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The coastal cliffs around the Roses Lighthouse (Cap de Creus, Mediterranean Costa Brava) display deformation structures generated during the emplacement of a syntectonic granodiorite and associated rocks (quartzdiorite enclaves and leucocratic dykes). These rocks were subjected to shearing and spectacular shear zones are present, which have been object of several scientific publications. The outcrops are considered of international high scientific value, being regularly visited by researchers and students from several European universities. In 2005, the site was included in the Geosite Inventory of Catalonia, but it does not have any special protection yet, despite decades of efforts to claim the need for protection and conservation in front of the constant deterioration and loss of outcrops due to strong urban and touristic pressure. A project of restoration, access improvement, and dissemination of geological values was finally executed between 2020 and 2021. The Roses case study leads us to the remark that urban and periurban geosites offer a good opportunity for promoting geological research, education, and tourism, provided its protection based on geoconservation criteria and a strong sustainable conservation management plan. We wish to thank Joan Esteve Danès, former councilor of the Roses town council, for his concern and awareness on the importance of this geosite and his involvement in dynamizing the project. We are grateful to two anonymous reviewers for their useful comments. Thank you also to Manuel Monge for providing a useful review of a previous manuscript presented at the ProGEO SW Europe Regional Working Group Virtual Conference on Geoconservation (March 2022). ED received funding by the Roses town council (Ajuntament de Roses—UAB contract GJ514392).

Complex folding patterns include folds with curved hinges and/or curved axial surfaces. In simple shear zones, folds commonly nucleate with hinges at a high angle to the shear direction and progressively rotate towards parallelism with the shear/extension direction, giving rise to sheath folds. Axial surfaces also change in attitude with increasing strain, becoming parallel to the shear plane. However, when folds do nucleate with hinges along the extension direction but oblique to a shear component, they are not subjected to hinge rotation, but can experience a variable amount and sense of rotation of axial surfaces, developing into polyclinal folds. Foliated quartzite beds from the Cap de Creus massif in the eastern Pyrenees exhibit complex fold patterns produced during a single transpressional event. While folds in the embedding schists are harmonic and asymmetric, folds in the quartzite are strongly disharmonic and polyclinal, displaying large axial surface rotations. A plausible interpretation is that folds nucleate with hinges closely parallel to the extension direction, developing thickened short limbs that rotate synthetically with regard to the shear component. This may lead to strain partitioning, with localized antithetic rotations enhanced by progressive softening of the quartzite. Thus, fold interference patterns are not necessarily linked to polyphase tectonics but they may result from single-phase progressive deformation. In the here described cases, unfolding during progressive deformation is highly improbable.

Early Paleozoic accretionary orogens dominated the Western Gondwana margin and were characterized by nearly continuous subduction associated with crustal extension and back-arc basin development. The southwestern margin is represented by Famatinian and Pampean basement realms exposed in South America, both related to the protracted Paleozoic evolution of the Terra Australis Orogen, whereas the northwestern margin is mainly recorded in Cadomian domains of Europe and adjacent regions. However, no clear relationships between these regions were so far established. Based on a compilation and reevaluation of geological, paleomagnetic, petrological, geochronological and isotopic evidence, this contribution focuses on crustal-scale tectonic and geodynamic processes occurring in Western Gondwana accretionary orogens, aiming at disentangling their common Early Paleozoic evolution. Data show that accretionary orogens were dominated by high-temperature/low-pressure metamorphism and relatively high geothermal gradients, resulting from the development of extended/hyperextended margins and bulk transtensional deformation. In this sense, retreating-mode accretionary orogens characterized the Early Paleozoic Gondwana margin, though short-lived pulses of compression/transpression also occurred. The existence of retreating subduction zones favoured mantle-derived magmatism and mixing with relatively young (meta)sedimentary sources in a thin continental crust. Crustal reworking of previous forearc sequences due to trenchward arc migration thus took place through assimilation and anatexis in the arc/back-arc regions. Therefore, retreating-mode accretionary orogens were the locus of Early Paleozoic crustal growth in Western Gondwana, intimately associated with major flare-up events, such as those related to the Cadomian and Famatian arcs. Slab roll back, probably resulting from decreasing convergence rates and plate velocities after Gondwana assembly, was a key factor for orogen-scale geodynamic processes. Coupled with synchronous oblique subduction and crustal-scale dextral deformation, slab roll back might trigger toroidal mantle flow, thus accounting for bulk dextral transtension, back-arc extension/transtension and a large-scale anticlockwise rotation of Gondwana mainland. Fil: Oriolo, Sebastián. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Schulz, Bernhard. Technische Universität Bergakademie Freiberg; Alemania Fil: Geuna, Silvana Evangelina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina Fil: Gonzalez, Pablo Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Río Negro. Sede Alto Valle. Instituto de Investigaciones en Paleobiología y Geología; Argentina Fil: Otamendi, Juan Enrique. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencias de la Tierra, Biodiversidad y Ambiente; Argentina Fil: Sláma, Jiří. The Czech Academy of Sciences. Institute of Geology; República Checa Fil: Druguet, Elena. Universitat Autònoma de Barcelona; España Fil: Siegesmund, Siegfried. Universität Göttingen; Alemania

The area of Cap de Creus, at the eastern termination of the Axial Zone of the Pyrenean Belt, exposes some of the most famous outcrops of ductile shear zones and shear zone networks (Carreras, 2001). Recent studies proposed that the nucleation and growth of such shear zones may have taken place by brittle processes (Fusseis et al., 2006; Fusseis and Handy, 2008).The present study investigates the geometrical relationships between fracture systems and some shear zones, the deformation temperature of these shear zones, and the processes leading to the nucleation and growth of shear zones along fracture planes. We selected two areas of the Cap de Creus, the Cala d’Agulles, and the Punta de Cap de Creus, because they are most intensely dissected by subparallel sets of shear zones and fractures. The orientation of the average shear zone planes is sub-parallel to the orientation of the major set of fractures, and the great extent and close spacing of some shear zones that we characterized by aerial photos from a drone, is similar to the distribution and extent of the fracture planes. These observations, in addition to those of Fusseis et al. (2006) suggest that the shear zones nucleated on previous fracture planes. These fractures are surrounded by haloes of nearly 1 cm thickness affecting the fabric of the country rock, an amphibolite-facies, biotite-andalusite bearing schist. Microscopic observations show that the haloes correspond to the wide-spread presence of thin (less than 2µm thickness) phosphate seams coating the grain boundaries, preferentially those oriented at low angle to the fracture plane, and to the alteration of plagioclase to white mica and sericite, and to the growth of tourmaline, also related to grain boundaries and micro-fractures.Deformation temperature in the shear zones is assessed by white mica thermometry and pseudosections. The calculated T of at least 350-400° C is consistent with qualitative observations showing the presence of stable biotite within very fine-grained (<< 10 µm) shear bands and the recrystallization of quartz by rotation of sub-grain boundaries.In summary, fractures formed at high temperature, possibly associated with the intrusion of tourmaline-bearing pegmatites and fluids, which predate the ductile mylonitic event (Druguet, 2001; Van Lichtervelde et al., 2017). Fluids altered and weakened a volume of approximately 2 cm thickness all along the fracture planes, whose extent may reach > 100 m. The inferred, relatively high T of ca. 400° C indicates that fracturing is not due to the proximity of the brittle-ductile transition. In addition, no significant micro-fracturing of the mylonites is observed in thin sections. Therefore, fracturing precedes the ductile shear zones, which nucleate on some of the “inherited” sets of thin, planar, weakened structures, the large majority of which remains undeformed. These observations raise the question on whether nucleation and propagation of ductile shear zones is mechanically unrelated to brittle fracturing. Their weakening of planar structures would originate from fluid migration along fracture planes, but fracturing would no longer be active during ductile deformation.

The Cap de Creus massif in the eastern Pyrenees is a renowned late Variscan fold-and-shear zone belt characterized by partitioning of an overall ductile strike-slip-dominated dextral transpression into coeval folding, ductile shearing and localized embrittlement. The local partitioning of deformation mode (fracture vs. ductile flow) can be related to rheologically contrasting lithologies and syntectonic infiltration of hydrothermal fluids that were likely residual fractions of earlier pegmatite intrusion. In particular, the influx of hydrothermal fluids results in cm-to m-sized damage zones of localized fractures and veins with associated hydrothermal alteration across most lithological units. Such damage zones systematically formed at a low angle to the axial surfaces of contemporaneous folds, even in cases with minimal shortening. In higher strained areas, evident by tighter folding and shearing, cataclasites developed along these same damage zones. This study provides an example of contemporaneous ductile and brittle structures, in this case resulting from localized embrittlement due to fluid flow.

Veins and dikes are often oriented subparallel to the axial surfaces of folds in the adjacent layered or foliated rocks. This implies an awkward situation, since veins would lay in planes close-to-parallel to the maximum stretching axis. A series of geometric models have been conceived in order to gain insight into the possible mechanisms for their formation. The models are based on the analysis of a varied selection of field structures and on the review of similar structures in the existing literature. A first categorization consists on distinguishing between axial-planar veins achieved by either progressive or polyphase deformation. Five models of axial-planar veins resulting from progressive deformation are described and discussed: (1) fold-related veins associated with the standard folding mechanisms, (2) fracture arrays localized along the short limbs of folds (asymmetric fold-related veins), (3) folds associated with rotation of extension veins (vein-related folds), (4) high strain and transposition of early veins, and (5) high strain and late veins parallel to axial planar foliations (axial planar foliation-related veins). The axial planar geometry is achieved through variable amounts of progressive rotational strain, except in model 5, in which the co-planarity is acquired at the time of vein intrusion. The possibility for axial-planar veins to have developed in two distinct phases in the context of polyphase or polyorogenic tectonics has also been explored and discussed. This study contributes to a better understanding of the intriguing interplays between deformation, metamorphic and magmatic processes in orogenic belts. Keywords: Dike, Fold, Fracture, Metamorphic rock, Migmatite, Shear

The SE Sardinia mafic dyke swarm intruded in Permian times into the Late Variscan granitoids of the Sarrabus massif. In order to characterize the structure of the dyke swarm and to assess the stress state and tectonic regime at the time of dyking, we have performed a multi-methodological study which encompasses paleostress analysis using the orientation distribution of dykes, estimation of crustal extension from dyke thickness/spacing ratios and true dilation direction from the matching geometry of offsets. The mean orientation of the dyke swarm is ∼N150°, with secondary main trends orientated ∼N77° and ∼N10°. The fracture network (mostly joints) exhibits multiple orientations grouped in four or more sets, being the orientation and density patterns in granitoid and dykes significantly different. Some of the pre-existing joints were exploited by the dykes, while others were reactivated as faults during and after dyke intrusion. The paleostress analysis yielded σ 1 sub-vertical, indicating that an extensional tectonic regime predominated in the area during the emplacement of the dyke swarm. σ 3 was sub-horizontal, sub-parallel to the mean NE–SW dilation direction. The inferred relative stress magnitudes are characterized by a σ 1 much larger than the other two principal stresses. In this context, intrusion of the dyke swarm occurred under low magma pressure conditions and preferentially into a pre-existing joint nerwork during a regional extensional event. The SE Sardinian dyke swarm has been compared with other contemporary mafic dykes of the western Mediterranean region, by attempting to restore the effects of the Neogene and eo-Alpine rotational events. The reconstruction gives a complex crustal-scale pattern in terms of dyke orientation, a fact that could be partly attributed to differential rotations associated with localized strike-slip movements that might have operated coevally with regional extension or transtension during Permian times.

The structural study of the Saint-Laurent – La Jonquera pluton (Eastern Pyrenees), a Variscan composite laccolithic intrusion emplaced in metasedimentary and gneissic rocks of the Roc de Frausa dome, by means of the anisotropy of magnetic susceptibility (AMS) technique has allowed the determination of the nature and orientation of its magmatic fabrics. The magmatic foliation has a predominant NE–SW strike and the mean lineation is also NE–SW trending with a shallow plunge. A strain gradient is measured so that the tonalites to granodiorites that form the basal parts of the pluton, and are intruded into amphibolite-facies metamorphic rocks, recorded the highest anisotropies, whereas the monzogranites and leucogranites, emplaced into upper crustal, low-grade metamorphic rocks, are weakly deformed. These results point to the synkinematic sequential emplacement of multiple granitoid sheets, from less to more differentiated magmatic stages, during the Late Carboniferous D 2 event characterized by an E–W-trending dextral transpression. The magmatic foliation appears locally disturbed by the effects of two tectonic events. The first of them (D 3 ) produced mylonitization of granitoids along NW–SE retrograding shear zones and open folds in the host Ediacaran metasediments of the Roc de Frausa massif, likely during late Variscan times. Interference between D 2 and D 3 structures was responsible for the dome geometry of the whole Roc de Frausa massif. The second and last perturbation consisted of local southward tilting of the granitoids coupled to the Mesozoic–Cenozoic cover during the Alpine.

International audience; The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group minerals (CGM), which are present in the different types of pegmatites from type I (K-feldspar pegmatites, least evolved) to type IV (albite pegmatites, most evolved) and therefore allow dating the different pegmatitic pulses. In a type III pegmatite where zircon and CGM are co-genetically associated in the same sample, both minerals were dated using zircon and tantalite reference materials, respectively, to avoid laser-induced matrix-dependent fractionation. In one sample, xenotime genetically associated with zircon was also dated. Two ages were obtained for type I and three ages for type III pegmatites. Three of these 5 ages range from 296.2 ± 2.5 to 301.9 ± 3.8 Ma and are allocated to the primary magmatic stage of crystallization and therefore to the emplacement event. Two younger ages (290.5 ± 2.5 and 292.9 ± 2.9 Ma) obtained on secondary zircon and xenotime, respectively, are interpreted as late post-solidus hydrothermal remobilization. There is no age difference between type I and type III pegmatites. The mean 299 Ma primary magmatic age allows the main late Carboniferous deformation event to be dated and is also synchronous with other peraluminous and calc-alkaline granites in the Pyrenees. However, the youngest ages around 292 Ma imply that tectonics was still active in Early Permian times in the Cap de Creus area.

A structural analysis has been performed in the Upper Permian lamprophyric dyke swarm of Aiguablava (Costa Brava, NE Iberia). Emplacement of sub-vertical dykes is related to the presence of a widespread joint network, mostly developed during the cooling and decompression of the late Variscan leucogranitic host rocks. The joint pattern consists on multiple sub-vertical joint sets among which two orthogonal sets at ≈ N23° and ≈ N113° are predominant. A sub-horizontal set is also prominent. The sub-vertical dykes have a mean N100°–N125° trend, which corresponds to the trend of one of the main joint sets. However, dyke segmentation is noticeable at the Dm- to cm-scale, and this is inferred to be related to dyke propagation and emplacement along the variably oriented pre-existing joints. A mean robust sub-horizontal NNE–SSW net dilation direction was measured from matching dyke jogs, markers in the host rock and analysis of maximum dyke thicknesses, and this is in line with the minimum principal stress axis ( 3 ) derived from a three-dimensional paleostress analysis from dyke orientations. The inferred maximum principal stress axis ( 1 ) is sub-vertical, indicating that dykes intruded under conditions of tectonic extension. Furthermore, a Mohr construction allowed calculation of the stress ratio φ = 0.29 (close to a prolate stress ellipsoid) and a driving pressure ratio R′ = 0.27, which corresponds to a magmatic pressure almost equal to the intermediate principal stress axis, σ 2 . It is inferred that many of the pre-existing joint sets were exploited by the magma, the WNW–ESE joint set (normal to σ 3 ) being the most favorable for dyke emplacement. The present study highlights the structural control of a pre-existing fracture network on emplacement of the Aiguablava lamprophyres in the upper crust during late Permian NNE–SSW brittle extension.

Among the many concepts that have contributed to the development of structural geology in the last half-century, two are particularly important. These are: (i) the link between the symmetry of the structure, the vorticity of the associated deformation process and the tectonic regime, and (ii) the widespread partitioning of strain. However, a clear understanding of these concepts and the links between them are not always apparent in structural analyses carried out to determine the prevailing tectonic regime of an area through the use of structural symmetries and kinematic indicators. This contribution, based on field studies from Cap de Creus, experimental data and theoretical concepts, highlights some of the problems encountered when attempting to deduce the type of strain and associated regional tectonic regime from field structures. The relation between the symmetry of a structure and its associated kinematics is not unique. For example, it is demonstrated that in mechanically anisotropic materials, symmetry variations do not necessarily reflect marked vorticity variations, but rather the angular variations between the kinematic framework and the anisotropy planes. Because of widespread strain partitioning, local and general kinematics do not generally match. This mismatch is especially accentuated in rheologically heterogeneous rocks. Nevertheless, correct interpretations are possible by performing continuous multi-scale structural analyses in which the impact of strain partitioning and of the presence of material anisotropies and heterogeneities are considered.

Tectonic lozenges are elongate bodies bounded by relatively more deformed rocks. The focus of this study is on the 2-D structure of tectonic lozenges developed during ductile shear in rocks with a pre-existing mechanical anisotropy. On the basis of a detailed analysis of shear zones in foliated rocks from the Cap de Creus area (Variscan of the eastern Pyrenees), five mechanisms to explain the development of different types of lozenges in foliated rocks are suggested. These mechanisms are explained on the basis of the orientation of the previous foliation relative to the bulk shearing direction. It is shown that the prevailing mechanism does not majorly depend on the bulk kinematics but on the angular relationship between the pre-existing foliation and the bulk kinematic axes, and on shear zone interaction. This has implications on the use of lozenge shapes in tectonic interpretations. The fact that there is a wide range of initial orientations, propagation modes and coalescence types implies that the final lozenge geometry is not univocally related neither to the type of strain nor to the kinematic regime.

The effects of postemplacement deformation on originally nonplanar dikes were tested experimentally and compared to field data from the Rainy Lake zone (Ontario, Canada) where irregular fold-like structures are observed. The analyses reveal that two processes are responsible for the irregular dike geometries. First, dikes intrude with varying orientations as they propagate across layers with rheology contrasts, thus developing nonplanar profiles. Second, with postemplacement ductile deformation, dikes that are more competent than the host rocks are folded and refracted in variable amounts, with the amount depending on the initial dike geometry, the heterogeneities in the host, and the regional strain. Deformed dikes and veins are often used as kinematic markers to evaluate regional tectonics, using methods that generally assume that veins had planar walls prior to deformation. The experimental results indicate that caution should be taken when using this approach, and they provide criteria to distinguish between intrusive and deformation structures in intensely deformed areas where distinction between the two is not readily apparent.

The Red Rocks Amphitheatre in Colorado, USA constitutes a paradigm for reconciling contemporary human actions and geological heritage conservation. The Amphitheatre, built upon red beds of the east flank of the Front Range of the Rocky Mountains, was constructed in the late 1930s with close attention to and respect for the existing geological landform. The park surrounding the performance space is incorporated in the Mountains Park System together with the adjoining Dinosaur Ridge/Morrison Fossil Area National Natural Landmark. Together, the Red Rocks Park and the Dinosaur Ridge provide access to an informative geological cross-section that exemplifies the geology of the Rocky Mountains, from the Precambrian crystalline basement to and across the Phanerozoic cover. Park visitors and concert goers may explore or encounter the transect along walks that are marked by geology information panels. The situation of the Amphitheatre performance space within the geological transect provides a powerful example of the coexistence of different values and multiple uses that may increase the heritage of the site. Settings like this that educate and increase civic awareness of locations of geological value are potentially positive for geoconservation.

A detailed structural analysis of an anastomosing shear zone network in metagabbros from the Archean Rainy Lake zone (Canada) revealed the existence of prevalent dextral and minor sinistral conjugate shear zones with the obtuse angle (>130°) facing the main shortening direction. A typology of shear zone intersections, confluences, and other features shows that all shears formed during a single deformation event, with dextral and sinistral shears being active together or in an alternating fashion. In spite of the difficulty of establishing a complete kinematic sequence, early and late shears can be distinguished. The final angular pattern between dextral and sinistral shears is not an original feature. Dextral and sinistral shears formed at nearly right angles, and the angles progressively opened towards the extension direction as a result of increasing strain. The obtuse angles were achieved by the combined effects of continued shearing on newly forming shears and internal deformation of the lozenge-shaped domains of lesser-deformed rock bounded by the shears. Through time, there was an increasing prevalence of dextral shears over sinistral ones. The studied pattern and sequential analysis indicate that the bulk deformation was noncoaxial with a deformation regime evolving from a pure shear-dominated dextral transpression to a higher vorticity dextral transpression.

Syntectonic magmatic veins are useful tools to identify the interaction between magmatic and deformation processes in the lithosphere. They can be present at all crustal levels, scales and tectonic regimes. The structural analyses of sets of leucocratic veins and dykes from the Rainy Lake zone (Canada) and from Cap de Creus area (Spain), combined with the results of analogue deformation experiments, allows distinction between structures related to intrusion and emplacement, and structures related to post-emplacement deformation. This study also gives an insight on the influence of host rock rheology, regional thermal conditions and deformation history on the developed structures.

An investigation on the effects of a strong rheological contrast in the deformation of layered anisotropic rocks is presented. The study focuses on the geometric and kinematic analysis of complex structures developed within and adjacent to a thin marble–metapsammite multilayer unit from the Cap de Creus tectonometamorphic belt (NE Spain). Zones of high ductile strain localise in the marble layers, which exhibit complex folds, whereas metapsammites show mostly brittle (boudinage) structures. These structures strongly contrast with coeval retrogressive discrete shear zones developed in the surrounding migmatitic schists. The extreme strain partitioning is due to the rheological contrast between different lithological layers. In addition, the specific orientation of this multilayer unit induces a reversal of local kinematics with regard to bulk kinematics. Consequently, caution should be exercised when interpreting regional tectonics in highly partitioned domains associated with rheological heterogeneities.

Networks of leucocratic veins are widespread in the Rice Bay–Redgut Bay domain of the Rainy Lake zone at the Wabigoon–Quetico subprovince boundary (Archean Superior Province, Canada). Vein geometries and their cross-cutting relationships with host rocks are indicative of syntectonic emplacement within a regional late Archean transpressional deformation event (Kenoran orogeny). The relative folding and boudinage of the veins compared to their host rocks indicate that they were emplaced syntectonically with the D2 deformation. Semi-quantitative strain and vorticity analyses confirm the syn-D2 timing of the veins. The observed structural features are interpreted as being formed during magma emplacement along dilatant fractures and subsequent solid-state deformation under overall ductile deformation conditions. The structures related to emplacement are better preserved in domains of low post-emplacement strain and veins intruded into competent host rocks, whereas the folds and boudins related to post-emplacement deformation are well developed in veins intruded into relatively incompetent host rocks. In domains of high strain, the primary intrusive structures are modified or even locally obliterated due to increasing deformation. It is envisaged that regional kinematics and the rheological state of host rocks are the main controls on the style of vein emplacement and deformation. The variety of observed structures is considered the result of deformation and lithological heterogeneity rather than several distinct magmatic events.

Small-scale faults with associated drag folds in brittle-ductile rocks can retain detailed information on the kinematics and amount of deformation the host rock experienced. Measured fault orientation (α), drag angle (β) and the ratio of the thickness of deflected layers at the fault (L) and further away (T) can be compared with α, β and L/T values that are calculated with a simple analytical model. Using graphs or a numerical best-fit routine, one can then determine the kinematic vorticity number and initial fault orientation that best fits the data. The proposed method was successfully tested on both analogue experiments and numerical simulations with BASIL. Using this method, a kinematic vorticity number of one (dextral simple shear) and a minimum finite strain of 2.5–3.8 was obtained for a population of antithetic faults with associated drag folds in a case study area at Mas Rabassers de Dalt on Cap de Creus in the Variscan of the easternmost Pyrenees, Spain.

The Kerdous massif (Anti-Atlas of Morocco) consists of outstanding geological features and landscapes, such as many fascinating erosion landforms. Moreover, the outcropping rocks in the area comprise a unique record of multiple processes in the Earth geological evolution. The first list, resulting of the preliminary inventory of the most relevant and representative geosites in the region includes four large zones of exceptional value. These are the granite landforms of Tafraoute (south of Tafraoute village), the Ameln valley (north of Tafraoute), the Ait-Mansour gorges (southeast of Tafraoute) and the Izerbi plain (south of the Kerdous inlier). Their features make the Kerdous area worthy of conservation as a natural-cultural site deserving a Global Geopark status. The protection of these geosites is compatible with their use as a cultural resource. Geoheritage-based tourism activities could be promoted under an appropriate management plan based on geoeducation and geoconservation.

Migmatites from the Cap de Creus tectonometamorphic belt display a wide variety of structures, from those formed when the leucosomes were melt-bearing, to those developed during solid-state deformation. The observed field structures have been modelled by means of analogue experiments. The materials used in the models are layered plasticine as a schist analogue, and chocolate as analogue of the crystallizing leucosome. A model for the development of syntectonic migmatites is proposed in which initial melt-bearing patches, preferentially formed within fertile pelitic layers, progressively evolve towards lens-shaped veins. Furthermore, heterogeneous deformation of anisotropic metasediments facilitates formation of extensional sites for further melt accumulation and transport. Melt crystallization implies a rapid increase in effective viscosity of leucosomes producing a reversal in competence contrast with respect to the enclosing schists. During the whole process, deformation localizes around crystallizing veins, giving rise to different and contrasting structures for melt-bearing and for solid-state stages.

Intrusive rocks may be arranged in the form of strings of lenses or beads, as found on the Cap de Creus Peninsula, NE Spain, and in the South Finland Migmatite-Granite Belt. These structures first appear to be the result of stretching and boudinage of intrusive sheets or dykes. However, closer examination reveals that they are not boudins, but are instead primary intrusive structures. A detailed study was performed on a swarm of pegmatite intrusions at Cap de Creus. Layering is often continuous between beads, and, in some cases, individual beads exhibit a very irregular shape. These observations are shown to be incompatible with an origin by boudinage. Analogue experiments were used to test the effect of the two models (boudinage and emplacement) on the structures around beads, and show that an emplacement model of local expansion and collapse of magmatic sheets is the most compatible with field observations. Such structures can only form when dykes intrude hot rocks, when magma solidifies slowly enough to allow enough ductile flow of the wall rock to accommodate the formation of the beads. The fact that the pegmatite bead strings are not boudins has repercussions for the interpretation of the deformation at Cap de Creus and necessitates caution in the interpretation of deformation based on apparent boudins in intrusive rocks in other areas. © 2004 Elsevier Ltd. All rights reserved.

Asymmetric boudinage structures are commonly used as shear sense indicators but their development is incompletely understood. This paper describes the influence of initial shape and kinematic parameters on the evolution of boudin trains using a numerical approach based on the finite difference code FLAC. Boudin trains are simulated as a series of competent objects embedded in a soft matrix subjected to general monoclinic ductile flow. Deformation of boudin trains includes heterogeneous stretching, rotation of boudins and offset along the neck regions. The sense of relative boudin offset is mainly influenced by the initial orientation of the interboudin plane in the boudinaging layer, while kinematic vorticity number of the flow and the orientation of the boudin train with respect to the flow extensional eigenvector, usually the shear zone boundary, also play a role. Viscosity ratio and aspect ratio influence the magnitude of offset along the neck regions and the amount of rotation of boudins but not the sense of slip and rotation on the interboudin plane. Knowledge of the orientation of the interboudin plane itself is insufficient to use asymmetric boudins as independent shear sense indicators. Details of the boudin geometry such as the sense of deflection of marker horizons along the interboudin plane must be used for this purpose.

New petrological and U–Pb zircon geochronological information has been obtained from intrusive plutonic rocks and migmatites from the Cap de Creus massif (Eastern Pyrenees) in order to constrain the timing of the thermal and tectonic evolution of this northeasternmost segment of Iberia during late Palaeozoic time. Zircons from a deformed syntectonic quartz diorite from the northern Cap de Creus Tudela migmatitic complex yield a mean age of 298.8±3.8 Ma. A syntectonic granodiorite from the Roses pluton in the southern area of lowest metamorphic grade of the massif has been dated at 290.8±2.9 Ma. All the analysed zircons from two samples of migmatitic rocks yield inherited ages from the Precambrian metasedimentary protolith (with two main age clusters at c. 730–542 Ma and c. 2.9–2.2 Ga). However, field structural relationships indicate that migmatization occurred synchronously with the emplacement of the quartz dioritic magmas at c. 299 Ma. Thus, the results of this study suggest that subduction-related calc-alkaline magmatic activity in the Cap de Creus was coeval and coupled with D2 dextral transpression involving NNW–SSE crustal shortening during Late Carboniferous – Early Permian time (c. 299–291 Ma). Since these age determinations are within the range of those obtained for undeformed (or slightly deformed) calc-alkaline igneous rocks from NE Iberia, it follows that the Cap de Creus massif would represent a zone of intense localization of D2 transpression and subsequent D3 ductile wrenching that extended into the Lower Permian during a transitional stage between the Variscan and Cimmerian cycles.

The Cap de Creus massif in the Eastern Pyrenees is a fragment of the Variscan mid-crust. Geological mapping and meso- and micro-scale analysis of the relationships between fold structures, metamorphic mineral assemblages and fabrics affecting igneous bodies suggest the interaction of three processes: deformation, metamorphism and magmatism. Low pressure prograde metamorphism grades laterally from greenschist to amphibolite facies over a distance of ∼5 km. Zones of intense metamorphism coincide with transpressional deformation and with the intrusion of small sheets of diorite and granitoid. Sillimanite schists and small migmatite pods are distributed around the small intrusions of basic–intermediate composition. The inferred maximum thermal gradient is >80°C/km. This thermal pattern is similar to patterns observed in other Variscan massifs in the Pyrenees, where high metamorphic gradients are interpreted in different ways. In the NE Cap de Creus, the type and distribution of prograde metamorphism was caused, or at least enhanced, by the intrusion of diorites and granitoids. Alternatively, deformation developed at prograde conditions and synchronously with magmatism, displays a highly heterogeneous distribution, producing a sub-vertical zone of high strain that coincides with domains of highest grade metamorphism and igneous activity. This zone of high strain, developed in a broad transpressive regime, could have favoured the injection of magmatic sheets from deep to mid-crustal levels. Progressive folding from prograde to retrograde metamorphic conditions might account for the narrowing of metamorphic zones.

Hercynian metamorphism and magmatism in the Cap de Creus peninsula (eastern Pyrenees) occurred contemporaneously with non-coaxial deformation in a transpressive regime. An example of this has been taken from a migmatite complex in the northern coast. The studied area is formed by partially melted sillimanite schists together with two different suites of igneous rocks: a calc-alkaline magmatic sequence, consisting of small granitoid bodies, and later peraluminous leucogranites and pegmatites. All these rocks occur within a NE–SW- to E–W-trending sub-vertical high-strain zone, where a first schistosity is tightly folded and transposed. The relations between folds and crenulation cleavage in the metasediments and deformational fabrics in the granitoids and migmatites provide good evidence for the penecontemporaneity of deformational processes, magmatism and migmatization. Furthermore, the analysis of cross-cutting relationships between different granitoids as well as the observation of their different degrees of deformation verifies that magmatism in this area took place as synkinematic consecutive intrusions from the more basic magmas to the peraluminous acid dykes.

The structural analysis of a high-strain zone developed in medium- to high-grade metamorphic micaschists from the Cap de Creus area, Spain provides an example of the complex relationships between geometry, strain and kinematics to be found in deep crustal shear zones. This high-strain zone is composed of E-W trending structural domains characterized by different strain intensities and associated with syntectonic emplacement of pegmatite dykes. The main phase of deformation discussed here, D2, affects steeply dipping bedding, boudinaged quartz veins and S1 developed parallel to bedding. D2 deformation of these features and of syn-D2 pegmatite dykes gives rise to fold/boudin structures. In map view, a D2 high-strain zone coincides with a km-scale dextral flexure of S0, S1 and S2, although all small-scale structures on outcrop surfaces close to horizontal indicate a prevalent sinistral shear sense. In addition, a subvertical stretching lineation is present approximately parallel to the axis of the foliation-deflection and thus normal to the apparent ‘displacement’ direction in the high-strain zone. It is proposed that this high-strain zone did not form by horizontal dextral simple shear with a flow plane parallel to the boundaries of high- and low-strain zones but acted as a zone of highly vortical sinistral non-coaxial flow with a strong vertical extension component. The dextral flexure of S0, S1 and S2 can be explained by considering that sinistral non-coaxial flow in the low-strain zones was either slower or earlier that in the high-strain core. This example stresses the necessity of being careful when interpreting displacement directions from the deflection of older fabric elements in deep-seated high-strain zones.

The Hercynian structure in the Pyrenees is characterized by the overprinting of several deformational events, each one associated with spatial changes in tectonic style. The variations in tectonic style depend on the lithological setting and on the tectonic regime, both changing in space and time. However, structural zonations also arise from inhomogeneity of deformation during one event. The studied area in the Cap de Creus is an example of the transition from low strain domains, where an earlier foliation is slightly folded, to a high strain domain, where tight or isoclinal folding caused the transposition of the earlier foliation. This structural inhomogeneity was developed from progressive deformation involving the generation of minor S-shaped folds and a major shear zone-like structure consisting on an open Z-bend. Both structures display steeply plunging axes. Initial flexural flow folding followed by limb stretching and shearing of the major structure is invoked to explain apparently contradictory symmetries and shear senses. This folding event, and the associated strain distribution, controlled the emplacement of a syntectonic pegmatite dike swarm. Dikes occur preferentially within the high strain domain, and are either boudinaged or folded depending on their orientation. A late system of narrow ductile shear zones overprint all earlier structures.

The Precambrian inliers in the Anti-Atlas of Morocco are extensively intruded by swarms of dolerite dykes. On the basis of detail analysis of foliation patterns around dykes from Kerdous and Zenaga inliers it is inferred that dyke emplacement was syntectonic with the main Panafrican collisional event

Some geological outcrops have a special scientific or educational value, represent a geological type locality and/or have a considerable aesthetical/photographic value. Such important outcrops require appropriate management to safeguard them from potentially damaging and destructive activities. Damage done to such rock exposures can include drill sampling by geologist for scientific purposes. In this work, we show how outcrops important to structural geology and petrology can be damaged unnecessarily by drill coring. Unfortunately, regulation and protection mechanisms and codes of conduct can be ineffective. The many resources of geological information available to the geoscientist community, e.g. via Internet, promote access to sites of geological interest, but can also have a negative effect on their conservation. Geoethical education on rock sampling is therefore critical for conservation of the geological heritage. Geoethical principles and educational actions are aimed to be promoted at different levels to improve geological sciences development and to enhance conservation of important geological sites.

Las fábricas anisótropas magmáticas en el plutón de Sant Llorenç-La Jonquera, determinadas mediante la técnica de la anisotropía de la susceptibilidad magnética (ASM), presentan una dirección predominante NE-SW y responden al emplazamiento sintectónico de una secuencia de granitoides durante la fase varisca transpresiva F2. La foliación magmática se encuentra localmente perturbada por el efecto de dos eventos tectónicos de naturaleza y edades distintas. Un primer tipo de perturbación es la derivada de la presencia de zonas de cizalla tardi-variscas (F3) de dirección NW-SE, como es el caso de la banda milonítica de El Pertús. El otro tipo de perturbación consiste en un basculamiento de eje WNW-ESE, localizado en el borde meridional del batolito y atribuible al plegamiento alpino. El presente estudio contribuye a esclarecer cuales son los efectos de la orogenia alpina en el zocalo varisco de los Pirineos

Shear bands are geologic structures widely used as kinematic indicators. Despite the large amount of studies about these structures, their mechanical development is not yet well known. This work presents an experimental study of shear band localization and evolution under coaxial deformation. Particular attention is given to the influence of the obliquity of anisotropy planes on the orientation of shear bands. During deformation, two conjugate sets of shear bands develop symmetrically for models with layers parallel to the extension axis, while for oblique orientations one set dominates. Anisotropy planes have a strong influence on the local stress field around conjugate fracture systems, which deviates from the applied boundary conditions