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Nature of the continent–ocean transition zone along the southern Australian continental margin: a comparison of the Naturaliste Plateau, SW Australia, and the central Great Australian Bight sectors

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Direen, NG and Borissova, I and Stagg, HMJ and Colwell, JB (2007) Nature of the continent–ocean transition zone along the southern Australian continental margin: a comparison of the Naturaliste Plateau, SW Australia, and the central Great Australian Bight sectors. In: Imaging, Mapping and Modelling Continental Lithosphere Extension and Breakup. Special Publications (282). Geological Society of London, London, pp. 239-263. ISBN 9781862392281

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Abstract

We document the interpretation of three crustal sections from coincident deep seismic
reflection, gravity and magnetic data acquired on Australia’s southern margin: one section from
the Naturaliste Plateau and the Diamantina Zone; and two in the Great Australian Bight
(GAB). Interpretations are based on an integrated study of deep multichannel seismic, gravity
and magnetic data, together with sparse sonobuoy and dredging information.
All interpreted sections of the margin show a transition from thinned continental crust, through a
wide continent ocean transition zone (COTZ). In the GAB the transition is to slow sea-floor
spreading oceanic crust that dates from breakup in the Campanian (c. 83 Ma); in the Naturaliste–
Diamantina margin the earliest oceanic crust is undated. The COTZ on these margins is
geologically and geophysically complex, but interpretation of all data, including dredge hauls,
is consistent with the presence of a mixture of modified continental lower crust, breakup
related volcanics and exhumed continental mantle. Serpentinized detachment faults are not well
imaged, but have been inferred from high-amplitude magnetic signatures interpreted to arise
from magnetite associated with the hydration of peridotites. Alternative models for the structure
of the COTZ, involving either mafic underplating or aborted sea-floor spreading, have been
explored, but are considered unlikely on this margin.
Similarity in the final architecture of these margins has major implications for the nature of
rifting in the Southern Rift System, and may point to the entire 4000 km-long system being
non-volcanic in character.
Second-order differences in geometry and morphology of the two areas studied are unlikely to
be a function of strain rate. Instead, they probably reflect complexities owing to the multiple tectonic
events that occurred during final Gondwanide fragmentation. The most dramatic of these is
the impact of hotspot activity in the Kerguelen Plateau, which commenced some 50 Ma prior to
final breakup in that sector.

Item Type: Book Section
Publisher: Geological Society of London
Page Range: pp. 239-263
Identification Number - DOI: 10.1144/SP282.1
Date Deposited: 07 Sep 2010 05:35
Last Modified: 18 Nov 2014 04:12
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