ABSTRACT: Tasman Sea Plate Reconstructions and Passive Margin Formation

COFFIN, MILLARD F., Institute for Geophysics, University of Texas at Austin, Austin, TX, and JAMES B. COLWELL, Bureau of Mineral Resources (Australia), Canberra, Australian Capital Territory, Australia

Development of the Tasman Sea began in the Late Cretaceous as Australia and the Lord Howe Rise separated, and continued into the early Eocene. We use crustal age and fracture zone data to produce models of plate kinematics. Oceanic crust is dated by marine magnetic anomalies and limited Deep Sea Drilling Project core samples. Fracture zone trends indicating past spreading directions are interpreted from bathymetry, satellite (Seasat and Geosat) altimetry, and marine seismic, gravity, and magnetic data. Two rift models have been proposed for the development of the conjugate eastern Australian-Lord Howe Rise margins: (1) pure shear, nonaxial breaching of a rift valley, and (2) simple shear faulting. The first model suggests that the entire pre-breakup rift valley remained attached to th Lord Howe Rise as Australia separated, thus accounting for the paucity of rift valley structures within the eastern Australian continental margin. The second model equates southeast Australia with an upper plate margin, characterized by only minor structure and an uplifted hinterland. The Lord Howe Rise is considered a lower plate margin, with an intensely structured western side and a basement platform to the east. Recent multichannel seismic, gravity, and magnetic data acquired by the Australian Bureau of Mineral Resources documents a continuous, mid-slope, basement ridge, truncated landward in places by landward-dipping faults, along the southeast Australian margin. These and other crustal features constrain the structural development of the conjugate margins.

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)