Armin Zeh

During the Middle Miocene Badenian Salinity Crisis (BSC), extensive evaporites formed across different tectonic settings in the Central Paratethys. Limited age constraints hamper evaporite correlation and identification of driving mechanisms. Here, we use U–Pb dating of zircon by LA‐ICP‐MS from tephra overlying the Tuzla Basin evaporites. The results indicate cessation of evaporitic conditions at 13.88 ± 0.11 Ma, coeval with the Mi3b event‐related global sea‐level fall. In Tuzla, a backarc‐extension‐related sill controlled both evaporite formation and subsequent reflooding, significantly shortening the evaporitic phase. Conversely, flexural subsidence in the Carpathian Foredeep postponed restriction by ~0.5 Myr and prolonged evaporite deposition in deeper settings. We hypothesise that during the BSC, tectonically induced sills governed the timing and distribution of evaporites, as in the well‐studied Mediterranean Messinian Salinity Crisis (MSC). Unlike the Gibraltar arc‐dominated MSC, multiple, rapidly evolving sills of comparable influence controlled the BSC, producing diachronous and spatially heterogeneous evaporites across the Central Paratethys.

Presently, little is known about the zircon age–Hf isotope record of (meta)sedimentary rocks exposed in the southernmost part of the Mid-German Crystalline Zone and adjacent Rhenohercynian Domain, preventing detailed reconstructions of the geodynamic evolution in Central Europe. In this study, such data are presented from Late Devonian to Viséan greywackes and granite gneisses of the Palatinate Forest (Mid-German Crystalline Zone) and the Harz Mountains (Rhenohercynian). These provide evidence that clastic sedimentary rocks in both realms were sourced from a so far unrecognized, juvenile oceanic arc terrane, which was initially formed at 490–570 Ma (εHf _t up to + 13.0), and internally reworked at ca. 500, 400, 370 and 335 Ma (εHf _t = + 2.0 to + 8.4), prior to Variscan collision and post-collisional magmatism at 330 Ma. Late Devonian arc reworking is indicated by zircon U–Pb ages of ca. 370 Ma estimated for the Albersweiler granite gneiss (εHf _t = + 3.6 to + 7.7) and an amphibolite-facies paragneiss; other reworking events are indicated by the detrital zircon record. The results of data compilation further suggest that the oceanic arc terrane remained widely isolated from continental input within the Prototethys–Rheic oceanic realm until its collision with Avalonia at 335 Ma. The relics of the arc system became widely dispersed within the Saxothuringian, Rhenohercynian, Teplá-Barrandian, and Moldanubian domains during the Variscan collision and collapse. Graphical abstract

In the Dinarides, a series of long-lived lakes, known as the Dinarides Lake System (DLS) developed during the Miocene. The Sinj Basin, situated in southern Croatia, is one of the best studied among them, providing valuable insights into the paleogeographic evolution of the region. Previous research established a chronostratigraphic framework in the NW part of the basin using paleomagnetic data calibrated by ⁴⁰ Ar/ ³⁹ Ar dating. Subsequent studies demonstrated that lacustrine flooding was diachronous. However, the influence of the Miocene Climatic Optimum (MCO) or the regional Miocene extensional tectonics is still debated. This study provides new constraints on the evolution of the Sinj Basin by integrating previous dating results with new LA–ICP–MS U–Pb–zircon dating of volcaniclastic and residual deposits from the NW, central, and SE parts of the basin. The obtained U-Pb ages range between ~ 17.7 and ~ 15.3 Ma and provide new constraints on the timing of initial lacustrine flooding. Correlation with the MCO suggests a close relationship between climate change and lacustrine development. Lake-level falls reflected by conglomerates and coals deposited in marginal and more distal parts of the basin, respectively, suggest environmental instability after ~ 15.3 Ma, towards the end of the MCO. Detrital zircon grains reveal a wide spectrum of ages from the Neoproterozoic to the Early Miocene, suggesting multiple redeposition cycles, starting with the Cadomian and Variscan orogenies, followed by Cretaceous–Oligocene uplift of the Dinarides, and the recycling of foreland basin deposits into the Miocene Sinj Basin. Finally, this study demonstrates the usefulness of LA–ICP–MS U–Pb dating for the reconstruction and correlation of isolated intramontane basins. Graphic Abstract

New LA-ICP-MS detrital zircon U–Pb age data from Saxo-Thuringia provide improved constraints on the evolution of Neoproterozoic to Early Ordovician sedimentary basins along the northern margin of Gondwana. Several investigated quartzitic successions previously assigned to the Neoproterozoic have robust maximum depositional ages (RMDA) of 499 ± 5 Ma (member 2 of the Clanzschwitz Group) and 485 ± 5 Ma (Seidewitz Formation), requiring their reassignment to the upper Cambrian–Lower Ordovician. The immature greywacke units of the Cadomian basement yield robust maximum depositional ages between 551 and 546 Ma, consistent with uniform deposition during the Late Neoproterozoic in a broad active continental margin setting. In contrast, Ordovician quartzites reveal variable source signatures. Some reflect exclusively recycling of Neoproterozoic (Avalonian–Cadomian orogenic belt) and older crustal material (West African Craton), while others show additionally significant input from younger Cambro–Ordovician magmatic rocks in the Saxo-Thuringian hinterland, highlighting diverse sediment sources along the Ordovician shelf margin. The detrital zircon U–Pb data confirm a West African provenance for all analysed units. Despite its younger age, a Carboniferous greywacke from the Görlitzer Schiefergebirge was also studied here due to its close lithological resemblance to Neoproterozoic greywackes and the absence of established differentiation criteria. Its detrital zircon assemblage reflects a recycled Cadomian basement signature, along with admixtures of Cambro–Ordovician zircons and juvenile grains (~ 375–370 Ma) derived from Upper Devonian magmatic rocks. In the absence of fossil evidence, this provides clear criteria to distinguish Neoproterozoic from Carboniferous greywackes in this part of Saxo-Thuringia. Graphic abstract

Presently, little is known about the provenance and depositional ages of clastic metasedimentary rocks of the Badenweiler–Lenzkirch Zone (BLZ), which is squeezed between high-grade gneisses of the Central and Southern Black Forest Gneiss complexes. This lack of knowledge prevents detailed correlations with other sedimentary units and limits our understanding of the pre- to syn-Variscan evolution in Central Europe. In this study, we present the first set of data combining U–Pb ages, Hf isotope data, and shape parameters of detrital zircon populations of nine samples collected from three formations of the BLZ: Sengalenkopfschist, Schleifenbachschist, and Protocanites Greywacke. Based on biostratigraphic record, these formations are assumed to be deposited from the Early Ordovician to Early Carboniferous. This interpretation, however, is at odds with the detrital zircon age record, revealing robust maximum depositional ages between 368 and 378 Ma for all three units. Age spectra show peaks at 380–400 Ma, 480–500 Ma, 600–620 Ma, 700–750 Ma, 0.9–1.1 Ga, 1.8–2.2 Ga, and 2.6 Ga, and Hf isotopes a juvenile input at 380–410 Ma (εHf_t up to + 5). Combined zircon age-Hf isotope data point to three major sources, which are similar to the metamorphic gneiss units exposed in southern Black Forest (Wiese-Wehra, Todtmoos, and Murgtal), hosting relics of different Gondwana-derived terranes, in addition to a Late Devonian arc-back arc system. The finding of abundant zircon grains of euhedral shape in all BLZ samples and similar zircon typologies additionally suggest supply from a proximal magmatic arc source. Graphical abstract

The minerals zircon, monazite, xenotime and rutile commonly occur in metasedimentary rocks as detrital but also authigenic grains, which can result from different fluid-driven processes. In this study such processes are investigated on the basis of detailed petrographic observations, mineral-geochemical data, and results of in situ U-Pb dating and Nd isotope analyzes in a kaolinitized micaschist. The data provide evidence for the preservation of detrital grains of zircon, rutile and monazite crystallized between ~ 3100 and 1150 Ma, and for authigenic zircon, xenotime, rutile and monazite formed at ca. 530 Ma. The authigenic character is indicated by zircon outgrowths closely intergrown with xenotime and rutile crystals. The outgrowths occur where detrital zircon faces are intensely dissolved in contact with Fe-Mg-rich phengitic muscovite, suggesting the involvement of an aqueous fluid enriched in K-Mg-Fe-Al-Ti-P near the thermal peak at 510 °C and > 0.8 GPa. In contrast, authigenic monazite rims overgrowing rounded cores were formed during the retrograde evolution, as indicated by their occurrence in assemblage with kaolinite, and results of geothermobarometry (T = 280 °C, P < 0.3 GPa). The monazite rims show very low U contents (4–14 µg/g), extremely high Th/U (up to 1670), and nearly identical ¹⁴³Nd/¹⁴⁴Nd_t (0.51184 ± 0.00006) values that markedly differ from those of the detrital cores (¹⁴³Nd/¹⁴⁴Nd_t = 0.51000 ± 0.00050; U = 162–16418 µg/g; Th/U = 2.6–153). The high Th/U points to the involvement of an oxidizing fluid, in line with late goethite formation. Monazite microstructures, and Nd isotope characteristics require a chain of processes, from partial dissolution of detrital monazite, through REE transport and Nd isotope homogenization in an aqueous fluid, to new monazite growth.

Xenoliths recovered from the post-Variscan Bode dike system of the eastern Harz Mountains provide evidence for the existence of an Early Devonian magmatic arc system hidden beneath very low-grade metasedimentary rocks of the Rhenohercynian Zone, but also for Late Carboniferous–Early Permian crust reworking. This interpretation is based on petrographic observations and whole-rock geochemical analyses of granite xenoliths, in addition to results of zircon U–Pb dating and Hf isotope analyses. Zircon grains recovered from variably deformed granite xenoliths yield ages between 419 and 393 Ma, interpreted to reflect the timing of granite intrusion. Rare zircon xenocrysts of Archean (ca. 2.92–2.65 Ga) and Proterozoic age (ca. 1.5 to 0.56 Ga), all with subchondritic εHf_{420 Ma} values (− 0.8 to − 5.5) indicate reworking of older crust. Compilation of age-Hf isotope data further suggests that the pre-Variscan granitoids beneath the Harz Mountains belong to the same magmatic arc system exposed widespread in the adjacent Mid-German Crystalline Zone, and interpreted to result from NW-ward subduction of the Rheic Ocean beneath Avalonia-Baltica. Zircon in xenoliths with granophyric texture yields ages at 400 Ma and 295–310 Ma, indicating re-melting of Devonian granitoid basement during post-Variscan rift-related magmatism, immediately prior to Bode dike intrusion. Graphical abstract Left: Late Devonian intrusion of magmatic arc granites during NW-ward subduction of the Rheic ocean beneath Avalonia-Baltica. Right: Formation of the Bode dike system and Harz granites during Late Carboniferous-Permian extension.