New Constraints on Plate Tectonic Puzzle of the SW Pacific

A long-standing problem in the tectonics of the southwest Pacific has been the lack of closure of the plate circuit linking the Antarctic, Australia, Lord Howe Rise, and Pacific plates in late Cretaceous and early Tertiary time [Molnar et al., 1975]. Avoiding unacceptable overlaps and underlaps in reconstructions of these plates requires invoking relative motion on one or more nebulous plate boundaries somewhere along the plate circuit, such as between East and West Antarctica, within West Antarctica [Stock and Molnar, 1987], or perhaps between the Lord Howe Rise and Challenger Plateau in the Tasman Sea [Lawver and Gahagan, 1994]. This problem is of more than mere local interest since the motion of the Pacific plate relative to the rest of the globe is constrained through its connection with West Antarctica.