Scholarly Works, Geosciences

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Open Educational Resources: Tailor Your Textbook, Not Your Course Design
Neser, Laura; Walz, Anita R.; Grey, Kindred (2025-02-13)
Instructors often design course content around commercial textbooks, which dictate the sequence of topics and impose financial burdens on students. This poster presentation explores an alternative: using existing open educational resources (OER) to create custom textbooks that align with your course structure. By adapting OER, instructors can organize topics in the order that best suits their teaching, providing students with free, accessible materials. Additionally, many institutions offer grants and technical assistance to support the development of these tailored resources, offering a flexible, cost-effective solution that prioritizes course objectives over predesigned textbooks.
Present-day vertical land motions (VLM) of the Chesapeake Bay region derived from robust network imaging of global navigation satellite system (GNSS) observations
Williams, Karen; Stamps, D. Sarah; Duda, James; Kreemer, Corné; Moore, William B.; Hensel, Philippe; Herring, Thomas; McKenna, Thomas E.; Kronebusch, Madeline; Walters, David C.; Carr, Joel (Springer, 2026-12-01)
The Chesapeake Bay region (defined as longitudes − 78° to -74° and latitudes 36.5° to 40°) experiences the highest rates of relative sea-level rise (RSLR) on the Atlantic Coast. Regional land subsidence influences RSLR, however quantified rates of vertical land motions (VLM) are inconsistent in published solutions. For 5 years from 2019 to 2023, new Global Navigation Satellite System (GNSS) campaign data were collected at over 60 sites across the Chesapeake Bay region annually. These data were processed and combined with continuous GNSS data (120 stations) from the region covering the same time-period using GAMIT-GLOBK to produce 3D velocities and their associated uncertainties. We use the Robust Network Imaging algorithm to interpolate GNSS-derived VLM to produce a new regional VLM solution of the Chesapeake Bay region. We find that land subsidence is ubiquitous throughout the region with rates varying from − 2.97 to -0.40 mm/yr. In major cities across the Chesapeake Bay region, VLM rates are − 1.1 ± 1.6 mm/yr (1-sigma) for Washington DC, -0.8 ± 1.4 mm/yr for Baltimore, MD, -2.4 ± 0.5 mm/yr for Ocean City, MD, and − 2.3 ± 1.0 mm/yr for Hampton, VA. When we compare our VLM rates with a geodetic-based solution from 1974, we observe meaningful shifts in the locations and rates of maximum subsidence. The results of this work underscore that regular monitoring of VLM and can be used to improve projections of relative sea-level changes as well as the associated coastal hazards for communities in the Chesapeake Bay region.
Evidence of Dislocation Mixed Climb in Quartz From the Main Central and Moine Thrusts: An Electron Tomography Study
Weidner, Timmo; Mussi, Alexandre; Castelnau, Olivier; Kronenberg, Andreas; Law, Richard D.; Cordier, Patrick (American Geophysical Union, 2024-07)
In this study we apply electron tomography to characterize 3D dislocation microstructures in two quartz mylonite specimens from the Moine and Main Central Thrusts, both of which accommodated displacements by dislocation creep in the presence of water. Both specimens show dislocation activity with dislocation densities of the order of 3–4 × 10¹² m⁻² and evidence of recovery from the presence of subgrain boundaries. 〈a〉 slip occurs predominantly on pyramidal and prismatic planes (〈a〉 basal glide is not active). [c] Glide is not significant. On the other hand, we observe a very high level of activation of 〈c + a〉 glide on the (Formula presented.), (Formula presented.), (Formula presented.) (n = 1,2) and even (Formula presented.) planes. Approximately 60% of all dislocations show evidence of climb with a predominance of mixed climb, a deformation mechanism characterized by dislocations moving in a plane intermediate between the glide and the climb planes. This atypical mode of deformation demonstrates comparable glide and climb efficiency under natural deformation conditions. It promotes dislocation glide in planes not expected for the quartz structure, probably by inhibiting lattice friction. Our quantitative characterization of the microstructure enables us to assess the strain that dislocations can generate. We show that glide systems indicated by the observed dislocations are sufficient to accommodate any arbitrary 3D strain by themselves. Although historically dislocation glide has been regarded as being primarily responsible for producing strain, activation of climb can also directly contribute to the finite strain. On the basis of this characterization, we propose a numerical modeling approach for attempting to characterize the local stress state that gave rise to the observed microstructure.
The making of Mt Everest: channel flow and low-angle normal faults in the compressional Himalayan orogen
Searle, Mike; Cottle, John; Jessup, Micah; Law, Richard D. (Geological Society of London, 2025-01-06)
Mt Everest (8849 m) spans the Greater Himalayan Sequence metamorphic rocks and the base of the unmetamorphosed Tethyan sedimentary rocks in the Nepal–South Tibet Himalaya. Two north-dipping, low-angle normal faults cut the massif: the upper Qomolangma Detachment placing Ordovician sedimentary rocks above Everest Series greenschist–amphibolite facies rocks; and the lower Lhotse Detachment placing Everest Series schists above sillimanite gneisses, migmatites and leucogranites. The two faults merge northwards into one large ductile shear zone (the South Tibetan Detachment). Pressure–temperature constraints and structural restoration show that the South Tibetan Detachment acted as a passive roof fault during extrusion of the footwall. At least 120 km of southward flow of the footwall rocks occurred during the Miocene, resulting in the exhumation of rocks that were buried to 5.5 kbar (c. 18–22 km depth) below the detachment, juxtaposing them against hanging wall rocks that are essentially unmetamorphosed. The low-angle normal faults were operative during north–south convergence and reflect the exhumation of a locked passive roof fault, unrelated to any crustal extensional processes. U–(Th)–Pb dating of peraluminous leucogranites exposed on Mt Everest (21–20 Ma), Nuptse (c. 19–18 Ma) and along the Rongbuk valley (15.6–15.4 Ma) show that ductile extrusion occurred during the Early Miocene, with brittle faulting at <15.4 Ma during exhumation.
The timing and significance of mid-crustal shearing and exhumation of amphibolite-facies rocks along the Great Glen Fault Zone, Scotland
Law, Richard D.; Thigpen, J. Ryan; Mako, Calvin A.; Kylander-Clark, Andrew; Caddick, Mark J.; Moore, Lowell R.; Becker, Cassandra; Holdsworth, Robert E.; Strachan, Robin A.; Leslie, A. Graham (Geological Society of London, 2025-07-07)
The Rosemarkie Inlier lies on the NW side of the Great Glen Fault Zone (GGFZ) and is composed of foliated and lineated Archean orthogneisses and Moine metasedimentary rocks. The mylonitic foliation strikes NE–SW (parallel to the GGFZ), dips steeply SE and contains a gently to moderately plunging mineral lineation. Microstructural and quartz c-axis fabric analyses indicate that oblique sinistral shearing occurred under amphibolite-facies conditions. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses on monazite rims in the gneisses yielded ²⁰⁶Pb/²³⁸U ages of 401.8 ± 4.8 Ma (including 2 (Formula presented.) uncertainty and a propagated additional 1% external uncertainty). Similar deformation and recrystallization temperatures indicated by quartz fabrics (610°C) and monazite–xenotime thermometry (616 ± 25°C), respectively, in the gneisses suggest that ductile sinistral shearing was ongoing at c. 402 Ma. The c. 402 Ma rim age is the youngest monazite age recorded in the Northern Highland Terrane (NHT) and indicates that sinistral shearing at mid-crustal levels was ongoing along the GGFZ in Lower Devonian (Emsian, 407–393 Ma) times when the thrust sheets of the NHT to the NW had already been exhumed. The Rosemarkie basement rocks are unconformably overlain by Middle Devonian (Eifelian, 393–387 Ma) sedimentary rocks, indicating time-averaged exhumation rates of c. 1.75 mm a⁻¹ between 402 and c. 390 Ma, assuming a geothermal gradient of 30°C km⁻¹.
Silica-Biomacromolecule Interactions: Toward a Mechanistic Understanding of Silicification
McCutchin, Christina A.; Edgar, Kevin J.; Chen, Chun-Long; Dove, Patricia M. (American Chemical Association, 2024-10-09)
Silica-organic composites are receiving renewed attention for their versatility and environmentally benign compositions. Of particular interest is how macromolecules interact with aqueous silica to produce functional materials that confer remarkable physical properties to living organisms. This Review first examines silicification in organisms and the biomacromolecule properties proposed to modulate these reactions. We then highlight findings from silicification studies organized by major classes of biomacromolecules. Most investigations are qualitative, using disparate experimental and analytical methods and minimally characterized materials. Many findings are contradictory and, altogether, demonstrate that a consistent picture of biomacromolecule-Si interactions has not emerged. However, the collective evidence shows that functional groups, rather than molecular classes, are key to understanding macromolecule controls on mineralization. With recent advances in biopolymer chemistry, there are new opportunities for hypothesis-based studies that use quantitative experimental methods to decipher how macromolecule functional group chemistry and configuration influence thermodynamic and kinetic barriers to silicification. Harnessing the principles of silica-macromolecule interactions holds promise for biocomposites with specialized applications from biomedical and clean energy industries to other material-dependent industries.
SS Precursor Imaging Reveals a Global Oceanic Asthenosphere Modulated by Sea-floor Spreading
Sun, Shuyang; Zhou, Ying (American Geophysical Union, 2025-09-17)
The asthenosphere is a weak layer in the upper mantle where geotherm may exceed mantle solidus and partial melt occurs. Although it has been suggested that an increase in seismic wavespeed at about 220 km depth represents the base of the asthenosphere, seismic studies to-date have not been able to provide evidence for the existence of such a global interface in the oceanic regions. In this study, we report observations of SS precursors reflected at this boundary throughout the global oceans. The average depth of the discontinuity is approximately 250 km, with a velocity jump of about 7% across the interface. Finite-frequency tomography of SS precursor traveltimes reveals large depth variations of the discontinuity over short spatial distances, which explains the absence of this discontinuity in previous global stacks. The depth perturbations are characterized by alternating linear bands of shallow and deep anomalies that roughly follow seafloor age contours, indicating a fundamental connection between seafloor spreading and asthenosphere convection. The base of the asthenosphere is smoother under seafloors formed at slow-spreading centers and becomes much rougher under seafloors formed at fast-spreading centers with a spreading rate greater than (Formula presented.) mm/yr. This observation suggests that different geophysical processes at slow and fast spreading centers generate lithospheric plates with different chemical compositions and physical properties, which in turn influences the convection in the oceanic asthenosphere.
Global finite-frequency tomography of the 220-km discontinuity
Sun, Shuyang; Zhou, Ying (Oxford University Press, 2026-02)
The asthenosphere is a weak layer in the upper maare available from the publicntle that supports the movement of the overriding tectonic plates and facilitates mantle convection. In this study, we compile a global data set of SS precursors reflected at the base of the asthenosphere, also known as the 220-km discontinuity. The global data set includes the oceanic SS precursors from Sun & Zhou and new measurements with bounce points in continental regions. Similar to the oceanic data set, the continental SS precursors are observed on about 45 per cent of the SS waves, with bounce points distributed across all tectonic regions—from orogeny belts to stable cratons. We image the depth of the discontinuity at a global scale using finite-frequency tomography. In oceanic regions, the depth of the 220-km discontinuity agree well with the previous study, with discontinuity depth structure characterized by alternating linear bands of shallow and deep anomalies that roughly follow seafloor age contours. In continental regions, the variations are not spatially oscillatory but are instead much broader, with prominent perturbations associated with convergent plate boundaries. The base of the asthenosphere is shallow along the southern border of the Eurasian plate, from the Mediterranean region to Southeast Asia. Shallow discontinuity anomalies are also observed in the continental interiors—in Eurasia, from the northern Tian Shan through Mongolia to eastern Siberia, and in North America east of the Rocky Mountains. These anomalies form a linear structure roughly parallel to the Pacific subduction zones. The average depth of the discontinuity, as well as the velocity contrast across the interface, is globally consistent across both oceans and continents, with an average depth of approximately 251 km and a velocity increase of about 7 per cent. Given that the continental lithosphere has been cooling for much longer than the oceanic lithosphere, the observed consistency in the average depth of the discontinuity implies that secular cooling does not significantly impact the thermal structure at the base of the asthenosphere.
Flow2Quake, an integrated multiphase flow, geomechanical and seismicity model for efficient forecasting of injection and extraction induced earthquakes
Acosta, Mateo; Ledevin, Thomas; Salha, Guillaume; Forestier, Charles; Michelin, Lucie; Fu, Xiaojing; Avouac, Jean-Philippe (Elsevier, 2025-07)
Efforts to secure and decarbonize the energy sector are driving various subsurface reservoir operations. These operations carry a risk of inducing surface deformation and earthquakes. To assess these risks, modeling tools integrating fluid flow, geomechanical and seismicity modeling are needed. Here, we demonstrate the use of an efficient Vertical Flow Equilibrium (VFE) multiphase fluid flow model in an integrated framework for deformation and seismicity modeling both under fluid extraction or injection configurations. The VFE-computed spatio-temporal pressure evolution is fed to a geomechanical module to compute surface deformation and stress changes in and around the reservoir. Stress changes feed a seismicity module to calculate earthquake probabilities. First, we apply the benchmarked model to gas extraction from Groningen. There, we can reduce the variance of pressure measurements by ∼38% with respect to a pre-existing single phase flow model while remaining computationally efficient. The surface deformation and seismicity simulations show remarkable agreement with observed data. Second, we study induced seismicity due to CO2 sequestration in the Decatur phase 1 project. We find that, for the Decatur phase 1 project, poroelastic stress changes can account for most of the non-clustered observed seismicity within modeling uncertainties. Finally we simulate scenarios for CO2 sequestration using the Quest field. The sloping reservoir topography significantly impacts the predicted position of the CO2 plume but the effects on geomechanical deformation (and seismicity) are minimal. Incorporating VFE models with geomechanical and seismicity forecasts with real-world case applications can allow real-time hazard assessment and mitigation procedures.
Single-well based control and optimization of hydraulic stimulation and induced seismicity: Application to the Otaniemi geothermal project
Kim, Taeho; Gutierrez-Oribio, Diego; Stefanou, Ioannis; Acosta, Mateo; Avouac, Jean-Philippe (Pergamon-Elsevier, 2026-01)
In this study, we apply control theory to mitigate earthquake hazards to a stress-based model of enhanced geothermal stimulation. The model considers pore pressure diffusion as the main stressing mechanism and rate-and-state friction as the shear failure mechanism. The controller is designed to follow a given average pressure and the probability of exceedance of a red-light earthquake (the magnitude at which the stimulation would have to stop by regulation) within chosen volumes surrounding the injection source and within a target time. We rigorously prove that the proposed controller can effectively force two output types within the system to given references, despite the presence of model uncertainties, and with minimal system information, using a continuous control signal. This framework is applied to a validated model of the 2018 Otaniemi geothermal stimulation. We use a suite of simulations to identify injection scenarios that outperform the 2018 Otaniemi stimulation. The optimal stimulation achieves higher average pressure in a shorter time with lower seismic hazard. The controller can help determine whether a combination of safety thresholds and optimization targets is feasible and economical. The control framework could be used to design stimulation schedules for enhanced geothermal systems.
SWOT Satellite: A New Tool for Fluvial Geomorphology
Stroud, Molly; Allen, George H.; Minear, J. Toby; Cisneros, Julia; Smith, Laurence C. (Geological Society of America, 2025-12-01)
Earth-observing satellites have revolutionized the field of fluvial geomorphology by providing large-scale and spatially contiguous observations. The recently launched Surface Water and Ocean Topography (SWOT) satellite’s novel interferometric synthetic aperture radar (inSAR) instrument delivers global measurements of several key geomorphic parameters, such as river surface water elevation, slope, and width, and thus presents the opportunity to study fluvial processes in new ways. Here we explore the utility of the SWOT satellite for advancing understanding of fluvial geomorphology across river systems in the United States, specifically focusing on water surface elevation variations in large braided rivers, temporally dynamic shear stress in bedrock rivers, and the processes associated with knickpoints and dam failures. We also discuss other relevant potential applications of SWOT satellite data related to fluvial geomorphology beyond the scope of these early explorations. By providing global multitemporal observations of several key variables in fluvial geomorphology, SWOT represents a major advance in our ability to quantify, monitor, and understand fluvial systems and their dynamics.
Global subsidence of river deltas
Ohenhen, Leonard O.; Shirzaei, Manoochehr; Davis, J. L.; Tiwari, A.; Nicholls, R.; Dasho, O.; Sadhasivam, N.; Seeger, K.; Werth, Susanna; Chadwick, A. J.; Onyike, F.; Lucy, J.; Atkins, C.; Daramola, Samuel; Ankamah, A.; Minderhoud, P. S. J.; Olsemann, J.; Yemele, G. C. (Springer, 2026-01-14)
River deltas sustain dense human populations, major economic centres and vital ecosystems worldwide1,2. Rising sea levels and subsiding land threaten the sustainability of these valuable landscapes with relative sea-level rise and associated flood, land loss and salinization hazards1-3. Despite these risks, vulnerability assessments are impeded by the lack of contemporary, high-resolution, delta-wide subsidence observations4. Here we present spatially variable surface-elevation changes across 40 global deltas using interferometric synthetic aperture radar. Using this dataset, we quantify delta surface-elevation loss and show the prevalence and severity of subsidence in river deltas worldwide. Our analysis of three key anthropogenic drivers of delta elevation changes shows that groundwater storage has the strongest relative influence on vertical land motion in 10 of the 40 deltas. The other deltas are either influenced by multiple drivers or dominated by sediment flux or urban expansion. Furthermore, we find that contemporary subsidence surpasses absolute (geocentric) sea-level rise as the dominant driver of relative sea-level rise for most deltas over the twenty-first century. These findings suggest the need for targeted interventions addressing subsidence as an immediate and localized challenge, in parallel with broader efforts to mitigate and adapt to climate change-driven global sea-level rise.
Hydrologic and geochemical drivers of aluminum, barium, and copper in two drinking water reservoirs in Southwestern Virginia, USA
Bauer, Carly E.; Wood, Cecelia E.; Lofton, Mary E.; Breef-Pilz, Adrienne; Carey, Cayelan C.; Schreiber, Madeline E. (IWA Publishing, 2025-11-24)
The water quality of drinking water reservoirs is critical for human and ecosystem health. In this study, we examined the drivers of three metals, aluminum (Al), barium (Ba), and copper (Cu), across two drinking water reservoirs in southwestern Virginia, USA, over 4 years. One reservoir has a hypolimnetic oxygenation system; the other does not. We used time series modeling and multivariate analysis of water column chemistry, suspended sediment, inflow, and precipitation data to assess the relative roles of hydrologic and geochemical drivers of metal behaviors in the two reservoirs. Results suggest that Al concentrations were primarily influenced by high-flow events, consistent with the mobilization of clays from physical weathering. In contrast, Ba showed stronger sensitivity to geochemical drivers, specifically redox conditions. Drivers of Cu behavior were obscured by low Cu concentrations. For all metals, patterns varied among years. Our findings highlight the importance of long-term monitoring and integrated approaches to evaluate the drivers of metal dynamics in reservoir ecosystems and inform strategies for maintaining safe drinking water supplies.
Mantle Transition Zone-Penetrating Upwellings Beneath the Eastern North American Margin and Beyond
Luo, Yantao; Long, Maureen D.; Rondenay, Stephane; King, Scott D.; Mazza, Sarah E.; Wolf, Jonathan (American Geophysical Union, 2025-04)
Low-velocity anomalies in the upper mantle beneath eastern North America, including the Northern Appalachian Anomaly (NAA), the Central Appalachian Anomaly (CAA), and the weaker Southern Coastal Anomaly (SCA), have been characterized by many continent-scale and regional seismic studies. Different models have been proposed to explain their existence beneath the passive margin of eastern North America, variously invoking the past passage of hot spot tracks, modern upwelling due to edge-driven convection, or other processes. Depending on the nature and origin of these anomalies, they may influence, and/or be influenced by, the mantle transition zone (MTZ) structure beneath them. Previous receiver function studies have identified an overall thinner MTZ beneath the eastern margin of the US than beneath the continental interior. In this study, we resolve the MTZ geometry beneath these low-velocity anomalies in unprecedented detail using the scattered wavefield migration technique. We find substantially thinned MTZ beneath the NAA and the CAA, and a moderately thinned MTZ beneath the SCA. In all cases, the thinning is achieved via a minor depression of the 410-km discontinuity and a major uplift of the 660-km discontinuity, which suggests the presence of a series of MTZ-penetrating deep upwellings beneath eastern North America. The upwellings beneath eastern North America and a similar style upwelling beneath Bermuda may initiate from ponded thermally buoyant materials below the MTZ fed by hot return flows from the descending Farallon slab in the deep mantle.
Neuroanatomical convergence between pterosaurs and non-avian paravians in the evolution of flight
Bronzati, Mario; Watanabe, Akinobu; Benson, Roger B. J.; Müller, Rodrigo T.; Witmer, Lawrence M.; Ezcurra, Martín D.; Montefeltro, Felipe C.; Belén von Baczko, M.; Bhullar, Bhart-Anjan S.; Desojo, Julia B.; Knoll, Fabien; Langer, Max C.; Lautenschlager, Stephan; Stocker, Michelle R.; Turner, Alan H.; Werneburg, Ingmar; Nesbitt, Sterling J.; Fabbri, Matteo (Elsevier, 2025-11)
The oldest known pterosaurs lived approximately 220 million years ago¹ and were already animals capable of powered flight,² an ability that later evolved independently among paravian dinosaurs, the group that includes living birds and their closest non-avian relatives.³ Flight is a complex locomotory mode that requires physiological adaptations⁴ and a dramatic transformation of the body plan, including changes in body proportions, specialized integument, and acquisition of novel neurosensory capabilities.⁵ Although pterosaurs and birds developed distinct skeletal and integumentary adaptations for flight, they are hypothesized to share neuroanatomical traits linked to aerial locomotion.⁶^,⁷^,⁸^,⁹ Here, we use geometric morphometrics and phylogenetically informed analyses to assess the origin and evolution of brain shape and size in pterosaurs, tracing the transformation from their non-volant closest relatives (lagerpetids), and compare their trajectory with that in the dinosaur-bird transition. Pterosaurs have globular brains with moderately enlarged hemispheres, more closely resembling non-avian paravians such as troodontids and Archaeopteryx lithographica than living birds. Whereas birds inherited their basic brain structure from their dinosaurian ancestors,¹⁰^,¹¹^,¹²^,¹³^,¹⁴^,¹⁵^,¹⁶^,¹⁷ pterosaurs share only the ventrolateralization of the optic lobe with their closest non-volant relatives, the lagerpetids. This suggests that, in contrast to the bird-line archosaurs, where exaptation may have played a central role in the stepwise assembly of the avian brain configuration, brain evolution in pterosaurs seems to have unfolded rapidly at the origin of flight.
Active faulting in the upper plate of the Himalayas: Paleoseismic insights from the Western Nepal fault system
Curtiss, Elizabeth R.; Bemis, Sean P.; Styron, Richard; Taylor, Michael H.; Murphy, Michael; Hoxey, Andrew K. R.; Daniel, Michael; Fan, Souya; Kafle, Manoj; Chamlagain, Deepak; Adhikari, Basanta R. (Geological Society of America, 2025-12-01)
Understanding the role of upper-plate faults in obliquely convergent margins is essential for assessing regional strain distribution and seismic hazards. In the Himalayas, paleoseismic research has focused on the Main Frontal thrust as the primary surface expression of the plate boundary, leaving the seismic potential of upper-plate faults like the Western Nepal fault system largely unstudied. This study presents new paleoseismic evidence from seven trench sites across five mapped fault segments of the ~250-km-long Western Nepal fault system, providing the first direct constraints on its earthquake history. Stratigraphic and geochronologic data reveal at least three Holocene surface-rupturing earthquakes, with age constraints indicating that at least one of these events overlapped in time with a major Himalayan earthquake within the past ~800 yr. This demonstrates that the Western Nepal fault system is a significant, cross-orogen fault system, playing an active role in accommodating strain in the region. These findings establish the Western Nepal fault system as an active seismogenic system that accommodates oblique plate convergence and contributes to regional strain partitioning. This challenges the prevailing view that seismic deformation in the Himalayas is primarily confined to the Main Frontal thrust and highlights the need to incorporate upper-plate fault systems into seismic hazard assessments.
Assembly of lower continental crust: A garnet Lu-Hf petrochronological investigation of the Ivrea-Verbano Zone, Italy
Connop, Charlotte H.; Smye, Andrew J.; Garber, Joshua M.; Moser, Amy C.; Caddick, Mark J.; Vervoort, Jeffrey D. (Elsevier, 2024-05-15)
Garnet from five metapelitic samples that span the archetypal Ivrea-Verbano Zone (IVZ) lower continental crust section were dated with the lutetium-hafnium (Lu-Hf) method. Dates systematically decrease from 311.27 +/- 1.90 Ma in the sub-solidus amphibolite-facies domain to 263.81 +/- 1.29 Ma in the granulite-facies section. Core-to-rim zonation in Lu and Ca in sub-solidus amphibolite-facies garnet grains constrains a phase of isothermal burial of 1-2 kbar to similar to 311 Ma. Garnet trace-element zonation and Lu-Hf systematics of a sample adjacent to the Mafic Complex preserves evidence for garnet core growth at or prior to 300 Ma and garnet rim growth concomitant with emplacement of the Mafic Complex (similar to 286-282 Ma). Garnet grains in a high-grade amphibolite facies sample and granulite-facies metapelites exhibit no evidence of Lu remobilization, indicating that their Lu-Hf dates of between 275.30 +/- 2.47 Ma and 263.81 +/- 1.29 Ma record the timing of garnet growth prior to cooling of the section during exhumation. The >50 Myr period of garnet growth recorded in this dataset implies that the IVZ lower continental crust remained at elevated temperatures, >650 degrees C, over a protracted period prior to the initiation of Tethyan rifting. When combined with constraints on the maximum depositional age for the IVZ metasediments, the P-T-t data presented here are consistent with entrainment of sedimentary rocks into the lower crust by tectonic underplating between similar to 440 and similar to 311 Ma, prior to the onset of regional Variscan metamorphism.
Reconciling Mars InSight Results, Geoid, and Melt Evolution With 3D Spherical Models of Convection
Murphy, J. P.; King, Scott D. (American Geophysical Union, 2024-05-01)
We investigate the geodynamic and melting history of Mars using 3D spherical shell models of mantle convection, constrained by the recent InSight mission results. The Martian mantle must have produced sufficient melt to emplace the Tharsis rise by the end of the Noachian-requiring on the order of 1-3 x 109 km3 of melt after accounting for limited (similar to 10%) melt extraction. Thereafter, melting declined; however, abundant evidence for limited geologically recent volcanism necessitates some present-day melt even in the cool mantle inferred from InSight data. We test models with two mantle activation energies and a range of crustal Heat Producing Element (HPE) enrichment factors and initial core-mantle boundary temperatures. We also test the effect of including a hemispheric (spherical harmonic degree-1) step in lithospheric thickness to model the Martian dichotomy. We find that a higher activation energy (350 kJ mol-1) rheology produces present-day geotherms consistent with InSight results, and crustal HPE enrichment factors of 5-10-times produce localized melting near or up to present-day. The 10-times crustal HPE enrichment is consistent with both InSight and geochemical results and also produces present-day geoid power spectra consistent with Mars. However, calculations that match the present-day geoid power spectra require more than 60% melt extraction to produce the Tharsis swell. The addition of a degree-1 hemispheric dichotomy, as an equatorial step in lithospheric thickness, does not significantly improve upon melt production or the geoid. Mars' mantle needed to produce an extremely high volume of melt by similar to 3.7 billion years ago in order to build the immense volcanic plateau of Tharsis. There is also abundant evidence for small volumes of geologically recent volcanism, yet the InSight mission results are consistent with a relatively cool present-day mantle. We use 3D numerical models of the Martian mantle to determine what properties can produce a melting history and present interior temperatures consistent with InSight results and Mars' volcanic history. We test sets of models with two different sensitivities of the mantle viscosity to changes in temperature (i.e., activation energy), and a range of enrichment factors in Heat Producing Elements in the crust. We also test the effect of including a simplified version of the Martian hemispheric dichotomy. Our models with the higher activation energy and 10-times crustal enrichment in HPEs (consistent with Mars' crustal composition) produce melt near the present-day as well as temperature profiles consistent with InSight. However, it is very difficult to produce sufficient melt to form Tharsis in such a cool mantle, without assuming most of the melt produced in the mantle reaches the surface. Addition the simplified dichotomy does not significantly improve our results. Our results favor a higher activation energy mantle rheology and 10-times crustal heat producing element enrichment factor Even with the cool mantle consistent with InSight results, we obtain models having melt up to present-day Producing sufficient melt to form Tharsis requires a degree of melt extraction 6-times as efficient as Earth's mid-ocean ridges
Influence of Belowground Biomass on Barrier-Island Evolution During Storms: A Computational Parameter Study
Irish, Jennifer L.; Cheng, Wei; Weiss, Robert; Patch, Stephanie M.; Beever, Megan A. (ASCE, 2024-05-01)
Barrier islands span 10% of the world's coastlines and dominate along the Atlantic and Gulf of Mexico coasts in the USA routinely exposed to storm surge. These islands serve as buffers between the open coast and the mainland, and protect the mainland from storm damage. During storms, significant morphological change can occur, including substantial erosion of the islands' vegetated dunes. In this study, the focus is on the influence of belowground biomass - namely dune plant roots - and dune topographic characteristics on barrier-island erosion during storms. The numerical model XBeach was employed to simulate storm-induced sediment transport. A parameter study was conducted by varying distance from the shoreline to the dune, dune shape, sediment grain size, and sediment mobility as an analogue for biomass. The influence of individual parameters and the collective impact of parameters were analyzed. The results help improve our knowledge of barrier island dynamics and lay a solid groundwork for future investigations.
Global patterns in river water storage dependent on residence time
Collins, Elyssa L.; David, Cedric H.; Riggs, Ryan; Allen, George H.; Pavelsky, Tamlin M.; Lin, Peirong; Pan, Ming; Yamazaki, Dai; Meentemeyer, Ross K.; Sanchez, Georgina M. (Nature Portfolio, 2024-05-01)
Accurate assessment of global river flows and stores is critical for informing water management practices, but current estimates of global river flows exhibit substantial spread and estimates of river stores remain sparse. Estimates of river flows and stores are hampered by uncertainties in land runoff, an unobserved quantity that provides water input to rivers. Here we leverage global river flow observations and an ensemble of land surface models to generate a globally gauge-corrected monthly river flow and storage dataset. We estimate a global river storage mean (+/- monthly variability) of 2,246 +/- 505 km3 and a global continental flow of 37,411 +/- 7,816 km3 yr-1. Our global river water storage time series demonstrates that flow wave residence time is a fundamental driver that can double or halve river water stores and their variability. We also reconcile the wide range in previous estimates of monthly variability in global river flows. We identify previously underappreciated freshwater sources to the ocean from the Maritime Continent (Indonesia, Malaysia and Papua New Guinea) amounting to 1.6 times the Congo River and illustrate our capability of detecting severe anthropogenic water withdrawals. A global gauge-corrected monthly river flow and storage dataset suggests that residence time is a key driver of water storage and variability and indicates substantial freshwater discharge to the ocean from the Maritime Continent.

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