Abstract

Development of Mesozoic and Cenozoic sedimentary basins in western North America was linked to the overall geodynamics of an active continental margin. The Cordilleran margin, now largely of Californian-type with a bounding transform, was Atlantic-type from late Precambrian to early Paleozoic, Japanese-type from late Paleozoic to early Mesozoic, and Andean-type from late Mesozoic to early Tertiary, when a continental-margin arc–trench system included the following tectonic elements from west to east: (a) the subduction complex at the main subduction zone; (b) forearc basins within the arc–trench gap; (c) the magmatic arc of generally andesitic volcanics and subjacent granitic plutons; (d) a backarc fold-thrust belt, commonly with an associated metamorphic infrastructure; and (e) the retroarc foreland basin adjacent to the craton. Progressive broadening of this tectonic system was achieved by tectonic accretion of oceanic elements to the edge of the continental block and by peeling of cover off rigid basement underthrust behind the arc along the edge of a zone of ductile lithosphere formed thermally beneath the arc. An initial Jurassic island arc evolved through the Cretaceous into a terrestrial Tertiary arc as subsiding forearc and retroarc basins were filled with sediment.

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