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 ◽  
...  
2009 ◽  
Vol 180 (3) ◽  
pp. 231-246 ◽  
Author(s):  
Patrick Rolin ◽  
Didier Marquer ◽  
Michel Colchen ◽  
Charles Cartannaz ◽  
Alain Cocherie ◽  
...  

AbstractThe Variscan continental collision has led to the development of large strike-slip shear zones in western Europe. Our study focuses on the regional deformation and shear zone patterns in the Massif Armoricain and the French Massif Central. The synthesis of granite emplacement ages associated to granite deformation fields, allow us to propose a geodynamic model for the tectonic evolution of this part of the Variscan belt between 370 Ma – 320 Ma (Late Devonian – Namurian).After the first steps of the continental subduction-collision, leading to high temperature and anatexis associated with N-S shortening at 380-370 Ma (Frasnian to Famennian), the southern part of the Massif Armoricain and western part of French Massif Central underwent large dextral shearing along N100-N130 trending shear zones up to early Visean time. These large-scale displacements progressively decreased at around 350-340 Ma, during the first emplacements of biotite bearing granites (Moulins-les Aubiers-Gourgé massif and Guéret massif intrusions).During middle Visean times, the shortening axis direction rotated towards a NNE-SSW direction implying changes in the regional deformation field. The occurrence of N070-N100 sinistral and N110-N130 dextral conjugate shear zones within leucogranites are related to that time. Finally, new N150-N160 dextral shear zones appeared in middle to late Visean times: as for examples, the Parthenay and the Pradines shear zones in the SE Massif Armoricain and the Millevaches massif, respectively. These shear zones were conjugated to the sinistral N020 Sillon Houiller in the French Massif Central. They reflect large scale brittle continental indentation in the French Variscan belt during the middle to late Visean.


2020 ◽  
Author(s):  
Olivier Bolle ◽  
Michel Corsini ◽  
Hervé Diot ◽  
Oscar Laurent ◽  
Raphaël Melis

<p>A significant portion of the Maures-Tanneron Massif (SE branch of the European Variscan Belt) is occupied by late orogenic, anatectic crustal granitoids that were emplaced at ca. 325-300 Ma (Upper Carboniferous)<sup>1,2</sup>. The Camarat granite<sup>3</sup> is one of the smallest representatives of these granitoids (~2.5 km<sup>2</sup>). It is a composite intrusion exposed in migmatitic gneisses of the Maures Massif, along the southern shore of the Saint-Tropez Peninsula. From west to east, it consists of an E-W strip of Ms-Bt-Crd leucogranite where coarse- and fine-grained facies are found in similar amounts, and two bodies of Bt-Ms leucogranite, dominantly coarse-grained.</p><p>Zircon and monazite from two samples of the Camarat granite have been analyzed by LA-ICP-MS for U-Pb dating. Sixteen monazite analyses from the fine-grained facies of the E-W granite strip give a Concordia age of 303.5 ± 1.8 Ma (2 S.E., MSWD = 0.9). Sixteen zircons from the coarse-grained facies of the easternmost intrusion provide a Concordia age of 304.6 ± 2.1 Ma (2 S.E., MSWD = 1.2). The two dates are identical within uncertainty and are considered to constrain crystallization of the Camarat granite at ~304 Ma (Kasimovian–Gzhelian limit).</p><p>Twenty-one measurements of the anisotropy of magnetic susceptibility (AMS) and direct textural quantifications through image analysis (IA) of 10 samples give agreeing results that reveal the fabric orientation in the Camarat granite. The foliation has a variable orientation, with a weighted average of N65°E/26°NNW for the AMS data and N77°E/17°NNW for the IA data (D = 10°). The lineation pattern is more homogeneous, displaying a consistent northerly shallow plunge (mean of N12°E/22°NNE vs. N22°E/20°NNE; D = 10°). The Camarat granite lineations are parallel to lineations in the gneissic country rocks. These were produced during the last Variscan tectonic event evidenced in the area, a partitioned transpression phase, localized along ca. N-S sinistral strike-slip shear zones<sup>4</sup>. It is proposed that the ascent of the Camarat granite was favoured by such strike-slip structures and that pull-aparts represent the sites of emplacement, as best exemplified by the E-W granite strip.</p><p>In the Corso-Sardinian Block, another portion of the SE Variscides formerly juxtaposed to the Maures-Tanneron Massif<sup>5</sup>, a model of progressive transition from orogen-parallel flow (late orogenic, Upper Carboniferous transpression) to orogen-perpendicular extension (post orogenic, Permian rifting) has been recently proposed<sup>6</sup>. Such a model may be extended to other areas of the SE Variscan Belt, in particular to the Maures-Tanneron Massif which is cut and bordered by ca. E-W Permian grabens<sup>7</sup>, implying that a ca. N-S direction of stretching, as recorded by the 304 Ma Camarat granite, was still prevailing in Permian times.</p><p> </p><ol><li>Duchesne et al., Lithos 162-163, 195-220 (2013). 2. Schneider et al., Geol. Soc. Spec. Pub. 405, 313-331 (2014). 3. Amenzou & Pupin, C. R. Acad. Sc. Paris (Série II) 303, 697-700 (1986). 4. Corsini & Rolland, C. R. Geoscience 341, 214-223 (2009). 5. Edel et al., Geol. Soc. Spec. Pub. 405, 333-361 (2014). 6. Casini et al., Tectonophysics 646, 65-78 (2015). 7. Toutin-Morin, Ann. Soc. géol. Nord 106, 183-187 (1987).</li> </ol>


2020 ◽  
Author(s):  
Stanislaw Mazur ◽  
Paweł Aleksandrowski ◽  
Łukasz Gągała ◽  
Piotr Krzywiec ◽  
Jerzy Żaba ◽  
...  

<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>


1991 ◽  
Vol 28 (12) ◽  
pp. 2024-2041 ◽  
Author(s):  
Jacques Beauchamp ◽  
Alain Izart ◽  
Alain Piqué

The evolution of marine sedimentary basins deformed by the Hercynian Orogeny was studied in Germany, France, Iberia, Northwest Africa, and North America in the Lower Carboniferous. These basins opened along strike–slip faults and were filled with turbidites and shelf deposits until the main compressive phase at the end of Visean and the Namurian. The infilling was interrupted with frequent volcanic episodes and gravity-induced movements. According to sedimentary vergence, these basins were set into two festoons on both sides of an elongated and emergent swell structured during the Devonian and corresponding to the internal zones of the orogen. These basins were filled during a general tectonic compression phase; they correspond to the foreland basins of the Hercynian belt.


2020 ◽  
Vol 109 (4) ◽  
pp. 1133-1160 ◽  
Author(s):  
Stanislaw Mazur ◽  
Paweł Aleksandrowski ◽  
Łukasz Gągała ◽  
Piotr Krzywiec ◽  
Jerzy Żaba ◽  
...  

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.


2014 ◽  
Vol 185 (3) ◽  
pp. 171-189 ◽  
Author(s):  
Patrick Rolin ◽  
Didier Marquer ◽  
Charles Cartannaz ◽  
Philippe Rossi

AbstractThe Variscan continental collision induced the development of large crustal melting in the western French Massif Central, accompanied by emplacement and deformation of syn- to post-tectonic granites spatially related to normal and strike slip faulting. Our study focuses on the regional deformation and shear zone patterns in the Millevaches massif, one of the largest magmatic area of the French Massif Central. In this massif, the syn-tectonic intrusions are related i) to the dextral wrenching along the Treignac-Pradines shear zones and the Creuse faults system, and ii) to the coeval extension along the N000°–N020° normal faults on the western edge of the Millevaches massif (Bourganeuf and Argentat faults). The analysis of deformation and kinematics correlated to new datations of granites allow us to propose a pull-apart model to explain the tectono-magmatic evolution of this part of the Variscan belt from 350 Ma to 325 Ma. At that time, these granites intruded a “pull-apart” system bounded by two major N140°–160° dextral strike-slip zones operating in the middle continental crust during a bulk N020° regional shortening.From 325 Ma to 320 Ma, a clockwise rotation of the regional shortening axis was responsible for the late reactivation of the N020° eastern Millevaches tectonic border as a dextral fault system (Felletin-Ambrugeat fault system). This NE-SW shortening displaced the N140°–160° Creuse fault system and induced a reverse motion along the northern border of the Millevaches massif (St-Michel-de-Veisse fault). This Visean tectono-magmatic event induced the late exhumation of the Millevaches massif with respect to surrounding units and favoured the widespread granite emplacement in this part of the Variscan belt.


2020 ◽  
Vol 3 (2) ◽  
pp. 781-790
Author(s):  
M. Rizwan Akram ◽  
Ali Yesilyurt ◽  
A.Can. Zulfikar ◽  
F. Göktepe

Research on buried gas pipelines (BGPs) has taken an important consideration due to their failures in recent earthquakes. In permanent ground deformation (PGD) hazards, seismic faults are considered as one of the major causes of BGPs failure due to accumulation of impermissible tensile strains. In current research, four steel pipes such as X-42, X-52, X-60, and X-70 grades crossing through strike-slip, normal and reverse seismic faults have been investigated. Firstly, failure of BGPs due to change in soil-pipe parameters have been analyzed. Later, effects of seismic fault parameters such as change in dip angle and angle between pipe and fault plane are evaluated. Additionally, effects due to changing pipe class levels are also examined. The results of current study reveal that BGPs can resist until earthquake moment magnitude of 7.0 but fails above this limit under the assumed geotechnical properties of current study. In addition, strike-slip fault can trigger early damage in BGPs than normal and reverse faults. In the last stage, an early warning system is proposed based on the current procedure. 


2020 ◽  
Vol 57 (1) ◽  
pp. 21-40
Author(s):  
Alexandra Wallenberg ◽  
Michelle Dafov ◽  
David Malone ◽  
John Craddock

A harzburgite intrusion, which is part of the trailside mafic complex) intrudes ~2900-2950 Ma gneisses in the hanging wall of the Laramide Bighorn uplift west of Buffalo, Wyoming. The harzburgite is composed of pristine orthopyroxene (bronzite), clinopyroxene, serpentine after olivine and accessory magnetite-serpentinite seams, and strike-slip striated shear zones. The harzburgite is crosscut by a hydrothermally altered wehrlite dike (N20°E, 90°, 1 meter wide) with no zircons recovered. Zircons from the harzburgite reveal two ages: 1) a younger set that has a concordia upper intercept age of 2908±6 Ma and a weighted mean age of 2909.5±6.1 Ma; and 2) an older set that has a concordia upper intercept age of 2934.1±8.9 Ma and a weighted mean age 2940.5±5.8 Ma. Anisotropy of magnetic susceptibility (AMS) was used as a proxy for magmatic intrusion and the harzburgite preserves a sub-horizontal Kmax fabric (n=18) suggesting lateral intrusion. Alternating Field (AF) demagnetization for the harzburgite yielded a paleopole of 177.7 longitude, -14.4 latitude. The AF paleopole for the wehrlite dike has a vertical (90°) inclination suggesting intrusion at high latitude. The wehrlite dike preserves a Kmax fabric (n=19) that plots along the great circle of the dike and is difficult to interpret. The harzburgite has a two-component magnetization preserved that indicates a younger Cretaceous chemical overprint that may indicate a 90° clockwise vertical axis rotation of the Clear Creek thrust hanging wall, a range-bounding east-directed thrust fault that accommodated uplift of Bighorn Mountains during the Eocene Laramide Orogeny.


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