Transient and Steady-State Dislocation Creep of Olivine Controlled by Dislocation Interactions at the Isostress Endmember
David Wallis (University of Cambridge)
Thomas Breithaupt (University of Cambridge)
Taco Broerse (TU Delft - Civil Engineering & Geosciences)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
The rheological behavior of olivine deforming by dislocation creep controls geodynamic processes that involve steady-state flow or transient viscosity evolution. Longstanding rheological models applied to both contexts assume that dislocation creep of olivine aggregates occurs close to the isostrain endmember with each grain deforming to the same strain but supporting different stress. Here, we test this assumption by constructing isostrain and isostress models based on flow laws for single crystals and comparing them to rheological data from aggregates. This analysis reveals that strain rates measured on olivine aggregates agree with those predicted by the isostress model but are an order of magnitude faster than those predicted by the isostrain model. When extrapolated to conditions typical of the shallow upper mantle, the isostress model predicts steady-state viscosities that are one to three orders of magnitude less than those predicted by the isostrain model. Furthermore, deformation close to the isostress endmember implies that transient creep occurs predominantly by dislocation interactions, suggesting viscosity changes that are approximately one order of magnitude greater than those predicted previously based on grain interactions associated with the isostrain model.
help_outline