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

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.

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

10.5194/egusphere-egu2020-3867 ◽

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

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&#176; 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.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.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.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.

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Metamorphic and structural evolution of the Maures-Tanneron massif (SE Variscan chain): evidence of doming along a transpressional margin

BSGF - Earth Sciences Bulletin ◽

10.2113/gssgfbull.180.3.217 ◽

2009 ◽

Vol 180 (3) ◽

pp. 217-230 ◽

Cited By ~ 21

Author(s):

Yann Rolland ◽

Michel Corsini ◽

Antoine Demoux

Keyword(s):

Lower Crust ◽

Late Phase ◽

Structural Evolution ◽

Strike Slip ◽

Current Situation ◽

Metamorphic Evolution ◽

Himalayan Belt ◽

Slip Displacement ◽

Regional Gradient ◽

Major Strike

Abstract The Variscan metamorphic and structural evolution of the Maures-Tanneron massif is divided in two main post-collisional phases: (1) a MP-MT regional gradient is developed during nappe-piling process between 350 and 320 Ma, followed by (2) LP-HT regional gradient coeval with doming between 320 and 300 Ma. During this late phase, the tectonic context was dominated by E-W shortening, which produced crustal-scale upright folds and major strike-slip displacement along trans-crustal faults. Symmetric extensional fabrics are observed on the limbs of crustal-scale anticlines, and are ascribed to local accommodation of lower crust exhumation. Heat and magma transfer are allowed by these large vertical strike-slip faults, and are thought to be the cause of the late metamorphic evolution. Therefore, structures and metamorphism argue for a transpressional context at the SE branch of the Variscan chain. Comparisons with current collisional settings such as syntaxial domains of the Himalayan belt show that the timing and PT conditions of metamorphic events are similar. These observations lead us to propose that the situation of the Variscan chain during the period 320-300 Ma was still a syn-convergent setting similar to the current situation of the Himalayan-Tibet system, and that extensional movements are not the cause of, but the result of exhumation of the lower crust in this ongoing shortening context along a transpressional wrench boundary.

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Structural Evolution of the Kohat Fold and Thrust Belt in the Shakardarra Area (South Eastern Kohat, Pakistan)

Geosciences ◽

10.3390/geosciences8090311 ◽

2018 ◽

Vol 8 (9) ◽

pp. 311

Author(s):

Hamid Hussain ◽

Zhang Shuangxi

Keyword(s):

Seismic Data ◽

Structural Evolution ◽

Vertical Axis ◽

Strike Slip ◽

Strike Slip Fault ◽

Thrust Faults ◽

Thrust Belt ◽

Fold And Thrust Belt ◽

Basal Detachment ◽

Northern Segment

The Kohat fold and thrust belt, located in North-Western Pakistan, is a part of Lesser Himalaya developed due to the collision between the Indian and Eurasian plates. The structural evolution records of this area indicate that it consists of tight anticlines and broad syncline structures. Previous studies show that the structural pattern of this area has been produced due to multiple episodes of deformation. In the present research, 2D seismic data has been integrated with our field surveys to clarify the role of active strike-slip faulting in reshaping the surface structures of Shakardarra, Kohat. At the surface, doubly plunging anticlines and synclines are evolved on evaporites as detachment folds, truncated by thrust faults along their limbs. Seismic data show that the thrust faults originate from basal detachment located at the sedimentary-crystalline interface and either cut up section to the surface or lose their displacement to splay or back thrusts. At the surface, the Shakardarra Fault, the Tola Bangi Khel Fault, the Chorlaki Fault, and the axial trend of fold change their strike from EW to NS showing that the thrust and axial trend of folds are rotated along the vertical axis by the influence of the Kalabagh strike-slip fault. Strike-slip motion dominates the style of deformation at the northern segment. The current deformation is concentrated on the splay faults in the northern segment of the Kalabagh Fault. We propose that Shakardarra is sequentially evolved in three episodes of deformation. In the first phase, the detachment folds developed on Eocene evaporites, which are truncated by thrust faults originated from the basal detachment in the second phase. In the third phase, early formed folds and faults are rotated along the vertical axis by the influence of Kalabagh strike-slip fault.

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Structural evolution of the northeast Asian continental margin: an example from the western Koryak fold and thrust belt (northeast Russia)

Geological Magazine ◽

10.1017/s0016756898008747 ◽

1998 ◽

Vol 135 (3) ◽

pp. 311-330 ◽

Cited By ~ 17

Author(s):

ANDREI K. KHUDOLEY ◽

SERGEI D. SOKOLOV

Keyword(s):

Structural Evolution ◽

Early Carboniferous ◽

Shear Zones ◽

Strike Slip ◽

Thrust Belt ◽

Northeast Russia ◽

Existing Structures ◽

Event Structures ◽

Fold And Thrust Belt ◽

Metamorphic Terranes

The western Koryak fold and thrust belt consists of a set of tectonostratigraphic terranes that contain units ranging from Lower Palaeozoic to Cenozoic. Three deformational events have been identified in the study area. The first event structures are folds, domes and shear zones with related high-pressure/low-temperature metamorphism. These structures are early Carboniferous and are only recognized in the metamorphic terranes. The second event structures are imbricate fans of thrusts and folds with southeast vergence, broken formation and serpentinite mélange. These are latest Jurassic to early Cretaceous (early Albian) and occur throughout the study area. During this event, thrusting was accompanied by dextral strike-slip faulting. The second event structures are overlapped by the Upper Albian sedimentary rocks with an angular unconformity at the base. During metamorphism associated with the first and second deformational events, some of the rocks were metamorphosed to blueschist grade and were affected by strain with axial ratios of up to 15[ratio ]1. The third deformational event is characterized by significant sinistral strike-slip displacement at higher crustal levels. This resulted in a new set of structures and rotation of pre-existing structures. The age of the sinistral strike-slip faults is interpreted to be late Cretaceous to Cenozoic. The kinematics of the second and third deformational events correspond to assumed proto-Pacific plate motions based on palaeomagnetic data.

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STRUCTURAL EVOLUTION OF THE SOUTHERN CADDO GAP QUADRANGLE, ARKANSAS: FIELD EVIDENCE FOR STRIKE-SLIP AND BACKTHRUST FAULTING IN THE OUACHITA MOUNTAINS

10.1130/abs/2018sc-310277 ◽

2018 ◽

Author(s):

Martin Messmer ◽

◽

Chris A. Barker

Keyword(s):

Structural Evolution ◽

Strike Slip ◽

Ouachita Mountains ◽

Field Evidence

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Spatio-temporal structural evolution of the Kohat fold and thrust belt of Pakistan

Journal of Structural Geology ◽

10.1016/j.jsg.2021.104310 ◽

2021 ◽

Vol 145 ◽

pp. 104310

Author(s):

Humaad Ghani ◽

Edward R. Sobel ◽

Gerold Zeilinger ◽

Johannes Glodny ◽

Irum Irum ◽

...

Keyword(s):

Structural Evolution ◽

Thrust Belt ◽

Fold And Thrust Belt ◽

Spatio Temporal

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Salt thickness and heterogeneity control the degree of coupling between sub- and supra-salt structure during salt-detached translation: evidence from physical models

10.5194/egusphere-egu21-12519 ◽

2021 ◽

Author(s):

Sian Evans ◽

Christopher Jackson ◽

Sylvie Schueller ◽

Jean-Marie Mengus

Keyword(s):

Structural Evolution ◽

Structural Complexity ◽

Vertical Movement ◽

Sediment Supply ◽

Physical Models ◽

Structural Development ◽

Salt Structure ◽

Regional Tectonic ◽

Base Salt ◽

Strain Coupling

Salt flows like a fluid over geological timescales and introduces significant structural complexity to the basins in which it is deposited. Salt typically flows seaward due to tilting of the basin margins, and is therefore influenced by the geometry of the surface that it flows across (e.g. fault scarps or folds on the base-salt surface). This can lead to coupling of sub- and supra-salt structures, with the orientation and distribution of base-salt structures reflected in the structure of the overburden. However, precisely what controls the degree of strain coupling during salt-detached translation is still poorly understood, in particular the role played by salt thickness and lithological heterogeneity. This partly reflects the fact that it can be difficult to deconvolve the relative contributions of natural variables such as the magnitude of relief, sediment supply, and regional tectonic regime. In addition, seismic data provide only the present structural configuration of salt basins, from which their formative kinematics must be inferred. If we can develop a better understanding of how sub-salt structure controls the types and patterns of supra-salt deformation, we can produce better kinematic (structural) restorations of salt basins and, therefore, have a better understanding of the related mechanics.In order to isolate the influence of salt thickness and heterogeneity on sub- to supra-salt strain coupling during salt-detached horizontal translation, we present a series of physical analogue models with controlled boundary conditions. We use a simple base-salt geometry comprising three oblique base-salt steps, and vary the thickness and composition of the ductile salt analogue in each experiment. X-ray tomography allows us to image the internal structure during model evolution and therefore gain a 4D picture of its structural development.Results show that thicker and more homogeneous salt units experience more vertical movement (i.e. minibasin subsidence and diapiric rise) and the overburden structure is less explicitly coupled with the underlying base-salt relief. Conversely, thinner and more heterogeneous salt units restrict vertical movement, and therefore the resulting overburden structure is dominated by lateral movement and more closely coupled to the geometry of the base-salt surface. These results highlight the important role of base-salt relief in the subsequent structural evolution of salt basins and why, despite broad similarities between different salt basins, there is significant variability in their structural styles.

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Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

Anais da Academia Brasileira de Ciências ◽

10.1590/0001-3765201420130173 ◽

2014 ◽

Vol 86 (3) ◽

pp. 1101-1113 ◽

Cited By ~ 6

Author(s):

FABRÍCIO A. CAXITO ◽

ALEXANDRE UHLEIN ◽

LUIZ F.G. MORALES ◽

MARCOS EGYDIO-SILVA ◽

JULIO C.D. SANGLARD ◽

...

Keyword(s):

Structural Analysis ◽

Structural Evolution ◽

Shear Zones ◽

Central Compartment ◽

Strike Slip ◽

Fold Belt ◽

Main Structure ◽

The North ◽

Brasiliano Orogeny ◽

Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

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