  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.
