Porcher Island Structural Geology.pdf

- Study Area: Porcher Island and surrounding region, northwestern British Columbia, near the eastern margin of the southern Alexander terrane.
- Purpose: To elucidate the structural history using detailed structural analysis and U-Pb geochronology.
- Previous Work: Mapping by Roddick (1970), Hutchison (1982), and Nelson et al. (2010a, 2010b, 2012).
- Geology: Alexander terrane rocks dominate, including Ordovician volcanic and sedimentary rocks, Devonian siliciclastic equivalents, and Permian plutonic rocks. The Kumealon unit, a felsic to mafic volcanic sequence, is also present. The Gravina belt and Yukon-Tanana terrane rocks are minor constituents.
- Previous Deformation: Mid-Cretaceous (110-87 Ma) sinistral transpression, with three northwest-striking sinistral shear zones (Grenville Channel, Kitkatla, Principe-Laredo). Farther north, west to southwest-vergent thrusting was also significant, with crustal-scale thrusts truncated by the younger Coast shear zone.
- New Findings: Late Silurian to Early Devonian tectonomagmatic event identified in the Ogden Channel complex. Sinistral and dextral shear zones were coeval, forming a conjugate set.