TRACKING THE FUGITIVE WRANGELLIAN ARC

A growing body of structural and stratigraphic evidence indicates that most North American Cordilleran arcs, including Wrangellia, and Neoproterozoic continental basement fragments of Baltican affinity, translated sinistrally around the Laurentian margin from Middle Devonian to middle Cretaceous times. Based on modern western Pacific analogues, a model of repeated backarc opening and closure during translation is presented. It suggests the Devonian arcs of Wrangellia, Stikinia and Finlayson formed by subduction retreat, and the Slide Mountain and Cache Creek terranes formed as oceanic backarc basins behind them. At ~300 Ma, Wrangellian arc-continent collision initiated closure of the Slide Mountain ocean, then Cache Creek, with the latter closure responsible for Quesnellia arc formation. Re-initiation of outboard subduction at ~230 Ma, associated with arc rifting, formed the Wrangellian “flood basalts” and Brooks Range Ophiolite, allowing the Wrangellia arc to migrate outboard, then southward past the Stikinia arc in the Jurassic. Juxtaposition of Quesnellia, Stikinia and Wrangellia arcs doubled the width of allochthonous Canadian Cordillera relative to its US counterpart. During the Late Cretaceous-Early Cenozoic, Wrangellia reversed motion and translated dextrally, approximately 1000 km northward to its present position.