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Published May 28, 2009 | Published
Journal Article Open

Enhanced convection and fast plumes in the lower mantle induced by the spin transition in ferropericlase

Abstract

Using a numerical model we explore the consequences of the intrinsic density change (Δρ/ρ ≈ 2–4%) caused by the Fe^(2+) spin transition in ferropericlase on the style and vigor of mantle convection. The effective Clapeyron slope of the transition from high to low spin is strongly positive in pressure-temperature space and broadens with high temperature. This introduces a net spin-state driving density difference for both upwellings and downwellings. In 2-D cylindrical geometry spin-buoyancy dominantly enhances the positive thermal buoyancy of plumes. Although the additional buoyancy does not fundamentally alter large-scale dynamics, the Nusselt number increases by 5–10%, and vertical velocities by 10–40% in the lower mantle. Advective heat transport is more effective and temperatures in the core-mantle boundary region are reduced by up to 12%. Our findings are relevant to the stability of lowermost mantle structures.

Additional Information

© 2009 American Geophysical Union. Received 10 February 2009; accepted 23 April 2009; published 28 May 2009. We obtained CitcomS version 3.0 from the Computational Infrastructure for Geodynamics (CIG), and we thank Eh Tan for technical advice. All figures in this paper were produced using GMT. We thank John Hernlund and an anonymous reviewer for their comments which improved the manuscript. JMJ acknowledges NSF (0711542) and COMPRES. Contribution number 10017 of the Division of Geological and Planetary Sciences, California Institute of Technology.

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