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Published March 1990 | public
Journal Article

Regionally extensive mid-Cretaceous west-vergent thrust system in the northwestern Cordillera: Implications for continent-margin tectonism


The Intermontane-Insular superterrane boundary zone represents a fundamental crustal boundary separating the two largest allochthonous crustal fragments in the North American Cordillera. Structural, stratigraphic, and geochronologic relations along this boundary indicate that substantial west-vergent compression and concomitant crustal thickening occurred there in mid-Cretaceous time. This orogenic zone extends for more than 1200 km along strike length, between southern southeast Alaska and northern Washington. In southern southeast Alaska and northwest British Columbia, rocks of the Insular superterrane were imbricated along a series of west- to southwest-vergent thrust faults. In northern Washington and southwestern British Columbia, a wide zone encompassing the margins of the two superterranes, as well as numerous intervening smaller fragments, was shortened principally along west-vergent thrusts. Known geologic relations do not discriminate among existing tectonic models that explain the origin of the mid-Cretaceous thrust system.

Additional Information

© 1990 Geological Society of America. Manuscript received June 29, 1989; Revised manuscript received October 2, 1989; Manuscript accepted October 9, 1989. Parts of this research were supported by National Science Foundation Grants EAR 86-05386 and EAR 88-03834 (to Saleeby) and EAR 81-07654 and EAR 85-08239 (to Cowan); additional support (to Rubin) was provided by a Geological Society of America Penrose Grant, a Sigma-Xi grant-in-aid, and by the U.S. Geological Survey, Alaska Branch. We thank Maria Luisa Crawford, John Garver, Meghan Miller, Bill McClelland, Jim Monger, and Margi Rusmore for helpful discussions regarding Cordilleran tectonics, and Maria Luisa Crawford, Bill McClelland, and Peter Van der Heyden for thorough and careful reviews of the manuscript.

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