Mineral physics of iron and of the core

Anderson, Orson L.

doi:10.1029/95rg00877

Cited by 27 publications

(12 citation statements)

References 84 publications

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“…Consequently, Prandtl numbers are likely to exceed 10 4 . Similarly, according to parameter values reported by Anderson [1995], the Prandtl number at the inner±outer core boundary can be estimated to be $20 and higher. The viscosity values given above are derived when the materials are in a totally molten state.…”

Section: Geochemistry Geophysicsmentioning

confidence: 85%

“…As a result, solidification beneath the core–mantle boundary and above the inner–outer core boundary must operate in the positive thermal Rayleigh number (i.e., R θ > 0) regime. Current thinking suggests [e.g., Anderson , 1995] that solidification within the core represents the removal of the heavy elements (i.e., the iron and nickel components) from the molten liquid mixture. Therefore the residual fluid will be less dense.…”

Section: Resultsmentioning

confidence: 99%

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Onset of thermal chemical convection with crystallization and its geological implications

Hsui

Riahi

2001

Geochem Geophys Geosyst

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[1] Abstract: Buoyancy forces derived from either thermal or compositional origins, or both, are the main driving mechanisms for dynamic instabilities within natural fluid systems. Crystallization can contribute to the compositional buoyancy due to density differences between the original bulk fluid and the residual fluid of crystallization. Depending on the density contrast, the compositionally induced buoyancy force may enhance or decrease the thermal buoyancy force established by the prevailing temperature gradient of the environment. The purpose of this paper is to examine the complex interactions between the compositional and the thermal buoyancy forces within a thermal chemical system incorporating the effects of crystallization. Like a thermal chemical system without crystallization (also known as an ordinary double-diffusive system), our results identify a dynamic and an oscillatory instability boundary in a traditional stability diagram. A dynamic instability boundary separates the stability diagram into two regimes. On one side of the boundary, fluid dynamic perturbations will grow indefinitely, leading to rigorous convection eventually. On the other side, perturbations decay in time, and the system will ultimately return to a static condition. In the absence of crystallization the oscillatory instability boundary defines a regime where perturbations lead to oscillatory motions. In the presence of crystallization, however, other investigators have observed the formation of convective layering. Despite these similarities, our results show significant differences in flow characteristic when crystallization is present. When crystallization is taken into consideration, the slope of a dynamic instability boundary is no longer governed by the diffusion coefficient ratio between heat and composition alone. The release of latent heat and the location of crystallization also play some roles. In addition, convective layering (i.e., the oscillatory instability regime) is no longer confined within a domain where fluid composition is stably stratified. It can extend into the compositionally unstable domain as well. Applications of our results to the solidification of magmatic bodies, the formation of columnar joints, and the cooling of the outer liquid core are examined. The existence of oscillatory instability within the compositionally unstable domain is significant because it suggests that the possible existence of convective layering within a cooling tholeiitic magma body cannot be ruled out, in contrast to a conclusion derived from double-diffusion studies in the absence of crystallization. Our analysis also suggests a possible criterion to test if columnar jointing has a double-diffusive origin. If columnar joints were thermal cracks formed along a preexisting double-diffusive fingering pattern as speculated, they should occur only in calc ± alkaline basaltic lava, and they are not expected to appear in tholeiitic basalts. Iron ± nickel precipitation above the inner ±outer core boundary operates in a composit...

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Section: Geochemistry Geophysicsmentioning

confidence: 85%

Section: Resultsmentioning

confidence: 99%

Onset of thermal chemical convection with crystallization and its geological implications

Hsui

Riahi

2001

Geochem Geophys Geosyst

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“…Birch (1964) measured the density and sound speed of different elements with the experiments and manifested that the iron was possibly the only one of main elements whose density under the pressure of the inner core was in agreement with the density of the inner core. Some mineralogy investigations displayed that the hexagonal close packed (hcp) iron (ε-phase) was the most likely phase on the conditions of the inner core, and the directional distributions of ε-phase iron caused the anisotropy of the inner core (Anderson, 1995;Stixrude and Cohen, 1995). Creager (1992) and Shearer (1994) discovered that in the inner core P wave velocity in the north-south direction was faster than that in the equatorial direction by about 3%.…”

Section: Discussion On the Structure Of The Earth's Inner Corementioning

confidence: 99%

Detection and interpretation of the Earth’s free oscillations excited by the great Sumatra-Andaman earthquake with GGP station data

2011

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The mode serials of the Earth's free oscillation provide some important information on the Earth's deep structure and superconducting gravimeters (SG) can investigate the phenomena of the Earth's free oscillations with high accuracy. The great Sumatra-Andaman earthquake fully excited the Earth's free oscillations and these signals were perfectly recorded by five superconducting gravimeters in the globe. After the pre-treatment and spectral analysis on the SG observation data, we obtained the experimented mode serials of the Earth's free oscillations consisting of 147 modes with GGP station data. These observed modes were themselves some new important data for the study of the Earth's deep structure. On the basis of the discussions on some checked inner-core-sensitive modes, we distinguished three layers from the inner core, and the boundary of the upper layer was compatible with the formerly known transition zone in the inner core based on seismic body waves and supported that there were the hemispherical variation and very lower shear velocity zone in the lower inner core.

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“… a References: 1, Zharkov [1986]; 2, Yoder et al [2003]; 3, Longhi et al [1992]; 4, Anderson [1995]; 5, Chopelas [1996]; 6, Hofmeister [1999]; 7, Karato and Wu [1993]. …”

Section: Implications For Marsmentioning

confidence: 99%

Early transient superplumes and the origin of the Martian crustal dichotomy

Ke¹,

Solomatov²

2006

J. Geophys. Res.

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[1] The large temperature difference between the core and mantle of Mars at the end of planetary accretion creates a hot, internally convecting thermal boundary layer at the base of the mantle, whose viscosity is several orders of magnitude lower than the viscosity of the mantle above it. Theoretical analysis and numerical simulations of the instability of this thermal boundary layer show that it is likely that only one large plume forms. This superplume may play a role in the formation of crustal dichotomy and generation of the magnetic field in the early history of Mars.

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Mineral physics of iron and of the core

Cited by 27 publications

References 84 publications

Onset of thermal chemical convection with crystallization and its geological implications

Onset of thermal chemical convection with crystallization and its geological implications

Detection and interpretation of the Earth’s free oscillations excited by the great Sumatra-Andaman earthquake with GGP station data

Early transient superplumes and the origin of the Martian crustal dichotomy

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