Core formation, evolution, and convection: a geophysical model

Ruff, Larry J.; Anderson, Don L.

doi:10.1016/0031-9201(80)90069-2

Cited by 48 publications

(20 citation statements)

References 96 publications

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“…A model of inhomogeneous accretion predicts a layer of refractory material at the top of the CMB, since this material is expected to be about 2% denser than normal mantle [Ruff and Anderson, 1980). However, as estimated by Ruff and Anderson, the refractories would have about 5% lower seismic velocity, so such composition is an unlikely candidate for aD" chemical layer consistent with the seismic discontinuity at its top.…”

Section: Discussionmentioning

confidence: 97%

Geodynamically consistent seismic velocity predictions at the base of the mantle

Sidorin¹,

Gurnis²

1998

The Core‐Mantle Boundary Region

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A model of thermoelastic properties for a chemically homogeneous adiabatic lower mantle is calculated. Constraints provided by this model are used in convection models to study dynamics of a chemically distinct layer at the bottom of the mantle. We find that the layer must be at least 2% denser than the overlying mantle to survive for a geologically significant period of time. Realistic decrease with depth of the thermal expansivity increases layer stability but is unable to prevent it from entrainment. Seismic velocities are computed for an assumed composition by applying the thermal and compositional perturbations obtained in convection simulations to the adiabatic values. The predicted velocity jump at the top of the chemical layer is closer to the CMB in the cold regions than in the hot. The elevation of the discontinuity above CMB in the cold regions decreases with increasing thermal expansivity and increases with increasing density contrast, while in the hot regions we find that the opposite is true. If the density contrast is small, the layer may vanish under downwellings. However, whenever the layer is present in the downwelling regions, it also exists under the upwellings. For a 4% density contrast and realistic values of expansivity, we find that the layer must be more than 400 km thick on average to be consistent with the seismically observed depth of the discontinuity. A simple chemical layer cannot be used to interpret the D" discontinuity: the required change in composition is large and must be complex, since enrichment in any single mineral probably cannot provide the required impedance contrast. A simple chemical layer cannot explain the spatial intermittance of the discontinuity.

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Section: Discussionmentioning

confidence: 97%

Geodynamically consistent seismic velocity predictions at the base of the mantle

Sidorin¹,

Gurnis²

1998

The Core‐Mantle Boundary Region

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“…The axes and sym- (13) 3.9 + 0.4 (13) Fe (a-phase) 7.092 2 0.004 (27) 167 ? 2 (28) 10.95 + 0.27 (11) 195 ? 10 (11) 4 ?…”

Section: Implications For the Core-mantle Boundarymentioning

confidence: 99%

“…That is, compositional density variations may be required to counteract the thermal buoyancy forces that reduce the temperature gradient by advection. Several mechanisms for developing chemical heterogeneities in the D layer have been proposed, including the accumulation of subducted slabs at the base of the mantle (2,10) or a phase change in the silicate components of the lower 200 km of the mantle (1 1-14).…”

mentioning

confidence: 99%

Earth's Core-Mantle Boundary: Results of Experiments at High Pressures and Temperatures

Knittle

Jeanloz

1991

Science

357

153

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Laboratory experiments document that liquid iron reacts chemically with silicates at high pressures (>/=2.4 x 10(10) Pascals) and temperatures. In particular, (Mg,Fe)SiO(3) perovskite, the most abundant mineral of Earth's lower mantle, is expected to react with liquid iron to produce metallic alloys (FeO and FeSi) and nonmetallic silicates (SiO(2) stishovite and MgSiO(3) perovskite) at the pressures of the core-mantle boundary, 14 x 10(10) Pascals. The experimental observations, in conjunction with seismological data, suggest that the lowermost 200 to 300 kilometers of Earth's mantle, the D" layer, may be an extremely heterogeneous region as a result of chemical reactions between the silicate mantle and the liquid iron alloy of Earth's core. The combined thermal-chemical-electrical boundary layer resulting from such reactions offers a plausible explanation for the complex behavior of seismic waves near the core-mantle boundary and could influence Earth's magnetic field observed at the surface.

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“…In the early Earth, the extent of heat sources available is sufficient for the entire mantle to have been molten to form a planetary magma ocean. These include short-lived radionuclides and potential energy release during core formation and large-scale impacts, such as that by which the moon is thought to have formed (Urey, 1955;Hanks and Anderson, 1969;Ruff and Anderson, 1980;Tonks and Melosh, 1993;Canup, 2004).…”

Section: Introductionmentioning

confidence: 99%

Structure, thermodynamics, and diffusion in CaAl2Si2O8 liquid from first-principles molecular dynamics

Koker

2010

Geochimica et Cosmochimica Acta

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Core formation, evolution, and convection: a geophysical model

Cited by 48 publications

References 96 publications

Geodynamically consistent seismic velocity predictions at the base of the mantle

Geodynamically consistent seismic velocity predictions at the base of the mantle

Earth's Core-Mantle Boundary: Results of Experiments at High Pressures and Temperatures

Structure, thermodynamics, and diffusion in CaAl2Si2O8 liquid from first-principles molecular dynamics

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