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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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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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Hallis LJ, Huss GR, Nagashima K, Taylor GJ, Halldórsson SA, Hilton DR, Mottl MJ, Meech KJ. Evidence for primordial water in Earth's deep mantle. Science 2015; 350:795-7. [PMID: 26564850 DOI: 10.1126/science.aac4834] [Citation(s) in RCA: 127] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The hydrogen-isotope [deuterium/hydrogen (D/H)] ratio of Earth can be used to constrain the origin of its water. However, the most accessible reservoir, Earth's oceans, may no longer represent the original (primordial) D/H ratio, owing to changes caused by water cycling between the surface and the interior. Thus, a reservoir completely isolated from surface processes is required to define Earth's original D/H signature. Here we present data for Baffin Island and Icelandic lavas, which suggest that the deep mantle has a low D/H ratio (δD more negative than -218 per mil). Such strongly negative values indicate the existence of a component within Earth's interior that inherited its D/H ratio directly from the protosolar nebula.
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Affiliation(s)
- Lydia J Hallis
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA.
| | - Gary R Huss
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA
| | - Kazuhide Nagashima
- Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA
| | - G Jeffrey Taylor
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Hawai'i Institute of Geophysics and Planetology, Pacific Ocean Science and Technology (POST) Building, University of Hawai'i, 1680 East-West Road, Honolulu, HI 96822, USA
| | - Sæmundur A Halldórsson
- Scripps Institution of Oceanography, University California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA
| | - David R Hilton
- Scripps Institution of Oceanography, University California San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0244, USA
| | - Michael J Mottl
- Department of Oceanography, University of Hawai'i, Marine Sciences Building 304, 1000 Pope Road, Honolulu, HI 96822, USA
| | - Karen J Meech
- NASA Astrobiology Institute, Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822-1839, USA. Institute for Astronomy, University of Hawai'i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
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Broad plumes rooted at the base of the Earth's mantle beneath major hotspots. Nature 2015; 525:95-9. [DOI: 10.1038/nature14876] [Citation(s) in RCA: 504] [Impact Index Per Article: 56.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 06/19/2015] [Indexed: 11/08/2022]
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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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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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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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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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Wen L. AnSHhybrid method and shear velocity structures in the lowermost mantle beneath the central Pacific and South Atlantic Oceans. ACTA ACUST UNITED AC 2002. [DOI: 10.1029/2001jb000499] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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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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11
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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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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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Steinberger B. Plumes in a convecting mantle: Models and observations for individual hotspots. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/1999jb900398] [Citation(s) in RCA: 290] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Dauphas N, Marty B. Heavy nitrogen in carbonatites of the kola peninsula: A possible signature of the deep mantle. Science 1999; 286:2488-90. [PMID: 10617459 DOI: 10.1126/science.286.5449.2488] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Nitrogen and argon isotopes were measured in carbonatites and associated rocks from the Kola Peninsula in Russia. The Kola mantle source, which is thought to be located in the deep mantle, is enriched in heavy nitrogen (+3 per mil relative to air) as compared to Earth's surface (atmosphere and crust, +2 per mil) and the shallow mantle (-4 per mil). Recycling of oceanic crust (+6 per mil) or metal-silicate partitioning may account for the nitrogen isotopic composition of the deep mantle.
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Affiliation(s)
- N Dauphas
- Centre de Recherches Petrographiques et Geochimiques, CNRS UPR 9046, 15 rue Notre-Dame des Pauvres, Boite Postale 20, 54501 Vandoeuvre-les-Nancy Cedex, France. Ecole Nationale Superieure de Geologie, rue du doyen Marcel Roubault, Boit
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Abstract
Seismic wave reflections from Earth's core recorded at seismic arrays in North America from events in the Caribbean Islands, Venezuela, and the Mid-Atlantic Ridge have observed slownesses more than 64 percent greater than predicted by the IASPEI91 standard Earth model. P waves turning in the lowermost mantle beneath the same region also have anomalous slowness. The slowness anomalies are not accompanied by significant travel time residuals and appear to be caused by lateral inhomogeneities in the velocity structure of the lower mantle.
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Affiliation(s)
- IM Tibuleac
- Department of Geological Sciences, Southern Methodist University, Dallas, TX 75275-0395, USA
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Karason H. Compositional heterogeneity in the bottom 1000 kilometers of Earth's mantle: toward a hybrid convection model. Science 1999; 283:1885-8. [PMID: 10082455 DOI: 10.1126/science.283.5409.1885] [Citation(s) in RCA: 315] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Tomographic imaging indicates that slabs of subducted lithosphere can sink deep into Earth's lower mantle. The view that convective flow is stratified at 660-kilometer depth and preserves a relatively pristine lower mantle is therefore not tenable. However, a range of geophysical evidence indicates that compositionally distinct, hence convectively isolated, mantle domains may exist in the bottom 1000 kilometers of the mantle. Survival of these domains, which are perhaps related to local iron enrichment and silicate-to-oxide transformations, implies that mantle convection is more complex than envisaged by conventional end-member flow models.
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