Journal of Geophysical Research: Solid Earth最新文献

Debate continues over the reducing mechanisms for the formation of unconformity-related uranium (URU) deposits. This paper evaluates, for the first time, the potential of iron-rich chlorite as a reductant for uranium mineralization using reactive fluid flow modeling method. Our results confirm that Fe²⁺, released from the breakdown of iron-rich chlorite, can reduce aqueous hexavalent uranium to precipitate economically significant URU deposits similar in size and grade to those formed with CH₄ as the reducing agent. The resulting uranium mineralization tends to occur in the basement and below the downwelling parts of overlying basinal fluid circulation cells, where oxidizing basinal fluid percolates across the unconformity and reacts with upward flowing reducing basement brine. Therefore, the basinal fluid circulation pattern controlled by the permeability of the sandstone aquifer is critical in determining the formation and distribution of URU deposits. When the sandstone layer is more permeable, the simulated uranium deposits become larger in size, and vice versa. If the sandstone permeability is <5 × 10⁻¹⁴ m², no obvious uranium deposits can be formed. In contrast, the permeability of fault zones does not have a significant effect on uranium mineralization, although it does affect fluid flow behaviors within the fault zone itself. We also demonstrate that fault zones do not appear to be a prerequisite for the formation of URU deposits when Fe⁺² serves as a reductant, which highlights important exploration implications. Uranium exploration should, in addition to continuing to target graphitic fault zones, also consider areas where faults and/or graphite units do not exist.

The Southern Puna plateau in the central Andes has a complicated tectonic history that includes episodes of distributed shortening and extension, lithospheric delamination, uplift and Quaternary backarc volcanism. In this study, the upper crustal structure and present-day deformation in this area is investigated using a new regional earthquake catalog derived with a deep-learning-based phase picker. Results show abundant strike-slip seismicity at shallow depths in the eastern Southern Puna plateau that reveals active fault systems in the area and indicates N-S extension/E-W compression that changes orientation and relative magnitude from north to south. A broad zone of seismic quiescence in the western plateau may indicate a zone of upper crustal decoupling from large-scale deformation. The region separating the western and eastern plateau exhibits a complex stress field that can be related to the boundary of east/west oriented middle-to-lower crustal flow in the main volcanic arc. Southeast of the plateau in the Sierras Pampeanas, crustal seismicity deepens and is dominated by conjugate reverse faulting structures associated with the direction of plate convergence. Vp and Vs seismic velocity models of the upper crust obtained through local earthquake tomography with the improved seismic catalog show low-velocity anomalies near intermontane basins, except in the Antofagasta basin where a high-velocity anomaly possibly represents shallow intrusive component of Quaternary basaltic volcanism. Below the Cerro Galan caldera, an upper crustal 10-day long earthquake swarm is observed which may indicate local stress perturbations from fluids at the top of the crustal magmatic system that feeds this volcano.

To understand the dislocation creep behavior of clinopyroxene in the upper mantle, hot-pressed diopside aggregates without predrying treatment were triaxially deformed under water-unsaturated conditions at a confining pressure of 300 MPa, temperatures of 1323–1523 K, and strain rates of 10⁻⁶–10⁻⁴ s⁻¹, using a Paterson gas-medium apparatus. Fourier transform infrared measurements of the water contents of the samples before and after deformation revealed that water diffusion loss occurred during the deformation process. A simple diffusion model based on Fick's law was established to predict the variation in the water content with respect to time during deformation. Fitting the mechanical data with a power flow law yielded a stress exponent n of 4.3 ± 0.3, an activation energy Q of 427 ± 31 kJ/mol and a water content exponent r of 1.2 ± 0.2 for the dislocation creep of the diopside aggregates under water-unsaturated conditions. When the flow law was extrapolated to anhydrous and water-saturated conditions, the calculated flow strengths of the diopside aggregates were generally in agreement with the strengths determined directly by deformation experiments, but there also existed contribution from grain boundary water under water-saturated conditions. The results of our study indicate that the strength of diopside or upper mantle clinopyroxene is comparable to the strength of olivine under anhydrous conditions but weaker than that of olivine under water-saturated conditions in the dislocation creep regime. Therefore, diopside might dominate the rheological behavior in some clinopyroxene-enriched and hydrous regions of the upper mantle.

The seismic potential of faults depends on the local mineralogy and can change upon mineral reactions. We conducted friction experiments on serpentinite, carbonate and carbonated serpentinite fault gouges at temperatures from 400°C to 630°C, under 100 MPa effective normal stress and fluid saturated conditions. Pure serpentinite fault gouges exhibited unstable slip with significant strain-hardening. Carbonate-bearing serpentinite fault gouges showed stable sliding at temperatures <500°C, but displayed unstable stick-slip behavior and strong strain weakening at temperatures ≥500°C. Microstructural analyses revealed localization and the formation of olivine and pyroxene from devolatilization reactions at temperatures ≥500°C. The degree of devolatilization increased near major slip planes and was enhanced by higher temperature and carbonate content, as shown by three-dimensional micro-computer tomography analyses. Nano-scale transmission electron microscopy analyses revealed the absence of hydrous and carbonate phases along major slip planes. We attribute the strong weakening and unstable slip behavior in carbonated serpentinite fault gouges to the formation of nano-sized anhydrous phases of olivine and pyroxene along the slip plane. Our results indicate that serpentinized fault zones may experience seismic event nucleation at temperatures approaching the thermodynamic stability limit of serpentine. This suggests that the absence of seismic events cannot exclusively be attributed to serpentinization. The formation of carbonates, through replacive and additive carbonation, can explain aseismic deformation in transform faults, but at elevated temperatures, devolatilization reactions in carbonated serpentinites cause strong localization and strain weakening, accompanied by laboratory seismicity.

The Nankai subduction zone presents significant seismic and tsunami risks, given its historical earthquakes exceeding magnitude 8 and the expectations of similar future events. Slow earthquakes, common at the shallow and deep plate interface, result from different frictional properties linked to interplate slip deficit accumulation. This study estimates slip deficit rates at the Nankai subduction zone using land and ocean-bottom geodetic data. Previous estimates encountered limitations, often smoothing slip deficits, omitting observational error differences between ocean-floor and land data, and relying on homogeneous structure models. To address these issues, we employ a novel trans-dimensional reversible jump Markov Chain Monte Carlo algorithm. This approach dynamically adjusts slip parameters, accommodating data resolution and producing a flexible slip distribution without predetermined spatial constraints. Additionally, it automatically weights data for observational errors and integrates elastic Green functions from a 3D structure of the Nankai region. Our results provide a finer, heterogeneous slip distribution, improving estimates in inland regions. However, limitations remain offshore in areas with sparse data. We revised the spatial distribution of Nankai slow earthquakes and confirmed a good agreement with intermediate slip deficit rates, identifying coupled and uncoupled regions. High slip deficit rates align with rupture areas of historic large earthquakes. Slow earthquakes occur at frictionally weak plate interfaces, and shallow slow earthquakes may result from subducting relief heterogeneities with important pore fluid pressure effects. We introduce an updated distribution of slip deficit rates for the Nankai subduction zone, considering observed slip deficit rates and the fast and slow earthquake occurrence.

Mineral chemistry records the pressure and temperature conditions of lithospheric processes. Active tectonic margins, however, are subjected to non-hydrostatic stresses wherein stress magnitudes vary directionally, and the impact of non-hydrostatic stress on mineral chemistry is uncertain. The work of materials scientists F. Larché and J. Cahn provides a framework for quantifying how stress affects mineral chemistry. Crystallographically and mechanically anisotropic, multicomponent minerals will have different compositions as a function of their orientation under a fixed stress meaning that grain-to-grain compositional variation can be used to estimate stress. We develop two “orientation piezometry” methods that use the chemistry and orientations of multicomponent, anisotropic minerals to estimate stress. The first method uses chemistry and orientation (“coupled orientation piezometry”) whereas the second method uses composition alone (“decoupled orientation piezometry”). We apply the methods to clinopyroxene and feldspar solid solutions using synthetic data sets. The first method determines the full stress tensor whereas the second method can only determine the differential stress magnitude unless additional a priori information is specified. Plausible scenarios for orientation piezometry include minerals undergoing diffusion creep, recrystallized grains formed during dislocation creep, and minerals grown statically under stress. Preliminary application of the decoupled piezometer to the famous eclogite facies shear zones on Holsnøy, Norway, suggests differential stresses in the range of 300–900 MPa, broadly consistent with previous estimates from the area. Thus, orientation piezometry techniques may provide valuable constraints on geodynamic processes and insights into long-standing geological problems such as the relationship between pressure and depth.

We describe the development and assessment of a new terrestrial reference frame (TRF) based on a combination of geodetic techniques at the observation level over the period 2010–2022. Included in the solution are observations from the Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI). A key feature of our solution strategy is the use of space ties in low-Earth orbit to connect SLR to GPS. Though the resulting TRF solution is based on only 12.6 years of data, it is competitive with the international (ITRF2020) standard in terms of fundamental frame parameters (origin and scale) and their temporal evolution, both linear and seasonal. The relative rates of origin (3D) and scale (at Earth's surface) are 0.2 mm $��{\text{yr}}^{�-�1�}�$ and 0.1 mm $��{\text{yr}}^{�-�1�}�$ respectively. Absolute scale and 3D origin (at epoch 2015.0) both differ by 2–3 mm. In addition to station positions and velocities, our combined solution includes Earth orientation parameters (EOP), low-degree zonal coefficients (J2 and J3) of the geopotential and precise orbit solutions for all participating satellites (GPS, GRACE and GRACE Follow-on tandems, Jason 2 and 3, and LAGEOS 1 and 2). We discuss potential benefits of our solution strategy and characterize the impacts of our new TRF on estimates of geocenter motion and sea level change from satellite altimetry.

The first three-dimensional (3-D) P and S wave attenuation (Qp and Qs) tomography of the crust and upper mantle of the northern Sumatra subduction zone is determined. We adopt an improved calculation scheme to precisely measure attenuation factor t* values from velocity amplitude spectral ratios among different stations that recorded the same earthquake. Our tomographic results show that the forearc accretionary wedge in Sumatra exhibits a significant high-attenuation (low-Q) zone along the trench. The seismic attenuation characteristics of the forearc accretionary wedge are probably influenced by variations in temperature and water content. The middle and upper crust beneath active arc volcanoes shows low-Q and high-Qp/Qs, while the lower crust exhibits less low-Q and low-Qp/Qs, probably reflecting hot volcanic roots with different water saturations from the upper to lower crust. Beneath the Toba volcano that had a super-eruption ∼74,000 years ago, a distinct low-Qp/Qs zone is revealed, which may reflect a transport pathway of fluids and/or local melts ascending from a slab window. The subducting Indo-Australian slab beneath the forearc island chain exhibits a low-Q and low-Qp/Qs belt, reflecting a moderate water saturation probably associated with backthrust faulting. High-Q and high-Qp/Qs zones appear along the slab surface, reflecting large amounts of fluids releasing from the slab dehydration, which may increase pore pressure and cause intense intraslab seismicity.