Constraints on past plate and mantle motion from new ages for the Hawaiian-Emperor Seamount Chain

Estimates of the relative motion between the Hawaiian and Louisville hot spots have consequences for understanding the role and character of deep Pacific‐mantle return flow. The relative motion between these primary hot spots can be inferred by comparing the age records for their seamount trails. We report 40Ar/39Ar ages for 18 lavas from 10 seamounts along the Hawaiian‐Emperor Seamount Chain (HESC), showing that volcanism started in the sharp portion of the Hawaiian‐Emperor Bend (HEB) at ≥47.5 Ma and continued for ≥5 Myr. The slope of the along‐track distance from the currently active Hawaiian hot spot plotted versus age is constant (57 ± 2 km/Myr) between ∼57 and 25 Ma in the central ∼1900 km of the seamount chain, including the HEB. This model predicts an age for the oldest Emperor Seamounts that matches published ages, implying that a linear age‐distance relationship might extend back to at least 82 Ma. In contrast, Hawaiian age progression was much faster since at least ∼15 Ma and possibly as early as ∼27 Ma. Linear age‐distance relations for the Hawaii‐Emperor and Louisville seamount chains predict ∼300 km overall hot spot relative motion between 80 and 47.5 Ma, in broad agreement with numerical models of plumes in a convecting mantle, and paleomagnetic data. We show that a change in hot spot relative motion may also have occurred between ∼55 Ma and ∼50 Ma. We interpret this change in hot spot motion as evidence that the HEB reflects a combination of hot spot and plate motion changes driven by the same plate/mantle reorganization. Key Points 40Ar/39Ar ages for new samples from the Hawaiian‐Emperor Seamount Chain (HESC) Hawaiian‐Emperor Bend (HEB) is at least 47.5 Myr old Remarkably linear age‐progression for 1900 km in the central part of the HESC