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ABSTRACT: Pre- to Syncollisional Sedimentation in the Middle Jurassic to Cretaceous Methow-Tyaughton Basin, Northern Washington, Southwestern British Columbia

J. I. Garver, P. J. Umhoefer, M. F. McGroder, J. Bourgeois

Palinspastic reconstruction of Cretaceous to Tertiary dextral-slip faults restores the Methow-Tyaughton basin to a 300+ km-long basin that contains Middle Jurassic to middle Cretaceous strata. Sedimentary rocks and structures within the basin record a transition from sedimentation on the western margin of the intermontane terrane to sedimentation within an actively deforming collision zone along the Intermontane and Insular terrane boundary in the middle Cretaceous. Following Middle Jurassic terrane amalgamation, the Methow-Tyaughton was a short-lived fore-arc basin in the Callovian. Oxfordian-Valanginian sedimentation was marked by low depositional rates of volcanic and plutonic debris, probably along a transform-rift margin. Hauterivian-Aptian sedimentary rocks are gene ally fine-grained turbidite packages with minor interbedded tuffs, and volcanic rocks are interbedded at the western basin margin. Hauterivian rocks reflect a change to a back-arc basin setting. Albian contraction within the basement Bridge River and Cadwallader terranes resulted in an intrabasinal uplift that supplied chert-rich detritus to two flanking subbasins. At the same time, west-derived, volcanic detritus shed off the volcanic cover to the Insular terrane, and east-derived arkosic sediment shed off the Omineca Crystalline belt. Tectonic subsidence and basin infilling occurred from about 110 to 95 Ma, capped by a thick sequence of nonmarine clastic rocks and andesites. Intrabasin deformation occurred from about 100 to 85 Ma. After the termination of andesitic volcanism and contra tional deformation, the basin was cut by dextral-slip faults (post 85 Ma) that likely were driven by oblique Kula-North America interaction.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990