Journal of Geophysical Research: Solid Earth最新文献

The global distribution of the Earth's lithospheric induced magnetization is examined through an inverse modeling approach that integrates constraints from both petrological data and satellite magnetic observations. The distribution of induced magnetization is characterized by the Vertical Integrated Susceptibility (VIS) of a spherical equivalent source layer. To reconstruct the long-wavelength structures of the lithospheric magnetic field, a prior petrologically derived VIS model (SM3-SI) is utilized to provide constraints at spherical harmonic degrees 0–16, while finer structures are constrained by satellite magnetic data. The resultant VIS model furnishes a higher-resolution and more accurate depiction of lithospheric induced magnetization. Significant variations in the resultant VIS model across different crustal types and basement ages are confirmed through a comprehensive analysis. High lithospheric magnetization is generally observed in Precambrian provinces characterized by cold and thick lithospheres, whereas orogenic belts and extended crustal regions exhibit lower magnetization due to reduced magnetic materials from crustal thinning. In oceanic regions, elevated lithospheric magnetization is mainly concentrated in oceanic plateaus which are associated with Cretaceous magmatic activity. Mantle-derived magnetic sources, which are related to an increased Curie depth caused by the cold subducted slabs and the serpentinization within the mantle wedge, are inferred to underlie the strong magnetization observed in island arcs and subduction zones.

Subduction initiation often begins with slow, forced convergence, switches “on” catastrophically as the slab collapses into the mantle, and then evolves to steady-state, self-sustained sinking that drives global plate movements. Numerical models suggest that the collapse phase implies sudden weakening of the plate interface. However, geological records of subduction infancy preserved as metamorphosed oceanic crust accreted beneath ophiolites (i.e., metamorphic soles) present a paradox. During the pre-collapse period that may last 2–15 million years, the nascent plate interface is hot, whereas during collapse, shear zone temperatures plummet, which typically strengthens rocks. So, how could cooling cause weakening? Here, we show microstructures of metamorphic sole rocks from Mont Albert (Québec, Canada) that demonstrate that upon cooling, metamorphic mineralogy became more heterogeneous, average grain size decreased, and deformation mechanisms shifted from dislocation-accommodated to fluid-assisted and grain size sensitive, which culminated in drastic rheological weakening. Quartz piezometry indicates that flow stress increased with cooling, but flow laws indicate that the colder rocks exhibited lower viscosity and therefore could localize strain. Interface viscosity initially rose with cooling, but upon reaching a threshold where major metamorphic minerals changed, dropped from >10¹⁸ to <10¹⁷ Pa-s. Cooling-induced mineral-mechanical changes thus drove rheological weakening, and provide a general mechanism explaining slab collapse and the transition to self-sustaining subduction. This implies that strain localization is inherent to modern metamorphosed oceanic lithosphere and does not require a “stress drop.” The next step to understanding subduction initiation is identifying causes of high temperatures and incipient cooling during the pre-collapse phase.

We perform Rayleigh wave ambient noise tomography to investigate crustal seismic velocity structure and sources of volcanism in Armenia. Armenia, a key part of the tectonically and volcanically active Caucasus-Anatolia region, is actively being deformed by the ongoing Arabian-Eurasian continental collision. Unlike typical intracontinental settings, Armenia exhibits exceptional diversity of volcanic compositions and eruption styles: large stratovolcanoes are interspersed among more broadly distributed monogenetic cones and extensive lava flows. This study presents the first seismic tomography model of Armenia with sufficient resolution to infer potential magma sources. We analyze ∼19 months of continuous ambient noise data recorded by 32 seismic stations, extracting Green's functions and Rayleigh wave dispersion curves. A two-step tomographic inversion first yields 2D group velocity maps, followed by a 3D shear-wave velocity model. Synthetic tests confirm the model's resolution and ability to detect lateral and vertical velocity anomalies. Our results reveal prominent low-velocity anomalies down to 25 km beneath monogenetic cones, likely indicating magma transport zones. At greater depths, velocity anomalies reverse sign. A high-velocity zone at 40 km depth beneath dispersed cones suggests crustal thinning and asthenosphere upwelling. Beneath Lake Sevan, we identify two distinct structures: a low-velocity anomaly in the NW linked to fault-related fracturing and fluid saturation, and a high-velocity anomaly in the SE that may represent a rigid block, possibly remnant oceanic crust. This study provides new insights into crustal structure beneath Armenia, shedding light on its magmatic and tectonic evolution.

Deep-origin carbonatite melts are considered to be the products of partial-melting of the oceanic crust in the subduction zones. In this study, we conducted electrical conductivity (EC) measurements on two samples, the composition of which resemble the partial-melting products atop the 410-km discontinuity and in the lower part of the transition zone. The EC of carbonatite melts was investigated using impedance spectroscopy combined with a multi-anvil press up to 20 GPa. Pressure has a great effect on the EC of the carbonatite melts. While the EC dropped overall by 0.6 log unit from 3 to 20 GPa for varying compositions, the pressure effect becomes weaker above 10 GPa. The Hashin-Shtrikman mixing model indicates that melt fraction of 0–0.3 vol% is necessary to account for the EC atop the 410-km discontinuity beneath NE China, north Philippine Sea, north Pacific, and Australian craton. However, this value soars to 1–4.5 vol% for the lower part of the transition zone in the same regions, and further increases to 3.7–7.3 vol% for cold subduction regions if the slab surface temperature is 300 K lower. The difference in the needed melt fraction at different depths implies that the magnitude of partial melting is much larger in the lower part of the mantle transition zone, and it is thus likely to be the main barrier to the recycled carbonates towards the deep interior.

Paleomagnetic data are usually retrieved by subjecting bulk samples, for example lavas, to laboratory measurement protocols. In many instances, the data related to these protocols yield uninterpretable results caused by the presence of particles with adverse magnetic properties that blur the signal of the reliable magnetic particles. With Micromagnetic Tomography (MMT) we focus on identifying the signal of particles with reliable properties. Their individual magnetic moments are computed by scanning the surface of a $��\sim �$3 $��{\text{mm}}^2�$ thin section with a quantum diamond microscope (QDM) and locating the magnetic recorders with computed tomography. Currently, the largest portion of all resolved magnetic moments is discarded due to numerical instability, making it difficult to obtain statistically relevant paleointensities and paleodirections based on the remaining magnetic moments. We improve the number of reliable magnetic moments from MMT experiments by making a QDM scan of both sides of the sample. Here, we conduct a combined numerical and empirical study to investigate the benefits and difficulties of adding this double-sided scanning (DSS) protocol to MMT. By investigating the theoretical gain of DSS for varying sample thicknesses, we show that DSS returns twice more numerically stable magnetic moments compared to single sided scanning for a sample thickness of 60 $��\mu �$m. By overcoming practical difficulties related to sample preparation and scanning, DSS will provide a significant boost in retrieved stable magnetic moments.

At the northern Hikurangi margin, Aotearoa New Zealand, slow slip events (SSEs) recur every 6–24 months to $��\sim �$30 km depth. Although shallow SSEs (0–10 km) are well-studied offshore, the deeper portion (10–30 km) remains poorly understood, limiting insight into SSE initiation. Here we investigate this deeper region and examine relationships between newly resolved SSEs and seismicity. Using time-dependent inversions, we resolve two small SSEs ($��M_W�$ 6.2 and 6.4), including one that extends from 15 to 30 km depth. Using data from a dense onshore seismograph network deployed directly above this deeper portion from December 2017 to October 2018, we construct a catalog of 3,071 high-quality earthquakes with hypocentral uncertainties $��\le �$5 km, located using a 3-D velocity model and a new 1-D model. Earthquake magnitudes range from −0.84 to 4.40, with a completeness magnitude of 1.7 and a b-value of 1.06. Focal mechanisms reveal numerous normal-faulting earthquakes, including some within the slab mantle. Vertically-aligned seismicity and normal-faulting earthquakes outline pathways linking the slab mantle to surface seeps of mantle-derived fluids. We infer that normal faults form due to slab bending and localized uplift of subducting seamounts, which roughen the plate interface, damage the upper plate, and promote fluid migration. Landward of $��\sim �$100 km from the trench, both surface seeps and normal-faulting mechanisms cease, coinciding with the downdip limit of shallow SSEs. Together, these results suggest that the Hikurangi margin's rough subducting plate interface exerts strong control on forearc dewatering and SSE genesis.

Induced shear failure is key for enhancing hot dry rock (HDR) resource exploitation, aiming to creating an extensive fracture network. Although the macroscopic shear behavior of HDR has been extensively investigated, its microscopic shear failure mechanisms remain unclear. In this study, microscale mode II shear fracture experiments were performed for the first time under various thermal cycling. Micro-scale double-edge notched cube specimens were fabricated from primary minerals and interfaces using micro-machining and subjected to in situ shear tests under a scanning electron microscope. The microscopic shear failure mechanisms and fracture parameters of the minerals and interfaces were investigated. The results showed that multiple thermal cycles reduced macroscopic shear strength by initiating thermal cracks rather than by reducing the strength of the microscale minerals. All three minerals exhibited L-shaped crack propagation below 300°C, with shear initiation and tensile failure. Biotite failed progressively, whereas feldspar and quartz failed catastrophically. High temperatures and multiple thermal cycles caused thermal voids and complex crack paths in feldspar and quartz, whereas biotite exhibited fiber-like plastic slip bands without thermal cracking. The orientation and strength of the mineral interfaces affected crack deflection and branching. Energy was dissipated by interlayer plastic slip in biotite and by micro-crack friction and slip in quartz and feldspar. The microscopic mode II fracture toughness and critical energy release rate were 0.5–3.3 MPa·m^0.5 and 0.01–0.11 kJ/m², respectively. This research provides novel insights into the microscale shear failure of HDR and a critical micromechanical basis for multiscale fracture modeling and macroscopic shear failure analysis.

Fluid transport properties at the base of the seismogenic zone exert a critical control on fault strength, slip behavior, and fluid circulation. However, quantitative constraints on permeability in deep fault rocks remain limited. We present new laboratory measurements of permeability, porosity, and specific storage on cataclasite- and pseudotachylyte-bearing mylonitic rocks along the Red River Fault (RRF), China. Experiments conducted at effective pressures up to 165 MPa reveal systematically low permeabilities, with mylonitized cataclasites and pseudotachylyte-bearing rocks exhibiting the lowest values (10⁻²²–10⁻²¹ m²), while mylonites display relatively higher permeabilities, up to 10⁻¹⁹ m². A key finding is the pronounced permeability anisotropy, where permeability parallel to foliation is up to two orders of magnitude greater than perpendicular values. This anisotropy reflects the microstructural alignment of phyllosilicate minerals and cavitation bands, which provides interconnected flow pathways along foliation while impeding cross-foliation transport. The hydraulic architecture of the RRF at the base of the seismogenic zone is thus characterized by overall low permeabilities with fluid flow facilitated along mylonitic foliation. Such fabric-controlled anisotropy persists even under mid-crustal pressure conditions, indicating that fault zones at the base of seismogenic depths can retain directional fluid pathways despite overall low permeabilities. Our results provide critical constraints on the hydraulic architecture of the RRF and offer broader insights into the role of anisotropy in controlling fluid flow and deformation at the base of the seismogenic zone.

The Okavango Rift Zone (ORZ) is an incipient continental rift in Botswana at the terminus of the Southwestern Branch of the East African Rift System. The lack of syn-rift magmatism and tectonic processes overprinting pre-rift structures provide an opportunity to investigate incipient-stage rift processes and the role of pre-existing structures in rift initiation and strain localization. We present SEISORZ, a ∼450-km-long wide-angle seismic transect across the ORZ and neighboring tectonic terranes. A 2.5-D V_P tomographic inversion reveals crustal thinning within a ∼130-km-wide section of the Damara Belt hosting the ORZ where Moho depth is 38.7 ± 3.4 km, shallower than in other Damara Belt terranes (46.3 ± 1.4 km) and the Kalahari Craton (45.6 ± 2.0 km). Mantle V_P is consistent with ultramafic lithologies without evidence for metasomatism, partial melt, or elevated temperatures. Crustal V_P is variable but consistent with geological information and with lower-crustal mafic lithologies. However, beneath the rifting region, the model shows low crustal velocities (ΔV_P = −0.26 ± 0.05 km/s) that we interpret as damage from rift-related faulting and deformation, and to a lesser extent elevated temperatures possibly from excess radiogenic heat production. Upper crustal heterogeneity correlates with known and newly detected intra-rift faults, suggesting that pre-existing structures promoted strain localization and establishment of the rift border fault system. Collectively, all these factors point to a rheologically weak section in the Ghanzi-Chobe zone which is more susceptible to deformation in response to far-field stresses than neighboring terranes, explaining why incipient rifting is localizing there and not across any other of the terranes that compose the Damara Belt.