Structural Transitions in Amorphous Mantle Phases

Dan Shim Massachusetts Institute of Technology

Thanks to: K. Catalli, T. Grove, NSF

CIDER 2004

Melting in EarthCore formation Magma Ocean

Top of the transition zoneBercovici and Karato (2003) Nature 425, 39+Revenaugh and Sipkin (1994) Nature 369, 474+

Core-Mantle BoundaryRevenaugh and Meyer (1997) Science 277, 670+ Williams et al (1998) Science 280, 546+

Stevenson (2008) Nature 451, 261+

Coordination Number increase in

Si--O

Stolper and Ahrens (1987) GRL 14, 1231+

Raman Spectra of Silicate Glasses

Shim and Catalli (2009) EPSL, in press

Monomer (Q0) Chain (Q2)

Raman Spectra

Shim and Catalli (2009) EPSL, in press

Differentiation in Magma Ocean

Boyet and Carlson (2005) Science 309, 576+

Magma Ocean Differentiation in Earth and Mars

Direct Measurements on Melts

Slotznick and Shim (2008) AM

Summary

In the present-day mantle, melting will further enhance the degree of differentiation atop the transition zone and the core-mantle boundary.

Si-rich melts undergo the structural transition at systematically lower pressure than Si-poor melts.

Mg-silicate glasses undergo a series of structural transitions at high pressure: increases in the Si—O coordination number and changes in the Si—O polyhedral connectivity.

The compositional sensitivity of the structural transition would result in Si-enrichment of the deeper part of the magma ocean. Therefore, the magma ocean would be compositionally stratified.