Tertiary-Quaternary intra-plate magmatism in Europe and its relationship to mantle dynamics

Anorogenic intra-plate magmatism was widespread in Europe from early Tertiary to Recent times, extending west to east from Spain to Bulgaria, and south to north from Sicily to northern Germany. Magmatism is spatially and temporally associated with Alpine-Pyrenean collisional tectonics, the development of an extensive lithospheric rift system in the northern foreland of the Alps, and, locally, with uplift of Variscan basement massifs (Massif Central, Rhenish Massif, Bohemian Massif). The volcanic regions vary in volume from large central volcanoes (e.g. Cantal, Massif Central;Vogelsberg, northern Germany), to small isolated plugs (e.g. Urach and Hegau provinces in southern Germany). Within the Mediterranean region, the Dinarides, the Pannonian Basin and Bulgaria, anorogenic volcanism locally post-dates an earlier phase of subduction-related magmatism. The major and trace element and Sr-Nd-Pb isotope characteristics of the most primitive mafic magmatic rocks (MgO > 6 wt %) provide important constraints on the nature of the mantle source and the conditions of partial melting.. These are predominantly sodic (melilitites, nephelinites, basanites and alkali olivine basalts); however, locally, potassic magma types (olivine leucitites, leucite nephelinites) also occur. In several localities (e.g., Sicily; Vogelsberg and the Rhine Graben, Germany; Calatrava, central Spain) olivine- and quartz-tholeiites form a significant component of the magmatism. The sodic magmas were derived by variable degrees of partial melting (~ 0.5 - 5 %) within a transitional zone between garnet-peridotite and spinel-peridotite mantle facies, close to the base of the lithosphere; the potassic magma types are interpreted as partial melts of enriched domains within the lithospheric mantle. Mantle partial melting was induced by adiabatic decompression of the asthenosphere, locally in small-scale, plume-like, diapirs which appear to upwell from ~ 400 km depth

PRAGIAN-EMSIAN BRACHIOPODS FROM THE RHENISH MASSIF (GERMANY): NEW DATA ON EVOLUTION AND BIOSTRATIGRAPHY

The succession of Pragian to Emsian (Early Devonian) brachiopod faunas from the Rhenish Massif (Germany) is briefly reviewed and interpreted with reference to a changing palaeoenvironment. A series of bioevents caused partial extinction or emigration of brachiopod species and succeeding immigration and dispersal of new species and speciation. The interplay of sea-level fluctuations, subsidence history and siliciclastic input from the Old Red Continent triggered the specific suitability of potential brachiopod habitats on the Rhenish Shelf. Three new taxa are proposed: Fascistropheodonta? wiltzensis n. sp., Ingentistrophia gen. n. and Pachyschizophoria amygdalina n. sp

Baltic provenance of top-Famennian siliciclastic material of the northern Rhenish Massif, Rhenohercynian zone of the Variscan orogen

The provenance of top-Famennian sedimentary rocks linked to the Hangenberg Crisis from the northern Rhenish Massif (Germany) was investigated by the means of detrital zircon U-Pb geochronology. Based on the obtained age spectra, three main tectonothermal domains are recognized as possible sources: Paleo- and Mesoproterozoic (~ 2000–1000 Ma) units of Baltica and Early Paleozoic Caledonian orogen (~ 500–400 Ma). Our interpretation of the detritus having been derived from northern source areas, i.e., Baltica and the Scandinavian Caledonides, with a minor input of German-Polish (Rügen-Pomeranian) Caledonides, contradicts the traditional view that, during the Upper Devonian, the northern Rhenish Massif was supplied by detritus from the south. Complementary mineralogical, textural and geochemical analyses point to a derivation of the detritus of Drewer and Hangenberg Sandstones mainly from felsic, recycled continental crust. The elevated concentrations of Pb and Zn in the studied sections are a feature attributed to hydrothermal alteration related to the terminal Devonian synsedimentary volcanism or post-depositional Variscan deformation

Grèzes litées and their genesis: the site of Enscherange in the Rhenish-Ardennes Massif as a case study

The freeze-thaw cycles in periglacial areas during the Quaternary glacials increased frost weathering, leading to a disintegration of rock formations. Transported downslope, clasts allowed in some areas the formation of stratified slope deposits known as "grezes litees". This study reviews the existing theories and investigates the grezes litees deposits of Enscherange and Rodershausen in Luxembourg. This process was reinforced by the lithostructural control of the parent material expressed by the dip of schistosity (66 degrees) and its orientation parallel to the main slopes in the area. This gave opportunities to activate the frost-weathering process on top of the ridge where the parent material outcropped. As the stratified slope deposits have a dip of 23 degrees and as there is no significant lateral variation in rock fragment size, slope processes that involve only gravity are excluded and transportation in solifluction lobes with significant slopewash and sorting processes is hypothesized. The Enscherange formation, the biggest known outcrop of grezes litees in north-western Europe, shows evidence of clear layering over the whole profile depth. A palaeolandscape reconstruction shows that ridges must have been tens of metres higher than presently. The investigation of the matrix composition shows Laacher See tephra in the overlying periglacial cover bed with infiltrations of the minerals in the reworked upper layer of the grezes litees deposit. Chronostratigraphic approaches using the underlying cryoturbation zone and Laacher See heavy minerals in the overlying topsoil place the formation of grezes litees deposits in the Late Pleistocene

Evolution of the lithosphere in the area of the Rhine Rift System

The Rhine Rift System (RRS) forms part of the European Cenozoic Rift System (ECRIS) and transects the Variscan Orogen, Permo-Carboniferous troughs and Late Permian to Mesozoic thermal sag basins. Crustal and lithospheric thicknesses range in the RRS area between 24-36km and 50-120km, respectively. We discuss processes controlling the transformation of the orogenically destabilised Variscan lithosphere into an end-Mesozoic stabilised cratonic lithosphere, as well as its renewed destabilisation during the Cenozoic development of ECRIS. By end-Westphalian times, the major sutures of the Variscan Orogen were associated with 45-60km deep crustal roots. During the Stephanian-Early Permian, regional exhumation of the Variscides was controlled by their wrench deformation, detachment of subducted lithospheric slabs, asthenospheric upwelling and thermal thinning of the mantle-lithosphere. By late Early Permian times, when asthenospheric temperatures returned to ambient levels, lithospheric thicknesses ranged between 40km and 80km, whilst the thickness of the crust was reduced to 28-35km in response to its regional erosional and local tectonic unroofing and the interaction of mantle-derived melts with its basal parts. Re-equilibration of the lithosphere-asthenosphere system governed the subsidence of Late Permian-Mesozoic thermal sag basins that covered much of the RRS area. By end-Cretaceous times, lithospheric thicknesses had increased to 100-120km. Paleocene mantle plumes caused renewed thermal weakening of the lithosphere. Starting in the late Eocene, ECRIS evolved in the Pyrenean and Alpine foreland by passive rifting under a collision-related north-directed compressional stress field. Following end-Oligocene consolidation of the Pyrenees, west- and northwest-directed stresses originating in the Alps controlled further development of ECRIS. The RRS remained active until the Present, whilst the southern branch of ECRIS aborted in the early Miocene. Extensional strain across ECRIS amounts to some 7km. Plume-related thermal thinning of the lithosphere underlies uplift of the Rhenish Massif and Massif Central. Lithospheric folding controlled uplift of the Vosges-Black Forest Arc

Quantification and dating of floodplain sedimentation in a medium-sized catchment of the German uplands: a case study from the Aar Valley in the southern Rhenish Massif, Germany

The distribution, thickness and composition of the floodplain sediments in the valleys of the Aar and its tributaries (Taunus Mountains) were investigated by way of extensive fieldwork at 25 locations. In the entire catchment area, 48.8 million tons of loamy floodplain fines could be assessed. Most of these were deposited since late medieval times due to extensive historical land use and forest clearing, especially in the mining region along the middle course of the Aar. In its lower course, the enhanced sedimentation ofloamy f loodplain sediments started during the Bronze Age

Palaeodiversity, palaeobiology and palaeoecology of Middle Devonian crinoids from the Eifel type region

This doctoral thesis deals with crinoids from the Middle Devonian (U. Eifelian to L. Givetian) of the Eifel Synclines (western Rhenish Massif, Germany) and secondary with U. Eifelian to U. Givetian crinoids of the eastern Rhenish Massif. The study focuses on new recovered material and on material deposit in historical collections. Since the classic monographs of the early 19th century, crinoids are nearly unstudied in modern view. They are only periphery mentioned within the standard works "Treatise on Invertebrate Paleontology" and "Fossil Crinoids". The Eifel has to be characterised as the global hotspot of Middle Devonian crinoids. Because of the high diversity, selected groups of each of the four occurring Palaeozoic subclasses are studied in the course of this work: 1. The subfamily Cupressocrininae (subclass Cladida); 2. the family Hexacrinitidae (subclass Camerata); 3. the genus Stylocrinus (subclass Disparida); 4. the genus Ammonicrinus (subclass Flexibilia). Altogether, four families, eight genera and 66 species are described taxonomically. 10 new species are erected newly. Based on the excellent three-dimensional preservation of the partly autochthon conserved skeletons and their ecological-/facial response, the Eifel crinoids gave important information about the palaeodiversity, palaeobiology and palaeoecology: Regeneration processes in cupressocrinitids and hexacrinitids correspond with that features defined for recent echinoderms. Because of their important functions, the regeneration of injured arms is more perfect than those of affected cups. Hexacrinites contra balanced the general smallness of the regenerative arms by an increased pinnulated surface. Pre- and postmortem skeletal modifications are distinguishable based on the presence or absence of a stereomatic response. In cupressocrinitids, obviously genetically modified anomalies must be separated from external caused skeletal modifications. The function morphology of Ammonicrinus indicates that the nutriment flow of several species was obviously enabled by an active ligament pumping mechanism of the stem via slowly stiffening and relaxing of their mutable connective tissues under ionic balance. The arms of Stylocrinus shows internally inclined edges adjoining laterally with adjacent brachials in an interlocking network to stabilise the closed arm crown and may allow settling in hydrodynamic turbulent environments. The cups of Hexacrinites show sloping morphologies in turbulent environments. Hexacrinites and Ammonicrinus show phylogenetic trends that obviously evince a predator driven evolution (e.g. platyceratid gastropods). Biogenous caused skeletal modifications in hexacrinitid-cups can be attributed to platyceratid gastropods. Epizoan encrusting of bryozoans, microconchids, corals and poriferas mostly occurred postmortem, while the bryozoan genus Cyclopelta premortem encrusted the stems of cupressocrinitids. Stylocrinus-morphotypes are controlled by the ecological and facial framework. The stratigraphic distribution of several taxa, e.g. of Robustocrinites, was controlled by regional-geological events. This have bearing on the fluctuation of the palaeodiversity: Within the Rheno-Ardennic Massif it can be shown that the Middle Devonian crinoids of the Eifel Synclines are linked to carbonatic shelf environments and displaced the crinoid associations of the U. Pragian to L. Eifelian, e.g. of the Hünsrückschiefer, which are adapted to deeper water habitats and show more filigree skeletal morphologies. With the establishment of biostromal developments, this association dominates up to the L. Givetian with successive increasing of the diversity and individual numbers. Within the L. Givetian, this palaeodiversity collapse presumably because of successive increasing of the sea level ("Lower Givetian Crinoid Decline"), although, outside the Eifel, this association can be traced up to the U. Givetian of the Bergisches Land and the Lahn-Dill region. With beginning of the Frasnian, a crinoid association, which is dominated by camerates, sets in and can be recognised within the Rheno-Ardennic Massif up to the Frasnian/Famennian boundary. This Melocrinites-Megaradialocrinus association was abruptly replaced by an extremely low diverse amabilicrinitid-dominated fauna, which already has a "Carboniferous character", and is the response of the Frasnian-Famennian Event ("Frasnian-Famennian Crinoid Decline")

Reply to Comment by M.F. Pereira, J.B. Silva and C. Gama on "Baltic provenance of top-Famennian siliciclastic material of the northern Rhenish Massif, Rhenohercynian zone of the Variscan orogen, by Koltonik et al., International Journal of Earth Sciences (2018) 107:2645–2669"

The authors of the Comment suggest that our geological overview map of the European Variscides is incorrect in the section showing SW Iberia (our Fig. 1a). However, our paper reports results of the provenance study from the northern Rhenish Massif, and does not attempt to discuss the architecture and tectonic evolution of the Appalachian-Variscan belt. The aim of Fig. 1 is to locate the study area in the geological context of the European Variscides and not to extrapolate the implications of our findings down to southern Portugal. The map is mostly based on Franke (2014) that is explicitly stated in the caption. Our results are neutral towards the hypothetical correlation between the Mid-German Crystalline High and the southern domains of the Ossa-Morena Zone that is shown on the map[…

Sulphur isotope geochemistry of black shale-hosted antimony mineralization, Arnsberg, northern Rhenish Massif, Germany

Vein-type and bedding-concordant mesothermal (180–410 °C) stibnite–sulphosalt mineralization at Arnsberg, NE Rhenish Massif, Germany, is hosted by Carboniferous pyrite-rich black shales and siliceous limestones. A detailed sulphur isotope study of the stibnite–sulphosalt mineralization and pyrite from a variety of regional host-rock lithologies has been carried out using an in situ laser combustion technique. The 34S values of stibnite of various textural types are distinctly negative and lie in a narrow range between -23.9 and -17.1 (mean -20.1). In contrast, regional sedimentary–diagenetic pyrites display a large variation of their 34S values between -45.4 and +9.3. There is little evidence for significant modification of the hydrothermal fluid during deposition and the S isotope signatures suggest that the sulphur of the stibnite mineralization was not locally derived. The 34S values of pyrite in Givetian shales display a significantly narrower range of -28.2 to -7.5 and their mean composition (-17.1) is close to the 34S values of the Arnsberg stibnite deposits. Considering the temperature-dependent isotopic fractionation between stibnite and reduced sulfur species, the 34S values of the mineralizing fluid (-16.8; 200 °C) and the Givetian rock source are essentially identical. Therefore, we propose a model of leaching and isotopic homogenization of sulphur from the Middle Devonian shales and a subsequent northward migration of these fluids. The fluids were trapped in permeability-controlled positions within anticlinal zones, where fluid cooling induced deposition of stibnite and sulphosalts