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This study employs dislocation electron tomography to investigate three-dimensional dislocation microstructures in quartz mylonites from the Main Central Thrust and the Moine Thrust, both of which experienced dislocation creep in the presence of water. Our analysis reveals a widespread occurrence of mixed climb, with nearly half of all dislocations exhibiting this atypical deformation mechanism.

Mixed climb is an atypical mechanism where dislocations move in a plane intermediate between the glide and climb planes, it occurs when climb and glide velocities are of similar orders of magnitude. This suggests that under natural conditions—high temperature and low strain rate—the mobilities of glide and climb are comparable. As a result, climb in these mylonites is not merely a recovery process but a significant contributor to strain, with plastic strains from climb being comparable to, if not greater than, those from glide.

These findings highlight fundamental differences between natural and experimental deformation conditions. In laboratory settings, where stress-driven glide dominates, the role of climb is often underestimated. However, at natural strain rates, diffusion-controlled climb has sufficient time to operate, leading to deformation mechanisms that differ markedly from those observed in experiments. This raises concerns regarding the extrapolation of laboratory data to natural settings, particularly since most analyses rely on crystal preferred orientations, which primarily reflect the kinematics of glide.

Additionally, our observations suggest that the interplay between glide and climb may facilitate dislocation motion on unconventional slip planes, warranting further investigation into its implications for quartz deformation and rheology. This hypothesis, grounded in preliminary observations, calls for further empirical and theoretical exploration.