Chaotic deposits are common in convergent margins and are crucial for understanding subduction dynamics and basin evolution. This study re-evaluates key chaotic deposits within the Western Ligurian Flysch, focusing on the Colla Domenica Shales and the overlying Leverone Formation along the European margin of the Piemontese–Ligurian Ocean. Traditionally interpreted as Cretaceous–Paleocene trench sediments influenced by mud diapirism, these deposits are reassessed using an integrated multidisciplinary approach combining fieldwork, sedimentological analysis, biostratigraphy, petrography, and geochemistry. Results indicate that chaotic intervals represent Paleocene–Eocene Mass-Transport Deposits deposited within a remnant oceanic basin developed in response to the subduction of oceanic crust. Key features such as disorganized clast distribution, irregular clast shapes, size variability, erosional bases, and matrix-supported fabrics, point to high-energy, gravity-driven processes at the accretionary prism front. Basalt clasts exhibit a Transitional-MORB signature, thus suggesting early oceanic magmatism later incorporated into the prism and remobilized during mass-failure events. Petrographic observations show a stratigraphic upward increase in sandstone immaturity, indicating shorter transport distances as the basin narrowed. Provenance analysis reveals siliciclastic sediments likely sourced from the Sardinia–Corsica segment of the European margin, while ophiolitic clasts suggest contributions from the prism interior. Despite local tectonic overprinting, structural data do not support a tectonic-mélange origin; instead, these deposits represent a polygenetic mélange formed by mass-transport events interlayered with basin-plain turbidites during trench infilling. These findings refine our understanding of chaotic deposits in collisional settings, shedding light on depocenter migration, sediment routing, and prism dynamics during the closure of the Piemontese–Ligurian Ocean.
Bone beds represent key archives for reconstructing coastal ecosystems, yet their depositional environments are often debated. Here we present an integrated sedimentological, palaeontological, ichnological, palynological and geochemical study of the Late Triassic Niederschönthal bone bed (Belchen Member, Klettgau Formation) in northern Switzerland. The bone bed occurs as a thin, laterally discontinuous conglomeratic layer resting on an erosive surface. It is dominated by coprolites, vertebrate remains, reworked lithoclasts and micritic pebbles. The vertebrate assemblage is diverse and dominated by osteichthyans and chondrichthyans, with subordinate phytosaurs and temnospondyl amphibians, alongside abundant charcoal and plant debris. Sedimentological features, including bored micritic pebbles with pyrite-rich rims, combined with stable isotope data, indicate deposition under sulfate-rich, at least polyhaline conditions. Palynological assemblages dominated by hygrophilous spores and characteristic Rhaetian dinoflagellates constrain the age to the middle Rhaetian and document a diverse lowland vegetation adapted to a humid environment. The faunal composition, coprolite assemblage and sedimentary structures point to repeated reworking and concentration of vertebrate remains during short-lived high-energy events. We interpret the Niederschönthal bone bed as having formed in a muddy coastal plain to lagoonal environment with fluvial-estuarine to marine channels having been periodically affected by small-scale transgressive pulses. This study reconciles earlier conflicting interpretations by demonstrating that the bone bed records a complex interplay of terrestrial, freshwater and marine influences rather than a fully marine or purely continental setting.
The remelting of felsic gneisses, migmatites and granite during a later orogenic cycle can produce rocks of different age with comparable field appearance, microstructure, mineralogical and chemical composition. Here, we compare two gneiss units in the Aar Massif (an External Crystalline Massif of the Central European Alps, Switzerland), which include migmatites and rocks with meta-igneous textures: the Erstfeld Gneiss Complex in the northern part and the Strem Granite unit in the south-eastern part of the Aar Massif. Both units show a range in zircon U-Pb dates of several hundred million years, which seemingly is caused by the presence of two melting events of Ordovician and Variscan age. A distinction between these two melting events is not possible based on field observations, but it becomes evident via in-situ U-Pb geochronology of distinct zircon growth domains identified through cathodoluminescence imaging. An Ordovician age group (ca. 455 Ma) is well preserved in zircon of both units. However, only in the southern unit is a Variscan overprint (ca. 310–315 Ma) recorded in zircon rims and by euhedral anatectic allanite with a U-Pb age of 315.1 ± 3.7 Ma. Geochronology and intrusive field relationships suggest that, during the late stage of the Variscan orogeny, Ordovician migmatites in the Strem Granite unit were remelted, forming a generation of anatectic granites that had not been previously identified. The remelting of Ordovician migmatites during Variscan high-grade metamorphism likely occurred at the minimum melt temperatures of the quartz-feldspar system through fluid-assisted melting. Due to the absence of any signs of dehydration melting, we propose that external water was advected through numerous trans-crustal shear zones that were active during the late stage of the Variscan orogeny. This melting episode is bracketed by pulses of late-orogenic magmatism between ca. 335 and 309 Ma. The initial Hf isotope composition of zircon provides evidence for multiple recycling of the late Proterozoic to early Ordovician chemical inheritance, restricting the addition of juvenile components to the latest stages of Variscan magmatism.
We explore the potential to monitor the evolution and extent of structurally controlled rock mass damage in faulted Opalinus Clay shale at the Mont Terri Underground Rock Laboratory (MT URL) using coda wave interferometry. In a dedicated experiment, a borehole was drilled through the main fault of the MT URL in October 2020. The borehole was continuously ventilated for 21 months and then resaturated from July 2022 onward. We performed repeated time-lapse seismic experiments using 12 acoustic emission sensors and 12 ultrasonic transmitters distributed across four monitoring boreholes. The first-arriving P waves remained largely unchanged, and their velocities provide valuable insights into the initial health state of the Opalinus Clay. However, the later-arriving coda waves show clear changes in seismic velocity and waveform. Using probabilistic inversion, we link these changes to variations in rock saturation and pore pressure, as well as to geometric alterations of the rock mass surrounding the experimental borehole caused by new fracture formation, slip along pre-existing tectonic faults, and borehole overbreaks.
Accurate 3D geological models are instrumental to the development of reliable digital twin frameworks for underground research and engineering, yet their development is hindered by the complexity of integrating multi-scale, multi-source, and heterogeneous datasets. Here, we present a set of comprehensive, multi-scale geological models of the area surrounding the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG—Bedretto Lab; Central Swiss Alps). Using an implicit geological modeling approach, we computed three interconnected models that capture the regional geologic and tectonic framework, the distribution of the main deformation structures, and domains with different structural and petrophysical properties along the Bedretto tunnel. These models integrate geological data from regional maps, remote sensing lineament analyses, field surveys, and tunnel-scale observations to produce georeferenced 3D meshes and visualizations. Our models can be adopted to visualize the geometry of deformation structures affecting the Rotondo granite and the Gotthard nappe hosting the Bedretto Lab. These models are instrumental for efficient outreach activity and communication in multidisciplinary research environments, such as those characterizing underground research facilities. They also provide a quantitative, georeferenced, and geologically sound framework to understand the spatial distribution of anisotropic properties in the underground. The models offer a high-resolution foundation for investigating hydro-seismo-mechanical processes, informing experimental design, and enabling advanced simulation workflows within a digital twin environment. 3D geological models are meant to be dynamic representations of the underground environment, evolving with the increasing amount of available knowledge resulting from geological, geophysical, monitoring, and modeling efforts.
Today, natural disasters in alpine valleys pose a continuous threat to urban areas and infrastructure. Investigating past mass movements and assessing their return periods enhances our ability to predict and mitigate future hazards. The Sierre landslide in the Rhone valley (Canton of Valais) is one of the largest yet least explored Alpine landslides. Spanning 12 km in length and with a present-day volume of 0.9 km3, the landslide's timing was previously unknown. A minimum bound of about 9 ka was inferred indirectly from 14C ages of wood found in channelized debris-flow deposits that incise the landslide deposit. In this study, we used detailed Quaternary geomorphological mapping, surface exposure dating, and dynamic modelling to determine when, how, and why the Sierre landslide occurred. Field investigations included mapping the landslide mass and release area in detail. To date the landslide deposits, 15 rock samples, 13 from boulders and 2 from the detachment surface, were collected and analyzed for cosmogenic 36Cl. The pre-landslide topography was reconstructed, and the runout was modeled using DAN3D (R). We found that the Sierre landslide occurred at 10.7 +/- 1.5 ka ago, during the transition from the Younger Dryas to the Early Holocene. Contrary to earlier hypotheses suggesting glacier interaction, our results demonstrate that the landslide was primarily a gravitational collapse governed by material properties and pre-failure topography. Dynamic modelling highlights the influence of low friction coefficients in the valley sediments, enabling the long runout distance. These insights challenge existing paradigms of glacier involvement in the Sierre landslide and contribute to understanding Alpine post-glacial landscape evolution. This study underscores the importance of investigating past mass movements and landscape evolution in alpine valleys to better assess and mitigate future hazards.
The Swiss Journal of Geosciences (SJG) is the scientific full Open-Access journal of the Swiss Geological Society. First published in 1888 as “Eclogae Geologicae Helvetiae”, it has a long tradition. From the 1920s until 2006, it was published in collaboration with “Birkhäuser”, a scientific publisher based in Basel which was sold to Springer in 1985. In 2006, the SJG merged with the «Schweizerische Mineralogische und Petrographische Mitteilungen (SMPM, first published in 1921), after which the journal was renamed to Swiss Journal of Geosciences (see Schmid, 2006; Schmid et al., 2007). From 2007 (Vol. 100) to 2019 the SJG was published with Springer, and since 2020 it has been published as a full Open Access Journal with SpringerOpen.
A significant part of the work of as reported by Argand (Comptes rendus de la XIIIe session du Congrès géologique international, Bruxelles 1922, Liège, fascicule, 1924a) «La tectonique de l’Asie» concerns the structure and kinematics of the Alps and the Mediterranean. Argand presented some entirely innovative concepts on the kinematics of these areas, showing for the first time, large-scale rotations of microplates and the structure of orogens including both the crust (Sial) and the mantle (Sima). In contrast to his previous alpine works, which were very rapidly accepted and emulated by the scientific community, these new interpretations of the Alpine and peri-Mediterranean chains were partly criticized, but mostly ignored. The scientific community continues to work and publish on these subjects disregarding the new concepts of as reported by Argand (Comptes rendus de la XIIIe session du Congrès géologique international, Bruxelles 1922, Liège, fascicule, 1924a) who presented the very first palinspastic reconstruction of the peri-mediterranean realm in addition to “lithospheric” sections across its chains and basins. Only after the acceptance of Plate Tectonics, geologists and geophysicists discovered on the base of paleomagnetic analyses that the Apennines, Sardinia, and Corsica had undergone anticlockwise rotations throughout the Miocene, thus confirming, the interpretations of Argand, presented in the “Tectonique de l’Asie”. However, most of these modern studies of the early 1970’s did not quote Argand, and still did not propose any lithospheric-scale model, nor paleogeographic reconstructions accounting for the entire western Mediterranean area, half a century after as reported by Argand (Comptes rendus de la XIIIe session du Congrès géologique international, Bruxelles 1922, Liège, fascicule, 1924a).
The Corbeyrier and Yvorne mass movement events that happened in the year 1584 have mainly been studied at the surface level such that the shallow subsurface structure remains largely unknown. Geophysical measurements allow for insights into the physical properties of the subsurface including the geometry of deposits after such events. We applied three methods with the specific interest of obtaining information about the spatial variation of thickness and lithology of the mass movement deposits: the horizontal to vertical spectral ratio of ambient seismic noise (54 measurements), electrical resistivity tomography (2 profiles) and ground-penetrating radar (7 profiles). These measurements were then complemented with a physical sample obtained from drilling a 10.6 m long core in the Luan forest. We found that the mass movement deposits contain angular clasts of gravel and cobbles in a clay matrix (~ 30%). We also saw a thinning of the deposits downslope such that they reached a thickness of 3.5 m in the Luan forest and a thickness greater than 10 m (estimated between 50 and 100 m) near the source region at Plan Falcon. We identified two areas which call for further investigation in terms of the possibility of sediment mobility of the deposits in the event of an earthquake: Plan Falcon and the mostly bare scree slope just below.
The present study investigates the coral bioherm and the associated «Echinodermenbrekzie» of the «Gisliflue Reef» at Gisliflue and Homberg, located northeast of Aarau, Switzerland. Sedimentological and palaeontological analyses were carried out on four outcrops along the prominent ridge, two outcrops each at Gisliflue and Homberg. Four stratigraphic sections were analysed palynologically using detailed dinoflagellate cyst stratigraphy to determine the biostratigraphic age of the coral reef development and the deposition of the coarse, echinoderm-rich, bioclastic limestone to the west. The investigation reveals that the lower part of the «Gisliflue Reef» consists of marly, strongly arenitic limestone with isolated platy corals, transitioning upwards into rock-forming platy corals such as Isastrea and Thamnasteria that form the distinctive cliff up to 20 to 40 m high. The top few metres of the summit of Gisliflue feature mainly branching corals, capped by a bored hardground that has formed at the earliest following the end of coral growth. The bioherm can be traced westward to the midsection of Homberg before it abruptly wedges out and transitions into an arenitic, bioclastic limestone that can be traced to the western end of the Homberg, where it has a fairly constant thickness of around 8 to 12 m. This stratigraphic succession, referred to as «Echinodermenbrekzie», is recognised both in the literature and on geological maps. Regional comparisons with neighbouring stratigraphic sections indicate a gradual lateral thinning of the «Echinodermenbrekzie» to the west. The palynological analyses revealed well-preserved dinoflagellate cysts in many of the samples, which date the «Gisliflue Reef», including the «Echinodermenbrekzie», to the Early Bajocian Humphriesianum Zone. The above following oolitic limestones of the Hauptrogenstein, which directly overlie the hardground at the summit of the Gisliflue, are dated to the Late Bajocian, Niortense Zone. Within the palynological samples a new stratigraphic marker species, Hypolytodinium argoviense, gen. nov. sp. nov. is formally described. The species is considered a useful stratigraphic marker for the late Early Bajocian Humphriesianum Zone, with its main occurrence in the Romani to Humphriesianum subzones.
Large areas of both the external Helvetic Aar Massif and the internal Helvetic Gotthard Nappe in the pre-Mesozoic basement of the European Alps are composed of felsic gneiss, augen-gneiss and metagranite, traditionally called “orthogneiss”. Based on the scarce existing geochronology, they have been tentatively associated with an active continental margin of late Ordovician age. New zircon LA-ICP-MS U–Pb age determinations confirm the late Ordovician age for the Gärsthorn Gneiss Complex of the southern Aar Massif and the Streifengneis Complex of the Gotthard Nappe, yielding a range of mean ages for individual samples from 441 to 454 Ma. The chemical characteristics of this slightly peraluminous gneiss association, the ubiquitous presence of inherited Proterozoic to Cambrian cores in zircon, and the widely variable Hf isotopic composition of inherited cores as well as of Ordovician growth zones point to a siliciclastic metasedimentary protolith. Our conceptual model involves the accumulation of Gondwana-derived detritus in a massively overthickened fore-arc wedge during the early Ordovician. This latter was molten during the late Ordovician, a cryptic mafic underplating during slab rollback and extension possibly triggering the anatexis. The existence of oscillatory-zoned high-uranium zircon rims around the Ordovician growth zones yielding a Mississippian-age ( 308–315 Ma) points to renewed melting of these rocks during the Variscan Orogeny and metamorphism.
Late Oligocene and Miocene east–west decoupling of the Alpine retro-wedge evolution along the Giudicarie fault system and the associated late-stage shortening within the eastern Southern Alps (ESA) are key features of the Neoalpine, post-collisional Adria-Europe convergence. A new thermochronological N-S transect across the Trento platform in the western ESA suggests a 25 Ma onset of exhumation in the Neoalpine fold-and-thrust belt. This requires a longer lasting transfer of shortening from the Eastern Alps, north of the Periadriatic fault system, into the evolving ESA, rather than a single and distinct Middle Miocene shift to a coupled state. Still, the highest exhumation rates are observed between 17 and 10 Ma, linking rapid ESA exhumation to the termination of folding within the Sub-Penninic interior of the Tauern Window. Prior to the Neoalpine evolution, the oblique Paleogene collision of northeast-Adria and Europe entailed Dinaric top-southwest thrusting on the Adriatic microplate. An Eocene antiformal basement structure and an assumed blind fault in the northwestern ESA, revealed by new thermochronological data, mark the northwestern extend of the Dinaric fold-and-thrust belt. Apart from Dinaric and Neoalpine exhumation related cooling, Adria was affected by Eocene to Oligocene subduction-related magmatism, Late Triassic–Early Jurassic extension, middle Triassic strike-slip tectonics, and Permian extension. Each event, as well as the Permian to Cretaceous burial, resulted in the thermal perturbation of the Adriatic crust and its sedimentary cover. Statistical analyses of apatite fission-track single-grain ages emphasize the imprint of the post-Permian thermal evolution, as detrital ages and magmatic formation ages are overprinted or obliterated throughout the study area. Jurassic and Cretaceous apatite fission-track data are attributed to a widespread exhumed partial annealing zone.
We present a completely revised and extended database of the crustal present-day orientation of the maximum horizontal stress SHmax for northern Switzerland and neighbouring regions. We analysed 32 deep boreholes located in the Molasse Basin of Switzerland from which we interpreted > 30 km of image and caliper logs and picked from these the stress-induced borehole breakouts, drilling induced tensile fractures, and petal centerlines. We also used 105 induced fractures from 139 microhydraulic fracturing tests in 8 boreholes. The interpretation of the data resulted in 64 data records of the SHmax orientation. In addition, we also used an extended and revised dataset of 704 earthquake focal mechanisms computed by the Swiss Seismological Service and derived SHmax orientations from these as well. Combining these data with data records from the World Stress Map database release 2016 resulted in a dataset with 948 data records. The overall regional pattern of the SHmax orientation in the Alpine foreland of Switzerland shows a counterclockwise rotation of approximately 50° from N–S in the northeast to NW–SE in the southwest supporting earlier interpretations that the SHmax orientation is primarily controlled by the gravitational potential energy of the Alpine topography. Beyond this large-scale pattern, no further lateral changes of the SHmax orientation imposed by structural elements or rock property contrasts are resolved due to the resolution limit of the dataset. On average, there is only one reliable data record in Switzerland per 140 km2 with predominant standard deviations of ± 20–25° for individual data records. Thus, small SHmax rotations as well as rotations on lateral scales of a few 10s of km are typically not resolved. We also investigated changes of the SHmax orientation with depth with an emphasis on a potential impact of a mechanical decoupling horizon between the Mesozoic sediments and the underlying basement, which is located in the Middle Muschelkalk (Triassic). For this we used a sub-dataset of 88 SHmax orientations located in northern Switzerland where we have a good coverage of data records in the sediments (n = 43) and in the basement (n = 45). The mean SHmax orientation in the sediments is 166 ± 12° and in the basement 159 ± 22° indicating that a potential decoupling horizon either does not leave an imprint in the SHmax orientation or that decoupling is not acting on a regional scale.
The northern Valaisian Alps represents a glacially overprinted landscape, characterized by abundant glacial deposits and landforms. Well-preserved moraine systems, commonly found in the region, were deposited by glacier fluctuations after the Last Glacial Maximum (LGM). In this study, we focus on the glacial evolution of the tributary valleys of Belalp and Luesgenalp, west of the Great Aletsch glacier, during the Lateglacial and Early Holocene. To reconstruct the glacier advances, a combination of geomorphological mapping, surface exposure dating with cosmogenic 10Be, and glacier reconstruction were used. Our results indicate that glacier fluctuations occurred at 12.0 ± 0.9 ka in the Belalp valley and 12.0 ± 1.0 ka in the Luesgenalp valley during the Younger Dryas cold phase. Based on the glacier reconstruction, an equilibrium line altitude (ELA) of 2700 m asl was estimated for the maximal extent of these paleoglaciers. ELA depressions of 330 m to 430 m relative to the Little Ice Age for the Unnerbaech paleoglacier in the Belalp valley and 400 m for the Hostock paleoglacier in the Luesgenalp valley were calculated, corresponding to annual temperature decreases of 2.1 to 2.8 °C and 2.6 °C, respectively. The precipitation pattern shows no significant change in the amount of precipitation between YD and today. Our findings are consistent with the YD paleoglaciers documented throughout the Alps and provide insights into the climate dynamics during the Egesen stadial in the Alps. Additionally, our findings contribute to the broader understanding of glacial responses to climatic fluctuations.
This report summarizes the seismicity in Switzerland and surrounding regions in the years 2019 and 2020. In 2019 and 2020, the Swiss Seismological Service detected and located 1660 and 1407 earthquakes in the region under consideration, respectively. The strongest event in the analysed period was the ML 4.3 Elm/Steinibach earthquake, which occurred in the Glarus Alps in eastern Switzerland on October 25, 2020. Received felt reports suggest intensities up to degree V for this earthquake. Modelled and instrumentally measured ground motions, however, hint at intensities approaching degree VI–VII at the epicentre. Derived focal mechanisms and relative hypocentre relocations of fore- and aftershocks image a dextral WSW–ENE to W–E striking multi-segment strike-slip fault zone with a total length of about 3.5 km. Well-constrained focal depths of 1–2 km indicate that the fault zone likely locates in the uppermost part of the crystalline basement of the eastern Aar Massif. Another exceptional earthquake sequence occurred between Anzère and Sanetschpass in the Rawil Depression in November 2019. Within 10 days, more than 300 earthquakes occurred in this cluster and 16 of those events reached ML magnitudes between 2.5 and 3.3. Focal mechanisms and relative hypocentre relocations derived for this sequence image the reactivation of a contractional stepover. The imaged stepover confirms the previously proposed segmented nature of the Rawil Fault Zone north of the Rhône valley in SW Switzerland. The ML 4.2 Novel earthquake, which occurred in the Préalpes region south of Lake Geneva on May 28, 2019, provides additional evidence for the recently proposed domain of NE–SW oriented extensional to transtensional deformation along the Alpine Front in the transition zone between Central and Western Alps. Evidence for transtensional deformation along the SW edge of the Mont-Blanc Massif is provided by another remarkable earthquake cluster near the Grandes Jorasses Mountain in the border region between France and Italy. The transtensional deformation of the Hegau-Bodensee Graben in the northern foreland is revealed by a vigorous earthquake sequence on the Bodanrück Peninsula in southern Germany in 2019. Finally, evidence for unusually shallow seismicity in the domain of the Dent-Blanche nappe is provided by the ML 3.5 Arolla earthquake. In conclusion, the seismic activity during the period 2019–2020 is exceptional in terms of absolute numbers of earthquakes as well as number of events with ML ≥ 2.5.
This paper presents a thermochronological study of the Western European basement in the Maures-Tanneron massif (MTM), using zircon and apatite fission-track data, in addition to apatite (U-Th-Sm)/He analyses. The combination of these methods with inverse thermal modelling allows us to trace the thermal history of this massif from the Late Triassic to the present day. The study identifies several thermal events that are linked to two major tectonic phases at 120–40 Ma and 40–15 Ma. These new results prompt us to re-evaluate the thermal evolution and exhumation of Western European basement of the Provence region. We distinguish four episodes. (i) A period characterized by constant temperature contemporaneous with Triassic magmatic activity and Tethys rifting (ii) a period of sedimentary burial heating of the MTM associated with the Cretaceous Pyrenean rift evolution (iii) subsequent N–S Pyrenean inversion at 75 Ma, causing cooling and exhumation of the MTM, (iv) opening of the West European rift system and the Liguro-Provençal basin, which resulted in heating from 35 to 15 Ma and post 15 Ma cooling of the MTM. This study also provides insights into the paleogeography of the MTM and demonstrates its evolution at the cross-roads between the Pyrenean and Alpine orogens.
In the context of a project of the International Continental Scientific Drilling Program (ICDP) (DOVE; Drilling Overdeepened Alpine Valleys), a series of boreholes were drilled into buried overdeepened glacial troughs in the central and eastern part of the northern Alpine foreland. The sedimentary records of these overdeepenings, reaching back to the Middle Pleistocene, are essential archives for paleoclimate and a key to better understanding past glaciations and landscape evolution. As part of the project, an over 250 m long succession of unconsolidated Quaternary sediments was recovered from the Basadingen Trough (ICDP 5068_2, NE Switzerland), belonging to the NW part of the former Rhine Glacier’s foreland lobe. The drill site is positioned on a high-resolution 2D seismic line, serving as the basis for a sequence and facies analysis. Acoustic wire-line logging data (vertical seismic profile—VSP) directly links the sediment succession with the seismic data, allowing the establishment of a detailed and unifying seismic- and core-based glacial sequence stratigraphy dividing the strata into chronostratigraphically distinct sedimentary units. Based on this stratigraphy, the overdeepened valley fill could be grouped into three overdeepened glacial sequences, reflecting three pulses of glacial advance and retreat. Furthermore, a 3D model of a segment of the Basadingen Trough was created by combining the 2D seismic lines with the local geological information (i.e., geological maps, existing bedrock models, and drill-logs from core and flush drillings), visualizing the shape of the initial bedrock incision, the multiphase trough-infill architecture, and the overlying non-overdeepened cover. A generic model for a glacio-seismic sequence is developed that underlines the benefits of combining complementary geological and geophysical data in these highly complex depositional settings. The close link of these sequences to glacial advance-retreat cycles contributes to the development of a local glaciation model, as shown for the Basadingen Trough. This approach can be applied to other similar settings in formerly glaciated areas.
Obtaining precise pressure–temperature-time constraints on the history of exhumation of orogenically thickened crust using rock-forming minerals of greenschist-facies rocks can be a challenging task. Rare examples exist where structurally distinct hydrothermal mineralisations have been used to pin-point specific stages during this evolution. This study combines hydrothermal fissure-quartz fluid and solid inclusion data with Ti-in-quartz thermometry, solute thermometry, and fissure monazite-(Ce) Th-Pb ion probe dating in order to establish a link between hydrothermal mineral crystallisation and major faulting events in the Grimsel Pass study area, central Aar Massif, Switzerland. Six fluid inclusion populations in quartz are distinguished in the older, steeply NNW-dipping fissure at the well-known Zinggenstock locality, four can be identified in quartz in younger, vertical fissures. All data together constrain formation and subsequent stepwise growth and evolution of the fissures to a P–T-t range of 450 °C/440 MPa and 300 °C/240 MPa between c. 15 and 7 Ma. In quartz zones containing rutile-whiskers in fluid inclusions, Ti-in-Qtz thermometry yields temperatures comparable to fluid inclusion solute thermometry. The combined data indicate that the oldest cleft quartz generation formed c.15 Ma ago during reverse faulting at 450 °C/440 MPa. A major change in the direction of the regional stress field linked with onset of dextral strike-slip movements along the Rhone-Simplon-Centovalli fault system then led to predominant dextral strike-slip faulting starting at c. 12–11 Ma, at P–T conditions between 375 °C/320 MPa and 330 °C/230 MPa. At Zinggenstock, the original cleft becomes overprinted by sinistral shear zones, and fluid advection at 330 °C/230 MPa. This CO2-bearing fluid led at the Zinggenstock location to the formation of white mica (muscovite-ferriphengite) at the expense of chlorite. At Oberaar, renewed dextral strike-slip reactivation occurred between c. 10 and at 7 Ma at conditions of 330 °C/230 MPa to 300 °C/240 MPa. Our data document variable stress regimes, locally associated with focused fluid flow, across an approximate depth interval of 16.3–8.5 km ( 440 to 230 °C) during unroofing of the orogenically thickened crust. Hydrothermal mineral formation ages precisely constrain the chronology of successive deformation events, thus offering valuable constraints for unravelling the mechanisms of tectonically and buoyancy-driven exhumation of peripheral domains of the NW European Alps. Together, these data permit to estimate exhumation and cooling rates independent of thermochronology.
