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

posted on 2023-05-28, 01:35 authored by Sayers, J, Symonds, PA, Nicholas DireenNicholas Direen, Bernadel, G
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.


Publication title

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


Geological Society special publication








School of History and Classics


Geological Society of London

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