The inversion of crystalline basement units of former passive continental margins is a typical feature of late-stage collisional mountain belts. In this study, a new large-scale 3D geological model of the main lithostratigraphic and structural units of the Aar Massif was built to investigate how the 3D geometry of the passive margin and inherited extensional structures influenced the tectonic evolution during late-stage continent-continent collision. Cross-section restoration of such units and of metamorphic peak temperature data allowed us to reconstruct the 4D geodynamic evolution of the massif during the late-stage Alpine orogeny. Our results show that: (i) The Aar Massif results from the inversion of the unevenly stretched proximal zone of the passive European margin. (ii) 20% of the present-day structural relief of the massif is a legacy of the 3D architecture of the Permian to Mesozoic passive continental margin. Mesozoic rifting structures formed larger-scale basins separated by a central topographic high subdividing the Aar Massif into three SW-NE trending basement blocks. (iii) The inherited spatial variations in graben/basins geometry and associated sediment and crustal thickness variations caused an in-sequence, non-cylindrical exhumation of the Aar Massif, controlled by a dense network of reverse and thrust faults. This interplay between crustal dynamics and crustal inheritance resulted in the uplift and emplacement of the Aar Massif. The results of this study highlight the importance of integrating regional-scale 3D geological modelling in the analysis of complex geological systems, such as orogens. By enabling a comprehensive understanding of their 4D evolution and geodynamic processes, this methodology opens the door to a wide range of applications in tectonics, resource exploration, and hazard assessment.

The Prealps represent a complex nappe system consisting of Mesozoic to early–middle Cenozoic sediments deposited in the Penninic domains, detached from its substratum during the Alpine orogeny. During subsequent phases of subduction and collision, these nappes were transported along the active plate interface between Adria and Europe far to the north. Today, they lay above the transition between the Helvetic Nappes and the Subalpine Molasse. As a result of long-term displacement and successive deformation, the Prealps exhibit a complex structural architecture that records the cumulative tectonic evolution. We developed a 3D model to yield a high-resolution visualization of the structural architecture and its spatial changes within the Préalpes Romandes. These observations allow us to correlate nappe internal deformation with movements of underlying nappes, which is the goal of this work.The Préalpes Romandes are crosscut by predominantly north–south–oriented sinistral strike-slip faults. These structures range from large-scale faults that transect the entire Prealps nappe stack and accommodate offsets of several kilometers, to minor faults with displacements of only a few meters to tens of meters. Smaller faults are commonly linked by lateral offsets to form continuous step-over fault systems and typically terminate within the detachment horizon. In contrast, larger strike-slip faults must breach the basal detachment of the Prealps to maintain a kinematic balance and are therefore rooted in deeper structural units. Despite a regional change in stratigraphic orientation of approximately 30° from east to west, the orientation of sinistral strike-slip faults remains largely unchanged. An increasing number of NW–SE–oriented dextral strike-slip faults in the eastern Préalpes Romandes indicate a change in the regional kinematic regime.Based on our results, we interpret that the Préalpes Romandes experienced a young (Miocene) phase of deformation following early stages of subduction related nappe transport. We relate this Miocene phase of deformation to the uplift of the Aar Massif. This caused differential motion beneath the Prealps, which is expressed by strike-slip deformation, rotation and back-thrusting within the Préalpes Romandes. We additionally invoke this motion to have controlled the differential migration within the nappe stack, resulting in ~30° counter-clockwise rotation and a general northwestward displacement of the eastern Préalpes Romandes. In addition, the presence of a northern backstop subsequently promoted the occurrence of a lateral escape along local dextral strike-slip faults. A correlation of our 3D model with seismically active zones at greater depth discloses the occurrence of structures that were offset in response to the uplift of the Aar massif during Miocene times. These observations document a complex multistage deformation sequence associated with late-stage collision and uplift tectonics in the subsurface, where the initial sinistral movement has been disrupted and partially reoriented by the latest tectonic evolution. It also highlights the role of strike-slip structures as key elements for understanding the long-term tectonic evolution of the region.High-resolution 3D modelling therefore provides a powerful framework to unravel internal structural relationships, integrate them with surrounding geology, and develop coherent palaeogeographic reconstructions through space and time.

Three-dimensional geological modelling is increasingly used to analyze and investigate the geological evolution of complex areas, offering advantages over classical 2D maps and cross-sections, to test and validate geometries and structural (topological) relationships against sparse field data.Within this context, 3D modelling in polymetamorphic belts poses different challenges, first the absence of formally defined stratigraphic surfaces that are transposed and cancelled by multi-stage tectono-metamorphic events. Alternative tectonostratigraphic or tectonometamorphic units are used when mapping in these environments, but the non-formal definition of these units and of their boundaries can lead to topological ambiguities and even inconsistencies in geological legends, that in turn lead to geo-ontological deficiencies in the modelling process – i.e. deficiencies in the explicit and formal shared conceptualization of the geological meaning and role assigned to units and boundaries.To address these issues, it is essential to explicitly integrate topological and ontological reasoning into the modelling workflow, building a consistent geological legend, in order to generate valid 3D models both in implicit and explicit modelling approaches.Here, we present the Structural Topology model (STm), a workflow grounded in classical structural geology’s thinking and field mapping knowledge, which systematically analyses scale-dependent topological relationships between surfaces and volumes to reconstruct a geologically valid and internally consistent 3D legend based on the concept of a generalized structural polarity. This is a vector that, depending on the geological environment and modelling purpose, can be defined as the younging direction (when relative or absolute ages are available), but also structural position with respect to some convenient reference, and cross-cutting relationships allowing to constrain a sequence of geological events. In this framework, units are classified as tectonometamorphic (TMU), tectonostratigraphic (TSU), stratigraphic (SU), intrusive (IU), or shear zone (SZ) according to their origin and evolution. Their boundaries may be conformal to the main foliation (in the broadest sense, including bedding) or discordant, e.g. at some tectonic contacts, shear zones and unconformities.The formal definition of units with internal polarity, conformal vs. discordant boundaries with polarity, and cross-cutting relationships, allow connecting geological ontology with a topological model that can be implemented in a 3D model. In addition, properly defining polarity for each model entity allows using implicit surface methods (that operate by interpolating a scalar field whose gradient is the polarity) at each stage of the modelling workflow.Here we present an implementation of the STm within the PZero open-source software (https://github.com/gecos-lab/PZero), including a lightweight graphical interface that enables the construction of STm-based geological legends from a Polarigram, where units are plotted against polarity. Examples from complex polymetamorphic areas in the Alps demonstrate that geological topology can be robustly defined even when geological ontology remains ambiguous and scale-dependent, providing a consistent foundation for 3D geological modelling.

Dieser Band bietet eine Einführung in die Entstehung und Geschichte der Erde. Im Zentrum steht die Plattentektonik als treibende Kraft einer dynamischen Erde, und die Prozesse, die zur Bildung von magmatischen, metamorphen und sedimentären Gesteinen führen. Dargestellt wird, wie Interaktionen zwischen der Lithosphäre, der Hydrosphäre und der Atmosphäre den globalen Wasserhaushalt und Klimawandel über geologische Zeiträume beeinflussen. basics – Lehrbücher mit einem klaren Konzept: - Definitionen, Beispiele und Zusammenfassungen erleichtern den Überblick - Zahlreiche Abbildungen veranschaulichen dynamische geologische Zusammenhänge und Prozesse - ideal für die Prüfungsvorbereitung

The properties of fault slip surfaces, gouge characteristics, and fluid-rock reactions are tightly coupled and control earthquake mechanics. To visualise and quantify the role of this coupling, we have developed a new operando imaging approach that allows the documentation of fast direct-shear deformation experiments in time-resolved 2- and 3-dimensional image data at low single-digit micrometer resolution. A direct-shear inset developed for the X-ray transparent Heitt Mjölnir triaxial deformation apparatus enables experiments at 20 MPa normal stress under fluid-pressurised conditions and allows real-time permeability measurements.We apply this platform to three fault systems: 1) Slip surfaces in basaltic rocks, imaged while sliding at 1 mm.s-1, reveal how asperities, phenocrysts, and surface roughness control stick-slip behavior and damage localization during fast slip. 2) Reactive quartz-gypsum gouges imaged during velocity stepping and healing experiments, enable the direct linking of evolving frictional properties to microphysical developments. 3) A shearing, dehydrating gypsum gouge provides insights into transient rheologies and the resulting strain distributions.These datasets demonstrate that 4D imaging resolves coupled mechanical, chemical, and hydraulic fault evolution in real time. Our approach allows documenting microphysical processes underlying the frictional properties of faults and thereby constitutes a potent tool for studying faults in a variety of tectonic settings.

Mid- to lower-crustal shear zones accommodate large strains by high-temperature viscous flow. Yet, strain localization is strongly modulated by transient thermal and chemical perturbations such as the presence of syn-kinematic melts or fluids.We aim at unravelling the general strain localization behavior, the role of fluid/melt presence on the rheology of polymineralic shear zones, with focus on potential changes from mid- to lower-crustal levels.For this purpose, we use the Cossato-Mergozzo-Brissago (CMB) and the Pogallo shear zone systems in the Southern Alps, Northern Italy (Handy, 1987) as a natural laboratory. Field observations and targeted sampling were combined with quantitative microstructural analysis of polymineralic mylonites and ultramylonites. Quartz paleopiezometry (monomineralic quartz bands) provides differential stress and Ti-in-biotite (Henry et al., 2005) provides temperature for felsic lithologies. Such data from natural mylonites are used as input for granitoid shear-zone flow laws (Nevskaya et al., 2025b) to derive strain rates and compare rheology across crustal depths.Field and microstructural observations indicate two endmember microfabric types. Type I (CMB) fabrics occur within a broad (~2-3 km) belt of felsic mylonites (grain size ~50-100 µm). Inside the mylonites, many dykes developed with episodic pulses of melt injection and syn-kinematic back veining (Handy and Streit, 1999). These mylonites commonly contain quartz-feldspars-mica domains with steady-state grain sizes stabilized by pinning and dissolution-precipitation processes. Ti-in-biotite thermometry indicates lower-crustal temperatures of ~680-730 °C.Type II (Pogallo) fabrics also represent microstructural steady states characterized by fine- to ultrafine-grained ultramylonites (grain size

To comprehend the rheology of the Earth's crust and the relevant rock properties, one key approach is to deform rocks and minerals at elevated pressures and temperatures and then extrapolate the measured stress and strain rate values to natural conditions using constitutive equations. Laboratory experiments are mostly conducted on monomineralic rocks, with quartz being considered as the weakest constituent of the middle continental crust. However, field observations suggest that this is an oversimplification, and polymineralic fault rocks may be weaker than monomineralic quartz rocks. This study presents the first experiments on fine-grained, solid, natural rock samples, containing their natural homogeneities and inhomogeneities, demonstrating that granitoid rocks may be weaker than quartz at mid-crustal conditions. It also highlights the importance of pre-existing faults and polymineralic fine-grained zones for strain localisation and proposes values for extrapolation to natural conditions and their use in numerical models of the deformation of the granitoid crust.Cylindrical granitoid ultramylonite samples, composed of qtz + ab + K-fsp + bt + ep, with grain sizes of 125-15 μm are deformed in a Grigg’s type apparatus at T=650°C, confining P=1.2 GPa, strain rates=10-3 to 10-5s-1, and 0.2 wt% H2O added. Mechanical data are combined with light microscope, SEM, TEM, and quantitative image analysis to connect microstructures with stress and strain evolution. We show that polymineralic granitoid rocks deform through other mechanisms than monomineralic quartz aggregates at pressure and temperature conditions characteristic for the middle crust: Ultra-fine grain size reduction down to

Dissolution-precipitation creep (DPC) is considered to be one of the main processes accommodating localized strain in polymineralic shear zones of the Earth's crust. Extensive field evidence for DPC in natural shear zones supports the importance of this process. The spatiotemporal evolution and the level of compositional heterogeneity that facilitate the nucleation of such polymineralic shear zones remain poorly understood. A series of new experiments was conducted on a granitoid fine-grained (average starting grain size similar to 15 mu m) ultramylonite to different strains at 650 degrees C and 1.2 GPa, with strain rates varying from 10-3 to 10-6 s-1. In Type I experiments, a fracture was induced (prior to reaching the pressure and temperature (P-T) conditions), whereas, in Type II experiments, no initial fracture was induced. Consequently, in the Type I experiments, viscous deformation localized strictly within the previous fracture in an similar to 20 mu m wide zone, with grain sizes being reduced to 150-10 nm. In the Type II experiments, viscous deformation was distributed in the sample, with grain size being reduced locally to 200-50 nm. This study supports two different hypotheses for shear zone nucleation in nature. In brittle-induced strain localization, DPC will be activated and lead to a rapid and strong strain localization, producing a very weak and fast-deforming high-strain zone. In viscously induced strain localization (without main fracture), deformation concentrates in zones distributed through the sample, requiring higher shear strains to reach mechanical and microstructural steady state at slower deformation rates compared to brittle-induced strain localization. In both end-member strain localization scenarios, the dominant viscous deformation mechanism in the shear zones is grain boundary sliding combined with pinning-assisted DPC. Our experiments indicate that chemical potentials in the microstructures in combination with different strain localization types may explain the often-observed concentration of strain in fine-grained polymineralic mylonites such as in granitoids but also other polymineralic rocks (e.g., peridotites, granulites etc.) in nature.

The Alps are a dynamic orogen, as evidenced by recent crustal uplift and seismic activity. Earthquakes are primarily occurring along the many pre-existing Neogene faults formed during the Alpine orogeny, making it challenging to predict which faults are being reactivated. Limited geophysical data, low strain rates, high erosion rates, and widespread faulting complicate the detection of active faults in low-strain regions. Currently there is a lack of knowledge about the abundance, architecture, and properties of active faults in the Alps, which is however critical for evaluating the regional seismic hazard. This study adopts an interdisciplinary approach to identify and characterize active faults in the Rawil depression and surrounding areas north of the Rhône-Simplon fault system, located in the southwestern Swiss Alps. A comprehensive seismotectonic description of the region is achieved by combining information from recent high-precision earthquake catalogs derived from relative relocations covering about 40 years, new fault maps using remote sensing and field surveys, updated stress inversion from extended focal mechanism catalogs and paleostress inversion from fault slip data, as well as GNSS data. Results from 3D imaging of active faults at depth, based on the high-precision hypocenter catalogs, reveal that subvertical faults, striking E-W, host most of the present-day earthquakes in the region. This imaging also uncovers previously unknown NW-SE striking active faults potentially contributing to the overall strain distribution in this part of the Alps. Compared to principal stress orientations in the upper crust derived from focal mechanisms, faults striking in both E-W and NW-SE directions appear to be optimally oriented for reactivation in the current stress field. Recent crustal stresses, consistent with the results obtained from paleostress inversion indicating NE/SW-directed transtension, suggest a relatively constant stress regime over the last couple of million years. This implies similarities between exhumed and seismically active faults at depth. The agreement between fault geometries exhumed at the surface and reconstructions of active faults at depth, as determined by hypocenter-based 3D imaging of active faults, support these findings. In conclusion, our study demonstrates that such interdisciplinary studies provide valuable insights into the deformation processes in tectonically active regions, contributing to refined seismic hazard assessments.

Meteoric water may or may not infiltrate deeply into high-relief mountain ranges. Along its subsurface circulation path, the water heats up according to the background geothermal gradient and eventually emerges at lower elevation as thermal springs. Whether such topographically-driven circulation establishes or not depends on the host rock’s permeability and/or the hydraulic head. In terms of permeability, fault zones play an important role as they can provide preferential flow paths for fluids. This is particularly the case of active fault zones along which recurring slip counteracts clogging caused by mineral precipitation often found along non-active structures. Thus, the investigation of 4D fault and fracture geometries and their kinematics is a means to understand the locations and dynamics of geothermal systems in orogenic belts. Here, we present preliminary results from the ongoing GeoTex research project, which aims at better defining the geothermal potential of the Rhône Valley, an area of rugged topography in SW Switzerland. The Rhône Valley represents a geothermally active zone within the Alpine orogen, which is characterised by numerous thermal springs, regional-scale faults and enhanced seismic activity. It is therefore a promising setting to explore further for exploitation. Based on structural data from fieldwork and quantitative remote sensing, we characterise fault geometries (i.e., spatial orientation, relationship of intersecting fault families as well as kinematics) in the vicinity of known thermal springs. Observable paleo-fluid pathways marked by veins and rock alteration are being considered as analogues for recent thermal water circulation. These circulation paths are linked to major Alpine structures in the underlying basement units, such as large-scale strike-slip faults or the axial planes of uplifting basement domes. Our results suggest spatial correlations between the locations of hydrothermal springs and the 3D structure of the host massifs. Specifically, basement–cover contacts exert geometric and lithologic control at some sites, whereas locally dilatant domains along strike-slip faults as well as intersections of fault families focus outflow at other sites. Through the above approach in combination with seismological data, we have derived conceptual models for fluid flow, which may help to predict the locations of blind active geothermal systems elsewhere in the Rhône Valley.

In the granitoid crust, phyllosilicate-rich fault gouges are prevalent in mature fault zones undergoing hydrothermal alteration and often exhibit lower frictional strength compared to framework minerals (e.g., qtz, fds) under deformation at room temperature. However, the mechanical behavior and deformation mechanisms of altered gouges under hydrothermal conditions are not fully understood so far.To investigate these effects, we conducted a series of experiments on three types of fault “gouge” material using a ring shear deformation apparatus. We used gouge mixtures obtained from (i) crushed granitoid ultramylonite, (ii) biotite- and (iii) muscovite-bearing gouges to represent quartzofeldspartic materials with (i) no alteration, (ii) high-temperature and (iii) low-temperature alteration, respectively (see Table 1 for the mineralogy). Deformation temperatures (T) ranged from 20-650°C, with a sliding velocity kept at 1 μm/s, and an imposed effective normal stress and pore fluid pressure at 100 MPa. At large shear strain (g ≈ 22-25) and T = 20-450°C, granitoid gouges consistently showed higher shear stresses (t = 73-81 MPa) than muscovite- (t = 47-69 MPa) and biotite-bearing gouges (t = 44-56 MPa). Granitoid gouges showed a decrease in t at T ≥ 450°C, while mica-rich gouges showed an increase in t with T at all tested conditions. Microstructurally, all gouges experienced strain localization into relatively fine-grained and dense principal slip zones (PSZs) at elevated T. The presence of newly percipitated minerals (e.g. bt, qtz) suggested the operation of dissolution-precipitation creep (DPC). However, the PSZs of granitoid and mica-rich gouges exhibited distinctive geometric features in their microstructure at 650°C. Granitoid gouges showed PSZs with ultrafine-grained (≤ 1 μm) relicts of porphyroclasts sparsely distributed within a dense matrix. In contrast, the PSZs of mica-rich gouges showed the anastomosing P-foliation of aligned micas with intervening shear band cleavages. Within these localized domains, quartz in mica-rich gouges exhibited larger grain sizes (1-4 μm) compared to those in granitoid gouges. Our observations indicate that in all tested gouges, frictional deformation gives way to grain-size sensitive creep mechanism as T rises, leading to the formation of fine-grained PSZs. We suggest that the ultrafine grain sizes in granitoid gouges promote DPC-accommodated viscous granular flow more efficiently, leading to the low shear stresses. In contrast, the strengthening of altered gouges with T was attributed to two factors: a less efficient DPC-assisted deformation due to generally larger grain sizes, and a less efficient viscous granular flow due to the development of foliation and shear bands inclined to the shear direction. Therefore, the mechanical behaviour of granitoids along the retrograde hydration-path depends not only on the evolving mineralogy, but also on microstructures and grain sizes.Table 1. List of Samples Used in This Study and Their Mineralogy According to Quantitative XRD. Sample Composition (wt%) Altreation type Granitoid ultramylonite 37% qtz, 49% fds, 8% bt, 6% ep No alteration Biotite-bearing natural fault gouge 35% qtz, 4% fds, 37% phl, 21% mus, 3% smc High-temperature Muscovite-bearing natural fault gouge 39% qtz, 5% fds, 38% mus, 11% ser, 6% chl, 1% cal Low-temperature Qtz:quartz, fds: feldspar, bt: biotite, ep: epidote, phl: phlogopite, mus: muscovite, ser: sericite, smc: smectite, chl: chlorite, cal: calcite

We review the results from twenty four experimental works conducted on the rheology of carbonates from the last fifty years to revisit the long-noted discordance in the experimental results from a range of limestones and marbles. Such an exercise is needed to bring together the various datasets generated in the twenty three years since the last major review, as many of them observe relationships that run contrary to existing rheological models. By revisiting the large data set, we find that most low and high stress experimental measurements can be explained by the combined effect of grain size and the molar fraction of magnesium carbonate (XMgCO3). Our results highlight that much of the calcite-dolomite series exists in a continuum of strength that changes with XMgCO3. In contrast to previous findings, we establish that diffusion creep in calcite is sensitive to both grain size and magnesium content, showing that an increase in XMgCO3 acts to weaken a rock. While in dislocation creep we confirm the observation that XMgCO3 has a strengthening effect but extend it beyond synthetic Mg-calcite samples to natural starting materials. Most notably our results suggest that when the composition of a carbonate is factored in then grain size can be shown to have a weakening effect in high temperature creep for fine grained rocks. This is the opposite finding to the currently accepted flow law for high homologous temperature deformation of calcite rocks where a decrease in grain size strengthens a rock. We contextualise these new results by combining them with data from natural shear zones to show that carbonates are much weaker than would be expected from previous flow laws in a crustal section. Ultimately our review provides new pragmatic flow laws for carbonates in the calcite-dolomite series for diffusion and dislocation creep.

Worldwide, fault zones in carbonates regularly host medium to large earthquakes including recent ones in the Mediterranean and Middle East. In addition to that, faults can control fluid flow by either acting as a conduit or seal for fluid pathways and should be considered in e.g., geothermal exploration. Hence, understanding the (micro-) structural evolution of these fault zones as well as fluid mediated geochemical processes involved in their dynamic deformation history allows to better address topics of societal and economic relevance ranging from seismic hazards to the exploitation of natural resources. Unfortunately, active in-situ deformation at depth is difficult to access, emphasising the need for investigations on suitable exhumed analogues.This study focuses on the microstructural and geochemical record of a recently exposed seismogenic dextral strike-slip fault zone in the seismically active southwestern Swiss Alps. Due to excellent outcrop conditions on glacially polished rock surfaces and a wide range of preserved tectonites and associated deformation structures, this particular fault zone provides a valuable record of potential paleoseismicity in carbonates. We combined microstructural analyses with micro-chemical and isotope data in order to reconstruct the spatio-temporal evolution of high-strain domains at variable crustal levels throughout exhumation. While the microstructural record allows us to differentiate between rate-dependent brittle and viscous deformation phases, we use the geochemical fingerprint to distinguish and characterize individual fluid pulses.Here, we present microstructural evidence of fast, possibly seismic, deformation along a principal slip zone. While injection structures containing fluidized material, suggest highest deformation rates as feasible for seismic events, repeated brittle deformation that was accompanied by the formation of cataclasites and calcite veins, hints towards fast seismic to sub-seismic rates.We also found that newly formed calcite crystals, in veins and linkage zones, show significantly decreasing δ18OSMOWvalues, as low as 5 ‰ δ18OSMOW, implying an influence of meteoric water. Clumped isotope thermometry of such calcites resulted in temperatures of 65-95°C, which are approximately 100°C lower than Tmax in the area. This suggests that the analyzed material did not record any potential shear heating. Moreover, the investigated tectonites have most likely formed along a retrograde exhumation path. In combination with detailed observations on the m- to 10er-m-scale our observations provide a dataset that allows direct comparison of different deformation processes and correlation of paleo-seismicity to fluid flow in fault zones. Further, we contribute to the longstanding discussion of differentiating microstructural evidence for seismic slip from slow or aseismic slip in carbonate hosted fault zones.

The U–Th–Pb system is a potential impactful tracer of fluid sources and pathways in the continental crust. Different rock types exhibit distinct U/Th/Pb ratios, and within a single rock, heterogeneities arise from different minerals having different U, Th and Pb contents. These differences result in distinct Pb isotope compositions over time, at the scale of mineral to whole rock. Fluids circulating in the continental crust thus inherit different Pb isotope ratios upon interaction with different rocks along their pathways. Feldspars dominate the granitic continental crust and typically contain tens of µg/g of Pb but negligible U or Th, and thus they retain their primary Pb isotope composition. However, feldspars are also readily altered by fluid–rock interaction processes, and they incorporate the Pb isotope composition of fluids with which they interact. Such modified feldspars can thus provide information on the nature of crustal fluids.This concept is applied to feldspars in post-Variscan mantle-derived granitoids from the Aar Massif (central Swiss Alps). In this setting, fluids circulated during Permian and Mesozoic rifting, and during the (Miocene) Alpine orogeny. The combination of Pb–Sr–O–H isotope data in hydrothermal epidote revealed that Permian and Miocene fluids had external sources and exploited various pathways to infiltrate the granitoids. Triassic seawater infiltration was inferred from biotite Rb–Sr data.Feldspar grains were separated from the granitoids, and subsequently leached to remove alteration minerals until they appeared transparent. Feldspar Pb isotope ratios were measured by solution MC-ICP-MS after acid digestion and ion exchange chromatography. The Pb isotope ratios in these leached feldspar fractions, reported here as 207Pb/206Pb ratios of 0.8249–0.8050 and 208Pb/206Pb ratios of 2.042–2.021 for direct comparison to LA-ICP-MS data of fluids, are more radiogenic than model values at the time of granitoid emplacement (ca. 300 Ma). This is attributed to post-magmatic processes resetting Pb isotope ratios of feldspars. This hypothesis is explored further by comparing the Pb isotope ratios of feldspars to that of Permian (207Pb/206Pb = 0.8326–0.8296; 208Pb/206Pb = 2.064–2.051) and Miocene fluids (207Pb/206Pb = 0.8118–0.7308; 208Pb/206Pb = 2.021–1.904), and to the Pb isotope evolution of the granitoids (whole rocks) from their emplacement until the present day.The agreement of feldspar Pb isotope data with those of Permian and Miocene fluids suggests that the fluids altered the initial Pb isotope ratios of feldspars, imparting a more radiogenic composition. However, the overlap of feldspar Pb isotope data with the Pb isotope evolution of the granitoids suggests that the Pb isotope composition of feldspars includes components inherited by redistributing Pb mobilized from variably U-/Th-enriched phases within the granitoids themselves. This suggests that the local, fluid-induced heterogeneities in Pb isotope ratios within the studied feldspars result from fluid-induced redistribution of Pb originating from the granitoids themselves, rather than by fluid-mediated addition of externally derived Pb. This hypothesis has implications for our understanding of Pb sources and redistribution – with possible enrichment into ore deposits – in the granitic continental crust.

Geological 3D modelling in metamorphic belts remains a significant challenge in structural geology due to both mathematical and geological complexities. These challenges stem from the need for software capable of interpolating polydeformed surfaces explicitly or implicitly, while at the same time addressing the geological and topological meaning of these surfaces, i.e., the “geological legend” of the 3D model.Traditional 3D geological modelling uses the boundary representation paradigm, where geological units are represented as hollow volumes bounded by discretized surfaces, typically stratigraphic boundaries or faults. Explicit interpolation methods generate these surfaces individually, possibly leading to inconsistencies. In contrast, implicit methods interpolate entire stratigraphic sequences in a single step, enabling faster workflows and ensuring mathematical consistency. Moreover, implicit methods produce a continuous (locally discontinuous at faults) volumetric “stratigraphic field” that assigns a scalar value representing a geological absolute or relative age, and boundaries are extracted a-posteriori (hence the name of the methods). Extensions of this approach, known as “GeoChron Model” or “time-aware geomodelling,” enable the assignment of ages to depositional, intrusive, or deformative events, linking the mathematical model to a well-defined sequence of geological events.Here we propose a workflow that combines implicit and explicit modelling to facilitate conceptual interpretation, ensuring topologically and geologically consistent 3D model reconstruction in metamorphic belts. These regions pose particular challenges because time-aware geomodelling is often inapplicable due to the ill-defined or heterogeneous ages of tectonic boundaries, lithologies in tectono-metamorphic units, and deformation-related features like metamorphic foliations.In our approach, 3D surfaces are analysed and labelled based on their topological relationships with surrounding geological objects in a preliminary conceptual modelling step, where both surface and volume perspectives are considered. Since boundary surfaces can have multiple roles depending on the geological context and might have been reactivated in polyphase deformation, it is essential to implement a systematic classification of volumes, that are distinguished as tectono-metamorphic, tectono-stratigraphic, or intrusive units (implying different boundary surfaces).A critical strategy is the use of a time-aware legend wherever possible, such as for geological bodies with known absolute or relative ages. When age information is unavailable, as in very old basement complexes, or for coeval but spatially distinct units (e.g., ophiolite sequences emplaced at different crustal levels), a reasonable pseudo-stratigraphy is adopted (e.g. using relative structural levels instead of stratigraphic age).Our combined workflow provides a structured and replicable methodology for addressing the unique challenges of 3D geological modelling in metamorphic belts. By systematically handling complex geological features, topological relationships, and polydeformed surfaces, it ensures more consistent and reliable geological models. This framework is expected to enhance interpretations in future studies and advance our understanding of metamorphic belts.

The base data for any seismotectonic study consist of accurate and precise hypocenter information, consistent magnitude estimates, and focal mechanisms derived either from the analysis of first-motion (FM) polarities or moment-tensor (MT) inversions. In this study, we present a new baseline seismotectonic earthquake catalog of Switzerland and surrounding regions (SECOS24), which covers the Central Alps (CA) region between 45.4°N/5.6°E and 48.4°N/11.1°E. The SECOS24 catalog includes instrumental seismicity routinely detected and located by the Swiss Seismological Service (SED) between 1975 and 2024 (about 49 years). For the digital era of the SED bulletin (phase picks and seismograms available in digital form) starting in 1984, hypocenters were consistently relocated in absolute terms using a recent Pg and Sg 3-D velocity model. Starting from these improved hypocenters, double-difference relative relocations were performed at different scales (single clusters as well as at regional scales), combining differential times from manual picks and waveform cross correlations. Based on available solutions and resulting location quality, a preferred solution was selected for each hypocenter of the SECOS24 catalog, in order to provide the maximum possible hypocenter accuracy and precision for each event. The SECOS24 catalog contains about 36,000 earthquakes with magnitudes ranging between ML -0.7 to 5.3. In addition to ML, the catalog reports complementary magnitudes for a subset of events. For 71 events, an MW magnitude was derived from a revised MT inversion for events starting in 1999. For events since 2009, a spectral MW was calculated if possible. This magnitude compilation allows for the assessment and improvement of existing ML-MW scaling relations. Finally, we linked each hypocenter with the revised MT catalog as well as solutions of an augmented FM catalog, which contains 492 high-quality, manually reviewed mechanisms based on P-wave first-motion polarities. The SECOS24 catalog is used for down-stream seismotectonic analysis of the CA region. In this presentation, we show updated maps of seismicity and moment release in the CA and their foreland. In addition, we provide updated maps of deformation regimes and stress orientations derived from the analysis and inversion of the FM data. Besides previously known features, the SECOS24 catalog reveals several new features in the CA and their foreland like newly imaged seismogenic fault zones, lateral changes in the deformation regime along the Alpine Front of the CA, and ongoing shortening at shallow crustal levels in the Jura fold-and-thrust belt. In addition, the updated stress inversion provides more stable results and, in several places, higher spatial resolution in comparison to previous studies. The SECOS24 catalog therefore contributes to an improved understanding of present-day tectonic processes in the CA region and is crucial input for next-generation seismic hazard models of the region.