scholarly journals The shape of the Variscan Belt in Central Europe: Strike-slip tectonics versus oroclinal bending

2020 ◽  
Author(s):  
Stanislaw Mazur ◽  
Paweł Aleksandrowski ◽  
Łukasz Gągała ◽  
Piotr Krzywiec ◽  
Jerzy Żaba ◽  
...  
Keyword(s):  
Bohemian Massif ◽  
Regional Distribution ◽  
Kinematic Model ◽  
Strike Slip ◽  
Alternative View ◽  
Variscan Belt ◽  
Borehole Data ◽  
Deformation Front ◽  
Isostatic Gravity ◽  
Reflection Seismics

<p>The European Variscan belt sharply changes its trend in easternmost Germany and western Poland, where the ENE- to NE-striking structures are replaced by the ESE- to SE-trending ones. The structures of still another, NNE-SSW strike, take the lead, however, along the SE margin of the Bohemian Massif. The Variscan belt seems, thus, to make nearly a U-turn, encircling the Bohemian Massif from the north. This has been explained for almost a century by assuming a 180° oroclinal loop, in which the Rhenohercynian and Saxothuringian tectonostratigraphic zones inarm the core of the Bohemian Massif. According to this classical view, the outermost tectonostratigraphic zone of the Variscan belt, the Rhenohercynian Zone, continues eastward in the deep substratum of the Permian-Mesozoic basin and reappears at the surface along the eastern rim of the Bohemian Massif.</p><p>Since the late 1970s an alternative view has gained an increasing attention that postulates a dextral transpressional regime during the final accretion of the Variscan terranes. This transpressional tectonic context is believed to have resulted from sublatitudinal, right-lateral displacements between Gondwana and Laurussia. Near the Carboniferous-Permian boundary, Gondwana decoupled from the newly formed European Variscan belt and proceeded westward, toward the southern edge of the Laurentian segment of Laurussia, owing to the development of the Appalachian subduction system. Concomitantly with the peak of the Alleghanian orogeny during early Permian, the European Variscan belt experienced a crosscut of its major tectonic zones along a set of dextral strike-slip faults.</p><p>In this study, we investigate directions and continuity of structural trends in the external zones of the Variscan orogen in Poland and map a foreland extent of Variscan deformations using seismic, gravimetric-magnetic and borehole data. These permit us testing the orocline- vs strike-slip concepts and develop an overall kinematic model for the NE Variscides.</p><p>Matched filtering of isostatic gravity, guided by results of spectral analysis, along with other derivatives of gravity and magnetic fields reveal a dominant WNW-ESE-trending pre-Permian structural grain in the external zones of the Variscan belt in Poland. This trend is confirmed by regional distribution of dips in Carboniferous and Devonian strata that were penetrated by boreholes beneath Permian-Mesozoic sediments. Seismic constraints on the position of the Variscan deformation front come from (1) the GRUNDY 2003 seismic experiment, combining wide-angle reflection-refraction measurements with the near-vertical reflection seismics in central Poland and (2) PolandSPAN and POLCRUST-01 deep reflection profiles in SE Poland. The WNW-ESE structural trend in the Variscan foreland is parallel to a set of major strike-slip fault zones in the area that are considered to convey a significant dextral displacement between Laurussia and Gondwana. The revised position of the Variscan deformation front shows a similar, uninterrupted, generally WNW-ESE trend, up to the SE border of Poland, which indicates an initial continuation of the more internal Variscan zones into the area of the present-day Carpathians. The geometry of the Variscan deformation front along with the pattern of the Variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external, non-metamorphic Variscan belt.</p>

scholarly journals Late Palaeozoic strike-slip tectonics versus oroclinal bending at the SW outskirts of Baltica: case of the Variscan belt’s eastern end in Poland

2020 ◽  
Vol 109 (4) ◽  
pp. 1133-1160 ◽  
Author(s):  
Stanislaw Mazur ◽  
Paweł Aleksandrowski ◽  
Łukasz Gągała ◽  
Piotr Krzywiec ◽  
Jerzy Żaba ◽  
...  
Keyword(s):  
Regional Distribution ◽  
Kinematic Model ◽  
Structural Evolution ◽  
Strike Slip ◽  
Variscan Belt ◽  
Deformation Front ◽  
Fold And Thrust Belt ◽  
Isostatic Gravity ◽  
Regional Tectonic ◽  
Major Strike

AbstractGeophysical and geological data from the eastern sector of the Central European Variscan belt are presented and reviewed in the regional tectonic context. Matched filtering of isostatic gravity, guided by results of spectral analysis, along with other derivatives of gravity and magnetic fields reveal a dominant WNW–ESE-trending pre-Permian structural grain in the external zones of the Variscan belt in Poland. This trend is confirmed by regional distribution of dips in Carboniferous and Devonian strata that were penetrated by boreholes beneath Permian-Mesozoic sediments. Based on these data, two alternative concepts explaining the connection of the Variscan belt and its NE foreland, those of strike-slip tectonics versus oroclinal bending, are discussed. The WNW–ESE structural trend in the Variscan foreland is parallel to a set of major strike-slip fault zones in the area, including those of Upper Elbe, Intra-Sudetic, Odra, Dolsk and Kraków-Lubliniec. These faults are considered to convey a significant dextral displacement between Laurussia and Gondwana. The revised position of the Variscan deformation front shows a similar, uninterrupted, generally WNW–ESE trend, up to the SE border of Poland, which indicates an initial continuation of the Variscan belt into the area of the present-day Western Carpathians. The geometry of the Variscan deformation front along with the pattern of the Variscan structural grain are inconsistent with the idea of an oroclinal loop affecting the external, non-metamorphic Variscan belt. However, the data presented do not entirely rule out an oroclinal loop within the Variscan internides. The still possible options are (1) a semi-oroclinal model postulating ~ 90° bending of the Variscan tectonostratigraphic zones into parallelism with the WNW–ESE strike-slip faults or (2) an orocline limited only to the belt linking the Wolsztyn High and Moravo-Silesian non- to weakly-metamorphic fold-and-thrust belt. Regardless of the kinematic model preferred, our data indicate that structural evolution of the Polish Variscides was concluded with the end-Carboniferous NNE–SSW shortening that resulted in the present-day extent of the Variscan deformation front.

Polykinematic foreland basins initiated during orthogonal convergence and terminated by orogen-oblique strike-slip faulting: An example from the northeastern Variscan belt

2019 ◽  
Vol 766 ◽  
pp. 379-397 ◽  
Author(s):  
Filip Tomek ◽  
František Vacek ◽  
Jiří Žák ◽  
Michael S. Petronis ◽  
Kryštof Verner ◽  
...  
Keyword(s):  
Strike Slip ◽  
Variscan Belt ◽  
Foreland Basins

scholarly journals Tectonic inversion of the Dnieper–Donetsk Basin. Part 2. Geodynamic situations and kinematic mechanism of riftogenic structure deformations

2020 ◽  
Keyword(s):  
Sedimentary Cover ◽  
Kinematic Model ◽  
Strike Slip ◽  
The Body ◽  
Donets Basin ◽  
Donetsk Basin ◽  
Kinematic Evolution ◽  
Tectonic Inversion ◽  
Reverse Thrust ◽  
Kinematic Mechanism

Formulation of the problem. In the second part of the article, the geodynamic mode and the kinematic mechanism of destruction of the Dnieper–Donetsk Basin by tectonic movements of the Late Hercynian and Alpine stages of tectogenesis were studied. New results of tectonophysical studies of the structural–kinematic evolution of the Earth's crust of Dnieper–Donetsk Basin at the collision stage are presented. The subject of research is a complex of deformation structures that complicate the sedimentary cover in the transitional zone of with Donetsk Foldbelt. Review of previous publications and studies. Using instrumental definitions of tectonite vergence, data of reconstruction of stress fields and quantitative modeling of deformations, a original kinematic model of tectonic inversion of the Dnieper–Donetsk Basin was developed. Methods. Structural–kinematic analysis of the structural drawings of collisional deformation and tectonics structures was used for regional geotectonic studies. Results. Tectonic inversion of the Dnieper-Donetsk Basin and Donbass began at the Late Hercynian epoch as a result of collisional movements of the compression orogen on the outskirts of the Paleotethis. Tangential compression of the southwestern direction led to the formation of gentle tectonic faults in the sedimentary cover of the Western Donets Graben, along which a lattice of thrust faults was formed. For a set of extrusion of sedimentary rocks in the reverse–thrust mode from the axial super-compressed zone, tectonic transport of geomas took place in the direction of the zones of "geodynamic shadow" on the southern side. Collisional deformations of horizons by the mechanism of longitudinal bending of the layers caused the formation of linear uplift-folding in the northern part of the Graben, and echelons of scaly thrust covers in the southern. At the Mesozoic and Cenozoic epochs, in the mode of interference of the reverse–thrust and horizontal-strike-slip fields, the Hercynian thrust lattice and the near-fault uplift folds underwent collisional deformation with the formation of coulisse–jointed folded zones and echeloned thrust covers. Based on the kinematic model of tectonic inversion of the Western Donets Graben, the geodynamics of the formation of the transition zone between the Dnieper–Donets Basin and the Donetsk Foldbelt is reconstructed. These data are the basis for adjusting the regional schemes of tectonic and oil and gas geological zoning. Scientific novelty and practical significance. The grouping of the compression axes in the western part of the Donbass caused the formation of a gorst-like geoblock-stamp, under the pressure of which the dislocated geomasses were thrusting onto the syneclisic cover of the southeastern segment of the depression. In the Western Donetsk Graben, the allochthonous stratum formed the body of the tectonic wedging geomas segment. Along the main strike–slip faults, which form the "tectonic rails" of the invasion, geodynamic zones of displacement of geomas were formed, composed of en-echelon articulated upthrust-folds. In its foreland, at the ends of the main strike–slip faults, an advanced scaly compression fan was formed, and in the hinterland, folded sutures were formed on the roots of the thrust covers. The main result of the research is a fundamentally new kinematic model of tectonic inversion of the Dnieper-Donetsk Basin. The model provides that the deformations of the riftogenic structure within the Graben were carried out according to the kinematic mechanism of the formation of a transverse orocline protruding under the pressure of the tectonic geoblock-stamp of the Donetsk Foldbelt.

scholarly journals A reconstruction of Iberia accounting for Western Tethys–North Atlantic kinematics since the late-Permian–Triassic

Solid Earth ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 1313-1332 ◽  
Author(s):  
Paul Angrand ◽  
Frédéric Mouthereau ◽  
Emmanuel Masini ◽  
Riccardo Asti
Keyword(s):  
North Atlantic ◽  
Kinematic Model ◽  
Plate Boundary ◽  
Strike Slip ◽  
Late Permian ◽  
Geological Evidence ◽  
Western Tethys ◽  
The North ◽  
Kinematic Evolution ◽  
Strike Slip Movement

Abstract. The western European kinematic evolution results from the opening of the western Neotethys and the Atlantic oceans since the late Paleozoic and the Mesozoic. Geological evidence shows that the Iberian domain recorded the propagation of these two oceanic systems well and is therefore a key to significantly advancing our understanding of the regional plate reconstructions. The late-Permian–Triassic Iberian rift basins have accommodated extension, but this tectonic stage is often neglected in most plate kinematic models, leading to the overestimation of the movements between Iberia and Europe during the subsequent Mesozoic (Early Cretaceous) rift phase. By compiling existing seismic profiles and geological constraints along the North Atlantic margins, including well data over Iberia, as well as recently published kinematic and paleogeographic reconstructions, we propose a coherent kinematic model of Iberia that accounts for both the Neotethyan and Atlantic evolutions. Our model shows that the Europe–Iberia plate boundary was a domain of distributed and oblique extension made of two rift systems in the Pyrenees and in the Iberian intra-continental basins. It differs from standard models that consider left-lateral strike-slip movement localized only in the northern Pyrenees in introducing a significant strike-slip movement south of the Ebro block. At a larger scale it emphasizes the role played by the late-Permian–Triassic rift and magmatism, as well as strike-slip faulting in the evolution of the western Neotethys Ocean and their control on the development of the Atlantic rift.

Kinematic data on major Variscan strike-slip faults and shear zones in the Polish Sudetes, northeast Bohemian Massif

1997 ◽  
Vol 134 (5) ◽  
pp. 727-739 ◽  
Author(s):  
P. ALEKSANDROWSKI ◽  
R. KRYZA ◽  
S. MAZUR ◽  
J. ŻABA
Keyword(s):  
Shear Zone ◽  
Fault Zone ◽  
Bohemian Massif ◽  
Early Carboniferous ◽  
Shear Zones ◽  
Strike Slip ◽  
Late Carboniferous ◽  
Late Devonian ◽  
The West ◽  
West Sudetes

The still highly disputable terrane boundaries in the Sudetic segment of the Variscan belt mostly seem to follow major strike-slip faults and shear zones. Their kinematics, expected to place important constraints on the regional structural models, is discussed in some detail. The most conspicuous is the WNW–ESE Intra-Sudetic Fault Zone, separating several different structural units of the West Sudetes. It showed ductile dextral activity and, probably, displacement magnitude of the order of tens to hundreds kilometres, during late Devonian(?) to early Carboniferous times. In the late Carboniferous (to early Permian?), the sense of motion on the Intra-Sudetic Fault was reversed in a semi-brittle to brittle regime, with the left-lateral offset on the fault amounting to single kilometres. The north–south trending Niemcza and north-east–southwest Skrzynka shear zones are left-lateral, ductile features in the eastern part of the West Sudetes. Similarly oriented (northeast–southwest to NNE–SSW) regional size shear zones of as yet undetermined kinematics were discovered in boreholes under Cenozoic cover in the eastern part of the Sudetic foreland (the Niedźwiedź and Nysa-Brzeg shear zones). One of these is expected to represent the northern continuation of the major Stare Mesto Shear Zone in the Czech Republic, separating the geologically different units of the West and East Sudetes. The Rudawy Janowickie Metamorphic Unit, assumed in some reconstructions to comprise a mostly strike-slip terrane boundary, is characterized by ductile fabric developed in a thrusting regime, modified by a superimposed normal-slip extensional deformation. Thrusting-related deformational fabric was locally reoriented prior to the extensional event and shows present-day strike-slip kinematics in one of the sub-units. The Sudetic Boundary Fault, although prominent in the recent structure and topography of the region, was not active as a Variscan strike-slip fault zone. The reported data emphasize the importance of syn-orogenic strike-slip tectonics in the Sudetes. The recognized shear sense is compatible with a strike-slip model of the northeast margin of the Bohemian Massif, in which the Kaczawa and Góry Sowie Units underwent late Devonian–early Carboniferous southeastward long-distance displacement along the Intra-Sudetic Fault Zone from their hypothetical original position within the Northern Phyllite Zone and the Mid-German Crystalline High of the German Variscides, respectively, and were juxtaposed with units of different provenance southwest of the fault. The Intra-Sudetic Fault Zone, together with the Elbe Fault Zone further south, were subsequently cut in the east and their eastern segments were displaced and removed by the younger, early to late Carboniferous, NNE–SSW trending, transpressional Moldanubian–Stare Mesto Shear Zone.

Evidence of tectonic reactivation after continental breakup in the Ceará Terrace, Equatorial margin of Brazil, from 2D reflection seismics

2020 ◽  
Author(s):  
Aline Cristine Tavares ◽  
David Lopes de Castro ◽  
Ole Rønø Clausen ◽  
Diógenes Custódio de Oliveira ◽  
Francisco Hilario R. Bezerra ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Evolutionary Process ◽  
Spreading Center ◽  
Equatorial Atlantic ◽  
Borehole Data ◽  
Reflection Seismic ◽  
Oceanic Spreading ◽  
Reflection Seismics ◽  
Seismic Sections ◽  
Transform Margin

<p>The Brazilian equatorial margin has its origin in the fragmentation of the supercontinent Pangea with the separation of the South American and African continents and is composed of divergent oblique and transform segments related to large oceanic fracture zones, which are typical of the Equatorial Atlantic (e.g., Saint Paul, Romanche, and Chain). The dynamic evolution of this margin is related to the generation of marginal ridges, which are basement highs that follow the same trend of the continental-oceanic boundary in a transform margin.</p><p>The Ceará Terrace (CT), the main target of this investigation, is an E-W-striking marginal ridge located south of the western end of the Romanche Fracture Zone (RFZ) in the continental margin of Brazil. The CT has a counterpart in the African margin, the Ivory Coast-Ghana Ridge (ICGR), which is located north of the eastern termination of the RFZ. Earlier studies show that the evolution of both marginal ridges (CT and ICGR) was mainly influenced by (1) tectonic uplift due to Late Albian-Cenomanian transpressional tectonics and (2) flexural uplift due to erosion and thermal changes caused by the passage of the oceanic spreading center.</p><p>While ICGR is the most intensely studied marginal ridge in the Atlantic equatorial margin, the CT still needs further analysis to unravel its evolutionary process. The objective of the present study is thus to map and analyze the CT to understand its time and spatial evolution. Therefore, we have used and interpreted 2D reflection seismic sections and boreholes from the Brazilian Agency of Oil and Gas.</p><p>Our study shows that the CT is an intensely deformed Lower Cretaceous structure, which originates from the Atlantic opening process. The CT is controlled by the RZF and preexisting fault zones in the continent such as the Transbrasiliano lineament (TB). The interpretation of the seismic sections shows an intense ductile and brittle deformation of the CT paleo structure (syn-rift sequence) and the sedimentary units deposited after it (drift sequence). It indicates that tectonic reactivation occurred in the period where the transform movements were already restricted to the furthest spreading center. There is also evidence that some faults affect the whole rift sequence suggesting a possible brittle reactivation of the offshore continuation of the TB due to changes in plate movements in the Late Albian. This plate shifts agrees with previous works that show compressional features concentrated in continental shelf near of CT and half-grabens linked with the offshore TB prolongation. On the other hand, there is no evidence of the influence of weakness zones in the CIGR, where the Kandi lineament (the prolongation of the TB in the African continent) is far more than 300 km of that marginal ridge.</p><p> </p><p>Acknowledgments:</p><p>This research was supported by Programa Institucional de Internacionalização - Coordenação de Aperfeiçoamento de Pessoal (PRINT-CAPES) and Aarhus University (AU). Brazilian Agency of Oil and Natural Gas (ANP) is thanked for providing the seismic and borehole data. We also thank Schlumberger for giving access to Petrel.</p>

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