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Book Chapter

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

By
Jacques Sayers
Jacques Sayers
Australian Geological Survey Organisation, GPO Box 378, Canberra, ACT 2601, Australia (e-mail: Jacques.Sayers@agso.gov.au)
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Philip A. Symonds
Philip A. Symonds
Australian Geological Survey Organisation, GPO Box 378, Canberra, ACT 2601, Australia (e-mail: Jacques.Sayers@agso.gov.au)
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Nicholas G. Direen
Nicholas G. Direen
Australian Geological Survey Organisation, GPO Box 378, Canberra, ACT 2601, Australia (e-mail: Jacques.Sayers@agso.gov.au)
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George Bernardel
George Bernardel
Australian Geological Survey Organisation, GPO Box 378, Canberra, ACT 2601, Australia (e-mail: Jacques.Sayers@agso.gov.au)
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Published:
January 01, 2001

Abstract

A region of 50-120 km 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 continent-ocean 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 Campanian time), later than the currently accepted 95 Ma 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.

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Contents

Geological Society, London, Special Publications

Non-Volcanic Rifting of Continental Margins: A Comparison of Evidence from Land and Sea

R. C. L. Wilson
R. C. L. Wilson
The Open University, UK
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R. B. Whitmarsh
R. B. Whitmarsh
Southampton Oceanography Centre, UK
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B. Taylor
B. Taylor
University of Hawaii, Hawaii
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N. Froitzheim
N. Froitzheim
University of Bonn, Germany
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Geological Society of London
Volume
187
ISBN electronic:
9781862394353
Publication date:
January 01, 2001

GeoRef

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