Journal articles: 'Variscan orogeny'

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García-Alcalde, Jenaro L. "En el extremo de la Zona Cantábrica (Artículo de divulgación basado en una conferencia dictada por el autor, en Arbejal, Palencia, a profesores de Enseñanza Media) At the Cantabrian zone edge (Dissemination article based on a lecture given by the author, in Arbejal, Palencia, to Secondary Education teachers)." Trabajos de Geología 36, no. 36 (September 12, 2018): 163. http://dx.doi.org/10.17811/tdg.36.2016.163-190.

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Resumen: Se describe a grandes rasgos la evolución paleogeográfica y estructural y las condiciones tectonosedimentarias de la Zona Cantábrica, durante las etapas Variscas preorogénica y sinorogénica, con foco principal en la Provincia del Pisuerga-Carrión, y se detalla algo más la estratigrafía del Devónico de la región y las huellas que dejaron en las rocas de esta edad diferentes eventos geo-biológicos con elevado interés como herramientas cronoestratigráficas.Palabras clave: paleogeografía, evolución tectonosedimentaria, Zona Cantábrica, provincia del Pisuerga-Carrión, orogenia Varisca, Silúrico-Carbonífero.Abstract: An overall description of the Variscan paleogeography and tectonosedimentary evolution of the Pisuerga-Carrion Province (eastern Cantabrian Zone, N Spain) is given. The Devonian stratigraphy of that province and the major geologic and paleontological events recorded in these successions are briefly discussed, emphasizing their significance as chronostratigraphic tools.Keywords: paleogeography, tectonosedimentary evolution, Cantabrian Zone, Pisuerga-Carrion province, Variscan orogeny, Silurian-Carboniferous.

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Dill, Harald. "A Model of Metallogenesis throughout Variscan Orogeny and Denudation of the Variscan Orogen in Southern Germany and Adjoining Areas." Zeitschrift der Deutschen Geologischen Gesellschaft 141, no. 1 (January 1, 1990): 129–38. http://dx.doi.org/10.1127/zdgg/141/1990/129.

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VACEK, FRANTIŠEK, and JIŘÍ ŽÁK. "A lifetime of the Variscan orogenic plateau from uplift to collapse as recorded by the Prague Basin, Bohemian Massif." Geological Magazine 156, no. 3 (November 10, 2017): 485–509. http://dx.doi.org/10.1017/s0016756817000875.

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AbstractThe Ordovician to Middle Devonian Prague Basin, Bohemian Massif, represents the shallowest crust of the Variscan orogen corresponding toc.1–4 km palaeodepth. The basin was inverted and multiply deformed during the Late Devonian to early Carboniferous Variscan orogeny, and its structural inventory provides an intriguing record of complex geodynamic processes that led to growth and collapse of a Tibetan-type orogenic plateau. The northeastern part of the Prague Basin is a simple syncline cross-cut by reverse/thrust faults and represents a doubly vergent compressional fan accommodatingc.10–19 % ~NW–SE shortening, only minor syncline axis-parallel extension and significant crustal thickening. The compressional structures were locally overprinted by vertical shortening, kinematically compatible with ductile normal shear zones that exhumed deep crust in the orogen's interior atc. 346–337 Ma. On a larger scale, the deformation history of the Prague Syncline is consistent with building significant palaeoelevation during Variscan plate convergence. Based on a synthesis of finite deformation parameters observed across the upper crust in the centre of the Bohemian Massif, we argue for a differentiated within-plateau palaeotopography consisting of domains of local thickening alternating with topographic depressions over lateral extrusion zones. The plateau growth, involving such complex three-dimensional internal deformations, was terminated by its collapse driven by multiple interlinked processes including gravity, voluminous magma emplacement and thermal softening in the hinterland, and far-field plate-boundary forces resulting from the relative dextral motion of Gondwana and Laurussia.

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Ptáček, Jiří, Radomír Grygar, Petr Koníček, and Petr Waclawik. "The impact of Outer Western Carpathian nappe tectonics on the recent stress-strain state in the Upper Silesian Coal Basin (Moravosilesian Zone, Bohemian Massif)." Geologica Carpathica 63, no. 1 (February 1, 2012): 3–11. http://dx.doi.org/10.2478/v10096-012-0002-x.

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The impact of Outer Western Carpathian nappe tectonics on the recent stress-strain state in the Upper Silesian Coal Basin (Moravosilesian Zone, Bohemian Massif) The Upper Silesian Coal Basin (USCB) represents a typical foreland basin developed during the Variscan orogenic phase of the Late Carboniferous. Later, during the Alpine orogeny the Outer Western Carpathian nappes were thrust over the post-Variscan foreland, to which the USCB belongs. Due to this complex tectonic history, redistribution of stress fields occurred in the post-Variscan basement. Furthermore, post-Variscan denudation processes probably also contributed to recent stress regimes. Nevertheless, the impact of the West Carpathian orogeny can be regarded as the most significant influence. The in-situ measurement of recent stress fields in deposits of the Karviná Formation of the USCB and structural analysis of the Czech part of the USCB, has focused on verification of the structure and stress interference of the Carpathian nappes and post-Variscan foreland basement. In the southernmost part of the Karviná Subbasin, the easternmost domain of the USCB, situated in the apical zone of the Variscan accretionary wedge, hydrofracturing and overcoring stress measurements have been recorded in coal seams from selected coal mines. The data have been supplemented by interpretation of focal mechanism solutions of mine induced seismic events. Measurements of recent in-situ stress regimes in the Karviná Formation of the USCB indicate a dominant generally NW-SE orientation of the maximum horizontal compression stress. The results demonstrate that the stress-strain regime in the Karviná Formation in the Variscan Upper Carboniferous basement is significantly influenced by the stress field along the Outer Western Carpathian nappes front. Besides improving our understanding of recent regional stress fields within an area of mutual structural-tectonic interference by both the Variscan and Alpine orogenies, the measured data may contribute to more optimal and safer mining activities in the coal basin.

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Balintoni, Ioan, Constantin Balica, Monica Cliveţi, Li-Qiu Li, Horst Hann, Fukun Chen, and Volker Schuller. "The emplacement age of the Muntele Mare Variscan granite (Apuseni Mountains, Romania)." Geologica Carpathica 60, no. 6 (December 1, 2009): 495–504. http://dx.doi.org/10.2478/v10096-009-0036-x.

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The emplacement age of the Muntele Mare Variscan granite (Apuseni Mountains, Romania)Like the Alps and Western Carpathians, the Apuseni Mountains represent a fragment of the Variscan orogen involved in the Alpine crustal shortenings. Thus the more extensive Alpine tectonic unit in the Apuseni Mountains, the Bihor Autochthonous Unit is overlain by several nappe systems. During the Variscan orogeny, the Bihor Unit was a part of the Someş terrane involved as the upper plate in subduction, continental collision and finally in the orogen collapse and exhumation. The Variscan thermotectonic events were marked in the future Bihor Unit by the large Muntele Mare granitoid intrusion, an S-type anatectic body. Zircon U-Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) dating yielded a weighted mean age of 290.9 ± 3.0 Ma and a concordia age of 291.1 ± 1.1 Ma. U-Pb isotope dilution zircon analyses yielded a lower intercept crystallization age of 296.6 + 5.7/-6.2 Ma. These two ages coincide in the error limits. Thus, the Muntele Mare granitoid pluton is a sign of the last stage in the Variscan history of the Apuseni Mountains. Many zircon grains show inheritance and/or Pb loss, typical for anatectic granitoid, overprinted by later thermotectonic events.

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Schulmann, Karel. "Mechanics of Variscan Orogeny: A modern view on orogenic research." Comptes Rendus Geoscience 341, no. 2-3 (February 2009): 97–102. http://dx.doi.org/10.1016/j.crte.2009.01.003.

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Fernández, F. J., and S. Llana-Fúnez. "Deformación asociada a la falla de Valdoviño (Noroeste del Macizo Ibérico) Deformation related to the Valdoviño fault (Northwest Iberian Massif)." Trabajos de Geología 36, no. 36 (September 12, 2018): 95. http://dx.doi.org/10.17811/tdg.36.2016.95-118.

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Resumen: La sección costera de la falla de Valdoviño expone rocas de falla deformadas en las proximidades de la base de la zona sismogénica de la corteza Ibérica Varisca, en la que estructuras frágiles discretas afectan una zona de deformación predominantemente dúctil. El núcleo de la falla contiene rocas ultramáficas, rocas máficas con granate, anfibolitas, neises cuarzo-feldespáticos y metavulcanitas básicas entre las facies deformadas del granitoide Varisco de A Espenuca. Este artículo describe la deformación y microestructuras relacionadas con la falla desarrolladas en el granitoides. La composición y características tectonometamórficas del resto de rocas presentes en el núcleo de la falla sugieren que las estructuras asociadas a la falla se superpusieron a fábricas tectónicas previas, similares a las que presentan las rocas de los complejos alóctonos del NO del Macizo Ibérico.Palabras clave: microestructura, rocas de falla, corteza continental, EBSD, Orógeno Varisco.Abstract: The coastal section across the Valdoviño fault exposes fault-related rocks deformed at the base of the seismogenic zone of the Iberian Variscan crust. Discrete brittle structures are superimposed over previous predominant ductile deformation fabrics in most rocks. The core of the fault contains ultramafic rocks, garnet-bearing mafic rocks, amphibolites, quartzo-feldspathic gneisses and basic metavulcanites, in between the deformed facies of the A Espenuca Variscan granitoid. We show the deformation and microstructures related to the fault developed in the Variscan granitoid. The composition and tectonometamorphic features of the rest of the related rocks at the core of the fault suggest that deformation structures are superposed onto earlier tectonic fabrics, similar to those present in the rocks of the allochthonous complexes of the NW Iberian Massif.Keywords: microstructure, fault-related rocks, continental crust, SEM-EBSD, Variscan Orogeny.

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Okay, Aral I., and Gültekin Topuz. "Variscan orogeny in the Black Sea region." International Journal of Earth Sciences 106, no. 2 (September 22, 2016): 569–92. http://dx.doi.org/10.1007/s00531-016-1395-z.

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Pastor-Galán, Daniel, Gabriel Gutiérrez-Alonso, and Arlo B. Weil. "The enigmatic curvature of Central Iberia and its puzzling kinematics." Solid Earth 11, no. 4 (July 8, 2020): 1247–73. http://dx.doi.org/10.5194/se-11-1247-2020.

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Abstract. The collision between Gondwana and Laurussia that formed the latest supercontinent, Pangea, occurred during Devonian to early Permian times and resulted in a large-scale orogeny that today transects Europe, northwest Africa, and eastern North America. This orogen is characterized by an “S” shaped corrugated geometry in Iberia. The northern curve of the corrugation is the well-known and studied Cantabrian (or Ibero–Armorican) Orocline and is convex to the east and towards the hinterland. Largely ignored for decades, the geometry and kinematics of the southern curvature, known as the Central Iberian curve, are still ambiguous and hotly debated. Despite the paucity of data, the enigmatic Central Iberian curvature has inspired a variety of kinematic models that attempt to explain its formation but with little consensus. This paper presents the advances and milestones in our understanding of the geometry and kinematics of the Central Iberian curve from the last decade with particular attention to structural and paleomagnetic studies. When combined, the currently available datasets suggest that the Central Iberian curve did not undergo regional differential vertical-axis rotations during or after the latest stages of the Variscan orogeny and did not form as the consequence of a single process. Instead, its core is likely a primary curve (i.e., inherited from previous physiographic features of the Iberian crust), whereas the curvature in areas outside the core is dominated by folding interference from the Variscan orogeny or more recent Cenozoic (Alpine) tectonic events.

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Van Baelen, Hervé, and Manuel Sintubin. "Kinematic consequences of an angular unconformity in simple shear: an example from the southern border of the Lower Palaeozoic Rocroi inlier (Naux, France)." Bulletin de la Société Géologique de France 179, no. 1 (January 1, 2008): 73–87. http://dx.doi.org/10.2113/gssgfbull.179.1.73.

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AbstractThe presence of an angular unconformity in combination with complex structures in the basement, lacking in the cover, is commonly seen as an indication for an orogenic event pre-dating the unconformity. The recognition of such an older orogenic event becomes, however, less evident in areas where both cover and basement were deformed together during an orogen post-dating the angular unconformity.The validity of this common interpretation has been evaluated at the southern border of the Lower Palaeozoic Rocroi basement inlier (Naux, northern France), where the basement-cover interface is very well exposed. This basement-cover interface, showing an angular unconformity, has classically been interpreted as evidence for an early Palaeozoic tectonometamorphic event, called the Ardennian orogeny, though only one penetrative cleavage, co-genetic with the structures present in both cover and basement, can be observed.A detailed geometrical study shows, however, that the presence of a tilted basement, involving the angular unconformity, provokes a rheological heterogeneity that causes a contrasting response of basement and cover with respect to the Variscan shortening. While Variscan progressive deformation gave rise to a rather regular cleavage refraction pattern in the subhorizontal multilayer cover sequence, a complex deformation, expressed by non-cylindrical folds, boudinage and shearing developed in the basement. The basement-cover interface itself played no rheological role, but has been passively sheared and folded as a consequence of the deformation of the basement. This study proves that the deformed basement-cover interface, allowing to link deformation in basement and cover, is a necessary tool to properly interpret complex deformation in the basement. With respect to the regional geodynamic evolution of the northern parts of the Central European Variscides, our kinematic model indeed demonstrates that this classical outcrop area bears no evidence for an early Palaeozoic orogenic event, and that the angular unconformity reflects the late Silurian – early Devonian onset of the Ardenne-Eifel basin development, rather than a middle Ordovician Ardennian orogeny.

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Balintoni, Ion, Constantin Balica, Antoneta Seghedi, and Mihai Ducea. "Peri-Amazonian provenance of the Central Dobrogea terrane (Romania) attested by U/Pb detrital zircon age patterns." Geologica Carpathica 62, no. 4 (August 1, 2011): 299–307. http://dx.doi.org/10.2478/v10096-011-0023-x.

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Peri-Amazonian provenance of the Central Dobrogea terrane (Romania) attested by U/Pb detrital zircon age patterns The Central Dobrogea Shield is a part of the Moesia, a Paleozoic composite terrane located southward of the North Dobrogea Alpine orogen. The two geological units are separated from each other by a trans-lithospheric discontinuity, the Peceneaga-Camena transform fault. Along this fault, remnants of a Variscan orogen (i.e. North Dobrogea), recycled during the Alpine orogeny come in contact with two lithological entities of the Central Dobrogea Shield, unaffected by the Phanerozoic orogenic events: the Histria Formation, a flysch-like sequence of Ediacaran age very low-grade metamorphosed and its basement, the medium-grade metamorphosed Altîn Tepe sequence. Southward, along the reverse hidden Palazu fault, the Histria Formation meets South Dobrogea, formed of quite different geological formations. Detrital zircon from the Histria Formation yielded U/Pb LA ICP MS ages that show provenance patterns typical of peri-Amazonian terranes. Such terranes were sourced by orogens ranging from Paleoarchean to Neoproterozoic. The ages between 750 and 600 Ma differentiate the Amazonian sources from the Baltican and Laurentian sources, since they are lacking from the last ones. The youngest ages of 587 and 584 Ma suggest for the Histria Formation a maximum late Ediacaran deposition age. At the same time, the continuity of the Ordovician sediments over the Palazu fault revealed by drill-cores favours a Cambrian junction between Central and South Dobrogea.

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Lardeaux, Jean-Marc. "Deciphering orogeny: a metamorphic perspective Examples from European Alpine and Variscan belts." Bulletin de la Société Géologique de France 185, no. 5 (May 1, 2014): 281–310. http://dx.doi.org/10.2113/gssgfbull.185.5.281.

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AbstractIn this paper we review and discuss, in a synthetic historical way, the main results obtained on Variscan metamorphism in the French Massif Central. First, we describe the pre-orogenic architecture of the French Massif Central on the base of available lithostratigraphic and geochemical constraints. Second, we portray the progressive metamorphic evolution through time and space with the presentation of 6 metamorphic maps corresponding to critical orogenic periods, namely 430–400 Ma, 400–370 Ma, 370–360 Ma, 360–345 Ma, 340–325 Ma and 320–290 Ma. We discuss the role of multiple subductions in orogeny, the metamorphic effects of continental collision (i.e. regional development of intermediate-pressure metamorphic series) as well as the links between post-thickening tectonics and the regional development of low-pressure metamorphic series coeval with crustal partial melting. As it was the case for the western Alps, we emphasize the lack of temporal data on high-pressure/low-temperature metamorphic rocks as well as the uncertainties on the sizes of rock units that have recorded the same metamorphic history (i.e. coherent P-T-t/deformation trajectories). Finally, we underline the main differences and similarities between the metamorphic evolutions of the western Alps and the French Massif Central.

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Rast, Nicholas. "Tectonic implications of the timing of the Variscan orogeny." Geological Society, London, Special Publications 38, no. 1 (1988): 585–95. http://dx.doi.org/10.1144/gsl.sp.1988.038.01.40.

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Kroner, U., and R. L. Romer. "Two plates — Many subduction zones: The Variscan orogeny reconsidered." Gondwana Research 24, no. 1 (July 2013): 298–329. http://dx.doi.org/10.1016/j.gr.2013.03.001.

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Aleksandrowski, P., R. Kryza, S. Mazur, C. Pin, and J. A. Zalasiewicz. "The Polish Sudetes: Caledonian or Variscan?" Transactions of the Royal Society of Edinburgh: Earth Sciences 90, no. 2 (1999): 127–46. http://dx.doi.org/10.1017/s0263593300007197.

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AbstractThe Polish Sudetes on the NE margin of the Bohemian Massif comprise a complex mosaic of pre-Permian basement units, traditionally included in the Variscides. A hypothesis of significant Caledonian orogenesis in this area originated in the 1920s, was subsequently rejected, and then was recently revived in models which invoked Early Palaeozoic to Early-Mid Devonian subduction and continental collision along a proposed extension of the Tornquist suture zone. We reassess the evidence invoked in support of the Caledonian orogeny, such as supposed regional pre-Upper Devonian unconformity, Ordovician bimodal magmatism and radiometric, palaeontological, palaeomagnetic and structural data, and suggest these are either inconclusive or misinterpreted. On the other hand, the Sudetes record Mid?-Late Devonian blueschist metamorphism followed by an Early Carboniferous regional high temperature event, widespread Late Devonian/Early Carboniferous flysch/molasse sedimentation and abundant granite intrusion in the Carboniferous to Early Permian. We discuss the usage of the term ‘Caledonian’ in a plate tectonic context and suggest it should not be used simply to denote Early to Mid-Palaeozoic tectonic activity. The tectonic evolution of the Sudetes was temporally different from, and resulted from convergence of different crustal domains than that of the British-Scandinavian-Pomeranian Caledonides. The Sudetic Palaeozoic sequences most probably developed on Armorican Neoproterozoic crust and in adjacent oceanic(?) domains and, therefore, the Sudetes form part of the Variscan orogenic belt.

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Johnston, J. D., J. A. Tait, G. J. H. Oliver, and F. C. Murphy. "Evidence for a Caledonian orogeny in Poland." Transactions of the Royal Society of Edinburgh: Earth Sciences 85, no. 2 (1994): 131–42. http://dx.doi.org/10.1017/s0263593300003539.

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AbstractThe Lower Palaeozoic tectonic history of central and eastern Europe is poorly understood because of extensive Variscan and/or Alpine reworking. The trace of the Tornquist Sea, the SE arm of the Lower Palaeozoic Iapetus Ocean, extended from NE Britain to Asia Minor. The site of this ocean is constrained by the tectonostratigraphy and faunal provinciality of Lower Palaeozoic inliers in northern Czechoslovakia, and southern Poland. In this paper, the collage of contrasting tectonostratigraphic histories of terranes in the Lower Palaeozoic of Poland is reviewed. Fossil evidence demonstrates that the Holy Cross Mountains and the Krakovian Belt display Lower Ordovician and Lower Devonian angular unconformities. Faunal data suggest that the Tornquist Suture Zone must lie south of the Holy Cross and between Upper Silesia and the Barrandian of the Czech Republic. Between these areas, in the Sudeten Mountains, a continental scale sinistral mylonite zone (along the line of the Intra-Sudetic Fault) was periodically active between the Middle Ordovician and the Upper Triassic. Various dismembered ophiolite, island arc and batholith terranes from alongside the Intra-Sudetic Fault have Ordocivian and Silurian magmatic and metamorphic zircon isotopic and fossil ages. Thus the often stated view that deformation in the Sudetes is Variscan (i.e. post-Middle Devonian) must be called into question. It is proposed instead that the Tornquist Suture is located within the Sudeten mountains, and as in the Holy Cross Mountains, much of the observed deformation is post-Cambrian and pre-Gedinnian in age, i.e. Caledonian.

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Keeley, M. L., C. L. E. Lewis, G. D. Sevastopulo, G. Clayton, and R. Blackmore. "Apatite fission track data from southeast Ireland: implications for post-Variscan burial history." Geological Magazine 130, no. 2 (March 1993): 171–76. http://dx.doi.org/10.1017/s0016756800009833.

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AbstractThe results of a reconnaissance apatite fission track study from southeast Ireland are compared with modelled ages and length distributions predicted using both traditional thermal histories and the thermal history indicated by the fission track age and length data. All samples have experienced total annealing during the Variscan orogeny. There is strong evidence for significant post-Variscan, pre-Mid Jurassic heating and cooling. The modelling also recognizes a third thermal event subsequent to 100 Ma. The implications of these results are examined in terms of the timing and extent of subsidence and inversion along the northern margin of the North Celtic Sea Basin.

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Wagner, T., and N. J. Cook. "Late-orogenic alpine-type (apatite)-quartz fissure vein mineralization in the Rheinisches Schiefergebirge, NW Germany: mineralogy, formation conditions and lateral-secretionary origin." Mineralogical Magazine 64, no. 3 (June 2000): 539–60. http://dx.doi.org/10.1180/002646100549418.

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AbstractMineralogical, geochemical and fluid inclusion investigations of a representative suite of fissure vein mineralizations in the Rheinisches Schiefergebirge, NW Germany indicate a link to the latest stage of the Variscan orogenic evolution. Model P-T-conditions during initiation of fibrous fissure vein quartz growth are in the range 370–420°C at 0.2–0.7 kbar. The dataset suggests significant fluid cooling during evolution of the vein systems. Minimum temperatures at the end of fibrous quartz growth lie in the range 140–190°C, with conductive heat transfer and heat consumption during interaction with wallrock believed to be the main mechanisms responsible. Wallrock alteration is characterized by leaching and mobilization of most of the dominant vein components (quartz, albite, apatite), notably Si, Na and P. The principal stage of vein formation is, on the basis of available data, believed to relate to a process of intra-formational redistribution or lateral secretion. However, part of those elements deposited both in wallrock and fissure veins were probably supplied directly by the external fluid. Rates of fissure opening and material deposition were in equilibrium during the principal growth stage of fibrous quartz. However, this situation evolved due to a slowing down of material supply and deposition coupled with an increased rate of fissure opening to produce open fissures and formation of idiomorphic quartz crystals within them. Deposition depths were in the range of 0.6–2.1 km, appreciably lower than estimations of overburden. We believe therefore that formation of the fissure vein systems took place along the retrograde late–orogenic exhumation path, in a transitional stage between Variscan collision and a late- to post-orogenic extensional regime. Fluid composition characteristics also strongly suggest a relationship to the latest stages of the Variscan mineralization cycle in which low–salinity brines dominate. Development of fissure vein systems during the latest stages of continental collision, identified here from the Variscan orogeny, can be considered analogous with similar phenomena in the Alpine orogenic belt.

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Faure, Michel, Philippe Rossi, Julien Gaché, Jérémie Melleton, Dirk Frei, Xianhua Li, and Wei Lin. "Variscan orogeny in Corsica: new structural and geochronological insights, and its place in the Variscan geodynamic framework." International Journal of Earth Sciences 103, no. 6 (May 10, 2014): 1533–51. http://dx.doi.org/10.1007/s00531-014-1031-8.

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Regorda, Alessandro, Jean-Marc Lardeaux, Manuel Roda, Anna Maria Marotta, and Maria Iole Spalla. "How many subductions in the Variscan orogeny? Insights from numerical models." Geoscience Frontiers 11, no. 3 (May 2020): 1025–52. http://dx.doi.org/10.1016/j.gsf.2019.10.005.

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Franke, W., L. R. M. Cocks, and T. H. Torsvik. "Detrital zircons and the interpretation of palaeogeography, with the Variscan Orogeny as an example." Geological Magazine 157, no. 4 (October 3, 2019): 690–94. http://dx.doi.org/10.1017/s0016756819000943.

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AbstractAnalysis of the distribution of detrital zircon grains is one of the few parameters by which Precambrian palaeogeography may be interpreted. However, the break-up of Pangea and the subsequent dispersal of some of its fragments around the Indian Ocean demonstrate that zircon analysis alone may be misleading, since zircons indicate their original derivation and not their subsequent plate-tectonic pathways. Based on analysis of Precambrian–Ordovician zircon distributions, the presence of microcontinents and separating oceans in the north Gondwanan realm has been rejected in favour of an undivided pre-Variscan continental northwards extension of Africa to include Iberia, Armorica and neighbouring southern European terranes, based on analysis of Precambrian–Ordovician zircon distribution. However, contrasting views, indicating the presence of three peri-Gondwanan oceans with complete Wilson cycles, are reinforced here by a critical reappraisal of the significance of that Variscan area detrital zircon record together with a comparison of the evolution of the present-day Indian Ocean, indicating that Iberia, Armorica and other terranes were each separate from the main Gondwanan craton during the early Palaeozoic Era.

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Drábek, Milan, and Holly Stein. "Molybdenite Re-Os dating of Mo-Th-Nb-REE rich marbles: pre-Variscan processes in Moldanubian Variegated Group (Czech Republic)." Geologica Carpathica 66, no. 3 (June 1, 2015): 173–79. http://dx.doi.org/10.1515/geoca-2015-0018.

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Abstract In an effort to contribute to the discussion concerning the age of rocks of the Moldanubian Variegated Group, we have undertaken Re-Os dating of molybdenite of banded carbonatite-like marbles (CLM) from the graphite mine Václav at Bližná (Southern Bohemia), which belong to the metamorphic sequence of this group. The Re-Os model ages for the molybdenites range between 493 and 497 Ma and apparently correspond to the early stages of metamorphism connected with pre-Variscan rift-related tectono-metamorphic events, which affected and recrystallized sedimentary CLM material rich in Mo-Th-Nb-REE. The molybdenite bearing carbonatite like marbles situated in the footwall of Bližná graphite mine have been interpreted as carbonates with a large share of volcano-detritic material derived from contemporaneous primitive alkaline (carbonatite-like) volcanism deposited in a shallow marine lagoonal environment. There is no geological evidence for the participation of fluids mobilized from host rocks in the formation of the CLM. Because the Re-Os chronometer in molybdenite is demonstrably stable through later Variscan facies metamorphism, the molybdenite chronometer has not been affected by subsequent thermal overprints associated with the Variscan orogeny.

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Lardeaux, Jean-Marc. "Deciphering orogeny: a metamorphic perspective. Examples from European Alpine and Variscan belts." Bulletin de la Société Géologique de France 185, no. 2 (February 1, 2014): 93–114. http://dx.doi.org/10.2113/gssgfbull.185.2.93.

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AbstractIn this paper we review and discuss, in a synthetic historical way, the main results obtained on Alpine metamorphism in the western Alps. First, we describe the finite metamorphic architecture of the western Alps and discuss its relationships with subduction and collision processes. Second, we portray the progressive metamorphic evolution through time and space with the presentation of 5 metamorphic maps corresponding to critical orogenic periods, namely 85-65 Ma, 60-50 Ma, 48-40 Ma, 38-33 Ma and 30-20 Ma. We underline the lack of temporal data on high-pressure/low-temperature metamorphic rocks as well as the severe uncertainties on the sizes of rock units that have recorded the same metamorphic history (i.e. coherent P-T-t/deformation trajectories). We discuss the role of subduction-driven metamorphism in ocean-derived protoliths and the conflicting models that account for the diachrony of continental subductions in the western Alps.

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Schulmann, Karel, José R. Martínez Catalán, Jean Marc Lardeaux, Vojtěch Janoušek, and Giacomo Oggiano. "The Variscan orogeny: extent, timescale and the formation of the European crust." Geological Society, London, Special Publications 405, no. 1 (2014): 1–6. http://dx.doi.org/10.1144/sp405.15.

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Channell, J. E. T., C. McCabe, T. H. Torsvik, A. Trench, and N. H. Woodcock. "Palaeozoic palaeomagnetic studies, in the Welsh Basin-recent advances." Geological Magazine 129, no. 5 (September 1992): 533–42. http://dx.doi.org/10.1017/s0016756800021695.

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AbstractIn the last two years, new palaeomagnetic data from Wales have resulted in radical revision of the Ordovician palaeogeography of Eastern Avalonia, part of the southern margin of the Iapetus Ocean. Combined with Palaeozoic palaeomagnetic data from Laurentia and Gondwana, these data suggest that Eastern Avalonia was a peri-Gondwanide high latitude continental fragment during at least part of Ordovician time, with a palaeolatitude of about 62° S and 51° S in Arenig and Llanvirn time, respectively. This implies a latitudinal width of the early Ordovician Iapetus Ocean between Eastern Avalonia and Laurentia of at least 30°. Geological evidence for the proximity of Eastern Avalonia and Laurentia suggests that the intervening Iapetus Ocean closed during Silurian time, from late Llandovery to early Ludlow. Recent palaeolatitude data from the Iapetus bordering continents are consistent with closure by middle to late Silurian time. New pre-Acadian early Devonian palaeomagnetic data from the Old Red Sandstone places the Welsh Basin at about 17° S, consistent with a palaeogeography in which Laurentia, Baltica, Avalonia, Armorica, and possibly Gondwana, were part of a single supercontinent. Pervasive late Carboniferous/early Permian remagnetization affects the Welsh Basin. The remagnetization is probably associated with fluids emanating from the Variscan thrust front. We do not observe remagnetization associated with Acadian orogeny and the remagnetizations, which have been studied in more detail in North America, appear to be a unique feature of the Variscan-Hercynian-Alleghenian orogeny.

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Pérez-Cáceres, Irene, José Fernando Simancas, David Martínez Poyatos, Antonio Azor, and Francisco González Lodeiro. "Oblique collision and deformation partitioning in the SW Iberian Variscides." Solid Earth 7, no. 3 (May 30, 2016): 857–72. http://dx.doi.org/10.5194/se-7-857-2016.

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Abstract. Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny in SW Iberia, which is characterized by a number of successive left-lateral transpressional structures developed in the Devonian to Carboniferous period. These structures resulted from the oblique convergence between three continental terranes (Central Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation gave way to both intense shearing at the suture-like contacts and transpressional deformation of the continental pieces in-between, thus showing strain partitioning in space and time. We have quantified the kinematics of the collisional convergence by using the available data on folding, shearing and faulting patterns, as well as tectonic fabrics and finite strain measurements. Given the uncertainties regarding the data and the boundary conditions modeled, our results must be considered as a semi-quantitative approximation to the issue, though very significant from a regional point of view. The total collisional convergence surpasses 1000 km, most of them corresponding to left-lateral displacement parallel to terrane boundaries. The average vector of convergence is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique collision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in the Variscan orogen. This particular kinematics of SW Iberia is understood in the context of an Avalonian plate salient currently represented by the South Portuguese Zone.

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Pérez-Cáceres, I., J. F. Simancas, D. Martínez Poyatos, A. Azor, and F. González Lodeiro. "Oblique collision and deformation partitioning in the SW Iberian Variscides." Solid Earth Discussions 7, no. 4 (December 9, 2015): 3773–815. http://dx.doi.org/10.5194/sed-7-3773-2015.

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Abstract. Different transpressional scenarios have been proposed to relate kinematics and complex deformation patterns. We apply the most suitable of them to the Variscan orogeny in SW Iberia, which is characterized by a number of successive left-lateral transpressional structures developed at Devonian to Carboniferous times. These structures resulted from the oblique convergence between three continental terranes (Central Iberian Zone, Ossa-Morena Zone and South Portuguese Zone), whose amalgamation gave way to both intense shearing at the suture-like contacts and transpressional deformation of the continental pieces in-between, thus showing strain partitioning in space and time. We have quantified the kinematics of the collisional convergence by using the available data on folding, shearing and faulting patterns, as well as tectonic fabrics and finite strain measurements. Given the uncertainties regarding the data and the boundary conditions modeled, our results must be considered as a semi-quantitative approximation to the issue, though very significant from a regional point of view. The total collisional convergence surpasses 1000 km, most of them corresponding to left-lateral displacement parallel to terrane boundaries. The average vector of convergence is oriented E–W (present-day coordinates), thus reasserting the left-lateral oblique collision in SW Iberia, in contrast with the dextral component that prevailed elsewhere in the Variscan orogen. This particular kinematics of SW Iberia is understood in the context of an Avalonian plate promontory currently represented by the South Portuguese Zone.

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Caroff, Martial, Bernard Le Gall, Christine Authemayou, Denise Bussien Grosjean, Cyrill Labry, and Marcel Guillong. "Relations between basalts and adakitic–felsic intrusive bodies in a soft-substrate environment: the South Ouessant Visean basin in the Variscan belt, Armorican Massif, France." Canadian Journal of Earth Sciences 53, no. 4 (April 2016): 441–56. http://dx.doi.org/10.1139/cjes-2015-0230.

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The metasedimentary and magmatic terranes in the southern part of the Ouessant Island (Western Brittany, France) are the offshore prolongation of the Léon Variscan metamorphic domain. They mainly consist of micaschists and subordinate amphibolitic lenses (meta-pillow lavas and volcaniclastic successions) cut by a swarm of trondhjemite sills, together with a large porphyritic monzogranite body, newly dated at 336 Ma, and later syeno-leucogranitic intrusions. A large spectrum of fluidal peperites, including spectacular “fiamme”-bearing breccias, is observable at the contact between metasediments and most of the intrusives. The coexistence of amphibolitized basalts, adakitic trondhjemites, and peraluminous granites in the inferred South Ouessant basin is assigned to a variety of deep subcontemporaneous processes, including asthenospheric partial melting, high-pressure fractionation in lithospheric reservoirs (or partial remelting of deep crystallized mafic intrusions), and continental crust melting. Implications of these new results are discussed in the Visean basinal framework of the Armorican Massif, formed at an early stage of the Variscan orogeny.

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Braga, R., H. J. Massonne, and L. Morten. "An early metamorphic stage for the Variscan Ulten Zone gneiss (NE Italy): evidence from mineral inclusions in kyanite." Mineralogical Magazine 71, no. 06 (December 2007): 691–702. http://dx.doi.org/10.1180/minmag.2007.071.6.691.

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Abstract The early P-T evolution of a garnet-kyanite gneiss from the Variscan Ulten Zone has been defined by detailed petrographic observations leading to the detection of chlorite-epidote- and staurolite-bearing assemblages enclosed in kyanite porphyroblasts. Calculations of P-T pseudosections in the system NaCaKFeMgAlSiHO allowed us to constrain the evolution of these relics to the earliest metamorphic stages. The overall path shows a P-T increase to a peak of 11–12 kbar and 600–650°C followed by decompressional heating to 720°C and 9–10 kbar and final cooling at 7 kbar, 550–600°C. This clockwise P-T path reflects crustal thickening and subsequent thermal decay related to the continental collision of the Variscan orogeny 330–340 Ma ago. Our study demonstrates that large kyanite porphyroblasts may preserve assemblages related to prograde metamorphic stages. As a result, the detection of mineral inclusions in kyanite can complement many similar studies on mineral suites hosted in garnet and zircon.

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EDWARDS, R. A., G. WARRINGTON, R. C. SCRIVENER, N. S. JONES, H. W. HASLAM, and L. AULT. "The Exeter Group, south Devon, England: a contribution to the early post-Variscan stratigraphy of northwest Europe." Geological Magazine 134, no. 2 (March 1997): 177–97. http://dx.doi.org/10.1017/s001675689700664x.

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The lower part of the post-Variscan succession around Exeter, south Devon, England, comprises some 800 m of breccias, with subordinate sandstones and mudstones, which rest upon Devonian and Carboniferous rocks folded during the Variscan Orogeny and are overlain, disconformably, by the Aylesbeare Mudstone Group (Early Triassic?). These deposits comprise the most westerly of the early post-Variscan successions preserved onshore in northwest Europe and lie to the south of the Variscan Deformation Front; they are assigned to the Exeter Group (new term). Geochronological and palaeontological studies, in conjunction with detailed geological mapping, show that the constituent formations comprise a lower (Late Carboniferous(?)–Early Permian) sequence separated from an upper (Late Permian) sequence by an unconformity which represents an hiatus with a duration of at least 20 m.y. The lower sequence contains volcanic rocks dated at between 291 and 282 Ma (Early Permian) and pre-dates intrusion of the nearby Dartmoor Granite (280 Ma). In the overlying, palynologically-dated, Late Permian sequence, older breccias contain clasts of the Dartmoor Granite aureole rocks, and younger ones contain clasts of that granite. The lower sequence occurs mainly within the Crediton Trough, an east–west trending, partly fault-bounded, sedimentary basin that probably formed by extensional reactivation of a Variscan thrust. Breccias in this sequence formed largely on alluvial fans; the common occurrence of debris flows and a down-fan passage from gravity flows into fluvially deposited sediments is typical of deposition on semi-arid fans. The upper (Late Permian) sequence is more widespread but includes similar deposits overlain, at the top of the Exeter Group, by aeolian dune and interdune deposits. Correlation within the laterally variable facies associations which comprise these sequences has been achieved using a combination of sedimentary facies analysis, sedimentary geochemistry, and petrographical and geochemical clast typing. The stratigraphy revealed within the Exeter Group is broadly comparable with that recognized in the early post-Variscan Rotliegend successions elsewhere in Europe. This similarity may, however, be deceptive; the upper part of the Exeter Group may be coeval with the Zechstein, and apparently correlatable major unconformities in the group and the Rotliegend may reflect different events in the Variscan fold-belt and Variscan Foreland areas, respectively.

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31

Andrés, Juvenal, Puy Ayarza, Martin Schimmel, Imma Palomeras, Mario Ruiz, and Ramon Carbonell. "What can seismic noise tell us about the Alpine reactivation of the Iberian Massif? An example in the Iberian Central System." Solid Earth 11, no. 6 (December 18, 2020): 2499–513. http://dx.doi.org/10.5194/se-11-2499-2020.

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Abstract. The Iberian Central System, formed after the Alpine reactivation of the Variscan Iberian Massif, features maximum altitudes of 2500 m. It is surrounded by two foreland basins with contrasting elevation: the Duero Basin to the north, located at 750–800 m, and the Tajo Basin to the south, lying at 450–500 m. The deep crustal structure of this mountain range seems to be characterized by the existence of a moderate crustal root that provides isostatic support for its topography. New seismic data are able to constrain the geometry of this crustal root, which appears to be defined by a northward lower-crustal imbrication of the southern Central Iberian crust underneath this range. Contrarily to what was expected, this imbrication also affects the upper crust, as the existing orogen-scale mid-crustal Variscan detachment was probably assimilated during the Carboniferous crustal melting that gave rise to the Central System batholith. In addition, the lower crust might have thinned, allowing coupled deformation at both crustal levels. This implies that the reactivated upper-crustal fractures can reach lower-crustal depths, thus allowing the entire crust to sink. This new model can explain the differences in topography between the Central System foreland basins. Also, it provides further constraints on the crustal geometry of this mountain range, as it seems to be that of an asymmetric Alpine-type orogen, thus hindering the existence of buckling processes as the sole origin of the deformation. The results presented here have been achieved after autocorrelation of seismic noise along the CIMDEF (Central Iberian Massif DEFormation Mechanisms) profile. Although the resolution of the dataset features limited resolution (0.5–4 Hz, stations placed at ∼ 5 km), this methodology has allowed us to pinpoint some key structures that helped to constraint the deformation mechanisms that affected Central Iberia during the Alpine orogeny.

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Zanchi, A., E. Garzanti, C. Larghi, L. Angiolini, and M. Gaetani. "The Variscan orogeny in Chios (Greece): Carboniferous accretion along a Palaeotethyan active margin." Terra Nova 15, no. 3 (June 2003): 213–23. http://dx.doi.org/10.1046/j.1365-3121.2003.00483.x.

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33

Cogné, J. "The Cadomian orogeny and its influence on the Variscan evolution of western Europe." Geological Society, London, Special Publications 51, no. 1 (1990): 305–11. http://dx.doi.org/10.1144/gsl.sp.1990.051.01.19.

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Stupnicka, Ewa. "The significance of the Variscan orogeny in the Świętokrzyskie Mountains (Mid Polish Uplands)." Geologische Rundschau 81, no. 2 (June 1992): 561–70. http://dx.doi.org/10.1007/bf01828615.

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35

Maierová, Petra, Ondřej Čadek, Ondrej Lexa, and Karel Schulmann. "A numerical model of exhumation of the orogenic lower crust in the Bohemian Massif during the Variscan orogeny." Studia Geophysica et Geodaetica 56, no. 2 (April 2012): 595–619. http://dx.doi.org/10.1007/s11200-011-0455-x.

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36

Vaškaninová, Valéria, and Petr Kraft. "A unique occurrence of a psammosteid heterostracan on the peri-Gondwanan shelf in the Lower/Middle Devonian boundary marine deposits." Fossil Imprint 72, no. 3-4 (December 30, 2016): 155–60. http://dx.doi.org/10.14446/fi.2016.155.

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A rare psammosteid heterostracan (Agnatha) occurrence in the Devonian of the Prague Basin is indicative of a dry land influence in the regional palaeogeography. This argument is strongly supported by the appearance of vascular plants, but the studied vertebrates allow us to presume a local brackish water environment. These conditions are considered to be related to a supposed land in the vicinity of the preserved relic of Devonian rocks in the Teplá-Barrandian unit. Such unique conditions were not repeated in the area despite the increasing extent of continental environment related to the rising Variscan Orogeny.

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37

Hatcher, Robert D. "Basement-cover relationships in the Appalachian-Caledonian-Variscan orogen: mid-Devonian (end of Acadian orogeny) to end of Permian." Geological Society, London, Special Publications 38, no. 1 (1988): 507–14. http://dx.doi.org/10.1144/gsl.sp.1988.038.01.34.

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38

MORTON, ANDREW, MARK FANNING, and NEIL JONES. "Variscan sourcing of Westphalian (Pennsylvanian) sandstones in the Canonbie Coalfield, UK." Geological Magazine 147, no. 5 (February 12, 2010): 718–27. http://dx.doi.org/10.1017/s0016756810000014.

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AbstractThe zircon age spectrum in a sample from the Canonbie Bridge Sandstone Formation (Asturian) of southern Scotland contains two main peaks. One is Early Carboniferous in age (348–318 Ma), and corresponds to the age of igneous activity during the Variscan Orogeny. The other is of late Neoproterozoic to early Cambrian age (693–523 Ma), corresponding to the Cadomian. Together, these two groups comprise 70 % of the zircon population. The presence of these two peaks shows unequivocally that a significant proportion of the sediment was derived from the Variscides of western or central Europe. The zircon population also contains a range of older Proterozoic zircons and a small Devonian component. These could have been derived from the Variscides, but it is possible that some were locally derived through recycling of northerly derived sandstones of Devonian–Carboniferous age. The zircon age data confirm previous suggestions of Variscide sourcing to the Canonbie area, made on the basis of petrographical, heavy mineral and palaeocurrent evidence, and extend the known northward distribution of Variscan-derived Westphalian sediment in the UK.

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Moazzen, Mohssen, Zohreh Salimi, Yann Rolland, Michael Bröcker, and Robab Hajialioghli. "Protolith nature and P–T evolution of Variscan metamorphic rocks from the Allahyarlu complex, NW Iran." Geological Magazine 157, no. 11 (March 18, 2020): 1853–76. http://dx.doi.org/10.1017/s0016756820000102.

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AbstractMetamorphic rocks associated with ophiolitic rocks occur on the eroded surface of a NW–SE-trending anticline in the Allahyarlu area, NW Iran, between the Caucasus and Zagros orogenic belts. Metapelitic rocks consist mainly of quartz, muscovite chlorite, altered biotite and garnet. S1 is the pervasive schistosity, wrapping garnet, which is folded by the second schistosity (S2). The amphibolite records only one phase of deformation as the main lineation. The rocks experienced metamorphism up to the amphibolite facies, then overprinted by greenschist facies condition. Thermobarometry indicates an average pressure of c. 5 kbar and an average temperature of c. 600 °C for the amphibolite facies metamorphism, corresponding to a ∼33 °C km−1 geothermal gradient in response to a thick magmatic arc setting. Greenschist facies metamorphism shows re-equilibration of the rocks during exhumation. Amphibolites whole rock geochemistry shows trace elements patterns similar to both island arc and back-arc basin basalts, suggesting that the protolith-forming magma of the amphibolites was enriched at shallow to medium depth of a subduction system. Negative Nb anomaly and slight enrichment in light rare earth elements (LREE) and large-ion lithophile elements (LILE) of the amphibolites indicate arc-related magmatism for their protolith and a back-arc sialic setting for their formation. 40Ar–39Ar dating on muscovite separated from two gneiss samples, and hornblende separated from three amphibolite samples, documents a Variscan (326–334 Ma) age. The magmatic and metamorphic rock association of the Allahyarlu area suggests the existence of an active continental margin arc during the Variscan orogeny, without clear evidence for a continental collision.

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Murphy, J. Brendan, and Gabriel Gutiérrez-Alonso. "The origin of the Variscan upper allochthons in the Ortegal Complex, northwestern Iberia: Sm–Nd isotopic constraints on the closure of the Rheic Ocean." Canadian Journal of Earth Sciences 45, no. 6 (June 2008): 651–68. http://dx.doi.org/10.1139/e08-019.

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Northwestern Iberia preserves a stack of allochthons in which the vestiges of a suture zone generated during the Variscan orogeny by the late Paleozoic collision between Laurussia and Gondwana are exposed. Lower allochthons contain Ordovician ophiolite (known as the Lower Ophiolite), and are structurally overlain by Devonian ophiolite (Upper Ophiolite), which are in turn structurally overlain by allochthons containing high-grade metamorphic rocks with continental affinities and Late Cambrian – Early Ordovician protolith ages (known as the Upper Units). Geochemical and Sm–Nd isotopic data from the Upper Ophiolite and the structurally overlying Upper Units exposed in the Ortegal Complex of Galicia show that these allochthons are derived from a variety of mantle and crustal sources and indicate that the suture zone juxtaposes a variety of oceanic assemblages. The general isotopic characteristics of each assemblage are similar to allochthons in other Variscan complexes in NW Iberia suggesting that the allochthons are each derived from a common source and may be regionally extensive. One of the bodies mapped within the Upper Ophiolite (Purrido amphibolite) is a composite body that, in addition to recently identified Mesoproterozoic mafic rocks, is characterized by a juvenile signature at ca. 395 Ma that was chemically modified from coeval intra-oceanic subduction. The very high ϵNd of this Late Devonian ophiolite is typical of several penecontemporaneous ophiolites within the Variscan orogen including the Lizard Complex (Britain) and the Massif Central (France), suggesting derivation from a regionally extensive anomalous mantle characterized by time-integrated depletion in Nd relative to Sm. Paleozoic mafic rocks in the Upper Units have ϵNd values typical of Paleozoic mafic rocks in Avalonia, which are thought to have been derived from subcontinental lithospheric mantle (SCLM) that was enriched at ca. 1.0 Ga. They exhibit elevated Th/Yb and Ce/Yb relative to Ta/Yb suggesting that their composition has been contaminated by subduction zone components, although the age of this contamination is unclear. Felsic rocks in the Upper Units were derived by melting of Mesoproterozoic or older (West African?) crust. These data, when combined with other geologic constraints, including the outboard position of the Upper Units relative to the ophiolite, support the hypothesis that the Upper Units collectively represent a crustal fragment that drifted from Gondwana during the formation of the Rheic Ocean, was transferred to Laurussia in Silurian or early Devonian times, and was subsequently thrust over the Gondwanan margin during the closure of the Rheic Ocean and the Variscan orogenesis.

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41

Ducassou, Céline, Christine Strullu-Derrien, Michel Ballevre, Marie-Pierre Dabard, Philippe Gerrienne, Hubert Lardeux, and Cécile Robin. "Age and depositional environment of the Sainte-Anne Formation (Armorican Massif, France): the oldest (Emsian) evidence for mountain erosion in the Variscan belt." Bulletin de la Société Géologique de France 180, no. 6 (October 1, 2009): 529–44. http://dx.doi.org/10.2113/gssgfbull.180.6.529.

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Abstract The palaeogeography of the internal zones of the Variscan belt during the early stages of the convergence remains unclear. Sedimentary sequences that recorded the denudation of an early relief have generally been removed by erosion. In the Chalonnes area (southeast of the Armorican Massif), the reefal carbonates of the Chalonnes Formation (Fm) are overlain by the immature, poorly-sorted sandstones of the Sainte-Anne Fm. This formation is characterised by the occurrence of gravity flow deposits and contains immature and poorly sorted sandstones with a large amount of plant debris and lithic fragments, suggesting a depositional environment in a delta front dominated by floods. A revision of the palaeoflora content allows to assign an Emsian age to the Sainte-Anne Fm. Lithic fragments are mainly of sedimentary and volcanic origin, suggesting moderate erosion level of the source area. Palaeocurrent data indicate a southern origin for the sediments. These features collectively demonstrate that the Sainte-Anne Fm is the record of the erosion of a continental area located farther south, and experiencing incipient tectonic uplift during the Emsian. The Sainte-Anne Fm could represent therefore the earliest record in France of the very first stages of the Variscan orogeny.

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42

Szopa, Krzysztof, Anna Sałacińska, Ashley P. Gumsley, David Chew, Petko Petrov, Aleksandra Gawȩda, Anna Zagórska, Ewa Deput, Nikolay Gospodinov, and Kamila Banasik. "Two-Stage Late Jurassic to Early Cretaceous Hydrothermal Activity in the Sakar Unit of Southeastern Bulgaria." Minerals 10, no. 3 (March 15, 2020): 266. http://dx.doi.org/10.3390/min10030266.

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Southeastern Bulgaria is composed of a variety of rocks from pre-Variscan (ca. 0.3 Ga) to pre-Alpine sensu lato (ca. 0.15 Ga) time. The Sakar Unit in this region comprises a series of granitoids and gneisses formed or metamorphosed during these events. It is cut by a series of post-Variscan hydrothermal veins, yet lacks pervasive Alpine deformation. It thus represents a key unit for detecting potential tectonism associated with the enigmatic Cimmerian Orogenic episode, but limited geochronology has been undertaken on this unit. Here we report age constraints on hydrothermal activity in the Sakar Pluton. The investigated veins contain mainly albite–actinolite–chlorite–apatite–titanite–quartz–tourmaline–epidote and accessory minerals. The most common accessory minerals are rutile and molybdenite. Apatite and titanite from the same vein were dated by U–Pb LA–ICP-MS geochronology. These dates are interpreted as crystallization ages and are 149 ± 7 Ma on apatite and 114 ± 1 Ma on titanite, respectively. These crystallization ages are the first to document two stages of hydrothermal activity during the late Jurassic to early Cretaceous, using U–Pb geochronology, and its association with the Cimmerian orogenesis. The Cimmerian tectono-thermal episode is well-documented further to the east in the Eastern Strandja Massif granitoids. However, these are the first documented ages from the western parts of the Strandja Massif, in the Sakar Unit. These ages also temporally overlap with previously published Ar–Ar and K–Ar cooling ages, and firmly establish that the Cimmerian orogeny in the studied area included both tectonic and hydrothermal activity. Such hydrothermal activity likely accounted for the intense albitization found in the Sakar Unit.

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Schulmann, K. "Rapid burial and exhumation during orogeny: Thickening and synconvergent exhumation of thermally weakened and thinned crust (Variscan orogen in Western Europe)." American Journal of Science 302, no. 10 (December 1, 2002): 856–79. http://dx.doi.org/10.2475/ajs.302.10.856.

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Leat, P. T., R. N. Thompson, M. A. Morrison, G. L. Hendry, and S. C. Trayhorn. "Geodynamic significance of post-Variscan intrusive and extrusive potassic magmatism in SW England." Transactions of the Royal Society of Edinburgh: Earth Sciences 77, no. 4 (1987): 349–60. http://dx.doi.org/10.1017/s0263593300023221.

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ABSTRACTPost-Variscan magmatism in SW England involved the synchronous emplacement of basaltic and potassic lavas, minette dykes and the Cornubian granite batholith at c. 290 Ma. The basaltic and potassic rocks have high contents of Ni and Cr, which suggest that both are not excessively fractionated. The basaltic lavas are moderately enriched in LREE and LIL elements relative to HREE, whereas the chemically-varied potassic lavas are more strongly enriched in LREE and LIL elements, with notable depletions in Nb, Ta and Ti relative to LREE. These features are consistent with the view that these rocks are subduction-related. Possibly the potassic rocks were derived from an ultimate source in lithosphere subducted or downthrust during the Variscan orogeny. The source of the basaltic rocks was probably in the asthenosphere. The minette dykes are chemically similar to the potassic lavas, suggesting that they are genetically related. Most dykes occur in a zone up to 25 km wide around the margin of the granite batholith, in a “shadow-zone” relationship. The granite batholith (c. 48,000 km3) is moderately enriched in Th and HFS elements, but is strongly enriched in Rb. Rb-Th relationships indicate an origin for the granite by fractionation from potassic magma in addition to melting of crust.

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Muchez, Philippe, and Marek Slobodnik. "Recognition and significance of multiple fluid inclusion generations in telogenetic calcites." Mineralogical Magazine 60, no. 402 (October 1996): 813–19. http://dx.doi.org/10.1180/minmag.1996.060.402.12.

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AbstractFerroan and non-ferroan calcites occur in fractures in the Lower Carboniferous of the Variscan foreland of southern Belgium. These fractures post-date the Variscan orogeny and the calcites have a telogenetic origin. The non-ferroan calcites formed by recrystallization of the ferroan calcites. Two types of monophase aqueous fluid inclusions are present in the ferroan calcite cement. Although both types of inclusions formed at a temperature not exceeding 50°C, one type contains a moderately saline fluid (3.6–16.3 eq. wt.% NaCl) and the other type fresh water (Tm ice = 0°C). The fluid inclusions in the non-ferroan calcite also contain fresh water.Detailed petrography of the fluid inclusions indicate that the fresh water migrated through the crystals along opened cleavage planes and microfractures. Therefore, they have a secondary origin. The recrystallization of the ferroan calcites to non-ferroan calcites occurred in this fresh water. The saline fluid inclusions are not related to the above mentioned microstructures and although their origin remains unknown, they could represent the ambient fluid from which the ferroan calcites precipitated. The study of the relationship between the occurrence of fluid inclusions and the microstructures seems promising for the identification of fluid inclusions representing post mineral formation fluid and temperature conditions in calcite cements.

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AWDANKIEWICZ, MAREK, RYSZARD KRYZA, and NORBERT SZCZEPARA. "Timing of post-collisional volcanism in the eastern part of the Variscan Belt: constraints from SHRIMP zircon dating of Permian rhyolites in the North-Sudetic Basin (SW Poland)." Geological Magazine 151, no. 4 (September 12, 2013): 611–28. http://dx.doi.org/10.1017/s0016756813000678.

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AbstractThe final stages of the Variscan orogeny in Central Europe were associated with voluminous granitic plutonism and widespread volcanism. Four samples representative of the main rhyolitic volcanic units from the Stephanian–Permian continental succession of the North-Sudetic Basin, in the eastern part of the Variscan Belt, were dated using the SIMS (SHRIMP) zircon method. Three samples show overlapping206Pb–238U mean ages of 294 ± 3, 293 ± 2 and 292 ± 2 Ma, and constrain the age of the rhyolitic volcanism in the North-Sudetic Basin at 294–292 Ma. This age corresponds to the Early Permian – Sakmarian Stage and is consistent with the stratigraphic position of the lava units. The fourth sample dated at 288 ± 4 Ma reflects a minor, younger stage of (sub)volcanic activity in the Artinskian. The silicic activity was shortly followed by mafic volcanism. The rhyolite samples contained very few inherited zircons, possibly owing to limited contribution of crustal sources to the silicic magma, or owing to processes involved in anatectic melting and magma differentiation (e.g. resorption of old zircon by Zr-undersaturated melts). The SHRIMP results and the stratigraphic evidence suggest that the bimodal volcanism terminated the early, short-lived (10–15 Ma) and vigorous stage of basin evolution. The Permian volcanism in the North-Sudetic Basin may be correlated with relatively late phases of the regional climax of Late Palaeozoic volcanism in Central Europe, constrained by 41 published SHRIMP zircon age determinations at 299–291 Ma. The Permian volcanism and coeval plutonism in the NE part of the Bohemian Massif can be linked to late Variscan, post-collisional extension.

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SANT’OVAIA, H., P. NOGUEIRA, J. CARRILHO LOPES, C. GOMES, M. A. RIBEIRO, H. C. B. MARTINS, A. DÓRIA, et al. "Building up of a nested granite intrusion: magnetic fabric, gravity modelling and fluid inclusion planes studies in Santa Eulália Plutonic Complex (Ossa Morena Zone, Portugal)." Geological Magazine 152, no. 4 (November 14, 2014): 648–67. http://dx.doi.org/10.1017/s0016756814000569.

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AbstractThe Santa Eulália Plutonic Complex (SEPC), located in the Ossa Morena Zone (south Portugal), is composed of a medium- to coarse-grained pink granite (G0-type) and a central grey medium-grained biotite granite (G1-type). Available Rb–Sr data indicates an age of 290 Ma. An emplacement model for the SEPC is proposed, taking into account magnetic fabric, 2D gravity modelling and fluid inclusion planes studies. The G0 and G1 types demonstrate different magnetic behaviour: G0 is considered a magnetite-type granite and G1 is an ilmenite-type granite. The formation of G0 required oxidized conditions related to the interaction of mafic rocks with a felsic magma. The 2D gravity modelling and subvertical magnetic lineations show that the feeder zone of the SEPC is located in the eastern part of the pluton, confirming the role of the Assumar and Messejana Variscan faults in the process of ascent and emplacement. The magma emplacement was controlled by ENE–WSW planar anisotropies related to the final brittle stages of the Variscan Orogeny. The emplacement of the two granites was almost synchronous as shown by their gradational contacts in the field. The magnetic fabric however suggests emplacement of the G0-type first, closely followed by emplacement of the G1-type, pushing the G0 laterally which becomes more anisotropic towards the margin. The G1-type became flattened, acquiring a dome-like structure. The SEPC is a nested pluton with G0-type granite assuming a tabular flat shape and G1-type forming a rooted dome-like structure. After emplacement, SEPC recorded increments of the late Variscan stress field documented by fluid inclusion planes in quartz.

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Chopin, Francis, Michel Corsini, Karel Schulmann, Mohamed El Houicha, Jean-François Ghienne, and Jean-Bernard Edel. "Tectonic evolution of the Rehamna metamorphic dome (Morocco) in the context of the Alleghanian-Variscan orogeny." Tectonics 33, no. 6 (June 2014): 1154–77. http://dx.doi.org/10.1002/2014tc003539.

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Villaseñor, Gabriel, Elizabeth J. Catlos, Igor Broska, Milan Kohút, Ľubomír Hraško, Kimberly Aguilera, Thomas M. Etzel, J. Richard Kyle, and Daniel F. Stockli. "Evidence for widespread mid-Permian magmatic activity related to rifting following the Variscan orogeny (Western Carpathians)." Lithos 390-391 (June 2021): 106083. http://dx.doi.org/10.1016/j.lithos.2021.106083.

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CALDWELL, W. G. E., and G. M. YOUNG. "Structural controls in the western offshore Midland Valley of Scotland: implications for Late Palaeozoic regional tectonics." Geological Magazine 150, no. 4 (February 1, 2013): 673–98. http://dx.doi.org/10.1017/s0016756812000878.

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AbstractNew detailed mapping and related field studies, together with re-assessment of prior investigations, have revealed that three groups of faults, orientated broadly NE, N and NW, have been the primary controls on stratigraphical, structural and geomorphological evolution in the upper Firth of Clyde since their initiation by proto-Variscan stresses in Late Devonian time. Extended control has been achieved through repeated episodic reactivation, during which existing lines of fracture were rejuvenated and others of similar orientation initiated. Movements on two (if not all three) groups of faults persisted until middle Palaeogene time at least. The faults have been augmented by two sets of irregularly distributed, open, plunging folds, broadly N–S and E–W in their axial orientations. Some N–S folds may be attributed to oblique or strike-slip movement on reactivated caledonoid faults, others to intermittent transpression, probably in Namurian–Westphalian times, affecting mainly the northeastern Midland Valley but stretching beyond the massif of the Clyde Lava Plateau to register a weakened presence as far W as the upper Firth. The N–S folds and dextral strike-slip movements on some faults may be far-field expressions of the Uralian Orogeny, whereas earlier, sinistral displacements on NE faults and the development of small, later and less-significant E–W folds may be related to different phases of long-lived Variscan compression from the S.

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Journal articles on the topic 'Variscan orogeny'

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