Bends in Pacific Hotspot Tracks and Eocene Global Climate Change: Are they Coeval?

A long-recognized profound change in Pacific basin tectonics is associated with the ~50 Ma Hawaiian-Emperor bend (HEB), a sharp ~60 degree change in trend of the Hawaiian-Emperor volcanic chain. The HEB coincides with a global re-organization of plate motions, but has also been argued to have recorded a profound change in mantle circulation patterns. The Early Eocene Climatic Optimum (EECO), the interval of the warmest sustained temperatures in the Cenozoic, occurred at about the same time (~53.3 to ~49.1 Ma [Westerhold et al. 2018]) as the HEB. The end of the EECO marks the beginning of global cooling leading to the transition from greenhouse to icehouse Earth.

To better resolve the timing of the HEB and related tectonic events, we determine an age model with the fewest significant adjustable parameters for three important Pacific plate hotspot tracks: the Hawaiian-Emperor, the Louisville, and the Rurutu hotspot tracks. These tracks are divided into two subtracks: a Hawaiian-age subtrack (0-~50 Ma) and an Emperor-age subtrack (~50-~80 Ma); we find a significant acceleration in the Hawaiian-age subtrack but not in the Emperor-age subtrack for all three hotspot tracks. The dispersion of the ages suggests 1σ seamount age uncertainties of ≈1-2 Ma and ≈3 Ma respectively for the Hawaiian and Emperor subtracks. These 1σ uncertainties are an order of magnitude larger than the published analytical uncertainties (O(~0.2 Ma)). No significant motion between tracks is evident with negligible rates of motion for the Hawaiian-age subtracks and nominally ≈15 to 20 mm/a for the Emperor age subtracks

Maximum likelihood estimates of the location and age of the bend in all three hotspot tracks suggest a marginally significant difference between the nominal ages of 47.1±1.1 Ma for an instantaneous HEB and 50.1±2.3 Ma for an instantaneous LVB. Assuming the three hotspots share a common geologically instantaneous bend age, we determine a maximum likelihood age of 47.8±0.9 Ma, just slightly younger than the end of the EECO. Thus the onset of a new global tectonic regime and the onset of global cooling are nearly coeval.