Geochemistry Geophysics Geosystems最新文献

{"title":"Depth-Partitioning of Particulate Organic Carbon Composition in the Rising and Falling Stages of the Amazon River","authors":"Sarah Z. Rosengard,&nbsp;Jose Mauro S. Moura,&nbsp;Robert G. M. Spencer,&nbsp;Carl Johnson,&nbsp;Ann McNichol,&nbsp;Andrew D. Steen,&nbsp;Valier Galy","doi":"10.1029/2023GC011273","DOIUrl":"https://doi.org/10.1029/2023GC011273","url":null,"abstract":"<p>The Amazon River mobilizes organic carbon across one of the world's largest terrestrial carbon reservoirs. Quantifying the sources of particulate organic carbon (POC) to this flux is typically challenging in large systems such as the Amazon River due to hydrodynamic sorting of sediments. Here, we analyze the composition of POC collected from multiple total suspended sediment (TSS) profiles in the mainstem at Óbidos, and surface samples from the Madeira, Solimões and Tapajós Rivers. As hypothesized, TSS and POC concentrations in the mainstem increased with depth and fit well to Rouse models for sediment sorting by grain size. Coupling these profiles with Acoustic Doppler Current Profiler discharge data, we estimate a large decrease in POC flux (from 540 to 370 kg per second) between the rising and falling stages of the Amazon River mainstem. The C/N ratio and stable and radiocarbon signatures of bulk POC are less variable within the cross-section at Óbidos and suggest that riverine POC in the Amazon River is predominantly soil-derived. However, smaller shifts in these compositional metrics with depth, including leaf wax <i>n</i>-alkanes and fatty acids, are consistent with the perspective that deeper and larger particles carry fresher, less degraded organic matter sources (i.e., vegetation debris) through the mainstem. Overall, our cross-sectional surveys at Óbidos highlight the importance of depth-specific sampling for estimating riverine export fluxes. At the same time, they imply that this approach to sampling is perhaps less essential with respect to characterizing the composition of POC sources exported by the river.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011273","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Volcanic Flank Collapse, Secondary Sediment Failure and Flow-Transition: Multi-Stage Landslide Emplacement Offshore Montserrat, Lesser Antilles","authors":"Michel Kühn,&nbsp;Christian Berndt,&nbsp;Sebastian F. L. Watt,&nbsp;Matthew J. Hornbach,&nbsp;Sebastian Krastel,&nbsp;Kristina Sass,&nbsp;Steffen Kutterolf,&nbsp;Tim Freudenthal,&nbsp;Katrin Huhn,&nbsp;Jens Karstens,&nbsp;Bettina Schramm,&nbsp;Judith Elger,&nbsp;Christoph Böttner,&nbsp;Dirk Klaeschen","doi":"10.1029/2024GC011564","DOIUrl":"https://doi.org/10.1029/2024GC011564","url":null,"abstract":"<p>Volcanic flank collapses, especially those in island settings, have generated some of the most voluminous mass transport deposits on Earth and can trigger devastating tsunamis. Reliable tsunami hazard assessments for flank collapse-driven tsunamis require an understanding of the complex emplacement processes involved. The seafloor sequence southeast of Montserrat (Lesser Antilles) is a key site for the study of volcanic flank collapse emplacement processes that span subaerial to submarine environments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from one of the most extensive mass transport deposits offshore Montserrat, which exemplifies multi-phase landslide deposition from volcanic islands. The deposits reveal emplacement in multiple stages including two blocky volcanic debris avalanches, secondary seafloor failure and a late-stage erosive density current that carved channel-like incisions into the hummocky surface of the deposit about 15 km from the source region. The highly erosive density current potentially originated from downslope-acceleration of fine-grained material that was suspended in the water column earlier during the slide. Late-stage erosive turbidity currents may be a more common process following volcanic sector collapse than has been previously recognized, exerting a potentially important control on the observed deposit morphology as well as on the runout and the overall shape of the deposit.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011564","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488228","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mobility of Magmas Within the Earth: Insights From the Elasticity and Transport Properties of Hydrous Albitic Melts","authors":"Aaron Wolfgang Ashley,&nbsp;Suraj Bajgain,&nbsp;Mainak Mookherjee","doi":"10.1029/2024GC011510","DOIUrl":"https://doi.org/10.1029/2024GC011510","url":null,"abstract":"<p>The continental crust is produced by the solidification of aluminosilicate-rich magmas which are sourced from deep below the surface. Migration of the magma depends on the density (<i>ρ</i>) contrast to source rocks and the melt viscosity (<i>η</i>). At the surface, these silica-rich melts are typically sluggish due to high <i>η</i> &gt; 1,000 Pa s. Yet at their source regions, the melt properties are complexly influenced by pressure (<i>P</i>), temperature (<i>T</i>), and water contents (<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>X</mi>\u0000 <mrow>\u0000 <msub>\u0000 <mi>H</mi>\u0000 <mn>2</mn>\u0000 </msub>\u0000 <mi>O</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${X}_{{mathrm{H}}_{2}mathrm{O}}$</annotation>\u0000 </semantics></math>). In this study, we examined the combined <i>P</i>-<i>T</i>-<span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <msub>\u0000 <mi>X</mi>\u0000 <mrow>\u0000 <msub>\u0000 <mi>H</mi>\u0000 <mn>2</mn>\u0000 </msub>\u0000 <mi>O</mi>\u0000 </mrow>\u0000 </msub>\u0000 </mrow>\u0000 <annotation> ${X}_{{mathrm{H}}_{2}mathrm{O}}$</annotation>\u0000 </semantics></math> effects on the behavior of melts with an albite stoichiometry (NaAlSi₃O₈). We used <i>first-principles</i> molecular dynamics simulations to examine anhydrous (0 wt % H₂O) and hydrous (5 wt % H₂O) melts. To constrain the <i>P</i> and <i>T</i> effects, we explored <i>P</i> ≤ 25 GPa across several isotherms between 2500 and 4000 K. The melts show anomalous <i>P</i>-<i>ρ</i> relationships at low <i>P</i> ∼ 0 GPa and high <i>T</i> ≥ 2500 K, consistent with vaporization. At lithospheric conditions, melt <i>ρ</i> increases with compression and is well described by a finite-strain formalism. Water lowers the melt density (<i>ρ</i>_hydrous &lt; <i>ρ</i>_anhydrous) but increases the compressibility, that is, 1/<i>K</i>_hydrous &gt;1/<i>K</i>_anhydrous or <i>K</i>_hydrous &lt; <i>K</i>_anhydrous. We also find that the melt <i>η</i> decreases with pressure and then increases with further compression. Water decreases the viscosity (<i>η</i>_hydrous &lt; <i>η</i>_anhydrous) by depolymerizing the melt structure. The ionic self-diffusivities are increased by the presence of water. The decreased <i>ρ</i> and <i>η</i> by H₂O increase the mobility of magma at crustal conditions, which could explain ","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011510","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488824","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sources and Chemical Weathering Implications of Strontium and Hydrochemistry in an Inland Alpine Permafrost Basin","authors":"Huiling Zhou,&nbsp;Zongxing Li,&nbsp;Baijuan Zhang,&nbsp;Fa Du,&nbsp;Jian Xue","doi":"10.1029/2024GC011432","DOIUrl":"https://doi.org/10.1029/2024GC011432","url":null,"abstract":"<p>The hydrochemical characteristics of river water are influenced by a multitude of factors, reflecting the surrounding geographical environment. The Shaliu River, located in the northeastern Tibetan Plateau (TP), serves as a typical inland alpine permafrost watershed. In this study, we compiled data on dissolved strontium (Sr) concentration, ⁸⁷Sr/⁸⁶Sr isotopic, and hydrochemical profiles from the Shaliu River during the ablation period (May–October). Additionally, we gathered information on the Sr concentration and ⁸⁷Sr/⁸⁶Sr in the sediment of the river. The pattern of spatial heterogeneity in observed strontium (Sr) compositions can largely be attributed to lithological characteristics encountered at different locations along the river. The chemical components of Sr in the waters are derived from a combination of carbonate and silicate materials, with carbonates contributing between 69% and 81% and silicates contributing 19%–31%. The annual dissolved Sr flux is estimated to be 132 t/a. In addition to the influence of lithology and weathering processes, we propose that freeze-thaw cycles within the permafrost layer may significantly affect the chemical mass flux in alpine permafrost watersheds because they generate substantial amounts of loose and easily erodible materials. Climate warming may further intensify the weathering processes in these watersheds, potentially leading to an increase in the Sr flux. This study is crucial for developing a comprehensive understanding of the geochemical composition of dissolved solutes in alpine permafrost regions, as well as for identifying the factors that regulate river water chemistry.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011432","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Testing Mantle Convection Simulations With Paleobiology and Other Stratigraphic Observations: Examples From Western North America","authors":"Victoria M. Fernandes,&nbsp;Gareth G. Roberts,&nbsp;Fred Richards","doi":"10.1029/2023GC011381","DOIUrl":"https://doi.org/10.1029/2023GC011381","url":null,"abstract":"<p>Mantle convection plays a fundamental role in driving evolution of oceanic and continental lithosphere. In turn it impacts a broad suite of processes operating at or close to Earth's surface including landscape evolution, glacio-eustasy, magmatism, and climate. A variety of theoretical approaches now exist to simulate mantle convection. Outputs from such simulations are being used to parameterize models of landscape evolution and basin formation. However, the substantial body of existing simulations has generated a variety of conflicting views on the history of dynamic topography, its evolution and key parameters for modeling mantle flow. The focus of this study is on developing strategies to use large-scale quantitative stratigraphic observations to assess model predictions and identify simulation parameters that generate realistic predictions of Earth surface evolution. Spot measurements of uplift or subsidence provide useful target observations for models of dynamic topography, but finding areas where tectonics have not also influenced vertical motions is challenging. To address this issue, we use large inventories of stratigraphic data from across North America with contextual geophysical and geodetic data to constrain the regional uplift and subsidence history. We demonstrate that a suite of typical geodynamic simulations struggle to match the amplitude, polarity and timing of observed vertical motions. Building on recent seismological advances, we then explore strategies for understanding patterns of continental uplift and subsidence that incorporate (and test) predicted evolution of the lithosphere, asthenosphere and deep mantle. Our results demonstrate the importance of contributions from the uppermost mantle in driving vertical motions of continental interiors.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011381","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141488736","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Sedimentology of Modern Bahamian Carbonate Slopes: Summary and Update","authors":"K. Fauquembergue,&nbsp;T. Mulder,&nbsp;J. Reijmer,&nbsp;V. Hanquiez,&nbsp;C. Betzler,&nbsp;E. Ducassou,&nbsp;A. Recouvreur,&nbsp;M. Principaud,&nbsp;J. Borgomano,&nbsp;S. Wilk,&nbsp;E. Poli","doi":"10.1029/2023GC011077","DOIUrl":"https://doi.org/10.1029/2023GC011077","url":null,"abstract":"<p>Slopes adjacent to the Bahamian carbonate platform revealed a large variety of depositional processes. In this study, we present a synthesis summarizing 109,000 km² of bathymetric and reflectivity data with ∼7,900 km of seismic lines and 311 m of sediment cores that were obtained over the last 50 years. These data are used to develop a conceptual model of sedimentation patterns on Quaternary carbonate slope systems and their interaction with the adjacent shallow-water carbonate platforms. Our data highlight that during the Quaternary, factors controlling large-scale sedimentation on Bahamian slopes have numerous similarities as they have higher sedimentation rates during interglacials. At a small scale, every slope has its own characteristics that are contemporary controlled by two main characteristics: (a) facies on the adjacent shallow-water platform, and (b) the impact of shallow- and deep-water currents. Large-scale tectonics influence sediment deposition as it determines the position of the islands and impacts platform facies distribution.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011077","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141441299","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Crust-Derived CO2 Production From a Shallow Pluton in Limestone Is Driven by Metamorphic Decarbonation, Not Assimilation","authors":"R. A. Morris,&nbsp;D. Canil","doi":"10.1029/2024GC011485","DOIUrl":"https://doi.org/10.1029/2024GC011485","url":null,"abstract":"<p>Traditionally, it is assumed that contributions of crust-derived CO₂ emissions at arc settings are minor, but this requires well-constrained field studies to determine the extent of magma-carbonate reaction and concomitant C released. The Jurassic Bonanza arc on Vancouver Island (Canada) was built on a Triassic limestone platform and makes for an ideal setting to examine arc magma-carbonate interactions beneath an island arc. We examine how km-scale magma bodies might react with carbonate from a well-constrained study of a gabbro pluton that intrudes limestone. The pluton shows muted to nil carbonate interaction preserving primary igneous ⁸⁷Sr/⁸⁶Sr values (∼0.703) except for a thin (&lt;2 m wide) marginal gabbro (∼0.706) in contact with a decarbonized metamorphic aureole. A lack of ⁸⁷Sr/⁸⁶Sr or δ¹⁸O_cpx enrichment in gabbro ∼10 to &gt;1,000 m from the contact suggests that any reaction with limestone wallrock is limited to at most the outer ∼10 m of the pluton. More enhanced magma-carbonate interaction and CO₂ production occurs via a network of shallow dikes and sills (&lt;0.2 GPa) compared to deeper plutons, consistent with experimental data showing increased carbonate assimilation at shallower depths (≤0.5 GPa). Plutons are an important heat source to release CO₂ from carbonate wallrock by contact metamorphism, where &gt;89% of crust-derived CO₂ is liberated by wallrock decarbonation and &lt;11% is liberated by magma that assimilated limestone. Nonetheless, we show that neither magmatic nor metamorphic crust-derived CO₂ contributions compare to mantle-derived CO₂. Our study places realistic and quantitative limits on arc-derived CO₂ from upper crustal limestone sources.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011485","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141441334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Probabilistic Determination of the Role of Faults and Intrusions in Helium-Rich Gas Fields Formation","authors":"D. T. Halford,&nbsp;R. Karolytė,&nbsp;M. W. Andreason,&nbsp;B. Cathey,&nbsp;M. Cathey,&nbsp;J. T. Dellenbach,&nbsp;J. J. Cuzella,&nbsp;S. A. Sonnenberg,&nbsp;A. Cheng,&nbsp;K. J. W. McCaffrey,&nbsp;J. G. Gluyas,&nbsp;C. J. Ballentine","doi":"10.1029/2024GC011522","DOIUrl":"https://doi.org/10.1029/2024GC011522","url":null,"abstract":"<p>Natural gas fields with economic helium (&gt;0.3 He %) require the radioactive decay of crustal uranium (U) and thorium (Th) to generate He and tectonic/structural regimes favorable to releasing and concentrating He. An unknown is determining the role of faults and structural features in focusing deep-seated He sources on shallow accumulations. We tested the correlation between high-He wells (<i>n</i> = 94) and structural features using a new high-resolution aeromagnetic survey in the Four Corners area, USA. A depth-to-basement map with basement lineaments/faults, an intrusion map, and a flattened basement structural high map were created using Werner deconvolution algorithms by combining magnetic, gravity, and topography data with magnetic and gravity depth profiles. We show quantitatively (via analysis of variance) that a non-random process controls the relationship between He (&gt;0.3%) and both basement faults and intrusions: 88% of high-He wells occur &lt;1 km of basement faults; and 85% of high-He wells occur &lt;1 km of intrusions. As He % increases, the distance to the structural features decreases. Strong spatial/statistical correlations of He wells to both basement faults and intrusions suggest that advective transport via faults/intrusions facilitates He migration. The role of gas phase buoyancy and structural trapping is confirmed: 88% of high-He occurs within basement structural highs, and 91% of the remaining wells are &lt;1 km from intrusions (potential structural high). We present a composite figure to illustrate how a probabilistic approach can be used as a predictive model to improve He exploration success by targeting zones of intersection of basement faults and intrusions within basement structural highs.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011522","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141439623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Iron Oxyhydroxide-Rich Hydrothermal Deposits at the High-Temperature Fåvne Vent Field, Mohns Ridge","authors":"Caroline Gini,&nbsp;John W. Jamieson,&nbsp;Eoghan P. Reeves,&nbsp;Amy Gartman,&nbsp;Thibaut Barreyre,&nbsp;Michael G. Babechuk,&nbsp;Steffen L. Jørgensen,&nbsp;Katleen Robert","doi":"10.1029/2024GC011481","DOIUrl":"https://doi.org/10.1029/2024GC011481","url":null,"abstract":"<p>The recently discovered Fåvne vent field, located at 3,040 m depth on the slow-spreading Mohns mid-ocean ridge between Greenland and Norway, is a high-temperature (≥250°C) vent field that is characterized by Fe oxyhydroxide-rich and S-poor chimneys and mounds. The vent field is located on both the hanging wall and footwall of a normal fault with a ∼1.5 km throw that forms the western edge of the ∼20 km wide ridge axial valley. Data collected during exploration of the site using a remotely operated vehicle as well as mineralogical and geochemical analyses of rock samples and sediments are used to characterize the geological setting of the vent field and composition of the hydrothermal deposits. The chimney walls are highly porous and lack defined chalcopyrite lined conduits, typical of high-temperature chimneys. Overall, abundant Fe oxyhydroxide precipitation at high-temperature vents at Fåvne reflects an excess of Fe over reduced S in the fluid, leading to precipitation of Fe oxide and oxyhydroxide minerals at high to moderate temperature vents (&gt;100°C), and as microbially mediated and abiotic precipitation of Fe oxyhydroxide minerals at low-temperature diffuse vents (&lt;100°C). The mounds and chimneys exhibit low base metal and reduced S concentrations relative to globally averaged seafloor deposits and suggest subseafloor mixing of hydrothermal fluid with seawater, causing metal sulfide precipitation. Cobalt enrichment at Fåvne may reflect a subsurface influence of an ultramafic substrate on circulating fluids, although ultramafic rocks are absent on the seafloor and no other elements typical of ultramafic deposits are present.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011481","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141439624","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Experimental Observation of a New Attenuation Mechanism in hcp-Metals That May Operate in the Earth's Inner Core","authors":"Simon A. Hunt,&nbsp;Andrew M. Walker,&nbsp;Oliver T. Lord,&nbsp;Stephen Stackhouse,&nbsp;Lewis Schardong,&nbsp;Lora S. Armstrong,&nbsp;Andrew J. Parsons,&nbsp;Geoffrey E. Lloyd,&nbsp;John Wheeler,&nbsp;Danielle M. Fenech,&nbsp;Stefan Michalik,&nbsp;Matthew L. Whitaker","doi":"10.1029/2023GC011386","DOIUrl":"https://doi.org/10.1029/2023GC011386","url":null,"abstract":"<p>Seismic observations show the Earth's inner core has significant and unexplained variation in seismic attenuation with position, depth and direction. Interpreting these observations is difficult without knowledge of the visco- or anelastic dissipation processes active in iron under inner core conditions. Here, a previously unconsidered attenuation mechanism is observed in zinc, a low pressure analog of <i>hcp</i>-iron, during small strain sinusoidal deformation experiments. The experiments were performed in a deformation-DIA combined with X-radiography, at seismic frequencies (∼0.003–0.1 Hz), high pressure and temperatures up to ∼80% of melting temperature. Significant dissipation (0.077 ≤ <i>Q</i>⁻¹(<i>ω</i>) ≤ 0.488) is observed along with frequency dependent softening of zinc's Young's modulus and an extremely small activation energy for creep (⩽7 kJ mol⁻¹). In addition, during sinusoidal deformation the original microstructure is replaced by one with a reduced dislocation density and small, uniform, grain size. This combination of behavior collectively reflects a mode of deformation called “internal stress superplasticity”; this deformation mechanism is unique to anisotropic materials and activated by cyclic loading generating large internal stresses. Here we observe a new form of internal stress superplasticity, which we name as “<i>elastic strain mismatch superplasticity</i>.” In it the large stresses are caused by the compressional anisotropy. If this mechanism is also active in <i>hcp</i>-iron and the Earth's inner-core it will be a contributor to inner-core observed seismic attenuation and constrain the maximum inner-core grain-size to ≲10 km.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":2.9,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011386","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141441375","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}