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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Paleoenvironmental Implications of Clay Minerals at Yellowknife Bay, Gale Crater, Mars

The Mars Science Laboratory (MSL) Rover, Curiosity spent approx 150 sols at Yellowknife Bay (YKB) studying a section of fluvio-lacustrine sedimentary rocks (with potential indications of volcanic influence), informally known as the Yellowknife Bay formation. YKB lies in a distal region of the Peace Vallis alluvial fan, which extends from the northern rim of Gale Crater toward the dune field at the base of Mt Sharp. Sedimentological and stratigraphic observations are consistent with the Yellowknife Bay formation being part of a distal fan deposit, which could be as young as middle Hesperian to even early Amazonian in age (approx. 3.5 to 2.5 Ga). The Yellowknife Bay formation hosts a unit of mudstone called the Sheepbed member. Curiosity obtained powdered rock samples from two drill holes in the Sheepbed Member, named John Klein and Cumberland, and delivered them to instruments in Curiosity. Data from CheMin, a combined X-ray diffraction (XRD)/X-ray fluorescence instrument (XRF), has allowed detailed mineralogical analysis of mudstone powders revealing a clay mineral component of approx. 20 wt.% in each sample. The clay minerals are important indicators of paleoenvironmental conditions and sensitive recorders of post-depositional alteration processes. The XRD pattern of John Klein reveals a 02l band consistent with a trioctahedral phyllosilicate. A broad peak at approx. 10A with a slight inflexion at approx. 12A indicates the presence of 2:1 type clay minerals in the John Klein sample. The trioctahedral nature of the clay minerals, breadth of the basal reflection, and presence of a minor component with larger basal spacing suggests that John Klein contains a trioctahedral smectite (probably saponite), whose interlayer is largely collapsed because of the low-humidity conditions. The XRD patterns show no evidence of corrensite (mixed-layer chlorite/smectite) or chlorite, which are typical diagenetic products of trioctahedral smectites when subjected to burial and heating >60 C in the presence of water. Given estimated geothermal gradients on Mars temperatures <60 C might still be consistent with (but do not require) moderate burial. However, our ability to identify interstratified minerals is greatly limited by the lack of access to traditional treatments methods used in the lab (e.g., ethylene glycol solvation). Our preferred explanation for the origin of trioctahedral smectites in Sheepbed mudstone is in situ production via reaction of olivine, water and Si-bearing amorphous material, an important mudstone component detected by XRD. Elevated levels of magnetite in the Sheepbed and the trioctahedral monomineralic nature of the clay minerals support this model. These observations, combined with previous studies of olivine stability, support the persistence of circum-neutral hydrous conditions for thousands of years at YKB.

MSL↗
DOE OSTI2023

What dictates soft clay-like lithium superionic conductor formation from rigid salts mixture

Abstract Soft clay-like Li-superionic conductors, integral to realizing all-solid-state batteries, have been recently synthesized by mixing rigid-salts. Here, through computational and experimental analysis, we clarify how a soft clay-like material can be created from a mixture of rigid-salts. Using molecular dynamics simulations with a deep learning-based interatomic potential energy model, we uncover the microscopic features responsible for soft clay-formation from ionic solid mixtures. We find that salt mixtures capable of forming molecular solid units on anion exchange, along with the slow kinetics of such reactions, are key to soft-clay formation. Molecular solid units serve as sites for shear transformation zones, and their inherent softness enables plasticity at low stress. Extended X-ray absorption fine structure spectroscopy confirms the formation of molecular solid units. A general strategy for creating soft clay-like materials from ionic solid mixtures is formulated.

25 ENERGY STORAGE↗
DOE OSTI2025

Relationship between clay minerals and microorganisms in underground hydrogen storage reservoirs: a mini review

Hydrogen (H 2 ) will play a vital role in the global shift towards sustainable energy systems. Due to the high cost and challenges associated with storing hydrogen in large quantities for industrial applications, Underground Hydrogen Storage (UHS) in geological formations has emerged as a promising solution. Clay minerals, abundant in subsurface environments, play a critical role in UHS by providing low permeability, cation exchange capacity, and stability, essential for preventing hydrogen leakage. However, microorganisms in the subsurface, particularly hydrogenotrophic species, interact with clay minerals in ways that can affect the integrity of these storage systems. Microbes form biofilms on clay surfaces, which can cause pore clogging and reduce the permeability of the reservoir, potentially stabilizing H 2 storage and limiting injectivity. Microbial-induced chemical weathering, through the production of organic acids and redox reactions, can degrade clay minerals, releasing metal ions and destabilizing the storage site. These interactions raise concerns about the long-term storage capacity of UHS, as microbial processes could lead to H 2 loss and caprock degradation, compromising the storage system’s effectiveness. This mini review aims to cover the current understanding of the interactions between clay minerals and microorganisms and how these dynamics can affect the safe and sustainable deployment of UHS .

Clark, Allison↗
NASA NTRS1976

Clays as possible catalysts for peptide formation in the prebiotic era

From the point of view of prebiotic synthesis, clays might have performed functions of concentration, catalysis, and protection of molecules. The degrees of polymerization obtained, when amino acid adenylates are added to montmorillonite suspensions in water, are much higher than those obtained by polymerization in the absence of such a clay. In addition, they are of a discrete spectrum, usually multiples of 6 or 7, and reach values of up to 40 mers. In the absence of clay a continuous spectrum of degrees of polymerization is obtained, and usually up to 4-6 mers only. Copolymerization in the absence of clays yields mostly random copolymers, in their presence mostly block copolymers are obtained. Optical density measurements show that after adsorption has taken place on the clay, stacking of its layers occurs. Polymerization starts only after these stacked layers have been formed

Paecht-Horowitz, M.↗
NASA NTRS1984

Clays and other minerals in prebiotic processes

Clays and other minerals have been investigated in context with prebiotic processes, mainly in polymerization of amino acids. It was found that peptides adsorbed on the clay, prior to polymerization, influence the reaction. The ratio between the amount of the peptides adsorbed and that of the clay is important for the yield as well as for the degrees of polymerization obtained. Adsorption prior to reaction produces a certain order in the aggregates of the clay particles which might induce better reaction results. Excess of added peptides disturbs this order and causes lesser degrees of polymerization. In addition to adsorption, clays are also able to occlude between their layers substances out of the environment, up to very high concentrations.

Paecht-Horowitz, M.↗
NASA NTRS1991

Field trip guidebook on environmental impact of clays along the upper Texas coast

The field trip was prepared to provide an opportunity to see first hand some the environmental hazards associated with clays in the Houston, Texas area. Because of the very high clay content in area soils and underlying Beaumont Formation clay, Houston is a fitting location to host the Clay Mineral Society. Examinations were made of (1) expansive soils, (2) subsidence and surface faulting, and (3) a landfill located southeast of Houston at the Gulf Coast Waste Disposal Authority where clay is part of the liner material.

Garcia, Theron D.↗
NASA NTRS1992

Reflectance Spectroscopy of Palagonite and Iron-Rich Montmorillonite Clay Mixtures: Implications for the Surface Composition of Mars

Mixtures of a Hawaiian palagonite and an iron-rich, montmorillonite clay (15.8 +/- 0.4 wt% Fe as Fe2O3) were evaluated as Mars surface spectral analogs from their diffuse reflectance spectra. The presence of the 2.2 microns absorption band in the reflectance spectrum of clays and its absence in the Mars spectrum have been interpreted as indicating that highly crystalline aluminous hydroxylated clays cannot be a major mineral component of the soil on Mars. The palagonite sample used in this study does not show this absorption feature in its spectrum. In mixtures of palagonite and iron-rich montmorillonite, the 2.2 microns Al-OH clay lattice band is not seen below 15 wt% montmorillonite. This suggests the possibility that iron-rich montmorillonite clay may be present in the soil of Mars at up to 15 wt% in combination with palagonite, and remain undetected in remotely sensed spectra of Mars.

Orenberg, James↗
NASA NTRS2001

Detection of Soluble and Fixed NH4+ in Clay Minerals by DTA and IR Reflectance Spectroscopy : A Potential Tool for Planetary Surface Exploration

Nitrogen is an essential element for life. It is the only element among the six major biogenic elements, C, O, S, O, P, H, whose presence in the Martian soil has not been positively and directly established. We describe here a study assessing the ability to detect NH4 in soils by two methods: differential thermal analysis (DTA) and infrared (IR) reflectance spectroscopy. Four standard clay minerals (kaolinite, montmorillonite, illite and attapulgite) and an altered tephra sample from Mauna Kea were treated with NH4 in this study. Samples of the NH4-treated and leached clays were analyzed by DTA and infrared (IR) reflectance spectroscopy to quantify the delectability of soluble and sorbed/fixed NH4. An exotherm at 270-280 C was clearly detected in the DTA curves of NH4-treated (non-leached) samples. This feature is assigned to the thermal decomposition reaction of NH4. Spectral bands observed at 1.56, 2.05, 2.12, 3.06, 3.3, 3.5, 5.7 and 7.0 microns in the reflectance spectra of NH4-treated and leached samples are assigned to the sorbed/fixed ammonium in the clays. The montmorillonite has shown the most intense absorbance due to fixed ammonium among the leached samples in this study, as a result of its high cation sorption capacity. It is concluded that the presence of sorbed or fixed NH4 in clays may be detected by infrared (IR) reflectance or emission spectroscopy. Distinction between soluble and sorbed NH4 may be achieved through the presence or absence of several spectral features assigned to the sorbed NH4 moietyi and, specifically, by use of the 4.2 micrometer feature assigned to solution NH4. Thermal analyses furnish supporting evidence of ammonia in our study through detection of N released at temperatures of 270-330 C. Based on these results it is estimated that IR spectra measured from a rover should be able to detect ammonia if present above 20 mg NH4/g sample in the surface layers. Orbital IR spectra and thermal analyses measured on a rover may be able to detect ammonia in soils as well but at higher abundances. The spectral features at 3.06 and 7.0 microns due to bound NH4 in clays and altered Hawaiian tephra appear to be the most promising for detection by orbital spectrometers. If N species are present on Mars the sedimentary deposits may be the best regions to look for them.

Janice, Bishop↗
NASA NTRS1994

Sm-Nd dating of Fig Tree clay minerals of the Barberton greenstone belt, South Africa

Sm-Nd isotopic data from carbonate-derived clay minerals of the 3.22-3.25 Ga Fig Tree Group, Barberton greenstone belt, South Africa, form a linear array corresponding to an age of 3102 +/- 64 Ma, making these minerals the oldest dated clays on Earth. The obtained age is 120-160 m.y. younger than the depositional age determined by zircon geochronology. Nd model ages for the clays range from approximately 3.39 to 3.44 Ga and almost cover the age variation of the Barberton greenstone belt rocks, consistent with independent evidence that the clay minerals are derived from material of the belt. The combined isotopic and mineralogical data provide evidence for a cryptic thermal overprint in the sediments of the belt. However, the highest temperature reached by the samples since the time of clay-mineral formation was <300 degrees C, lower than virtually any known early Archean supracrustal sequence.

Non-NASA Center↗
NASA NTRS2013

The First X-ray Diffraction Patterns of Clay Minerals from Gale Crater

The Mars Science Laboratory (MSL) Rover, Curiosity spent approx 150 sols at Yellowknife Bay (YKB) studying a section of fluvio-lacustrine sedimentary rocks (with potential indications of volcanic influence), informally known as the Yellowknife Bay formation. YKB lies in a distal region of the Peace Vallis alluvial fan, which extends from the northern rim of Gale Crater toward the dune field at the base of Mt Sharp. Sedimentological and stratigraphic observations are consistent with the Yellowknife Bay formation being part of a distal fan deposit, which could be as young as middle Hesperian to even early Amazonian in age (approx 3.5 to 2.5 Ga). The Yellowknife Bay formation hosts a unit of mudstone called the Sheepbed member. Curiosity obtained powdered rock samples from two drill holes in the Sheepbed Member, named John Klein and Cumberland, and delivered them to instruments in Curiosity. Data from CheMin, a combined X-ray diffraction (XRD)/X-ray fluorescence instrument (XRF), has allowed detailed mineralogical analysis of mudstone powders revealing a clay mineral component of approx 20 wt.% in each sample. The clay minerals are important indicators of paleoenvironmental conditions and sensitive recorders of post-depositional alteration processes. The XRD pattern of John Klein reveals a 021 band consistent with a trioctahedral phyllosilicate. A broad peak at approx 10A with a slight inflexion at approx 12A indicates the presence of 2:1 type clay minerals in the John Klein sample. The trioctahedral nature of the clay minerals, breadth of the basal reflection, and presence of a minor component with larger basal spacing suggests that John Klein contains a trioctahedral smectite (probably saponite), whose interlayer is largely collapsed because of the low-humidity conditions. The XRD patterns show no evidence of corrensite (mixed-layer chlorite/smectite) or chlorite, which are typical diagenetic products of trioctahedral smectites when subjected to burial and heating >60degC in the presence of water. Given estimated geothermal gradients on Mars temperatures <60 degC might still be consistent with (but do not require) moderate burial. However, our ability to identify interstratified minerals is greatly limited by the lack of access to traditional treatments methods used in the lab (e.g., ethylene glycol solvation). Our preferred explanation for the origin of trioctahedral smectites in Sheepbed mudstone is in situ production via reaction of olivine, water and Si-bearing amorphous material, an important mudstone component detected by XRD. Elevated levels of magnetite in the Sheepbed and the trioctahedral monomineralic nature of the clay minerals support this model. These observations, combined with previous studies of olivine stability, support the persistence of circum-neutral hydrous conditions for thousands of years at YKB.

Bristow, Thomas↗
NASA NTRS2016

Ground Truthing Orbital Clay Mineral Observations with the APXS Onboard Mars Exploration Rover Opportunity

NASA's Mars Exploration Rover Opportunity has been exploring approximately 22 km diameter Endeavour crater since 2011. Its rim segments predate the Hesperian-age Burns formation and expose Noachian-age material, which is associated with orbital Fe3+-Mg-rich clay mineral observations [1,2]. Moving to an orders of magnitude smaller instrumental field of view on the ground, the clay minerals were challenging to pinpoint on the basis of geochemical data because they appear to be the result of near-isochemical weathering of the local bedrock [3,4]. However, the APXS revealed a more complex mineral story as fracture fills and so-called red zones appear to contain more Al-rich clay minerals [5,6], which had not been observed from orbit. These observations are important to constrain clay mineral formation processes. More detail will be added as Opportunity is heading into her 10th extended mission, during which she will investigate Noachian bedrock that predates Endeavour crater, study sedimentary rocks inside Endeavour crater, and explore a fluid-carved gully. ESA's ExoMars rover will land on Noachian-age Oxia Planum where abundant Fe3+-Mg-rich clay minerals have been observed from orbit, but the story will undoubtedly become more complex once seen from the ground.

Schroeder, C.↗
NASA NTRS2020

Glen Torridon Mineralogy and the Sedimentary History of the Clay Mineral Bearing Unit

Clay minerals are common in ancient terrains on Mars and their presence at the surface alludes to aqueous processes in the Noachian to Early Hesperian (>3.5 Ga). Gale crater was selected as Curiosity’s landing site largely because of the identification of clay mineral rich strata from orbit. On Earth, the types of clay minerals (i.e., smectites) identified in Gale crater are typically juvenile weathering products that ultimately record the interaction between primary igneous minerals with the hydrosphere, atmosphere, and biosphere. Trioctahedral and dioctahedral smectite were identified by Curiosity in units stratigraphically below the Clay Mineral-Bearing Unit (CBU) identified from orbit. Compositional and sedimentological data suggest the smectite formed via authigenesis in a lake environment and may have been altered during early diagenesis. The CBU is stratigraphically equivalent to a hematite-rich unit to the north and stratigraphically underlies sulfate-rich units to the south, suggesting a dynamic environment and evolving history of water in the ancient Gale crater lake. Targeting these clay mineral rich areas on Mars with rover missions provides an opportunity to explore the aqueous and sedimentary history of the planet.

Thorpe, M. T.↗
DOE OSTI2023

Electronic Structure and Mechanical Properties of Solvated Montmorillonite Clay Using Large-Scale DFT Method

Montmorillonite clay (MMT) has been widely used in engineering and environmental applications as a landfill barrier and toxic waste repository due to its unique property as an expandable clay mineral that can absorb water easily. This absorption process rendered MMT to be highly exothermic due to electrostatic interactions among molecules and hydrogen bonds between surface atoms. A detailed study of a large supercell model of structural clay enables us to predict long-term nuclear waste storage. Herein, a large solvent MMT model with 4071 atoms is studied using ab initio density functional theory. The DFT calculation and analysis clarify the important issues, such as bond strength, solvation effect, elasticity, and seismic wave velocities. These results are compared to our previous study on crystalline MMT (dry). The solvated MMT has reduced shear modulus (G), bulk modulus (K), and Young’s modulus (E). We observe that the conduction band (CB) in the density of states (DOS) of solvated MMT model has a single, conspicuous peak at –8.5 eV. Moreover, the atom-resolved partial density of states (PDOS) summarizes the roles played by each atom in the DOS. These findings illuminate numerous potential sophisticated applications of MMT clay.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Recycling of Pretreated Polyolefin-Based Ocean-Bound Plastic Waste by Incorporating Clay and Rubber

Plastic waste found in oceans has become a major concern because of its impact on marine organisms and human health. There is significant global interest in recycling these materials, but their reclamation, sorting, cleaning, and reprocessing, along with the degradation that occurs in the natural environment, all make it difficult to achieve high quality recycled resins from ocean plastic waste. To mitigate these limitations, various additives including clay and rubber were explored. In this study, we compounded different types of ocean-bound (o-HDPE and o-PP) and virgin polymers (v-LDPE and v-PS) with various additives including a functionalized clay, styrene-multi-block-copolymer (SMB), and ethylene-propylene-based rubber (EPR). Physical observation showed that all blends containing PS were brittle due to the weak interfaces between the polyolefin regions and the PS domains within the polymer blend matrix. Blends containing clay showed rough surfaces and brittleness because of the non-uniform distribution of clay particles in the polymer matrix. To evaluate the properties and compatibility of the blends, characterizations using differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and small-amplitude oscillatory shear (SAOS) rheology were carried out. The polymer blend (v-LDPE, o-HDPE, o-PP) containing EPR showed improved elasticity. Incorporating additives such as rubber could improve the mechanical properties of polymer blends for recycling purposes.

42 ENGINEERING↗
DOE OSTI2021

Evolution of anisotropy with saturation and its implications for the elastoplastic responses of clay rocks

Many clay rocks have distinct bedding planes. Experimental studies have shown that their mechanical properties evolve with the degree of saturation (DOS), often with higher stiffness and strength after drying. For transversely isotropic rocks, the effects of saturation can differ between the bed-normal (BN) and bed-parallel (BP) directions, which gives rise to saturation-dependent stiffness and strength anisotropy. Accurate prediction of the mechanical behavior of clay rocks under partially saturated conditions requires numerical models that can capture the evolving elastic and plastic anisotropy with DOS. In this study, we present an anisotropy framework for coupled solid deformation-fluid flow in unsaturated elastoplastic media. Here we incorporate saturation-dependent strength anisotropy into an anisotropic modified Cam-Clay (MCC) model and consider the evolving anisotropy in both the elastic and plastic responses. The model was calibrated using experimental data from triaxial tests to demonstrate its capability in capturing strength anisotropy at various levels of saturation. Through numerical simulations, we demonstrate the role of evolving stiffness and strength anisotropy in the mechanical behavior of clay rocks. Plane strain simulations of triaxial compression tests were also conducted to demonstrate the impacts of material anisotropy and DOS on the mechanical and fluid flow responses.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Competitive Sorption of H 2 O and CO 2 in Clay Mineral Interlayers

The first-reported competitive CO 2 –H 2 O sorption isotherms on a naturally occurring expandable clay mineral (saponite) exchanged with Na, K, and Cs at near ambient CO 2 concentrations (1% CO 2 ) are reported by combining ATR-FTIR spectroscopy with gravimetric sorption methods. Little CO 2 sorption was observed at high relative humidity (RH) but increased significantly at low RH. Unlike prior work where CO 2 sorption was reported on samples that were previously subjected to heating and/or evacuation treatment to remove sorbed H 2 O, this study manipulated CO 2 sorption by controlling RH. CO 2 sorption increased in the order Cs- > K- > Na-exchanged saponite and was anticorrelated with the Gibbs energy of hydration of the exchangeable cation. As expected, H 2 O sorption followed the opposite trend, with increased H 2 O sorption occurring in the order Na > K > Cs. The amount of CO 2 sorbed using 1 atm CO 2 (p/p o = 1.0) ranged from 50 to 30 mg CO 2 /g clay and from 1.25 to 0.8 mg CO2 /g clay for 1% CO 2 (p/p o = 0.01) in N 2 . The sensitivity of the ATR-FTIR measurements is demonstrated by detecting the CO 2 stretch of adsorbed CO 2 from air containing 500 ppmv CO 2 . The spectral features of sorbed CO 2 were minimally affected by the nature of the exchangeable cation or variations in H 2 O content. However, the position of the HOH bending band shifted significantly from 1638 to 1610 cm –1 as H 2 O content decreased, reflecting changes in intermolecular hydrogen bonding between H 2 O molecules in the saponite interlayer. The shift in position of the HOH bending band to lower energy was coincident with increased CO 2 sorption. CO 2 sorption in clay mineral interlayers is consistent with sorption on weakly hydrated partially hydrophobic sites found on low charge density smectites and is enhanced by lower RH and by the presence of weakly hydrated exchangeable cations like Cs + or K + . In conclusion, the greatest CO 2 sorption occurs on Cs-saponite because this is the least hydrated cation of the three used in the study and indicates that CO2 sorption occurs on the neutral portion of the siloxane surface.

Johnston, Cliff T. [Purdue Univ., West Lafayette, ↗
DOE OSTI2023

The Role of Clay in Limiting Frictional Healing in Fault Gouges

Abstract Frictional healing is fundamental to the seismic cycle and plays a role in the energy balance, dynamics, and recurrence interval of earthquakes and slow slip events. Although the healing behavior of quartz has been studied extensively, the role of clay content is less understood. We tested synthetic mixtures of quartz and smectite (10%–100% smectite) in a double‐direct shear configuration to measure frictional healing. We show that the magnitude and rate of healing decreases systematically with higher clay content (from 0.008/decade at 10% smectite to 0.002/decade at 100% smectite). Healing scales with both the magnitude of stress relaxation during holds and layer‐normal compaction of the gouge. We suggest this reflects the alignment of clay minerals, leading to saturation of the real area of contact that limits restrengthening during holds. The low healing rates of clay‐rich faults—together with rate‐neutral to rate‐strengthening friction—should promote frequent, small failures or stable sliding.

58 GEOSCIENCES↗
DOE OSTI2025

Control Mechanisms for Self‐Sealing in Activated Clay‐Rich Faults Through Controlled Hydraulic Injection Experiment

Abstract In a high‐pressure injection fault activation experiment conducted at the Mont Terri underground research laboratory in Switzerland, the transmissivity of the Opalinus Clay fault significantly increased due to opening and shearing. The fluid injection, spanning a few hours, generated a 10 m radius fault activation patch. Subsequent pressure pulse tests conducted bi‐weekly for a year revealed the gradual return of fault transmissivity to its initial state. The study utilized fluid pressure decay analysis, optical fiber monitoring, continuous active source seismic measurements and borehole displacement sensors for measuring fault displacements. The fault zone exhibited a dilation of approximately 1.4 mm, associated with both normal and tangential movements during activation, resulting in a sudden transmissivity increase from 1 × 10 −12 to 3.2 × 10 −7 m 2 /s. Early post‐activation, transient compaction and the subsequent slow compaction were observed, transitioning to an extension regime. The pressure pulse tests demonstrated a rapid transmissivity drop by more than two orders of magnitude within the first 10 days, followed by a gradual and less pronounced decrease. Plastic shear and compaction dominated the transmissivity evolution until 70 days after injection ended, followed by a period where additional factors, such as clay mineral swelling, influenced the behavior. Extrapolation suggested a sealing process taking at least 50 years after the initial activation. Plain Language Summary A field‐scale fault activation experiment offers valuable insights into the elasto‐plastic processes governing the sealing of shale faults. The experiment reveals a rapid increase in the fault's transmissivity by approximately five orders of magnitude during activation. Subsequent observations show a gradual transmissivity decrease by about three orders of magnitude post‐activation, with slow long‐term plastic shear and compaction of the fault competing against secondary processes, notably clay mineral swelling. All conceptual models employed to interpret these field data converge on the estimation that the fault's return to its initial low transmissivity state would require a minimum of 50 years. Key Points High‐pressure injection fault activation experiment at the Mont Terri underground research laboratory Continuous transmissivity measurements record self‐sealing inside a clay‐rich fault zone Transmissivity undergoes a phase of domination by slow plastic compaction and shearing during the initial post‐activation period, with mineral swelling exerting its influence over the long term

Guglielmi, Yves↗