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Zhang Y, Wang W, Li Y, Wu Z. Superionic iron hydride shapes ultralow-velocity zones at Earth's core-mantle boundary. Proc Natl Acad Sci U S A 2024; 121:e2406386121. [PMID: 39163332 PMCID: PMC11363269 DOI: 10.1073/pnas.2406386121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2024] [Accepted: 07/23/2024] [Indexed: 08/22/2024] Open
Abstract
Seismological studies have exposed numerous ultralow velocity zones (ULVZs) exhibiting extraordinary physical attributes at Earth's core-mantle boundary, yet their compositions and origins remain controversial. Water-iron reaction can generate unique phases under lowermost-mantle conditions and likely plays a crucial role in forming ULVZs. Through first-principles molecular dynamic simulations with machine learning techniques, we determine that iron hydride, the product of water-iron reaction, is stable as a superionic phase at the core-mantle boundary. This superionic iron hydride has much slower velocities and a higher density than the ambient mantle under lowermost-mantle conditions. Accumulation of iron hydride, created through either a chemical reaction between subducted water and iron or solidification of core material entrained in the lower mantle by convection, can explain the seismic observations of ULVZs particularly those associated with subduction. This work suggests that water may have a substantial role in creating seismic heterogeneities at the core-mantle boundary.
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Affiliation(s)
- Yu Zhang
- Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
| | - Wenzhong Wang
- Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
- National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Hefei230026, China
- Chinese Academy of Sciences Center for Excellence in Comparative Planetology, USTC, Hefei, Anhui230026, China
| | - Yunguo Li
- Chinese Academy of Sciences Center for Excellence in Comparative Planetology, USTC, Hefei, Anhui230026, China
- State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei230026, China
| | - Zhongqing Wu
- Laboratory of Seismology and Physics of Earth’s Interior, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui230026, China
- National Geophysical Observatory at Mengcheng, University of Science and Technology of China, Hefei230026, China
- Chinese Academy of Sciences Center for Excellence in Comparative Planetology, USTC, Hefei, Anhui230026, China
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2
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Khan A, Huang D, Durán C, Sossi PA, Giardini D, Murakami M. Evidence for a liquid silicate layer atop the Martian core. Nature 2023; 622:718-723. [PMID: 37880439 PMCID: PMC10600012 DOI: 10.1038/s41586-023-06586-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Accepted: 08/29/2023] [Indexed: 10/27/2023]
Abstract
Seismic recordings made during the InSight mission1 suggested that Mars's liquid core would need to be approximately 27% lighter than pure liquid iron2,3, implying a considerable complement of light elements. Core compositions based on seismic and bulk geophysical constraints, however, require larger quantities of the volatile elements hydrogen, carbon and sulfur than those that were cosmochemically available in the likely building blocks of Mars4. Here we show that multiply diffracted P waves along a stratified core-mantle boundary region of Mars in combination with first-principles computations of the thermoelastic properties of liquid iron-rich alloys3 require the presence of a fully molten silicate layer overlying a smaller, denser liquid core. Inverting differential body wave travel time data with particular sensitivity to the core-mantle boundary region suggests a decreased core radius of 1,675 ± 30 km associated with an increased density of 6.65 ± 0.1 g cm-3, relative to previous models2,4-8, while the thickness and density of the molten silicate layer are 150 ± 15 km and 4.05 ± 0.05 g cm-3, respectively. The core properties inferred here reconcile bulk geophysical and cosmochemical requirements, consistent with a core containing 85-91 wt% iron-nickel and 9-15 wt% light elements, chiefly sulfur, carbon, oxygen and hydrogen. The chemical characteristics of a molten silicate layer above the core may be revealed by products of Martian magmatism.
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Affiliation(s)
- A Khan
- Institute of Geochemistry and Petrology, ETH Zürich, Zurich, Switzerland.
- Institute of Geophysics, ETH Zürich, Zurich, Switzerland.
| | - D Huang
- Institute of Geochemistry and Petrology, ETH Zürich, Zurich, Switzerland.
| | - C Durán
- Institute of Geophysics, ETH Zürich, Zurich, Switzerland
| | - P A Sossi
- Institute of Geochemistry and Petrology, ETH Zürich, Zurich, Switzerland
| | - D Giardini
- Institute of Geophysics, ETH Zürich, Zurich, Switzerland
| | - M Murakami
- Institute of Geochemistry and Petrology, ETH Zürich, Zurich, Switzerland
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3
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Quantification of Small-Scale Heterogeneity at the Core–Mantle Boundary Using Sample Entropy of SKS and SPdKS Synthetic Waveforms. MINERALS 2022. [DOI: 10.3390/min12070813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Qualitative and quantitative analysis of seismic waveforms sensitive to the core–mantle boundary (CMB) region reveal the presence of ultralow-velocity zones (ULVZs) that have a strong decrease in compressional (P) and shear (S) wave velocity, and an increase in density within thin structures. However, understanding their physical origin and relation to the other large-scale structures in the lowermost mantle are limited due to an incomplete mapping of ULVZs at the CMB. The SKS and SPdKS seismic waveforms is routinely used to infer ULVZ presence, but has thus far only been used in a limited epicentral distance range. As the SKS/SPdKS wavefield interacts with a ULVZ it generates additional seismic arrivals, thus increasing the complexity of the recorded wavefield. Here, we explore utilization of the multi-scale sample entropy method to search for ULVZ structures. We investigate the feasibility of this approach through analysis of synthetic seismograms computed for PREM, 1-, 2.5-, and 3-D ULVZs as well as heterogeneous structures with a strong increase in velocity in the lowermost mantle in 1- and 2.5-D. We find that the sample entropy technique may be useful across a wide range of epicentral distances from 100° to 130°. Such an analysis, when applied to real waveforms, could provide coverage of roughly 85% by surface area of the CMB.
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4
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Chen J. Tracking the origin of ultralow velocity zones at the base of Earth's mantle. Natl Sci Rev 2021; 8:nwaa308. [PMID: 34691621 PMCID: PMC8288332 DOI: 10.1093/nsr/nwaa308] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Revised: 12/20/2020] [Accepted: 12/29/2020] [Indexed: 11/27/2022] Open
Affiliation(s)
- Jiuhua Chen
- Center for the Study of Matters at Extreme Conditions, Department of Mechanical and Materials Engineering, Florida International University, USA
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5
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Affiliation(s)
- Meghan S. Miller
- Research School of Earth Sciences, Australian National University, Canberra, Australia
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6
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New Candidate Ultralow-Velocity Zone Locations from Highly Anomalous SPdKS Waveforms. MINERALS 2020. [DOI: 10.3390/min10030211] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Ultralow-velocity zones (ULVZs) at the core–mantle boundary (CMB) represent some of the most preternatural features in Earth’s mantle. These zones most likely contain partial melt, extremely high iron content ferropericlase, or combinations of both. We analyzed a new collection of 58,155 carefully processed and quality-controlled broadband recordings of the seismic phase SPdKS in the epicentral distance range from 106° to 115°. These data sample 56.9% of the CMB by surface area. From these recordings we searched for the most anomalous seismic waveforms that are indicative of ULVZ presence. We used a Bayesian approach to identify the regions of the CMB that have the highest probability of containing ULVZs, thereby identifying sixteen regions of interest. Of these regions, we corroborate well-known ULVZ existence beneath the South China Sea, southwest Pacific, the Samoa hotspot, the southwestern US/northern Mexico, and Iceland. We find good evidence for new ULVZs beneath North Africa, East Asia, and north of Papua New Guinea. We provide further evidence for ULVZs in regions where some evidence has been hinted at before beneath the Philippine Sea, the Pacific Northwest, and the Amazon Basin. Additional evidence is shown for potential ULVZs at the base of the Caroline, San Felix and Galapagos hotspots.
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7
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Yuan K, Romanowicz B. Seismic evidence for partial melting at the root of major hot spot plumes. Science 2018; 357:393-397. [PMID: 28751607 DOI: 10.1126/science.aan0760] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 06/19/2017] [Indexed: 11/02/2022]
Abstract
Ultralow-velocity zones are localized regions of extreme material properties detected seismologically at the base of Earth's mantle. Their nature and role in mantle dynamics are poorly understood. We used shear waves diffracted at the core-mantle boundary to illuminate the root of the Iceland plume from different directions. Through waveform modeling, we detected a large ultralow-velocity zone and constrained its shape to be axisymmetric to a very good first order. We thus attribute it to partial melting of a locally thickened, denser- and hotter-than-average layer, reflecting dynamics and elevated temperatures within the plume root. Such structures are few and far apart, and they may be characteristic of the roots of some of the broad mantle plumes tomographically imaged within the large low-shear-velocity provinces in the lower mantle.
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Affiliation(s)
- Kaiqing Yuan
- Berkeley Seismological Laboratory, Berkeley, CA 94720, USA
| | - Barbara Romanowicz
- Berkeley Seismological Laboratory, Berkeley, CA 94720, USA. .,Collège de France, Paris, France.,Institut de Physique du Globe, Paris, France
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8
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Li M, McNamara AK, Garnero EJ, Yu S. Compositionally-distinct ultra-low velocity zones on Earth's core-mantle boundary. Nat Commun 2017; 8:177. [PMID: 28769033 PMCID: PMC5540928 DOI: 10.1038/s41467-017-00219-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Accepted: 06/09/2017] [Indexed: 11/09/2022] Open
Abstract
The Earth’s lowermost mantle large low velocity provinces are accompanied by small-scale ultralow velocity zones in localized regions on the core-mantle boundary. Large low velocity provinces are hypothesized to be caused by large-scale compositional heterogeneity (i.e., thermochemical piles). The origin of ultralow velocity zones, however, remains elusive. Here we perform three-dimensional geodynamical calculations to show that the current locations and shapes of ultralow velocity zones are related to their cause. We find that the hottest lowermost mantle regions are commonly located well within the interiors of thermochemical piles. In contrast, accumulations of ultradense compositionally distinct material occur as discontinuous patches along the margins of thermochemical piles and have asymmetrical cross-sectional shape. Furthermore, the lateral morphology of these patches provides insight into mantle flow directions and long-term stability. The global distribution and large variations of morphology of ultralow velocity zones validate a compositionally distinct origin for most ultralow velocity zones. Ultralow velocity zones are detected on the core-mantle boundary, but their origin is enigmatic. Here, the authors find that the global distribution and large variations of morphology of ultralow velocity zones are consistent with most having a compositionally-distinct origin.
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Affiliation(s)
- Mingming Li
- Arizona State University, School of Earth and Space Exploration, PO Box 871404, Tempe, AZ, 85287-1404, USA.
| | - Allen K McNamara
- Michigan State University, Department of Earth and Environmental Sciences, Natural Science Building, East Lansing, MI, 48824, USA
| | - Edward J Garnero
- Arizona State University, School of Earth and Space Exploration, PO Box 871404, Tempe, AZ, 85287-1404, USA
| | - Shule Yu
- Arizona State University, School of Earth and Space Exploration, PO Box 871404, Tempe, AZ, 85287-1404, USA
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9
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Thomas CW, Liu Q, Agee CB, Asimow PD, Lange RA. Multi-technique equation of state for Fe2SiO4melt and the density of Fe-bearing silicate melts from 0 to 161 GPa. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/2012jb009403] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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10
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Rost S, Garnero EJ, Thorne MS, Hutko AR. On the absence of an ultralow-velocity zone in the North Pacific. ACTA ACUST UNITED AC 2010. [DOI: 10.1029/2009jb006420] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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11
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Duffy TS. Some recent advances in understanding the mineralogy of Earth's deep mantle. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2008; 366:4273-4293. [PMID: 18826921 DOI: 10.1098/rsta.2008.0172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Understanding planetary structure and evolution requires a detailed knowledge of the properties of geological materials under the conditions of deep planetary interiors. Experiments under the extreme pressure-temperature conditions of the deep mantle are challenging, and many fundamental properties remain poorly constrained or are inferred only through uncertain extrapolations from lower pressure-temperature states. Nevertheless, the last several years have witnessed a number of new developments in this area, and a broad overview of the current understanding of the Earth's lower mantle is presented here. Some recent experimental and theoretical advances related to the lowermost mantle are highlighted. Measurements of the equation of state and deformation behaviour of (Mg,Fe)SiO3 in the CaIrO3-type (post-perovskite) structure yield insights into the nature of the core-mantle boundary region. Theoretical studies of the behaviour of MgSiO3 liquids under high pressure-temperature conditions provide constraints on melt volumes, diffusivities and viscosities that are relevant to understanding both the early Earth (e.g. deep magma oceans) and seismic structure observed in the present Earth (e.g. ultra-low-velocity zones).
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Affiliation(s)
- Thomas S Duffy
- Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
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12
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Mao WL, Mao HK, Sturhahn W, Zhao J, Prakapenka VB, Meng Y, Shu J, Fei Y, Hemley RJ. Iron-Rich Post-Perovskite and the Origin of Ultralow-Velocity Zones. Science 2006; 312:564-5. [PMID: 16645091 DOI: 10.1126/science.1123442] [Citation(s) in RCA: 179] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The boundary layer between the crystalline silicate lower mantle and the liquid iron core contains regions with ultralow seismic velocities. Such low compressional and shear wave velocities and high Poisson's ratio are also observed experimentally in post-perovskite silicate phase containing up to 40 mol% FeSiO3 endmember. The iron-rich post-perovskite silicate is stable at the pressure-temperature and chemical environment of the core-mantle boundary and can be formed by core-mantle reaction. Mantle dynamics may lead to further accumulation of this material into the ultralow-velocity patches that are observable by seismology.
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Affiliation(s)
- Wendy L Mao
- Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
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13
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Helmberger D, Lay T, Ni S, Gurnis M. Deep mantle structure and the postperovskite phase transition. Proc Natl Acad Sci U S A 2005; 102:17257-63. [PMID: 16217029 PMCID: PMC1297654 DOI: 10.1073/pnas.0502504102] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2005] [Indexed: 11/18/2022] Open
Abstract
Seismologists have known for many years that the lowermost mantle of the Earth is complex. Models based on observed seismic phases sampling this region include relatively sharp horizontal discontinuities with strong zones of anisotropy, nearly vertical contrasts in structure, and small pockets of ultralow velocity zones (ULVZs). This diversity of structures is beginning to be understood in terms of geodynamics and mineral physics, with dense partial melts causing the ULVZs and a postperovskite solid-solid phase transition producing regional layering, with the possibility of large-scale variations in chemistry. This strong heterogeneity has significant implications on heat transport out of core, the evolution of the magnetic field, and magnetic field polarity reversals.
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Affiliation(s)
- D Helmberger
- Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA.
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14
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Rost S, Garnero EJ, Williams Q, Manga M. Seismological constraints on a possible plume root at the core-mantle boundary. Nature 2005; 435:666-9. [PMID: 15931220 DOI: 10.1038/nature03620] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Accepted: 04/06/2005] [Indexed: 11/09/2022]
Abstract
Recent seismological discoveries have indicated that the Earth's core-mantle boundary is far more complex than a simple boundary between the molten outer core and the silicate mantle. Instead, its structural complexities probably rival those of the Earth's crust. Some regions of the lowermost mantle have been observed to have seismic wave speed reductions of at least 10 per cent, which appear not to be global in extent. Here we present robust evidence for an 8.5-km-thick and approximately 50-km-wide pocket of dense, partially molten material at the core-mantle boundary east of Australia. Array analyses of an anomalous precursor to the reflected seismic wave ScP reveal compressional and shear-wave velocity reductions of 8 and 25 per cent, respectively, and a 10 per cent increase in density of the partially molten aggregate. Seismological data are incompatible with a basal layer composed of pure melt, and thus require a mechanism to prevent downward percolation of dense melt within the layer. This may be possible by trapping of melt by cumulus crystal growth following melt drainage from an anomalously hot overlying region of the lowermost mantle. This magmatic evolution and the resulting cumulate structure seem to be associated with overlying thermal instabilities, and thus may mark a root zone of an upwelling plume.
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Affiliation(s)
- Sebastian Rost
- Department of Geological Sciences, Arizona State University, Box 871404, Tempe , Arizona 85287-1404, USA.
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15
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Mao WL, Shen G, Prakapenka VB, Meng Y, Campbell AJ, Heinz DL, Shu J, Hemley RJ, Mao HK. Ferromagnesian postperovskite silicates in the D'' layer of the Earth. Proc Natl Acad Sci U S A 2004; 101:15867-9. [PMID: 15520393 PMCID: PMC528774 DOI: 10.1073/pnas.0407135101] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Natural olivine with 12 mol % Fe(2)SiO(4) and synthetic orthopyroxenes with 20% and 40% FeSiO(3) were studied beyond the pressure-temperature conditions of the core-mantle boundary. All samples were found to convert entirely or partially into the CaIrO(3) postperovskite structure, which was recently reported for pure MgSiO(3). The incorporation of Fe greatly reduces the pressure needed for the transition and establishes the new phase as the major component of the D'' layer. With the liquid core as an unlimited reservoir of iron, core-mantle reactions could further enrich the iron content in this phase and explain the intriguing seismic signatures observed in the D'' layer.
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Affiliation(s)
- Wendy L Mao
- Department of the Geophysical Sciences, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637.
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16
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Humayun M, Qin L, Norman MD. Geochemical Evidence for Excess Iron in the Mantle Beneath Hawaii. Science 2004; 306:91-4. [PMID: 15459385 DOI: 10.1126/science.1101050] [Citation(s) in RCA: 181] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Chemical interaction of Earth's mantle with the liquid outer core should influence the mantle's iron content. Osmium isotope ratios in Hawaiian lavas indicate a mass flux of </=1% core to the mantle, which is the immediate source of these lavas. We present precise measurements of the Fe/Mn ratio for Hawaiian lavas, revealing an increase of 1 to 2% in the mole fraction of iron in the mantle beneath Hawaii. This corresponds to a density anomaly of about 0.5%, about the same magnitude observed in seismic tomography models of the Pacific superswell region. These data also rule out a role for Mn-rich sediments as the source of the Hawaiian Os isotope signal.
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Affiliation(s)
- Munir Humayun
- Department of the Geophysical Sciences, 5734 South Ellis Avenue, Chicago, IL 60637, USA.
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17
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Ross AR, Thybo H, Solidilov LN. Reflection seismic profiles of the core-mantle boundary. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002515] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- A. R. Ross
- Geological Institute, University of Copenhagen; Copenhagen Denmark
| | - H. Thybo
- Geological Institute, University of Copenhagen; Copenhagen Denmark
| | - L. N. Solidilov
- Center for Regional Geophysical and Geoecological Studies; Moscow Russia
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18
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Thorne MS, Garnero EJ. Inferences on ultralow-velocity zone structure from a global analysis ofSPdKSwaves. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2004jb003010] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Michael S. Thorne
- Department of Geological Sciences; Arizona State University; Tempe Arizona USA
| | - Edward J. Garnero
- Department of Geological Sciences; Arizona State University; Tempe Arizona USA
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19
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Persh SE, Vidale JE. Reflection properties of the core-mantle boundary from global stacks ofPcPandScP. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002768] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Steven E. Persh
- Department of Earth and Space Sciences; University of California; Los Angeles California USA
| | - John E. Vidale
- Department of Earth and Space Sciences; University of California; Los Angeles California USA
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20
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Rost S, Revenaugh J. Small-scale ultralow-velocity zone structure imaged byScP. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2001jb001627] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Sebastian Rost
- Department of Earth Sciences, Institute of Geophysics and Planetary Physics, Center for the Study of Imaging and Dynamics of the Earth; University of California; Santa Cruz USA
| | - Justin Revenaugh
- Department of Earth Sciences, Institute of Geophysics and Planetary Physics, Center for the Study of Imaging and Dynamics of the Earth; University of California; Santa Cruz USA
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21
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Rondenay S. Constraints on localized core-mantle boundary structure from multichannel, broadbandSKScoda analysis. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2003jb002518] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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Abstract
Data from earthquakes in the Tonga-Fiji region recorded at a seismic array in northern Australia show evidence for rigid zones at the top of the outer core. The ScP waveforms can be modeled by thin (0.12 to 0.18 kilometer) zones of molten iron mixed with solid material with a small, but positive, S-wave velocity (0.6 to 0.8 kilometer per second) that enables the propagation of S-waves in the outermost core. The zones may be topographic highs of the core-mantle boundary filled by light core sediments and might be important for variation of Earth's nutation and for convection of the outer core.
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Affiliation(s)
- S Rost
- Department of Earth Sciences, University of California, Santa Cruz, CA 95064, USA.
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23
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Thiemens MH, Savarino J, Farquhar J, Bao H. Mass-independent isotopic compositions in terrestrial and extraterrestrial solids and their applications. Acc Chem Res 2001; 34:645-52. [PMID: 11513572 DOI: 10.1021/ar960224f] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
In 1983, Thiemens and Heidenreich reported the first chemically produced mass-independent isotope effect. This work has been shown to have a wide range of applications, including atmospheric chemistry, solar system evolution, and chemical physics. This work has recently been reviewed (Weston, R. E. Chem. Rev. 1999, 99, 2115-2136; Thiemens, M. H. Science 1999, 283, 341-345). In this Account, observations of mass-independent isotopic compositions in terrestrial and Martian solids are reviewed. A wide range of applications, including formation and transport of aerosols in the present atmosphere, chemistry of ancient atmospheres and oceans, history and coupling of the atmosphere-surface in the Antarctic dry valleys, origin and evolution of oxygen in the Earth's earliest environment, and the chemistry of the atmosphere and surface of Mars, are discussed.
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Affiliation(s)
- M H Thiemens
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, California 92093-0356, USA
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24
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Kuo BY, Garnero EJ, Lay T. Tomographic inversion ofS-SKStimes for shear velocity heterogeneity in D″: Degree 12 and hybrid models. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900334] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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25
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Reasoner C, Revenaugh J. ScP constraints on ultralow-velocity zone density and gradient thickness beneath the Pacific. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900331] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Abstract
In the atmosphere, many chemical processes are controlled by open-shell radical species. While these species are present in relatively small number densities, they initiate many of the cycles that control the chemistry of the atmosphere. The purpose of this Account is to examine recent studies of radical-water complexes that are composed of atmospherically important species. We hope this Account will provide a report on the status of this topical field, while encouraging new research directions.
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Affiliation(s)
- S Aloisio
- Departments of Chemistry and Earth and Atmospheric Sciences, Purdue University, West Lafayette, Indiana 47907-1393, USA
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Helmberger D, Ni S, Wen L, Ritsema J. Seismic evidence for ultralow-velocity zones beneath Africa and eastern Atlantic. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900143] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Castle JC, Creager KC, Winchester JP, van der Hilst RD. Shear wave speeds at the base of the mantle. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900193] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
At the boundary between Earth's mantle and its core, physical properties such as density change dramatically. In their Perspective, Garnero and Jeanloz discuss the competing models of this boundary's structure. Distinguishing between the models will require more high-quality seismic data.
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Hedlin MAH, Shearer PM. An analysis of large-scale variations in small-scale mantle heterogeneity using Global Seismographic Network recordings of precursors toPKP. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900019] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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31
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Montague NL, Kellogg LH. Numerical models of a dense layer at the base of the mantle and implications for the geodynamics of D″. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/1999jb900450] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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32
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Kamber BS, Collerson KD. Origin of ocean island basalts: A new model based on lead and helium isotope systematics. ACTA ACUST UNITED AC 1999. [DOI: 10.1029/1999jb000258] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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33
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Abstract
Diamond is a remarkable mineral and has been long recognized for its unusual physical and chemical properties: robust and widespread in industry, yet regally adorned. This diversity is even greater than formally appreciated because diamond is recognized as an extraordinary recorder of astrophysical and geodynamic events that extend from the far reaches of space to Earth's deep interior. Many diamonds are natural antiques that formed in presolar supernovae by carbon vapor deposition, in asteroidal impacts and meteorite craters by shock metamorphism, and in Earth's mantle 1 to 2 billion years after planetary accretion from fluids and melts. The carbon in diamond is primordial, but there are unexplained isotopic fractionations and uncertainties in heterogeneity.
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Affiliation(s)
- SE Haggerty
- Department of Geosciences, University of Massachusetts, Amherst, MA 01003, USA
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34
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Thomas C, Weber M, Wicks CW, Scherbaum F. Small scatterers in the lower mantle observed at German broadband arrays. ACTA ACUST UNITED AC 1999. [DOI: 10.1029/1999jb900128] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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