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.
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.
Serpentinite-hosted carbonate rocks (i.e., ophicarbonates) are an important rock type for the deep C cycle because they can occur either in the slab or in the mantle wedge. We present a case study of ophicarbonate rocks from the Zermatt-Saas unit, Western Alps, that were subducted up to eclogite facies conditions at 2.5 GPa, 560 °C. In the study area, ophicarbonates overlie a large body of partially dehydrated serpentinites. This allows us to understand whether fluids released from the serpentinites infiltrated the ophicarbonates or not, and to what extent decarbonation reactions occurred in an open or closed system. We investigated three carbonate-bearing rock types: ophicarbonates, olivine-carbonate veins, and a talc-magnesite reaction rind at the contact between ultramafic and mafic/felsic lithologies. Our petrological and geochemical investigation, as well as thermodynamic modeling, reveal that the metamorphic evolution of the ophicarbonate was in a closed system, where calcite/aragonite was replaced by metamorphic dolomite and diopside, and that this reaction is nearly CO2 conservative, with the released fluid composition close to pure water. Limited carbonate mobility is indicated by the occurrence of minor olivine-carbonate veins. In situ LA-ICP-MS trace element analysis shows that carbonate in veins is most likely sourced from the ophicarbonates suggesting CO2 transport on the 10 m scale. The silicate-oxide-sulfide redox buffering assemblage indicates that both ophicarbonates and olivine-carbonate veins are equilibrated at redox conditions at or below FMQ. Field and thermodynamic modeling show that C-rich fluids circulated during exhumation along major structures and/or lithological interfaces. This leads to the formation of metasomatic talc-magnesite rocks during early exhumation between 9 and 13 kbar and 530–460 °C, at XCO2 between 0.007 and 0.009. Our study demonstrates that in the absence of external fluid infiltration, carbonates in ultramafic lithologies are stable at subduction zone conditions and can efficiently return C to the deep mantle.
The Baden-Baden thermal springs, among the hottest in Germany, emerge on the south-eastern slope of Florentinerberg, c. 25 m above the Oos valley floor. These Na-Cl-rich waters, with temperatures up to 69 °C, originate from a deep reservoir within the crystalline basement, likely the Nordschwarzwald batholith. New investigations, including hydrochemistry, isotopic data, geothermometry, and structural geological data reveal a deep origin for these waters with reservoir temperatures of c. 176 °C as constrained from various methods. Although the thermal waters (springs, boreholes) emerge from different lithologies (granites, metamorphic schists, Upper Carboniferous rocks), major and trace element concentrations are very similar implying no or only little impact of the different lithologies. The thermal waters are of Holocene age, recharged by meteoric water in c. 900 m asl. Holocene age is backed up by recalculated 14C data yielding a mean residence time of 10,800 years. Hydrochemical and isotopic data indicate interaction with granitic rocks in the subsurface. NE-trending structures in Baden-Baden likely act as hydraulic barriers forcing the thermal waters to the surface. While none of the faults in the thermal spring area is favorably oriented in the stress field it is suggested that the steep SE-plunging intersection of their damage zones facilitate their ascent.
Understanding temporal shifts of thrust transport direction and the interplay between thrusting and normal faulting during mountain building is important for better understanding orogeny. Current tectonic models of the Alps envisage Cretaceous E–W directed thrusting and subsequent extension in the same direction, mainly preserved in the upper plate (Austroalpine unit), followed by Paleogene N–S shortening. The Austroalpine-Pennine boundary region is at the transition between dominantly E–W and N–S directed orogenic movements. This study focuses on metabasite rocks of the Pennine Avers nappe, which retain evidence for early E–W directed shortening extending into the Eocene, thus conflicting with the standard orogenic models. Our new kinematic and geochronological constraints from the Avers nappe demonstrate that top-to-the-W nappe imbrication progressed into the South Pennine realm under blueschist facies conditions. Rb–Sr multimineral isochron ages constrain the waning stages of top-to-the-W shear between 47.26 ± 0.26 and ≥ 43.5 ± 0.6 Ma (2σ uncertainties). Subsequent deformation during incipient decompression from blueschist-facies metamorphism associated with N–S shearing occurred between 41.1 ± 1.7 and 40.7 ± 1.6 Ma. A summary of previously published geochronological and kinematic data shows that Cretaceous to Eocene (until ≥ 43.5 ± 0.6 Ma) deformation is best described by an overcritically tapered orogenic wedge model. The subsequent deep underthrusting and underplating of the distal European margin is considered to have caused a change in orogenic wedge dynamics, leading to extruding wedge tectonics associated with N–S shortening.
Abstract The Basel-1 geothermal deep well has been drilled in 2006 to a final depth of 5 km. The recovered core material from 4.9 km depth shows coarse grained biotite-hornblende quartz-monzodiorite from the Variscan basement. The primary igneous rock is locally altered and contains prehnite, pumpellyite, mica and chlorite as major alteration products. Locally small amounts of hydrogarnet formed from pyrite oxidation and fluorine derived from the alteration of primary F-rich biotite. The local low-grade alteration products are consistent with the in-situ measured temperature of about 200 °C. The assemblage of low-grade minerals formed in distinct zones separated by sharp reaction fronts from the primary monzodiorite. The bulk of the alteration zones may have formed from reaction of the monzodiorite with the pre-drilling formation fluid. However, also the external stimulation fluid rapidly readjusted its composition by reaction with the rock at depth. This follows from the temperature derived from fluid composition thermometers applied to recovered stimulation fluid which is consistent with measured temperatures at depth.
Abstract A displaced segment of the Late Triassic–Late Jurassic Greater Adriatic margin of the Neotethy Ocean was investigated in NE Hungary. In this area, the Mesozoic basement is largely covered by the Palaeogene—Miocene infill of the North Hungarian Palaeogene Basin and the Pannonian Basin. Micropaleontological, sedimentological and structural investigation of more than thirty wells resulted in the detailed characterisation and 3D depositional model of the area, which may have formed in the eastern continuation of the Slovenian Basin or in a similar sub-basin. The sedimentation in its Bajocian–early Callovian extensional half-grabens was characterised by pelagic limestones followed by dark shales with sandstone intercalations. Mass-flow deposits derived from both the footwalls of graben-bounding normal faults and the Adriatic Carbonate Platform were frequent. The most basin-ward segment of the latter one was penetrated by the south-westernmost well of the area. Both the Middle Jurassic extension of the formerly extended continental crust and the lower plate source of the sediments have great importance, while they change the tectonic interpretation of the basins. In the overlying Tarna olistostrome sedimentation lasted at least until the Tithonian, as indicated by nannofossils. This is the oldest possible age for the overthrusting of the ophiolite nappe over this segment of the Greater Adriatic continental margin. The now eroded ophiolite nappe is underlain by the Darnóhegy Mélange, a typical sub-ophiolitic mélange, which was formed further to the south-east during the Callovian–Oxfordian, at an earlier, intraoceanic stage of the Neotethyan subduction.
Abstract The Western Vardar ophiolite, a thrust sheet of oceanic crust and mantle obducted onto the Adriatic passive margin in the Late Jurassic, crops out along the entire Balkan Peninsula. The Mirdita Ophiolite forms the northern Albanian segment of this unit. In northeast Albania near Bajram Curri, a 200–700 m thick metamorphic sole is preserved at its base. The assembly of obducted mantle rocks and metamorphic sole constitutes a plate interface that formed during the intraoceanic subduction stage preceding obduction; we call this a fossil intraoceanic plate interface in this paper. This setting allows to study the interrelated tectonometamorphic evolution and rock-water interaction between the subducted and exhumed metamorphic sole and concomitant mantle wedge serpentinization in the overlying units. We combined detailed lithological and structural mapping with micro-scale analyses along this plate interface. Three tectonic units were distinguished. Mylonitic harzburgites overlie a tightly folded, tectonised subophiolitic mélange along a SE-dipping contact that defines the fossil intraoceanic plate interface. The tectonised subophiolitic mélange itself was separated into a structurally lower non-metamorphic broken formation and a higher metamorphic sole, separated by an isoclinally folded thrust. Within the metamorphic sole, the temperature and degree of deformation increase towards the structural top. Shear sense indicators in calcschists of the metamorphic sole show top to the west transport of the overriding units. All metamorphic sole lithologies were overprinted at lower greenschist-facies conditions, reflecting their exhumation from intraoceanic subduction. Corresponding microstructures indicate mineral growth at isotropic stresses, suggesting that deformation migrated into structurally lower, frontally accreted non-metamorphic units of the sub-ophiolitic mélange marking the start of obduction onto the passive Adriatic margin. Ongoing westward transport led to folding of the entire sub-ophiolitic succession. Harzburgites are more deformed towards the plate interface, forming a mylonitic fabric. There, harzburgites contain accessory Cr-rich spinel and the foliation is dissected by multiple generations of veins containing serpentine and magnetite. Vein density is highest along the plate interface and decreases up-section, suggesting that serpentinisation was triggered by devolatilisation reactions in the sediments of the metamorphic sole that were subducting below the harzburgites, and the upwards migration of volatiles into the overlying mantle wedge.
Carbon Capture and Storage (CCS) technologies play a critical role in achieving global and Swiss climate goals, particularly with Switzerland aiming to domestically store some of its residual CO_2 emissions. In situ mineralization presents a promising avenue for stable and permanent CO_2 sequestration. This study aims to evaluate the potential of CO_2 storage via in situ mineralization in the Swiss underground. A set of technical/geological criteria was defined and used to identify, evaluate, and classify the various geological formations. The selected areas identified and evaluated include alpine tectonic units with large volumes of mafic and ultramafic rocks. Despite the presence of suitable rock types, these units are marked by alpine deformation with highly complex structures, rock mixtures, and complex bedrock hydrogeology. The old, altered, and metamorphic nature of the alpine mafic and ultramafic rock formations results in minimal permeability and porosity, consequently impeding CO_2 injectivity and mineralization kinetics, particularly given the low average geothermal gradient. Additionally, challenges related to water resource requirements, storage site location and accessibility, financial costs, regulation, social acceptance, and environmental impacts further impact feasibility negatively. This study concludes that CO_2 sequestration via in situ mineralization in the Swiss context is unfeasible in the near term and possibly unsuitable in the long one.
