Viscosity undulations in the lower mantle: The dynamical role of iron spin transition

Autor(es)

Justo, J. F. ^[1] ; Morra, G. ^{[2, 3]} ; Yuen, D. A. ^{[4, 5]}

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Escola Politecn, BR-05424970 Sao Paulo, SP - Brazil

^[2] Univ Louisiana Lafayette, Dept Phys, Lafayette, LA 70504 - USA

^[3] Univ Louisiana Lafayette, Sch Geosci, Lafayette, LA 70504 - USA

^[4] Univ Minnesota, Dept Earth Sci, Minneapolis, MN 55455 - USA

^[5] China Univ Geosci, Sch Environm Studies, Wuhan 430074 - Peoples R China

• Tipo de documento: Artigo Científico
• Fonte: Earth and Planetary Science Letters; v. 421, p. 20-26, JUL 1 2015.
• Citações Web of Science: 8

Resumo

A proper determination of the lower-mantle viscosity profile is fundamental to understanding Earth geodynamics. Based on results coming from different sources, several models have been proposed to constrain the variations of viscosity as a function of pressure, stress and temperature. While some models have proposed a relatively modest viscosity variation across the lower mantle, others have proposed variations of several orders of magnitude. Here, we have determined the viscosity of ferropericlase, a major mantle mineral, and explored the role of the iron high-to-low spin transition. Viscosity was described within the elastic strain energy model, in which the activation parameters are obtained from the bulk and shear wave velocities. Those velocities were computed combining first principles total energy calculations and the quasi-harmonic approximation. As a result of a strong elasticity softening across the spin transition, there is a large reduction in the activation free energies of the materials creep properties, leading to viscosity undulations. These results suggest that the variations of the viscosity across the lower mantle, resulting from geoid inversion and postglacial rebound studies, may be caused by the iron spin transition in mantle minerals. Implications of the undulated lower mantle viscosity profile exist for both, down- and up-wellings in the mantle. We find that a viscosity profile characterized by an activation free energy of G{*}(z(0)) similar to 300-400 kJ/mol based on diffusion creep and dilation factor delta = 0.5 better fits the observed high velocity layer at mid mantle depths, which can be explained by the stagnation and mixing of mantle material. Our model also accounts for the growth of mantle plume heads up to the size necessary to explain the Large Igneous Provinces that characterize the start of most plume tracks. (C) 2015 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 09/14082-3 - Simulação e modelagem de minerais a altas pressões
• Beneficiário: Joao Francisco Justo Filho
• Modalidade de apoio: Auxílio à Pesquisa - Temático