HR: 1340h
AN: T53B-1318    [Abstracts]
TI: Oblique, ultra-slow Australian-Antarctic spreading mechanism explains lateral differences in transitional crust
AU: Whittaker, J
EM: j.whittaker@geosci.usyd.edu.au
AF: School of Geosciences, The University of Sydney, Building H11 Codrington St University of Sydney, Sydney, NSW 2006, Australia
AU: * Müller, R D
EM: dietmar@geosci.usyd.edu.au
AF: School of Geosciences, The University of Sydney, Building H11 Codrington St University of Sydney, Sydney, NSW 2006, Australia
AU: Goncharov, A
EM: Alexey.Goncharov@ga.gov.au
AF: Geoscience Australia, Cnr Jerrabomberra Ave & Hindmarsh Drive SYMONSTON, Canberra, ACT 2609, Australia
AB: A zone of transitional crust, up to 120 km in width, separates continental and oceanic crust on the Southern Australian and East Antarctic conjugate margins. Offshore southern Western Australia the transition zone is composed of the very rough E-W oriented ridges of the Diamantina Zone, while further east the crust changes to be composed of rough tilted basement blocks. A matching pattern exists in the conjugate Antarctic transition zone. The different types of transitional crust formed during a period of oblique northwest-southeast relative Australian-Antarctic plate motion that occurred until 50 Ma, ~30 million years longer than previously thought (Whitttaker et al., Major Australian-Antarctic plate reorganization at Hawaiian-Emperor bend time, Science, in press). During this period relative motion was slower and more oblique at the western end of the rift system compared to the east due to relative counter-clockwise motion of Australia. We have established a clear relationship between the rate and obliquity of plate motions and the roughness of the crust. The ultra-slow and very oblique motion in the west corresponds to the very rough E-W oriented ridges of the Diamantina Zone, while the slightly faster and less oblique motion in the east corresponds with the less rough, tilted fault block fabric of the central Australian Bight. Along the entire margin the boundary between the rough basement and normal ocean floor corresponds with the change in relative Aus-Ant plate motions from NW-SE to N-S at ~50 Ma.
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8157 Plate motions: past (3040)
DE: 9330 Australia
SC: Tectonophysics [T]
MN: 2007 Fall Meeting