The Fate of Liquids Trapped During the Earth's Inner Core Growth

Lasbleis, Marine; Kervazo, Mathilde; Choblet, G.

doi:10.1029/2019gl085654

Cited by 12 publications

(8 citation statements)

References 68 publications

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“…However, disagreement of IC models based on seismic data with hcp iron studies have been attributed to further phase changes at depth or impurities deep within the IC, including the existence of multiple phases of iron (e.g., Beghein & Trampert, 2003; Mattesini et al., 2013; Tkalčić, 2010). There is also evidence from numerical modeling to suggest that a structurally different IMIC may be due to delayed nucleation during IC growth (Lasbleis et al., 2020).…”

Section: Resultsmentioning

confidence: 99%

Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm

2021

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The Earth's solid inner core (IC) remains one of the most enigmatic parts of our planet, despite numerous studies in the fields of seismology, geodynamics, mineral physics, and materials science. Making up only 1% of the Earth's total volume with a temperature of over 5,000°C, understanding the structure, current dynamics, and evolution of the IC is vital to understanding the Earth's thermal history (see Tkalčić [2017] for an in-depth discussion). In particular, this provides insights into the geodynamo, without which life would not exist as we know it today. Since its discovery, new models for the structure of the IC are being proposed with increasing complexity in terms of both seismic velocity and attenuation. Discussions on IC anisotropy arose following a study by Poupinet et al. (1983), who observed that a laterally homogeneous velocity model does not fit the global PKP differential travel time data. Later, Morelli et al. (1986) noticed that absolute PKIKP phases travel up to 3 s faster parallel to the Earth's rotational axis. Anisotropy, rather than isotropic heterogeneity was confirmed in the same year by Woodhouse et al. (1986), who used the hypothesis of IC anisotropy to explain the previously enigmatic observation of the IC sensitive normal modes (e.g., 10 S 2). The seismic body waves sensitive to the IC structure and the corresponding travel time data used predominantly in IC research are illustrated in Figure 1.

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Section: Resultsmentioning

confidence: 99%

Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm

2021

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“…Recently, the possibility of delayed crystallization of the inner core due to super‐cooling has been proposed (Huguet et al., 2018). If this is the case, a substantial amount of melt is trapped in the innermost inner core, whereas compaction of a solid matrix extract melts in the upper inner core (Lasbleis et al., 2020). These are the possible origins of the boundary with different physical properties inside the inner core.…”

Section: Discussionmentioning

confidence: 99%

Impurity Resistivity of the Earth's Inner Core

Gomi,

Hirose

2023

JGR Solid Earth

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Seismic observations suggest that the Earth's inner core has a complex structure (e.g., the isotropic layer at the top, innermost inner core, and hemispherical dichotomy). These characteristics are believed to reflect the history of dynamics and temperature profile of the inner core. One critical physical property is the inner core's thermal conductivity. The thermal conductivity of metals can be estimated from their electrical resistivity using the Wiedemann‐Franz law. Recent high‐pressure and temperature experiments revealed that the temperature dependence of electrical resistivity is small for Fe‐Si alloys. The small temperature coefficient means that it is essential to determine the impurity resistivity of Fe alloys to constrain the inner core's thermal conductivity. Therefore, this study systematically calculated the impurity resistivities of 4‐ and 6‐component alloys at inner core pressure by combining the Korringa‐Kohn‐Rostoker method with the coherent potential approximation. As a result, we obtained the thermal conductivity of the inner core to be 150–263 W/m/K. The inner core cannot maintain thermal convection with such a high thermal conductivity, resulting in a flat temperature profile. In materials science, it is widely known that polycrystals soften suddenly at high temperatures a few percent below their melting temperature. If such a pre‐melting occurs in the inner core, the flat temperature profile due to high thermal conductivity causes variations in the attenuation within the inner core. This may explain the observation that the upper inner core is more strongly attenuated than the innermost inner core.

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“…The onset age of 550 Ma, midway between the available Ediacaran and earliest Cambrian PDMs, implies a high core thermal conductivity (89–121 W mK −1 ) 7 . If there is delayed nucleation of the inner core 46 , the paleointensity history suggests it was limited to the ultralow geomagnetic field strength, which may have spanned several tens of millions of years during the Ediacaran Period (Fig. 3 b).…”

Section: Discussionmentioning

confidence: 99%

Early Cambrian renewal of the geodynamo and the origin of inner core structure

et al. 2022

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Paleomagnetism can elucidate the origin of inner core structure by establishing when crystallization started. The salient signal is an ultralow field strength, associated with waning thermal energy to power the geodynamo from core-mantle heat flux, followed by a sharp intensity increase as new thermal and compositional sources of buoyancy become available once inner core nucleation (ICN) commences. Ultralow fields have been reported from Ediacaran (~565 Ma) rocks, but the transition to stronger strengths has been unclear. Herein, we present single crystal paleointensity results from early Cambrian (~532 Ma) anorthosites of Oklahoma. These yield a time-averaged dipole moment 5 times greater than that of the Ediacaran Period. This rapid renewal of the field, together with data defining ultralow strengths, constrains ICN to ~550 Ma. Thermal modeling using this onset age suggests the inner core had grown to 50% of its current radius, where seismic anisotropy changes, by ~450 Ma. We propose the seismic anisotropy of the outermost inner core reflects development of a global spherical harmonic degree-2 deep mantle structure at this time that has persisted to the present day. The imprint of an older degree-1 pattern is preserved in the innermost inner core.

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The Fate of Liquids Trapped During the Earth's Inner Core Growth

Cited by 12 publications

References 68 publications

Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm

Evidence for the Innermost Inner Core: Robust Parameter Search for Radially Varying Anisotropy Using the Neighborhood Algorithm

Impurity Resistivity of the Earth's Inner Core

Early Cambrian renewal of the geodynamo and the origin of inner core structure

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