June K. Wicks 


Email:   wicks "at" caltech . edu
Office:   062b Arms

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 High pressure sound velocity measurements using NRIXS A geodynamic and mineral physics model of a solid ULVZ



Ultralow-velocity zones are small structures on the core-mantle boundary that are characterized by extremely low sound velocities. To explain these low velocities, we propose that they contain iron-rich oxide.

Collaborator Dan Bower took the idea of a solid ultralow-velocity zone and explored its stability in numerical simulations.  This work explored the morphologies of solid-state ULVZs in a two-dimensional dynamic model, determining the steady-state thickness and shape of ULVZs as a function of prescribed initial thickness and chemical vs thermal buoyancy. By exploring a range of thicknesses and chemical density anomalies, this study creates a range of candidate ULVZ sizes and shapes that can be compared to mineral physics and seismic models.

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Examples of steady-state behavior of a thin iron-rich (Mg,Fe)O-containing layer. The ULVZ component is contained within the green outline and the CMB. (left) Sluggish convection (B = 4, dch = 16, permeable domain). (right) Counter-circulation driven by viscous coupling (B = 1.25, dch = 16, impermeable domain). Figure adapted from Bower et al., 2011.  


Mw+Pv     Let's assume, for example, that (Mg0.16Fe0.84)O exists in ULVZs, and that it is in equilibrium with (Mg,Fe)SiO3-perovksite. We model an aggregate mixture of (Mg0.16Fe0.84)O+(Mg0.72Fe0.28)SiO3 by calculating Voigt-Reuss-Hill curves. Small velocity drops in ULVZs can be correlated to taller structures, while larger velocity drops correspond to flatter, wider ULVZs. 

    More realistic models can be made as once we learn more about the dependence of sound velocities on Fe content and temperature.


Relevant Publications
Bower, D. J., J. K. Wicks, M. Gurnis, and J. M. Jackson (2011).  A geodynamic and mineral physics model of a solid-state ultralow-velocity zone.  Earth. Planet. Sci. Lett. 303, 193--202, doi:10.1016/j.epsl.2010.12.035. (pdf reprint)

Wicks, J. K., J. M. Jackson, and W. Sturhahn (2010).  Very low sound velocities in iron-rich (Mg,Fe)O: Implications for the core-mantle boundary region.  Geophys Res. Lett. 37, L15304, doi:10.1029/2010GL043689. (pdf reprint)









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