Tectonic and microfabric studies along the Penninic Front between Pelvoux and Argentera massifs (Western Alps, France)

Chapter 1: Apparent divergence of thrusting directions horth and south of the Pelvoux massif: implications for the evolution of the Western Alpine Arc: In the Western Alps, the Penninic Basal Contact (PBC, Ceriani et al. 2001) defines the tectonic boundary between the external Dauphinois domain and the interanl Penninic units. During the Eocene, the PBC corresponds to the suture between Dauphinois and Subriançonnais/Briançonnais domains related to the subduction of the Valais ocean (Ceriani et al. 2001). In the Oligo-Miocene, i.e. during a second and post-collisional stage, Eocene structures were passively transported towards the WNE along a major out-of-sequence thrust, the Roselend thrust (RT), partially coinciding with and reactivating the PBC. Structural analysis of key outcrops combined with microfabric investigations of calcyte ultramylonites allowed to trace the southern continuation of the RT in a broad shear zone at the rim of the Pelvoux massif and further south along the Briançonnais front (Tricart 1980) at the rear of the Embrunais Ubaye nappe stack. The RT finally branches into a sinistral strike slip zone NE of the Argentera massif. The area south of the Pelvoux massif is additionally characterized by SW-directed thrusting, a feature totally absent north of it. Detailed investigations of outcrops found along strike of the RT, the basal decollement of both Dauphinois para-autochthonous Tertiary cover and Helmenthoid Flysch of the Embrunais Ubaye nappe stack reveal that top-SW thrusting is a younger (i.e. D2) event, overprinting earlier features linked to D1 WNW-directed displacements. The youngest deformation event found in the area (D3) is consistent with normal faulting along the Durance system. On a larger scale, it is concluded that the whole Adriatic indenter was thrusted onto the European plate along the RT during Oligo-Miocene times. Activity along this structure is linked to dextral movements along the Rhone-Simplon line and sinistral movements at the rear of the Argentera massif. Additionally, it is proposed that the onset of D3 SW-directed movements finds its origin in the opening of the western Mediterranean basin and the foramtion of the Appenine chain in middle Miocene times. Chapter 2: Microfabrics of calcite ultramylonites recording coaxial and non-coaxial deformation kinematics: examples from the Rocher de l'Yret shear zone (Western Alps): Microfabrics were analysed in calcite mylonites from the rim of the Pelvoux massif (Western Alps, France). WNW-directed emplacement of the internal Penninic units onto the Dauphinois domain has lead to intense deformation of an Eocene-age nummulitic limestone under lower anchizone metamorphic conditions (slightly below 300°C). Two types of microfabrics developed during deformation under coaxial or non-coaxial kinematics, respectively, primarily by dislocation creep accompanied by dynamic recrystallization in the absence of twinning. Coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry. Their texture is characterized by two c-axis maxima at the periphery of the pole figure, symmetrically oriented at 15° from the normal to the macroscopic foliation. Non-coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterized by a single oblique c-axis maximum tilted with the sense of shear by about 15°. From the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures developed in coaxial kinematics fabour activity of and slip along the f- and r-planes, respectively, with minor contributions of basal slip. In contrast, the monoclinic textures developed during simple shear are most suited for duplex slip along the basal plane. The transition between orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallization upon texture development. Calcite textures alone should not be used as unequivocal shear sense indicators, but need to be complemented by microstructural criteria such as shape preferred orientations, grain size estimates and amount of twinning. Chatper 3: Microfabric analysis of calcitic marbles from the area investigated in the Western Alps and the Gavernie basal contact (Central Pyrenees): In the previous chapter, a model of microfabric evolution of calcite ultramylonites, plastically deformed at temperatures lower than 350°C, has been presented. The very specific setting of the outcrop investigated in great details at the "Rocher de l'Yret" shear zone (RYSZ) allowed for the recognition of both coaxial and non-coaxial deformation kinematics. The samples deformed with a dominant component of rotational deformation show a c-axis distribution tilted synthetically with the sense of shear. In the absence of twinning, this feature, commonly observed for quartz tectonites, can be used as a reliable shear sense indicator. Additionally, the model allows for the recognition of incipient rotational deformation in the bulk flow accommodated in the rock. The structural data presented in chapter 1 will now be completed by means of a microfabric analysis of a series of calcitic marbles, found in abundance in the investigated area. The results of investigations on calcite ultramylonites found along the Roselend Thrust (RT) are presented first. four localities along the RT have been investigated between the eastern rim of the Pelvoux massif in the North and the rear of the Argntera massif in the South (sites BFY, Laux, Reot and Arg in fig 3.1). This study aims to 1) independently confirm the overall WNW-directed sense of transport along the RT, 2) deduce the type of strain along this structure and its possible variations using the model of microfabric evolution presented in chapter 2. In a second step, the basal decollement of the Dauphinois parautochthonous cover from the southeastern rim of the Pelvoux massif will be investigated. Such decollement occurred within the nummulitic limestone layer intensively mylonitised in the Dormillouse valley (site Dorm, see fig. 3.1 and 3.2). This study confirms the overall top-SW overprinting deformation recorded in this domain and documents important bulk flow partionning within the basal decollement level of the Eocene stratigrahpic series. Finally the restults of investigations on samples from the Gavernie thrust from the central Pyrenees (courtesy J.H.P. de Bresser) will be presented (see fig. 3.37). The restults are in accordance with the overall top-S directed emplacement of the Gavernie nappe during Pyrenean orogeny and give evidence for strain variations within the shear zone developed along the Gavarnie basal thrust

Véhicules électriques : la géothermie, future source d'approvisionnement en lithium ? The Conversation

The Conversation https://theconversation.com/vehicules-electriques-la-geothermie-future-source-dapprovisionnement-en-lithium-205072Le Parlement européen a voté le 14 février 2023 la fin de la production de véhicules thermiques à l'horizon 2035 pour les habitants des pays membres de l'Union européenne. En pratique, cela revient à l'arrêt des ventes de voitures et véhicules utilitaires légers neufs à essence et diesel dans l'UE à cette date, ainsi que des hybrides (essence-électrique), au profit de véhicules 100 % électriques. Cette décision s'inscrit dans un schéma plus large de recours aux véhicules électriques. Ainsi, selon l'Agence internationale de l'énergie (AIE), environ 2 milliards de véhicules électriques seront en circulation d'ici 2050, alors que les ventes n'étaient que de 10 millions en 2022 (avec une projection de +35 % en 2023 pour atteindre 14 millions). Cette augmentation du nombre de véhicules électriques va très logiquement s'accompagner de besoins de plus en plus importants en batteries, et donc en leurs composants, comme le lithium. Les exploitations habituelles étant déjà sous tension, les saumures géothermiques pourraient-elles devenir une source essentielle d'approvisionnement de la filière lithium européenne

Very low-grade metamorphism in the para-autochtonous sedimentary cover of the Pelvoux massif (Western Alps, France)

International audienceThe metamorphic grade from the para-autochtonous cover of the Pelvoux Massif (PM, western Alps, France) was investigated in Priabonian metamarls, through mineral assemblages, simultaneous measurements of illite and chlorite "crystallinity", K-white mica b cell dimension and K-white mica polytypes content. Kübler (KI) and Árkai (ÁI) indexes display values characteristic for uppermost diagenetic to low anchizonal conditions. These results are supported by the incomplete transformation of K-white mica polytypes from 1M d to 2M 1 and are in line with the not annealed status of zircon fission tracks in the southeast zone of the Pelvoux Massif (Seward et al. 1999). Our findings differ from previous results, which suggested epizonal conditions at several places in the northern part of our field area, but are coherent with the temperature estimation suggested by the mineral assemblage described in the literature. These results are further supported by temperature values deduced from fluid inclusion investigations. A small decrease of KI and ÁI values is observed within the basal decollement level of the Priabonian cover, when going from the least deformed zones to the most deformed ones. K-white mica b cell dimensions in micas of the area are in the range 9.000-9.040 Å, which corresponds to an inferred geothermal gradient of 25-35°C/Km, similar to the values found further north in the Dauphinois domain (Ceriani et al. 2003). Based on Ferreiro Mählmann (2001), this can supposed a long stady state heat flow corresponding to a long term metamorphic event like in the eastern Alps

Evidence for 40–41 km of dextral slip on the southern Death Valley fault: Implications for the Eastern California shear zone and extensional tectonics

International audienceRecognition of a pair of pre-Neogene markers together with analysis of published data indicate ∼40 km of dextral slip across the southern Death Valley fault zone, California, USA. Stratigraphic overlaps on fault rocks indicate much of the dextral slip predates the late Miocene, placing a significant fraction of the dextral slip in the same time window as regional extension and challenging interpretations that the modern strike-slip system became active post-6-3 Ma. However, these results are consistent with regional evidence that dextral transtension began by ca. 12 Ma

Fracture Spacing Variability and the Distribution of Fracture Patterns in Granitic Geothermal Reservoir: A Case Study in the Noble Hills Range (Death Valley, CA, USA)

International audienceScanlines constitute a robust method to better understand in 3D the fracture network variability in naturally fractured geothermal reservoirs. This study aims to characterize the spacing variability and the distribution of fracture patterns in a fracture granitic reservoir, and the impact of the major faults on fracture distribution and fluid circulation. The analogue target named the Noble Hills (NH) range is located in Death Valley (DV, USA). It is considered as an analogue of the geothermal reservoir presently exploited in the Upper Rhine Graben (Soultz-sous-Forêts, eastern of France). The methodology undertaken is based on the analyze of 10 scanlines located in the central part of the NH from fieldwork and virtual (photogrammetric models) data. Our main results reveal: (1) NE/SW, E/W, and NW/SE fracture sets are the most recorded orientations along the virtual scanlines; (2) spacing distribution within NH shows that the clustering depends on fracture orientation; and (3) a strong clustering of the fracture system was highlighted in the highly deformed zones and close to the Southern Death Valley fault zone (SDVFZ) and thrust faults. Furthermore, the fracture patterns were controlled by the structural heritage. Two major components should be considered in reservoir modeling: the deformation gradient and the proximity to the regional major faults

Multiscale Characterization of Fracture Patterns: A Case Study of the Noble Hills Range (Death Valley, CA, USA), Application to Geothermal Reservoirs

International audienceIn the basement fractured reservoirs, geometric parameters of fractures constitute the main properties for modeling and prediction of reservoir behavior and then fluid flow. This study aims to propose geometric description and quantify the multiscale network organization and its effect on connectivity using a wide-ranging scale analysis and orders scale classification. This work takes place in the Noble Hills (NH) range, located in the Death Valley (DV, USA). The statistical analyses were performed from regional maps to thin sections. The combination of the length datasets has led to compute a power law exponent around −2, meaning that the connectivity is ruled by the small and the large fractures. Three domains have been highlighted in the NH: (1) domain A is characterized by a dominance of the NW/SE direction at the fourth order scale; (2) domain B is characterized by a dominance of the E/W and the NW/SE directions at respectively the fourth and third order scales; (3) domain C is also marked by the E/W direction dominance followed by the NW/SE direction respectively at the fourth and third order scale. The numerical simulations should consider that the orientation depends on scale observation, while the length is independent of scale observation

Multiple-Criteria Decision-Making for Assessing the Enhanced Geothermal Systems

International audienceThis paper presents the main features of a multiple-criteria decision-making tool for economic and environmental assessment of enhanced geothermal systems projects. The presented holistic approach takes into account important influencing factors such as technical specifications, geological characteristics, spatial data, energy and heat prices, and social and environmental impact. The multiple-criteria decision-making approach uses a weighted decision matrix for evaluating different enhanced geothermal systems alternatives based on a set of criterions which are defined and presented in this paper. The paper, defines and quantifies new criterions for assessing enhanced geothermal systems for a particular site. For evaluation of the relative importance of each criterion in decision making, the weight is associated with each of the listed criterions. The different scenarios of end-use applications are tested in the case study. Finally, in the case study, the data and statistics are collected from real geothermal plants. The case study provides results for several scenarios and the sensitivity analysis based on which the approach is validated. The proposed method is expected to be of great interest to investors and decision makers as it enables better risk mitigation