Effects of rotation on crystal settling in a terrestrial magma ocean: Spherical shell model

Abstract:

Like Moon or Mars, Earth experienced one or several deep magma ocean periods of global
extent in a later stage of its accretion. The crystallization of these magma oceans is of key
importance for the chemical structure of Earth, the mantle evolution and the onset of plate
tectonics. Due to the fast rotation of early Earth and the small magma viscosity, rotation
probably had a profound effect on differentiation processes. For example, Matyska et al.
[1994] propose that the distribution of heterogeneities like the two large low shear velocity
provinces (LLSVP) at the core mantle boundary is influenced by rotational dynamics
of early Earth. Further Garnero and McNamara [2008] suggest that the LLSVPs are
very long-living anomalies, probably reaching back to the time of differentiation and
solidification of Earth. However, nearly all previous studies neglect the effects of rotation.
In our previous work using a Cartesian model, a strong influence of rotation as well as
of latitude on the differentiation processes in an early magma ocean was revealed. We
showed that crystal settling in an early stage of magma ocean crystallization crucially
depends on latitude as well as on rotational strength and crystal density.
In order to overcome the restrictions as to the geometry of the Cartesian model, we are
currently developing a spherical model to simulate crystal settling in a rotating spherical
shell. This model will allow us not only to investigate crystal settling at the poles and
the equator, but also at latitudes in-between these regions, as well as the migration of
crystals between poles and equator.

References
E. J. Garnero and A. K. McNamara. Structure and dynamics of earth’s lower mantle.
Science, 320(5876):626–628, 2008.
C. Matyska, J. Moser, and D. A. Yuen. The potential influence of radiative heat transfer
on the formation of megaplumes in the lower mantle. Earth and Planetary Science
Letters, 125(1):255–266, 1994.