Cenozoic and Late Cretaceous Apparent Polar Wander of the Pacific Plate: Implications for True Polar Wander and Global Plate Motion Circuits

The apparent polar wander (APW) path of the Pacific plate during Cenozoic and Late Cretaceous time has important paleogeographic, global tectonic, geodynamic, and paleoclimatic implications. Here we present recent progress on our assessment of Pacific plate APW with a focus on new poles determined from analysis of the skewness of marine magnetic anomalies due to seafloor spreading, which produces high precision paleomagnetic poles.

Our recent and new results include paleomagnetic poles for chron C24r (57–54 Ma; Woodworth et al. 2023), chron 21n (48−46 Ma; Woodworth et al. in preparation), chron 27r (63−62 Ma; Gaastra et al., in preparation), and chron 30n−31n (69−66 Ma; Ritchey et al., in preparation).  The new chron 24r pole extends the northward progression of the 69–58 Ma track in the previously determined Pacific plate apparent polar wander path beyond the southern end of the 46–10 Ma track, which is now extended by our chron 21n pole.  That the two tracks overshoot one another implies either a brief interval during which the Pacific plate moved substantially and rapidly southward relative to a mantle reference frame or to an episode of true polar wander (TPW, the re-orientation of the solid Earth relative to the spin axis).  The reconstructed plate geometry and relative plate motions are inconsistent with ancient plate driving forces having been capable of driving the plate southward.  Considering our results together with drill-core paleomagnetic paleolatitudes, we find that the most likely explanation is a ≈7° episode of TPW between ≈54 Ma and ≈50 Ma.  

The new high precision paleomagnetic poles for the Pacific plate, when compared with continental paleomagnetic results from Torsvik et al. (2012) reconstructed to a common frame of reference, allow an updated test of two plate motion circuits relating the Pacific plate to the circum-Pacific continents. Analysis of the plate-motion circuit through Antarctica (or through Australia) continues to indicate a significant paleomagnetic misfit that increases with age during Cenozoic time up to a maximum of ≈7−8° at ≈50 Ma. Analysis of the fixed hotspot circuit indicates a smaller insignificant misfit of up to ≈5° that also increases with age.

If the plate circuit through Antarctica is flawed, as indicated by the paleomagnetic results, any or all of the following may have contributed to the flaw: (1) intraplate deformation (cf., Kreemer & Gordon, 2014), (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).