Paleostress inversion methods based on fault slip data (i.e. “fault slip inversion methods” or FSIMs) were formalised fifty years ago to become, shortly after, classical tools in structural geology and tectonics. The great popularity quickly gained by the methods was as remarkable as the enduring scepticism they prompted in the geological community. FSIMs belong to the rather narrow collection of methods, which allow for bridging traditional field observations and measurements (of fault planes and their respective slickenlines in the present case) to the stress tensor, a complex mathematical object. The latter statement highlights the originality of the approach and, perhaps, the roots of FSIM scepticism: stress are “observed” (or derived from observation of the nature) and not “measured” with the help of physical instrumentation, as it is traditionally done. FSIMs are thus methods that involve mathematical processing of field data after adequate encoding of these. They rely primarily on the so-called “Wallace-Bott hypothesis”, which assumes parallelism between the measured fault stria and the computed maximum resolved shear stress, and on additional background conditions. The purpose of the present contribution is to discuss the limits of FSIMs in the light of their theoretical background and of realistic geological situations. The discussion will mostly focus on key-issues (e.g. is the stress restored by FSIMs in agreement with the formal definition of mechanical stress?) and will try to propose some future research tracks.

We conducted comparative measurements of thermal properties of samples from nine cores of the ICDP COSC-1 borehole and four widely used rock references, using a steady-state and a transient divided-bar device, a transient plane source device, a modified & Aring;ngstr & ouml;m device, as well as two optical thermal conductivity scanners. In addition, a caloric method provided benchmark values for specific heat capacity. A complementary thin-section analysis of the COSC-1 samples allowed us to calculate specific heat capacity according to Kopp's law and thermal conductivity according to commonly used mixing models. Our results demonstrate agreement between the various test methods within $\pm 10$ per cent for about one half of the investigated samples. Furthermore, almost all results for specific heat capacity agree with the predictions of Kopp's law, though the significance of this correspondence is limited owing to large uncertainties in the experimental and theoretical values. The results for thermal conductivity fall within the most extreme theoretical bounds that account for anisotropy but for an amphibolite. Thermal anisotropy seems to contribute significantly to the deviations between results of the different transient methods that, however, cannot be reconciled by the available theoretical relations for apparent thermal conductivity of transversely isotropic materials. The combination of characteristic investigation volume of the individual methods and sample heterogeneity has to be considered responsible for variability of results, too, an issue whose clarification is calling for dedicated numerical modelling in the future, with the prospect to characterize thermal heterogeneity from observed differences.

The Collisional Orogeny in the Scandinavian Caledonides (COSC) project focuses on processes related to the closure of the Iapetus Ocean, causing the Ordovician-Silurian continent- continent collision between Baltica and Laurentia. The rock succession in the second drill core (COSC-2) from the J & auml;mt land County, central Sweden, provides the base for detailed sedi- mentological, stratigraphic, geophysical, geochemical, geothermal and structural studies. The basement, comprising 1.66-1.65 Ga Transscandinavian Igneous Belt porphyries intruded by 1.47 Ga and 1.27-1.26 Ga mafic dykes and sills, is heavily weathered towards the top. Here it grades into typical saprock and saprolite (including immature soil reflecting the sub-Cambrian peneplain). The overlying sedimentary sequence starts with basal conglomerates and heterogeneous sediments with shell fragments, indicating an early Cambrian rather than a Neoproterozoic age for the marine transgression in the area. The developing early Cambrian basin was rapidly filled, initially by mostly coarse-grained sediment gravity flows. These strata are covered by sandstone turbidites that show an upward transition into the Alum Shale Formation, representing a tectonically quieter period (mid-Cambrian/Maolingian to Early Ordovician/Tremadocian). The upper part of the Alum Shale Formation is overlain by a late Early Ordovician turbidite succession. Local sources of sediments below the Alum Shale Formation and the extended deposition period may indicate continuous sedimentation in a pull-apart basin pre served in a window beneath the Caledonian thrust sheets.

The understanding of heat transport in fractures is crucial for mining geothermal systems. Studies of heat transport in natural fractures at scales comprised between those of laboratory experiments and those of field tracer tests are seldom. To bridge the gap, a joint surface with characteristic plumose was scanned in the field using LiDAR technology. The scanned surface was used to build a numerical model of mode 1 fracture. Fluid flow and heat transport were modeled solving the steady-state Stokes equation and assuming Fourier transport, respectively. We considered three different fracture apertures and varied systematically roughness in order to investigate the impact of plumose on fluid and heat transport. The 3D velocity flow fields were characterized by mean hydraulic aperture and by statistics on the directional components of the velocity vector. The method of temporal moments was used to extract first and second moments from temperature breakthrough curves. Heat transport parameters (local and macroscopic) were calculated from first and second moments. We show that hydraulic aperture and the longitudinal component of the velocity vector decrease with increasing roughness. The local variation of heat transport parameters is controlled by fracture roughness. For the macroscopic transport parameters, several transport regimes were identified. At low fracture aperture (i.e. 1 mm), conductive regime dominates heat transport in agreement with low Peclet numbers. In this case, fracture roughness affects the transport parameters via the loss of hydraulic aperture. With higher aperture (i.e. 3 mm) geometrical dispersion regime is dominant, roughness controlling the amplitude of transport parameters. At 5 mm aperture, transition from geometrical to Taylor dispersion occurs and the roughness tends to decrease dispersion and dispersivity according to the mean flow velocity.

Dans le cadre du projet COPING (Covid pandemic institutional management), cet article se propose d’étudier les éventuelles variations des perceptions des patients hospitalisés pendant l’épidémie de Covid-19. Pour ce faire, une comparaison entre les périodes confinées et non confinées a été menée à partir des résultats de l’enquête e-Satis disponibles dans les quatre centres hospitaliers universitaires (CHU) de la région Auvergne-Rhône-Alpes (Hospices civils de Lyon, CHU Grenoble-Alpes, CHU de Saint-Étienne, CHU de Clermont-Ferrand). Ce travail permet de constater qu’il existe peu de différences importantes entre les périodes, certaines statistiquement significatives en raison de la puissance de l’étude. Les patients de ces CHU ont vécu pendant l’ensemble de la période une expérience assez similaire à celle des années « non-Covid-19 ». Néanmoins, la période « Covid-19 » est marquée par une contradiction. D’un côté, on observe un renforcement global de la vision positive de l’hôpital et des soignants, ce qui se reflète dans les appréciations portées sur les éléments matériels (des repas et des chambres plus confortables) et immatériels (soins, accueil). De l’autre côté, la baisse de satisfaction concernant les visites et les variations observées tout au long de la période interrogent sur la manière dont des catégories de patients ont appréhendé ces transformations.

The scientific drilling project “Collisional Orogeny in the Scandinavian Caledonides” (COSC), supported by ICDP and the Swedish Research Council, involved the drilling of two vertical boreholes through carefully selected sections of the Paleozoic Caledonian orogen in Central Sweden. The main objectives of the COSC geothermal team are: a) to determine the vertical variation of the geothermal gradient, heat flow and thermal properties, and to determine the required corrections for shallow (< 1 km) heat flow data; b) to advance basic knowledge about the thermal regime of Palaeozoic orogenic belts, ancient shield areas and high heat-producing plutons; c) to improve understanding of climate change at high latitudes (i.e. Scandinavia), including historical global changes and recent palaeoclimate development (since last ice age); d) to explore the geothermal potential of the Åre-Järpen area; e) to assess to what degree the conductive heat transfer is affected by groundwater flow in the uppermost crust, and f) to determine the heat generation input and impact from the basement and the alum shales.The present contribution focuses on themes “b” and “f” and evaluates the likely paleothermal state of the lithosphere of Baltica, in the region of the COSC boreholes, at the onset of the Caledonian orogeny. We concentrated on the results obtained from COSC-1, which was drilled, fully cored and repeatedly logged for temperature down to ~2.5 km depth. Average heat generation of the penetrated Caledonian metamorphic rocks was derived from the spectral gamma ray logs. The analysis yields a low average value of 0.8 µW/m3. Thermal conductivities were determined from 105 core samples. On average, thermal conductivity equals 2.8±0.4 W/(m K), down to ~2 km depth, and increases to 4.1±1 W/(m K) in the lowermost section of the borehole. The thermal gradient shows obvious paleoclimatic disturbances but seems largely unaffected below ~2 km depth and no advective signal is detected. The calculated heat flow for the deepest section of the well amounts to ~82 mW/m2. This unusually high heat flow value for cratonic lithosphere reflects, most likely, dominant input from the underlying highly radioactive Transscandinavian Igneous Belt (TIB), which is Late Proterozoic in age. We therefore propose that the lithosphere of Baltica involving the TIB was relatively warm at the time of the Caledonian orogeny. We anticipate that the relatively high temperatures of the margin of Baltica strongly influenced deformation style.

The present contribution introduces new heat flow data from northern Norway, a region of the Baltic Shied and Scandinavian Caledonides that has been poorly covered until now. We computed heat flow values based on data gathered in ten boreholes reaching total depths ranging between -390 m and 960 m below ground level. Abundant core material for five of the studied boreholes allowed for precise determination of thermal conductivity profiles. The new determinations represent significant improvement with respect to the few pre-existing heat flow values that were based on shallow drillholes and lake measurements. The obtained heat flow values range between -40 and 70 mW/m2, after corrections, and suggest significant heat flow decrease (i.e. -10-20 mW/m2) from chiefly Proterozoic terrains to the Archean nucleus in NE Norway. The results suggest also sharp decrease in heat flow from the NE Atlantic to the Lofoten-Vesteralen margin but rather smooth gradients from the Barents Shelf to the continent. The former may be associated with abrupt deepening of the base of the lithosphere below the Lofoten-Vesteralen margin, as already suggested by previous seismic tomography studies and consistent with drastic strain focusing and the formation of a narrow margin. In contrast, gradual deepening of the base lithosphere towards the continent appears to be in agreement with the observed diffuse deformation that took place in the comparatively wide Western Barents Shelf.

Although much evidence points to a Late Mesozoic large silicic igneous province in SE South China (SESC), diverse Andean-type and non-Andean-type models have been proposed to explain its origins. New age, isotope, and trace element data on zircon from wells in East China Sea (ECS) and offshore-onshore tectonomagmatic comparisons allow reassessment of the geodynamic interactions (ca. 200-86 Ma) between the Cathaysia-based arc and intraplate activity from a large mantle wedge framework. In region, remnants of the West ECS arc, Ryukyu-Taiwan me & PRIME;lange, and SESC intraplate define a trench-arc-intraplate architecture. Changes in arc magmatic states (flare-ups and lulls; high U/Yb, low T, variable & epsilon;Hf(t)) permit identification of a cycle of arc initiation, thickening, decline, arc-root removal, and arc migration, highly correlating with changes of Izanagi subduction beneath East Asia. Voluminous intraplate silicic magmatism operated in response to the slab stag -nation dynamics: slab dehydration, lithospheric delamination, fluid-fluxed crustal anataxis, and crustal-mantle melt hybridization in crustal hot zones. Such geodynamic scenarios, unlike an Andean-type continental margin, instead result in the construction of a Late Mesozoic Cathaysian-type active continental margin.

Svalbard is a High Arctic Archipelago at 74-81 degrees N and 15-35 degrees E under the sovereignty of Norway. All settlements in Svalbard, including the capital of Longyearbyen (population 2400), currently have isolated energy systems with coal or diesel as the main energy source. Geothermal energy is considered as a possible alternative for electricity production, as a heat source in district heating systems or harnessed for heating and cooling using geothermal heat pump installations. In this contribution we present the until now fragmented data sets relevant to characterize and assess the geothermal potential of Svalbard. Data sets include petroleum and deep research boreholes drilled onshore Svalbard, 14 of which have recorded subsurface temperature data at depths below 200 m. Geothermal gradients on Spitsbergen vary from 24 degrees C/km in the west to 55 degrees C/km in the south-east, with an average of 33 degrees C/km. Four deep research boreholes were fully cored and analyzed for thermal conductivity. These analyses were complemented by thermal conductivity calculated from wireline logs in selected boreholes and four measurements on outcrop samples. 1D heat flow modelling on five boreholes calibrated with the measured thermal conductivities offers insights into heat transfer through the heterogeneous sedimentary suc-cession. Offshore petroleum boreholes in the south-western Barents Sea and marine heat flow stations around Svalbard provide a regional framework for discussing spatial variation in heat flow onshore Svalbard, with emphasis on the effects of erosion and deposition on the thermal regime. We conclude that Svalbard's geology is well suited for geothermal exploration and potential production, though challenges related to permafrost, the presence of natural gas, heterogeneous reservoir quality and strongly lateral varying heat flow need to be adequately addressed prior to geothermal energy production. Specifically for Longyearbyen, high geothermal gradients of 40-43 degrees C/km in the nearest borehole (DH4) suggest promising sub-surface thermal conditions for further exploration of deep geothermal potential near the settlement.

Since 1963, the International Heat Flow Commission has been fostering the compilation of the Global Heat Flow Database to provide reliable heat-flow data. Over time, techniques and methodologies evolved, calling for a reorganization of the database structure and for a reassessment of stored heat-flow data. Here, we provide the results of a collaborative, community-driven approach to set-up a new, quality-approved global heat-flow database. We present background information on how heat-flow is determined and how this important thermal parameter could be systematically evaluated. The latter requires appropriate documentation of metadata to allow the application of a consistent evaluation scheme. The knowledge of basic data (name and coordinates of the site, depth range of temperature measurements, etc.), details on temperature and thermal-conductivity data and possible perturbing effects need to be given. The proposed heat-flow quality evaluation scheme can discriminate between different quality aspects affecting heat flow: numerical uncertainties, methodological uncertainties, and environmental effects. The resulting quality codes allow the evaluation of every stored heat-flow data entry. If mandatory basic data are missing, the entry is marked accordingly. In cases where more than one heat-flow determination is presented for one specific site, and all of them are considered for the site, the poorest evaluation score is inherited to the site level. The required data and the proposed scheme are presented in this paper. Due to the requirements of the newly developed evaluation scheme, the database structure as presented in 2021 has been updated and is available in the appendix of this paper. The new quality scheme will allow a comprehensible evaluation of the stored heat-flow data for the first time.

The pressing need for renewables prompted geothermal research in Norway recently. These studies confirmed rocks with high heat-generation rates in the Oslo Region, covered locally by sediments. Although the geology appeared favourable to the operation of deep geothermal resources in the most densely populated area of Norway, no attempt was made to estimate underground temperatures. In the present work, subsurface temperatures were computed for the Oslo-Asker area by means of 3D numerical modelling. We conclude that deep temperatures are too low to be of economic use with present-day technology. Shallow temperatures (i.e. < 500 m depth below ground level) appear high enough for direct use and heating. There is, however, a crucial need for new data from deep boreholes in order to better constrain the predictions of the models.

We explored and discussed various paleostress inversion methods in the previous chapters and noted that all allow for the determination of the orientations of the principal axes of stress, and additional quantities, but none of them is capable to restore the six parameters of the stress tensor. In the present chapter, we present different techniques to derive the missing components of the stress tensor. Firstly, the use of failure and friction laws to adjust Mohr circles obtained after inversion of fault slip data will be introduced. Thereafter, we will learn how one can potentially tackle the critical issue of deriving pore fluid paleopressures by means of analysing fluid inclusions. Finally, the last section will address a recent development in paleostress research, namely stylolithe paleopiezometry.

The quantification of tectonic forces or, alternatively, stresses represents a significant step toward the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we tried to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as a natural laboratory, and focused on the measurement of subhorizontal quartz veins, which are favorably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled the vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulfide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of rupture laws and obtained the six parameters of the paleostress tensor that prevailed during the vein formation. Our results suggest a NW–SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressures of ~300 MPa, and differential stress lower than ~20 MPa.

We propose a novel method to reconstruct the six parameters of the paleostress tensor. The method involves three major steps: (1) measurement and inversion of vein attitudes to determine the reduced paleostress tensor, (2) determination of pore pressures using fluid inclusion (FI) isochores and mineral geothermometry, (3) final adjustment of the Mohr circle and estimation of stress magnitudes using geomechanical constraints from the literature. Owing to its outstanding 3D exposures, we selected Panasqueira Mine, central Portugal, as natural laboratory to develop and test our approach. We measured 684 quartz veins,-800 FIs in quartz and the geochemical composition of 10 arsenopyrite samples. The inversion of the veins resulted in a reverse stress regime with sigma 1 trending -NW-SE, phi = 0.6 and a driving stress ratio of R' = 0.19. We estimated a lithostatic pressure of 270 MPa (min. 230 MPa and max. 300 MPa) during the major mineralisation stage of the veins of Panasqueira (i.e. MOSS-MSS stage). Finally, the adjustment of the Mohr circle resulted in differential stresses too low to trigger shear failure and in the range from 45 to 89 MPa, and pore pressures exceeding lithostatic pressure by 8.5-17 MPa to open the discontinuities during MOSS-MSS mineralisations.

After having presented extensively different theoretical and methodological aspects of paleostress reconstruction methods, the purpose of the final chapter is to introduce recommendations for their practical use in tectonic problems. The discussion focuses on paleostress inversion of fault slip data, the latter being both the most elaborated and the most employed method. Detailed practical advice is given to conduct a paleostress study efficiently, starting with data acquisition in the field, proceeding with subsequent computation of paleostress tensors and ending with the reporting of the results and of their subsequent interpretations.

The quantification of tectonic forces or, alternatively, stresses represents a significant step towards the understanding of the natural processes governing plate tectonics and deformation at all scales. However, paleostress reconstructions based on the observation and measurement of natural fractures are traditionally limited to the determination of four out of the six parameters of the stress tensor. In the present study, we attempt to reconstruct full paleostress tensors by extending the methodologies advanced by previous authors. We selected Panasqueira Mine, Central Portugal, as natural laboratory, and focused on the measurement of sub-horizontal quartz veins, which are favourably exposed in three dimensions in the underground galleries of the mine. Inversion of the vein data allowed for quantifying the respective orientations of the stress axes and the shape ratio of the stress ellipsoid. In order to reconstruct an additional stress parameter, namely pressure, we extensively sampled vein material and combined fluid inclusion analyses on quartz samples with geothermometric analyses on sulphide minerals. Finally, we adjusted the radius of the obtained Mohr circle with the help of mechanical parameters, and obtained the six parameters of the paleostress tensor that prevailed during vein formation. Our results suggests a NW-SE reverse stress regime with a shape ratio equal to ~0.6, lithostatic pore pressure of ~250 MPa and differential stress between ~40 and ~90 MPa.

Paleostress reconstruction by means of inversion of tensile fracture data is a relatively recent method. The method considers the spatial distribution of tensile fractures (e.g. dykes and veins) of a given fracture set to determine the orientations of the principal axes of stress, the degree of stress anisotropy and the relative pore pressure of the fluids that promote fracture opening. A detailed account of the physical foundations of the method will be given before introducing the principles of the numerical inversion. To conclude this chapter, we will discuss the drawbacks of this recent method and suggest some possible improvements.