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Subduction zone dynamics are strongly influenced by the mechanical properties of subduction interface shear zones (Behr et al., 2022). However, the relevant properties of subduction interfaces, such as their widths, rock types, and internal structure, cannot be determined via geophysical observation. Instead, field-and microscale observations of exhumed shear zones that were active during subduction are needed to fill this knowledge gap. Subduction dynamics and thermal gradients evolve as they mature (e.g., Holt & Condit, 2021), and subduction zones can encompass a broad range of environments (Chelle-Michou et al., 2022), for example, when influenced by atypical subduction geometries like ridge subduction (e.g., Brown, 1998;DeLong et al., 1979;Sakaguchi, 1996). A more complete inventory capturing the variability of subduction interfaces is therefore needed to better understand their behavior.The Canadian Cordillera potentially exposes numerous subduction-related structures as it was assembled through a series of accretionary orogenies. One candidate structure is the Leech River Fault (Figure 1), a terrane-bounding fault located on southern Vancouver Island in British Columbia that juxtaposes mafic volcanic and igneous rocks of the Metchosin Igneous Complex (MIC) to the south with the predominantly metapelitic Leech River Complex (LRC). For clarity, we will term this structure the "Leech River Shear Zone" (LRSZ) to differentiate it from the recently active "Leech River Fault," which is locally coincident (

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