Journal of Geophysical Research: Solid Earth最新文献

In this study, we numerically investigated the multi-scale flow features of 43 types of geofluids (including 18 real geofluids and 25 parametric fluids) within rock fractures under different roughness and hydrodynamic conditions. Our findings demonstrate that the generalized Forchheimer equation, an extension of Darcy's law for nonlinear flows, effectively captures the nonlinear flow features of these diverse fluids. While changes in fluid properties have minimal impact on Darcy's viscous permeability, they significantly influence Forchheimer inertial permeability and the critical Reynolds number. These dependencies are mechanistically attributed to the regulation of eddy growth rate in fractures by fluid properties. Building on these mechanistic insights, we developed two types of models for predicting inertial permeability and critical Reynolds number across various geofluids within a unified framework. One model extrapolates predictions from the results of classical standard water flow, while another enables direct prediction based on the mean and variance of the fracture aperture field.

Four decades of seismic reflection, onshore-offshore and ocean-bottom seismic data are integrated to constrain a high-resolution 3-D P-wave velocity model of the Hikurangi subduction zone. Our model shows wavespeeds in the offshore forearc to be 0.5–1 km/s higher in south Hikurangi than in the central and northern segments (V_P ≤ 4.5 km/s). Correlation with onshore geology and seismic reflection data sets suggest wavespeed variability in the overthrusting plate reflects the spatial distribution of Late Jurassic basement terranes. The crustal backstop is 25–35 km from the deformation front in south Hikurangi, but this distance abruptly increases to ∼105 km near Cape Turnagain. This change in backstop position coincides with the southern extent of shallow slow-slip, most of which occurs updip of the backstop along the central and northern margin. These relationships suggest the crustal backstop may impact the down-dip extent of shallow conditional stability on the megathrust and imply a high likelihood of near/trench-breaching rupture in south Hikurangi. North of Cape Turnagain, the more landward position of the backstop, in conjunction with a possible reduction in the depth of the brittle ductile transition, reduces the down-dip width of frictional locking between the southern (∼100 km) and central Hikurangi margin by up-to 50%. Abrupt transitions in overthrusting plate structure are resolved near Cook Strait, Gisborne and across the northern Raukumara Peninsula, and appear related to tectonic inheritance and the evolution of the Hikurangi margin. Extremely low forearc wavespeeds resolved north of Gisborne played a key role in producing long durations of long-period earthquake ground motions.

Fe and FeH form a binary eutectic system above ∼40 GPa. Here we performed melting experiments in a laser-heated diamond-anvil cell and obtained the Fe-FeH eutectic melting curve between 52 and 175 GPa. Its extrapolation shows the eutectic temperature to be 4,350 K at the inner core boundary (ICB), which is lower than that in Fe-FeSi but is higher than those in the Fe-S, Fe-O, and Fe-C systems. In addition, its dT/dP slope is comparable to those of the melting curves of Fe and FeH endmembers, suggesting that the eutectic liquid composition changes little with increasing pressure and is about FeH_0.6 at the ICB pressure. We also estimated the effect of each light element on depressing the liquidus temperature at 330 GPa based on a combination of binary eutectic temperature and composition and found that the effect is large for C and S and small for H, O, and Si when considering the amount of each element that reduces a certain percentage of a liquid iron density. Furthermore, we searched for a set of possible outer core liquid composition and ICB temperature (the liquidus temperature of the former at 330 GPa should match the latter), which explains the outer core density deficit that depends on core temperature. The results demonstrate that relatively low core temperatures, lower than the solidus temperature of a pyrolitic lowermost mantle at the core-mantle boundary (CMB), are possible.

Subduction of oceanic slabs introduces chemical heterogeneities in the Earth's interior, which could further induce thermal, seismic, and geodynamical anomalies. Thermal conductivity of slab minerals crucially controls the thermal evolution and dynamics of the subducted slab and ambient mantle, while such an important transport property remains poorly constrained. Here we have precisely measured high pressure-temperature thermal conductivity of hydrous aluminous post-stishovite (Λ_Hy-Al-pSt) and aluminum-rich calcium ferrite-type phase (Λ_CF), two important minerals in the subducted basaltic crust in the lower mantle. Compared to the dry aluminous stishovite and pure stishovite, hydration substantially reduces the Λ_Hy-Al-pSt, resulting in ∼9.7–13.3 W m⁻¹ K⁻¹ throughout the lower mantle. Surprisingly, the Λ_CF remains at ∼3–3.8 W m⁻¹ K⁻¹ in the lower mantle, few-folds lower than previously assumed. Our data modeling offers better constraints on the thermal conductivity of the subducted oceanic crust from mantle transition zone to the lowermost mantle region, which is less thermally conductive than previously modeled. Our findings suggest that if the post-stishovite carries large amounts of water to the lower mantle, the poorer heat conduction through the basaltic crust reduces the slab's temperature, which not only allows the slab bringing more hydrous minerals to greater depth, but also increases slab's density and viscosity, potentially impacting the stability of heterogeneous structures at the lowermost mantle.

Interseismic deformation in the Pacific Northwest is constrained by the horizontal crustal velocity field derived from the Global Positioning System (GPS) in addition to vertical rates derived from GPS, leveling, and tide gauge measurements. Such measurements were folded in to deformation models of fault slip rates as part of the 2023 National Seismic Hazard Model update. Here I build upon one of the contributing models, the viscoelastic earthquake-cycle model of Pollitz (2022, https://doi.org/10.1785/0220220137). This model permits inclusion of effects of time-dependent viscoelastic relaxation within earthquake cycles (i.e., “ghost transients”) and laterally variable elastic and/or ductile material properties. I leverage these capabilities to incorporate the Cascadia megathrust into Western U.S.-wide deformation models in which crustal fault slip rates are estimated simultaneously with slip deficit rates along the interplate boundary between the descending Juan de Fuca plate and North American plate. This effort includes construction of a margin-wide model of viscoelastic structure founded on the Slab 2.0 model and probes different models of the ductile properties of the surrounding oceanic asthenosphere, continental lower crust, and mantle asthenosphere. This results in new estimates of the distribution of slip deficit rate along the $��\sim �1000�$ km long margin, highlights the importance of correcting for glacial-isostatic adjustment effects, and permits assessment of sensitivity of results to assumed ductile properties.

The Kiaman Reversed Superchron (∼260–318 Ma) is the longest known period of single geomagnetic polarity in Earth history (∼55 million years). It is associated with anomalously low dispersion of virtual geomagnetic poles and some high estimates of Earth's dipole moment. However, many of these strong paleointensity data are of poor or unknown quality. Here we report full-vector paleomagnetic measurements from a series of mid-Kiaman (∼282–302 Ma) lamprophyre dykes from Orkney, Scotland. A total of 258 paleointensity experiments were performed alongside rock magnetic experiments and scanning electron microscopy. Eleven dykes produced virtual dipole moment estimates indicating that the field was weak (between 0.1 and 2.9 × 10²² Am²) at 302 Ma and only moderately stronger (between 2.7 and 7.1 × 10²² Am²) at 282 Ma. These new data challenge the paradigm of a uniquely strong field in the Kiaman superchron and are especially intriguing when considered alongside recent studies of geomagnetic field behavior during the later Cretaceous Normal Superchron (∼84–121 Ma). Average dipole moment may be marginally elevated and paleosecular variation moderately suppressed during the superchrons but, in other respects, the field can appear similar to that encountered during other times. The deep-Earth conditions allowing for the generation of a geomagnetic field that is capable of weak, unstable behavior and transitory polarity inversions, while nevertheless maintaining a dominant single polarity for tens of millions of years, is not yet clear. The challenge of explaining superchrons and their geodynamic origin motivates further study integrating paleomagnetic observations with predictions from geodynamo simulations.

Degassing of volatiles within convergent plate margins, investigated through systematic variations in gas geochemistry, provides crucial insights into the recycling process, the lithospheric structure, and the dynamics of plateau growth. To date, such processes in the India-Asia continental collision zone remains poorly constrained in northern Tibet due to a dearth of detailed geochemical data on volatiles. Here, we report new data on chemical compositions and He–C isotopic ratios of hydrothermal volatiles in the northern plateau. CO₂-rich samples exhibit elevated ³He/⁴He ratios (0.11 R_A–0.39 R_A) compared to crustal values, as well as displaying heavy δ¹³C (−4.66–0.02‰) and high CO₂/³He ratios ((36–9,400) × 10⁹), indicating in summary the occurrence of carbonate in the mantle-derived components. We have developed a coupled He–C isotope model incorporating depleted mantle (DM), recycled carbonate (RC), and crustal carbon endmember (CCE) reservoirs to explore quantitatively the nature of the hydrothermal volatiles emitted. The results of model calculations reveal an increasing proportion of RC together with a decreasing proportion of CCE from south to north that is accompanied by an increasing contribution from DM, all suggesting the presence of a carbonated mantle beneath northern Tibet. Degassing of helium from hydrothermal activities exhibits relatively high fluxes of total ³He (10⁴–10⁵ atoms/m²/s), indicating a tectonically active degassing of volatiles in the Tibetan Plateau under ongoing continental convergence between India and Asia. Systematic variations in He–C isotopes, mantle helium fluxes and RC/CEE proportions along hydrothermal activities spanning from the Himalayas to the Qaidam-Gonghe basin are consistent with a dual continental subduction model acting beneath the whole Tibetan Plateau.

Fluids affect the mechanical behavior of geomaterials, including properties such as unconfined compressive strength and brittleness. However, their impact on mode I fracture toughness (K_Ic) has been less explored. This study investigates the impact of saturating fluids on the K_Ic of three rock types: a porous siliceous sandstone (Corvio) and two high-strength, low-porosity granites (Blanco Mera and Blanco Alba). Pseudo-compact tension (pCT) specimens (diameter ∼50–54 mm, thickness ∼25 mm, notch depth ∼16 mm) were saturated with seven different fluids (deionized water, methanol, NaCl-saturated water, mineral oil, diesel fuel, an acidic HCl solution and a caustic NaOH solution) and tested under identical conditions. Results show that all fluids reduce K_Ic, but the extent varies with rock type and fluid properties. Aqueous fluids caused the most significant reductions, with deionized water having the greatest impact on granites (∼18%–30%) and the acid solution on sandstone (∼70%). Non-polar hydrocarbon fluids, despite their lack of reactivity, caused moderate effects attributed to poro-mechanical effects. Additionally, pH-shift experiments, involving sequential exposure to alkaline and acidic solutions, mitigated fluid-induced weakening. This behavior is hypothesized to stem from silica dissolution in the alkaline phase, followed by rapid nucleation and precipitation during the acidic phase, forming silica-rich coatings on mineral surfaces. Fracture energy was not equally distributed, with higher post-peak energy absorption due to crack bifurcation, grain rotation or friction. These findings underscore the interplay of lithological factors, fluid properties and chemical processes in fracture behavior, with implications for subsurface engineering and modeling of fluid-rock interactions.

At the time that the 2017–2027 Decadal Survey for Earth Science and Applications from Space was released, there was a strong emphasis on reducing the possibility of a substantial gap between the GRACE Follow-On mission and a successor mission. This has led to the subsequent rapid development of a successor mission in partnership between NASA and DLR, GRACE-Continuity (GRACE-C), expected to launch in 2028, to continue the timeseries of Earth system mass change established by GRACE and GRACE-FO. In parallel, ESA continues development of a pair of satellites called Next Generation Gravity Mission (NGGM), targeted for an inclination between 65° and 75° to complement GRACE-C, launching in the early 2030s. NGGM offers the possibility for reduced noise in measuring short-period variations in the satellite separation using an improved accelerometer relative to what is flying on GRACE-C. One pathway for this is by using a simplified version of the Gravitational Reference Sensors demonstrated on the LISA Pathfinder Mission in 2016. And, if the measurement accuracy is much improved, it appears desirable to fly NGGM with a fixed ground track and an approximately 5-day orbit repeat period.