Magnetization of Pacific Seamounts: A preliminary polar curve for the northeastern Pacific

The direction and intensity of magnetization of a uniformly magnetized seamount can be computed if its shape and associated magnetic anomaly are known. This technique has been applied to nine seamounts close to Hawaii, twelve seamounts close to the tip of Baja California, and twenty-eight seamounts surveyed during the Pioneer survey. All available paleomagnetic results from the Pacific basin have been used to establish a preliminary polar curve relative to the northeastern Pacific. This polar curve is weighted in favor of the Cretaceous point. This point at 61°N, 16°E is the mean pole position of seventeen seamounts and has an α95 of only 8°. The curve confirms earlier results indicating a 30° northward movement of the Northeastern Pacific since the Cretaceous. Paleomagnetic results obtained from seamounts near Japan suggest that, since the Cretaceous, the northwestern and northeastern Pacific have not always been rigidly connected. The pattern of long linear fracture zones in the South Pacific can be used to determine the motion of the Pacific plate relative to Antarctica since the Upper Cretaceous. Paleomagnetic data show that Antarctica has remained stationary in latitude over the same time span. A comparison of the paleomagnetic data obtained on the northeastern Pacific and on Antarctica yields a relative motion in conflict with that predicted by the South Pacific fracture zones. This conflict can be resolved if these two areas of the Pacific were decoupled some time between the Cretaceous and the present. Thus, it appears likely that the present Pacific plate is a composite of at least three distinct plates. Volcanic aseismic ridges within the Pacific Ocean may be the fossil boundaries of these plates now coalesced into a single plate.