The Neoproterozoic terranes of Saxony (Germany)

Abstract

The Precambrian of Germany mainly outcrops in the states of Saxony and Thuringia. The Proterozoic units are surrounded by the Palaeozoic of the Saxo-Thuringian, which is one of the Hercynian fold belts. In Thuringia, the sedimentary record from the Neoproterozoic to the Hercynian flysch stage (Lower Carboniferous) is nearly completely developed (Schwarzburg anticline). In contrast, Neoproterozoic sedimentation at least in two cases in Saxony was interrupted by the Cadomian orogenesis that was connected with the intrusion of 699-540 Ma old granodiorites. These Proterozoic complexes are foreign crustal fragments of a former, Cadomian consolidated orogenic belt enclosed in the Palaeozoic and must be classified as terranes (complexes I and II of the Lusatian terrane). The reconstruction of complex II is particulary complicated, because this part is separated into several parts by a dextral strike-slip fault cluster within the Elbe zone that was active during the uplift of the Hercynian orogen. Amphibolite- to granulite-grade metamorphic Precambrian units are probably par-autochthonous crustal derivates of the Hercynian basement (Ore Mountains anticline, Granulite Mountains anticline) and allochthonous Precambrian fragments enclosed in Hercynian nappes (Münchberg unit, Saxonian “Zwischengebirge”). The sedimentary rocks of the Proterozoic terranes and of the autochthonous Proterozoic of the Schwarzburg anticline enclosed in the Palaeozoic of the Saxo-Thuringian were deposited in submarine fans and consist of siliciclastics (predominantly greywackes, but also quartzite, pelitic siliciclastic rocks and other lithologies). The Weesenstein group, part of complex II of the Lusatian terrane, consists of proximal submarine fan-system deposits. The sedimentation regime was regulated by a rapid glacio-eustatically controlled fall of the sea level. By consideration of the glacio-eustatically influenced sedimentation, and by making use of new radiometric data, the sedimentary part of complex II of the Lusatian terrane (Weesenstein group and Clanzschwitz group) is dated as Cryogenian. The terrane-complex II is characterised as a splinter of an early Cadomian part of a former orogenic belt. The siliciclastics of the Leipzig group and the Lusatian group (complex I of the Lusatian terrane) were most probably deposited in Vendian time. The Lusatian terrane was a part of a late Cadomian fold belt. It therefore seems likely that the Cadomian consolidated terranes of Saxony were parts of peri-Gondwana.