Cretaceous–Palaeogene Plate Boundary Evolution at the Pacific Margins of Zealandia and West Antarctica

Improved satellite‐derived gravity data support updated interpretations and models of ancient plate boundaries and plate motions affecting Zealandia and West Antarctica. The models combine to confidently resolve hundreds of kilometres of Late Cretaceous–Eocene motion between the Pacific and Lord Howe plates, confirming that plate circuit constructions via the Southeast Indian Ridge and Tasman Sea cannot resolve absolute Pacific plate motion. Calculated motion instead contextualises evidence for oblique collision and subduction east of Lord Howe Rise and, less confidently, transtension followed by transpression at a proto‐Alpine Fault plate boundary in Aotearoa New Zealand. Southwards, a diffuse or unstable Palaeogene plate boundary produced scattered faults and narrow basins in the outer Ross Sea before Australian–Antarctic plate motion focussed on a mid‐ocean ridge segment east of the Balleny Fracture Zone by 54 Ma. Trends of fracture zones in the Amundsen and Bellingshausen seas and off Chatham Rise infer the Bellingshausen plate is a product of ~87 Ma fragmentation of the Phoenix plate by pivoting subduction. New calculations of Bellingshausen–Antarctic displacements permit interpretation of the Antarctic margin in the Amundsen Sea as a site of collision and subduction that transitioned around 71 Ma to a wide continental rift zone in the east and, further west, a more focussed rift that evolved to a mid‐ocean ridge.