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The structure of the continental margin off Wilkes Land and Terre Adelie coast, East Antarctica


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Colwell, J B, Stagg, H M J, Direen, NG and Bernardel, G 2005 , 'The structure of the continental margin off Wilkes Land and Terre Adelie coast, East Antarctica', in D K Futterer and D Damaske and G Kleinschmidt and H Miller and F Tessensohn (eds.), Antarctica: Contributions to global earth sciences. , Springer-Verlag, Berlin, Heidelberg, New York, pp. 325-338.

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In 2001 and 2002, the Australian Government acquired
approximately 9 000 km of high-quality geophysical data over the
margin of East Antarctica between 110–142° E that provide a sound
framework for understanding the geology of the region. The data
comprise 36-fold deep-seismic, gravity and magnetic data and nonreversed
refraction/wide-angle reflection sonobuoys recorded
along transects that extend from the lower continental slope out
to oceanic crust at a spacing along the margin of approximately
90 km. The continental slope is underlain by a major rift basin beneath
which the crust thins oceanwards through extensive faulting
of the rift and pre-rift sedimentary section and by mainly ductile
deformation of the crystalline crust. Outboard of the margin rift
basin, the 90 to 180 km wide continent-ocean transition zone is interpreted
to consist primarily of continental crust with magmatic
components that can account for the lineated magnetic anomalies
that have been interpreted in this zone. The thick sedimentary section
in the COT zone is floored by dense lower crustal or mantle
rocks indicating massive (>10 km) thinning of the lower and middle
crust in this zone. The boundary between the margin rift basin and
the COT is marked by a basement ridge which potential field modelling
indicates is probably composed of altered/serpentinised peridotite.
This ridge is similar in form and interpreted composition to a
basement ridge located in a similar structural position at the inboard
edge of the COT on the conjugate margin of the Great Australian
Bight. On both margins, the ridge is probably the product of
mantle up-welling and partial melting focussed at the point of
maximum change/necking of crustal thickness. Integrated deepseismic
and potential field interpretations point very strongly to the
boundary between unequivocal oceanic crust and largely continental
crust of the continent-ocean transition as lying in very deep water,
and considerably seaward of most previous interpretations (often
based on inadequate seismic data or magnetic data only). We
consider the continent-ocean boundary to be well-constrained from
124–131° E and unequivocal from 131-140° E, but open to debate in
the sector from 110-124° E. There is a strong degree of pre-breakup
symmetry between the conjugate margins of southern Australia and
East Antarctica east of about 120° E. In addition to the crustal symmetry,
there is also a strong correlation in seismic character between the
margins, which allows us to date the major uncon-formities as probably
of base Turonian, Maastrichtian and early Middle Eocene age.

Item Type: Book Section
Authors/Creators:Colwell, J B and Stagg, H M J and Direen, NG and Bernardel, G
Publisher: Springer-Verlag
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