Authors / CoAuthors
Stagg, H.M.J. | Borissova, I. | Direen, N.G. | Colwell, J.B. | Bernardel, G.
Abstract
The continental margin of East Antarctica between Dronning Maud and George V Lands shows no evidence of widespread breakup-related volcanism, other than adjacent to the southern Kerguelen Plateau, and it therefore constitutes one of the largest tracts of non-volcanic rifted margin on the planet. The integrated interpretation of deep-seismic, velocity and potential field data acquired in 2001/02 shows that there are first-order structural variations between the two main sectors of this margin. In the west, the Enderby Land margin formed by the separation of Greater India from Antarctica, commencing in the Valanginian (ca. 131 Ma). Seawards of a major basement fault zone underlying the continental slope, deep-seated continental crust is characterised by high-angle brittle faulting; seismic data provide little information on the style of the deeper crustal deformation. The other prominent structural features of this margin are a sharp continent-ocean boundary (COB), characterised by an oceanwards step-up in the basement level of up to 1 km, and an earliest phase of ocean crust that is distinctive for its rich internal reflection fabric and strong Moho reflection. Potential field modelling indicates that the gross margin structure is relatively simple, and that both the continental and oceanic crusts have behaved as a semi-rigid plate that has been depressed landwards by the thick (4-9 km) post-rift sediment loading. In the east, the Wilkes Land margin formed during the separation of Australia and Antarctica, commencing with very slow seafloor spreading in the early Campanian (ca. 83 Ma). This margin is dominated by the broad and highly structured transition from the attenuated continental crust inboard on the margin, to the mechanically extended and largely amagmatic oceanic crust that formed during the initial seafloor spreading. From inboard to outboard across this zone, the structuring is characterised by: ? plastic and brittle deformation of the lower continental crust and upper mantle; ? a ridge of interpreted serpentinised peridotite that can be traced along strike on the margin for a distance of at least 800 km; ? a sedimentary basin outboard of the ridge that appears to be underlain by fragments of crystalline continental crust; and ? a COB between mechanically extended continental and oceanic crust that is complex and not readily delineated. The structures of the Wilkes Land margin are very similar to those on the conjugate southern Australian margin, indicating that at least the final stage of rifting between Antarctica and Australia was inherently symmetrical. The wide differences between the structural styles documented on the Enderby and Wilkes Land margins indicate that tectonic processes forming non-volcanic rifted margins may differ significantly depending on a range of factors that may include pre-existing heterogeneities in the continental crust, the thermal regime and the pre-breakup intra-plate stress regime.
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nonGeographicDataset
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60527
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- External PublicationAbstract
- ( Theme )
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- continental margins
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- AQ
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2003-01-01T00:00:00
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