THE HAWAII-EMPEROR BEND: PLATE MOTION, PLUME MOTION, OR BOTH?

The Hawaii-Emperor Bend (HEB) has become a lightening rod for studies of absolute plate motion. Initially seen as the clearest evidence for an absolute plate motion change over an approximately stationary hotspot, recent studies have suggested that the HEB represents no change in plate motion at all, instead implying there was a rapid retardation of the southward motion of the underlying plume at ~ 50 Ma while the Pacific plate continued an otherwise undisturbed westward motion. Although several lines of inquiry have lead to this conclusion, there are in particular two principal observations that have prompted this major revision: (a) Paleolatitudes inferred from basalt samples recovered from drill cores at several sites along the Emperor chain systematically imply a volcanic origin much further north than the present latitude of the Hawaiian hotspot would suggest, and (b) the age progressions along the Emperor chain and the contemporaneous portion of the Louisville chain inferred from dated rock samples begin to diverge for ages older than ~55 Ma when a fixed hotspot reference frame is used. While the latter discrepancy can be modeled with relative minor changes in the inter-hotspot distance or by appealing to limited hotspot-ridge interactions, the paleolatitude anomaly at 78 Ma is almost 15˚. The magnitude of this anomaly requires a significant revision of Pacific tectonic history and may ultimately a drive a stake through the heart of the hotspot hypothesis. The HEB itself is constrained to have formed around 50-47 Ma, i.e., approximately Chron 21, which is a period of significant and global plate reorganizations. Thus, it continues to be the view of many that it seems unlikely that a change in plate motion has played no role in the HEB formation. Given existing paleolatitude, age, and chain geometry data I will examine reasonable bounds on the likely roles that plate and plume motion have played in the formation of the Hawaii-Emperor chain.