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Nature of the continent-ocean transition on the non-volcanic rifted margin of the central Great Australian Bight


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Sayers, J, Symonds, PA, Direen, NG and Bernadel, G 2001 , 'Nature of the continent-ocean transition on the non-volcanic rifted margin of the central Great Australian Bight', in RCL Wilson and RB Whitmarsh and B Taylor and N Froitzheim (eds.), Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea , Geological Society special publication (187) , Geological Society of London, London, pp. 51-76.

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A region of 50- 120km width defines the continent-ocean transition (COT) in
the central Great Australian Bight. It is characterized by a thin apron of post-break-up sediments
overlying complexly deformed sediments and intruded crust bounded landward by a
basement ridge complex and oceanward by rough oceanic basement. Recently acquired
deep reflection and refraction seismic data have significantly enhanced understanding of
the COT and basement ridge. Modelled gravity and magnetic data, and features interpreted
from seismic data, are consistent with aspects of extensional and break-up models proposed
for the West Iberia margin. Many of the features and relationships observed beneath
the outer margin of the central Great Australian Bight can be explained by extension
within a lithosphere-scale 'pure-shear' environment involving four layers: brittle upper
crust and upper mantle, and ductile lower crust and lower lithospheric mantle. The COT is
interpreted to be underlain by extended continental lithosphere. Thus, the continentocean
boundary is unequivocally defined between oceanic crust and the COT and appears
to be associated with sea-floor spreading magnetic anomaly 33, indicating that break-up
and sea-floor spreading did not commence until c. 83 Ma (early Carnpanian time), later
than the currently accepted 95Ma age. The major part of the basement ridge complex is
probably a combination of serpentinized peridotites and mafic intrusions or extrusions
derived by mantle upwelling and limited partial melting. The magmatic products of this
process probably cooled during chron 34 producing a distinctive magnetic anomaly, but
one that does not relate to break-up and sea-floor spreading.

Item Type: Book Section
Authors/Creators:Sayers, J and Symonds, PA and Direen, NG and Bernadel, G
Publisher: Geological Society of London
DOI / ID Number: 10.1144/GSL.SP.2001.232.01.28
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