Abstract
Paleomagnetic data reviewed along an 800-km transect extending from northeastern Oregon into southwest Montana indicate adjacent crustal blocks experienced post-Jurassic vertical-axis clockwise rotation relative to North America. From west to east, rotated blocks include relict island-arc and related terranes of the Blue Mountains province (Oregon: >60° rotation), calc-alkaline plutons along the arc–continent boundary (Idaho: ~30° rotation), and displaced passive margin strata in the Rocky Mountain foreland (Montana: ≤60° rotation). Assessment of polyphase contractional deformation shows oroclinal bending (~35° westward swing) of the Blue Mountains block concurrent with clockwise turning of the entire terrane province (our variant of conventional model; S.W. Carey, 1955—), with an approximated hinge along the Olympic–Wallowa lineament (~N30W). Restoration of clockwise rotation (~66°; Blue Mountains) reveals collisional mountain-building below a promontory buttress, coeval with torsional displacement on the continental interior.
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