Early geodynamo powered by magnesium exsolution?
Abstract
Earth's magnetic field is generated by a convective dynamo in the outer core. The power driving this convection is likely a mix of thermal and compositional sources that rely on the steady cooling of the core. As such, the overlying mantle also plays a major role in magnetic field generation as it modulates the core cooling rate, and the convective sources in the core. Therefore understanding the nature of the core is of primary importance to understand the history of Earth's dynamo and mantle dynamics. Magnesium, present at a value as small as 1-2 wt%, may provide sufficient energy to drive an early geodynamo (O'Rourke and Stevenson, 2016), in spite of newly proposed high thermal conductivity of core materials (e.g. Pozzo et al., 2012). Much is still unknown about the plausibility of Mg in Earth's core, while recent studies suggest appreciable amount of magnesium might be present in liquid iron above 4000K (Wahl and Militzer, 2013, Badro et al., 2016). In this study, we examine different potential energy sources for driving the geodynamo over geologic history and we present new experiments for light element (e.g., Mg, Si, and O) partitioning between liquid metal and molten silicate using the laser-heated diamond anvil cell. Recovered samples are processed with focused ion beam milling and analyzed by field-emission electron microscopy. Our partitioning data are in disagreement with previous reports (Wahl and Militzer, 2013, Badro et al., 2016) and we explore the implications of our new partitioning results on the thermal and magnetic history of the core.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFMDI42A..02D
- Keywords:
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- 1015 Composition of the core;
- GEOCHEMISTRYDE: 1507 Core processes;
- GEOMAGNETISM AND PALEOMAGNETISMDE: 3924 High-pressure behavior;
- MINERAL PHYSICSDE: 7207 Core;
- SEISMOLOGY