Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massif: speculations on palinspastic reconstructions

Abstract

AbstractNd crustal residence ages combined with xenocrystic and detrital zircon ages of Neoproterozoic and early Palaeozoic granitoid gneisses and metasediments from the NE Bohemian Massif (West Sudetes and Erzgebirge) suggest an origin from a basement with significant Grenvillian and Svecofennian-Birimian-Amazonian age components. Large contributions from Archaean crust appear to be missing. Nd model ages of 1.4–1.7 Ga as well as Meso- to Palaeoproterozoic zircon xenocrysts ages for the Lugian Domain (Jizerské, Krkonoše, and Orlica-Sniezník Mountains) are interpreted as evidence for a predominantly Palaeoproterozoic basement that underwent rejuvenation during Meso- and Neoproterozoic-Ordovician magmatic events. Our interpretation of the Nd model ages may be relevant for the western part of the Variscan Belt, where a similar range of Nd model ages characterizes large crustal segments. Samples from the Silesian Domain (Desná Dome Staré Město Belt, Velké Vrbno Unit) of the Brunia Microcontinent, in thrust contact with the Lugian Domain, yielded Nd crustal residence ages of 1.1–1.3 Ga, which coincide with the oldest ages of xenocrystic zircons. Brunia is interpreted as a predominantly juvenile Grenvillian-age crustal segment, possibly constituting a former arc batholith outboard from the more ensialic setting of the Lugian Domain. Nd crustal residence ages for our 77 whole-rock samples, including 41 new data, as well as 185 xenocrystic and detrital zircon ages from the northern and northeastern Bohemian Massif agree with those of Neoproterozoic rocks from northern South America and support an origin from a northwest Gondwana palaeogeographical location.