Abstract Blueschists are a defining component of subducting oceanic crust and influence slab and interface rheology across thermal regimes. Glaucophane, the dominant sodic amphibole in blueschist, is a key rheology‐controlling phase, yet its dislocation‐based strength is poorly constrained. We conducted load‐stepping experiments in a Griggs apparatus at 600–700C and 1.0 GPa over shear strain rates from ∼ to 1.2, using a starting grain size of <63 μm. Mechanical data show a stress exponent transition from 2.8 to 3.2 at relatively low stresses (dislocation creep) to 13–19 at high stresses (dislocation glide). Undulose extinction, subgrain development, and recrystallized grains corroborate dislocation activity. We derive flow laws for dislocation creep n = 3, Q = 450 15 kJ/mol, A = 2.32 × and dislocation glide A = , = 22 GPa, H = 800 kJ/mol, p = 1, and q = 2. Extrapolation to geologic conditions suggests that dislocation glide will not operate under steady‐state subduction‐interface conditions, and is likely only relevant during transient high stress perturbations. Dislocation creep dominates at temperatures above 450°C at grain sizes of ∼1 mm or larger. Comparison with published quartz/metasediment and eclogite flow laws indicates that blueschist strengths are intermediate between these endmembers, implying a meaningful contribution to long‐term interface strength in mafic‐dominated (sediment‐poor) margins. Together, these results refine glaucophane‐controlled blueschist rheology and its implications for subduction zone mechanics.
Hufford et al. (Sun,) studied this question.