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Yuan Q, Li M, Desch SJ, Ko B, Deng H, Garnero EJ, Gabriel TSJ, Kegerreis JA, Miyazaki Y, Eke V, Asimow PD. Moon-forming impactor as a source of Earth's basal mantle anomalies. Nature 2023; 623:95-99. [PMID: 37914947 DOI: 10.1038/s41586-023-06589-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2022] [Accepted: 08/30/2023] [Indexed: 11/03/2023]
Abstract
Seismic images of Earth's interior have revealed two continent-sized anomalies with low seismic velocities, known as the large low-velocity provinces (LLVPs), in the lowermost mantle1. The LLVPs are often interpreted as intrinsically dense heterogeneities that are compositionally distinct from the surrounding mantle2. Here we show that LLVPs may represent buried relics of Theia mantle material (TMM) that was preserved in proto-Earth's mantle after the Moon-forming giant impact3. Our canonical giant-impact simulations show that a fraction of Theia's mantle could have been delivered to proto-Earth's solid lower mantle. We find that TMM is intrinsically 2.0-3.5% denser than proto-Earth's mantle based on models of Theia's mantle and the observed higher FeO content of the Moon. Our mantle convection models show that dense TMM blobs with a size of tens of kilometres after the impact can later sink and accumulate into LLVP-like thermochemical piles atop Earth's core and survive to the present day. The LLVPs may, thus, be a natural consequence of the Moon-forming giant impact. Because giant impacts are common at the end stages of planet accretion, similar mantle heterogeneities caused by impacts may also exist in the interiors of other planetary bodies.
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Affiliation(s)
- Qian Yuan
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA.
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
| | - Mingming Li
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | - Steven J Desch
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | - Byeongkwan Ko
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
- Department of Earth and Environmental Sciences, Michigan State University, East Lansing, MI, USA
| | - Hongping Deng
- Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, China
| | - Edward J Garnero
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | | | | | - Yoshinori Miyazaki
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
| | - Vincent Eke
- Institute for Computational Cosmology, Department of Physics, Durham University, Durham, UK
| | - Paul D Asimow
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
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2
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Effects of iron on the lattice thermal conductivity of Earth's deep mantle and implications for mantle dynamics. Proc Natl Acad Sci U S A 2018; 115:4099-4104. [PMID: 29610319 DOI: 10.1073/pnas.1718557115] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Iron may critically influence the physical properties and thermochemical structures of Earth's lower mantle. Its effects on thermal conductivity, with possible consequences on heat transfer and mantle dynamics, however, remain largely unknown. We measured the lattice thermal conductivity of lower-mantle ferropericlase to 120 GPa using the ultrafast optical pump-probe technique in a diamond anvil cell. The thermal conductivity of ferropericlase with 56% iron significantly drops by a factor of 1.8 across the spin transition around 53 GPa, while that with 8-10% iron increases monotonically with pressure, causing an enhanced iron substitution effect in the low-spin state. Combined with bridgmanite data, modeling of our results provides a self-consistent radial profile of lower-mantle thermal conductivity, which is dominated by pressure, temperature, and iron effects, and shows a twofold increase from top to bottom of the lower mantle. Such increase in thermal conductivity may delay the cooling of the core, while its decrease with iron content may enhance the dynamics of large low shear-wave velocity provinces. Our findings further show that, if hot and strongly enriched in iron, the seismic ultralow velocity zones have exceptionally low conductivity, thus delaying their cooling.
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3
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Tidal tomography constrains Earth's deep-mantle buoyancy. Nature 2018; 551:321-326. [PMID: 29144451 DOI: 10.1038/nature24452] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2017] [Accepted: 09/22/2017] [Indexed: 11/09/2022]
Abstract
Earth's body tide-also known as the solid Earth tide, the displacement of the solid Earth's surface caused by gravitational forces from the Moon and the Sun-is sensitive to the density of the two Large Low Shear Velocity Provinces (LLSVPs) beneath Africa and the Pacific. These massive regions extend approximately 1,000 kilometres upward from the base of the mantle and their buoyancy remains actively debated within the geophysical community. Here we use tidal tomography to constrain Earth's deep-mantle buoyancy derived from Global Positioning System (GPS)-based measurements of semi-diurnal body tide deformation. Using a probabilistic approach, we show that across the bottom two-thirds of the two LLSVPs the mean density is about 0.5 per cent higher than the average mantle density across this depth range (that is, its mean buoyancy is minus 0.5 per cent), although this anomaly may be concentrated towards the very base of the mantle. We conclude that the buoyancy of these structures is dominated by the enrichment of high-density chemical components, probably related to subducted oceanic plates or primordial material associated with Earth's formation. Because the dynamics of the mantle is driven by density variations, our result has important dynamical implications for the stability of the LLSVPs and the long-term evolution of the Earth system.
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4
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Wang H, Agrusta R, van Hunen J. Advantages of a conservative velocity interpolation (CVI) scheme for particle-in-cell methods with application in geodynamic modeling. GEOCHEMISTRY, GEOPHYSICS, GEOSYSTEMS : G(3) 2015; 16:2015-2023. [PMID: 27840594 PMCID: PMC5089062 DOI: 10.1002/2015gc005824] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Accepted: 05/15/2015] [Indexed: 06/06/2023]
Abstract
The particle-in-cell method is generally considered a flexible and robust method to model the geodynamic problems with chemical heterogeneity. However, velocity interpolation from grid points to particle locations is often performed without considering the divergence of the velocity field, which can lead to significant particle dispersion or clustering if those particles move through regions of strong velocity gradients. This may ultimately result in cells void of particles, which, if left untreated, may, in turn, lead to numerical inaccuracies. Here we apply a two-dimensional conservative velocity interpolation (CVI) scheme to steady state and time-dependent flow fields with strong velocity gradients (e.g., due to large local viscosity variation) and derive and apply the three-dimensional equivalent. We show that the introduction of CVI significantly reduces the dispersion and clustering of particles in both steady state and time-dependent flow problems and maintains a locally steady number of particles, without the need for ad hoc remedies such as very high initial particle densities or reseeding during the calculation. We illustrate that this method provides a significant improvement to particle distributions in common geodynamic modeling problems such as subduction zones or lithosphere-asthenosphere boundary dynamics.
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Affiliation(s)
- Hongliang Wang
- Department of Earth Sciences Durham University Durham UK
| | - Roberto Agrusta
- Department of Earth Sciences Durham University Durham UK; Department of Earth Science and Engineering Imperial College London London UK
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5
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Solomatov VS, Reese CC. Grain size variations in the Earth's mantle and the evolution of primordial chemical heterogeneities. ACTA ACUST UNITED AC 2008. [DOI: 10.1029/2007jb005319] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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6
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Tan E, Gurnis M. Compressible thermochemical convection and application to lower mantle structures. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006jb004505] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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7
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Ogawa M. Superplumes, plates, and mantle magmatism in two-dimensional numerical models. ACTA ACUST UNITED AC 2007. [DOI: 10.1029/2006jb004533] [Citation(s) in RCA: 24] [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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8
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Zhong S. Constraints on thermochemical convection of the mantle from plume heat flux, plume excess temperature, and upper mantle temperature. ACTA ACUST UNITED AC 2006. [DOI: 10.1029/2005jb003972] [Citation(s) in RCA: 159] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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9
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Wookey J, Stackhouse S, Kendall JM, Brodholt J, Price GD. Efficacy of the post-perovskite phase as an explanation for lowermost-mantle seismic properties. Nature 2005; 438:1004-7. [PMID: 16355222 DOI: 10.1038/nature04345] [Citation(s) in RCA: 176] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2005] [Accepted: 10/18/2005] [Indexed: 11/09/2022]
Abstract
Constraining the chemical, rheological and electromagnetic properties of the lowermost mantle (D'') is important to understand the formation and dynamics of the Earth's mantle and core. To explain the origin of the variety of characteristics of this layer observed with seismology, a number of theories have been proposed, including core-mantle interaction, the presence of remnants of subducted material and that D'' is the site of a mineral phase transformation. This final possibility has been rejuvenated by recent evidence for a phase change in MgSiO3 perovskite (thought to be the most prevalent phase in the lower mantle) at near core-mantle boundary temperature and pressure conditions. Here we explore the efficacy of this 'post-perovskite' phase to explain the seismic properties of the lowermost mantle through coupled ab initio and seismic modelling of perovskite and post-perovskite polymorphs of MgSiO3, performed at lowermost-mantle temperatures and pressures. We show that a post-perovskite model can explain the topography and location of the D'' discontinuity, apparent differences in compressional- and shear-wave models and the observation of a deeper, weaker discontinuity. Furthermore, our calculations show that the regional variations in lower-mantle shear-wave anisotropy are consistent with the proposed phase change in MgSiO3 perovskite.
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Affiliation(s)
- James Wookey
- School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
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10
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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: 2.2] [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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11
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McNamara AK, Zhong S. Thermochemical structures beneath Africa and the Pacific Ocean. Nature 2005; 437:1136-9. [PMID: 16237440 DOI: 10.1038/nature04066] [Citation(s) in RCA: 350] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2004] [Accepted: 07/21/2005] [Indexed: 11/08/2022]
Abstract
Large low-velocity seismic anomalies have been detected in the Earth's lower mantle beneath Africa and the Pacific Ocean that are not easily explained by temperature variations alone. The African anomaly has been interpreted to be a northwest-southeast-trending structure with a sharp-edged linear, ridge-like morphology. The Pacific anomaly, on the other hand, appears to be more rounded in shape. Mantle models with heterogeneous composition have related these structures to dense thermochemical piles or superplumes. It has not been shown, however, that such models can lead to thermochemical structures that satisfy the geometrical constraints, as inferred from seismological observations. Here we present numerical models of thermochemical convection in a three-dimensional spherical geometry using plate velocities inferred for the past 119 million years. We show that Earth's subduction history can lead to thermochemical structures similar in shape to the observed large, lower-mantle velocity anomalies. We find that subduction history tends to focus dense material into a ridge-like pile beneath Africa and a relatively more-rounded pile under the Pacific Ocean, consistent with seismic observations.
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Affiliation(s)
- Allen K McNamara
- Department of Physics, University of Colorado, Boulder, Colorado 80309-0390, USA.
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12
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Xie S, Tackley PJ. Evolution of U-Pb and Sm-Nd systems in numerical models of mantle convection and plate tectonics. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2004jb003176] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Shunxing Xie
- Department of Earth and Space Sciences; University of California; Los Angeles California USA
| | - Paul J. Tackley
- Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics; University of California; Los Angeles California USA
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13
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McNamara AK, Zhong S. Thermochemical structures within a spherical mantle: Superplumes or piles? ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002847] [Citation(s) in RCA: 185] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
| | - Shijie Zhong
- Department of Physics; University of Colorado; Boulder Colorado USA
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14
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Saltzer RL, Stutzmann E, van der Hilst RD. Poisson's ratio in the lower mantle beneath Alaska: Evidence for compositional heterogeneity. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003jb002712] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Rebecca L. Saltzer
- Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA
| | | | - Robert D. van der Hilst
- Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA
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15
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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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16
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17
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Castle JC, van der Hilst RD. Searching for seismic scattering off mantle interfaces between 800 km and 2000 km depth. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2001jb000286] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- John C. Castle
- Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA
| | - Rob D. van der Hilst
- Department of Earth, Atmospheric and Planetary Sciences; Massachusetts Institute of Technology; Cambridge Massachusetts USA
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18
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Johnson CL. A conceptual model for the relationship between coronae and large-scale mantle dynamics on Venus. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2002je001962] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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19
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Forte AM, Mitrovica JX, Espesset A. Geodynamic and seismic constraints on the thermochemical structure and dynamics of convection in the deep mantle. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2002; 360:2521-2543. [PMID: 12460479 DOI: 10.1098/rsta.2002.1079] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
We revisit a recent study by Forte & Mitrovica in which global geophysical observables associated with mantle convection were inverted and the existence of a strong increase in viscosity near a depth of 2000 km was inferred. Employing mineral-physics data and theory we also showed that, although there are chemical anomalies in the lowermost mantle, they are unable to inhibit the dominant thermal buoyancy of the deep-mantle mega-plumes below Africa and the Pacific Ocean. New Monte Carlo simulations are employed to explore the impact of uncertainties in current mineral-physics constraints on inferences of deep-mantle thermochemical structure. To explore the impact of the high-viscosity peak at a depth of 2000 km on the evolution of lower-mantle structure, we carried out time-dependent convection simulations. The latter show that the stability and longevity of the dominant long-wavelength heterogeneity in the lowermost mantle are controlled by this viscosity peak.
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Affiliation(s)
- Alessandro M Forte
- Department of Earth Sciences, University of Western Ontario, London, Canada
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20
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Tackley PJ, Xie S. The thermochemical structure and evolution of Earth's mantle: constraints and numerical models. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2002; 360:2593-2609. [PMID: 12460482 DOI: 10.1098/rsta.2002.1082] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Geochemical observations place several constraints on geophysical processes in the mantle, including a requirement to maintain several distinct reservoirs. Geophysical constraints limit plausible physical locations of these reservoirs to a thin basal layer, isolated deep 'piles' of material under large-scale mantle upwellings, high-viscosity blobs/plums or thin strips throughout the mantle, or some combination of these. A numerical model capable of simulating the thermochemical evolution of the mantle is introduced. Preliminary simulations are more differentiated than Earth but display some of the proposed thermochemical processes, including the generation of a high-mu mantle reservoir by recycling of crust, and the generation of a high-(3)He/(4)He reservoir by recycling of residuum, although the resulting high-(3)He/(4)He material tends to aggregate near the top, where mid-ocean-ridge melting should sample it. If primitive material exists as a dense basal layer, it must be much denser than subducted crust in order to retain its primitive (e.g. high-(3)He) signature. Much progress is expected in the near future.
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Affiliation(s)
- Paul J Tackley
- Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, 595 Charles Young Drive East, 90095-1567, USA.
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21
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Affiliation(s)
- V. S. Solomatov
- Department of Physics; New Mexico State University; Las Cruces New Mexico USA
| | - L.-N. Moresi
- Australian Geodynamics Cooperative Research Centre; CSIRO Exploration and Mining; Nedlands Western Australia Australia
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22
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Forte AM, Mitrovica JX. Deep-mantle high-viscosity flow and thermochemical structure inferred from seismic and geodynamic data. Nature 2001; 410:1049-56. [PMID: 11323661 DOI: 10.1038/35074000] [Citation(s) in RCA: 287] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Surface geophysical data that are related to the process of thermal convection in the Earth's mantle provide constraints on the rheological properties and density structure of the mantle. We show that these convection-related data imply the existence of a region of very high effective viscosity near 2,000 km depth. This inference is obtained using a viscous-flow model based on recent high-resolution seismic models of three-dimensional structure in the mantle. The high-viscosity layer near 2,000 km depth results in a re-organization of flow from short to long horizontal length scales, which agrees with seismic tomographic observations of very long wavelength structures in the deep mantle. The high-viscosity region also strongly suppresses flow-induced deformation and convective mixing in the deep mantle. Here we predict compositional and thermal heterogeneity in this region, using viscous-flow calculations based on the new viscosity profile, together with independent mineral physics data. These maps are consistent with the anti-correlation of anomalies in seismic shear and bulk sound velocity in the deep mantle. The maps also show that mega-plumes in the lower mantle below the central Pacific and Africa are, despite the presence of compositional heterogeneity, buoyant and actively upwelling structures.
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Affiliation(s)
- A M Forte
- Department of Earth Sciences, University of Western Ontario, Biology & Geology Building, London, Ontario, N6A 5B7 Canada.
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23
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Cormier VF. D″ as a transition in the heterogeneity spectrum of the lowermost mantle. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/2000jb900141] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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24
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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: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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25
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The Quest for self-consistent generation of plate tectonics in mantle convection models. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/gm121p0047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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26
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Davaille A. Simultaneous generation of hotspots and superswells by convection in a heterogeneous planetary mantle. Nature 1999. [DOI: 10.1038/45461] [Citation(s) in RCA: 326] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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27
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Ishii M, Tromp J. Normal-mode and free-Air gravity constraints on lateral variations in velocity and density of Earth's mantle. Science 1999; 285:1231-6. [PMID: 10455043 DOI: 10.1126/science.285.5431.1231] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
With the use of a large collection of free-oscillation data and additional constraints imposed by the free-air gravity anomaly, lateral variations in shear velocity, compressional velocity, and density within the mantle; dynamic topography on the free surface; and topography on the 660-km discontinuity and the core-mantle boundary were determined. The velocity models are consistent with existing models based on travel-time and waveform inversions. In the lowermost mantle, near the core-mantle boundary, denser than average material is found beneath regions of upwellings centered on the Pacific Ocean and Africa that are characterized by slow shear velocities. These anomalies suggest the existence of compositional heterogeneity near the core-mantle boundary.
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Affiliation(s)
- M Ishii
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, Massachusetts 02138, USA
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