Geophysics

Core-Mantle Boundary Cells

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Science  14 Sep 2001:
Vol. 293, Issue 5537, pp. 1955
DOI: 10.1126/science.293.5537.1955b

The core-mantle boundary (CMB) marks a major chemical and physical contrast between an outer core of liquid iron alloy and a lower mantle of solid silicate minerals. The two phases may mix on a grain-size scale so that the liquid infiltrates the solid and some minerals dissolve. This allows the liquid to become saturated with lighter elements, and this saturated liquid can form a distinct layer at the CMB.

Narteau et al. developed a cellular automata method to simulate this mixing to determine the fine-scale structure at the boundary. They used three types of centimeter-sized square cells: iron liquid, iron liquid saturated with silicon and oxygen, and solid silicate. Adjacent cells were allowed to interact and change their state based on plausible rates of dissolution, crystallization, and diffusion. The simulations predict a 65-cm-thick layer of saturated liquid at the CMB after about 5 years, and over longer time scales, thicker layers with undulations form. The formation of a stable saturated layer with undulations may change mantle convection and fluid core motions, leading to larger scale effects on core-mantle coupling and on the whole Earth. — LR

Earth Planet. Sci. Lett.191, 49 (2001).

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