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 degrees rotation), calc-alkaline plutons along the arc-continent boundary (Idaho: similar to 30 degrees rotation), and displaced passive margin strata in the Rocky Mountain foreland (Montana: <= 60 degrees rotation). Assessment of polyphase contractional deformation shows oroclinal bending (similar to 35 degrees 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 (similar to N30W). Restoration of clockwise rotation (similar to 66 degrees; Blue Mountains) reveals collisional mountain-building below a promontory buttress, coeval with torsional displacement on the continental interior.
NSTL
Elsevier