In situ investigation of diapirism as a core formation mechanism using high-pressure synchrotron X-ray radiography (Invited)
Abstract
Geochemical evidence from Hf/W chronometer constrains the timing of the core formation in Earth to be < 30 Myr after the solar system formation. The mechanism of core formation during the "dark age" of Earth’s history, however, remains poorly understood. Several scenarios have been proposed for metal-silicate segregation, including percolation of molten iron through solid silicates (e.g. Shannon and Agee, 1998) and sinking of iron-rich diapirs through a viscous silicate mantle by Rayleigh-Taylor instability (e.g. Stevenson, 1981; Samuel and Tackley, 2008). In comparison with the percolation mechanism, penetration of dense metallic diapirs may be a more rapid process to separate molten iron alloys from silicates (Stevenson, 1981; Rubie et al., 2007; Golabek et al., 2008). The diapirism mechanism needs be tested by high pressure experiments under carefully controlled conditions. In this study, we performed high-pressure X-ray radiography experiments to measure the Stokes sinking velocity of a diapir through solid silicates and to observe possible drainage processes under simultaneously high pressure and high temperature in the large volume press at Sector 13 (GSECARS) of the Advanced Photon Source (Argonne National Laboratory). Preliminary results show that at 10 and 14 GPa the diapir of molten iron alloys sank into the underlying olivine/wadsleyite layer within hours on sub-millimeter scale, confirming that diapirism of molten iron alloys is an efficient way to segregate core and mantle materials. Applying the general scaling laws for diapir sinking velocities derived by Samuel and Tackley (2008), we can place constraints on the timing of the core formation by metal-silicate separation on the planetary scale.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMMR41B..01C
- Keywords:
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- 1015 GEOCHEMISTRY / Composition of the core;
- 1507 GEOMAGNETISM AND PALEOMAGNETISM / Core processes;
- 3625 MINERALOGY AND PETROLOGY / Petrography;
- microstructures;
- and textures;
- 3630 MINERALOGY AND PETROLOGY / Experimental mineralogy and petrology