Electrical and thermal conductivity of Fe alloys at Earth's core conditions and the evolution of the geodynamo
Abstract
Earth's magnetic field has been maintained by the geodynamo through rigorous convective motions in the liquid outer core [1]. The geodynamo is powered by the cooling of the core that is mainly composed of Fe-Ni alloyed with some light elements [2]. Therefore, the transport properties of Fe alloys at Earth's core conditions play an important role in geodynamo and thermal evolution of Earth's core [3]. Here we measured the electrical resistivity of Fe-Ni and Fe-Si alloys up to the relevant pressure-temperature of the Earth's core using four-probe van der Pauw method in double-side laser-heated Diamond Anvil Cells. Our results show a quasi-linear relation between temperature and resistivity in hcp-Fe-Ni and hcp-Fe-Si up to ~3,400 K at high pressures. Compared with hcp-Fe [4], the impurities like Ni and Si can elevate iron's resistivity but they show drastically different magnitudes. Thermal conductivity of an Fe-Ni-Si alloy as a candidate core composition show that the core's thermal conductivity could be strongly reduced by the impurities. Our results are combined with thermodynamic model to show how a present-day geodynamo is driven by thermal-compositional convections.
References: [1] Roberts and Glatzmaier, Rev. Mod. Phys. 72, 1081-1123 (2000) [2] Davies et al. Nat. Geosci. 8, 678-685 (2015) [3] Williams Annu. Rev. Earth Planet. Sci. 46: 47-66 (2018) [4] Zhang et al. Under review, (2019)- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMDI23B0048Z
- Keywords:
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- 1507 Core processes;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 1510 Dynamo: theories and simulations;
- GEOMAGNETISM AND PALEOMAGNETISM;
- 3924 High-pressure behavior;
- MINERAL PHYSICS;
- 7207 Core;
- SEISMOLOGY