Age of the basement beneath the Mesozoic Lusitanian Basin revealed by granitic xenoliths from the Papôa volcanic breccia (West Iberia)

The dyke of the Papôa volcanic breccia cross-cutting the Lower Jurassic sequence of the Lusitanian Basin (West Iberia) contains granitic xenoliths. In this study, for the first time, U-Th-Pb zircon analysis of two xenoliths yielded 298±4Ma for biotite granite and of 292±2Ma for two-mica granite, indicating that the pre-Mesozoic basement of the Lusitanian Basin includes Permian intrusions. These ages are close within the margin of error of the age of the Late Carboniferous granites of the Berlengas isle that with the Late Devonian high-grade metamorphic rocks of the Farilhões isles, located northwest of the study area, which form the pre-Mesozoic basement of the Lusitanian Basin. These new geochronological findings enable it to be established that Permo-Carboniferous magmatism lasted at least 13Ma, in this region of the Appalachian-Variscan belt. Furthermore, a comparison with available data from Paleozoic tectonic units of the Appalachian-Variscan belt located both in the Iberian Massif and outside it enables the suggestion to be made that the Lusitanian Basin (Peniche) most probably rests on the South Portuguese Zone, which may also be correlated with the Rhenohercynian Zone present in southwest England, and the Meguma terrane of Nova Scotia.

ICHNOFOSILIE MYSLEJOVICKÉHO SOUVRSTVÍ DRAHANSKÉHO KULMU (SPODNÍ KARBON, MORAVSKOSLEZSKÁ JEDNOTKA ČESKÉHO MASIVU)

The research in this study is focused on trace fossils of the Myslejovice Formation, which is one of the lithostratigraphical units in the Lower Carboniferous sequences of the Drahany Culm Basin that belongs to the large area of Rhenohercynian Zone of the Variscan orogenetic flysch belt. Ichnofossils have mainly been collected in the southeastern part, near Vyškov. The material comes from the collection of Mr. Veleslav Lang which is nowadays stored in the Regional Museum of Olomouc. From this collection total 615 specimens in 10 ichnogenera and 13 following ichnospecies were determined and redefi ned: ?Alcyonidiopsis isp., Cosmorhaphe isp., Dictyodora liebeana, Diplocraterion parallelum, Gordia isp., Chondrites cf. intricatus, Chondrites isp., Nereites missouriensis, Nereites isp., Phycosiphon incertum, Planolites beverleyensis, Planolites isp. and Rhizocorallium isp. The revised material comes from the following locations: Opatovice, Habrovany, Hamiltony, Ježkovice, Lhota, Luleč, Myslejovice, Nemojany – Blatická dolina, Nemojany, Otaslavice, Pístovice, Radslavice and Rychtářov. The overall character of ichnoassemblages indicates conditions of Nereites ichnofacies, which is typical for the distal parts of the suprafan turbidite lobes. Compared to other areas of Culm facies in Middle Europe, assemblages of the Myslejovice Formation belong among the less diversified.