ALBERT

Description: Mechanical twins are common microstructures in deformed calcite. Calcite twins have been used for a long time as indicators of stress/strain orientations and magnitudes. Developments during the last decade point toward significant improvements of existing techniques as well as new applications of calcite twin analysis in tectonic studies. This review summarises the recent progress in the understanding of twin formation, including nucleation and growth of twins, and discusses the concept of CRSS and its dependence on several factors such as strain, temperature and grain size. Classical and recent calcite twin measurement techniques are also presented and their pros and cons are discussed. The newly proposed inversion techniques allowing for the use of calcite twins as indicators of orientations and/or magnitudes of stress and strain are summarized. Benefits for tectonic studies are illustrated through the presentation of several applications, from the scale of the individual tectonic structure to the continental scale. The classical use of calcite twin morphology (e.g., thickness) as a straightforward geothermometer is critically discussed in the light of recent observations that thick twins do not always reflect deformation temperature above 170–200 °C. This review also presents how the age of twinning events in natural rocks can be constrained while individual twins cannot be dated yet. Finally, the review addresses the recent technical and conceptual progress in calcite twinning paleopiezometry, together with the promising combination of this paleopiezometer with mechanical analysis of fractures or stylolite roughness.

Description: The long-term sustainability of fractures within rocks determines whether it is reasonable to utilize such formations as potential EGS reservoirs. Representative for reservoirs in Variscan metamorphic rocks, three long-term (one month each) fracture permeability experiments on saw-cut slate core samples from the Hahnenklee well (Harz Mountains, Germany) were performed. The purpose was to investigate fracture permeability evolution at temperatures up to 90 °C using both deionized water (DI) and a 0.5 M NaCl solution as the pore fluid. Flow with DI resulted in a fracture permeability decline that is more pronounced at 90 °C, but permeability slightly increased with the NaCl fluid. Microstructural observations and analyses of the effluent composition suggest that fracture permeability evolution is governed by an interplay of free-face dissolution and pressure solution. It is concluded that newly introduced fractures may be subject to a certain permeability reduction due to pressure solution that is unlikely to be mitigated. However, long-term fracture permeability may be sustainable or even increase by free-face dissolution when the injection fluid possesses a certain (NaCl) salinity.

Description: The mobility of arsenic (As) and antimony (Sb) in soils is controlled by several processes (adsorption/desorption, (co)precipitation/dissolution and oxidation/reduction), depending on various environmental factors that are often convoluted and site-dependent. This study investigated: (i) the content and solid-phase distribution of geogenic As and Sb in a vertical soil profile (0–130 cm) of an agricultural wetland subject into alternating oxic and anoxic conditions induced by periodic waterlogging and (ii) identifies the stability of the As and Sb host phases during soil reduction (laboratory incubation) using a sequential extraction procedure (fractions: loosely and strongly adsorbed, carbonates, easily reducible, reducible, oxidable and residual). The field results showed that, in the deeper, permanently water-saturated soil layers (

Description: We have performed several sensitivity studies to assess the ability of the Full Wave Inversion method to detect, delineate and characterize faults in a crystalline geothermal reservoir from OVSP data. The distant goal is to apply the method to the Soultz-sous-Forêts site (France). Our approach consists of performing synthetic Full Wave 2D Inversion experiments using offset vertical seismic and comparing the estimated fields provided by the inversion, i.e., the estimated underground images, to the initial reference model including the fault target. We first tuned the inversion algorithmic parameters in order to adapt the FWI software, originally dedicated to a sedimentary context, to a crystalline context. In a second step, we studied the sensitivity of the FWI fault imaging results as a function of the acquisition geometry parameters, namely, the number of shots, the intershot distance, the maximum offset and also the antenna length and well deviation. From this study, we suggest rules to design the acquisition geometry in order to improve the fault detection, delineation and characterization. In a third step, we studied the sensitivity of the FWI fault imaging results as a function of the fault or the fault zone characteristics, namely, the fault dip, thickness and the contrast of physical parameters between the fault materials and the surrounding fresh rocks. We have shown that a fault with high dip, between 60 and 90° as thin as 10 m (i.e. lower than a tenth of the seismic wavelength of 120 m for Vp and 70 m for Vs) can be imaged by FWI, even in the presence of additive gaussian noise. In summary, for a crystalline geological context, and dealing with acceptable S/N ratio data, the FWI show a high potential for accurately detecting, delineating and characterizing the fault zones.

Description: The interpretation of eruptive mechanisms accumulating ancient submarine volcaniclastic sequences is still extremely challenging, particularly when no spatial nor temporal constraints are identifiable. The present work reviews petrographic results gained during the last few decades on three different Paleogene Formations accumulated around the Alpine and Apennine Mountain belts, discussing how their detritus could have been formed and moved from the volcanic centers to the depo-centers, taking into account the volcanic mechanisms which are at the base of the production, transportation and accumulation of volcaniclastic detritus. In doing this, we reconsider the classical diagrams of Folk and Gazzi–Dickinson, rediscussing their significance on the basis of how orogenic volcanism delivers detritus to the environment. In addition, this work highlights the need of the scientific community for gaining new petrographic data on modern sedimentary systems to better constrain interpretative criteria for the petrographic study of ancient volcano–sedimentary sequences.

Description: As a mitigation measure against a tsunami inundation, vegetation-embankment hybrid structures received attention after the 2011 Great East Japan Tsunami, and some structures have already been constructed or are under construction in Japan. The present study conducted a series of numerical simulations using a hybrid system comprised of an artificial structure (an embankment, moat) and a natural component (vegetation) that was experimentally proposed in previous studies as an effective structure for tsunami mitigation. After validating the numerical model using published data, this study investigated differences in the performance of the hybrid system by changing the tsunami period and height characteristics of the tsunami-like surge-type flow. As a result, the delay in tsunami arrival time (ΔT) was not affected by the tsunami wave period for the investigated hybrid structures. Among the investigated structures, Case Ve40ME (where Ve40, M, and E represent vegetation, moat, and embankment, respectively, in that order from seaward) showed the maximum performance of ΔT. The reductions of overflow volume (ΔQ), fluid force index (RFI), and moment index (RMI) declined during the tsunami period. The tsunami mitigation effect is closely related to the relationship between the development times of backwater rise, hydraulic jump, and the tsunami period. Case Ve40ME was effective for ΔT, ΔQ, and RMI. Case EMVe40 was especially effective for RFI. When the tsunami period is short, the water level at the shoreline starts to decrease before full development of the hydraulic jump generated in the hybrid system. Thus, overflow volume to landward decreases, and the mitigation effects increase. When the tsunami period is long, the receding phenomenon at the peak water level does not affect the maximum values, thus the mitigation effects become smaller compared with the short period. However, the superiority to other structures is maintained in Case Ve40ME and Case EMVe40 with seaward vegetation and landward vegetation, respectively.

Description: A combined ultrasonic treatment, with de-ionized H2O, dilute HAc or dilute HCl, of three Mid-Miocene glauconite samples was applied to K–Ar date the different separates in order to compare the results with those obtained by the Rb–Sr method using the same three samples and that were analyzed strictly in the same way. Two aliquots yield opposite elemental and K–Ar trends, which suggests different initial mineral compositions for the various pellets. The K–Ar data of two untreated and leached L7 and L8 aliquots are almost within analytical uncertainty from 17.3 ± 0.6 Ma to 19.6 ± 0.7 Ma (2σ), while those of the third L10 sample are slightly higher at 22.1 ± 1.2 Ma (2σ). Comparatively, the earlier published Rb–Sr ages of the three untreated samples and of the leached aliquots gave similar data for the L7 aliquots by an isochron at 18.1 ± 3.1 (2σ) Ma and for the sample L8 by an isochron with an age of 19.6 ± 1.8 (2σ) Ma, while the untreated L10 aliquot yields a very high Rb–Sr date of 42.1 ± 1.6 (2σ) Ma. This untreated L10 glauconite fraction contains blödite, a Sr-rich carbonate that impacted the two isotopic systems differently. Generally, dilute HCl or HAc acids dissolve carbonates, sulfates, sulfites and oxides, while they do not affect the clay-type crystals such as glauconites. These soluble minerals can be identified indirectly, as here, by X-ray diffraction and the amounts of leached Na2O, CaO and Fe2O3 contents. Together with the leaching of some metallic trace elements, those of NaO confirm the leaching of metals and of blödite that are both hosted by the glauconite pellets. The occurrence of this Sr-enriched mineral explains the age differences of the non-treated aliquots and suggests a systematic leaching of any glauconite separate before isotope determination and, possibly, a comparison of the Rb–Sr and K–Ar results. Ultrasonic shaking appears appropriate for physical disaggregation of any contaminating grains that may remain hosted within the pellets, even after a preliminary H2O wash, which may dissolve and remove the soluble minerals but not the H2O-insoluble silicates. The K–Ar study completed here as a complement to a previous Rb–Sr study highlights, again, the importance of the preparation step in isotopic studies of glauconite-type and, by extension, of any clay material, as all occurring minerals can interfere in the final age determinations and, therefore, differently in the mineral assemblages. All those not in isotopic equilibrium need to be removed before analysis, including the soluble Sr or alkali-enriched ones.

Description: The eccentric dipole (ED) is the next approach of the geomagnetic field after the generally used geocentric dipole. Here, we analyzed the evolution of the ED during extreme events, such as the Matuyama-Brunhes polarity transition (~780 ka), the Laschamp (~41 ka) and Mono Lake (~34 ka) excursions, and during the time of two anomalous features of the geomagnetic field observed during the Holocene: the Levantine Iron Age Anomaly (LIAA, ~1000 BC) and the South Atlantic Anomaly (SAA, analyzed from ~700 AD to present day). The analysis was carried out using the paleoreconstructions that cover the time of the mentioned events (IMMAB4, IMOLEe, LSMOD.2, SHAWQ-Iron Age, and SHAWQ2k). We found that the ED moves around the meridian plane of 0–180° during the reversal and the excursions; it moves towards the region of the LIAA; and it moves away from the SAA. To investigate what information can be extracted from its evolution, we designed a simple model based on 360-point dipoles evenly distributed in a ring close to the inner core boundary that can be reversed and their magnitude changed. We tried to reproduce with our simple model the observed evolution of the ED, and the total field energy at the Earth’s surface. We observed that the modeled ED moves away from the region where we set the dipoles to reverse. If we consider that the ring dipoles could be related to convective columns in the outer core of the Earth, our simple model would indicate the potential of the displacement of the ED to give information about the regions in the outer core where changes start for polarity transitions and for the generation of important anomalies of the geomagnetic field. According to our simple model, the regions in which the most important events of the Holocene occur, or in which the last polarity reversal or excursion begin, are related to the regions of the Core Mantle Boundary (CMB), where the heat flux is low.

Description: Spring water geochemistry is applied here to evaluate the geothermal potential in Rhenohercynian fold and thrust belt around the deepest borehole in Belgium (Havelange borehole: 5648 m MD). Fifty springs and (few) wells around Havelange borehole were chosen according to a multicriteria approach including the hydrothermal source of “Chaudfontaine” (T ≈ 36 °C) taken as a reference for the area. The waters sampled, except Chaudfontaine present an in-situ T range of 3.66–14.04 °C (mean 9.83 °C) and a TDS (dry residue) salinity range of 46–498 mg/L. The processing methods applied to the results are: hierarchical clustering, Piper and Stiff diagrams, TIS, heat map, boxplots, and geothermometry. Seven clusters are found and allow us to define three main water types. The first type, locally called “pouhon”, is rich in Fe and Mn. The second type contains an interesting concentration of the geothermal indicators: Li, Sr, Rb. Chaudfontaine and Moressée (≈5 km East from the borehole) belong to this group. This last locality is identified as a geothermal target for further investigations. The third group represents superficial waters with frequently high NO3 concentration. The application of conventional geothermometers in this context indicates very different reservoir temperatures. The field of applications of these geothermometers need to be review in these geological conditions.

Description: Geostructural rock mass surveys and the collection of data related to discontinues provide the basis for the characterization of rock masses and the study of their stability conditions. This paper describes a multiscale approach that was carried out using both non-contact techniques and traditional support techniques to survey certain geometrical features of discontinuities, such as their orientation, spacing, and useful persistence. This information is useful in identifying the possible kinematics and stability conditions. These techniques are extremely useful in the case study of the Elva valley road (Northern Italy), in which instability phenomena are spread across 9 km in an overhanging rocky mass. A multiscale approach was applied, obtaining digital surface models (DSMs) at three different scales: large-scale DSM of the entire road, a medium-scale DSM to assess portions of the slope, and a small-scale DSM to assess single discontinuities. The georeferenced point cloud and consequent DSMs of the slopes were obtained using an unmanned aerial vehicle (UAV) and terrestrial photogrammetric technique, allowing topographic and rapid traditional geostructural surveys. This technique allowed us to take measurements along the entire road, obtaining geometrical data for the discontinuities that are statistically representative of the rock mass and useful in defining the possible kinematic mechanisms and volumes of potentially detachable blocks. The main purpose of this study was to analyse how the geostructural features of a rock mass can affect the stability slope conditions at different scales in order to identify road sectors susceptible to different potential failure mechanisms using only kinematic analysis.