The Plate Motion Circuit Relating the Motion of the Pacific Plate to the Continental Plates

The position of the Pacific plate relative to the continental plates during Cenozoic and Late Cretaceous time has important global tectonic and geodynamic implications. Two main approaches have been used: (1) assuming fixed hotspots and (2) the plate reconstruction circuit through Antarctica. Here we review evidence that can be used to test the veracity of each approach.

Recent additions of high precision paleomagnetic poles to the Pacific plate apparent polar wander path from analyses of skewness of marine magnetic anomalies (e.g., Ritchey et al., this meeting) allow an updated test of the two plate motion circuits. Preliminary analysis of the circuit through Antarctica continues to indicate a paleomagnetic misfit that increases with age during the Cenozoic up to a maximum of ~7-8 degrees at ~50 Ma. Preliminary analysis of the fixed hotspot circuit indicates a misfit up to ~5 degrees that also tends to increases with age.

Wessel & Conrad (2019) also present potential evidence of a flaw in the circuit through Antarctica. They estimated the lateral motion of the Hawaii and Louisville hotspots relative to a deep mantle reference frame by comparing their observed tracks with those predicted from the motion of Africa relative to Indo-Atlantic hotspots combined with the plate motion circuit through Antarctica. Their reconstructions indicate that both the Hawaiian and Louisville hotspots moved hundreds of kilometers northward (with varying amounts of east-west motion) between ~80 to 60 Ma. If true, it conflicts with the hypothesis that the Hawaiian hotspot moved rapidly southward through the mantle over the same time interval, as proposed by some researchers.

If the hotspot circuit is flawed, motion between hotspots is the main explanation. If the plate circuit through Antarctica is flawed, (1) intraplate deformation. (2) unrecognized diffuse oceanic plate boundaries (e.g., Gordon & Stein, 1992), (3) motion between East and West Antarctica not localized across mid-ocean ridge segments, and (4) horizontal extension across large expanses of submerged continental area in the south Pacific (e.g., Sutherland et al., 2020) may have caused the plate-circuit flaw.