AuthorsD. R. Müller, C. Gaina and S. Clark
EditorsJ. J. Veevers
TitleSeafloor Spreading Around Australia
AfilliationScientific Computing
Project(s)No Simula project
Publication TypeBook Chapter
Year of Publication2000
Book TitleBillion-year Earth History of Australia and Neighbours in Gondwanaland
PublisherGEMOC Press
Place PublishedSydney, Australia
ISBN Number1-876315-04-0

The Australian Plate has undergone major changes in plate boundary geometry and relative plate velocities since the breakup of Gondwanaland. We illustrate the history of seafloor spreading around Australia by reconstructing gridded ocean floor ages and plate boundary configurations in a fixed Australian reference frame. In the Argo Abyssal Plain, seafloor spreading started at M25 dated as 154.3 Ma Late Jurassic (Oxfordian). The onset of seafloor spreading west of Australia at \~136 Ma marks the breakup between Greater India and Australia. Roughly at the same time, long-lived subduction east of Australia ceased, probably due to subduction of the Phoenix-Pacific spreading ridge, changing this plate boundary to a transform margin. A drastic change in spreading direction between the Indian and Australian plates from NW-SE to N-S occurred at about 99 Ma. Slightly later, at 95 Ma, rifting started between the Lord Howe Rise and eastern Australia, resulting in the opening of the Tasman Sea. The spreading direction between Australia and Antarctica changed from NW-SE to N-S at chron 27 (\~61 Ma), accompanied by the initiation of rifting between Broken Ridge and the Kerguelen Plateau. The Coral Sea started opening off NE Australia at the same time and the direction of spreading between the Pacific and Antarctic plates changed. Both the 99 Ma and 61 Ma events could have been caused by the stepwise subduction of the Neo-Tethyan Ridge; the 99 Ma event could also be due to a change in absolute motion of the Pacific Plate. Preliminary reconstructions to close the Pacific-Australian plate circuit based on recently collected geophysical data indicate that a tectonic event at about 43 Ma may mark the onset of renewed subduction east of Australia. Prior to 43 Ma a triple junction formed north of the Ross Sea, accommodating incipient motion between East and West Antarctica. At the same time spreading in the Wharton Basin between India and Australia ceased. Around Late Eocene, subduction of the Solomon Plate north of Papua New Guinea was initiated. Major tectonic events since 20 Ma include the breakup of the Indo-Australian plate, and various collisional processes and plate boundary reorganizations north and east of Australia.