Paleomagnetic evidence for tectonic rotation of the Oregon Coast Range

Abstract

Paleomagnetic directions from lower, middle, and upper Eocene sedimentary and volcanic rocks in the Oregon Coast Range point 50° to 70° east of the expected Eocene field direction. This discrepancy is attributed to the tectonic rotation of a block at least 225 km in length extending from just north of the Klamath Mountains to north of Newport, Oregon. Two models are developed for the tectonic evolution of the Pacific Northwest. In the first, the coastal block is rotated seaward about a pivot point near its southern end in order to restore it to its Eocene position. In the second, it is assumed that the coastal block extends all the way to the Olympic Peninsula. Rotating the block back about a pivot near its northern end moves the southern end and the Klamath Mountains eastward across Oregon and restores the Klamath metamorphic belts to a position against the line of Cretaceous batholiths in northwestern Nevada.