Abstract Geological evidence, supported by biogeographical data and in accord with palaeomagnetic constraints, indicates that “one ocean” models for the Variscides should be discarded, and confirms, instead, the existence of three Gondwana-derived microcontinents which were involved in the Variscan collision: Avalonia, North Armorica (Franconia and Thuringia subdivided by a failed Vesser Rift), and South Armorica (Central Iberia/Armorica/Bohemia), all divided by small oceans. In addition, parts of south-eastern Europe, including Adria and Apulia, are combined here under the new name of Palaeo-Adria, which was also Peri-Gondwanan in the Early Palaeozoic. Oceanic separations were formed by the break-up of the northern Gondwana margin from the Late Cambrian onwards. Most of the oceans or seaways remained narrow, but – much like the Alpine Cenozoic oceans – gave birth to orogenic belts with HP-UHP metamorphism and extensive allochthons: the Saxo-Thuringian Ocean between North and South Armorica and the Galicia-Moldanubian Ocean between South Armorica and Palaeo-Adria. Only the Rheic Ocean between Avalonia and peri-Gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism, and its north-western arm closed before or during the Emsian in Europe. Ridge subduction under the northernmost part of Armorica in the Emsian created the narrow and short-lived Rheno-Hercynian Ocean. It is that ocean (and not the Rheic) whose opening and closure controlled the evolution of the Rheno-Hercynian foldbelt in south-west Iberia, south-west England, Germany, and Moravia (Czech Republic). Devonian magmatism and sedimentation set within belts of Early Variscan deformation and metamorphism are probably strike-slip-related. The first arrival of flysch on the forelands and/or the age of deformation of foreland sequences constrains the sequential closure of the Variscan seaways (Galicia-Moldanubian in the Givetian; Saxo-Thuringian in the Early Famennian; Rheno-Hercynian in the Tournaisian). Additional Mid- to Late Devonian and (partly) Early Carboniferous magmatism and extension in the Rheno-Hercynian, Saxo-Thuringian and Galicia-Moldanubian basins overlapped with Variscan geodynamics as strictly defined. The Early Carboniferous episode was the start of episodic anorogenic heating which lasted until the Permian and probably relates to Tethys rifting.
Cadomian magmatic complexes of the Brunovistulian Domain crop out at the eastern termination of the Bohemian Massif. However, the age, nature and geotectonic affinity of some of pre-Variscan (meta-)igneous rock complexes from this domain are still unknown. Geochronological and geochemical study of the granitic rocks across the Brunovistulian Domain reveals new information about the timing and nature of this magmatic activity originally situated along the northern margin of Gondwana. Zircon U–Pb ...
#2Bernhard Schulz(Freiberg University of Mining and Technology)H-Index: 21
Last. Esther Schmädicke(FAU: University of Erlangen-Nuremberg)H-Index: 19
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New in situ electron microprobe monazite and white mica 40Ar/39Ar step heating ages support the proposition that the Odenwald–Spessart basement, Mid-German Crystalline Zone, consists of at least two distinct crustal terranes that experienced different geological histories prior to their juxtaposition. The monazite ages constrain tectonothermal events at 430 ± 43 Ma, 349 ± 14 Ma, 331 ± 16 Ma and 317 ± 12 Ma/316 ± 4 Ma, and the 40Ar/39Ar analyses provide white mica ages of 322 ± 3 Ma and 324 ± 3 M...
Using full-colour palaeogeographical maps from the Cambrian to the present, this interdisciplinary volume explains how plate motions and surface volcanism are linked to processes in the Earth's mantle, and to climate change and the evolution of the Earth's biota. These new and very detailed maps provide a complete and integrated Phanerozoic story of palaeogeography. They illustrate the development of all the major mountain-building orogenies. Old lands, seas, ice caps, volcanic regions, reefs, a...
Sedimentary petrography and zircon ICP-MS laser ablation ages from synorogenic clastic sediments in the Rheno-Hercynian Belt of Germany (Rheinisches Schiefergebirge, Harz) reveal basal tectonic accretion followed by exhumation and recycling of Baltica-derived Devonian shelf sediments. The recycled sediment volume demands a substantial palinspastic addition to the passive, northern margin of the Rheno-Hercynian basin. Detrital zircon ages from the Late Carboniferous foreland basin and their possi...
#2Ricardo Arenas(Complutense University of Madrid)H-Index: 44
Last. Jerónimo Matas(Instituto Geológico y Minero de España)H-Index: 8
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An integrated interpretation of the late Paleozoic structural and geochronological record of the Iberian Massif is presented and discussed under the perspective of a Gondwana-Laurussia collision giving way to the Variscan orogen. Compressional and extensional structures developed during the building of the Variscan orogenic crust of Iberia are linked together into major tectonic events operating at lithosphere scale. A review of the tectonometamorphic and magmatic evolution of the Iberian Massif...
Abstract NW Iberia includes a rather complete section of a Variscan suture, where different terranes with continental or oceanic affinities appear with clear structural relationships. Three groups of terranes, namely Upper, Ophiolitic and Basal units and a frontal tectonic melange appear in Galicia, in Cabo Ortegal, Ordenes and Malpica-Tui complexes. They constitute a huge allochthonous pile thrust over the Iberian parautochthonous and autochthonous domains, which represent the section of the Go...
Abstract The tectonics, dynamics, and biogeographic landscape of the early Paleozoic were dominated by the opening and expansion of one large ocean—the Rheic—and the diminution to terminal closure of another—Iapetus. An understanding of the evolution of these oceans is thus central to an understanding of the early Paleozoic, but their chronicle also presents a rich temporal profile of the Wilson cycle, illustrating continental-scale rifting, microcontinent formation, ocean basin development, arc...
ABSTRACT In the Iberian Variscides several first order arcuate structures have been considered. In spite of being highly studied their characterization, formation mechanisms and even existence is still debatable. The main Ibero-Armorican Arc (IAA) is essentially defined by a predominant NW–SE trend in the Iberian branch and an E–W trend in the Brittany one. However, in northern Spain it presents a 180° rotation, sometimes known as the Cantabrian Arc (CA). The relation between both arcs is contro...
Abstract Finding of ca. 620 Ma old zircons in a volcanic rock of the Loma del Aire unit, one of many structural divisions in the Ossa Morena Zone, some years ago, attracted much attention to this unit, which would contain, if proven, the oldest rocks so far dated not only in Ossa Morena but also in the entire Iberian Massif. In this paper, new field, petrographic, whole-rock geochemical and Sm–Nd isotope data as well as new TIMS U–Pb zircon ages are presented, which collectively allow a much bet...
Last. Martin Hand(University of Adelaide)H-Index: 62
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Abstract Iberia, Avalonia and the “Armorican” terranes form key constituents of the Variscan–Appalachian orogen, but their Neoproterozoic origins along the northern Gondwanan margin continue to be strongly debated. Here, we present a new detrital zircon U–Pb–Hf dataset from Neoproterozoic–Silurian sedimentary sequences in NW Iberia and Avalonia, in conjunction with the comprehensive existing datasets from potential source cratons, to demonstrate that the provenance of each terrane is relatively ...
#2Pavla Štípská(UDS: University of Strasbourg)H-Index: 30
Last. Ondrej Lexa(Charles University in Prague)H-Index: 31
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Abstract null null Previously unrecognized mafic and felsic plutonic rocks, formerly interpreted as an anatectic part of the amphibolite-eclogite Marianske Lazně Complex (MLC, Bohemian Massif) were examined together with a possible upper-crustal equivalent represented by the Cista pluton intruding continental crust farther east. These plutonic rocks were studied by whole-rock geochemistry (major and trace elements, Sr-Nd isotopes) and zircon U-Pb geochronology. The MLC magmatic rocks range from ...
#1Martial Caroff(CNRS: Centre national de la recherche scientifique)H-Index: 5
#2Jean-Alix Barrat(CNRS: Centre national de la recherche scientifique)H-Index: 51
Last. B. Le Gall(CNRS: Centre national de la recherche scientifique)H-Index: 19
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Abstract null null Kersantite is the international designation for hypabyssal lamprophyres essentially made up of dark micas and plagioclase. Kersantites from the type locality (Kersanton hamlet) and the W-Armorican surrounding area are Serpukhovian/Bashkirian in age. They are systematically associated in the field with hypabyssal microgranodiorites, both types being intruded synchronously as syn-compressional magmatic bodies that postdated pre-tectonic Tournaisian/Visean dolerites. The kersanti...
Abstract null null Eclogites, metagabbros, and paragneisses from the Variscan Munchberg Massif record a complex succession of igneous, hydrothermal and metamorphic processes. The geodynamic setting related to the protolith formation and the impact of different types of fluid-rock interactions have been uncertain up to now. We use major and trace element chemistry as well as oxygen isotopes to disentangle the geochemical signatures related to the different stages of the rocks' history. null In th...
Abstract null null Large-scale magnetic susceptibility (MS) variations in ancient sediments are usually interpreted as related to sea-level and climate changes affecting the erosional regime and the amount of detrital input. To constrain such environmental changes during the Famennian, we compared MS records in representative sections of pelagic limestones of (1) the Avalonian margin of Laurussia [Sessacker (SES) and Beringhauser Tunnel (BHT), Rhenish Slate Mountains, Germany] and (2) in Gondwan...
Abstract The present study reviews the main geochemical, sedimentological, and paleontological events associated with one of the largest perturbations in the Phanerozoic carbon cycle, the Mid-Ludfordian Carbon Isotope Excursion (MLCIE), which is globally documented in Late Silurian marine successions. Climate changes associated with the MLCIE are not yet well documented in contrast to most other Silurian CIEs. We report sea-water surface temperature changes across the entire MLCIE using δ18Oapat...
Last. Andreas Mulch(Goethe University Frankfurt)H-Index: 37
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Abstract null null We present the first stable isotope paleoaltimetry estimates for the hinterland of the eroded Variscan Belt of Western Europe based on the hydrogen isotope ratios of muscovite from syntectonic leucogranites that have been emplaced at ∼315 Ma. We focus on the Limousin region (Western Massif Central, France) where peraluminous granites are spatially associated with strike-slip and detachment shear zones that developed as a consequence of Late Carboniferous syn- to post-orogenic ...
#2S. Weinert(Technische Universität Darmstadt)H-Index: 3
Last. Ingo Sass(Technische Universität Darmstadt)H-Index: 17
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Abstract The crystalline basement of the Upper Rhine Graben is a major target for deep geothermal exploration due to the generally high reservoir temperatures and the increased radiogenic heat production. The geothermal potential is strongly dependent on the lithology, because mainly the thermal but also the hydraulic properties are affected the rock type. For this reason, the so far most detailed 3D model of the basement in the northern Upper Rhine Graben was developed, based on existing struct...
Last. Shengyao Yu(Ocean University of China)H-Index: 21
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Abstract null null The Alps, as part of the Alpine-Mediterranean Mountain chain, are one of the classical localities for orogenic studies, where the Mesozoic-Cenozoic tectonic evolution is well known, and many classical models have been proposed to explain the tectonic evolution from Mesozoic rifting and breakup to Late Mesozoic-Cenozoic subduction, plate collision, and exhumation. However, the pre-Mesozoic tectonic evolution of the pre-Alpine basement remains poorly known because of the lack of...
Abstract The Ossa-Morena Zone in Iberia, and equivalent terranes in northern France and Central Europe, are thought to be paleogeographically linked to the West African Craton at Ediacaran to early Paleozoic times. Evidence is mainly based on metasedimentary rock detrital zircon age spectra, characterized by two dominant populations of Paleoproterozoic and Cryogenian-Ediacaran ages, with a systematic lack of late Stenian – early Tonian zircon grains. We report here U-Pb-Hf results on detrital zi...