Abstract Fold-and-thrust belts occur worldwide, have formed in all eras of geological time, and are widely recognized as the most common mode in which the crust accommodates shortening. Much current research on the structure of fold-and-thrust belts is focused on structural studies of regions or individual structures and on the geometry and evolution of these regions employing kinematic, mechanical and experimental modelling. In keeping with the main trends of current research, this title is devoted to the kinematic evolution and structural styles of a number of fold-and-thrust belts formed from Palaeozoic to Recent times. The papers included in this book cover a broad range of different topics, from modelling approaches to predict internal deformation of single structures, 3D reconstructions to decipher the structural evolution of groups of structures, palaeomagnetic studies of portions of fold-and-thrust belts, geometrical and kinematical aspects of Coulomb thrust wedges and structural analyses of fold-and-thrust belts to unravel their sequence of deformations.

Abstract Fold-and-thrust (FAT) belts occur worldwide and have long been the focus of research of structural geologists who have devised a variety of techniques to image, characterize and model their main structural features. This introductory chapter reviews the principal geological features of FAT belts formed in different settings, emphasizing aspects related to their kinematic evolution and structural styles. Despite great advances, challenges remain, particularly in the understanding of the spatial and temporal evolution (4D) of FAT belts and their controlling factors. These research efforts are being assisted by the growing availability to researchers of relatively new tools to collect field data, high quality 3D seismic data, and computer and laboratory modelling tools. This volume includes technical papers presented in the conference ‘International Meeting of Young Researchers in Structural Geology and Tectonics (YORSGET-08)’ held in Oviedo (Spain), together with other papers on the same theme. These papers deal with FAT belts in different parts of the world and cover a broad range of different aspects, from detailed structural analysis of single structures to regional issues, and from studies based on classical field structural geology to modelling.

Abstract Deformation predictive methods are useful for structural analysis from the scientific and industry point of view. We apply a strain simulation technique based on the inclusion of graphical strain markers in a cross;-section, and subsequent cross-section restoration and numerical processing of strain markers, to the seismic-scale Maiella Mountain anticline (Central Apennines, Italy) considered a carbonate reservoir analogue for Apennines oil fields. The procedure followed involves field mapping and structural data collection, construction of cross-sections, sequential cross-section restoration, and application of the strain simulation technique. The cross-sections presented were constructed adopting one of the various structural interpretations proposed for this structure by different authors. According to this interpretation the Maiella Mountain structure resulted from Messinian–Early Pliocene extension and subsequent Late Pliocene shortening. According to our structural model the Maiella structure is a break-thrust fold and the comparison between the present-day and the restored cross-sections yields 1.3–4.6% of extension associated with two main normal faults and 21.5–22.1% and 2.5–3.4% of shortening due to a major thrust and folding respectively. The simulation of deformation distribution shows high deformation intensity in both limbs and low deformation in the anticline crest and part of the thrust footwall.

Abstract A 2D discrete-element modelling technique is used to explore the effects of complex mechanical stratigraphy and syn-kinematic sedimentation in the development of the Pico del Águila anticline (External Sierras, Southern Pyrenees). The stratigraphy (Middle Triassic–Oligocene in age) involved in this structure is characterized by a gross interlayering of competent and incompetent units, which leads to a striking variation in outcrop-scale deformation of the units observed in the field. The numerical model attempts to reproduce the stratigraphic variation seen in the field by using a mechanical stratigraphy that contains a complex interlayering of competent/incompetent units. Two experiments are presented. Model 1 tests the response of this complex mechanical stratigraphy to shortening under conditions that lead to the formation of a detachment fold. This experiment shows that folding mechanisms vary abruptly depending on the mechanical properties of the materials involved: the incompetent units are strongly internally deformed, accommodating much layer-parallel shearing; the competent units deform by rigid-body translation/rotation, localized faulting and minor internal shearing. Model 2 tests the effect of syn-kinematic sedimentation under identical boundary conditions: these sediments stabilize the fold against gravitational instabilities and cause a concentration of deformation in the core of the structure, leading to a tighter, narrower fold.

Abstract The Western Irish Namurian Basin (WINB) developed into a fold-and-thrust belt at the front of the northward-propagating Variscan orogenic wedge. Part of this basin is well exposed along the coast of County Clare, Ireland. From a detailed study that used an integrated GPS mapping approach, we produced a c . 50 km long, balanced cross-section, parallel to the tectonic transport vector. We sequentially decompacted and retro-deformed the Namurian strata in 7 stages to evaluate the palinspastic situation of the basin and the amount of shortening. By using passive markers in the model and a highly-detailed timescale, we were able to determine that shortening of the WINB, from the onset of Central Clare Group sedimentation was 7.44% (or 4.07 km) of which shortening due to folding accounts for c . 2.64% ( c . 1.37 km), and therefore c . 4.80% ( c . 2.69 km) was solely because of thrusting. The rate of horizontal shortening ranges from 1–34 mm a −1 ; this is within typical orogenic values.

Abstract A kinematical model for the Utrillas thrust is proposed, including reconstruction of the incremental slip history, progressive internal deformation and tectono-sedimentary relationships at the Montalbán (foreland) and Aliaga (piggy-back) Tertiary basins. A 3D geometrical model of the main thrust surface, defined by ramps oriented NE–SW, east–west, NW–SE and north–south, is reconstructed from cross-sections. Besides, the thrust sheet is internally deformed by two main, frequently superposed fold sets, trending NW–SE to NNW–SSE (earlier) and east–west (later), respectively. A total ‘arrow’ (finite horizontal displacement) of about 5.9 km towards N032°E is estimated by means of schematic, plan-view retrodeformation of the distinctly oriented ramps making its front. Orientation and cross-cut relationships of mesoscopic kinematical indicators at the thrust front provide a scenario of successive transport directions towards the ENE, NNE and north, which is consistent with the progressive development of internal folding, as well as with the evolution of intraplate compressive stress fields through Tertiary times.

Abstract Anisotropy of magnetic susceptibility (AMS) combined with structural analysis are used in this work with the aim to characterize the tectonic evolution of the Triassic flysch within the eastern Tethyan Himalaya Thrust Belt in SE Tibet. The attitude of the magnetic foliation and lineation are concordant with the planar and linear structures of tectonic origin defined by the preferred orientation of the iron-bearing silicates. Two different tectonic domains can be defined: (a) the southern domain is controlled by the Eohimalayan tectonic foliation (S1) recorded in the magnetic foliation which trends east–west and dips to the north; (b) the northern domain is dominated by the Neohimalayan magnetic foliation with WNW–ESE strike and dips to the south opposite to the vergence of the main structures. A slightly prolate magnetic ellipsoid has been found in between the two domains recording the intersection of S1 and the subtle development of the S2 tectonic foliation. Hinterland propagation of the deformation lead to the Great Counter backthrust generation, pointed out by the SSW steeply plunging magnetic lineation. Furthermore different orientations of magnetic foliation may indicate an Early Miocene c. 20° clockwise vertical-axis rotation.

Abstract Time-calibrated balanced-cross sections of the eastern Fuegian Thrust–Fold Belt reveal many complex pro- and retro-vergent structures, rooted at the base of Cretaceous and within Paleocene rocks. These structures involve the unconformity-bounded syntectonic sequences of the Austral foreland basin, and accommodate a minimum shortening of c . 41.8 km. The complex kinematics of the thrust–fold belt are recorded by: (1) propagation of the basal décollement into the foreland, and forward-directed thrusting during the Ypresian; (2) out-of-sequence thrusting in the Lutetian; (3) subsidence and sedimentation from the Late Lutetian to the Oligocene; (4) backthrusting during the Oligocene; and (5) a renewed stage of forward-directed thrusting between the latest Oligocene and the Early Miocene, probably related to accretion below the sole fault in the hinterland. This thrust sequence is interpreted as the result of critical Coulomb wedge behaviour during the first stage of thrust–fold belt expansion, with accretion of new material that led to a taper decrease. The subsequent period of internal deformation corresponds to a subcritical stage, during which backthrusting accommodates significant shortening ( c . 15%). After growth and taper increase, the last period of forward thrusting at the wedge's front marks the inception of a new critical stage.

Abstract Despite the fact that most fold–thrust belts around the world share many features, successfully explained by the critical wedge model, the details of their geometric evolution and tectonic style development are poorly understood. In the classic section of the southern Canadian Rocky Mountains the dominant tectonic style consists of imbricate thrust sheets with relatively little internal deformation of the individual slices. In the Mexican fold–thrust Belt (Central Mexico), the age of deformation, the overall structural pattern and the total amount of shortening are similar, but the individual thrust sheets exhibit much more internal deformation as manifest by metre-scale buckle folds. One of the differences between these localities is the lateral variation of facies resulting in massive platform limestone separated by thinly-bedded basinal limestone in the Central Mexico section. Strain is concentrated toward the margins between platforms and basins. In Canada, thick platform carbonates form continuous resistant units across the Front Range. Possible reasons for the differences in tectonic style between the two sections include the dominant lithology, distribution of lithologies, taper angle of the tectonic wedges, amount of friction along the basal detachment and the degree of anisotropy of the basin facies rocks.

Abstract A new sequence of Variscan deformations is proposed for the Palaeozoic rocks of the Central Pyrenees. The non-metamorphic units include south-directed thrust systems and related folds with a poorly developed cleavage. In the metamorphic units north-verging, recumbent to inclined folds (D1), associated with a subhorizontal to south dipping cleavage, are refolded by south-verging, upright to inclined folds (D2), with a subvertical to north-dipping axial plane cleavage, and offset by south-directed thrusts approximately coeval with D2. The structural evolution of these units suggests a subdivision of the Variscan Central Pyrenees into two different regions consistent with the zones known for a long time in the core of the Ibero-Armorican or Asturian arc (northern part of the Iberian Variscan Massif). The structure of the Pyrenean non-metamorphic units has foreland affinities and is comparable to that of the Cantabrian Zone, whereas the deformation observed in the Pyrenean metamorphic units is characteristic of the hinterland and is consistent with the features of the West Asturian–Leonese Zone or Central–Iberian Zone. Since the Pyrenean non-metamorphic units are located southwards of the metamorphic ones and the Variscan thrusts are south-directed, we tentatively correlate the Variscan Pyrenees with the northern branch of the Ibero-Armorican or Asturian arc.

Abstract The Forcarei Synform is a kilometric fold developed in the hinterland of the NW Iberian Variscan belt. A detailed analysis of the synform, based on quartz fabrics and kinematic markers, shows pervasively deformed rocks that have been continuously deformed during the last two main Variscan deformation phases (D 2 and D 3 ). Variscan D 2 minor structures related to the synform were formed under general non-coaxial flow and have a sub-horizontal maximum finite stretching toward the SSE. Later a coaxial D 3 produced a sub-vertical crenulation cleavage, and type 2 and 3 refolded folds figures at the meso- and micro-scale. Consequently, the strike of the foliations (S 2 and S 3 ) become sub-parallel and lineation (L 2 and L 3 ) are sub-horizontal. The geometry of the synform and the related structures can be interpreted in the context of D 3 . However the dominantly sinistral shear sense indicators, observed in both limbs of the synform (in map view), seem to be most probably developed during D 2 . A model is proposed involving the progressive clockwise rotation of a sub-horizontal shear, with general top-to-the-south sense, during the simultaneous development of shear zone and foliation in agreement with the kinematic indicators.

Abstract In the South Portuguese Zone (Iberian Massif), thin-skinned tectonics linked to the collision with the Ossa-Morena Zone produced the inversion of previous extensional basins in Carboniferous times. Its central domain, namely the Iberian Pyrite Belt, underwent two deformation phases at mostly low-grade metamorphic conditions linked to a progressive deformation migrating upwards from a basal detachment and from north to south. The Puebla de Guzmán Antiform is one of the most outstanding cartographic structures in the Iberian Pyrite Belt, representing a imbricate fan thrust system developed during the second regional deformation phase. In the Puebla de Guzmán Antiform, the first deformation phase gave rise to a penetrative slaty cleavage (S 1 ), which is also recognized in the whole Iberian Pyrite Belt and constitutes the main foliation all over the region. Its genesis is possibly linked to the coetaneous development of thrusts at deeper crustal levels and SSW-vergent folds at all levels above these thrusts. First phase structures were deformed by large-scale imbricated thrust systems with lateral (NNE–SSW) and frontal (WNW–ESE) ramps, which constitute the most relevant regional cartographic structures. This second deformation phase generated thrusts, two set of folds with WNW–ESE and NNE–SSW-oriented axes, as well as two related axial plane crenulation cleavages. These relatively brittle to ductile-brittle second phase structures have been identified in many areas of the Iberian Pyrite Belt, and especially in the southern limb of the Puebla de Guzmán Antiform. The second phase thrusts reported from the Puebla de Guzmán Antiform have not been folded according to both the geological map of the area and the analysis of maximum shortening and stretching axes.

Abstract The presence of two different coeval pre-flysch carbonate facies juxtaposed in numerous profiles in the southern part of the Moravian Karst proves that the Variscan nappe tectonics affected the pre-flysch basement of the main Culmian flysch nappes. Two main thrust events were recognized: (1) a ‘thin-skinned’ event, during which two sedimentary facies were juxtaposed along bedding sub-parallel thrusts, and (2) a ‘thick-skinned’ event, which generated younger thrusts oblique to bedding, involved crystalline rocks of the Brno Massif, and resulted in refolding of the older thrusts.

Abstract The Pavlov Hills are formed by separated limestone blocks previously identified as klippen. A new flat-ramp-flat thrust model of the Pavlov Hills is formulated in this paper. The main tectonic detachment is located at the base of the limestone plate and other subsidiary detachments are located within the nodular limestone horizon and also at the base and top of the Upper Cretaceous deposits. The ramps are situated in the Klentnice Fm and Ernstbrunn Lst. The ramp angle was determined by structural evidence combined with interpretation of seismic profiles. Two parallel antiformal structures plunging to the NE are recognized within the study area. The antiformal fold axes are gently plunging to the NE so the anticlines are not ideal for 3-point hydrocarbon trap setting. These anticlines were subsequently cut by sinistral strike-slip faults perpendicular to the fold axis which resulted in the formation of a large-scale pseudo en-echelon structure in an approximate north–south direction.

ABSTRACT A new method is presented for unraveling some aspects of the kinematic evolution of thrust-related folds. This technique consists of measuring crestal structural relief, shortening, and the area of a fold for different amplification stages, and then plotting the crestal structural relief and the fold area versus the shortening. One of the main advantages of this technique is that the data can be obtained from different sources: a section across a fold with associated syntectonic sediments, different sections across a fold that underwent a lateral shortening gradient, or different sections across a fold at different amplification stages. This technique has been applied to theoretical, natural, and experimental thrust-related folds. The analyses carried out show that each fold had a different kinematic evolution. They show also that, except for the theoretical examples, the kinematic evolution may be very complex, because different folding mechanisms may operate during fold amplification and increases/decreases of fold area and thickening/thinning of beds may occur. Therefore, to model or sequentially restore natural/experimental thrust-related folds, we recommend the application of techniques such as the one we propose here, when possible. This would avoid the automatic application of forward models based on kinematic assumptions and geometric resemblance between the model and the actual example.