Abstract: Mesozoic Construction of Cordilleran "Collage," Central British Columbia to Central California

G. A. Davis, J. W. H. Monger, B. C. Burchfiel

The western or "eugeosynclinal" part of the Cordilleran orogen is a composite and accreted terrane--an orogenic "collage." The Mesozoic collage was constructed across and against an Early to Middle Triassic continental margin of diverse type. This margin appears to have been essentially accretional in areas north of the Klamath Mountains. In the south an accreted Paleozoic arc and the continent itself had been subjected to faulting, possibly of left-lateral transform type, that produced a truncated, northwest-trending margin. In Late Triassic-earliest Jurassic time this geologically diverse margin became the site of oblique(?) convergence and subduction of Pacific lithosphere along its entire length. Subsequently, areas north of 48°N lat. and south of 44°N had s rikingly different Mesozoic histories. The northern accreted terrane owes its greater breadth to the inclusion of two exotic volcanic arcs of largely Paleozoic age (Stikine block and "Wrangellia"). We regard the northern Cascades as a component of the Paleozoic-Mesozoic continental margin displaced northwestward from westernmost Idaho by dextral strike-slip faulting, and not an exotic element of the Cordillera. No exotic arc terranes comparable to those of the north are recognized in the southern Cordillera. The Middle and Late Jurassic Klamath Mountains-Sierra Nevada are most probably a single arc complex constructed across a sutured plate boundary between continental basement and western oceanic rocks. Internal imbrication of this arc is believed to be an intraplate response to continued plate convergence to the west.

AAPG Search and Discovery Article #90963©1978 AAPG/SEG/SEPM Pacific Section Meeting, Sacramento, California