Paleomagnetic rotations and continental deformation



One of the most interesting results obtained in the last 2 decades in the study of crustal deformation has been the recognition that large regions of continental crust undergo rotations about vertical axes during deformation. Proof of these rotations, for which usually there is little or no visible field evidence, has come through paleomagnetic studies, which reveal rotations when the paleomagnetic declinations within the deforming zone are discordant compared with those determined from stable units outside this region.

Such discordant declinations were first described in Oregon by Allan Cox, then, following this pioneering work, in the North American Cordillera and Southern California and were totally unpredicted by the existing geological studies. Rotations have subsequently been found in other areas of recent tectonic activity, such as the Basin and Range province, New Zealand, Greece, western Turkey, and the Andes, so that they appear as an important feature of continental deformation.