Cretaceous crustal section through the proposed Insular-Intermontane suture, North Cascades, Washington

The North Cascades of Washington consists of rocks that were deformed and recrystallized during a middle Cretaceous orogeny that was driven by the collision of the Insular and Intermontane superterranes. We reconstruct a composite vertical crustal section through the orogen on the basis of geobarometric data the Skagit Gneiss and on stratigraphic and structural data from supracrustal rocks exposed east of the Skagit Gneiss. We propose that, at the end of the orogeny, the upper 30 km of crust consisted of Skagit Gneiss overlain by two structural couplets, each composed of Methow basin strata underlain by Hozameen terrane rocks. We suggest that the Insular-Intermontane suture lies between the Skagit Gneiss and the overlying Hozameen terrane rocks. -Authors