Fig. 6: Sketch illustrating the strong coupling model of the studied metachert block along the North Qilian paleo-subduction channel at a depth of approximately 55 km.

The high differential stress recorded in the metachert block, with a lower pore fluid factor (λ) compared to the calcschist matrix, likely results from transient block interactions driven by the stress amplification effect along the subduction channel. Such a phenomenon led to the widespread formation of foliation-parallel micro-shear zones at strain rates of 10⁻⁹ s⁻¹ (as shown in the inset microstructure). These micro-shear zones preserved in the block provide direct geological evidence of the transient dislocation-based creep, interpreted here as related or triggered by the surrounding large-scale multi-fault network associated with the SSEs, and represented by the plateau-like peak of the red strain rate curve. Note that the inset sketch depicts the geometric configuration where block-block interaction occurred. Such interaction, which requires a high abundance of blocks within the mélange, is proposed to have occurred only transiently during the lifespan of subduction channel activity.