Back to the suture: Bridge River−Hozomeen ribbon cherts reveal long-lived ocean plate stratigraphy and polarity of subduction in western North America

Oceanic sutures are important components of accretionary orogens. This study focuses on the Bridge River−Hozomeen terrane, which straddles the Canada-USA border in the Coast-Cascade mountains, and is involved in the debate on the number of oceanic sutures of western North America and their relationships to paleo-Pacific plates (i.e., Andean versus Archipelago models). Currently exposed as two paleo-accretionary complexes offset by Eocene strike-slip faulting, the terrane is dominated by large volumes of mafic rocks and radiolarian chert (ocean plate stratigraphy). Revising the age and distribution of 96 radiolarian localities bearing 350 taxa reveals a long-lived record from the Mississippian to the Middle or Late Jurassic, spanning 170−190 m.y. The radiolarian assemblages are characterized by open-ocean, mixed Tethyan and Panthalassan signatures, likely associated with low-latitude ocean transit scenarios. The distribution of chert ages within the restored accretionary complex suggests a west-younging polarity of the accreted oceanic rocks, which is more consistent with an east-dipping subduction. The Bridge River−Hozomeen suture appears to wrap around the Insular superterrane toward the western oceanic units of Washington state, USA, while another major suture represented by the Cache Creek terrane has more affinities with the Baker terrane in Oregon, USA, and the central Klamath terranes in California, USA. Though exposed on a relatively short segment of the Cordillera, the Bridge River−Hozomeen terrane stands out as a significant paleo-oceanic “window” of western North America.