Escape hypothesis for the Stikine block

Abstract

Comparison of stratigraphic, faunal, and paleomagnetic characteristics of the Stikine terrane of British Columbia with other terranes in the Cordilleran collage reveals broad similarities with a group of terranes that formed a volcanic belt marginal to North America in Paleozoic and early Mesozoic time. Unlike Stikine, these terranes lie inboard of another belt of terranes that represents an early Mesozoic subduction complex or melange belt. Thus, in British Columbia the marginal volcanic belt is apparently doubled. In the Columbia embayment region, the marginal volcanic and melange belts are missing, and rocks of the outermost major component of the collage, the Wrangellia superterrane, are juxtaposed directly against cratonic rocks. We propose that Stikine is the missing fragment from the Columbia embayment; its northward "tectonic escape" was driven by the early stages of collision of the Wrangefia superterrane with North America in Middle to Late Jurassic time. The escaped fragment was then trapped between melange and more northerly, later arriving parts of the Wrangellia superterrane in Early to mid-Cretaceous time.