Explore the vast range of titles available.

Greywackes make up a substantial part of the Cadomian basement of Saxo-Thuringia. Here, their classification as greywackes and the timing of metamorphic overprint are re-evaluated using a multi-method approach. Immature monotonous greywacke sequences from the Lausitz (Lausitz Block) and Leipzig groups (North Saxon Anticline), as well as from the eastern Thuringian Basin and parts of the Weesenstein Group (Elbe Zone) probably belong to a coherent unit, based on microscopic investigations supported by SEM Automated Mineralogy analyses and point counting data. However, due to the low matrix content (< 15%), the sedimentary rocks are more likely classified as lithic sandstones. The heterogeneous composition and in particular the highly mature character of the Clanzschwitz Group (North Saxon Anticline) and parts of the Weesenstein Group (Seidewitz Formation) suggest a younger, Late Cambrian to Early Ordovician sedimentation age. Typically, the metamorphic overprint of the “greywacke units” is very weak. Previous assumptions of Cadomian contact metamorphism triggered by Early Cambrian intrusions (ca. 540 Ma) could not be confirmed due to the local differences in the determined metamorphic ages. Late Cambrian to Early Ordovician (521–461 Ma) Th–U–Pb monazite ages are likely related to the tectonic transition from the collisional regime of the Cadomian orogeny to extensional processes in the course of the opening of the Rheic Ocean. Sporadic Late Ordovician (458–445 Ma) Th–U–Pb monazite and K–Ar fine-fraction ages were also obtained but the specific thermal trigger is still subject of debate. The Permo-Carboniferous metamorphic ages (314–286 Ma) indicate high-temperature metamorphism related to the post-Variscan extensional processes of Central Europe during this period. The youngest dated monazites are Jurassic in age and may have grown in association with the hydrothermal activity known from Central Europe at that time. Graphical abstract

In collision belts, the upper plate is generally less deformed than the lower one that underwent syn-metamorphic ductile shearing, and frequently late-collisional crustal melting. Concerning the Variscan orogeny, it is widely accepted that the Armorica microcontinent represented the upper plate of the collision system. In France, the Central-North-Armorican Domain belonged to this upper plate whose southern margin in the Pontivy–Coray area exposes metamorphic rocks. There, structural and metamorphic studies indicate that an early tectono-metamorphic event (M0-M1) with biotite–garnet–staurolite–kyanite assemblage, crystallized at 0.9 GPa and 500 °C, is characterized by a top-to-the NW shearing. This event was followed by an HT event (M2) at ca 800–900 °C, coeval with a domal structure. In micaschists, monazite yields an LA-ICP-MS age at 351 Ma ascribed to M2. M0-M1-M2 events developed before the Late Carboniferous pluton emplacement at ca 315 Ma (M3 event). The tectono-metamorphic succession documents that Armorica was not a rigid block but underwent a synmetamortphic ductile deformation during the Famennian–Tournaisian (360–355 Ma) collision redefined here as the late episode of the “Bretonian orogenic phase”, whereas the pre-Famennian Bretonnian episode is ascribed to oceanic subduction. These new data allow us to reassess the geodynamic evolution of this part of the Variscan orogen.

Issue Title: \"The Avalonian-Cadomian Belt and related peri-Gondwana Terranes\" Neoproterozoic rocks in the Saxo-Thuringian part of Armorica formed in an active margin setting and were overprinted during Cadomian orogenic processes at the northern margin of Gondwana. The Early Palaeozoic overstep sequence in Saxo-Thuringia was deposited in a Cambro-Ordovician rift setting that reflects the separation of Avalonia and other terranes from the Gondwana mainland. Upper Ordovician and Silurian to Early Carboniferous shelf sediments of Saxo-Thuringia were deposited at the southern passive margin of the Rheic Ocean. SHRIMP U/Pb geochronology on detrital and inherited zircon grains from pre-Variscan basement rocks of the northern part of the Bohemian Massif (Saxo-Thuringia, Germany) demonstrates a distinct West African provenance for sediments and magmatic rocks in this part of peri-Gondwana. Nd-isotope data of Late Neoproterozoic to Early Carboniferous sedimentary rocks show no change in sediment provenance from the Neoproterozoic to the Lower Carboniferous, which implies that Saxo-Thuringia did not leave its West African source before the Variscan Orogeny leading to the Lower Carboniferous configuration of Pangea. Hence, large parts of the pre-Variscan basement of Western and Central Europe often referred to as Armorica or Armorican Terrane Assemblage may have remained with Africa in pre-Pangean time, which makes Armorica a remnant of a \"Greater Africa\" in Gondwanan Europe. The separation of Armorica from the Gondwana mainland and a long drift during the Palaeozoic is not supported by the presented data.[PUBLICATION ABSTRACT]

The U–Pb age and trace element composition of detrital rutile provide information about the metamorphic history of the source region that cannot be constrained by traditional U–Pb dating of detrital zircon. Previous provenance investigations focussed on only one of these methods. Based on a large LA-ICP-MS trace element and U–Pb isotopic dataset of detrital rutile and U–Pb isotopic data of detrital zircon from late Ordovician sedimentary rocks of Saxo-Thuringia, Germany, this paper discusses the application and significance of combining these methods in provenance investigations. U–Pb age spectra from the detrital zircons analysed show multiple age components (multimodal age spectra) in all samples. This is in contrast with the detrital rutile data, as only one sample yielded a multimodal U–Pb age distribution. Multimodal age spectra of detrital rutile are most likely preserved in sediments from (large) catchment areas with complex geological histories. They may also be related to specific sedimentation events, such as glacial washout during the retreat of large ice shields (e.g. the Hirnantian glaciation of Gondwana). Unimodal age spectra are however not restricted to small catchment areas, if the provenance region is characterized by a pervasive thermal overprint such as the Pan-African orogeny throughout Gondwana. Unimodal age distributions may further consist of overlapping age cluster detectable by different trace element composition of the detrital rutile grains. The combined U–Pb age and trace element data from detrital rutile grains demonstrate that rutile sourced from metapelitic rocks yield reliable and precise U–Pb ages. In contrast, detrital rutile classified to be of metamafic origin generally has too low uranium concentrations to be dated reliably by LA-ICP-MS. Detrital rutile records low- to medium-grade metamorphic events in the source region and therefore has the potential to better constrain the maximum depositional age of sedimentary rocks in comparison to U–Pb dating of detrital zircon.

LA-ICP-MS U–Pb data from detrital zircons of the Ediacaran to Cambrian siliciclastic sequence of the Torgau-Doberlug Syncline (TDS, Saxo-Thuringia, Germany) are reported for the first time. The majority of 203 analysed zircon grains is Proterozoic with minor amount of Archean and Palaeozoic grains. The U–Pb ages fall into three groups: 2.8–2.4 Ga (3%), Neoarchean to earliest Palaeoproterozoic; 2.3–1.6 Ga (46%), early to late Palaeoproterozoic; 1.0–0.5 Ga (47%), Neoproterozoic to Cambrian. This age distribution is typical for the West African Craton as the source area and for Cadomian orogenic events in northwestern Gondwana. The samples show an age gap between 1.6 and 1.0 Ga, which is characteristic for West African provenance and diagnostic in distinguishing this unit from East Avalonia and Baltica. The dataset shows clusters of Palaeoproterozoic ages at 2.2–1.7 Ga, that is typical for western Gondwana, which was affected by abundant magmatic intrusions (ca. 2.2–1.8 Ga) during the Eburnean orogeny (West African craton). Neoarchean zircon ages (3%) point to recycling of magmatic rocks formed during the Liberian and Leonian orogenies. Ediacaran to earliest Cambrian rocks of the TDS originated in an active margin regime of the Gondwanan shelf. The following early Palaeozoic overstep sequence was deposited within rift settings that reflects instability of the West-Gondwanan shelf and the separation of terranes from Ordovician onward. The results of this study demonstrate distinct northwestern African provenance of the Cambrian siliciclastics of the TDS. Due to Th–U ratios from concordant zircon analysis, igneous origin from felsic melts is concluded as the source of these grains.

We present geochronological data for late-Variscan magmatism in the Lausitz Block of the Saxo-Thuringian Zone, Germany. The Th–U–total Pb age of uraninite and the Re–Os age of molybdenite from the composite biotite–monzogranite pluton of Königshain overlap at the 2σ confidence limit: 328.6 ± 1.9 Ma (uraninite), and 327.0 ± 1.3 Ma and 327.6 ± 1.3 Ma (molybdenite), indicating that crystallization of magmatic uraninite and deposition of molybdenite were nearly contemporaneous. These data imply that magmatic processes in this part of the Variscan orogen already started in latest Visean time, about 10 Ma earlier than previously assumed (315–320 Ma). The new ages correspond to ages for plutonic rocks in the Elbe Zone immediately west of the Lausitz (around 335–325 Ma) and the bulk of late-Variscan igneous rocks in the Saxo-Thuringian Zone (335–320 Ma).

Purpose Cambrian to Ordovician sequences in Germany are known from only a few regions of limited geographic extent. One of the largest of these regions is represented by the Torgau–Doberlug Syncline (TDS) where fossiliferous early to mid-Cambrian strata occur in the subsurface. Cambrian skeletal fauna and archaeocyathan-calcimicrobial reef mounds from this area indicate a West-Gondwanan Mediterranean palaeogeographic affiliation. However, organic-walled microfossils were not studied so far. Methods New palynological research on the old and recently sampled, but hitherto non-investigated drilling core Wis BWA 1686-81 provided a moderately diverse acritarch microflora. Results The moderately diverse acritarch assemblage is dominated by diverse leiosphaerids and the stratigraphically important genera Cristallinium , Eliasum , and Timofeevia associated with specimens representing most probably the “galeate” acritarch plexus (particularly Cymatiogalea , Priscogalea , and Stelliferidium ) and a few further acritarch genera. This microflora points to a biostratigraphic position within the Cambrian Series 3 to possibly early-Furongian age including indicating for the first time that there was deposition in this palaeogeographic region continuing to the latest mid-Cambrian. The hitherto assumed sedimentary gap from early mid-Cambrian until Ordovician which seems to be common in whole Saxo-Thuringia is now slightly shorter. Conclusion The results support the model of a connected Cambro-Ordovician “Mediterranean shelf” with closely related internal areas and with well comparable early Palaeozoic sequences from Spain in the Southwest of Europe until East-Central Europe at least with the TDS as their today northernmost occurrence.