Migration rate of volcanism along the Foundation Chain, SE Pacific

Abstract

Volcanism has migrated along the NW–SE-trending Foundation Chain, SE Pacific, at a rate of 91±2 mm/y for the past 21 million years (My). The Foundation Chain is at least 1900 km long, and was erupted mostly in the interior of the Pacific plate. The linear migration of intraplate, often geochemically enriched, volcanism along the Foundation Chain can be explained by the theory of tectonic plate drift over a narrow, stationary plume of hot mantle material upwelling from depth. The present hotspot (or at least its eastern extent) generated by this Foundation plume is now located on, or close to, the Pacific–Antarctic spreading-axis. Local spreading/microplate boundaries have migrated systematically towards the Foundation plume for at least the past 21 My, a process that was, however, interrupted by the creation of the Selkirk microplate. The Foundation Chain has erupted, therefore, onto ocean crust ranging in age from ∼17 Ma to ≥0 Ma, with distances between the Foundation plume and local spreading/microplate boundaries varying from ∼900 km to ≥0 km. Such interplay between the Foundation plume and local seafloor, spreading and microplate boundaries — probably in combination with changing stresses in the lithosphere — apparently induced major changes in the fabric (and composition) of the Foundation Chain, e.g., the switch from individual seamounts to elongated, en echelon, ridges at ≥5 Ma. It can also explain why ages for a few Foundation seamounts located at the edges of the Selkirk microplate do not lie along the overall linear trend of migrating volcanism. The linear velocity of the Pacific plate over the Foundation plume, calculated on the basis of the migration rate of volcanism along the Foundation Chain, is predicted by a number of rotation poles for the motion of the Pacific plate in a fixed hotspot reference frame. The fact that the measured migration rates of volcanism along the Foundation and Hawaiian chains are predicted by these rotation poles (1) confirms that the distribution of Foundation Chain ages records the absolute motion of the Pacific plate, and (2) supports the fundamental assumption of stationary mantle plumes in the case of Hawaii versus Foundation for at least the past 21 My. The Foundation Chain was created by a weak plume, primarily as relatively small, probably rapidly erupted (≤1 My) individual seamounts or seamount clusters at a rate of approximately one every My. Linear migration rates of volcanism are most likely defined unequivocally along such types of hotspot chain, on the basis of age–distance data. It should also be easier to identify and characterize volcanism created as a result of plume interactions with local spreading/microplate boundaries. Rotation poles for Pacific plate drift show that the initial stages of volcanism along the southern Austral Chain (≥34 Ma) could have been created by the Foundation plume, suggesting that the path of Pacific plate drift over the stationary Foundation plume could be at least 3000 km long.