Uncertainties in the relative positions of the Australia, Antarctica, Lord Howe, and Pacific Plates since the Late Cretaceous

Abstract

We determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the Pacific and Antarctica plates, between Australia and Antarctica, and between the Lord Howe Rise and Australia. We combined these to yield a range of possible finite rotations describing the relative positions of the Pacific, Australia, Antarctica, and Lord Howe plates since the Late Cretaceous. If the Pacific‐Australia plate boundary has had its present trend since anomaly 18 time, reconstructions show 330±110 km of motion of the Pacific plate relative to the Lord Howe Rise since anomaly 5 time (9.8 m.y.), 420±110 km since anomaly 6 time (19.5 m.y.), 770±330 km since anomaly 13 time (35.6 m.y.), and 820±260 km since anomaly 18 time (43.0 m.y.). We examined two cases for times prior to anomaly 18, assuming a Late Cretaceous age of Australia‐Antarctica separation. If a plate boundary existed between the Lord Howe Rise and Pacific plates since the Late Cretaceous, with no plate boundary in Antarctica, reconstructions with the Lord Howe Rise fixed predict 610 ± 200 km of westward motion of the Pacific plate between the times of anomalies 31 and 22, followed by 260±100 km of northward motion between the times of anomalies 22 and 18. If the Lord Howe Rise was fixed to the Pacific plate until the Eocene, but a plate boundary existed between East and West Antarctica, reconstructions show very little motion across this boundary between the times of anomalies 31 and 22, followed by convergence between the times of anomalies 22 and 18. This second case also brings 70–80 m.y. paleomagnetic poles from the Pacific and East Antarctica plates into better agreement than the first case, but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated.Appendices are available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document J82‐01; $1.00. Payment must accompany order.