Abstract
Over the last three decades the first-order correlation in morphology and orientation of seamount trails has been called upon to support the concept of a "fixed" Pacific hot spot frame of reference and to explain the Hawaii-Emperor bend (HEB) by a dramatic change in Pacific plate motion. In this paper, however, we present (super 40) Ar/ (super 39) Ar ages for the Gilbert Ridge and Tokelau Seamounts (Pacific) that show similar changes or bends in their orientation, but at different geological times, up to 20 Myr earlier than the HEB. Changes in Pacific Plate motion alone cannot explain these observations, because these asynchronous bends should have been reflected in the morphology of each of these seamount trails. Together with the lack of (linear) age progressions and inconsistent apparent local plate velocities of 131 and 87 mm/yr, we rule out a fixed hot spot origin for the Gilbert Ridge and Tokelau Seamount trails. Instead we invoke secondary or alternate processes to explain the complex age systematics and morphologies in these seamount trails. We propose here that the HEB-type bends in these seamount trails were likely formed by short-term "jerk-like" plate extensions in the studied southwestern region of the Pacific Plate, reactivating a preconditioned lithosphere that can be characterized by a complex structure and precursory magmatic impingements. The remarkable differences observed in these colinear seamount trails fundamentally question the existence of HEB-type bends in the formation of Pacific volcanic lineaments. They also show us that applying geometric and morphologic observations alone is insufficient in constraining past plate motions. Nevertheless, the need and search for alternate volcano-tectonic mechanisms offer opportunities to better understand intraplate volcanism in general.