Earth Model Research Articles

Kinematic vorticity of shear zones that accommodate vertical crustal advection: Implications for metamorphic core complexes and pluton emplacement

Kinematic analysis of ductile shear zones is an important method to interpret the dynamic evolution of many tectonic and magmatic processes on Earth, such as orogeny, rifting, and plutonism. Despite decades of study, kinematic vorticity analysis is an underutilized tool to interpret the dynamic drivers of shear zones. Determination of the kinematic vorticity number (Wk) quantifies the relative contributions of pure- versus simple-shear strain in shear zones. Here we systematically investigated Wk from mylonitic shear zones associated with metamorphic core complexes (MCCs) developed across the central and southern North American Cordillera using electron backscatter diffraction (EBSD) data that allows consistent and reproducible results from a large number of recrystallized grains. We investigated samples from four distinct MCC systems and the structural aureole of a Cordilleran pluton to investigate their kinematics. We find that most MCC samples display pure-to-general-shear strain (average 70 % pure shear), consistent with significant bulk shear-zone shortening (>80 % shortening) observed in many of the MCC systems. Such strain patterns are remarkably similar to deformation observed around plutons that were forcefully emplaced as diapirs. To further validate and investigate these results, we constructed the Wk field of these geologic processes using numerical simulations to highlight that pure shear kinematics are more common with diapirism and coupled wallrock deformation compared with discrete detachment-involved normal fault systems. These observations support that buoyant doming can be a viable end-member process to form the investigated MCCs. Our results also suggest that pure shear deformation may be a diagnostic strain characteristic for diapir-like crustal processes, and therefore Wk analyses could be used to test similar processes like dome-and-keel models for Early Earth.

Rejuvenating exploration opportunities in Egypt's Mediterranean region using basin-scale 3D seismic reprocessing and subsurface evaluations

The Eastern Mediterranean region has proven to be a key province for natural gas resources over the last two decades. Gas discoveries in the Nile Delta Basin, Levantine Basin, and over the Eratosthenes platform have proven that an efficient working petroleum system extends to the deepwater areas and into the distal parts of the Nile Delta and Levantine basins. While the suprasalt biogenic post-Messinian play is adequately imaged in various areas in the Eastern Mediterranean region, seismic imaging of the deeper subsalt pre-Messinian plays is challenged by legacy seismic acquisition and processing techniques. Moreover, the complexity of the Messinian salt structures and the heterogeneity of the lithology of the Messinian layer across the Mediterranean basins represent a key subsurface challenge. In phase 1 of the study presented in this paper, we reprocessed 12 legacy 3D seismic data sets over 12,000 km2 and constructed a consistent basin-scale earth model from the shelf areas offshore Sinai to the deepwater areas around the Zohr carbonate platform. The data processing and imaging sequences incorporate full-waveform inversion and tomography in the earth model building process followed by a basin-to-lead evaluation to delineate exploration opportunities in phase 1. The evaluations resulted in delineating Cretaceous and Oligo-Miocene untested structures. Furthermore, potential deepwater Lower Miocene sand fairways were outlined, supported by improved regional seismic imaging and consistent seismic attributes over multiple legacy surveys. The authors of this paper expect to update the results of their work after completing the earth model building and the prestack depth migration workflows of an additional 13 legacy surveys over 35,000 km2 in phase 2 of the study.

Construction of Mechanical Earth Modeling for Mitigating Wellbore Instability in Tanuma Shaly Formation -Southern Iraqi Oil Field

Wellbore instability has become an increasing concern for horizontal and extended-reach wells, especially through shale cap rocks. This paper presents a comprehensive analysis of the factors that led to the wellbore being unstable in the Tanuma Formation, the Nasiriyah oilfield in southern Iraq. By constructing a mechanical earth model using open-hole wireline data from two drilled wells. Mohr-Coulomb, Mogi-Coulomb, and Modified Lade failure criteria are used to analyze the breakouts and determine the density of mud that is required for a safe wellbore wall. The results indicated that the Mogi-Coulomb criterion is more similar to the actual well failure than the other two criteria. The wellbore instability findings showed that the most stable wells are those that are vertical and have a low deviated angle (less than 10°), and it is advised that these wells be drilled with a mud weight of 11.3 to 14 ppg. The acceptable range for the weight of the mud for horizontal and greatly deviated wells is between 11.9 and 13.8 ppg. Consequently, the future wells development plan for the studied region is improved and leads to cost reductions.

Scaling-up dynamic elastic logs to pseudo-static elastic moduli of rocks using a wellbore stability analysis approach in the Marun oilfield, SW Iran

Wellbore stability analysis is a critical component of petroleum engineering, evaluating the risks of sanding, reservoir compaction, and casing failures. Laboratory rock mechanical measurements must be scaled up to reservoir scales to achieve accurate results. One challenge lies in upscaling dynamic measurements from petrophysical logs to pseudo-static elastic properties, which has significant implications for oil and gas operations. We present a novel approach that combines laboratory rock mechanical measurements with well-log data to develop a mechanical earth model (MEM) for an Iranian oilfield with over 350 wells. We conducted static elastic property measurements on 40 core samples from various layers and depths of carbonate and sandstone rocks, demonstrating the practical application of our approach. By integrating these measurements with dynamic log data and static-dynamic correlations, we established a framework for evaluating the mechanical properties of different layers. Our findings indicate that the safe mud weight window ranges from 41.5 to 118.59 pcf, while the stable mud weight window ranges from 41.5 to 156 pcf. We demonstrate the importance of conducting parallel rock mechanical studies on cores and logs to reduce uncertainties, costs, and risks during oil and gas operations. We also propose a novel methodology combining lithological characteristics, abnormally high pressure, and borehole instability mechanisms to evaluate the stability of borehole walls. This framework provides a fresh perspective on wellbore stability analysis and offers practical solutions for the industry. Essential novel techniques include developing a geomechanical model that integrates laboratory rock mechanical measurements with well-log data to evaluate mechanical properties and calculate safe and stable mud-weight windows. Our study advances wellbore stability analysis by providing a new method for addressing this long-standing challenge. It offers valuable insights for petroleum engineers working in the oil and gas industry.

Long-range LBL underwater acoustic navigation considering Earth curvature and Doppler effect

The accuracy of underwater acoustic navigation is significantly influenced by geometry configuration and systematic errors coming from geophysical environment. Long baseline (LBL) systems exhibit superior positioning precision than other acoustic navigation systems, primarily attributable to the better Geometric Dilution of Precision (GDOP). However, the geometry configuration tends to degrade when the underwater vehicle is far away from the seafloor beacons. Factors such as acoustic ray bending error, Doppler effect and Earth curvature may seriously affect the navigation accuracy. To address these issues, we present a robust Kalman filter with systematic error compensation for long-range LBL systems. Firstly, a reversed acoustic ray tracking method is proposed for a unique phenomenon in acoustic wave propagation. Following that, we construct an acoustic positioning model with a time bias parameter, to weaken the impact of Doppler effect on acoustic ranging. This additional parameter was estimated with the state of the user vehicle in real time. At last, an observation equation of pressure gauge considering Earth curvature is presented for depth constraint. Long-range LBL experiments conducted in the South China Sea is employed to validate the performance of the proposed methods, taking the positioning results of inverted ultra-short baseline (iUSBL) system as reference. The results show that the proposed method outperform traditional method with a decrease of about 60 % in the three-dimensional root mean square (3DRMS) of navigation errors. With mentioned three improvements, the 3DRMS of the long-range LBL system with the longest distance of 20 km from the beacon center is less than 14 m. These findings can provide theoretical basis for other long-range LBL systems.

Spatial positioning method based on range-only measurement of multi-station radar

Aiming at the characteristics that affect the high ranging accuracy of shipborne radar, a multi station radar spatial positioning method based on ranging is proposed. This method is based on the ECEF (Earth Centered Earth Fixed) coordinate system, and adopts the method of intersecting the detection distances of multiple radars to the target, and directly calculates the spatial position of the target. This method only needs the geodetic coordinates of each radar station and the detection range of the target to calculate the geodetic coordinates of the target, which can effectively solve the coordinate conversion problem caused by the curvature of the earth, and does not involve higher-order equations and multi-value solutions, and it does not involve iterative initial value calculation. The positioning system can not only obtain high positioning accuracy, but also has a long operating distance, which can better solve the multi-radar range measurement intersection positioning problem.

Limited sensitivity of Antarctic GIA mass change estimates to lateral viscosity variations

The Gravity Recovery and Climate Experiment (GRACE) has revealed spatiotemporal mass changes in the Antarctic Ice Sheet. However, GRACE data must be corrected for the gravity changes due to glacial isostatic adjustment (GIA). Here we investigate the sensitivity of GIA-induced gravity changes in Antarctica to the lithospheric thickness and upper mantle viscosity using a one-dimensional (1-D) model that assumes a radially varying Earth structure. The sensitivity is assessed using several Antarctic ice-history models that have been widely used to correct GRACE data. The results indicate a trade-off between lithospheric thickness and upper mantle viscosity in evaluating the Antarctic GIA correction. This trade-off exists for all ice-history models; however, the reason for the trade-off differs among models. Furthermore, since there is a sharp contrast in the Earth structure between West and East Antarctica, the adopted ice histories are separated into West and East Antarctic components to examine their contributions to the Antarctic GIA correction. We consider 1-D Earth structures that are averaged from the seismically derived three-dimensional Earth structure for West and East Antarctica. These results indicate that the contributions of the East and West Antarctic loads do not significantly affect the GIA corrections for the West and East Antarctic regions, respectively, and that the trade-off between lithospheric thickness and upper mantle viscosity results in minimal divergence in the assessment of the Antarctic GIA correction between the averaged Earth models of West and East Antarctica. Therefore, the contrast in Earth structure beneath Antarctica may have a limited effect on the ice-mass change estimates for the entire Antarctic Ice Sheet.

Impact of long-term depletion on horizontal wellbore stability in tight reservoirs-including changes in petrophysical and geomechanical properties

The development of tight reservoirs using a horizontal well requires caution owing to the reservoir sensitivity to stress. Predicting the horizontal wellbore instability during reservoir depletion is critical for tight reservoirs. The present study investigated the wellbore failure criteria and stress orientation changes with reservoir depletion of a horizontal well in a tight reservoir, considering rock sensitivity to stress with pressure reduction. An integrated reservoir model coupled with geomechanics was used to predict pore pressure. A mechanical earth model (MEM) was constructed to examine the stability of horizontal wells. The unconfined compressive strength (UCS) was correlated with changes in porosity due to stress changes. The MEM shows that the failure criteria around the horizontal wellbore, including breakout, loss, and breakdown pressures, change considerably with reservoir depletion. A more significant response was observed in the stress-sensitive layer, which was characterised by a higher permeability. The safe mud weight window of the studied horizontal well narrowed significantly after production for five years, whereas the stability was completely absent after ten years. The deterioration of stability with depletion is governed mainly by permeability reduction, which may cause severe pressure reduction, whereas the stability improvement due to the increase in UCS caused by porosity reduction seems marginal. Relatively small changes in the direction of the stresses around the wellbore with depletion were observed, with the stress distribution concentrated in the predominant direction as the depletion continued. This study indicates that the sensitivity of petrophysical and geomechanical properties to stress amplifies the instability in tight reservoirs, particularly around wellbores.

A High-Precision Sub-Grid Parameterization Scheme for Clear-Sky Direct Solar Radiation in Complex Terrain—Part I: A High-Precision Fast Terrain Occlusion Algorithm

In atmospheric modeling, sub-grid parameterization is an important method for studying the topographic effects of solar radiation using high-resolution Digital Elevation Model (DEM) data. For reducing the amount of computation, some approximate methods that can lead to errors are used in existing sub-grid parameterization schemes for clear-sky direct solar radiation (SPS-CSDSR). The lack of a high-precision fast terrain occlusion algorithm (HPFTOA) remains one of the biggest constraints in this field. This study proposed an HPFTOA. It mainly uses two kinds of acceleration algorithms. One method is to use a dynamic, lossless, and fast occlusion search radius. Another way is to use the rectangular grid for calculations within the accuracy of DEM data to avoid coordinate projection conversions. The test results indicate that the HPFTOA can carry out large-scale computation based on DEM data with a resolution of 90 m. Because it rarely uses approximation algorithms and considers the curvature of the Earth, SPS-CSDSR can achieve unprecedented precision. The HPFTOA can also be used in the fields of mountain solar energy assessment, remote sensing, and telemetry, including terrain-obscuring the probe. As computer performance improves and algorithms and execution code are optimized, the application prospects will be very broad.

Thermal Earth model for the conterminous United States using an interpolative physics-informed graph neural network

This study presents a data-driven spatial interpolation algorithm based on physics-informed graph neural networks used to develop a thermal Earth model for the conterminous United States. The model was trained to approximately satisfy Fourier’s Law of conductive heat transfer by simultaneously predicting subsurface temperature, surface heat flow, and rock thermal conductivity. In addition to bottomhole temperature measurements, we incorporated other spatial and physical quantities as model inputs, such as depth, geographic coordinates, elevation, sediment thickness, magnetic anomaly, gravity anomaly, gamma-ray flux of radioactive elements, seismicity, electrical conductivity, and proximity to faults and volcanoes. With a spatial resolution of 18km2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$18 \\ km^2$$\\end{document} per grid cell, we predicted heat flow at surface as well as temperature and rock thermal conductivity across depths of 0-7km\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0-7 \\ km$$\\end{document} at an interval of 1km\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$1 \\ km$$\\end{document}. Our model showed temperature, surface heat flow and thermal conductivity mean absolute errors of 6.4∘C\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$6.4^\\circ C$$\\end{document}, 6.9mW/m2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$6.9 \\ mW/m^2$$\\end{document} and 0.04W/m-K\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.04 \\ W/m-K$$\\end{document}, respectively. This thorough modeling of the Earth’s thermal processes is crucial to understanding subsurface phenomena and exploiting natural underground resources. Our thermal Earth model is available as web application at https://stm.stanford.edu, feature layers on ArcGIS at https://arcg.is/nLzzT0, and tabulated data on the Geothermal Data Repository at https://gdr.openei.org/submissions/1592.

From the Spherical Earth Model to the Globe: The Effectiveness of a Planetary Model-Building Intervention

From the Spherical Earth Model to the Globe: The Effectiveness of a Planetary Model-Building Intervention

Meshfree modelling of magnetotelluric and controlled-source electromagnetic data for conductive earth models with complex geometries

Meshfree modelling of magnetotelluric and controlled-source electromagnetic data for conductive earth models with complex geometries

Towards a new standard for seismic moment tensor inversion containing 3-D earth structure uncertainty

SUMMARY Moment tensor (MT) inversion is a classical geophysical inverse problem that infers a force-equivalent model of a seismic source from seismological observations. Like other inverse problems, the accuracy of the inversion depends on the reliability of the forward problem simulating waveforms from the source location through an Earth structural model. Apart from errors in data, the error in forward waveform simulation, also known as theory error, is a significant source of error contributing to the misfit function between the predicted and observed waveforms. Here, we set up numerical experiments to comprehensively probe the sensitivity of the linearized MT inversion to 3-D regional earth model errors, a known predominant factor of the theory error. Using the Monte Carlo method, we estimate the empirical structural covariance matrices to characterize the waveform mismatch due to the imperfect knowledge of Earth's structure. First, although the inversion accuracy deteriorates with increasing model errors, incorporating the structural covariance matrices into the misfit function improves the accuracy of inversion results for all theorized error distributions. Secondly, we propose a slightly modified form of the structural covariance matrix, which further enhances the inversion outcome. Lastly, as the true structural errors are likely spatially correlated, we highlight the importance of adequately treating the correlation into the MT inversion because of its significant impact on inversion. Overall, as a preliminary effort in quantifying 3-D structural errors on MT inversion, this study proves the computational feasibility by means of numerical experiments and will hopefully provide a way forward for future work on this topic.

Contourite-like deposits suggest stronger-than-present circulation in the Plio-Pleistocene Red Sea

Red Sea Deep Water is presently slow-moving, but was this true of the earlier Plio-Pleistocene (PP)? In seismic reflection records, the PP deposits are distorted by halokinetic deformation of their underlying Miocene evaporites. However, if reflections are flattened to a prominent reflector representing the top of the Miocene, they reveal mounded deposits within the earlier PP along both sides of the sea. Off Egypt, a plastered drift occurs along a salt wall. In the central Red Sea, they are mounded drifts. Seismic reflections from these deposits change shape gradually upwards to the modern seabed, which is commonly flatter, suggesting a gradual change in depositional conditions. To explain their origins, we appeal to other evidence. DSDP cores from the Late Pleistocene contain the rigid aragonite cements formed by restricted conditions, but not the lower and middle PP. Furthermore, mid-PP sedimentary δ18O values are similar to global ocean δ18O for that time, not enhanced as expected from excess evaporation. These data suggest that there was a greater exchange of Red Sea waters with the Indian Ocean during the mid-PP. That exchange may have allowed waters densified by evaporation in shallow regions of the northern Red Sea to flow south vigorously (the mounds would then be contourites). Alternatively, as the Pliocene seabed was shallower, wind-driven eddies may have affected more of the water column. Overall, the results indicate for the first time that deep circulation was stronger in the earlier PP compared with the present day. That circulation needs to be considered when evaluating organism dispersions across the Red Sea, regional climate, and influence of Red Sea Outflow Water on Indian Ocean Intermediate Water. Plain language summaryDuring the Pliocene (about 3–5 million years ago), temperatures on Earth's surface were similar to those predicted in some models of Earth's future climate. This has led to researchers becoming interested in studying geological evidence of conditions during the Pliocene as a clue to Earth's future. In detail, however, the comparison may not be exact. In our article, we describe mounds of sediment that were originally formed on the bed of the Red Sea in the Pliocene. They appear similar to snow drifts, and like snow drifts, may have formed under steady currents. Sea water becomes dense with evaporation (making it more saline). At the present day, dense water created in the Gulf of Suez cascades down into the deep Red Sea as a slow current. Perhaps such movements were more vigorous in the Pliocene, helped by the water escaping through a deeper barrier in the south into the Indian Ocean? Alternatively, these mounds were formed by giant eddies, such as those on the surface of the modern Red Sea, which are moved by strong winds. In either case, the deep waters of the Pliocene Pliocene Red Sea were more vigorously moving compared to the quiescent deep waters of the modern-day.

Seismic modeling using pseudo-impedance derived from physical models

Building accurate numerical models of the earth for simulation is both challenging and time consuming. The subsurface complexity must be captured in sufficient detail for the results to be of practical use for geophysical analysis. Physical models provide an efficient way to add realistic detail to numerical models. Physical models, for example, are scaled simulations of large-scale geologic systems that provide great insight into understanding the interplay between sedimentation, salt tectonics, and faulting. The integration of geophysical workflows with sandbox models has been the subject of previous research, primarily to create synthetic data to compare with observed field data. However, capturing the detail from the physical model is challenging. A novel workflow is presented that uses pixel intensity values from photographic images of the analogue model to create a pseudo-impedance perturbation, mimicking the acoustic impedance contrasts that are encountered in the earth. This solution enables the detailed sedimentary architecture from the sandbox to be transferred to the digital earth model. Acoustic wave equation forward modeling and reverse time migration imaging have been applied using the generated pseudo-impedance model for a Gulf of Mexico-style salt canopy model. The images produced show clear definition of the salt/sediment interface and capture the sedimentary stratigraphy and faulting observed in the original sandbox model.

Generating extremely low-dimensional representation of subsurface earth models using vector quantization and deep Autoencoder

Geological model compression is crucial for making large and complex models more manageable. By reducing the size of these models, compression techniques enable efficient storage, enhance computational efficiency, making it feasible to perform complex simulations and analyses in a shorter time. This is particularly important in applications such as reservoir management, groundwater hydrology, and geological carbon storage, where large geomodels with millions of grid cells are common. This study presents a comprehensive overview of previous work on geomodel compression and introduces several autoencoder-based deep-learning architectures for low-dimensional representation of modified Brugge-field geomodels. The compression and reconstruction efficiencies of autoencoders (AE), variational autoencoders (VAE), vector-quantized variational autoencoders (VQ-VAE), and vector-quantized variational autoencoders 2 (VQ-VAE2) were tested and compared to the traditional singular value decomposition (SVD) method. Results show that the deep-learning-based approaches significantly outperform SVD, achieving higher compression ratios while maintaining or even exceeding the reconstruction quality. Notably, VQ-VAE2 achieves the highest compression ratio of 667:1 with a structural similarity index metric (SSIM) of 0.92, far surpassing the 10:1 compression ratio of SVD with a SSIM of 0.9. The result of this work shows that, unlike traditional approaches, which often rely on linear transformations and can struggle to capture complex, non-linear relationships within geological data, VQ-VAE's use of vector quantization helps in preserving high-resolution details and enhances the model's ability to generalize across varying geological complexities.

Investigation of Wellbore Instability in Southern Rumaila Oil Field

This study aims to address the issue by providing valuable insights into the factors contributing to the wellbore instability and proposing effective measures to mitigate the problem in the southern part of the Rumaila oil field. A comprehensive one-dimensional mechanical earth model (1D MEM) was developed by utilizing various logs data from 4 wells across the south part of this field, including gamma ray, bit size, caliper, bulk density, and sonic compression and shear logs. The model was validated with laboratory tests, including Brazilin and Triaxial tests, as well as repeated formation tests. To analyze the wellbore stability, three different failure criteria, namely Mohr-Coulomb, Mogi-Coulomb, and Modified lade, were employed. The results indicated that the Mogi-Coulomb criterion was the most accurate failure criterion in predicting rock failure. Wellbore instability problems had been observed across the shale sections throughout the Rumaila oil field, particularly through Tanuma, Khasib, top and bottom of Ahmadi, Nahr Umr, and Upper Shale members and Middle Shale members of Zubair formations. The 1D MEM results indicated that Shaly formations exhibited low stiffness rocks (low Young's Modulus (YME)), low rock strength, and high Poisson's ratio (PR), suggesting potential challenges related to wellbore instability in the Tanuma, top and bottom of Ahmadi, Nahr-Umr, and Zubair formations. A sensitivity analysis was performed to determine the safest mud weight and the optimum well trajectory for future drilling operations. According to the updated mud window of this field in 2023, the pressure in the Mishrif and Zubair formations was reinforced by injection wells, as it was noted that the pressure behavior shifted from depletion (2000 Psi). Based on the findings of this study, the good inclination of (0-25°) can be drilled with the mud weight of 1.24-1.26 sg, while the good inclination of (25-40°) can be drilled with the mud weight of 1.28-1.30 sg in all directions (i.e., all azimuths). The stress regime in most of the formations was found to be a strike-slip to a normal fault regime. The findings of this study can significantly benefit the oil industry and enhance overall productivity.

Oxidized Sulfur Species in Slab Fluids as a Source of Enriched Sulfur Isotope Signatures in Arcs

AbstractRecycling of oxidized sulfur from subducting slabs to the mantle wedge provides simultaneous explanations for the elevated oxygen fugacity (fO2) in subduction zones, their high hydrothermal and magmatic sulfur outputs, and the enriched sulfur isotopic signatures (i.e., δ34S > 0‰) of these outputs. However, a quantitative understanding of the abundance and speciation of sulfur in slab fluids consistent with high pressure experiments is lacking. Here we analyze published experimental data for anhydrite solubility in H2O‐NaCl solutions to calibrate a high‐pressure aqueous speciation model of sulfur within the framework of the deep earth water model. We characterize aqueous complexes, required to account for the high experimental anhydrite solubilities. We then use this framework to predict the speciation and solubility of sulfur in chemically complex fluids in equilibrium with model subducting mafic and ultramafic lithologies, from 2 to 3 GPa and 400 to 800°C at log fO2 from FMQ‐2 to FMQ+4. We show that sulfate complexes of calcium and sodium markedly enhance the stability of sulfate in moderately oxidized fluids in equilibrium with pyrite at fO2 conditions of FMQ+1 to +2, causing large sulfur isotope fractionations up to 10‰ in the fluid relative to the slab. Such fluids could impart oxidized, sulfur‐rich and high δ34S signatures to the mantle wedge that are ultimately transferred to arc magmas, without the need to invoke 34S‐rich subducted lithologies.

A Hybrid Normal Mode‐Collocation Method for Finding the Response of Laterally Homogeneous Compressible Maxwell Viscoelastic Earth Models

A Hybrid Normal Mode‐Collocation Method for Finding the Response of Laterally Homogeneous Compressible Maxwell Viscoelastic Earth Models

Mapping geodetically inferred Antarctic ice surface height changes into thickness changes: a sensitivity study

Abstract. Determining recent Antarctic ice volume changes from satellite altimeter measurements of ice surface height requires a correction for contemporaneous vertical crustal deformation. This correction must consider two main sources of crustal deformation: (1) ongoing glacial isostatic adjustment (GIA), that is, the deformational, gravitational, and rotational response to Late Pleistocene and Holocene ice and ocean mass changes and (2) modern ice mass change. In this study, we seek to quantify the uncertainties associated with each of these corrections. Corrections of ice surface height changes for correction 1 have generally involved the adoption of global models of GIA defined by some preferred combination of ice history and mantle viscoelastic structure. We have computed the GIA correction generated from a coupled ice sheet–sea level model and a realistic Earth model incorporating three-dimensional viscoelastic structure. Integrating the difference between this correction and those from recent GIA analyses widely adopted in the literature yields an uncertainty in total present-day ice volume change equivalent to approximately 10 % of Antarctic ice mass loss inferred for the period 2010–2020. This reinforces earlier work indicating that ice histories characterized by relatively high excess ice volume at the Last Glacial Maximum may be introducing a significant error in estimates of modern melt rates. Regarding correction 2, a spatially invariant scaling has commonly been used to convert GIA-corrected ice surface height changes obtained from satellite altimetry to ice volume estimates. We adopt modeling results based on a projection of Antarctic ice mass change over the period 2015–2055 to demonstrate a spatial variability in the scaling of up to 10 % across the ice sheet. Furthermore, using these calculations, we find a systematic error of ∼ 3 % in the projected net ice volume change, with most of the difference arising in areas of West Antarctica above mantle zones of low viscosity.