Enhanced convection and fast plumes in the lower mantle induced by the spin transition in ferropericlase.
Using a numerical model we explore the consequences of the intrinsic density change ({Delta}{rho}/{rho} {approx} 2-4%) caused by the Fe{sup 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.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States)
- DOE Contract Number:
- DE-AC02-06CH11357
- OSTI ID:
- 960364
- Report Number(s):
- ANL/XSD/JA-64165; GPRLAJ; TRN: US200923%%334
- Journal Information:
- Geophys. Res. Lett., Vol. 36, Issue May 28, 2009; ISSN 0094-8276
- Country of Publication:
- United States
- Language:
- ENGLISH
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