Journal of Geophysical Research: Solid Earth最新文献

Fluids released from subducting hydrated rocks influence volcanism, tectonics, and geochemical cycling, but the mechanisms of fluid escape in subduction zones remain poorly understood. We address this issue by investigating the Erro-Tobbio meta-serpentinites (ET-MS), Italy, exhumed serpentinite rocks that preserve extensive dehydration vein networks formed by the porosity-generating breakdown of antigorite and brucite. We characterized the structure and morphology of these self-organized vein networks and evaluated their hydrodynamic properties using a novel approach. Specifically, we combined X-ray tomography and drone imagery with generative machine learning, electron microscopy, and equilibrium thermodynamics to model and analyze fluid pathways in the ET-MS. In both natural and simulated samples, these dehydration vein networks act as efficient drainage systems, enabling rapid fluid percolation even at porosities below 1%. The maximum network permeability is $��\approx �1�0^{�-�15�}�{��m�}^2�$, several orders of magnitude higher than that of intact serpentinite. Fe-rich olivine and monticellite occur alongside relict brucite and magnetite in these veins. This assemblage indicates that the high permeability arises from porosity localized along brucite- and magnetite-rich veins, where infiltration of reducing fluids enhanced dehydration reactions. These findings demonstrate that serpentinite dehydration in subduction zones can produce flow-optimized vein structures that efficiently channel fluids at low porosity, potentially influencing fluid migration on local to regional scales before widespread dehydration occurs.

This study investigates whether seismicity in the New Madrid Seismic Zone (NMSZ), specifically the Axial Fault, is predominantly influenced by fluids or fault locking. Previous resistivity studies in the region were restricted by their focus, MT station spacing, and equipment bandwidth, which limited the resolution of resistivity structures near fault zones. We conducted a comprehensive investigation using broadband magnetotelluric (MT) soundings from December 2021 to March 2023. Data were collected along five profiles spanning frequencies from 0.00005 to 10,000 Hz. Four shallow-focus profiles were located near Steele and Caruthersville in the Missouri Bootheel region, while a deeper cross-section extended from Obion, TN to Wardell, MO, reaching a depth of 80 km and crossing the Reelfoot Rift's Axial Fault. Our findings indicate that earthquakes cluster within a highly resistive zone (1,000–10,000 Ω-m), suggesting a fault-locking mechanism in the brittle zone because they coincide with low velocity anomalies from previous studies. The profiles usually have a conductive anomaly on the SE side of the fault at a depth of 2–30 km. That conductive anomaly may be interpreted as a weaker, more ductile zone adjacent to the stronger brittle zone associated with the fault. These results suggest that both fault locking and fluid presence significantly influence NMSZ seismicity, with their effects varying by depth and location.

The Appalachian-Caledonian orogen was built during the Paleozoic by accretion of peri-Gondwanan terranes onto Laurentia, culminating in the formation of Pangea. During the Mesozoic, Pangea broke apart, displacing one section of the belt to eastern North America and another to northwestern Europe. These areas share aspects of their tectonic history but have been shaped differently by later Paleozoic orogenesis and Mesozoic rifting; therefore, comparisons between these regions offer an opportunity to understand which processes have been responsible for shaping their present-day crustal structure. This study compares the crustal structure across the Laurentian and peri-Gondwanan sutures in these regions and explores how it has been shaped by their tectonic histories. We use receiver functions with harmonic decomposition to analyze the geometry of Laurentia, Ganderian and Avalonian crust beneath Ireland and Britain and compare them with New England, northeastern USA. The Laurentian crustal thickness beneath Ireland and Britain ranges from ∼26 to 32 km, whereas that of the peri-Gondwanan terranes varies from ∼32 to 38 km. Our analysis also provides insight into dipping interfaces and anisotropy near the Moho, which vary considerably across the study area. In contrast to our findings in Ireland and Britain, beneath New England Laurentian crust is significantly thicker (∼44 km) than accreted terrane crust (∼32 km). We hypothesize that Mesozoic rifting led to significant thinning of Laurentian crust beneath Ireland and Britain, and that regionally specific orogenic processes during the middle and late Paleozoic controlled the evolution of accreted terrane crust differently in these areas.

The Greater Alpine crust provides a natural laboratory for investigating tectonic and geodynamic processes owing to its strong structural and lithological heterogeneity. A key challenge is constraining its thermal and compositional properties, given the limited direct observations and the uncertainties of existing models. We analyze two years of seismic ambient noise recorded at about 700 broadband seismic stations, and eight years of teleseismic earthquakes recorded at approximately 400 broadband stations. Using ambient noise tomography and receiver functions, we derive the Vs of the crust, the average Vp/Vs ratio, and a new Moho depth map for the Greater Alpine region. Moho depths range from 15 to 55 km, and Vp/Vs ratios vary from <1.65 in the Variscan domain to >1.8 in the Apennines, Dinarides and sedimentary basins. Thermodynamic modeling translates these seismic results into quantitative estimates of silica content and linear thermal gradients. We find that the Variscan crust is relatively cold (<20°C/km) and silica-rich (>62 wt% $��S�i�O_2�$), in contrast with Alpine–Apenninic domains that show elevated thermal gradients (>25°C/km) and more mafic compositions (<60 wt% $��S�i�O_2�$). However, elastic velocities predicted by mineral physics systematically exceed observed seismic velocities, reflecting effects of sediments, porosity, anelastic relaxation, and non-equilibrium processes not captured in thermodynamic equilibrium models. We apply empirical corrections to address these discrepancies, emphasizing caution when interpreting seismic velocities from mineral physics models. These quantitative constraints refine the thermal and chemical distinction between stable Paleozoic lithosphere and actively deforming orogens in the Greater Alpine crust.

Magma intrusion often drives uplift of the overburden and free surface. Analytical modeling of such surface uplift at active volcanoes allows us to estimate intrusion geometries and positions, as well as volume and pressure changes; these insights have proven critical to forecasting volcanic unrest and eruptions. However, it is rarely possible to compare geodetic source parameters retrieved from analytical models to known intrusion geometries. Seismic reflection data offer an opportunity to image and quantify ancient, buried intrusion geometries and their overburden deformation (i.e., a forced fold). Here, we use 3D seismic reflection data offshore NW Australia to investigate an Early Cretaceous forced fold developed above a laccolith emplaced at ∼0.6–1 km depth. We remove the effects of post-emplacement, burial-related compaction and estimate surface displacement patterns for the forced fold. Analytical modeling of these surface displacements, using both thin plate bending and elastic half-space solutions, suggest source (intrusion) estimates of position and lateral dimensions are similar to those of the actual laccolith. There are some differences between measurements of the laccolith and modeled source estimates, which we attribute to syn-intrusion space-making mechanisms (e.g., compaction). We particularly find penny shaped crack and rectangular dislocation elastic half-space solutions underestimate source emplacement depth by ∼0.2–0.9 km, probably reflecting a lack of heterogeneity (layering) in our models. Our novel approach highlights seismic reflection data is a powerful tool for understanding and testing how magma emplacement translates into surface deformation at active volcanoes.

The study of silicate glasses is important to understand the physical and chemical properties of silicate melts under high-pressure conditions relevant to planetary interiors. We conducted in situ Brillouin spectroscopy measurements on two endmember, low-impurity CaSiO₃ glasses and one Fe, Al, Mg, Ti-bearing CaSiO₃ glass up to 23 GPa. We obtained pressure-dependent acoustic velocities and derived elastic moduli that exhibit discontinuities indicative of structural transitions in all compositions. The endmember CaSiO₃ glasses exhibit velocity softening below 2.6 GPa, consistent with earlier findings in other silicate glasses, while the Fe, Al, Mg, Ti-bearing CaSiO₃ glass displays a delayed onset of softening and densification. This softening is attributed to intermediate-range structural rearrangements. Above ∼8 GPa, both glasses show rapid increases in velocities and elastic moduli, reflecting densification associated with structural transitions. Comparison with other silicate glasses demonstrates that Ca acts as a strong network modifier, significantly reducing the stiffness of the glasses, while the addition of Fe, Al, Mg, and Ti collectively has a mixed effect on elasticity. CaSiO₃ glass crosses over in density with its counterpart crystal, wollastonite, at only ∼3 GPa—a pressure lower than any other crossover pressure observed in silicate glasses—suggesting that Ca-rich melts may become gravitationally stable at much shallower depths in planetary interiors than other silicate melts. These results provide new constraints on the structural evolution and elasticity of Ca-rich silicate glasses under compression and have implications for modeling the mobility of silicate melts in deep planetary environments.

We performed laboratory experiments to study the effects of fluid-induced precipitation and dissolution on pore space geometry and corresponding acoustic velocity in carbonate rocks. This approach separates the impact of pore structure changes from other factors like compaction and tracks only variations in acoustic velocity alongside changes in porosity resulting from calcium carbonate cementation and dissolution. In the precipitation experiments, the degree of velocity variation is strongly influenced by the specific location of cementation. Grain-contact cementation strengthens the rock framework, which results in a marked increase in acoustic velocity, while the growth of intrapore aragonite crystals usually produce more intricate, softer frameworks that have a minimal effect on velocity yet generally cause a slight reduction. Dissolution predominantly eliminates non-load-bearing small particles, which leads to increased porosity yet results in only a marginal decrease in acoustic velocity. The dissolution creates bigger void spaces in the rock without increasing its structural complexity while maintaining its inherent strength. Using the parameters of internal pore geometry, including dominant pore size and perimeter-over-area ratio, we demonstrate that pore geometry has a greater influence on elastic properties and acoustic velocity than porosity by itself. These results question standard porosity-velocity models while demonstrating the need for quantitative pore geometry parameters in rock physics models that analyze seismic reflection data. Without integrating pore geometry parameters, seismic data analysis risks underestimating porosity in dissolution areas or incorrectly classifying grain-contact cementation as lithological changes.

Earthquake ruptures often exhibit complex behaviors, including abrupt arrest followed by delayed re-nucleation. While on-fault stress heterogeneity is a recognized contributing factor, as it can arrest or slow down rupture propagation, its interaction with propagating ruptures remains complex and not fully understood. Here, we study frictional ruptures under controlled laboratory conditions by imposing a heterogeneous stress field along an artificial fault. This setup consistently led to the spontaneous emergence of a well-defined stress barrier. Our results show that the presence and strength of the stress barrier systematically influence rupture propagation, sometimes in non-trivial ways. As expected, strong barriers tend to arrest ruptures, while weaker ones reduce their velocity, inducing a time delay in the rupture propagation. However, we also observe several less-intuitive outcomes, including static triggering, barrier-induced supershear transition, and dynamic triggering. We elucidate the physics behind each interaction mechanism through Linear Elastic Fracture Mechanics (for the arrest and deceleration mechanisms) and the Rate-and-State framework (for the static triggering). Interestingly, static triggering and barrier-induced supershear transitions can enable rupture propagation beyond barriers that are expected to arrest ruptures. Similarly, dynamic triggering can accelerate the onset of rupture beyond barriers that decelerate ruptures. Moreover, our experiments show that the barrier efficiency evolves over successive earthquake cycles, weakening with repeated partial ruptures and becoming permanent once complete ruptures break through the fault. This experimental study underscores the critical role of stress heterogeneity in controlling the dynamics of frictional ruptures and offers new insights into the physics of delayed rupture triggering.

We present new vector paleomagnetic data from 13 radiometrically dated lava-flows in southern La Palma (Canary Islands) spanning from 1 to 56 ka, which covers most of the Late Pleistocene to prehistoric Holocene volcanic record in the island. Using a paleointensity multimethod approach including Thellier-type and Shaw-type techniques, and combining detailed rock magnetic and mineralogical analyses, we assess the reliability and possible biases in paleointensity estimations in volcanic rocks affected by low-temperature oxidation and coarse ferromagnetic grains. Results indicate a strong viscous component linked to maghemitization, which compromises paleointensity reliability and accuracy. Low temperature demagnetization pretreatments significantly mitigated the viscosity contribution, improving success rates by highlighting the original thermoremanent magnetization (TRM) and revealing possible overestimations in standard Thellier-type treated samples affected by maghemitization. The full vector results, compared with several paleosecular variation curves, exhibited both low and high field intensity periods, including a relative paleointensity minimum at ∼27 ka (VADM ∼26 ZAm²) and the record of the Levant intensity high (VADM ∼108 ZAm²). This study contributes with valuable constraints for improving geomagnetic models, especially for low-latitude regions, and underscores the importance of integrating magnetic mineralogy with paleointensity protocols to mitigate bias in geomagnetic reconstructions.

Mineral precipitation is ubiquitous in subsurface environments, influencing processes such as karst evolution and carbon mineralization. While precipitation dynamics have been extensively studied in porous media, the pattern formation and transitions in fractured media remain underexplored. In this study, we develop a novel experimental system to investigate precipitation dynamics in microfluidic fractures by integrating charge-coupled device camera, micro-PIV, and confocal microscopy. Flow-through experiments on CaCO₃ precipitation are performed by co-injecting Na₂CO₃ and CaCl₂ under controlled flow rates Pe and saturation indices SI. Real-time imaging of precipitation dynamics and velocity fields revealed two distinct patterns. At low Pe and low SI, mineral precipitation exhibits precipitation band acting as a barrier that inhibits mixing of the reactants and results in minimal permeability reduction. In contrast, at high Pe and high SI, the system transitions to precipitation clusters, characterized by widespread particle distribution that significantly reduces permeability. We demonstrate that this pattern shift is governed by the balance between fluid shear forces and repulsive forces between CaCO₃ particles. When repulsive forces dominate, particles cannot aggregate, leading to band formation, whereas shear-induced aggregation promotes cluster growth. Theoretical analysis is developed to interpret the regime transition, and a phase diagram mapping precipitation regime as a function of Pe and SI shows well agreement with experimental results. These findings provide critical insights into fracture mineral precipitation, which are crucial for predicting injectivity and permeability in CO₂ mineralization processes.