant terrigenous metasediments suggest that the felsic–mafic volcanic suite was generated during intracontinental rifting. This process, widespread in Western and Central Europe during the Early Palaeozoic, is evidence of large‐scale fragmentation of the northern margin of the Gondwana supercontinent. Copyright © 2001 John Wiley & Sons, Ltd.