Only few data from geothermal exploited reservoirs are available due to the restricted accessibility by drilling, which limits the understanding of the entire reservoir. Thus, analogue investigations are needed and were performed in the framework of the H2020 MEET project. The Noble Hills range, located along the southern branch of the Death Valley pull-apart (CA, USA), has been selected as a possible granitic paleo-reservoir. The aim is to characterize the pervasive alteration processes affecting this granite, away from the influence of the faults, in terms of mineralogical, petrophysical and chemical changes. Various methods were used as petrographic, geochemical and petrophysical analyses. Mineral changes, clay mineralogy, bulk rock chemical composition, calcite content and porosity were determined on different granite samples, collected in the Noble Hills granite, far from the faults and in the Owlshead Mountains, north of the Noble Hills, considered as its protolith. In order to complete the granite characterization, the metamorphic grade has been studied through the Noble Hills granite body. This complete characterization has allowed distinguishing the occurrence of three stages of alteration: (1) a pervasive propylitic alteration characterized by calcite-corrensite-epidote-K-white mica assemblage, (2) a more local one, only present in the Noble Hills granite, producing illite, kaolinite, illite/smectite, calcite and oxides, characteristic of the argillic alteration, which overprints the propylitic alteration and (3) weathering evidenced by the presence of montmorillonite in the Owlshead Mountains, which is considered as negligible in both granites. Alteration was also outlined by the correlation of the loss on ignition, representing the hydration rate, to porosity, calcite content and chemical composition. Moreover, the Kübler Index calculated from illite crystals allowed to identify a NW-SE temperature gradient in the Noble Hills.

Fracture connectivity within fractured granitic basement geothermal reservoirs is an important factor controlling their permeability. This study aims to improve the understanding of fluid–rock interaction processes at low to moderate regional strain. The Noble Hills range (Death Valley, CA, USA) was chosen as a naturally exhumed paleo geothermal reservoir. A series of petrographic, petrophysical, and geochemical investigations, combined with a fracture distribution analysis, were carried out on samples collected across fracture zones. Our results indicate that several generations of fluids have percolated through the reservoir. An increase of (1) the alteration degree; (2) the porosity values; and (3) the calcite content was observed when approaching fracture zones. No correlation was identified among the alteration degree, the porosity, or the calcite content. At a local scale, samples showed that the degree of alteration does not necessarily depend on the fracture density or on the amount of the strain. It is concluded that the combined influence of strain and coeval fluid–rock interaction processes drastically influence the petrophysical properties of fracture zones, which in turn impact geothermal production potential.

The building and construction sector is the largest emitter of greenhouse gases, accounting for 37% of global emissions. The production and use of materials such as cement, steel, and aluminum contribute significantly to this carbon footprint. Utilizing valorized agricultural by-products, such as hemp shiv and sunflower pith, in construction can enhance the insulating properties of materials and reduce their environmental impact by capturing CO₂. Additionally, during the formulation process, molecules such as polyphenols and sugars are released, depending on process parameters like pH and temperature. In some cases, these releases can cause issues, such as delaying the hardening of agro-based concrete or serving as binding agents in binderless particle boards. This study focuses on the molecules released during the processing of these materials, with particular attention to the effects of pH and temperature, and the modifications to the plant particles resulting from these conditions. Physical, chemical, and morphological analyses were conducted on the treated hemp shiv particles (HS1 and HS2). No physical or morphological differences were observed between the samples. However, chemical differences, particularly in the lignin and soluble compound content, were noted and were linked to the release of plant substances during the process.

Between -16.9 and -13.8 Ma a hyperthermal event called the Middle Miocene Climatic Optimum (MMCO) took place (Hansen et al. 2013). During the MMCO, the climate in Western Europe was subtropical to semi-arid (Costeur & Legendre 2008), with temperatures 4 to 5 °C higher than today (Hansen et al., 2013). The Centre-Val de Loire region, located south-west of the Paris Basin, was characterised by various depositional environments (lacustrine, fluvial and shallow-marine; Fig. 1) (Mégnien et al. 1980), recorded in 5 Formations encompassing the Miocene and thus providing geological data for the entire MMCO: 1- The Beauce lacustrine limestone formation (Oligocene-Aquitanian), which covers a large part of Beauce and Sologne (Ginsburg, 2000). 2- The Orléanais and Blésois sand and marl formation (Burdigalien-Langhien), which extends between Orléans and Angers, corresponds to a series of terrigenous sediments of fluvio-lacustrine origin. These sediments are channelized by folded plicative East-West tectonic structures inherited from the Alpine orogeny. 3- The Faluns Formation (Langhien), which is a shallow marine lateral equivalent of the Orléans and Blésois sands and marls. It is exposed from the Loire-Atlantique to Blois. Locally, the marine sedimentation continues until the Tortonian (Gagnaison 2020). 4 & 5- The fluvio-lacustrine formation of the Sologne sands and clays (Middle Miocene-Pliocene), which outcrops in the east of the Loire sedimentary basin and grades westwards to the Redonian marine sands formation. The aim of this study is to refine the dating of these different sedimentary formations to characterize the palaeoenvironmental changes associated to the MMCO.