Stress heterogeneities in exhumed high-pressure rocks shed light on deep subduction interface transient coupling

Stress distribution and creep mechanisms along modern subduction interfaces remain poorly understood, due to the lack of high-resolution constraints on the rheology of the heterogeneous plate interface and associated fluid distribution in the so-called transition zone (40–60 km depth), where deep slow slip events (SSEs) occur. Here, we document the presence of dislocation-based creep in a blueschist facies metachert block exhumed from the North Qilian paleo-subduction interface, NE Tibet. This block exhibits foliation-parallel micro-shear zones inferred to have formed under relatively fast strain rates of 10−9 s−1 and shear stresses exceeding 100 MPa. These values are paradoxical, as they are significantly higher than those estimated for the surrounding, weaker calcschist matrix, raising questions about their physical origin. We propose that the observed micro-shearing in the block, formed over a duration on the order of decades, sheds light on the local coupling induced by transient block interactions during large-scale SSEs along the deep subduction channel. Geological evidence from the North Qilian paleo-subduction channel shows that strong blocks deform by dislocation creep, sustain >100 MPa stresses, and their interactions transiently tighten plate coupling, shedding light on deep slow-slip dynamics.