Y. A. Engbers, D. Thallner, R. K. Bono, C. J. Sprain, M. J. Murray, K. Bristol, B. Handford, T. Torsvik, A. J. Biggin
Paleosecular variation analysis is a primary tool for characterizing ancient geomagnetic behavior and its evolution through time. This study presents a new high-quality directional data set, paleosecular variation of the Paleogene (PSVP), with and without correction for serial correlation, compiled from 1,667 sites from 45 different localities from the Paleogene and late Cretaceous (84–23 Ma). The data set is used to study the variability, structure, and latitude dependence of the geomagnetic field during that period by varying selection criteria and PSV models. Modeled values for the equatorial virtual geomagnetic pole (VGP) dispersion have over-lapping uncertainty intervals within their uncertainty bounds between 8.3° and 18.6° for the past 250 Ma. We investigate the suitability of two descriptive models of PSV, Model G-style quadratic fits and covariant Giant Gaussian Process models, and find that both styles of model fail to satisfactorily reproduce the latitude dependent morphology of PSV, but suggest that estimates of the equatorial VGP dispersion may still robustly characterize aspects of Earth's long-term field morphology. During this time where the PSV behavior has not changed substantially, the reversal frequency has varied widely. The lack of a clear relationship between PSV behavior and reversal frequency is not trivially explained in the context of published findings regarding numerical geodynamo simulations.
{"title":"A Global Paleosecular Variation Database for the Paleogene: Stationary Secular Variation Behavior Since the Triassic?","authors":"Y. A. Engbers, D. Thallner, R. K. Bono, C. J. Sprain, M. J. Murray, K. Bristol, B. Handford, T. Torsvik, A. J. Biggin","doi":"10.1029/2023GC011203","DOIUrl":"https://doi.org/10.1029/2023GC011203","url":null,"abstract":"<p>Paleosecular variation analysis is a primary tool for characterizing ancient geomagnetic behavior and its evolution through time. This study presents a new high-quality directional data set, paleosecular variation of the Paleogene (PSVP), with and without correction for serial correlation, compiled from 1,667 sites from 45 different localities from the Paleogene and late Cretaceous (84–23 Ma). The data set is used to study the variability, structure, and latitude dependence of the geomagnetic field during that period by varying selection criteria and PSV models. Modeled values for the equatorial virtual geomagnetic pole (VGP) dispersion have over-lapping uncertainty intervals within their uncertainty bounds between 8.3° and 18.6° for the past 250 Ma. We investigate the suitability of two descriptive models of PSV, Model G-style quadratic fits and covariant Giant Gaussian Process models, and find that both styles of model fail to satisfactorily reproduce the latitude dependent morphology of PSV, but suggest that estimates of the equatorial VGP dispersion may still robustly characterize aspects of Earth's long-term field morphology. During this time where the PSV behavior has not changed substantially, the reversal frequency has varied widely. The lack of a clear relationship between PSV behavior and reversal frequency is not trivially explained in the context of published findings regarding numerical geodynamo simulations.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011203","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141424883","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}
The proliferation of microbial carbon fixation is a key control on the evolution of the biosphere and global carbon cycle. Most records of these metabolisms in ancient rocks come from organic matter or fossils, which are not always preserved. Here, we present a potential proxy for microbial carbon fixation (autotrophy) based on the isotopic composition of carbonate minerals. Autotrophs influence carbonate chemistry in the cellular microenvironment by decreasing CO2 concentration and increasing the carbonate saturation state. This can induce rapid precipitation of carbonate minerals that are out of isotopic equilibrium with their environment. Recent work has identified disequilibrated dual clumped isotope compositions (∆47 and ∆48) in the skeletal fossils of marine calcifying organisms. Here we test whether the same is true of non-skeletal carbonate fabrics associated with microbial autotrophs in modern and Eocene lakes. We found that microbial carbonate formed via autotrophic metabolism recorded lower ∆47 and higher ∆48 values (−∆47/+∆48) than predicted for thermodynamic equilibrium mineral formation. Our findings are supported by models of dual clumped isotope kinetics in the DIC system, and disequilibrium in the oxygen isotope system. We hypothesize that the inverse trajectory away from the equilibrium line (+∆47/−∆48) should be recorded by carbonates formed in association with alkalinizing heterotrophs, such as sulfate reducers. If so, carbonate dual clumped isotopes could be a powerful tool to identify the proliferation and rate of heterotrophic and autotrophic metabolisms in the carbonate rock record on Earth and (perhaps) other planets.
{"title":"Microbial Autotrophy Recorded by Carbonate Dual Clumped Isotope Disequilibrium","authors":"Miquela Ingalls, Hanna C. Leapaldt, Max K. Lloyd","doi":"10.1029/2024GC011590","DOIUrl":"https://doi.org/10.1029/2024GC011590","url":null,"abstract":"<p>The proliferation of microbial carbon fixation is a key control on the evolution of the biosphere and global carbon cycle. Most records of these metabolisms in ancient rocks come from organic matter or fossils, which are not always preserved. Here, we present a potential proxy for microbial carbon fixation (autotrophy) based on the isotopic composition of carbonate minerals. Autotrophs influence carbonate chemistry in the cellular microenvironment by decreasing CO<sub>2</sub> concentration and increasing the carbonate saturation state. This can induce rapid precipitation of carbonate minerals that are out of isotopic equilibrium with their environment. Recent work has identified disequilibrated dual clumped isotope compositions (∆<sub>47</sub> and ∆<sub>48</sub>) in the skeletal fossils of marine calcifying organisms. Here we test whether the same is true of non-skeletal carbonate fabrics associated with microbial autotrophs in modern and Eocene lakes. We found that microbial carbonate formed via autotrophic metabolism recorded lower ∆<sub>47</sub> and higher ∆<sub>48</sub> values (−∆<sub>47</sub>/+∆<sub>48</sub>) than predicted for thermodynamic equilibrium mineral formation. Our findings are supported by models of dual clumped isotope kinetics in the DIC system, and disequilibrium in the oxygen isotope system. We hypothesize that the inverse trajectory away from the equilibrium line (+∆<sub>47</sub>/−∆<sub>48</sub>) should be recorded by carbonates formed in association with alkalinizing heterotrophs, such as sulfate reducers. If so, carbonate dual clumped isotopes could be a powerful tool to identify the proliferation and rate of heterotrophic and autotrophic metabolisms in the carbonate rock record on Earth and (perhaps) other planets.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011590","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141329401","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}
Mita Uthaman, Chandrani Singh, Arun Singh, György Hetényi, Abhisek Dutta, Gaurav Kumar, Arun Kumar Dubey
Anomalously overturned thrust faults, lineaments and segmentation causing cross-cutting basement structures characterize the tectonic setting of Sikkim Himalaya. However, its seismotectonics is poorly constrained along with the speculated northward extension of the Dhubri-Chungthang Fault Zone (DCFZ) causing segmentation. Here, we utilize the precise location of newly acquired local earthquake data and fault plane solutions using full-waveform moment tensor inversion to better constrain seismically active zones. Transtensional shearing along the Main Himalayan Thrust in central Sikkim is possibly incited by fluid-rich upper-crust. Cessation of the mapped 20 km wide mid-crustal seismogenic zone of DCFZ at Chungthang and its northward discontinuation into the Higher Himalayas is confirmed by the striking variation in focal mechanisms. Earthquakes along imbricated segments in the lower-crust originate possibly in response to crustal shortening. Extensional shearing along the Moho triggers seismicity to the northwest of Sikkim. Such complex tectonic dynamics instigating persistent seismicity indicates high potential for future great earthquakes in Sikkim Himalaya.
{"title":"Complex Multi-Fault Dynamics in Sikkim Himalaya: New Insights From Local Earthquake Analysis","authors":"Mita Uthaman, Chandrani Singh, Arun Singh, György Hetényi, Abhisek Dutta, Gaurav Kumar, Arun Kumar Dubey","doi":"10.1029/2023GC011363","DOIUrl":"https://doi.org/10.1029/2023GC011363","url":null,"abstract":"<p>Anomalously overturned thrust faults, lineaments and segmentation causing cross-cutting basement structures characterize the tectonic setting of Sikkim Himalaya. However, its seismotectonics is poorly constrained along with the speculated northward extension of the Dhubri-Chungthang Fault Zone (DCFZ) causing segmentation. Here, we utilize the precise location of newly acquired local earthquake data and fault plane solutions using full-waveform moment tensor inversion to better constrain seismically active zones. Transtensional shearing along the Main Himalayan Thrust in central Sikkim is possibly incited by fluid-rich upper-crust. Cessation of the mapped 20 km wide mid-crustal seismogenic zone of DCFZ at Chungthang and its northward discontinuation into the Higher Himalayas is confirmed by the striking variation in focal mechanisms. Earthquakes along imbricated segments in the lower-crust originate possibly in response to crustal shortening. Extensional shearing along the Moho triggers seismicity to the northwest of Sikkim. Such complex tectonic dynamics instigating persistent seismicity indicates high potential for future great earthquakes in Sikkim Himalaya.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011363","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141329370","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}
K. Dayton, E. Gazel, P. E. Wieser, V. R. Troll, J. C. Carracedo, M. Aulinas, F. J. Perez-Torrado
The 2021 La Palma eruption (Tajogaite) was unprecedented in magnitude, duration, and degree of monitoring compared to historical volcanism on La Palma. Here, we provide data on melt inclusions in samples from the beginning and end of the eruption to compare the utility of both melt and fluid inclusions as recorders of magma storage. We also investigated compositional heterogeneities within the magmatic plumbing system. We found two populations of olivine crystals: a low Mg# (78–82) population present at the beginning and end of eruption, recording the maximum volatile contents (2.5 wt % H2O, 1,800 ppm F, 700 ppm Cl, 3,800 ppm S) and a higher Mg# (83–86) population sampled toward the end of the eruption, with lower volatile contents. Despite their host composition, melt inclusions share the same maximum range of CO2 concentrations (1.2–1.4 wt %), indicating olivine growth and inclusion capture at similar depths. Overall, both melt and fluid inclusions record similar pressures (450–850 MPa, ∼15–30 km), and when hosted in the same olivine crystal pressures are indistinguishable within error. At these mantle pressures, CO2 is expected to be an exsolved phase explaining the similar range of CO2 between the two samples, but other volatile species (F, Cl, S) behave incompatibly, and thus, the increase between the two olivine populations can be explained by fractional crystallization prior to eruption. Finally, based on our new data, we provide estimates on the total volatile emission of the eruption.
{"title":"Magmatic Storage and Volatile Fluxes of the 2021 La Palma Eruption","authors":"K. Dayton, E. Gazel, P. E. Wieser, V. R. Troll, J. C. Carracedo, M. Aulinas, F. J. Perez-Torrado","doi":"10.1029/2024GC011491","DOIUrl":"https://doi.org/10.1029/2024GC011491","url":null,"abstract":"<p>The 2021 La Palma eruption (Tajogaite) was unprecedented in magnitude, duration, and degree of monitoring compared to historical volcanism on La Palma. Here, we provide data on melt inclusions in samples from the beginning and end of the eruption to compare the utility of both melt and fluid inclusions as recorders of magma storage. We also investigated compositional heterogeneities within the magmatic plumbing system. We found two populations of olivine crystals: a low Mg# (78–82) population present at the beginning and end of eruption, recording the maximum volatile contents (2.5 wt % H<sub>2</sub>O, 1,800 ppm F, 700 ppm Cl, 3,800 ppm S) and a higher Mg# (83–86) population sampled toward the end of the eruption, with lower volatile contents. Despite their host composition, melt inclusions share the same maximum range of CO<sub>2</sub> concentrations (1.2–1.4 wt %), indicating olivine growth and inclusion capture at similar depths. Overall, both melt and fluid inclusions record similar pressures (450–850 MPa, ∼15–30 km), and when hosted in the same olivine crystal pressures are indistinguishable within error. At these mantle pressures, CO<sub>2</sub> is expected to be an exsolved phase explaining the similar range of CO<sub>2</sub> between the two samples, but other volatile species (F, Cl, S) behave incompatibly, and thus, the increase between the two olivine populations can be explained by fractional crystallization prior to eruption. Finally, based on our new data, we provide estimates on the total volatile emission of the eruption.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011491","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141329393","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}
The shapes of mantle plumes are sensitive to mantle viscosity, density structure, and flow patterns. Increasingly, global tomographic models reveal broad plume conduits in the lower mantle and highly tilting conduits in the mid and upper mantle. Previous studies mostly relied on 2D slices to analyze plume shapes, but fully investigating the complexity of 3D plume structures requires more effective visualization methods. Here, we use immersive headset-based virtual reality (VR) to visualize the full-waveform global tomographic models SEMUCB-WM1 and GLAD-M25. We develop criteria for the identification of plume conduits based on the relationship between the plume excess temperature and the VS anomaly (δVS). We trace 20 major plume conduits, measure the offsets of the conduits in azimuth and distance with respect to the hotspots, calculate the tilt angle, and evaluate the δVS along all traced conduits. We compare our traced conduits with the conduits predicted by global mantle convection models and vertical conduits. The wavespeed variations along conduits traced from each tomographic model are slower than modeled or vertical conduits, regardless of which tomographic model they are evaluated in. The shapes of traced conduits tend to differ greatly from modeled conduits. Plume ponding and the emergence of secondary plumes, which could result from a combination of compositional variations, phase transitions, small-scale convection, and variations in viscosity, can contribute to the complex observed plume shapes. The variation of δVS along the traced conduits and complex plume shapes suggest a thermochemical origin of many plumes.
地幔羽流的形状对地幔粘度、密度结构和流动模式很敏感。越来越多的全球层析成像模型揭示了下地幔中宽阔的羽流导管和中上地幔中高度倾斜的导管。以往的研究大多依赖二维切片来分析羽流形状,但要充分研究三维羽流结构的复杂性,需要更有效的可视化方法。在这里,我们使用基于沉浸式头显的虚拟现实(VR)来可视化全波形全球层析成像模型SEMUCB-WM1和GLAD-M25。我们根据羽流过量温度与 VS 异常(δVS)之间的关系,制定了识别羽流导管的标准。我们追踪了 20 条主要的羽流导管,测量了导管相对于热点的方位角和距离偏移,计算了倾斜角,并评估了所有追踪导管的 δVS。我们将所追踪的导管与全球地幔对流模型预测的导管和垂直导管进行了比较。无论采用哪种层析成像模式,沿每个层析成像模式追踪的导管的波速变化都慢于模型或垂直导管。跟踪导管的形状往往与模型导管有很大不同。羽流的积聚和次级羽流的出现可能是成分变化、相变、小尺度对流和粘度变化等综合作用的结果,这可能是造成观测到的羽流形状复杂的原因。沿追踪导管的 δVS 变化和复杂的羽流形状表明,许多羽流起源于热化学。
{"title":"A Synoptic View of Mantle Plume Shapes Enabled by Virtual Reality","authors":"Qianyi Lu, Maxwell L. Rudolph","doi":"10.1029/2024GC011517","DOIUrl":"https://doi.org/10.1029/2024GC011517","url":null,"abstract":"<p>The shapes of mantle plumes are sensitive to mantle viscosity, density structure, and flow patterns. Increasingly, global tomographic models reveal broad plume conduits in the lower mantle and highly tilting conduits in the mid and upper mantle. Previous studies mostly relied on 2D slices to analyze plume shapes, but fully investigating the complexity of 3D plume structures requires more effective visualization methods. Here, we use immersive headset-based virtual reality (VR) to visualize the full-waveform global tomographic models SEMUCB-WM1 and GLAD-M25. We develop criteria for the identification of plume conduits based on the relationship between the plume excess temperature and the <i>V</i><sub><i>S</i></sub> anomaly (<i>δV</i><sub><i>S</i></sub>). We trace 20 major plume conduits, measure the offsets of the conduits in azimuth and distance with respect to the hotspots, calculate the tilt angle, and evaluate the <i>δV</i><sub><i>S</i></sub> along all traced conduits. We compare our traced conduits with the conduits predicted by global mantle convection models and vertical conduits. The wavespeed variations along conduits traced from each tomographic model are slower than modeled or vertical conduits, regardless of which tomographic model they are evaluated in. The shapes of traced conduits tend to differ greatly from modeled conduits. Plume ponding and the emergence of secondary plumes, which could result from a combination of compositional variations, phase transitions, small-scale convection, and variations in viscosity, can contribute to the complex observed plume shapes. The variation of <i>δV</i><sub><i>S</i></sub> along the traced conduits and complex plume shapes suggest a thermochemical origin of many plumes.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011517","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141329394","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}
A. O. Indraswari, J. Frieling, T. A. Mather, A. J. Dickson, H. C. Jenkyns, E. Idiz
Understanding the behavior of mercury (Hg) in organic-rich sediments as they undergo thermal maturation is important, for example, because enrichment of Hg in sedimentary deposits has become a widely used proxy for volcanism from Large Igneous Provinces (LIPs). In this study, we evaluate the effects of such processes on sedimentary Hg concentrations by investigating a common stratigraphic interval in three drill cores with different levels of thermal maturity (immature, mature and post-mature) in Toarcian sediments (Posidonienschiefer Formation) from the Lower Saxony Basin, Germany. We present Hg concentrations, bulk organic geochemistry, and total sulfur data. Mercury concentrations in the mature and post-mature sediments are increased >2-fold relative to the immature material, which is greater than any potential differences in original Hg concentrations in the studied successions prior to burial. Organic-carbon and host-rock mass loss during thermal maturation may have concentrated Hg in the mature sediments to some extent, provided Hg is considered effectively immobile. The increased Hg, TOC-normalized Hg, and TS-normalized Hg are most likely linked to the “closed system” behavior of Hg in sedimentary basins and the relatively low temperatures (70–260°C) during maturation that resulted in limited Hg mobility. More speculatively, a certain degree of redistribution of Hg within the mature sediments is suggested by its enrichment in distinct stratigraphic levels. Regardless of the exact mechanisms at play, the elevated Hg concentrations in mature sediments amplify both Hg/TOC and Hg/TS, implying that thermal effects must be considered when using normalized Hg as a proxy for far-field volcanic activity.
{"title":"Investigating the Behavior of Sedimentary Mercury (Hg) During Burial-Related Thermal Maturation","authors":"A. O. Indraswari, J. Frieling, T. A. Mather, A. J. Dickson, H. C. Jenkyns, E. Idiz","doi":"10.1029/2024GC011555","DOIUrl":"https://doi.org/10.1029/2024GC011555","url":null,"abstract":"<p>Understanding the behavior of mercury (Hg) in organic-rich sediments as they undergo thermal maturation is important, for example, because enrichment of Hg in sedimentary deposits has become a widely used proxy for volcanism from Large Igneous Provinces (LIPs). In this study, we evaluate the effects of such processes on sedimentary Hg concentrations by investigating a common stratigraphic interval in three drill cores with different levels of thermal maturity (immature, mature and post-mature) in Toarcian sediments (Posidonienschiefer Formation) from the Lower Saxony Basin, Germany. We present Hg concentrations, bulk organic geochemistry, and total sulfur data. Mercury concentrations in the mature and post-mature sediments are increased >2-fold relative to the immature material, which is greater than any potential differences in original Hg concentrations in the studied successions prior to burial. Organic-carbon and host-rock mass loss during thermal maturation may have concentrated Hg in the mature sediments to some extent, provided Hg is considered effectively immobile. The increased Hg, TOC-normalized Hg, and TS-normalized Hg are most likely linked to the “closed system” behavior of Hg in sedimentary basins and the relatively low temperatures (70–260°C) during maturation that resulted in limited Hg mobility. More speculatively, a certain degree of redistribution of Hg within the mature sediments is suggested by its enrichment in distinct stratigraphic levels. Regardless of the exact mechanisms at play, the elevated Hg concentrations in mature sediments amplify both Hg/TOC and Hg/TS, implying that thermal effects must be considered when using normalized Hg as a proxy for far-field volcanic activity.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011555","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141326589","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}
Susannah M. Dorfman, Han Hsu, Farhang Nabiei, Marco Cantoni, James Badro, Vitali B. Prakapenka
(Mg,Fe)O ferropericlase-magnesiowüstite has been proposed to host the majority of Earth's sodium, but the mechanism and capacity for incorporating the alkali cation remain unclear. In this work, experiments in the laser-heated diamond anvil cell and first-principles calculations determine the solubility of sodium and favorability of sodium incorporation in iron-rich magnesiowüstite relative to (Mg,Fe)SiO3 bridgmanite. Reaction of Mg/(Mg + Fe) (Mg#) 55 and 28 olivine with NaCl at 33–128 GPa and 1600–3000 K produces iron-rich magnesiowüstite containing several percent sodium, while iron-rich bridgmanite contains little to no detectable sodium. In sodium-saturated magnesiowüstite, sodium number [Na/(Na + Mg + Fe)] is 2–5 atomic percent at pressures below 60 GPa and drastically increases to 10–20 atomic percent at deep lower mantle pressures. For these two compositions, there is no significant dependence of the results on Mg#. Our calculations not only show consistent results with experiments but further indicate that such an increase in solubility and partitioning of Na into magnesiowüstite is driven by the spin transition in iron. These results provide fundamental constraints on the crystal chemistry of sodium at lower-mantle conditions. If the sodium capacity of (Mg,Fe)O is not strongly dependent on Mg#, (Mg,Fe)O in the lower mantle may have the capacity to store the entire sodium budget of the Earth.
{"title":"High Sodium Solubility in Magnesiowüstite in Iron-Rich Deep Lower Mantle","authors":"Susannah M. Dorfman, Han Hsu, Farhang Nabiei, Marco Cantoni, James Badro, Vitali B. Prakapenka","doi":"10.1029/2023GC011390","DOIUrl":"https://doi.org/10.1029/2023GC011390","url":null,"abstract":"<p>(Mg,Fe)O ferropericlase-magnesiowüstite has been proposed to host the majority of Earth's sodium, but the mechanism and capacity for incorporating the alkali cation remain unclear. In this work, experiments in the laser-heated diamond anvil cell and first-principles calculations determine the solubility of sodium and favorability of sodium incorporation in iron-rich magnesiowüstite relative to (Mg,Fe)SiO<sub>3</sub> bridgmanite. Reaction of Mg/(Mg + Fe) (Mg#) 55 and 28 olivine with NaCl at 33–128 GPa and 1600–3000 K produces iron-rich magnesiowüstite containing several percent sodium, while iron-rich bridgmanite contains little to no detectable sodium. In sodium-saturated magnesiowüstite, sodium number [Na/(Na + Mg + Fe)] is 2–5 atomic percent at pressures below 60 GPa and drastically increases to 10–20 atomic percent at deep lower mantle pressures. For these two compositions, there is no significant dependence of the results on Mg#. Our calculations not only show consistent results with experiments but further indicate that such an increase in solubility and partitioning of Na into magnesiowüstite is driven by the spin transition in iron. These results provide fundamental constraints on the crystal chemistry of sodium at lower-mantle conditions. If the sodium capacity of (Mg,Fe)O is not strongly dependent on Mg#, (Mg,Fe)O in the lower mantle may have the capacity to store the entire sodium budget of the Earth.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011390","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141315486","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}
We analyzed 49,592 teleseismic receiver functions (RFs) recorded by 278 CEArray stations to image the mantle transition zone (MTZ) beneath the South China Block to understand the origins of deep velocity anomalies and their potential links to subduction and intraplate volcanism. We employed a fast-marching method and a high-resolution 3-D velocity model (FWEA18) derived from full waveform inversion in computing P-to-S conversion times to better image the 410- and 660-km discontinuities. Our results indicate that the common-conversion-point stacking of RFs using 3-D conversion times yielded better migration images of the two discontinuities. The images revealed a slightly depressed 410-km with a few small uplifted patches, and showed that the 660-km beneath the western Yangtze Craton is depressed by 10–25 km, which is likely caused by the stagnant Paleo-Pacific slab. The 660-km beneath the southern Cathaysia Block has a 5–15 km high plateau with a topographic low at its central part. The lateral dimension of the topographic low is ∼150 km and is located beneath the central Pearl River Mount Basin near Hong Kong. We speculate that the topographic low occurs within the Hainan plume with a temperature excess of ∼300–400 K and is caused by the garnet phase transition. The displaced deep plume enters the MTZ and spreads nearly horizontally at the base. The plume evolves into two channels with a minor one toward the northeast and a major one toward the southwest, which keep moving upward to the 410-km. The southwest channel is likely the source that feeds the Hainan volcanoes.
{"title":"A Displaced Lower Mantle Source of the Hainan Plume in South China Revealed by Receiver Function Imaging of the CEArray","authors":"Yan Zhang, Fenglin Niu, Jieyuan Ning, Chunquan Yu","doi":"10.1029/2023GC011292","DOIUrl":"https://doi.org/10.1029/2023GC011292","url":null,"abstract":"<p>We analyzed 49,592 teleseismic receiver functions (RFs) recorded by 278 CEArray stations to image the mantle transition zone (MTZ) beneath the South China Block to understand the origins of deep velocity anomalies and their potential links to subduction and intraplate volcanism. We employed a fast-marching method and a high-resolution 3-D velocity model (<i>FWEA18</i>) derived from full waveform inversion in computing P-to-S conversion times to better image the 410- and 660-km discontinuities. Our results indicate that the common-conversion-point stacking of RFs using 3-D conversion times yielded better migration images of the two discontinuities. The images revealed a slightly depressed 410-km with a few small uplifted patches, and showed that the 660-km beneath the western Yangtze Craton is depressed by 10–25 km, which is likely caused by the stagnant Paleo-Pacific slab. The 660-km beneath the southern Cathaysia Block has a 5–15 km high plateau with a topographic low at its central part. The lateral dimension of the topographic low is ∼150 km and is located beneath the central Pearl River Mount Basin near Hong Kong. We speculate that the topographic low occurs within the Hainan plume with a temperature excess of ∼300–400 K and is caused by the garnet phase transition. The displaced deep plume enters the MTZ and spreads nearly horizontally at the base. The plume evolves into two channels with a minor one toward the northeast and a major one toward the southwest, which keep moving upward to the 410-km. The southwest channel is likely the source that feeds the Hainan volcanoes.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC011292","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141315487","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}
The seismicity of the Philippines and Taiwan provides insight into the tectonics and seismic hazards of a region characterized by subduction and collision. We summarize the seismotectonics of the Philippines and Taiwan by documenting the distribution of hypocenters for earthquakes of magnitude M ≥ 4.6 and focal mechanisms for earthquakes of magnitude M ≥ 5.0 over ∼21 years. We quantify seismicity rates (earthquake frequency) and compare seismicity distributions with proposed tectonic and faulting models. 6,187 earthquakes of magnitude M ≥ 4.6 occurred between 1 January 2000 and 31 March 2021, 79% at depths <70 km and 70% having magnitudes M < 5.0. Approximately 88 earthquakes of magnitude M ≥ 5.0 occur per year, with 12 events of magnitude M ≥ 7.0 occurring since January 2000. Seismic activity decreases exponentially between 50 and 210 km depth at a rate ∼10% faster than the global average. Intermediate and deep earthquakes at depths >70 km trace the Wadati-Benioff zones of subducting slabs, most of which are only seismically active to depths of ∼250 km. The distribution of earthquakes at depths >70 km is likely influenced by the subduction of young lithosphere, slab tearing, and phase boundary interactions between depths of 410 and 660 km. Shallow earthquakes at depths ≤70 km are generated by megathrust, crustal, and intraslab faulting. Crustal thrust and strike-slip faulting are the most abundant and prevalent sources of damaging earthquakes. The Philippines and Taiwan are subject to high seismic risk, similar to nearby Indonesia.
{"title":"Seismotectonics of the Philippine and Taiwan Subduction Systems and Implications for Seismic Hazards","authors":"Sean J. Hutchings, Walter D. Mooney","doi":"10.1029/2023GC010990","DOIUrl":"https://doi.org/10.1029/2023GC010990","url":null,"abstract":"<p>The seismicity of the Philippines and Taiwan provides insight into the tectonics and seismic hazards of a region characterized by subduction and collision. We summarize the seismotectonics of the Philippines and Taiwan by documenting the distribution of hypocenters for earthquakes of magnitude <i>M</i> ≥ 4.6 and focal mechanisms for earthquakes of magnitude <i>M</i> ≥ 5.0 over ∼21 years. We quantify seismicity rates (earthquake frequency) and compare seismicity distributions with proposed tectonic and faulting models. 6,187 earthquakes of magnitude <i>M</i> ≥ 4.6 occurred between 1 January 2000 and 31 March 2021, 79% at depths <70 km and 70% having magnitudes <i>M</i> < 5.0. Approximately 88 earthquakes of magnitude <i>M</i> ≥ 5.0 occur per year, with 12 events of magnitude <i>M</i> ≥ 7.0 occurring since January 2000. Seismic activity decreases exponentially between 50 and 210 km depth at a rate ∼10% faster than the global average. Intermediate and deep earthquakes at depths >70 km trace the Wadati-Benioff zones of subducting slabs, most of which are only seismically active to depths of ∼250 km. The distribution of earthquakes at depths >70 km is likely influenced by the subduction of young lithosphere, slab tearing, and phase boundary interactions between depths of 410 and 660 km. Shallow earthquakes at depths ≤70 km are generated by megathrust, crustal, and intraslab faulting. Crustal thrust and strike-slip faulting are the most abundant and prevalent sources of damaging earthquakes. The Philippines and Taiwan are subject to high seismic risk, similar to nearby Indonesia.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2023GC010990","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141315488","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}
Fluctuations in the geomagnetic field occur over a broad range of timescales. Short-period fluctuations are called secular variation, whereas excursions and reversals are viewed as anomalous transient events. An open question is whether distinct mechanisms are required to account for these different forms of variability. Clues are sought in trends b of the axial dipole moment from six time-dependent geomagnetic field models. Variability in b has a well-defined dependence on the time interval (or window) for the trend. The variance of b reveals a simple relationship to trends during excursions and reversals. This connection hints at a link between reversals, excursions and secular variation. Stochastic models exhibit a similar behavior in response to random fluctuations in dipole generation. We find that excursions, reversals and secular variation can be distinguished on the basis of trend durations rather than differences in the underlying physical process. While this analysis does not rule out distinct physical mechanisms, the paleomagnetic observations suggest that such distinctions are not required.
地磁场波动的时间范围很广。短周期波动被称为世俗变化,而偏移和逆转则被视为异常瞬变事件。一个悬而未决的问题是,这些不同形式的变化是否需要不同的机制来解释。我们从六个随时间变化的地磁场模型的轴偶极矩 b 的变化趋势中寻找线索。b 的变化与趋势的时间间隔(或窗口)有明确的关系。b 的方差与偏移和逆转期间的趋势有简单的关系。这种关系暗示了逆转、偏移和世俗变化之间的联系。随机模型在偶极子产生的随机波动中也表现出类似的行为。我们发现,偏移、逆转和世俗变化可以根据趋势持续时间而不是基本物理过程的差异来区分。虽然这一分析并不能排除不同的物理机制,但古地磁观测结果表明,这种区分并不是必需的。
{"title":"Excursions, Reversals, and Secular Variation: Different Expressions of a Common Mechanism?","authors":"B. A. Buffett","doi":"10.1029/2024GC011604","DOIUrl":"https://doi.org/10.1029/2024GC011604","url":null,"abstract":"<p>Fluctuations in the geomagnetic field occur over a broad range of timescales. Short-period fluctuations are called secular variation, whereas excursions and reversals are viewed as anomalous transient events. An open question is whether distinct mechanisms are required to account for these different forms of variability. Clues are sought in trends <i>b</i> of the axial dipole moment from six time-dependent geomagnetic field models. Variability in <i>b</i> has a well-defined dependence on the time interval (or window) for the trend. The variance of <i>b</i> reveals a simple relationship to trends during excursions and reversals. This connection hints at a link between reversals, excursions and secular variation. Stochastic models exhibit a similar behavior in response to random fluctuations in dipole generation. We find that excursions, reversals and secular variation can be distinguished on the basis of trend durations rather than differences in the underlying physical process. While this analysis does not rule out distinct physical mechanisms, the paleomagnetic observations suggest that such distinctions are not required.</p>","PeriodicalId":50422,"journal":{"name":"Geochemistry Geophysics Geosystems","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-06-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1029/2024GC011604","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141308781","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}