Late Neogene motion of the Pacific Plate

Oceanic crust between 38°S and 65°S along the Pacific‐Antarctic ridge records a complete history of Neogene Pacific‐Antarctic motion. We have modeled magnetic stages corresponding to portions of isochrons 1, 2, 2A, 3, 3A, 4, and 5 from 17 high‐quality marine magnetic traverses of the ridge to determine the Neogene finite rotation poles for this plate pair. We chose to model velocities over time intervals of about 0.5 m.y. because this greatly increased the number of estimates of Pacific‐Antarctic plate velocity. Our analysis shows that a change in Pacific‐Antarctic relative motion occurred between chron 2A, 3.40 Ma, and the beginning of chron 3 time, 3.86 Ma. We used 203 estimates of Pacific‐Antarctic spreading velocity to calculate a 0–3.4 Ma and 3.86–10.3 Ma Euler pole. Combined with tracks of seamounts that record the passage of the Pacific plate over mantle plumes our data show that this change in relative motion corresponds to a change in the absolute motion of the Pacific plate with respect to the hotspot frame of reference. Using these Euler poles to calculate Pacific‐Antarctic‐Africa‐North America circuit Euler poles show that this recent change in Pacific plate absolute motion corresponds to a change from strike‐slip to transpressive motion along the coastal California Pacific‐North America plate boundary. Interestingly, this age of increased tectonism agrees in time with deformation in New Zealand and northern Japan.