Dislocation interactions in olivine control postseismic creep of the upper mantle

TL;DR

This study shows that dislocation interactions within olivine significantly influence transient creep behavior in the upper mantle across a wide temperature range, impacting models of mantle viscosity evolution.

Contribution

It demonstrates that intragranular dislocation stress accumulation contributes to transient creep at high temperatures, suggesting a need for models incorporating these processes.

Findings

Stress heterogeneities of ~1 GPa found at both low and high temperatures.

Similar dislocation-induced stress distributions at different temperatures.

Implication for models of mantle viscosity and earthquake cycle dynamics.

Abstract

Changes in stress applied to mantle rocks, such as those imposed by earthquakes, induce a period of evolution in viscosity and microstructure. This transient creep is often modelled based on stress transfer among slip systems due to grain interactions. However, recent experiments have demonstrated that the intragranular accumulation of stresses among dislocations is the dominant cause of strain hardening in olivine at low temperatures, raising the question of whether the same process contributes to transient creep at higher temperatures. Here, we demonstrate that olivine samples deformed at 25{\deg}C or 1150 to 1250{\deg}C both contain stress heterogeneities of ~1 GPa that are imparted by dislocations and have correlation lengths of ~1 micrometre. The similar stress distributions formed in both temperature regimes indicate that accumulation of stresses among dislocations also provides a contribution to transient creep at high temperatures. The results motivate a new generation of models that capture these intragranular processes and may refine predictions of evolving mantle viscosity over the earthquake cycle.