This study focuses on a new geological cross-section and forward model of the Mont Tendre and Mont Risoux anticlines within the Internal Jura of the Jura fold-and-thrust belt. The results are based on fieldwork, remote sensing, data compilation of previous studies and geological maps. We propose a refined understanding of the wedge geometry, especially the near top basement surface. We identify a large-scale structural unit with an important along-strike continuity, formed by the main regional Vallée de la Saine thrust. This thrust has a 15 km long flat in the Cretaceous units and accommodates a displacement of 17 km, which lead to the formation of the Mont Risoux nappe. The importance of major thrusting in the clay-rich Middle Cretaceous series is recognised as a corollary of the structural modelling. The interpretation of the Risoux-1 deep well has led to the determination of the significant secondary décollement levels in the clay-rich Lower to Middle Jurassic series that lead to the formation of important flats, fishtail and pop-up geometries in structurally higher levels. The activation of the Vallée de Joux frontal thrust resulted in the formation of the Mont Tendre anticline, which lead to the dissection of the Mont Risoux nappe into a sub-unit in the SE, the Mont Tendre nappe. The formation of the Vallée de Joux thrust was followed by a backstepping sequence and a locally oscillating thrust sequence. This detailed interpretation of the sequential development, highlighting the importance of top to the south thrusting (backthrusting), confirms the mechanics of a low-tapered wedge with the décollement in the weak evaporites promoting backthrusting. Moreover, the tectonic nappes demonstrate the lateral structural subdivision by primary thrusts, which have a NE-SW orientation, and by the primary strike-slip faults, which have a NNW-SSE and ESE-WNW orientation. We propose a kinematically viable solution for the activation of the Vallée de la Saine thrust and the formation of the Mont Tendre anticline, which were active between 14 Ma and 4 Ma and accommodated a shortening of some 20 km.

The Caquerelle Anticline is situated within the Internal Jura (Switzerland). Here, inherited basement faults developed during Paleogene have influenced the deformation of the detached Mesozoic and Cenozoic sedimentary cover, likely contributing to the formation of the Del & eacute;mont Basin. The Caquerelle Anticline has thus become a key area for understanding the geodynamics of the basin. In this work, we combined (i) pre-published geological maps and numerous journal publications, (ii) fieldwork integrating classical field methodologies and drone surveys, and (iii) meticulous digital mapping of the digital elevation model 'swissALTI3D', to create a 1:25,000 high-resolution geological-tectonic map of the Caquerelle Anticline and surrounding geological features. According to our interpretation, the Caquerelle Anticline divides two areas with different shortening directions. This phenomenon is attributed to at least one east-dipping basement fault located in the study area. This fault influenced the following compressive deformation of the overlying sedimentary cover, into a transpressive setting.

In foreland fold-and-thrust belts, the distribution of deformation and of the associated stress field can notably be perturbed due to local-scale features such as tectonic structures or surface topography. In the context of geothermal exploration and the planning of the future circular collider (CERN) in the Geneva Basin, it is of particular interest to constrain possible future deformation in the area and the associated stress state. If current seismicity indicates that the Geneva Basin is tectonically active, few data regarding the state of stress in the area are currently available. The goal of this study is to understand under which conditions deformation could localise in the study area, by using numerical modelling based on Limit Analysis. In a first regional part of the study, we investigate the impact of the basal décollement strength on the deformation and on the stress field along a 2D section. Knowing the weak décollement property in the area, results indicate that future deformation is more likely to localise in the Geneva Basin or at the frontal part of the Jura fold-and-thrust belt. Location of deformation in the Geneva Basin depends more on surface topography rather than on décollement geometry. The décollement geometry influences the presence of stress concentrations, which could lead to weakness zones within the section. In the second part of the study, we used a simplified prototype section based on interpretation of a seismic surveys in the Geneva Basin. The impact of the inherited faults strength on incipient deformation was investigated. Results indicate that existing faults can be reactivated by decreasing their friction angle. In the Geneva Basin, the Humilly Fault is the less likely to be reactivated, due to its orientation, compared to the Reculet and Salève thrusts. The failure potential is thus strongly determined by the internal structure of the considered prototype, the frictional properties, and orientations of the existing faults. In the case where deformation localises in the Geneva Basin, the differential stress distribution depends on the décollement strength and geometry, and of the strength of the existing faults.

In this paper we explore the stress orientation and magnitudes associated with faults in the larger Geneva Basin in the frame of the detached Alpine Foreland fold and thrust belt in Switzerland and France. The interpretation is based on shallow earthquake focal mechanisms from strike-slip faults. The area of investigation comprises the westernmost Molasse Basin, the Vuache mountain range formed by the Vuache Fault Zone and the meridional thrusts and folds of the Haute Chaine Jura (Internal Jura). All these domains are detached along a main décollement in the Triassic Keuper Group evaporites and transported by some 30 km to the NW. The whole foreland is presently in a state of critical stress, considering the ongoing seismic activity, with hydrostatic fluid pressure conditions and an Andersonian stress setting. It is thus possible to derive locally the full stress tensor and analyze the stress state of known individual faults. The Mohr circle analysis and the distance to criticality demonstrate that the hydrostatic fluid pressure conditions allow seismic activity on optimally oriented vertical faults. Less optimally oriented faults require an additional raise in fluid pressure conditions. Differential stress values are in the range of 100–150 MPa, and maximum horizontal stress values range up to 200 MPa. Similar values are derived from 2D numerical mechanical analysis using limit analysis theory of the basin applied to a very weak décollement and steep reverse faults. In this approach different friction states were explored. The fact that not all faults are hydraulically conductive, despite favorable orientation, suggest that a valve pressure system and repeated sealing of the faults is a likely process operating in the area. This has profound consequences on fluid circulation models in geothermal systems.

The Jura fold and thrust belt is characterised by dominant thin-skinned thrusting of the Mesozoic-Cenozoic sedimentary cover and variable interaction with inherited structures and deep-seated (i.e., sub-detachment) faults. In its central parts, this fold-and-thrust belt is detached from an underlying mechanically stiffer basement, along Triassic evaporites and displaced up to 30 km. The eastern termination of the fold and thrust belt is characterised by (i) a much lower amount of shortening (on the order of the hundreds of meters), (ii) a significant thickness reduction of evaporites of the Muschelkalk Group, and (iii) interaction of the décollement with steps associated with faults bounding an underlying Permo-Carboniferous graben (Constance-Frick Trough; CFT). Using recently processed seismic data (Nördlich Lägern 3D), we document the role exerted by the inherited structures rooted in the Permo-Carboniferous basin fill and basement in the development of the different styles of deformation and structures in an area located northwest of the city of Zürich. The ENE-striking master normal fault bounding the CFT to the south displays evidence of reactivation, during both extensional and compressional episodes, illustrated by apparent normal steps, alignments with no apparent displacement, and gentle folding of the Permo-Carboniferous basin fill. The investigated seismic volume indicates that contractional deformation is concentrated in two major ENE trending fold-thrust zones involving the Triassic-Jurassic epicontinental platform succession and the stratigraphically overlying Cenozoic Molasse Basin deposits. The northern fold-thrust zone (NFTZ), manifested at the surface by the Siglisdorf anticline, consists of an up to 2 km wide pop-up structure linked to thrusting in the detached cover series. The structure is located in correspondence with steps in the topography of the base Mesozoic unconformity produced by south dipping ENE striking minor faults rooted in the Permo-Carboniferous sequence without affecting the detachment integrity. The southern fold-thrust zone (SFTZ), corresponding to the Baden-Irchel-Herdern Lineament, is located above a north dipping major fault of the Late Paleozoic half-graben. The overlying deformation structures in the SFTZ, comprising multiple thrusts and backthrusts, that form fish-tail structures in a narrow, steep zone involving the Mid-Triassic-Jurassic series, are interpreted as the result of layer-parallel shortening associated with buckling of the Mesozoic multilayer. In contrast, the Mesozoic succession is characterized by low deformation and absence of major faults in the area over the central part of the graben (comprised between the Weiach – Glattfelden – Eglisau Lineament – WGEL – to the north and the south fold-thrust zone). The WGEL separates a sub-horizontal to gently folded Mesozoic rock panel to the south from a gently dipping panel to the north. This suggests that fault reactivation may have been accompanied by mild basin shortening and inversion. In conclusion, different modes of interaction between the Mesozoic multilayer (including the weak evaporite level at its base) and underlying Upper Paleozoic basin fill with inherited basement faults have produced a marked contrast in structural style among the detachment-dominated NFTZ, the buckling-dominated SFTZ, and a low deformation central area.

This study unravels the intricate relationship between fault geometry, stress fields, in the La Sarraz-Mormont Fault Zone - a key dextral strike-slip structure at the Jura Mountains–Molasse Basin transition (Switzerland). Through integrated kinematic analysis of 518 fault-striation pairs across 17 sites and paleostress modeling, we demonstrate that this fault zone operates as a multi-order Riedel shear system with remarkable self-similarity. Three hierarchical strands of imbricated faults generate complex, scale-invariant deformation patterns, rotating local stress orientations by >90° despite a consistent regional NW-SE compression. The fault hierarchy dictates stress rotation, not polyphase tectonics. Field evidence from exceptional exposures in Eclépens Quarry reveals how fluid overpressure critically enables fault slip: calcite-filled veins and breccias permeate damage zones, reducing friction and facilitating lateral displacements of 80–500 m. Paradoxically, the main La Sarraz – Mormont fault zone aligns parallel to the modern maximum horizontal stress (SH ≈ N116°), yet accommodates significant shear through probably fluid-assisted weakening—resolving the apparent mechanical enigma.

In 2021, a remarkable natural earthquake sequence initiated in the Haute-Ajoie region (Canton Jura, Switzerland), which provides new insights on how present-day deformation is accommodated in the Jura fold-and-thrust belt (JFTB) in the northern foreland of the Alps. The ML 4.1 mainshock of December 24. 2021, located south of the village of Réclère, triggered an unusual earthquake sequence that has been lasting for at least 3 years. Initially, few aftershocks occurred in the days after the ML 4.1 mainshock, and aftershock activity rapidly ceased within the first week. On March 22. 2023, the sequence was reactivated by an ML 4.3 earthquake, which was followed by an intense sequence of aftershocks. Additional seismic stations were installed in the epicentral area to improve detection thresholds and hypocenter location qualities of aftershocks. Earthquake activity remained high between March 2023 and October 2024, with 14 earthquakes of ML ≥ 2.5. By December 2024, the Swiss Seismological Service (SED) detected and located more than 430 earthquakes with standard methods and derived high-quality focal mechanisms for 17 earthquakes of this sequence.Relative relocations in combination with the focal mechanisms image a complex fault-zone structure within the pre-Mesozoic basement at depths of about 5-6 km. It consists of a system of reverse-to-transpressive faults hosting the ML 4.1 and ML 4.3 earthquakes, which are limited to the west by an adjacent, roughly N-S oriented strike-slip fault zone. The spatio-temporal analysis of the sequences suggests that the reverse-to-transpressive ruptures activated the adjacent strike-slip fault zone and seismicity migrates predominantly southward since March 2023. We complement our study by an enhanced earthquake catalog derived from a cross-correlation based template-matching procedure and the analysis of the stress field at various scales.Our preliminary results indicate significant differences in the b-value parameter over distances of few hundred meters and between the reverse-to-transpressive and strike-slip fault zones. Similarly, a Mohr-circle analysis points to differences in the distance to criticality between the two fault zones. Our results therefore provide new insights into the variability of stress and fracture conditions across upper-crustal fault zones at scales of few hundred meters and raise the question on the possible role of fluids to explain these variations. Besides adding new constraints to present-day seismotectonic processes within the JFTB, our observations are also of general relevance for geothermal exploration targeting complex fault zones.

In this paper we explore the stress orientation and magnitudes of the Greater Geneva Basin in the detached Alpine Foreland in Switzerland and France. The interpretation is based on shallow earthquake focal mechanisms from strike-slip faults. The area of investigation comprises the westernmost Molasse Basin, the Vuache mountain range formed by the Vuache Fault Zone and the meridional thrusts and folds of the Haute Chaine Jura (Internal Jura). All these domains are detached along a main décollement in the Triassic Keuper Group evaporites and transported by some 30 km to the NW. The whole foreland is presently in a state of critical stress, considering the ongoing seismic activity, with hydrostatic fluid pressure conditions and an Andersonian stress setting. It is thus possible to derive locally the full stress tensor and analyze the stress state of known individual faults. The Mohr circle analysis and the distance to criticality demonstrate that the hydrostatic fluid pressure conditions allow seismic activity on optimally oriented vertical faults. Less optimally oriented faults require an additional raise in fluid pressure conditions. Differential stress values are in the range of 100-150MPa, and max horizontal stress values range up to 200MPa. Similar values are derived from 2D numerical mechanical analysis using limit analysis theory of the basin applied to a very weak décollement and steep reverse faults. In this approach different friction states were explored. The fact that not all faults are hydraulically conductive, despite favorable orientation, suggest that a valve pressure system and repeated sealing of the faults is a likely process operation in the area. This has profound consequences on fluid circulation models in geothermal systems.

The balancing technique, called 2D kinematic forward modelling, is a powerful tool to understand the kinematic evolution of fold-and-thrust belts. This study presents a new 2D kinematic forward model for the westernmost Internal Jura fold-and-thrust belt (FTB), situated immediately adjacent to the Geneva Basin. The technique used not only provides a new valid balanced cross-section but also offers new insights regarding the kinematic evolution of the Western Internal Jura FTB. Our model proposes a pure thin-skinned style dominated by forward stepping deformation accompanied by minor back-stepping thrust sequences. A first deformation step is attributed to the thrusting of the Crêt de la Neige Anticline, followed by the Crêt Chalam Thrust and its imbrications. This is followed by thrusting along the Tacon and the Bienne thrusts. Imbricate fault-bend folding explains the steep southern limb of the Crêt de la Neige and the Bellecombe anticlines. 2D kinematic forward modelling yields a total amount of shortening by 23.6 km for the Western Internal Jura FTB. In addition to the primary décollement located at the base of the Keuper Group evaporites, three other décollements are found within the marly layers of the Aalenian “faciès de transition” units, the Oxfordian “Couches d’Effingen-Geissberg” members and the Berriasian Goldberg formation. The multiple thrust horizon approach is supported by new precise seismic interpretations. Our model provides a valid alternative to previous models that either propose local thickening of the Triassic evaporites or inversion of normal faults in the basement. This fully explains the elevated position of the Mesozoic cover in the Jura FTB.

Abstract—The results of U–Th–Pb-isotope dating of accessory zircons from basalts of the Goitkh volcanic region (GVR) in the West Caucasus are presented. A sample for isotope dating was taken from basalt porphyrites of the Chataltopa volcanic complex at the Tuapse River basin. Isotope geochronology using an ion probe showed that the basalts of this complex in the GVR were discharged during the Jurassic at the Aalenian–Bajocian boundary (169 Ma) within the period of the tectonic transformation of an axial trough in the rifting basin of the Greater Caucasus. Zircons in the basalts are characterized by a low Th/U ratio that is peculiar to rocks of an acidic composition; this indirectly confirms that the evolution of Jurassic rifting magmatism in the Caucasus proceeded via the assimilation of continental crust.

The Northern Alpine foreland is divided into two domains: the Molasse Basin and the Jura fold-and-thrust belt (FTB). The Mesozoic and Cenozoic sedimentary cover of this area is deformed by thrust-related folds and strike-slip faults. The main structures root in a basal Triassic décollement. The Geneva Basin, located in western Switzerland, is part of the Plateau Molasse (belonging to the Molasse Basin), and is limited to the NW by the Jura FTB, to the SW by the Vuache fault, and to the SE by the Mont Salève ramp related anticline and the Subalpine Molasse. If current seismicity indicates that the Geneva Basin is tectonically active, few data regarding the state of stress in the area are currently available. The goal of this study is to densify the knowledge of the state of stress in the Geneva Basin and in the adjacent Jura FTB, by using numerical modelling. The first part of the study is a regional study. In a 2D section, we study the impact of the friction along the basal décollement, on the localisation of deformation and on the associated stress field. Results indicate that depending on the friction, deformation will localise at the rear of the Mont Salève, in the Geneva Basin or at the frontal part of the Jura FTB. In the range of frictions where deformation localises in the Geneva Basin, the distribution of stress varies. Differential stress is higher and more localised for higher basal frictions. The second part of the study is more local. The prototype section is based on seismic interpretation of a seismic surveys in the Geneva Basin. We study the impact of friction along the inherited faults on incipient deformation. Results indicate that a decrease in the fault’s friction allows forwards propagation of deformation and allows reactivation of inherited faults. If the friction in the faults is too low, deformation will localise at the first inherited fault (i.e. the Salève thrust in this case study). The stress fields vary depending on the localisation of deformation. Stress magnitudes are lower and more distributed when all faults have the same friction. The more deformation is localised on a structure, the more stress concentration is observed. These results allow to better constrain the mechanical context of these sections and to populate this part of the Northern Alpine foreland with stress data.

The Greater Caucasus doubly-vergent orogenic system has its origin in a Mesozoic-Early Cenozoic back-arc-type basin, floored by an extensively stretched and heavily intruded continental crust that has subsequently been inverted. Our field investigations along the Georgian Military Road in the eastern Central Greater Caucasus provide insights in its tectonic structure and reveal a bivergent orogenic wedge geometry. The southward propagating pro-wedge comprises the Southern Slope tectonic imbricate system developed in the Mesozoic-Early Cenozoic basin infill and the Transcaucasian Kartli foreland fold-and-thrust belt and is actively underthrust by the Transcaucasian Dzirula-Shatsky Block. The retro-wedge, on the other hand, incorporates the Northern Slope tectonic zones (including the Homocline Range) and the North Caucasian Terek-Sunzha foreland fold-and-thrust belt that developed in the Mesozoic-Cenozoic cover of the Scythian Platform. The Main Range forms the axial zone of the mountain belt where crystalline, pre-Mesozoic basement is locally brought to the surface at almost 3000 m altitude along the Main Caucasus Thrust.Our study of the regional geology, in combination with paleotectonic reconstructions suggests that the presentday tectonic units of the Caucasus correspond to distinct pre-collisional paleotectonic domains that existed in the Mesozoic-Early Cenozoic Neotethys-Eurasia ocean-continent convergence zone. The focus of our study lies on the tectonic interpretation of the Greater Caucasus fold-and-thrust belt. We propose to interprete the major thrusts of the orogen as former normal listric detachments occurring in the Greater Caucasus Basin, that were reactivated as reverse faults and thrusts during the collisional events of the Arabia-Eurasia convergence since the Late Eocene-Oligocene (Alpine inversion stage).

The arcuate Jura Mountains Fold-and-Thrust Belt (FTB) is situated in the NW Alpine Foreland and its formation is related to the Alpine orogeny. The western part of the Jura FTB, investigated here, is situated in France to the north of the Geneva Basin (Switzerland). The geothermal project “GEothermie2020” of the larger Geneva area allowed us to re-assessed the structural geology and the kinematic evolution of the internal part of Western Jura FTB from the Geneva Basin (Switzerland) to the Bienne Valley (France). Stratigraphic harmonization, new geological and tectonic maps, new seismic interpretation, and a new near top Basement surface were used to construct a kinematic model. This model using forward modelling techniques has been developed in the software Movetm by Petroleum Experts. The forward model relies on fault-bend fold, trishear, and fault-parallel flow algorithms, and provides a valid and balanced cross-section. The model is constrained by surface, well and seismic data. Therefore, the depth of the near base Mesozoic horizon has been well constrained by seismic depth-converted lines. Thus, we can show, that the top basement under the Jura domain is dipping 1.7° to the SE, whereas under the Geneva Basin it is dipping between 2.7°-3.3° to the SE. The results of our modelling show a shortening of 23.6 km for the western Internal Jura FTB along a basal detachment and a forward stepping deformation accompanied by minor back-stepping thrust sequences. The first deformation is attributed to the thrusting of the Crêt de la Neige anticline followed by the Crêt Chalam thrust and its imbrications. Then, the Tacon thrust and finally the Bienne thrust nucleate. Imbricate fault-bend folding explains the high southern slopes of the anticlines found in this area. In addition to the primary décollement level situated at the base of the Keuper Group evaporites, three other detachment levels are found in marly layers. Using such a multiple thrust horizon approach avoids having to introduce thick unaccounted for evaporitic duplexes in the Keuper units, basement horst, or inverted Permo-Carboniferous grabens. The change in dip of the top basement located under the SE flank of the Crêt de la Neige anticline, at the transition of the Jura FTB to the Molasse Basin, is considered to be linked to a preexisting Paleozoic normal fault and could correspond to the northern edge of a suspected Permo-Carboniferous graben interpreted on seismic lines under the Geneva Basin. This step can be considered as an initiation point for structures developing in the detached cover.

The Jura Mountains in France and Switzerland are a classical thin-skinned fold-and-thrust belt (FTB), which developed as part of the Alpine orogenic foreland, together with the Western Alpine Molasse Basin. The Molasse Basin initiated as a flexural basin and evolved into a wedge-top Basin following the initiation of the main foreland décollement level. The Jura FTB thus forms the frontal portion of the Alpine foreland, which enjoyed a transport of some 30km towards the foreland along the main décollement in the mechanically weak Triassic salt-rich evaporites. Overall the Jura FTB behaves as a mechanical wedge in hydrostatic conditions, that is propagating towards the Alpine foreland. Wedge-internal accommodations, due to changes in the surface topography and the basal décollement inclination, as well as in the basal friction, are operated by oscillating forward and backward stepping sequences of thrusting and related fold development. Basement topography associated with inherited faults leads to a kinematic preconditioning of the structures developing in the detached cover. Analogue modelling has helped show that oblique steps in the basement topography lead to the formation of normal and reverse faulting and oblique fold structures in the cover. Herein we will discuss the link of different types of faults observed in the field, such as normal faults, inverted inherited faults, thrust faults and strike-slip faults, to major tectonic processes such as flexural bending, rifting, faulting due to steps in basement topography, and thrusting inside a mechanical wedge. Works on relative chronology of faults, combined with new results from kinematic section modelling and data on published and new deformation ages from calcites (using U-Pb) make it possible to assess the timing of deformation. It is thus possible to show that thrust faults and strike-slip faults, as well as, normal and inverted faults were active at different times and witness superposed events. Deformation in the Jura FTB is partitioned and distributed along discrete faults that clearly operate in a forward and backward oscillating manner. We further can identify different structural domains that can be considered as distinct tectonic nappes. These domains are bound by major strike-slip faults (acting as inherited, rigid boundaries), progressive en-echelon relay zones and major thrusts. The present-day deformation involving both the detached cover and the mechanical basement will be discussed.

Lake Afdera is a hypersaline endorheic lake situated at 112 m below sea-level in the Danakil Depression. The Danakil Depression is located in the northern part of the Ethiopian Afar and features an advanced stage of continental rifting. The remoteness and inhospitable environment explain the limited scientific research and knowledge about this lake. Bathymetric data were acquired during 2 weeks expeditions in January/February 2016 and 2017 using an easily deployable echosounder system mounted on an inflatable motorized boat. This study presents the first complete bathymetric map of the lake Afdera. Bathymetric results show that the lake has an average depth of 20.9 m and a total volume of 2.4 km3. The maximum measured depth is 80 m, making Lake Afdera the deepest known lake in Afar and the lowest elevation of the Danakil Depression. Comparison with historical reports shows that the lake level did not fluctuate significantly during the last 50 years. Two distinct tectonic basins to the north and the south are recognized. Faults of different orientations control the morphology of the northern basin. In contrast, the southern basin is affected by volcano-tectonic processes, unveiling a large submerged caldera. Comparison between the orientation of faults throughout the lake with the regional fault pattern indicates that the lake is part of two transfer zones: the major Alayta–Afdera Transfer Zone and the smaller Erta Ale–Tat’Ali Transfer Zone. The interaction between these Transfer Zones and the rift axis forms the equivalent of a developing nodal basin which explains the lake’s position as the deepest point of the depression. This study provides evidence for the development of an incipient transform fault on the floor of the Afar depression.

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 similar to 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.

Pre-existing faults in the mechanical basement are believed to play an important role in controlling deformation of the thin-skinned Jura Mountains fold-and-thrust belt, which constitutes the northernmost extension of the European Alps. We use brittle-viscous analogue models to investigate the influence of frontal and oblique basement steps on the subsequent evolution of structures during thin-skinned shortening. Vertical offset between two rigid baseplates (simulating the mechanical basement) causes the formation of reverse faults and grabens in the overlying brittle layers that are not reactivated during subsequent thin-skinned shortening. However, baseplate steps localise deformation, causing a temporary frontward propagation of deformation in an early stage and inhibiting propagation afterwards. Downward baseplate steps induce very strong deformation localisation and foster the formation of fault-bend folds. Models featuring upward steps develop step-controlled pop-up structures with imbricated fronts and viscous ramps that shorten dynamically with progressive contraction. We find that deformation localisation increases both with higher step-throws and lower obliquity (alpha) of the strike of the step (e.g. frontal step alpha = 0 degrees). With increasing step-throws, alpha = 30 degrees and alpha = 45 degrees oblique upward-steps lead to a characteristic imbrication of the brittle cover with laterally confined thrust-slices and step-parallel obliquethrusts, which rotate up to 15 degrees about a vertical axis over time. Step-controlled backthrusts preceding the formation of thrust-slices do not show notable rotation and hence constitute excellent indicators for the orientation of oblique upward-steps. The topographic patterns of oblique-step models resemble individual thin-skinned structures of the Internal Jura (i.e. Pontarlier and Vuache fault zones, the nappe system SE of Oyonnax and the Chasseral anticline), strongly suggesting that pre-existing NNE-SSW and NW-SE striking oblique upwardsteps in the basement controlled deformation in the overlying cover. Our model results may be applied to other thin-skinned fold-and-thrust belts worldwide that formed above pre-existing basement structures.

The Jura Mountains are a thin-skinned fold-and-thrust belt (FTB) in the northern foreland of the European Alps, extending over northern and western Switzerland and eastern France. The Jura FTB was detached in Triassic evaporites during Late Miocene and Pliocene compression. Prior to this, the pre-Mesozoic basement was intensely pre-structured by inherited faults that had been reactivated under changing stress fields during the Mesozoic and Cenozoic structural evolution of continental Europe. In order to understand the connection between thin-skinned FTB formation and pre-existing basement structures, we compiled boreholes and geological cross-sections across the Northern Alpine Foreland and derived elevation, thickness and erosion models of defined Mesozoic units and the top of the pre-Mesozoic basement. Our models confirm the presence of basement faults concealed underneath the detached cover of the Jura Mountains. The pre-Mesozoic basement shows differences in structural altitudes resulting from partially overlapping lithospheric processes. They include graben formation during evolution of the European Cenozoic Rift System (ECRIS), flexural subsidence during Alpine forebulge development and lithospheric long-wavelength buckle folding. Faults in connection with these processes follow structural trends that suggest the reactivation of inherited Variscan and post-Variscan fault systems. We discuss the spatio-temporal imprint of lithospheric signatures on the pre-Mesozoic basement and their consequence on the formation of the Jura Mountains FTB. Untangling structures within the pre-Mesozoic basement leads us to a modern understanding of the long-term evolution of the detached Mesozoic cover. Furthermore, it allows us to improve the prediction of ages that are potentially preserved within the Mesozoic cover of the Jura FTB.

The results of the isotope dating of the crystalline basement of the Greater Caucasus (the Elbrus subzone of the Main Caucasus Range) within of the high-temperature gneiss–migmatite area of the Gondaray metamorphic complex is discussed. The relationships between regional metamorphism, migmatization, and heat flows in the lithosphere are considered. The measurements of the zircon isotope compositions were performed on a SHRIMP-II ion microprobe at the CIR VSEGEI (St. Petersburg). All zircon crystals from gneiss sample 526 have a zonal structure with ancient detrital cores. Almost all U–Pb isotope dating points lie on the concordant line and show a wide age range from 320–1000 Ма, partially inherited from detrital zircon grains from primary pelitic sediments. The youngest ages (320 Ма) were measured in the regeneration zones of zircon grains recrystallized during stage of the anatexis and migmatization. The other points of detrital zircons form an age cluster of 540–1000 Ма, which indicates their origin from different magmatic sources that existed during the formation of the protometamorphic protolith. Several detrital zircon grains yielded a Cambrian age; this is evidence for an Early Paleozoic age of the metamorphic protolith, which was traditionally suggested to be Precambrian or even Archean. The ages of the rims of recrystallized zircons (320 Ма) have a direct correlation with the postmetamorphic granitoid ages of the Greater Caucasus. The thermochronological modeling of the transformation of the Gondaray metamorphic complex during the retrogressive stage of metamorphism demonstrates that its cooling from the temperature of migmatite crystallization (650°С) to the closure of the temperature of the K–Ar biotite isotope system (350°С) was relatively rapid (the rate of cooling was 8–10°С/Ma) under subisobaric conditions and during a time range approximately 30–40 Ма.