CaltechAUTHORS
  A Caltech Library Service

Modeling viscosity of (Mg,Fe)O at lowermost mantle conditions

Reali, R. and Jackson, J. M. and Van Orman, J. and Bower, D. J. and Carrez, P. and Cordier, P. (2019) Modeling viscosity of (Mg,Fe)O at lowermost mantle conditions. Physics of the Earth and Planetary Interiors, 287 . pp. 65-75. ISSN 0031-9201. https://resolver.caltech.edu/CaltechAUTHORS:20190103-135311509

[img] PDF - Published Version
Creative Commons Attribution Non-commercial No Derivatives.

2576Kb

Use this Persistent URL to link to this item: https://resolver.caltech.edu/CaltechAUTHORS:20190103-135311509

Abstract

The viscosity of the lower mantle results from the rheological behavior of its two main constituent minerals, aluminous (Mg,Fe)SiO_3 bridgmanite and (Mg,Fe)O ferropericlase. Understanding the transport properties of lower mantle aggregates is of primary importance in geophysics and it is a challenging task, due to the extreme time-varying conditions to which such aggregates are subjected. In particular, viscosity is a crucial transport property that can vary over several orders of magnitude. It thus has a first-order control on the structure and dynamics of the mantle. Here we focus on the creep behavior of (Mg,Fe)O at the bottom of the lower mantle, where the presence of thermo-chemical anomalies such as ultralow-velocity zones (ULVZ) may significantly alter the viscosity contrast characterizing this region. Two different iron concentrations of (Mg_(1–x)Fe_x)O are considered: one mirroring the average composition of ferropericlase throughout most of the lower mantle (x = 0.20) and another representing a candidate magnesiowüstite component of ULVZs near the base of the mantle (x = 0.84). The investigated pressure-temperature conditions span from 120 GPa and 2800 K, corresponding to the average geotherm at this depth, to core-mantle boundary conditions of 135 GPa and 3800 K. In this study, dislocation creep of (Mg,Fe)O is investigated by dislocation dynamics (DD) simulations, a modeling tool which considers the collective motion and interactions of dislocations. To model their behavior, a 2.5 dimensional dislocation dynamics approach is employed. Within this method, both glide and climb mechanisms can be taken into account, and the interplay of these features results in a steady-state condition. This allows the retrieval of the creep strain rates at different temperatures, pressures, applied stresses and iron concentrations across the (Mg,Fe)O solid solution, providing information on the viscosity for these materials. A particularly low viscosity is obtained for magnesiowüstite with respect to ferropericlase, the difference being around 10 orders of magnitude. Thus, the final section of this work is devoted to the assessment of the dynamic implications of such a weak phase within ULVZs, in terms of the viscosity contrast with respect to the surrounding lowermost mantle.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.pepi.2018.12.005DOIArticle
ORCID:
AuthorORCID
Jackson, J. M.0000-0002-8256-6336
Bower, D. J.0000-0002-0673-4860
Cordier, P.0000-0002-1883-2994
Additional Information:© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/). Received 21 June 2018, Revised 12 November 2018, Accepted 25 December 2018, Available online 26 December 2018. Financial support by the European Research Council under the Seventh Framework Program (FP7), ERC Grant No. 290424 Rheoman, is gratefully acknowledged. Computational resources have been provided by the CRI–Université de Lille 1. J.M.J. is thankful for support from the National Science Foundation (NSF) under EAR–CSEDI–1316362 and W. M. Keck Institute for Space Studies. We are thankful to the CIDER program set at the Kavli Institute for Theoretical Physics, University of California, Santa Barbara (NSF EAR-1135452, funded under the FESD Program). DJB acknowledges SNSF Ambizione Grant 173992. The geodynamic calculations were performed on UBELIX (http://www.id.unibe.ch/hpc), the HPC cluster at the University of Bern. We thank the Computational Infrastructure for Geodynamics (http://geodynamics.org) which is funded under awards NSF–EAR–0949446 and EAR–1550901.
Group:Seismological Laboratory, Keck Institute for Space Studies
Funders:
Funding AgencyGrant Number
European Research Council (ERC)290424
NSFEAR-1316362
Keck Institute for Space Studies (KISS)UNSPECIFIED
NSFEAR-1135452
Swiss National Science Foundation (SNSF)173992
NSFEAR-0949446
NSFEAR-1550901
Subject Keywords:(Mg,Fe)O; 2.5D Dislocation Dynamics; Viscosity; Core−Mantle Boundary; Ultralow−Velocity Zones
Record Number:CaltechAUTHORS:20190103-135311509
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190103-135311509
Official Citation:R. Reali, J.M. Jackson, J. Van Orman, D.J. Bower, P. Carrez, P. Cordier, Modeling viscosity of (Mg,Fe)O at lowermost mantle conditions, Physics of the Earth and Planetary Interiors, Volume 287, 2019, Pages 65-75, ISSN 0031-9201, https://doi.org/10.1016/j.pepi.2018.12.005. (http://www.sciencedirect.com/science/article/pii/S0031920118301833)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:92044
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:03 Jan 2019 22:04
Last Modified:03 Oct 2019 20:40

Repository Staff Only: item control page