No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central German platform
Abstract
The structural evolution of Central Europe reflects contrasting tectonic regimes after the Variscan orogeny during Mesozoic – Cenozoic time. The brittle deformation related to each tectonic regime is localized mainly along major fault zones, creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events. By contrast, fracture patterns in less deformed domains often provide a pristine structural inventory. We investigate the brittle deformation of a relatively stable, wide area of the central German platform using fault-slip data to identify the regional stress fields required to satisfy the data. In a non-classical approach, and in order to avoid local stress variations and misinterpretations, the fault-slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks. Direct stress tensor inversion was performed through an iterative refining process, and the computed stress tensors were verified using field-based observations. Criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events, which begins with a post-Triassic normal faulting regime with σ3 axis trending NE-SW. The deformation then follows by strike-slip and thrust faulting regimes with a change of σ1 axis from N-S to NE-SW, supposedly in the Late Cretaceous. Two younger events are characterized by Cenozoic normal and oblique thrust faulting regimes with NW-SE-trending σ3 and σ1 axes, respectively. The fracture patterns of both the cover and basement rocks appear to record the same states of stress.
Supplementary resource (1)
... Ziegler et al. 1995;Cloetingh & van Wees, 2005). In this region, several palaeostress analyses reveal multiple alternating and overlapping phases of contractional and extensional deformation during the Mesozoic and Cenozoic times (Bergerat, 1987;Blés et al. 1989;Hibsch et al. 1995;Peterek et al. 1996;Kley & Voigt, 2008;Sippel et al. 2009Sippel et al. , 2010Coubal et al. 2015;Navabpour et al. 2017). Such phases of deformation were linked to the opening of the Neotethys during the Permian to Early Mesozoic time, the onset of Atlantic rifting, and the development of an active margin between the European and African plates . ...
... For most parts of Central Europe, including large parts of SE Germany, normal faults bounding NW-SE striking graben systems were active at that time, e.g. grabens of the South German Basin Zulauf & Duyster, 1997;Walter, 2007;Kley & Voigt, 2008;Scheck-Wenderoth et al. 2008;Sippel et al. 2009;Navabpour et al. 2017). According to Navabpour et al. (2017) this phase of normal faulting is also recorded in Middle Triassic rocks in the Thuringian Basin towards the north. ...
... grabens of the South German Basin Zulauf & Duyster, 1997;Walter, 2007;Kley & Voigt, 2008;Scheck-Wenderoth et al. 2008;Sippel et al. 2009;Navabpour et al. 2017). According to Navabpour et al. (2017) this phase of normal faulting is also recorded in Middle Triassic rocks in the Thuringian Basin towards the north. ...
The Franconian Platform of SE Germany and the underlying Permian and Triassic rocks that developed from latest Permian to Triassic time were affected by multiple compressional and extensional events that created a complex fracture, fault and stylolite network. We reconstructed the spatio-temporal variations of post-Triassic palaeostress fields in the Franconian Platform and Triassic strata using fault-slip and tectonic stylolite inversion. Our highly resolved stress inversion enables us to demonstrate a cyclic stress evolution from the stress regime of normal faulting to thrusting, strike-slip and back to normal faulting. Five main stress fields correlating with two stress cycles are determined for Late Jurassic to Cenozoic time. The first cycle consists of: (SF1) an initially NE-SW-directed horizontal extension during Late Jurassic to Early Cretaceous time; (SF2) NNE-SSW-directed horizontal compression with an early set of tectonic stylolites prior to the development of reverse and thrust faults; and (SF3) a strike-slip-dominated setting with (N)NE-(S)SW horizontal compression representing a first relaxation. The second cycle comprises (SF4) NW-SE-directed horizontal extension during Oligocene-Miocene time; and (SF5) a second strike-slip-dominated regime with WNW-ESE to NW-SE horizontal compression during the Alpine shortening, creating the youngest set of tectonic stylolites. In addition, we consider the transitional stages between thrusting and a strike-slip regime as a snapshot in the process of intraplate tectonics.
... We analyzed the twinned calcite in this suite and compared our results with twinning strain and fabric studies obtained within the Alpine orogen: the Jura folds, [36,37], the Molasse basin, [36,38], the Pre-Alpine nappes [39], the Helvetic nappes [40][41][42] and the Helvetic-Penninic nappes [40,43]. With this robust data set, we hope to (1) interpret the variations in stress-strain response of the oroclinal Tertiary Alpine orogen across the region into the gently warped foreland (i.e., Paris basin, Purbeck thrust-monocline, London basin, etc.) toward a better understanding of thrust mechanics and (2) couple the twinning strain results associated with Pre-Alpine intra-plate deformation [44][45][46] and the opening of the North Atlantic (58 Ma), Tertiary Alpine deformation and the modern Icelandic margin [47]. ...
... Calcite and quartz tectonites have been studied in the Tauern window and the Penninic nappes [43,75,76] where calcitic pseudotachylite is found [75]. In the Alpine foreland, Lacombe et al. [7] first used a calcite twin paleostress (not strain) method to propose a complex tectonic history adjacent to the Jura Mountains, an approach similar to proxy structural methods (e.g., FAULTKIN, see [31,44,46,[77][78][79][80]) and Ring and Gerdes ([45]; with U-Pb calcite ages) to interpret~84 Ma of tectonic history in the European plate as Iberia accreted, the Atlantic Ocean opened, the Alps developed, and the ECRIS rift system evolved [81,82]. ...
... The tectonic evolution of western Europe was a prolonged (~100 Ma) and complex process of accretion (Iberia), extension and shearing (sinistral opening of the Atlantic Ocean), collision of Apulia and subsequent ECRIS rifting [23,31,33,[44][45][46]79,80,139,140]. Lacombe et al. [7,130] was the first to report calcite twinning paleostress data in a complex pattern in the Alpine foreland. ...
We present a data set of calcite twinning strain results (n = 209 samples; 9919 measured calcite twins) from the internal Alpine nappes northwestward across the Alps and Alpine foreland to the older extensional margin along the Atlantic coast in Ireland. Along the coast of Northern Ireland, Cretaceous chalks and Tertiary basalts are cross-cut by calcite veins and offset by calcite-filled normal and strike-slip faults. Both Irish sample suites (n = 16 with four U-Pb vein calcite ages between 70–42 Ma) record a sub-horizontal SW-NE shortening strain with vertical extension and no strain overprint. This sub-horizontal shortening is parallel to the margin of the opening of the Atlantic Ocean (~58 Ma), and this penetrative fabric is only observed ~100 km inboard of the margin to the southeast. The younger, collisional Alpine orogen (~40 Ma) imparted a stress–strain regime dominated by SE-NW sub-horizontal shortening ~1200 km northwest from the Alps preserved in Mesozoic limestones and calcite veins (n = 32) in France, Germany and Britain. This layer-parallel shortening strain (−3.4%, 5% negative expected values) is preserved across the foreland in the plane of Alpine thrust shortening (SE-NW) along with numerous outcrop-scale contractional structures (i.e., folds, thrust faults). Calcite veins were observed in the Alpine foreland in numerous orientations and include both a SE-NW layer-parallel shortening fabric (n = 11) and a sub-vertical NE-SW vein-parallel shortening fabric (n = 4). Alpine foreland strains are compared with twinning strains from the frontal Jura Mountains (n = 9; layer-parallel shortening), the Molasse basin (n = 26; layer-parallel and layer-normal shortening), Pre-Alp nappes (n = 39; layer-parallel and layer-normal shortening), Helvetic and Penninic nappes (Penninic klippe; n = 46; layer-parallel and layer-normal shortening plus four striated U-Pb calcite vein ages ~24 Ma) and calcsilicates from the internal Tauern window (n = 4; layer-normal shortening). We provide a chronology of the stress–strain history of the European plate from 58 Ma through the Alpine orogen.
... The basin has experienced several major regional events occurring syn-and post-sedimentation along the pre-existing Varsican structures, commencing with a major compressive phase of deformation that occurred during a Late Cretaceous Inversion causing steep-angled reverse and NW-SE-trending strike-slip faults (e.g. Peterek et al. 1993Peterek et al. , 1996Peterek et al. , 1997Mazur et al. 2005;Kley & Voigt, 2008;Navabpour et al. 2017;Voigt et al. 2021). Compressional structural features related to this phase are primarily found within the main thrust fault zones whilst the strike-slip components are formed in the areas between faults (Peterek et al. 1996). ...
... Similar structures have been observed in surrounding basins (e.g. Thuringian Basin) and can be related to the continued subsidence in the Central European Basin System throughout the Mesozoic (Scheck-Wenderoth et al. 2008;Stollhofen et al. 2008;Navabpour et al. 2017;S Köhler et al., unpub. data). ...
... It is observed in Kirchleus that this is a multiphase event whereby the initial deformation is primarily composed of the reactivated reverse faults (Fig. 3b) and its culmination characterized by strike-slip faults (Fig. 3d). Furthermore, it is observed that an intermediary transitional phase occurs during the inversion event which forms the oblique reverse faults (Fig. 3c) within the quarry, possibly due to local stress variations and disturbances (Kley and Voigt, 2008;Sippel et al. 2010;Navabpour et al. 2017;S Köhler et al., unpub. data. ...
Faulted and fractured systems form a critical component of fluid flow, especially within low-permeable reservoirs. Therefore, developing suitable methodologies for acquiring structural data and simulating flow through fractured media is vital to improve efficiency and reduce uncertainties in modelling the subsurface. Outcrop analogues provide excellent areas for the analysis and characterization of fractures within the reservoir rocks where subsurface data are limited. Variation in fracture arrangement, distribution and connectivity can be obtained from 2D fractured cliff sections and pavements. These sections can then be used for efficient discretization and homogenization techniques to obtain reliable predictions on permeability distributions in the geothermal reservoirs. Fracture network anisotropy in the Malm reservoir unit is assessed using detailed structural analysis and numerical homogenization of outcrop analogues from an open pit quarry within the Franconian Basin, Germany. Several events are recorded in the fracture networks from the Late Jurassic the Alpine Orogeny and are observed to be influenced by the Kulmbach Fault nearby with a reverse throw of 800 m. The fractured outcrops are digitized for fluid flow simulations and homogenization to determine the permeability tensors of the networks. The tensors show differences in fluid transport direction where fracture permeability is controlled by orientation compared to a constant value. As a result, it is observed that the orientation of the tensor is influenced by the Kulmbach Fault, and therefore faults within the reservoirs at depth should be considered as important controls on the fracture flow of the geothermal system.
... West and southwest of the Lichtenfels Fault, the structural architecture of the study area is dominated by NW-SE normal faults such as the Staffelstein and Bamberg faults and the prominent Kissingen-Haßfurt fault zone (Fig. 1). Studies of regional upper-crustal paleostress patterns reveal multiple changes in stress field orientations since the Paleozoic comprising normal faulting and both extensional and compressional strike-slip faulting, implying multiple fault reactivation events (Peterek et al., 1996aBergerat and Geyssant, 1982;Coubal et al., 2015;Navabpour et al., 2017;Köhler et al., 2022). ...
... These intermontane basins are mainly located in the hanging wall of normal faults in graben and half-graben settings accumulating continental clastic sediments with rapid lateral thickness changes (Mc-Cann et al., 2006). Fault-bounded Rotliegend basins in SE Germany are also interpreted to have developed in an extensional and/or transtensional setting during latest Carboniferous and Permian times, as evidenced by rather abrupt lateral thickness and sedimentary facies changes across oblique slip normal faults (Schröder, 1988(Schröder, , 1987Peterek et al., 1996b;Leitz and Schröder, 1985;Arthaud and Matte, 1977;Dill, 1988;Müller, 1994;Peterek et al., 1997;McCann et al., 2006;Helmkampf et al., 1982). Rotliegend sedimentary rocks in the study area are exposed in the footwall and hanging wall of the FFS from NW to SE in the Stockheim, Rugendorf, Wirsberg, and Weidenberg outcrops (Fig. 1). ...
... Similar rapid thickness changes of the Rotliegend units were also observed in the Weidenberg, Erbendorf, Weiden, and Schmidgaden areas, all originally interpreted as small, isolated fault-bounded basins but now interpreted as individual exposures of one coherent depositional area, the NW-SE Naab Basin, where the Rotliegend reaches up to 2800 m thickness (Paul and Schröder, 2012). The Naab Basin is bordered by normal faults, some of which were reactivated as reverse faults or crosscut by younger reverse faults (Müller, 1994). In addition to exposures along the FFS, several wells in the western parts of the study area (e.g., Staffelstein 1, Mürsbach 1 and 6, and Eltmann) also encountered Rotliegend that relates to the SW-NE Kraichgau Basin (Table 1, Fig. 1), of which the NW-SE Naab Basin is considered a basin compartment (Paul, 2006). ...
The Bohemian Massif exposes structures and metamorphic rocks remnant from
the Variscan orogeny in central Europe and is bordered by the Franconian
Fault System (FFS) to the west. Across the FFS, Variscan units and
structures are buried by Permo-Mesozoic sedimentary rocks. We integrate
existing DEKORP 2D seismic reflection, well, and surface geological data with
the newly acquired FRANKEN 2D seismic survey to investigate the possible
westward continuation of Variscan tectonostratigraphic units and structures
and their influence on latest to post-Variscan basin development. Subsurface
Permo-Mesozoic stratigraphy is obtained from available wells and tied to
seismic reflection profiles using a synthetic seismogram calculated from
density and velocity logs. Below the sedimentary cover, three main basement
units are identified using seismic facies descriptions that are compared
with seismic reflection characteristics of exposed Variscan units east of
the FFS. Our results show upper Paleozoic low-grade metasedimentary
rocks and possible Variscan nappes bounded and transported by Variscan shear
zones ca. 65 km west of the FFS. Basement seismic facies in the footwall of
the Variscan shear zones are interpreted as Cadomian basement and overlaying
Paleozoic sequences. We show that the location of normal fault-bounded
latest to post-Variscan late Carboniferous–Permian basins are controlled by
the geometry of underlying Variscan shear zones. Some of these late
Carboniferous–Permian normal faults reactivated as steep reverse faults
during the regional Upper Cretaceous inversion. Our results also highlight
that reverse reactivation of normal faults gradually decreases west of the
FFS.
... While some authors have argued for a NW-SE-directed dextral strike-slip fault system by attributing the uplifts to restraining bends and related basins to transtension (Ziegler, 1990a;Wrede, 1988;Uličný, 2001), most authors have agreed that frontal thrusting was the main process that developed the observed structures Kley and Voigt, 2008;Nielsen and Hansen, 2000;Deckers and van der Voet, 2018). This was also confirmed by small-scale structural features (slickensides, fold axes, and fault orientations), which in many cases preserved both the extensional phase and N-S to NE-SW convergence (Vandycke, 2002;Franzke et al., 2004;Kley, 2018;Malz et al., 2020;Coubal et al., 2014;Navabpour et al., 2017). The strike-slip model addresses the problem that the principal faults should be orientated in an E-W direction to explain the subsidence anomalies at the assumed releasing Riedel shears, which were in fact never observed. ...
... On the basis of a detailed structural analysis of faults, Navabpour et al. (2017) were able to detect an early phase of N-S compression, oblique to the main NW-SE-striking faults, between the extension phase and the frontal thrusting. Nevertheless, this event has not been precisely dated yet. ...
... A possible explanation for this is the separate evolution of several small uplifts, which later unified to form a single source area, and the integration of the separated depocentres into one marginal trough. Alternatively, the oblique convergence phase observed by Navabpour et al. (2017) in small-scale structures, and which predates the frontal thrusting, could have induced the subsidence of oblique en échelon subbasins. ...
Central and western Europe were affected by a compressional
tectonic event in the Late Cretaceous, caused by the convergence of Iberia
and Europe. Basement uplifts, inverted graben structures, and newly formed
marginal troughs are the main expressions of crustal shortening. Although
the maximum activity occurred during a short period of time between 90 and 75 Ma, the
exact timing of this event is still unclear. Dating of the start and end of Late
Cretaceous basin inversion gives very different results depending on the
method applied. On the basis of borehole data, facies, and thickness maps,
the timing of basin reorganization was reconstructed for several basins in
central Europe. The obtained data point to a synchronous start of basin
inversion at 95 Ma (Cenomanian), 5 Myr earlier than commonly
assumed. The end of the Late Cretaceous compressional event is difficult to
pinpoint in central Europe, because regional uplift and salt migration
disturb the signal of shifting marginal troughs. Late Campanian to Paleogene
strata deposited unconformably on inverted structures indicate slowly
declining uplift rates during the latest Cretaceous. The differentiation of
separate Paleogene inversion phases in central Europe does not appear
possible at present.
... Choi et al., 2001;Homberg, Bergerat, et al., 2002;Lacombe, Mouthereau, et al., 2006;T. Q. Lee & Angelier, 2000;Madritsch & Hammer, 2012;Madritsch, Schmid, et al., 2008;Navabpour et al., 2016;Saintot & Angelier, 2002;Sippel, Saintot, et al., 2009). Thus, one principal stress axis must be nearly/vertical to the Earth's surface while the other two axes must be in sub/horizontal directions, parallel to the Earth's surface. ...
... A similar paleostress tensor has already been described in the Rhine-Bresse transfer zone (Lacombe, Angelier, Bergeret, et al., 1990;Lacombe, Angelier, Byrne, et al., 1993;Madritsch, 2008;Madritsch, Kounov, et al., 2009;Rocher, Chevalier, et al., 2003), in the Upper Rhine graben area (Larroque & Laurent, 1988;Villemin & Bergerat, 1987), in the vicinity of Paris Basin (Lacombe & Obert, 2000;Rocher, Cushing, et al., 2004), in the Burgundy area of France , at the western Border fault zone (Franconian fault) of the Bohemian Massif (Bergerat & Geyssant, 1983;Peterek et al., 1997), in southernmost France (Lacombe, Angelier, & Laurent, 1992;Rocher et al., 1998Rocher et al., , 2000, throughout the JFTB (Homberg, Bergerat, et al., 2002;Ustaszewski & Schmid, 2006), and in other parts of the European Platform (Bergerat, 1987;Letouzey, 1986;Letouzey & Trémolières, 1980;Navabpour et al., 2016;Parrish et al., 2018;Sippel, Scheck-Wenderoth, et al., 2008;Figure 12a). Most of the previous authors situate this regime in the Eocene ( Figure S7). ...
... JFTB, Jura fold-and-thrust belt; N-I, R-I, S-I, and S-II, paleostress tensors detected in this study. the general strike of Late Oligocene-Early Miocene basaltic dykes that are integral parts of the European rift system (Navabpour et al., 2016), and is responsible for the abundant occurrence of normal faults with numerous tension gashes in the close vicinity of the Saone graben . ...
We present insights into the Cenozoic tectonic evolution of the region around the Pontarlier strike‐slip fault zone within the Jura fold‐and‐thrust belt by combined study of paleostress and geomorphic analyses. A preliminary separation of heterogeneous fault‐slip data and bedding‐tilt correction was performed before determining the paleostress axes orientations. The paleostress results provide evidence of multiphase deformation history consisting of four successive events. These events include a strike‐slip stress regime with ∼N‐S directed compression, a NW‐SE directed extensional stress regime, a NW‐SE trending compressional stress regime, and a strike‐slip stress regime with a mean NW‐SE directed compression. The directions of extension and compression for the second and third events are consistent with the general direction of maximum horizontal far‐field stress near the northern segment of the Pontarlier fault and generally deviate from those found near the southern segment.
Geomorphic analysis of selected rivers along the southern segment of the Pontarlier fault, together with sub/surface geological observations provides new clues on Late Cenozoic strike‐slip reactivation of inherited extensional structure of Mesozoic age. These clues include (i) anomalous zones of high gradient within uniform bedrock lithology that spatially coincide with an obvious change in the depth to top Mesozoic layers; and (ii) right‐lateral offset of river channels, which is consistent with NW‐SE compression related to the youngest paleostress and current stress field. A combination of paleostress and geomorphic analyses provides a useful complementary approach for unraveling the Cenozoic tectonic evolution of the region characterized by a general lack of outcrop of Cenozoic rocks.
... While some authors have argued for a NW-SE-directed dextral strike-slip fault system by attributing the uplifts to restraining bends and related basins to transtension (Ziegler, 1990a;Wrede, 1988;Uličný, 2001), most authors have agreed that frontal thrusting was the main process that developed the observed structures Kley and Voigt, 2008;Nielsen and Hansen, 2000;Deckers and van der Voet, 2018). This was also confirmed by small-scale structural features (slickensides, fold axes, and fault orientations), which in many cases preserved both the extensional phase and N-S to NE-SW convergence (Vandycke, 2002;Franzke et al., 2004;Kley, 2018;Malz et al., 2020;Coubal et al., 2014;Navabpour et al., 2017). The strike-slip model addresses the problem that the principal faults should be orientated in an E-W direction to explain the subsidence anomalies at the assumed releasing Riedel shears, which were in fact never observed. ...
... On the basis of a detailed structural analysis of faults, Navabpour et al. (2017) were able to detect an early phase of N-S compression, oblique to the main NW-SE-striking faults, between the extension phase and the frontal thrusting. Nevertheless, this event has not been precisely dated yet. ...
... A possible explanation for this is the separate evolution of several small uplifts, which later unified to form a single source area, and the integration of the separated depocentres into one marginal trough. Alternatively, the oblique convergence phase observed by Navabpour et al. (2017) in small-scale structures, and which predates the frontal thrusting, could have induced the subsidence of oblique en échelon subbasins. ...
Central Europe was affected by a compressional tectonic event in the Late Cretaceous, caused by the convergence of Iberia and Europe. Basement uplifts, inverted graben structures and newly formed marginal troughs are the main expressions of crustal shortening. Although the maximum activity occurred in a short period between 90 and 75 Ma, the exact timing of this event is still unclear. Dating of start and end of basin inversion is very different depending on the applied method. On the basis of borehole data, facies and thickness maps, the timing of basin re-organisation was reconstructed for several basins in Central Europe. The obtained data point to a synchronous start of basin inversion already at 95 Ma (Cenomanian), 5 Million years earlier than commonly assumed. The end of the Late Cretaceous compressional event is more difficult to pinpoint, because regional uplift and salt migration disturb the signal of shifting marginal troughs. Unconformities of Late Campanian to Paleogene age on inverted structures indicate slowly declining uplift rates.
... It marks the transition to a phase of tectonic quiescence and uniform sedimentation lasting until the Late Jurassic (Ziegler, 1990). NE-SW directed tensional stress (Navabpour et al., 2017;Rauche and Franzke, 1990;Sippel et al., 2009) persisting from Late Jurassic to Early Cretaceous caused the subdivision of the Central European Basin into several sub-basins (e.g. the Lower Saxony Basin; cf. Betz et al., 1987) and local (half-)graben systems Kockel, 2002). ...
... These observations support the interpretations from wide areas of Central Europe, where normal faulting was associated with NE-SW extension (cf. Baldschuhn and Kockel, 1999;Betz et al., 1987;Krzywiec, 2006b;Malz and Kley, 2012;Ziegler, 1990 and references therein), and correspond to the results of paleostress analysis (Navabpour et al., 2017;Rauche and Franzke, 1990;Sippel et al., 2009). The late Early Cretaceous (Middle Albian) marine transgression marks the end of Mesozoic extension and the beginning of a short phase of tectonic quiescence. ...
... Stille, 1924) event of intraplate shorting, which was associated with a far-field NE-SW-directed compressional stress regime (cf. Navabpour et al., 2017 and references therein) due to the convergence of the African, Iberian and European plates (Kley and Voigt, 2008). Although thrusting, folding and uplift occurred, it has to be noted that major uplift of crustal blocks is limited to the southern rim of our research area (Fig. 18C). ...
The Central European Basin is an intracontinental basin that initially formed due to long-lasting thermal subsidence accompanied with several tectonic phases of extension during Mesozoic times. Locally, thick evaporites were incorporated in the deformation and led to the formation of detached structures, salt pillows and diapirs. At the end of the Late Cretaceous, the formation of (sub-) basins and (half-) grabens became interrupted by a short-term event of contraction. Especially along the northern and southern edges of the basin, lithospheric shortening resulted in basin inversion and the uplift of large basement blocks. Hence, the present day's structural framework shows a complex pattern of kinematically and chronologically variable structures. Herein, we unravelled these structures for the Altmark region in northern Saxony-Anhalt (Central Germany). We used regional depth maps, reflection seismics and borehole data analysed by use of large-scale subsurface mapping and 3D modelling techniques to completely re-evaluate the structures in the Late Palaeozoic to Cenozoic sedimentary basin succession. Our results show a high variability of tectonic structures: narrow and distributed, in parts reactivated normal fault zones, huge inverted basins, thin-skinned thrust faults, detachment folds and large basement thrusts. The style of deformation significantly changed during the region's evolution. This is indicated by particular structural, kinematic, thermal and rheological conditions, which existed for the individual phases of basin formation and inversion and probably persist until today.
... Plus loin dans l'avant-pays, à plusieurs centaines de kilomètres du front de chaîne, la déformation associée à la formation d'un orogène est de plus faible intensité qu'à proximité du prisme orogénique mais peut néanmoins être également caractérisée à l'aide des observations de terrain ou des modèles numériques ou analogiques. Elle est exprimée dans ces secteurs sous la forme de (1) flambage lithosphérique (Ziegler et al. 1995;Gerbault et al. 1999;Cloetingh et al. 1999;Sokoutis et al. 2005; Stephenson & Cloetingh 1991), (2) réactivation de structures tectoniques régionales héritées (Wyns 1980;Ziegler et al. 1995;Cazes et al. 1985), (3) joints et microstructures de faible déplacement (Navabpour et al. 2017;Missenard et al. 2017). ...
... In the absence of such information, their age has been deduced by comparison with the generally well-constrained tectonic timeline of the adjacent domains based on stress orientation from the structure directions, on syntectonic sedimentary record, on thermochronology, etc. (Ziegler et al. 1995;Navabpour et al. 2017) -a comparison that could in some cases lead to erroneous age attributions (see Parrish et al. (2018)). although a syntectonic sedimentary record associated with these structures is lacking (Constantin et al. 2002;De Charpal et al. 1974;Macquar 1973;Peyaud 2002 (Curnelle & Dubois 1986;Dercourt et al. 1986). ...
En géodynamique, l’essentiel des déformations est accommodé aux limites des plaques tectoniques. Pourtant, la propagation de la contrainte au-delà de ces frontières est à l’origine de déformations dites « intraplaques », d’intensité modérée mais qui contrôlent notamment des circulations de fluides et minéralisations. Ces déformations, et en particulier leur lien avec l’agenda tectonique établi en limite de plaque, sont aujourd’hui encore mal comprises : sont-elles antérieures, contemporaines, postérieures à la formation des orogènes ? S’agit-il d’épisodes uniques ou multiples, et sur quelle durée ? Les travaux présentés tentent de répondre à ces questions en s’appuyant sur la caractérisation du domaine intraplaque situé au Nord de la chaîne Pyrénéenne, dans la région des Corbières, du Languedoc et des Grands Causses. La méthode de datation U-Pb sur calcite de faille, développée en partie au laboratoire GEOPS au cours de ce travail, est couplée à une analyse structurale de chacune des zones afin de dater de manière absolue la déformation compressive dans les divers secteurs. Les résultats obtenus permettent ainsi de (1) préciser/établir les calendriers géodynamiques de chacun des secteurs (2) replacer ces déformations intraplaques dans le contexte géodynamique global et (3) établir le lien entre les déformations dans le domaine intraplaque et celles en bordure de plaque. Les travaux réalisés dans la région des Corbières, au front de l’orogène, mettent en évidence une phase de déformation au Lutétien, en décalage avec le paroxysme d’exhumation de la chaîne à l’Eocène supérieur. La région a également enregistré un évènement tectonique au Miocène, contemporain d’une phase d’exhumation de la chaîne, de la formation des surfaces « perchées » des Pyrénées et d’un épisode de déformation décrit sur le versant espagnol des Pyrénées. Le secteur du Languedoc, et en particulier le système de faille des Cévennes, enregistre une déformation associée à la compression pyrénéenne continue tout au long de l’Eocène. Par ailleurs les données U-Pb indiquent une activité à l’Albien de ce faisceau de failles, contemporaine de l’ouverture des bassins pyrénéens. Enfin, la région des Grands Causses correspondant au secteur d’étude le plus distal à la chaîne enregistre une déformation longue et continue du Crétacé inférieur à l’Eocène supérieur. L’ensemble de ces travaux démontre ainsi que la déformation en domaine intraplaque n’est pas limitée à l’enregistrement des phases paroxysmales de déformation en limite de plaque comme cela a pu être proposé auparavant, mais que le domaine intraplaque présente une grande sensibilité aux déformations en bordure de plaque, et donc une forte déformabilité sur des durées importantes avant, pendant et après la formation des orogènes en limite de plaque.
... From the dip data, an orientation analysis was conducted to determine the optimal orientation for the cross sections. The calculated fold axis trends WNW-ESE, indicating a shortening direction consistent with the regional NNE-SSW extension and contraction directions deduced from the analysis of small-scale fault populations (Navabpour et al., 2017). Hence, approximately plain-strain deformation conditions for the profiles can be assumed for both the extensional and the contractional phase. ...
... Other authors proposed predominantly dip-slip contraction (Martini, 1937;Seidel, 1938;Rauche and Franzke, 1990;Kockel, 2003;Kley and Voigt, 2008); see Wrede (2008Wrede ( , 2009) and Voigt et al. (2009) for a focused version of that debate. To our knowledge, conclusive evidence from kinematic indicators has been presented for dipslip motion (Franzke et al., 2007;Kley and Voigt, 2008;Sippel et al., 2009;Kley, 2013;Navabpour et al., 2017) but not for transpression. ...
Lens-shaped slivers of Permian (Zechstein) amid Triassic
units appearing along the master fault of the Sontra Graben in central
Germany on the southern margin of the Central European Basin System (CEBS)
were studied by means of detailed map analysis, a semi-quantitative forward
model, and two balanced cross sections. We show how partial reactivation of
the graben's main normal fault and shortcut thrusting in the footwall during
inversion, combined with a specific fault geometry involving flats in low-shear-strength horizons, can produce the observed slivers of “exotic”
Zechstein. This conceptual model implies that the Sontra Graben was created
by about 1200 m of extension followed by some 1000 m of contraction,
resulting in the few hundred meters of net extension observed today. Gentle
dips and comparatively extensive exposure of some slivers suggest they are
backthrust onto the reactivated normal fault's hanging wall,
an interpretation corroborated in one location by shallow drilling.
Backthrusting appears to have wedged some Zechstein slivers into incompetent
Triassic units of the hanging wall. Based on regional correlation, extension
most likely occurred in Late Triassic to Early Cretaceous time, while the
contraction is almost certainly of Late Cretaceous age. The main aim of this
paper is to describe an uncommon structural feature that we interpret to
originate from inversion tectonics in an evaporite-bearing succession with
multiple detachment horizons but without the presence of thick salt.
... This deformation, several hundred kilometres away from the orogeny, is generally expressed by (1) kilometre scale denudation generally associated with lithospheric folding, (2) reactivations of crustal scale inherited faults, and (3) small-scale fracturing including low-displacement faults and tectonic joints sets-all of them being able to trigger, for instance, significant fluid flow and potential mineralization. These far-field phenomena have been characterized with numerical or analogue modelling or field studies (see examples in Cloetingh et al. [6], Gerbault et al. [7], or Sokoutis et al. [8] for lithospheric folding, Ziegler et al. [9] for intraplate fault reactivations, and Navabpour et al. [10] for small-scale fracturing), but the question of their age and the time relationships with the building of the orogen itself has remained puzzling. Lithospheric buckling relative dating can be asserted using analogue modelling. ...
... Nonetheless, dating of crustal scale brittle deformations in the intraplate domain is still challenging, due to the lack of (1) syntectonic sedimentary records, in relation to very low displacements, and (2) adequate materials to be dated in the fault zones or joints. In the absence of such information, their age has been deduced by comparison with the generally well-constrained tectonic timeline of the adjacent domains based on stress orientation from the structure directions, on syntectonic sedimentary record, on thermochronology, etc. [9,10]-a comparison that could in some cases lead to erroneous age attributions (see Parrish et al. [12]). ...
Although tectonic plates are usually considered as rigid blocks, intraplate deformation such as lithospheric buckling or diffuse brittle deformation has been recognized for a long time. However, the origin of these deformations remains puzzling. Indeed, whereas the chronology of deformation at plate boundaries can be constrained by numerous methods (syntectonic sedimentary record, thermochronology, etc.), dating of brittle structures (faults, veins, and joints) in the far-field domains remains challenging, preventing a global interpretation of the system as a whole. In this contribution, we have combined a tectonic study with a synkinematical geochronological study of fault-related calcites of the Grands Causses intraplate domain, north of the Pyrenean orogeny. We show that these faults record a much longer history of deformation than previously thought. The Mesozoic extension, usually attributed to an early Jurassic Tethysian rifting event, probably lasted until the Barremian-Aptian epoch, in response to the Pyrenean basin’s opening. The so-called “Pyrenean deformation” of the Grands Causses domain, usually associated with the paroxysm of deformation in the belt during the late Eocene, began much earlier, around 100 Ma, and lasted for more than 60-70 Ma. This study demonstrates the high sensitivity of an intraplate domain (Grands Causses area) to record extensional or compressional deformations occurring at the edge of neighbouring plates.
... In a convergence context, intra-plate deformations occur during orogenic processes several hundred kilometers away from the mountain belt front (Jolivet et al., 2021;Lacombe & Mouthereau, 1999). They are accompanied by uplifting following lithospheric folding (Gerbault et al., 1999;Ziegler et al., 1995), tectonic reactivation (Gorczyk et al., 2013;Navabpour et al., 2017;Parizot et al., 2022), and the formation of new fault and joint networks (Duperret et al., 2012;Missenard et al., 2017). However, far-field deformation takes place sometimes at the onset of convergence resulting in the inversion of pre-existing structures such as rift (Frizon et al., 2000) or passive margins (Leffondré et al., 2021) and in the folding of the lithosphere (Cloetingh and Burov, 2011). ...
In Western Europe, the deformations related to the opening of the Bay of Biscay and the formation of the Pyrenean belt are well described in the southern part of the Aquitaine Basin, but little is known about the impact of these geodynamic events towards the Northern Aquitaine Platform. In this paper, we combine field observation with Unmanned Aerial Vehicle (UAV) imagery and calcite U-Pb geochronology to determine precisely the tectonic evolution in the Vendée Coastal domain. We evidence two main tectonic events: (1) At the transition between the Late Jurassic to Early Cretaceous, WNW-ESE striking normal faults formed horsts and grabens at the onset of the opening of the Bay of Biscay. The reactivation of Variscan faults during this tectonic event is consistent with oblique extension. This event triggered ascending fluid flows that mix with Basin fluids responsible for barite-pyrite-quartz mineralizations near the unconformity. (2) During the Late Cretaceous, fractures, wide-open folds, veins, and joints are consistent with the N-S shortening direction during the earliest stages of the Pyrenenan compression.
In both cases, the Northern Aquitaine Platform records the early stages of the main regional tectonic events in a far-field position. In the northern Aquitaine Basin, as in many other places in Europe, the tectonic study of sedimentary platforms located far from the plate boundaries provides new constraints on the early diffuse deformation process that predate the main tectonic phases.
... Am Südrand des Kyffhäusers im Bereich der heutigen Barbarossahöhle herrschten im frühen Jura bis zur frühen Kreide sowie in der späten Kreide bis ins Paläogen und/oder im Oligozän Spannungsregime, die die beobachteten Extensionsklüfte hervorgebracht haben könnten (NAVABPOUR et al. 2017 ...
In the Barbarossa Cave in Thuringia, Germany, stratiform folds on a centimetre scale are found in the finely laminated layers of the Werra Anhydrite, which can be subdivided into four different structural types. The genesis of these enterolithic folds (German: Schlangengips; lit. “snake gypsum”) is still debated. In this paper we report on new field work in the cave, and we present a new model for the formation of the folded gypsum layers. Special focus was placed on the structural types that are predominantly found in the Lower Werra Anhydrite. The occurrence of these enterolithic folds was increasingly observed in the vicinity of sulphate concretions, fractures, and chicken-wire-anhydrite. Based on macroscopic, microscopic and X-ray diffraction studies as well as considerations concerning the observed deformation, we propose models for the genesis of the folded layers. In all models, the genesis of the enterolithic folds is tied to the presence of fluids. Those are either released in the form of crystal water during the early diagenetic subsidence-related transformation of gypsum into anhydrite in sulphate concretions and chicken-wire-anhydrite or the fluids are transported along fractures in the anhydrite rock. These fluids can migrate into more permeable sulphate layers and cause swelling of the layers due to an increase in volume during the phase transformation from anhydrite to gypsum. In addition to this increase in volume, sulphate phases can crystallise from sulphate-saturated fluids, which lead to a further increase in volume.
... By the late Jurassic, Central Europe underwent a phase of NE-SW extension, which is well documented in the North German Basin by thick syntectonic strata (Kockel 2003;Voigt et al. 2008). This extension also slightly affected more peripheral parts of the Central European Basin system, including the study area (Malz & Kley 2012;Kley 2013;Malz 2014;Navabpour et al. 2017). ...
We present new results from a fission track (FT) and U-Pb Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) double dating approach on zircon and apatite from the Thuringian Forest, a prominent fault-bounded basement high in central Germany, and its southwestern periphery exposing Mesozoic strata. Samples were collected from seven exposures of igneous rocks as well as from lower to upper Permian (Rotliegend) continental red beds and volcanics recovered from a borehole southwest of the Thuringian Forest. U-Pb LA-ICP-MS data on zircons from surface exposures of igneous rocks yielded ages between 330 and 300 Ma, confirming emplacement of granitoids into Upper Proterozoic to Lower Palaeozoic Variscan-deformed country rocks. Apatite FT ages range between 86 and 70 Ma, suggesting rock uplift associated with a well-documented and regionally important phase of NNE-SSW-directed intraplate contraction, resulting in spatially homogeneous removal of ca. 3 km of Upper Palaeozoic to Mesozoic rocks. No change in apatite FT ages was detected across the regional-scale Franconian Fault system at the southwestern margin of the Thuringian Forest. Additionally , apatite FT ages of borehole samples southwest of the Thuringian Forest from depths between 963 and 2,712 m range from 57 to 18 Ma, suggesting post-Late Cretaceous cooling of this peripheral region. Our data hence support recent models of a continued large-scale domal uplift of Central Germany without verifiable or detectable involvement of individual faults.
... In the centre of this anomaly this fault system coincides with the Itztal-Regnitztal fault system(Gudden 1981). At the moment, the area of geothermal interest in the Franconian Basin is in a "NE-SW to ENE-WSW transtensional strike-slip regime with maximum principal stress axis oriented NW-SE […]NAVABPOUR et al. 2017)" (KÄMMLEIN 2020). This regime thus corresponds to the specific kinematics for the basement east of the Franconian Line(SEHT et al. 2006). ...
To use geothermal energy in Bavaria even more, a precise knowledge of the underground, which serves as a reservoir, is essential. The present work examines the most promising areas within Bavaria. It concerns the North Alpine Forland Basin, SE Germany in the area around Munich and the Franconian Basin in NE Bavaria.
In the North Alpine Foreland Basin, SE Germany the carbonates of the Upper Jurassic are already successfully used as a reservoir (also known as Malm aquifer) for hydrothermal geothermal energy. For the characterization of the Upper Jurassic aquifereleven core drillings were investigated. A total of 449core samples were taken from depths ranging from 243 m to 5,225 m. The drill cores originated from different stratigraphic intervals, and have different lithologies and facies. In the north–east of Bavaria, petrothermal geothermal energy should be used in the future.
In the Franconian Basin there is a demonstrable anomaly with elevated underground temperatures. The reservoir rocks are probably granites below the Franconian Basin, which could be the origin of the geothermal anomaly. Due to the absence of samples from this area, sample material similar to the reservoir rock was examined from twelve outcrops in the Fichtelgebirge. A total of 358 analogue samples were produced. These rocks are considered the closest analogue material for the rocks below the Franconian Basin.
Drill cores and analogue samples were prepared for laboratory investigations. The resulting test samples were characterized geomechanically using both non-destructive as well as destructive testing methods. The non-destructive laboratory investigations were ultrasonic tests. The destructive laboratory investigations included Uniaxial Compression Tests, BrazilianTensile Tests, Point Load Tests, Cerchar Abrasivity Tests and LCPC Abrasivity Tests. All testing results are listed in the appendix of the thesis.
The wells/borehole and outcrops are described individually and the most important characteristic values are listed in each case. In addition, the testing results are summarised for the respective reservoir. The testing results of the Upper Jurassic aquifer are classified according to their stratigraphy, lithology and facies. The testing results of the granites from the Fichtelgebirge are classified according to their age of intrusion (G types) and their orientation.
The results for the North Alpine Forland Basin, SE Germany show that the Upper Jurassic aquifer has very heterogeneous geomechanical characteristics. No directional dependences of the parameter examined over the different stratigraphic units as well as lithologies was found. For the types of facies in each lithology, most of the values decrease with the increasing particle size. The results of the analogue samples show that if applicable granites present below the Franconian Basin in NE Bavaria have very homogeneous geomechanical characteristics. It is not possible to identify G type and orientation based on the data from the laboratory investigations. In destructive laboratory tests, characteristic value ranges were found.
In this thesis the determined characteristic values serve as input parameters for various scenarios in the numerical simulation of the borehole stability. For both locations a stress distribution in the near-field of the borehole was carried out with the program RS2 from Rocsience. The depth of failure around the borehole was also determined.
In the North Alpine Foreland Basin, SE Germany for all lithologies, borehole stability decreases with increasing depth. The depth of failure around the borehole hardly differs between the individual lithologies when considering the UCS mean values.
In NE Bavaria the borehole stability is found to be very low for all G types for all UCS values. If the calculated values for the stress field are correct, a successful drilling in NE Bavaria is unlikely.
The determined parameter ranges can be used in the future to check existing models and also create new models. They allow for a more precise understanding of the sedimentary and crystalline reservoirs and a more effective use of geothermal energy in Bavaria.
... This study focuses on the evolution of the upper Cretaceous to Quaternary tectonic stress regime using brittle structures; this kind of methodology has been found to be useful in various researches such as stress field rotation or block rotation in the Lake Mead fault system (Ron et al. 1993), variation of relative paleostress magnitudes and orientations (Kaymakci 2006), paleostress regimes of brittle structures (Heuberger et al. 2010), paleostress field reconstruction (Sippel et al. 2010), paleostress reconstructions of Jabal Hafit Structures United Arab Emirates (UAE) (Zaineldeen 2011), paleostress reconstruction and multiphase weak deformation in cratonic interior (Tripathy and Saha 2015), brittle structural data evaluation and paleostress calculation (Sasvari and Baharev 2014), late Cartaceous and Cenozoic paleostress history (Coubal et al. 2015), kinematic development and paleostress pattern of the Edremit Basin, western Turkry (Gürer et al. 2016), paleostress of Huangshan Basin of southeastern China (Xu et al. 2016), brittle deformation and state of paleostress constrained in the central German platform (Navabpour et al. 2017), stress regime changes in the Main Boundary Thrust zone, Eastern Himalaya (Patra and Saha 2019), and exhumation of granitoid plutons in the Eastern Iran (Samimi et al. 2020). ...
Eastern Iran, including the Sistan suture zone, comprises the boundary between Lut block and Afghan block. This research aims to reconstruct the stress regime evolution from the upper Cretaceous to Quaternary based on the brittle tectonic analysis. In this study, three episodic changes in stress regimes were recognized in the Shekarab Mountain using data inversion. In places where conglomerate outcrops are present, the Quaternary stress state is obtained using the youngest slickensides. The Quaternary stress state indicates that the direction of σHmax is close to N026°, which is compatible with the present-day Arabia-Eurasia convergence direction. Reconstruction of stress fields using age and sense of motion of faults shows that the stress regime during the Cretaceous was compressional, which caused the uplift of peridotites and ophiolites in the eastern part of the study area. The state of stress in the upper Eocene and Oligocene was transpressional; in the eastern part of the study area, there is a change from transpression to transtension. The exhumation of igneous rocks in the eastern part of the Shekarab Mountains is due to the local change of the stress regime. According to the results of this study, the first stage of stress state in the Shekarab Mountains was compressive and the average direction of maximum stress axis (σ1) was toward N337°. In Eocene, the tectonic regime was transpressional and the average direction of maximum stress axis (σ1) was toward N003°. In Quaternary, the tectonic regime is strike-slip and the average direction of maximum stress axis (σ1) is toward N026°. This implies that at least 49° clockwise rotation of σ1 happened in the Shekarab Mountain.
... Such hydraulic basement connections may be assumed especially for the areas of intersection of NW-SE to NNW-SSE striking steeply dipping faults (Donhauser 2017), which are orientated (sub)parallel to the recent stress field . Considering that the study area is presently placed in a NE-SW to ENE-WSW extensional strike-slip regime with the maximum principal stress axis oriented NW-SE (world stress map; Reiter et al. 2016;Navabpour et al. 2017), transtensional movements along curved NW-SE to NE-SW trending faults and/or local pull-apart effects at fault intersections may provide pathways for convective heat transfer. ...
Exploration activities for hydrocarbons and thermal waters between the 1960s and 1980s consolidated the assumption
of a positive temperature anomaly in the Franconian Basin of SE Germany. However, the geological causes of the
temperature high are not known yet. In addition, an up-to-date compilation of temperature data from deep wells and thermal
conductivity data of the Permo-Triassic section and of the basement rocks is lacking.
In this study, we present a homogenised dataset of uniformly corrected temperature readings from 18 deep wells and new
reliable conductive surface heat flow densities. We further apply a vertical Péclet number analysis on equilibrated temperature
logs for quantifying convective and conductive components in heat transfer.
The isotherms of calculated equilibrium temperature gradients >30.0–48.9 °C km-1 constrain the presence of elevated
temperatures in the Franconian Basin within an area of ~100 × 65 km2. The elevated temperatures in the centre of the
anomaly presumably originate in the basement but rapidly decrease away from the centre. The geothermal potential of the
area is locally high, with surface heat flows exceeding 100 mW m-2 and reaching a maximum of 134 (±16) mW m-2 in the
central part of the anomaly.
The NW–SE elongated shape of the anomaly implies that the strike of the major regional fault system has a significant
control on the present-day temperature field. A Péclet number analysis and the correlation of T-log breaks with the new
thermal conductivity data prove a predominantly conductive heat transfer regime. However, signatures of convective heat
transfer have been proven for the aquifers of the Buntsandstein, Muschelkalk and Keuper groups.
The study also reveals significant data gaps in the Franconian Basin, which strongly limit a reliable three-dimensional representation
of the temperature field and a further limitation of possible cause(s) of the temperature anomaly. Namely, these
are missing temperature data of the basement and a generally low density and the partially low depth level of available
temperature data.
... The Thuringian northern forest border fault exhibits a very significant displacement of Paleozoic (Thuringian Forest) vs. Mesozoic strata (Thuringian Syncline), while the fault zones within the Thuringian Syncline reveal displacement only within the Mesozoic sediments. The fault zones evolved due to regional NE-SW directed extension during the Late Jurassic to Early Cretaceous (Ziegler, 1990;Kockel, 2002;Navabpour et al., 2017) and resulted in a subdivision of the Thuringian Syncline into approximately 20 km wide non-deformed areas separated by narrow (up to 2 km wide) fault zones (Katzung and Ehmke, 1993;Malz, 2014). During the latest Cretaceous to early Paleogene, the entire Central Europe including the Thuringian Syncline underwent a phase of regional intraplate shortening and uplift (Ziegler, 1978(Ziegler, , 1990Betz et al., 1987;Kley and Voigt, 2008). ...
Vein mineralization observed in boreholes, quarries and outcrops of Upper Permian and Mesozoic sediments in the Thuringian Syncline, Germany, was investigated for the first time by petrography, electron microprobe analysis and stable isotope analysis. The objective was a characterization of paleo-fluid systems within this basin. Veins are mostly restricted to NW-SE trending fault systems and comprise carbonates (calcite, dolomite), minor sulfates (gypsum/anhydrite, celestite, barite), and rarely sulfides. They are variably distributed within the Late Paleozoic to Mesozoic succession. Calcite vein mineralization occurs in almost all Triassic strata, though dominating in the Lower Muschelkalk subgroup (mu). Gypsum/anhydrite veins occur in the Middle Keuper subgroup (km), Middle Muschelkalk subgroup (mm), Middle and Upper Buntsandstein subgroup (sm, so) as well as in the Upper Permian (Zechstein). Sulfate and carbonate isotope analyses indicate that most vein mineralization dominantly crystallized from intraformational fluids within the Upper Permian and Triassic sediments. Crystallization from descending meteoric waters was observed especially for calcite veins in the Lower Muschelkalk, but also for gypsum/anhydrite veins in the Upper Buntsandstein. Mineralization from ascending, carbonate-pH-buffered, warm waters was restricted to individual parts of the southern, deep reaching main border fault zone of the Thuringian Syncline. Mixing and fault crossing fluid movements are subordinate within the Thuringian Syncline. We conclude that no large scale cross-formational fluid flow occurred in Thuringian Syncline over the last millions of years.
... This event was accompanied by an uplift of 1-2 km in the area of the studied field (Lohr et al., 2007). It resulted in fault reactivation as thrusts and with a strike-slip component (Navabpour et al., 2017) and development of associated fractures. Today's stress regime has been present since the late Oligocene, where a counterclockwise rotation of NE -SW to NW -SE Alpine compression started (Betz et al., 1987;Fleckenstein et al., 2004;Glennie and Underhill, 1998;Kley and Voigt, 2008;Reiter et al., 2016). ...
Understanding the orientation and connectivity of fracture systems in tight reservoirs is essential to reduce uncertainties in reservoir development and production. However, the actual flow potential of the fractures can be controlled by the present-day stress field. Dilation- and slip tendency analyses can improve fracture permeability evaluations and thus, aid in estimating the hydrocarbon recovery of a field. This study focuses on a naturally-fractured, relatively tight (matrix permeabilities of 0.01–1 mD) and gas-producing Late Permian (Zechstein) reservoir in the Southern Permian Basin, northern Germany. Fracture data are obtained from resistivity image log data of a 775 m long horizontal well, and show principal NE – SW orientation with main dip angles steeper than 70°. To quantify the potential of those fractures that contribute to the flow within the reservoir, dilation (Td)- and slip (Ts) tendencies are calculated. Two different stress scenarios are defined based on known variations in the orientation of the horizontal stresses between formations below and above the Zechstein salt in an offset field approximately 5 km away. Results of Td and Ts strongly depend on the strike and dip angle of the fractures, with sub-vertical fractures showing highest potential to dilate while fractures with dip angles of 60° are favorably oriented for slip. Fractures with orientations parallel to the principal horizontal stress have highest slip- and dilation tendencies. Adding this information to the calculation of fracture permeability results in a significant reduction of the calculated flow potential due to the influence of the stress field. Thus, incorporating stress field data helps reducing risks in field development planning.
... In fact, many parts of these regions are crossed by pre-Late Cretaceous normal faults (e.g. Franzke, Müller, Voigt, & von Eynatten, 2007;Navabpour et al., 2017;Rauche & Franzke, 1990). Thus, it is likely that here sub-salt extension triggered most salt structures. ...
In this paper, a literature‐based compilation of the timing and history of salt tectonics in the Southern Permian Basin (Central Europe) is presented. The tectono‐stratigraphic evolution of the Southern Permian Basin is influenced by salt movement and the structural development of various types of salt structures. The compilation presented here was used to characterize the following syndepositional growth stages of the salt structures: (a) “phase of initiation”; (b) phase of fastest growth (“main activity”); and (c) phase of burial’. We have also mapped the spatial pattern of potential mechanisms that triggered the initiation of salt structures over the area studied and summarized them for distinct regions (sub‐basins, platforms, etc.). The data base compiled and the set of maps produced from it provide a detailed overview of the spatial and temporal distribution of salt tectonic activity enabling the correlation of tectonic phases between specific regions of the entire Southern Permian Basin. Accordingly, salt movements were initiated in deeply subsided graben structures and fault zones during the Early and Middle Triassic. In these areas, salt structures reached their phase of main activity already during the Late Triassic or the Jurassic and were mostly buried during the Early Cretaceous. Salt structures in less subsided sub‐basins and platform regions of the Southern Permian Basin mostly started to grow during the Late Triassic. The subsequent phase of main activity of these salt structures took place from the Late Cretaceous to the Cenozoic. The analysis of the trigger mechanisms revealed that most salt structures were initiated by large‐offset normal faults in the sub‐salt basement in the large graben structures and minor normal faulting associated with thin‐skinned extension in the less subsided basin parts.
Study area (Shekarab Mountains) is located in Sistan suture zone. The aim of this research is to investigate the variation of stress pattern (direction of stress tensors and stress ellipsoids shape) in Neogene units, Paleogene units and older units. In this research characteristics of brittle structures (faults) were interpreted using Win-Tensor software. Structural analysis and analysis of Steps of applied Paleo stress in Shekarab Mountains indicate that in Cretaceous time stress regime operation tectonic was pressure with the direction of the main stress axes σ1=337/26, σ2=070/06, σ3=172/64 and stress ratio was 0.1 which caused the uplifting of peridotites and ophiolites in eastern part of study area. The second step of stress has been strike slip and transpressive with the direction of the main stress axes σ1=003/31, σ2=110/26, σ3=232/47 and stress ratio was 0.29, more exhumation of igneous units is related to in the eastern part of Shekarab Mountains in these regions units' stress regime has been displaced locally from strike slip to transpressive that is due to local changes of stress direction in this regions. The third step of stress regime of in Shekarab Mountains is strike slip with the direction of the main stress axes σ1=060/10, σ2=227/72, σ3=152/08 and stress ratio 0.5. Results of stress analysis indicate that major stress axis (σ1) in Cretaceous units had N337 trend, in Eocene units had N003 trend and in Quaternary units has N060 trend.
A brief, regional-scale review of the Late Cretaceous–early Palaeogene inversion-related tectonic structures affecting the Sudety Mountains and their foreland at the NE margin of the Bohemian Massif is presented and complemented with results of new seismic studies. The Sudetes expose Variscan-deformed basement, partly overlain by post-orogenic Permo-Mesozoic cover, containing a wide spectrum of tectonic structures, both brittle and ductile, in the past in this area referred to as young Saxonian or Laramide. We have used newly reprocessed legacy seismics to study these structures in the two main post-Variscan structural units of the area: the North Sudetic and Intra-Sudetic synclinoria. The results were discussed together with regionally distributed examples of tectonic structures from quarries and underground mines as well as those known from the literature. The Late Cretaceous–early Palaeogene tectonic structures in consecutively reviewed Sudetic tectonic units, from the north to the south, typically include gentle to moderately tight buckle folds, locally of detachment type or fault-related and high-angle reverse and normal faults, as well as low-angle thrusts – often rooted in the crystalline basement. The structures termed grabens in the local literature are at the same time frequently interpreted as bounded by reverse faults (hence we use here the term “reverse grabens”) and typically reveal a strongly synclinal pattern of their sedimentary fill. The top of the crystalline basement, as imaged by seismic data in the North Sudetic Synclinorium below the faulted and folded cover, is synformally down-warped with a wavelength of up to 30 km, whereas on the elevated areas, where the basement top is exposed at the surface, it is tectonically up-warped (i.e. antiformally buckled). The compressional structures typically show an orientation that fits the regionally known Late Cretaceous–early Palaeogene tectonic shortening direction of NE–SW to NNE–SSW. The same applies to the regional jointing pattern, typically comprising an orthogonal system of steep joints of ca. NW–SE and NE–SW strikes. All the reviewed structures are regarded as being due to the Late Cretaceous–early Palaeogene tectonic shortening episode, although some of the discussed faults with a strike-slip component of motion may have been modified, or even produced, by late Cenozoic tectonism.
The Bohemian Massif exposes structures and metamorphic rocks remnant from the Variscan Orogeny in Central Europe and is bordered by the Franconian Fault System (FFS) to the west. Across the FFS, possible presence of Variscan units and structures are buried by Permo-Mesozoic sedimentary rocks. We integrate existing DEKORP 2D seismic reflection, well and surface geological data with the newly acquired FRANKEN 2D seismic survey to investigate the possible westward continuation of Variscan tectonostratigraphic units and structures, and their influence on latest to post-Variscan basin development. Subsurface Permo-Mesozoic stratigraphy is obtained from available wells and are tied to seismic reflection profiles using a synthetic seismogram calculated from density and velocity logs. Below the sedimentary cover, three main basement units are identified using seismic facies descriptions that are compared with seismic reflection characteristics of exposed Variscan units east of the FFS. Our results show that Upper Paleozoic low-grade metasedimentary rocks and possible Variscan nappes are bounded and transported by Variscan shear zones to ca. 65 km west of the FFS. Basement seismic facies in the footwall of the Variscan shear zones are interpreted as Saxothuringian basement. We show that the location of normal fault-bounded latest to post-Variscan Upper Carboniferous-Permian basins are controlled by the geometry of underlying Variscan shear zones. Some of these Upper Carboniferous-Permian normal faults reactivated as steep reverse faults during the regional Upper Cretaceous inversion. Our results also highlight that reverse reactivation of normal faults gradually decreases west of the FFS.
A brief, regional-scale review of the Late Cretaceous – Early Palaeogene inversion-related tectonic structures affecting the Sudetes and their foreland at the NE margin of the Bohemian Massif is presented and complemented with results of new seismic studies. The Sudetes expose Variscan-deformed basement, partly overlain by post-orogenic Permo-Mesozoic cover, containing a wide spectrum of tectonic structures, both brittle and ductile, in the past in this area referred to as young Saxonian or Laramide. We have used newly reprocessed legacy seismics to study these structures at the two main post-Variscan structural units of the area, the North-Sudetic and Intra-Sudetic synclinoria, and discuss the results together with regionally-distributed examples coming from quarries and underground mines as well as those from the literature. The Late Cretaceous – Early Palaeogene tectonic structures in consecutively reviewed Sudetic tectonic units, from the north to south, typically include gentle to moderate buckle folds of detachment type or fault-related, high-angle reverse and normal faults, as well as low-angle thrusts – often rooted in the crystalline basement. The structures hitherto described as grabens, are frequently believed to be bounded by reverse faults (hence we use the term ‘reverse grabens’) and typically reveal strongly synclinal pattern of their sedimentary fill. The crystalline basement top, as imaged by seismic sections in the North Sudetic Synclinorium below the detachment-folded cover, is synformally down-warped with a wavelength of up to 30 km, whereas on the elevated areas, where the basement top is exposed at the surface, it is up-warped (i.e. tectonically buckled). The reviewed compressional structures typically show an orientation fitting the regionally-known Late Cretaceous – Early Palaeogene tectonic shortening direction of NE-SW to NNE-SSW The same applies to the regional joint pattern, typically comprising an orthogonal system of steep joints of c. NW-SE and NE-SW strikes. All the reviewed structures are considered as due to the Late Cretaceous – Early Palaeogene tectonic shortening episode, although some of the discussed faults with a strike-slip component of motion may have been modified, or even produced, by later, Late Cenozoic, tectonism.
With the Late Cretaceous onset of Africa‐Iberia‐Europe convergence Central Europe experienced a pulse of intraplate shortening lasting some 15–20 Myr. This deformation event documents area‐wide deviatoric compression of Europe and has been interpreted as a far‐field response to Africa‐Iberia‐Europe convergence. However, the factors that governed the compression of Europe and conditioned the transient character of the deformation event have remained unclear. Based on mechanical considerations, numerical simulations, and geological reconstructions, we examine how the dynamics of intraplate deformation were governed by the formation of a convergent plate boundary fault between Iberia and Europe. During the Late Cretaceous, plate convergence was accommodated by the inversion of a young hyperextended rift system separating Iberia from Europe. Our analysis shows that the strength of the lithosphere beneath this rift was initially sufficient to transmit large compressive stresses far into Europe, though the lithosphere beneath the rift was thinned and thermally weakened. Continued convergence forced the formation of the plate boundary fault between Iberia and Europe. The fault evolved progressively and constituted a lithospheric‐scale structure at the southern margin of Europe that weakened rheologically. This development caused a decrease in mechanical coupling between Iberia and Europe and a reduction of compressional far field stresses, which eventually terminated intraplate deformation in Central Europe. Taken together, our findings suggest that the Late Cretaceous intraplate deformation event records a high force transient that relates to the earliest strength evolution of a lithospheric‐scale plate boundary fault.
The complex fault and fracture patterns commonly observed in metamorphic terranes are the cumulative expression of repeated episodes of brittle deformation. The temporal sequence of deformation remains, however, often obscure due to the general lack of systematic overprinting relationships and absolute geochronological constraints. Here, we present a multipronged approach combining remote sensing, field work, structural analysis and paleostress inversion with mineralogical characterization and K-Ar dating of brittle features to develop an evolutionary model for one such complex fracture pattern. We applied this methodological approach to pervasively-fractured Early to Mid Ordovician intrusive rocks in the northern Bømlo islands, SW Norway. The local brittle structural record is interpreted as reflecting a sequence of six deformation stages, three ascribable to the Caledonian orogenic cycle and three to the rift evolution of the North Sea. The Caledonian structures are assigned to (1) Late Ordovician NNW-SSE transpression, (2) Silurian WNW-ESE compression and (3) Devonian NW-SE transtension. Rift-related structures formed during (4) Permian to Mid Triassic ENE-WSW extension (~ 290-245 Ma), (5) Late Triassic to Late Jurassic E-W extension (~ 210-160 Ma) and (6) Early Cretaceous WNW-ESE extension (~ 125 Ma). The reconstructed gradual rotation of the extensional stress field during the Mesozoic might reflect the continuous northward migration of the rift activity from the North Sea toward the mid-Norwegian margin. Our multipronged approach may be applied to the unraveling of complex and commonly long brittle histories stored in exhumed metamorphic terranes elsewhere.
This dissertation focuses on brittle tectonic evolution of the inner zones of the Zagros fold-and-thrust belt in the Fars and Kermanshah provinces of Iran. A palaeostress reconstruction of the former Arabian passive margin and its collision with the Iranian continental plate is carried out. Complex brittle structures, as evidenced by field-based analyses on geometric and chronologic relationships between faults, syn-tectonic sediments and folds, reveal major changes in stress regimes. The Mesozoic history of Arabian margin was characterised by extensional structures inherited from the Permian–Triassic rifting and the Neo-Tethyan oceanic opening. During the continental collision, subsequent inversion of these inherited structures resulted in an orogenic structural pattern, which helped reconstructing not only the geometry of passive margin but also the Neo-Tethyan closure process, as characterised by discontinuous ophiolite obduction and diachronous continental collision. The mid-late Cenozoic continental collision is characterised by compressional and strike-slip structures, revealing stress reorientation. This stress reorientation has been fairly consistent with a gradual change in plate kinematics in Fars, but not chronologically consistent with the plate kinematic change in Kermanshah, where orogenic-scale deformation partitioning occurs under an oblique plate convergence. The change in stress state has more likely been related to the late collisional plate reorganisation, as highlighted by an increase in coupling between the plates.
This article summarizes the results of an extensive fieldwork-based analysis of outcrop-scale fractures across central northern Switzerland in the distal northern foreland of the Central Alps. The study focuses on the delineation of a relative fracture formation chronology, the fracture kinematics and their tectonic interpretation with the aim of enhancing the understanding of the study area’s brittle deformation characteristics and history. The most commonly observed fractures within the analyzed outcrops of Middle and Upper Jurassic limestones are bedding-orthogonal joints, which show only minor increments of displacement (mode-II fractures). These structures formed relatively early during the tectonic evolution of the region and were repeatedly reactivated during later deformation events. Faults showing measurable displacements were observed comparatively rarely. Together with the results of fault-slip analyses, the outcrop-scale fracture patterns allow clear distinction of three major Cenozoic deformation steps in the study area: (1) formation of bedding-orthogonal joints lacking offsets and most likely related to regional uplift in Latest Mesozoic to Eocene times; (2) an only locally recognized phase of extension manifested by normal faults in the vicinity of the Hegau-Lake Constance Graben that onset after the Early Miocene; (3) shortening of the Alpine foreland from the Late Miocene onwards. Regionally recognizable NW–SE to NNW–SSE shortening, manifested by the strike-slip reactivation of bedding-orthogonal joints and normal faults, started prior to the comparatively late formation of mapscale folds in the easternmost Jura Mountains but continued to be active throughout this deformation event. Only locally recognizable NNE–SSW to NE–SW directed shortening is also interpreted in the context of Late Miocene Alpine shortening and does not represent an independent regional stress field. The latter has apparently changed little from Late Miocene to recent times.
(see below for English abstract)
Der Begriff „Saxonische Tektonik“ wurde im frühen 20. Jahrhundert geprägt und bezeichnete alle Deformationsereignisse, die sich in Mitteleuropa und Teilen von Westeuropa von der Trias bis heute abgespielt haben. Es ist heute weitgehend anerkannt, dass diese Deformation einen langen Zeitraum von Extension und Grabenbildung von der Trias bis zur frühen Kreide umfasst, gefolgt von einem oder mehreren Pulsen der Einengung und Inversion in später Kreide und Paläogen. Dehnungs- und Einengungsstrukturen sind oft stark durch Salzbewegungen verändert. Erneute Dehnung schuf seit dem Eozän das Europäische Riftsystem. Der durch Inversion geprägte Baustil, der viele saxonische Strukturen charakterisiert, wurde ursprünglich „Bruchfaltentektonik“ genannt. Beide Bezeichnungen sind noch nicht völlig verschwunden. Dem heutigen Kenntnisstand über die wechselnden tektonischen Regimes, ihren zeitlichen Ablauf und die Kontrolle bestimmter Baustile durch Stratigraphie, Lithologie, thermische und tektonische Geschichte werden sie nicht mehr gerecht. Ich rate deshalb dazu, die Ausdrücke „Saxonische Tektonik“ und „Bruchfaltentektonik“ nicht mehr zu verwenden. Viele Arbeiten, in denen die Konzepte entwickelt wurden, sind aber auch heute noch äußerst interessant zu lesen. Vor allem die aus den 30er Jahren zur – damals noch anders genannten – Inversionstektonik nehmen manche späteren Entwicklungen um 50 Jahre vorweg.
(English)
This paper deals with the German term „Saxonische Tektonik“ (Saxonian tectonics) and problems related to it. These are specific to the German geoscience literature and community – that is why this paper is written in German. The term was coined in the early 20th century and came to describe essentially all deformation that had taken place in central Europe and parts of western Europe from Triassic time to the present. It is today understood that this deformation comprises a protracted history of extension and graben evolution from Triassic to Early Cretaceous time, followed by one or several pulses of contraction and inversion in the Late Cretaceous to Paleogene. Both extensional and contractional structures are often strongly modified by salt movement. Renewed extension from Eocene time onward created the European rift system. Originally, the characteristic, inversion-related style of many Mesozoic “Saxonian” structures was called “Bruchfaltentektonik” (“Fracture-fold tectonics”). Both terms linger to the present day in the German literature, despite no longer being adequate to our knowledge of changing tectonic regimes, their sequence over time, and the control exerted on specific structural styles by stratigraphy, lithology and the thermal and tectonic history. I therefore propose to abandon the terms “Saxonische Tektonik” and “Bruchfaltentektonik” for good now. Nevertheless, many of the articles in which the original concepts were developed are still highly interesting to read. In particular those from the 30s dealing with inversion tectonics – if still under a different name – anticipated later developments by some 50 years.
An analysis of fault-slip data from the Lusatian Fault Belt, limiting the Lusatian Block of the Bohemian Massif in the SW, yielded parameters of eight successive paleostress patterns, Late Cretaceous to Plio-Pleistocene in age. These patterns were linked with specific stages in fault kinematics and fault-belt deformation. They include (1) α1, NE- to NNE-directed compression in reverse fault regime (σ3 vertical) associated with major thrusting and drag zone formation in the latest Cretaceous, preceded by pre-drag origin of deformation bands α0; (2) αβ1–2, WNW-directed extension associated with emplacement of polzenite-group volcanics (≈80–61 Ma) and influx of hydrothermal fluids, overlapping in time with α1; (3) α2, N-directed compression in reverse fault regime, probably Paleocene in age, associated with thrusting and intensive shear faulting in adjacent parts of blocks; (4) αβ3, Early Oligocene W- to WNW-directed extension in a regime of strike-slip faulting (σ2 vertical), probably connected with an emplacement of phonolitic magmas and influx of hydrothermal fluids; (5) α3, NNW-directed compression associated with activation of transverse/oblique faults of the fault belt, close in age to αβ3 with unclear mutual superposition; (6) β, Late Oligocene–Early Miocene multi-stage N- to NE-directed extension in normal fault regime, specific to the Bohemian Massif, responsible for downfaulting of the hangingwall block; (7) γ, Mid to Late Miocene NE-directed compression in a reverse fault regime associated with thrusting; (8) δ, Pliocene (to Pleistocene?) NW- to NNW-directed compression in a strike-slip regime, associated with transverse faulting in the fault belt. The identified paleostress patterns show a good correlation with the hitherto identified paleostress fields transmitted to the Alpine foreland and refine the temporal sequence of paleostress states, especially in the post-Lower Miocene period.
Die NW-SE streichende Zone von Finne-Gera-Jachymov (Joachimsthal) ist seit dem Ausgang der variscischen Tektogenese nachweisbar.Indikationen für ein höheres Alter und deutliche Tiefenreichweite bis in die Mittelkruste ergeben sich aus der Tiefenseismik. Die jüngere Aktivität ist im NW-Abschnitt als Hermundurische Scholle erwiesen, die sich nach Südosten variscischen Strukturen überlagert. Das hat dort zum deutlichen Anstieg der Strainwerte geführt, die aus Störungsdaten abgeleitet worden sind. Rezent beeinflußt die Zone den Verlauf der maximalen horizontalen Hauptspannungsrichtung.
Triassic facies development in Central Europe is characterized by two different palaeogeographic settings: (1) the NW Tethys shelf area (Tethyan or Alpine realm) and (2) the northern, peripheral, semi-closed Germanic Basin (Germanic realm). The sedimentary successions of both realms reflect the long-term transgressive evolution following a global sea-level lowstand at the end of the Permian, and a recovery of marine and terrestrial ecosystems after the most severe mass extinction in Earth's history. Deposits of the Alpine realm document a marine development associated with the westward opening of the Tethys Ocean. In contrast, the Germanic Basin was lacking open marine conditions for most of the Triassic period. Marine incursions were controlled by connecting seaways between the Germanic Basin and the NW Tethys shelf. Major flooding occurred in the Pelsonian and at the time around the Fassanian-Longobardian boundary. These flooding phases affected both domains and are clearly documented in the sedimentary record by the presence of open-marine faunal elements. Within the Alpine realm, an increasing differentiation of depositional environments occurred from Ladinian times onwards. This resulted in the development of reef-dominated platforms, intrashelf and open-marine basins. In the Germanic realm, the marine evolution of the basin terminated in the early Carnian. A subsequent major flooding phase commenced during mid-Rhaetian times and gave rise to the transgressive systems of the succeeding Lower Jurassic stage. Facies diachroneity is a common feature in the Germanic Basin and is a result of the Tethyan ingressions. Tectonic movements are documented in both realms during the Triassic. They are represented by major unconformities and the deposition of seismites. Biostratigraphic correlation of Alpine and Germanic deposits is most successful using palynology, which is applicable in both continental and marine environments. Recent magnetostratigraphic data provide a good basis for stratigraphie refinement. Depositional sequences have been described from Alpine and Germanic sedimentary successions but these require further refinement, in particular with respect to high-resolution sequence stratigraphy and cyclostratigraphy in the Milankovitch frequency band. A. Wetzel (Basel) is thanked for helpful suggestions and improvements to the section on Switzerland. We thank R. Hoffmann and K. Hlawatsch (Halle) for drafting many of the figures, and T. Bechstädt (Heidelberg) for reviewing this chapter. We are very grateful to an anonymous reviewer who did a very thorough review of the manuscript and made many comments and suggestions that substantially contributed to improving this chapter.
The Rychlebské hory Mountain region in the Sudetes (NE Bohemian
Massif) provides a natural laboratory for studies of postorogenic
landscape evolution. This work reveals both the exhumation history of
the region and the paleoactivity along the Sudetic Marginal Fault (SMF)
using zircon (U-Th)/He (ZHe), apatite fission track (AFT), and apatite
(U-Th)/He (AHe) dating of crystalline basement and postorogenic
sedimentary samples. Most significantly, and in direct contradiction of
traditional paleogeographic reconstructions, this work has found
evidence of a large Cretaceous sea and regional burial (to >6.5 km)
of the Carboniferous-Permian basement in the Late Cretaceous
(˜95-80 Ma). During the burial by sediments of the Bohemian
Cretaceous Basin System, the SMF acted as a normal fault as documented
by offset ZHe ages across the fault. At 85-70 Ma, the basin was
inverted, Cretaceous strata eroded, and basement blocks were exhumed to
the near surface at a rate of ˜300 m/Ma as evidenced by Late
Cretaceous-Paleocene AFT ages and thermal modeling results. There is no
appreciable difference in AFT and AHe ages across the fault, suggesting
that the SMF acted as a reverse fault during exhumation. In the late
Eocene-Oligocene, the basement was locally heated to <70°C by
magmatic activity related to opening of the Eger rift system. Neogene or
younger thermal activity was not recorded in the thermochronological
data, confirming that late Cenozoic uplift and erosion of the basement
blocks was limited to less than ˜1.5 km in the study area.
In the Subhercynian Cretaceous Basin, six Upper Cretaceous angular unconformities can be observed. The first unconformity, at the base of the Cenomanian transgressive deposits, is not related to the development of the basin. While the second (Lower to Middle Coniacian) unconformity is almost limited to the northern basin margin, four unconformities are developed at the Harznordrand Thrust and span the short period from the Middle Santornian to the late Early Campanian (about 3 Ma). The intra-Coniacian unconformity at the northern basin margin proves tilting of the basin floor to the south-east and is possibly related to the development of the thrust too. The Santonian to Campanian unconformities at the Harznordrand Thrust reflect the formation of a continuously growing fault-propagation fold. Deposition above unconformities occurred when the rate of eustatic sea-level rise exceeded thrusting rate. Transgressions occurred in the earliest Middle Santonian, in the Late Santonian (intra-Marsupites Zone), in the earliest Campanian (granulataquadrata Zone) and in the late Early Campanian (Offaster pilula Zone). The ages of unconformities correlate well with the transgressive pulses proved in Western and Middle Europe and are not related to discrete deformational events.
Extract
An extensive rift system developed within the northern foreland of the Variscan orogenic belt during Late Carboniferous-Early Permian times, post-dating the Devonian-Early Carboniferous accretion of various Neoproterozoic Gondwana-derived terranes on to the southern margin of Laurussia (Laurentia-Baltica; Fig. 1). Rifting was associated with widespread magmatism and with a fundamental change, at the Westphalian-Stephanian boundary, in the regional stress field affecting western and central Europe (Ziegler 1990; Ziegler & Cloetingh 2003). The change in regional stress patterns was coincident with the termination of orogenic activity in the Variscan fold belt, followed by major dextral translation between North Africa and Europe.
Rifting propagated across a collage of basement terranes with different ages and thermal histories. Whilst most of the Carboniferous-Permian rift basins of NW Europe developed on relatively thin lithosphere, the highly magmatic Oslo Graben in southern Norway initiated within the thick, stable and, presumably, strong (cold) lithosphere of the Fennoscandian craton. The rift basins in the North Sea, in contrast, developed in younger Caledonian age lithosphere, which was both thinner and warmer than the lithosphere of the craton to the east.
A regional hiatus, corresponding to the Early Stephanian, is evident in much of the Variscan foreland, with Stephanian and Early Permian red beds unconformably overlying truncated Westphalian series (e.g. McCann 1996) (Fig. 2). Regional uplift coincides with the onset of voluminous magmatism across the region, raising the possibility that uplift could have been related to the presence of a widespread thermal anomaly within the upper mantle (i.e. a mantle plume or, possibly, several plumes). In
In this study we demonstrate how a combined structural, sedimentological and palaeomagnetic approach provides a new perspective on the tectonic evolution of the Holy Cross Mountains. In the field, we performed a structural and sedimentological analysis of Palaeozoic rocks. Our analysis was complemented by a palaeomagnetic study and by the restoration of balanced cross sections in Palaeozoic and Mesozoic rocks. Different steps of deformation were restored for a c.350 Ma period. (1) The extensional tectonics of the Devonian basin was unravelled: the resulting normal fault system constituted the fundamental structural control for the later Variscan tectonic inversion and Alpine deformations. (2) The style of Variscan folding is characterized and quantified by way of a cross section across the Holy Cross Mountains. (3) The role of the reactivation of Variscan faults during the Permo-Triassic initiation of the Polish Basin was examined. (4) The localized Alpine compressive deformation was quantified and shown to contribute only to a minor degree to the present-day state of deformation in the Holy Cross Mountains. The Holy Cross Fault zone is the product of the interplay of changing transtensional and transpressional settings during the Variscan diastrophic cycle, with the final effect of the Variscan evolution being the flower-like structure of the Holy Cross Fault zone.
The World Stress Map Project compiles a global database of contemporary tectonic stress information of the Earth's crust. Early releases of the World Stress Map Project demonstrated the existence of first-order (plate-scale) stress fields controlled by plate boundary forces and second-order (regional) stress fields controlled by major intraplate stress sources such as mountain belts and zones of widespread glacial rebound. The 2005 release of the World Stress Map Project database provides, for some areas, high data density that enables us to investigate third-order (local) stress field variations, and the forces controlling them such as active faults, local inclusions, detachment horizons, and density contrasts. These forces act as major controls on the stress field orientations when the magnitudes of the horizontal stresses are close to isotropic. We present and discuss examples for Venezuela, Australia, Romania, Brunei, western Europe, and southern Italy where a substantial increase of data records demonstrates some of the additional factors controlling regional and local stress patterns.
The results of 40 years of reflection seismic prospecting in northeastern Germany are summarized in a series of depth and thickness contour maps. Five depth and four thickness maps show the structural situation within the Permian to Tertiary strata. The main features of the structural development are:
regional subsidence up to Middle Triassic times;
local halokinetic movements that began in Middle Triassic times and continued with changing intensity until Cenozoic times;
large-scale movement of Zechstein salt into diapirs that occurred within the central areas of the most intensive salt tectonics.
This paper deals with results of an investigation of the paleo stress field evolution in the overburden of the Werra potash deposit and adjoining areas. By means of microtectonical methods we investigated the fault activities and deduced a sequence of correlated stress fields during the Mesozoic and Cenozoic up to nearly present time. The investigations allowed to describe 2 pre-basaltic, 2 syn-basaltic and 2 post-basaltic stress field patterns in the Werra region. Normal faulting is widespread and dominant, interrupted by three compressional impulses in the Late Cretaceous, Miocene and the near present time. The underlying ductile salt beds of Zechstein cause the high mobility of the overburden reacting during the tensional phases of stress field evolution in bookshelf or domino style. -from Authors
Describes the Middle Clay Keuper in the Thuringian basin as the series between upper boundary of the horizon D and the Dietendorf limestone. An important element is the main clay carbonaceous sandstone which by a dolomite horizon in the middle part is subdivided into a lower and an upper component. In regional comparison, this dolomite is equivalent to the Alberti. It is hinted that further microstratigraphic correlations of the most important horizons can be made. In the eastern part of the Thuringian basin, the thickness of the Middle Clay Keuper varies between 10,5 and 25,85 m. By mapping of the sand-clay ratio a meridional sandstone string could be detected from the east of the Schillingstedt syncline via Soemmerda to Neudientendorf. This sandstone string is a part of a palaeo-flow systems with drainage to south-west; the position and the course of this flow system is determined by hidden subsurface structures and the contour of the Bohemian-Vindelician rise. -after English summary
The Rhenish Massif is studied with ari enormous number of occurrences of volcanic rocks, with ages reaching from the Middle Cretaceous to the youngest Pleistocene. K-Ar and 14C dating are the main tools for establishing their distribution in time. The oldest post-Permian volcanic rock occurs in the Wittlich basin and has an age of more than 100 m.y. The main volcanicity of the Rhenish Massif starts in the Hocheifel area during the Upper Eocene, where it continues until the Middle Miocene. Volcanic activity in the Siebengebirge, Westerwald and Rhon unfolded during the Upper Oligocene and Lower Miocene. During the Middle Miocene, the Vogelsberg and the Northern Hessian volcanic province were active.
Quaternary volcanic activity is essentially confined to the West and East Eifel. K-Ar dates and paleomagnetic polarity narrow its time of activity down to the interval between 0.7 m.y. and about 10,000 a. The well-established sequence of the Rhine terraces can be dated in the younger section by its relation to the volcanic rocks, while for the older part one has to rely exclusively on paleomagnetic observations.
By now the distribution of the Tertiary volcanism in time and space is fairly well established, but the information on the Quaternary volcanism is still so scarce that further work is needed.
Where available stratigraphic information cannot constrain the order of succession of multiple tectonic events in a region, this order must be reconstituted by combining numerous relative chronology data collected in various sites for various couples of events. Contradictory data are present due to various factors such as observation errors and simplified assumptions adopted in order to identify events according to their mechanisms. The use of a square matrix for chronological classification allows one not only to solve the problem, but also to compare the best solutions, to determine how far the problem is constrained and to estimate the amount of contradictions. A common example (7 events) is presented. There is an abridged English version. -English summary
The present-day Zagros mountain belt of SW Iran corresponds to the former Arabian passive continental margin of the southern Neo-Tethyan basin, which existed since a Permian-Triassic rifting episode and underwent later collisional deformation in mid-to late Cenozoic time. In West Zagros, the Kermanshah Radiolarian Trough, separated from the Neo-Tethyan basin by the narrow continental platform of the Bisotun Limestone, resulted from the Triassic-Jurassic rifting of the passive margin. Brittle tectonic analyses of syndepositional normal fault slip data have been undertaken to study the extensional history of the passive margin in terms of palaeostress reconstruction. Dominant east-west trends of the inherited rift-related normal faults in West Zagros indicate an approximately north-south trend of extension that prevailed during the entire Mesozoic syn- to post-rift evolution of the radiolarian trough. This extension characterizes a stretched continental margin similar to the present-day passive margin of the British Isles. Considering the structural pattern of the inherited basement faults, as revealed by the present-day earthquake focal mechanisms, an oblique crustal stretching model is proposed for the rifting process.
The Thuringian Basin is the oldest hydrocarbon province in Eastern Germany wet gas and oil accumulations have been discovered since 1930. After a long inactive period of about twenty years, exploration for hydrocarbons now continues with improved methods. Carbonates and evaporites of the Permian Zechstein comprise the source, reservoir and seal for the main gas and oil play in the area Today, they are buried less than 1000 m deep over the major part of the basin. Modelling of the burial history of the basin indicates that up to 1500 m of Mesozoic strata were eroded during a Late Cretaceous inversion event. Peak hydrocarbon generation occurred just prior to this inversion, implying that hydrocarbons have been effectively trapped in the reservoirs since that time. In addition, dry gas and nitrogen appear to have been sourced from pre-Zechstein intervals, which, with respect to nitrogen, poses a severe exploration risk.
We present new results for the microseismic activity in the northern Upper Rhine Graben by analyzing seismogram recordings from two temporary networks of up to 13 broad-band stations in combination with data from permanent stations. Previous studies have mainly focused on the southern and intermediate sections of the Upper Rhine Graben, where the station coverage by regional networks is more dense. Between October 2010 and September 2013 we recorded 56 earthquakes that occurred within the immediate vicinity of the northern Upper Rhine Graben with local magnitudes ranging from 0.5 to 3.2. The majority of the hypocenters are located beneath the eastern graben shoulder and in the graben itself, while activity observed along the western graben shoulder is lower. A further active region is located along the southern rim of the Taunus Mountains to the northwest of the study area. The seismicity extends to a depth of 25 km; the hypocentral depth distribution exhibits a pronounced peak of seismic energy release in the depth range between 12-18 km. Fault plane solutions for a total of 58 earthquakes (including data from previous recordings) were derived from P-polarities and SV/P amplitude ratios. This new data set more than quadruples the number of available data for regional stress field analysis. The majority of the focal mechanisms show predominantly strike-slip movements; only a few events are of reverse or normal-faulting type. T-axis trends are oriented NE-SW. The calculated focal mechanisms presented in this study confirm that the area is in transtension, however, in contrast to previous studies, a stronger strike-slip component is identified. We also derived the azimuths of the principle stress axes by inverting the fault plane solutions and calculated the direction of the maximum horizontal stress, which is mainly oriented N135°E.
The block-faulted southwestern margin of the Bohemian Massif is superimposed on a Permo-Carboniferous graben, major faults of which became repeatedly reactivated during the Mesozoic and Cenozoic. Inversion of sedimentary basins associated with this fault system occurred during the Early Cretaceous and again during the latest Cretaceous-Early Cenozoic.
We investigate the source of non-purely gravitational horizontal stresses in the Paris basin, a nowadays tectonically quiet intracatonic basin, in its eastern border of which outstandingly dense stress measurements are available. Based on a synthesis of published data, the stress state in the basin is first shown to be very close to the one that may be extrapolated for the underlying basement, in terms of principal stress orientations and horizontal to vertical stress ratios. This is in favour of a mechanical coupling between the basement and its sedimentary cover, which may seem contradictory to the presence of several weak rock layers in the basin fill, e.g. an argillite layer that was shown to bear low deviatoric stresses, and salt layers that are implicated in a major décollement elsewhere. To unravel this apparent contradiction, a 3D-numerical modelling is performed, following a rigorous inverse problem approach, to determine the long-term elastic properties of both the basement and the basin rocks. The objective is to find the set of elastic constants that provides the best fit between the calculated stress state in the basin and the in situ data, by assuming that the stress state in the basement is known. This methodology provides a realistic set of mechanical parameters, in agreement with previous studies, which leads to the conclusion that the horizontal stresses in the basin constitute its mechanical response to the stresses that developed in the underlying basement during and since the last tectonic event (Alpine phase). The fact that horizontal stresses could be transmitted across the weak horizons, contrary to what may be expected at first glance, is explained both by the geometry of the basin and the fact that, over the long term, the stiffnesses of the various sedimentary rocks are only slightly different from each other.
The Zagros fold-and-thrust belt of SW Iran represents deformation of the former Arabian passive margin since Permian–Triassic opening of the Neo-Tethys ocean. The Zagros belt is characterized by a present-day structural salient-recess setting inherited from past marginal embayment-promontory geometry, which was involved in discontinuous ophiolite obduction and diachronous continental collision. We examine outcrop-scale Mesozoic extensional brittle tectonics, preserved as syn-depositional normal faults within the folded strata, in terms of stress tensor inversion. The result is then integrated with belt-scale isopach, seismic and topographical data to delineate the geometry of a major irregularity along the passive margin originating from oblique oceanic opening. The implication of this configuration within the tectonic framework of oceanic closure is discussed.
The Osning Thrust is a 100 km-scale NW-SE fault separating the Lower
Saxony Basin to the NE from the Münsterland Basin to the SE. The
fault has accommodated a polyphase deformation that started at least
when it acted as one of the normal border faults of the Jurassic Lower
Saxony Basin. Tectonic inversion of the basin in Late Cretaceous-Early
Paleocene times led to the development of the SE-vergent Osning Thrust
and to folding of rocks. A paleostress analysis was carried out in order
to decipher the polyphase kinematics of the Osning Thrust. The fault
slip data were collected in the folded Albian to Turonian stratigraphic
units of the Münsterland basin, in the SE vicinity of a 20 km-long
steep segment of the Osning Thrust. Fault slip data in sufficient amount
to perform paleostress inversion were collected in 10 sites among 23
visited outcrops. Abundant minor faults trend sub-parallel to the NW-SE
steep segment of the Osning Thrust but, surprisingly, they are dextral
(and not reverse) in type. Another major set of E-W striking minor
faults is remarkable. It corresponds to conjugate systems of either
reverse or normal faults and to oblique- to strike-slip faults in a less
extent. The paleostress tensors reveal a ca. N-S compression recorded in
5 locations under which the NW-SE steep faults were dextral and the E-W
striking S- and N- dipping faults were reverse. Six stress tensors fit
with a ca. N-S extension. They are calculated from E-W striking S- and
N- dipping normal to oblique normal faults. The same N-S trend of
minimum stress axis is also recorded with NNE-SSW dextral and E-W
sinistral faults. We propose that along the studied segment of the
Osning Thrust a N-S compressional stress field led to the inversion of
the Lower Saxony Basin and that slip along the Osning Thrust was oblique
reverse. At two locations, the N-S compressive stress states affected
the rock prior to tilting of the beds (herein, due to folding) and at
one site, the normal faults of the N-S extension clearly cut across
reverse faults of the N-S compression. These two observations allow to
propose a chronology between the reconstructed stress fields. While the
N-S compression is presumably linked to the Late Cretaceous-Early
Palaeocene inversion of the Lower Saxony Basin, the successive E-W
extension is not constrained in age. However, it is known that tensional
stresses have largely affected the west European platform in Oligocene
times and this N-S extension revealed by the present study might be
related to this tectonic event.
Der Begriff „Saxonische Tektonik“ wurde im frühen 20. Jahrhundert geprägt und bezeichnete alle Deformationsereignisse, die sich in Mitteleuropa und Teilen von Westeuropa von der Trias bis heute abgespielt haben. Es ist heute weitgehend anerkannt, dass diese Deformation einen langen Zeitraum von Extension und Grabenbildung von der Trias bis zur frühen Kreide umfasst, gefolgt von einem oder mehreren Pulsen der Einengung und Inversion in später Kreide und Paläogen. Dehnungs- und Einengungsstrukturen sind oft stark durch Salzbewegungen verändert. Erneute Dehnung schuf seit dem Eozän das Europäische Riftsystem. Der durch Inversion geprägte Baustil, der viele saxonische Strukturen charakterisiert, wurde ursprünglich „Bruchfaltentektonik“ genannt. Beide Bezeichnungen sind noch nicht völlig verschwunden. Dem heutigen Kenntnisstand über die wechselnden tektonischen Regimes, ihren zeitlichen Ablauf und die Kontrolle bestimmter Baustile durch Stratigraphie, Lithologie, thermische und tektonische Geschichte werden sie nicht mehr gerecht. Ich rate deshalb dazu, die Ausdrücke „Saxonische Tektonik“ und „Bruchfaltentektonik“ nicht mehr zu verwenden. Viele Arbeiten, in denen die Konzepte entwickelt wurden, sind aber auch heute noch äußerst interessant zu lesen. Vor allem die aus den 30er Jahren zur – damals noch anders genannten – Inversionstektonik nehmen manche späteren Entwicklungen um 50 Jahre vorweg.
The Finne fault zone, located in central Germany to the southwest of the Harz mountains, was studied by means of detailed map analysis, investigations of fault displacement and balanced cross-sections for the most strongly deformed area in the center of the fault zone (ca. 50 % of total fault zone length). The system of the Finne fault zone shows a nearly 100-km-long straight flexure that symbolizes the morphological and geological northeastern border of the Thuringian basin. In the central part, which should be surveyed here, the fault zone corresponds to a distinctive narrow band of highly deformed Triassic sedimentary rocks. The northwestern and especially the southeastern parts of the research area are developed as several parallel branch faults. In the southeastern elongation of the fault zone, which is not part of our survey, the sedimentary cover is missing. Here, it is possible to gain insight to the fact that the basement is also involved to the kinematics of the fault zone. Based on our results, we propose a subdivision of the fault zone into four sectors. From the northwest to the southeast, we interpret the structure of these sectors to reflect (1) a compressional flexure, (2) an overthrust graben, and (3) a partially inverted and folded half graben. In the extreme southeast (4), the fault zone is characterized by an anticline with some strike-slip movement parallel to the fold axis. This segmentation is caused by a thrust fault system whose strike direction deviates slightly from that of the earlier formed graben system. The structural configuration can be explained by a two-phase deformation, in which the contractional strain exceeded the preceding extensional deformation. In the investigated area, the horizontal shortening attains a maximum of ca. 1 km. The present study confirms many earlier hypotheses, presents new results on the deformation history of the fault zone, and attempts to evaluate the deformation in a regional geological context. The results of earlier studies were refined and revised using modern methods, and a unified structural and kinematic model of the Finne fault zone was created.
Apatite fission-track (AFT) dating applied to uplifted Variscan basement blocks of the Bavarian Forest is employed to unravel the low-temperature history of this segment of the Bohemian Massif. Twenty samples were dated and confined track lengths of four samples were measured. Most samples define Cretaceous APT ages between 110 and 82 Ma (Albian to Campanian) and three samples give older ~148–140 Ma (Jurassic–Cretaceous boundary) ages. No discernible regional age variations exist between the areas north-east and south-west of the Pfahl shear zone, but >500 m post-Jurassic and post-Cretaceous vertical offsets along this and other faults can be inferred from elevation profile analyses. The AFT ages clearly postdate the Variscan exhumation history of the Bavarian Forest. Thermal modeling reveals that the ages are best explained by a slight reheating of the basement rocks to temperatures within the apatite partial annealing zone during the middle and late Jurassic and/or by late Cretaceous marine transgression causing burial heating, which affected marginal low-lying areas of the Bohemian Massif and the Bavarian Forest. Late Jurassic period was followed by enhanced cooling through the 120–60 °C temperature interval during the subsequent exhumation phase for which denudation rates of ~100 m myr−1 were calculated. On a regional scale, Jurassic–Cretaceous AFT ages are ubiquitous in marginal structural blocks of the Bohemian Massif and seem to reflect the exhumation of these zones more distinctly compared to central parts.
Whereas most of the stress inversion methods using fault slip data only minimize the angle between the measured striation and a computed shear stress to find the best fitting reduced stress tensor, Angelier (1990) proposed an alternative method named INVD that also takes into account the relative shear stress magnitude which allows the fault to move. Using artificial datasets and particular fault geometries we compare this method with one of the classical methods based on the minimization of the shear-slip angles (R4DT; Angelier, 1984) and we show that in most cases the new method has improved the quality of the results. Furthermore, as proposed by Angelier, we point out that the quality of the stress inversion primarily depends on the quality of the field data. We give advice and warn about some pitfalls concerning determination of sense of slip on fault planes, recognition of successive faulting events and their chronology, drawer (or wedge) faults, stress permutations, faults in vertical bedding. We also argue that, in case of tilted sequences, fault diagrams should not be presented without bedding planes. But we show that stress inversions, when realized with caution and with the correct method, can have much more applications than reconstructing stress fields, like for determining: the paleo-horizontal, the nature and the sense of motion of large faults, the chronology and age of large structures.
The present-day Zagros fold-and-thrust belt of SW-Iran corresponds to the former Arabian passive continental margin of the southern Neo-Tethyan basin since the Permian–Triassic rifting, undergoing later collisional deformation in mid–late Cenozoic times. In this paper an overview of brittle tectonics and palaeostress reconstructions of the Zagros fold-and-thrust belt is presented, based on direct stress tensor inversion of fault slip data. The results indicate that, during the Neo-Tethyan oceanic opening, an extensional tectonic regime affectedthe sedimentary cover in Triassic–Jurassic times with an approximately N–S trend of the σ3 axis, oblique to the margin, which was followed by some local changes to a NE–SW trend during Jurassic–Cretaceous times. The stress state significantly changed to thrust setting, with a NE–SW trend of the σ1 axis, and a compressional tectonic regime prevailed during the continental collision and folding of the sedimentary cover in Oligocene–Miocene times. This compression was then followed by a strike-slip stress state with an approximately N–S trend of the σ1 axis, oblique to the belt, during inversion of the inherited extensional basement structures in Pliocene–Recent times. The brittle tectonic reconstructions, therefore, highlighted major changes of the stress state in conjunction with transitions between thin- and thick-skinned structures during different extensional and compressional stages of continental deformation within the oblique divergent and convergent settings, respectively.
The evolution of the Cenozoic Upper Rhine Grabenwas controlled by a repeatedly changing stress field and the reactivationof a complex set of crustal discontinuities that had come into evidence duringPermo-Carboniferous times. A comparison of the spatial and temporal thicknessdistribution of synrift deposits with preexisting fault patterns permits toinfer a sequence of distinct basin subsidence phases that can be related tochanges in the ambient stress field. Reactivation of a system of late Palaeozoicfault systems, outlining troughs and highs, controlled the nucleation of initiallyseparated middle and late Eocene basins, the depocenters of which coincidedwith a preexisting WSW-ENE trend. During Oligocene crustal extension the individualbasins coalesced, resulting in the development of the SSW-NNE striking UpperRhine Graben. During the late Oligocene (Chattian) change in stress field,the Upper Rhine Graben was probably reactivated as a dextral strike-slip systemwith the central graben segment forming a releasing bend. During the earlyMiocene (Aquitanian), a major reorientation of the regional stress field isheld responsible for the main subsidence phase of the northern parts of theUpper Rhine Graben. This is reflected by a counterclockwise rotation and northeastwardshift of the depocenter axis and later by the middle Miocene uplift and erosionof the southern parts of the Upper Rhine Graben. During the Plio-Quaternary,the Upper Rhine Graben was reactivated as a sinistral strike-slip system withthe central graben segment forming a restraining bend.
The present Zagros mountain belt of SW Iran is known to be the former NE Arabian passive continental margin of the southern Neo-Tethyan basin, which originated by Permian- Triassic rifting, and has a late Cenozoic collisional imbricate structure. We carried out brittle tectonic analyses of syndepositional normal fault slip data in the High Zagros Belt of the Fars Province to reconstruct the extensional deformation of the passive margin during the Mesozoic era in terms of stress tensor inversion. This reconstruction revealed two main directions of extension, developing from a north-south margin-oblique trend to a NE-SW margin-perpendicular one. Considering the basement structures and the existence of the basal Infracambrian salt detachment, we infer that a transtensional extension could have initiated two major periods of crustal stretching: a Permian-Triassic thick-skinned phase with the basement faults developing in an oblique rifting, and a Mesozoic thin-skinned phase with the sedimentary cover being affected by successive extensional structures and block tilting. This extensional tectonic history probably continued during the early Tertiary period, prior to the continental collision. Fault slip geometries and structural patterns of both the Mesozoic extension and the late Cenozoic compression indicate inversion of the inherited structures in the Zagros collision during the subsequent thin- and thick-skinned stages of crustal shortening.
The W-Zagros of Iran is characterized by a deformation partitioning pattern with a right-lateral strike-slip motion along the Main Recent Fault and a shortening component across the Zagros Simple Fold Belt under the late Cenozoic N-S oblique collision between the Arabian and Iranian continental plates. In this study, we examined the brittle structures that developed during the mountain building process in the High Zagros Belt of Kermanshah Province, which is structurally located between the two partitioned components of deformation, to decipher the history of polyphase deformation and variations in stress fields within the sedimentary cover since the onset of collision. The earthquake focal mechanisms of W-Zagros were analysed to evaluate the recent stress fields within the basement. Analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors. Brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of the corresponding stress tensor, with reference to folding. Our stress reconstruction indicates a major change in stress state from a Miocene-Pliocene syn-folding compressional regime to a Pliocene-Recent post-folding strike-slip system, with a significant anticlockwise reorientation of the horizontal sigma1 stress axis from NE-SW to N-S. The results of the recent stress states indicate that the stress trends are similar throughout the basement and sedimentary cover. The differences between stress and strain axes suggest different possible degrees in partitioning of seismic and aseismic deformation, as revealed by earthquake focal mechanisms in the basement and geodetic surveys at the surface of the sedimentary cover. The integrated palaeostress results on the regional tectonic framework suggest that the late Cenozoic brittle tectonic evolution of the W-Zagros was achieved through the transition from thin- to thick-skinned deformation under the oblique plate convergence, highlighting a southwestward shift of the deformation partitioning during the final Pliocene collisional reorganization.
An analysis of Cenozoic brittle deformation in the European platform has been carried out between the Bohemian Massif to the east and the Western Mediterranean Sea to the west. A succession of four main paleostress fields has been defined: (1) N-;S compression of late Eocene age. This event induced the formation of the “German-Czech triangle,” bounded on the east by the NW-SE dextral strike-slip faults of Pfahl and Franconia and on the west by the NNE-SSW sinistral strike-slip faults along the axis of the future west European Rift, (2) E-W Oligocene extension that opened the west European Rift. (3) NE-SW compression, early Miocene in age, that reactivated the Pfahl fault line (as a reverse fault) and the main faults of the Rhinegraben (as dextral strike-slip faults). (4) Finally, since the end of the Miocene, a fan-shaped distribution of directions of compression has developed at the periphery of the Alpine arc. However, farther from the Alpine chain, a more consistent direction of compression has dominated (first NW-SE, then NNW-SSE). A comparison with plate tectonic data demonstrates that this succession of tectonic events is compatible with the reconstruction of relative movements between Africa and Eurasia during the Cenozoic collision. However, some local stress patterns, close to the Alps, are clearly related to the local evolution of the Alpine arc.