To avoid the negative consequences of climate change, there is an urgent need to remove carbon dioxide from the atmosphere. Carbon mineralization-the conversion of injected CO2 into stable carbonate minerals-offers a promising pathway for large-scale, permanent geologic storage. While projects such as CarbFix have demonstrated its feasibility, optimizing and scaling in situ mineralization requires a deeper understanding of rock-fluid interactions and how carbonate precipitation alters rock properties. Previous studies have shown that elasticity, porosity, and permeability are all sensitive to mineral precipitation, but few have monitored their concurrent evolution. Here, we present flow-through experiments on thermally cracked vesicular Iceland basalt in which permeability, porosity, ultrasonic velocity, and outlet fluid chemistry were tracked during carbonate precipitation from reactive fluids. Experiments were conducted with the apparatus inside an X-ray micro-computed tomography (CT) scanner, which provided 3D whole-rock data sets at 11.5 m resolution every 20-40 min during flow. Results show that permeability decreases by one to two orders of magnitude within hours, while porosity declines by less than 4% over 24-90 hr. In contrast, ultrasonic velocity increases by up to 10% in step with permeability loss, demonstrating strong sensitivity to precipitation in critical flow pathways. Scanning electron microscope and CT imaging reveal a transition from dendritic and sheet-like morphologies at high flow and supersaturation to rhombic calcite crystals as permeability and flow decrease. These findings highlight the coupling between precipitation dynamics, pore-scale heterogeneity, and bulk rock properties, and offer avenues for optimizing and monitoring carbon mineralization in the field.

Three models have been proposed to explain the downdip limit of the subduction seismogenic zone. The first is a temperature-controlled transition in rate-and-state frictional properties between 350–510°C, which inhibits earthquake nucleation. The second places the limit at the frictional and viscous failure envelope intersection. The third combines thermal and lithological controls, where 'warm' subduction zones are controlled by a 350°C frictional transition and 'cold' subduction zones are limited by the overriding plate Moho. To evaluate these hypotheses, we integrate thermal models with seismicity catalogs from 17 subduction zones. Observed depth limits remain remarkably consistent (~50 km) across a temperature range exceeding 250°C, indicating that the temperature-controlled rate-and-state friction model cannot fully explain observed depths. While warm subduction zones can be reasonably explained as a rate-and-state stability transition, the overriding plate Moho in cold subduction zones is too shallow, challenging the combined thermal-lithological model. To test the frictional-viscous model, we analyze power law creep and low-temperature plasticity for quartz, feldspar, olivine, antigorite, and talc. We find that power law creep in any tested mineral is overly temperature sensitive. In contrast, wet olivine, antigorite, and talc low-temperature plasticity fits observed depth limits to a ~6 km misfit. However, only talc is consistent with the weak megathrust paradigm of effective friction coefficients <0.1 and shear strengths of tens of MPa. We conclude that a frictional-viscous transition with a weak and temperature-insensitive viscous mechanism, such as talc low-temperature plasticity, is most consistent with the downdip seismicity limit and constraints on megathrust strength.

Abstract Dynamic weakening during earthquake ruptures is essential for accommodating fault slip and controlling seismic energy release. This weakening is localized within narrow principal slip zones (PSZs) that commonly contain nanoparticles in both natural and experimental faults. Although weakening is dominated by thermally activated mechanisms, the thermal and mechanical effects of extreme grain‐size reduction in PSZs remain poorly constrained. We examine the melting behavior of dry granitoid fault rocks ball‐milled to mean grain sizes from 150 μm to 300 nm. Differential scanning calorimetry reveals a decrease in melting temperature, from 1,270°C to 1,090°C, with decreasing grain size. Our results demonstrate that extreme grain‐size reduction lowers the temperatures required for dynamic weakening via melting. Comparisons with previous studies suggest PSZs are enriched in ultrafine, mechanically weak mineral phases that can influence frictional melt composition. In natural faults, this effect is likely amplified by complex mineralogy, high pressure–temperature conditions, and fluids.

Slip-induced heating is crucial for understanding fault mechanics and energy partitioning during earthquakes. The strongest heating occurs in a thin, millimeter to sub-millimeter-scale zone, which poses a challenge for existing geothermometers because they lack spatial resolution or are limited to specific rock compositions. Here, we utilize the recently developed quantum diamond microscope (QDM) to resolve thermal demagnetization at micrometer resolution around experimentally produced slip zones, thereby quantifying the near-field slip-induced temperature excursion. This new technique also enables us to observe similar to 300 mu m-scale along-fault heterogeneities in heating intensity, highlighting the role of localized stress and deformation in guiding frictional evolution. A simple 1-dimensional heat diffusion model can simultaneously satisfy the temperature estimates from QDM, far-field thermocouple measurements, and microstructural observations of localized melting. This model constrains the thermal energy density during slip to be 52-65 kJ/m2 during our laboratory earthquakes, which accounts for 52%-75% of the total energy budget. We also estimate that the average friction coefficient during rapid slip is 0.2-0.3, suggesting significant weakening during slip. Our results provide new insights into the role of localized heating during earthquake-like failure and illuminate the role of thermal weakening mechanisms at pressures corresponding to the base of the seismogenic crust.

The habitability of icy moons in the outer Solar System is linked to their ability to maintain warm subsurface oceans through time. While most heat generation in response to tidal forcing is thought to occur in icy crusts and water oceans, the actual response of silicic material to deformation under relevant planetary conditions has not previously been studied comprehensively in a laboratory setting. Similar meteoritic material is often studied at room pressure instead of at the 10s to 100s of MPas of pressure present at depth in moons, and subjected to dynamic forces to simulate impacts rather than observed under quasistatic loading and deformation. In the absence of laboratory constraints on peak strength and deformation behavior, large errors remain for estimates of heat contribution from the mantles, as well as in models of seismic and elastic properties of icy moon interiors. We experimentally deformed samples of the Kilabo meteorite, an LL6 chondrite, under axial strain rates of 10-5 s-1 and confining pressures up to 100 MPa. We recorded the strength of the material, calculated energy dissipation through acoustic emission events, and measured how ultrasonic wavespeeds evolved as a function of confining pressure. Dissipative microcracking events occurred at all pressures, even at low stresses during isotropic pressurization and nominally “elastic” deformation. These events were most common at low confining pressures. The mechanical behavior of the meteoritic material also evolved as a function of confining pressure: peak strength occurred at 50 MPa laboratory confining pressure, and material continuously stiffened as pressure increased. These pressure-dependent properties indicate that larger icy planetary bodies may have stiffer, less deformable silicate layers than those found in small icy satellites. Rocky interior deformation could therefore contribute to the bulk heat budget required to maintain subsurface oceans in Ariel and Miranda, along with many other smaller icy moons in the outer Solar System.

Mafic blueschist is ubiquitous along the plate interface from the base of the seismogenic zone to blueschist-to-eclogite transition depths in many subduction zones. Currently, the deformation mechanisms of the rheology-controlling mineral glaucophane in blueschists are controversial. Dislocation creep, diffusion creep, and semi-brittle deformation have all been proposed, with specific implications for each in modulating slip behavior. We document the preserved deformation mechanisms in a lawsonite blueschist that equilibrated at similar to 300 degrees C and 1.0 GPa in the Catalina Schist on Pimu'nga (Santa Catalina Island, California, USA) through a novel method coupling weighted Burgers vector (WBV) and misorientation analyses of glaucophane. Electron backscattered diffraction-based analyses reveal strong crystallographic and shape preferred orientations in glaucophane and dislocations organized into subgrain boundaries. Misorientation distributions further illustrate dislocation-accommodated deformation and dynamic recrystallization by subgrain rotation (SGR). Subgrain boundaries show WBVs composed primarily of <100>, <010>, and <110> components, with lower representation of "easy" slip on <001> WBVs. Misorientation analysis demonstrates mother-daughter relationships between elongated core grains and recrystallized grains. Limited chemical zoning along microfractures suggests subsidiary diffusion creep during exhumation. Our results clearly document blueschist deformation primarily accommodated by dislocation creep and SGR recrystallization at pressure-temperature conditions of the base of the seismogenic zone.

Understanding the interplay of various energy sinks during seismic fault slip is essential for advancing earthquake physics and improving hazard assessment. However, quantifying the energy consumed by major dissipative processes remains a challenge. In this study, we investigate energy partitioning during laboratory earthquakes ("lab-quakes") by performing general shear stick-slip experiments on synthetic granitic cataclasites at elevated confining pressure. Using ultrasound, microstructural, and novel magnetism-based thermal analyses, we independently quantified the energy allocated to seismic radiation, new surfaces, and heat dissipation. These estimates showed good agreement with far-field measurements of mechanical work during the lab-quake. Our findings revealed that under the experimental conditions the majority of the released energy (68%-98%) is dissipated as heat, while seismic radiation accounts for 1%-8%, and the creation of new surfaces consumes <1%-32%. Microstructural observations indicate pre-failure deformation, which includes comminution and development of the principal slip zone, significantly influences energy partitioning. This effect is further evident in the measured shear stress drops, where events with higher stress drops proportionally emitted more energy as seismic waves. This study is the first to constrain the full energy budget of lab-quakes from an observational standpoint, providing critical insights into the dynamics of fault rupture and energy dissipation processes.

The interplay between melt, crystals, andvolatile bubbles controls the physical properties of magmas in Earth's crust, the rate of phase separation, and, by extension, chemical differentiation. The mechanical processes that couple crystals, bubbles, and melt are nonlinear, and their expression in magmatic systems can vary greatly with the relative phase proportions in the magma. In this review we propose a multiscale perspective on multiphase magmas under crustal storage conditions, with a specific focus on phase separation mechanisms. We start with an inventory of forces acting on a single crystal or volatile bubble in a silicate melt. We follow with a discussion of different upscaling strategies to simplify the description of the dynamics at greater scales, relevant to the evolution of magma reservoirs.We discuss recent progress in the development of models to study the internal dynamics of magma reservoirs, highlight current challenges, and propose possible paths for further progress. ▪ The mechanical interaction between the constituents (melt, crystals, and bubbles) at the scale of crystals controls the properties of magmas. ▪ The choice of upscaling strategy is controlled by the processes that are considered. ▪ Melt-crystal separation processes and their efficiency vary with the relative proportion of the phases involved. ▪ Melt extraction by repacking is fast compared to compaction but stalls as the mush reaches the maximum packing.

The rheology and deformation mechanisms of mafic blueschists play a key role in the mechanical behavior of subducting oceanic crust in subduction zones. While mafic blueschists are often ubiquitous along the plate interface from the base of the seismogenic zone (~35 km) to the sub-arc depths (~100 km), the strength of this lithology still remains poorly constrained. Observations of blueschists from exhumed subduction terranes suggests that blueschist can accommodate significant strain, largely partitioned into the sodic amphibole glaucophane. However, it remains an open question whether the observed deformation is accommodated by dislocation or diffusion deformation processes.We present microstructural and textural analyses to investigate the glaucophane fabric and deformation mechanisms in three naturally deformed blueschists exhumed from variable P-T conditions: (1) a lawsonite blueschist from the Catalina Schist (Santa Catalina Island, CA, USA), (2) higher-grade epidote blueschist from the Bandon blueschist (Bandon, OR, USA) and (3) an epidote-blueschist from the Cycladic Blueschist Unit (Tinos, GR). We used electron backscatter diffraction (EBSD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to interpret the textural and geochemical record of deformation mechanisms that were active during the subduction history of these exhumed blueschists. All three blueschists display well-developed foliations and lineations which are defined by interconnected layers of glaucophane. EBSD microstructural analysis of glaucophane in the samples reveals evidence of dislocation accommodated deformation including: (1) strong crystallographic preferred orientation (CPO) development, (2) intragranular orientation gradients, (3) activity of dislocation motion on multiple slip systems, and (4) subgrain boundary formation. Core-mantle structures in which the daughter grains display evidence of a weakened CPO inherited from the mother (core) grains imply the activity of subgrain boundary recrystallization in the samples. Taken together, this microstructural evidence implies that dislocation creep accommodated deformation was active in all three blueschists during their deformation history. SEM images and EDS maps of glaucophane reveal evidence of chemical zoning in grains with higher Ca and Al concentrations in the rims and along the walls of (micro)fractures within the grains (Bandon, OR Sample). The Catalina lawsonite blueschist displays interspersed evidence of microfractures with higher concentrations of Fe and lower Al and Mg concentrations. This chemical zoning and microfractures suggest micro-boudinage and/or coupled dissolution-precipitation occurred in these samples, and that potential fluid-mediated diffusion accommodated deformation processes may be preserved in these two mafic blueschists. We leverage the relationships between the textural and chemical evidence in concert with P-T estimates for their host terranes to interpret the deformation histories of these samples during subduction and exhumation. Crosscutting relationships between the chemical zoning and intragranular orientation gradients in the samples suggests that dislocation-related deformation was prograde and predates diffusion-related processes which became active in the Catalina and Bandon samples at or near peak conditions and during retrogression. Together, these results suggest that glaucophane can readily deform by dislocation creep, and also record fluid-mediated processes during deformation.

The conventional observables to identify a habitable or inhabited environment in exoplanets, such as an ocean glint or abundant atmospheric O$_2$, will be challenging to detect with present or upcoming observatories. Here we suggest a new signature. A low carbon abundance in the atmosphere of a temperate rocky planet, relative to other planets of the same system, traces the presence of substantial amount of liquid water, plate tectonic and/or biomass. We show that JWST can already perform such a search in some selected systems like TRAPPIST-1 via the CO$_2$ band at $4.3\,\rm \mu m$, which falls in a spectral sweet spot where the overall noise budget and the effect of cloud/hazes are optimal. We propose a 3-step strategy for transiting exoplanets: 1) detection of an atmosphere around temperate terrestrial planets in $\sim 10$ transits for the most favorable systems, (2) assessment of atmospheric carbon depletion in $\sim 40$ transits, (3) measurements of O$_3$ abundance to disentangle between a water- vs biomass-supported carbon depletion in $\sim100$ transits. The concept of carbon depletion as a signature for habitability is also applicable for next-generation direct imaging telescopes.

In the Earth's upper crust, rocks deform mostly by means of brittle fracturing processes. At the micro-scale these processes involve the formation and growth of microcracks in the vicinity of defects such as open fissures, pores and other cavities. Large defects can produce strong enough perturbations of the stress field to activate and/or intensify brittle damage around them. Here we considered the ideal cases of smooth cylindrical and spherical pores inside an infinite solid body subjected to remote triaxial compressive stresses (i.e., the intermediate and minimum principal stresses are assumed equal). We first established the resulting local stress field around one of those large pores and then verified whether certain brittle damage processes could be activated in these conditions. We mainly considered the formation of tensile microcracks and micro shear bands. The former requires the presence of tensile stresses in some regions around the pore, while the latter needs sufficiently large shear stresses on pre-existing optimally inclined microcracks to overcome their frictional resistance to sliding. We find that shear driven deformation remains localized in the vicinity of the pore. On the other hand, dilatational, tensile cracks can propagate large distances away from the pore but cannot form at and above some threshold ratio of the least to the largest principal stresses. Faulting associated with interacting tensile cracks is therefore suppressed with increasing depth. Our analysis leads to conclusions generally consistent with published experimental observations and provides some clues to discuss the physical cause of the brittle-ductile transition in rocks.

Before large volumes of crystal poor rhyolites are mobilized as melt, they are extracted through the reduction of pore space within their corresponding crystal matrix (compaction). Petrological and mechanical models suggest that a significant fraction of this process occurs at intermediate melt fractions (ca. 0.3-0.6). The timescales associated with such extraction processes have important ramifications for volcanic hazards. However, it remains unclear how melt is redistributed at the grain-scale and whether using continuum scale models for compaction is suitable to estimate extraction timescales at these melt fractions. To explore these issues, we develop and apply a two-phase continuum model of compaction to two suites of analog phase separation experiments-one conducted at low and the other at high temperatures, T, and pressures, P. We characterize the ability of the crystal matrix to resist porosity change using parameterizations of granular phenomena and find that repacking explains both data sets well. A transition between compaction by repacking to melt-enhanced grain boundary diffusion-controlled creep near the maximum packing fraction of the mush may explain the difference in compaction rates inferred from high T + P experiments and measured in previous deformation experiments. When upscaling results to magmatic systems at intermediate melt fractions, repacking may provide an efficient mechanism to redistribute melt. Finally, outside nearly instantaneous force chain disruption events occasionally recorded in the low T + P experiments, melt loss is continuous, and two-phase dynamics can be solved at the continuum scale with an effective matrix viscosity. Magma chambers in the continental crust are believed to be "mushy," meaning they are reservoirs rich in both crystals and magma. The magma occupies the pore space between a connected network of crystals and the difference in density between crystal and magma leads to separation. During the separation process, the crystal networks behave like a sponge and magma percolates upward and is extracted as the pore space in the network of crystals closes. Magma collects atop the "sponge" and can potentially go on to feed volcanic eruptions at the Earth's surface. Therefore, how quickly it can separate has implications for monitoring volcanic hazards. When the porosity of the "sponge" is sufficiently low, the closing of pore space can only proceed if individual crystals are deformed (bent, for instance) and the process is slow. At larger porosities, however, the pore space can be closed by the sliding or rotation of crystals. We model this sliding process and compare our model to analog experiments and find that sliding may allow for this process to be efficient. Continuum model fits repacking experiments data of Hoyos et al. (2022) despite their stochastic nature At intermediate melt fractions, mechanical repacking of particles may contribute significantly to the resistance of mushes to compaction Particle-particle friction, rather than hydrodynamic effects, dominates viscous resistance associated with repacking

Seismic anisotropy constitutes a useful tool for imaging the structure along the plate interface in subduction zones, but the seismic properties of mafic blueschists, a common rock type in subduction zones, remain poorly constrained. We applied the technique of electron backscatter diffraction (EBSD) based petrofabric analysis to calculate the seismic anisotropies of 14 naturally deformed mafic blueschists at dry, ambient conditions. The ductilely deformed blueschists were collected from terranes with inferred peak P-T conditions applicable to subducting slabs at or near the plate interface in active subduction zones. Epidote blueschists display the greatest P wave anisotropy range (AVp similar to 7%-20%), while lawsonite blueschist AVp ranges from similar to 2% to 10%. S wave anisotropies generate shear wave splitting delay times up to similar to 0.1 s over a thickness of 5 km. AVp magnitude increases with glaucophane abundance (from areal EBSD measurements), decreases with increasing epidote or lawsonite abundance, and is enhanced by glaucophane crystallographic preferred orientation (CPO) strength. Two-phase rock recipe models provide further evidence of the primary role of glaucophane, epidote, and lawsonite in generating blueschist seismic anisotropy. The symmetry of P wave velocity patterns reflects the deformation-induced CPO type in glaucophane-an effect previously observed for hornblende on amphibolite P wave anisotropy. The distinctive seismic properties that distinguish blueschist from other subduction zone rock types and the strong correlation between anisotropy magnitude/symmetry and glaucophane CPO suggest that seismic anisotropy may be a useful tool in mapping the extent and deformation of blueschists along the interface, and the blueschist-eclogite transition in active subduction zones. The directional dependence of seismic wave speeds in the subsurface, or seismic anisotropy, can allow us to map the Earth's structure in subduction zones. To improve the interpretation of seismic data collected in active subduction zones, we characterized the range of seismic anisotropy created by blueschists (a common subduction zone rock-type) that were returned to the surface after being deformed in ancient subduction margins. We calculate the anisotropy of each blueschist rock from mineral orientations collected in the lab combined with the elastic properties of these minerals. Trends in seismic anisotropy were compared to the changes in composition and preferred orientations of minerals (produced by deformation). We found that blueschists can generate a broad range of seismic anisotropy, and that this anisotropy is enhanced by increasing amounts of the mineral glaucophane. The seismic anisotropy is further increased when the glaucophane minerals are more uniformly oriented, as is typical in rocks that have experienced higher levels of deformation. The seismic anisotropy and seismic wave speeds of blueschists are distinctive from those of other common subduction zone rocks. Therefore, these results suggest blueschist seismic anisotropy can be used to improve our ability to map structure and deformation occurring in active subduction zones. Calculated blueschist Vp anisotropy up to similar to 20% with a plateau at similar to 10%, with lineation-parallel fast axis and foliation-normal slow axis The anisotropy magnitude increases with glaucophane modal abundance/crystallographic preferred orientation (CPO) strength and is diluted by epidote/lawsonite abundance The glaucophane CPO type correlates with the Vp pattern and increasing AVp magnitude in mafic blueschists

The habitability of icy moons in the outer Solar System is linked to their ability to maintain warm subsurface oceans through time, but the mechanisms leading to heat generation in small icy moons are not well constrained. While most heat generation in response to tidal forcing is thought to occur in icy crusts and water oceans, the deformation of chondritic material thought to make up rocky cores and mantles has not previously been studied comprehensively in a laboratory setting under relevant planetary conditions. We experimentally deformed samples of the Kilabo meteorite, an LL6 chondrite, under axial strain rates of 10-5 s-1 and confining pressures up to 100 MPa. We recorded the strength of the material, measured energy dissipation through acoustic emission events, and observed ultrasonic wavespeeds as a function of confining pressure. Our results suggest that dissipative brittle deformation is possible even during isotropic pressurization, as well as at low stresses and strains during nominally “elastic” deformation, due to the porous nature of the material. However, energetic acoustic emission events associated with brittle deformation become less powerful as confining pressure increases. The mechanical behavior of the meteoritic material also evolved as a function of increasing confining pressure: peak strength occurred at 50 MPa confining pressure, and material continuously stiffened as pressure increased. These pressure-dependent properties indicate that larger icy moons could have stiffer, less deformable silicate layers than those found in small icy moons, corresponding to a lower relative contribution of silicate deformation to the bodies’ total heat budgets. Future experiments on carbonaceous chondrites under oscillatory loading conditions are necessary to fully measure the potential magnitude of tidal heating in rocky silicate cores of icy moons.

As the high-frequency analogue to field-scale earthquakes, acoustic emissions (AEs) provide a valuable complement to study rock deformation mechanisms. During the load-stepping creep experiments with CO2-saturated water injection into a basaltic sample from Carbfix site in Iceland, 8791 AE events are detected by at least one of the seven piezoelectric sensors. Here, we apply a cross-correlation-based source imaging method, called geometric-mean reverse-time migration (GmRTM) to locate those AE events. Besides the attractive picking-free feature shared with other waveform-based methods (e.g. time-reversal imaging), GmRTM is advantageous in generating high-resolution source images with reduced imaging artefacts, especially for experiments with relatively sparse receivers. In general, the imaged AE locations are found to be scattered across the sample, suggesting a complicated fracture network rather than a well-defined major shear fracture plane, in agreement with X-ray computed tomography imaging results after retrieval of samples from the deformation apparatus. Clustering the events in space and time using the nearest-neighbour approach revealed a group of 'repeaters', which are spatially co-located over an elongated period of time and likely indicate crack, or shear band growth. Furthermore, we select 2196 AE events with high signal-to-noise-ratio (SNR) and conduct moment tensor estimation using the adjoint (backpropagated) strain tensor fields at the locations of AE sources. The resulting AE locations and focal mechanisms support our previously assertion that creep of basalt at the experimental conditions is accommodated dominantly by distributed microcracking.