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Chaotic topography, mantle flow and mantle migration in the Australian–Antarctic discordance

Nature volume 394, pages 637–644 (1998)Cite this article

Abstract

Oceanic crust formed over the past 30 million years at the Australian–Antarctic discordance (AAD) is characterized by chaotic sea-floor topography, reflecting a weak magma supply from an unusually cold underlying mantle. During the past 3–4 million years, however, a source of increased magma supply, coinciding with the known Indian–Pacific mantle isotopic boundary, has propagated into the eastern AAD, displacing the chaotic terrain and replacing it with normal sea floor. Pacific mantle reached the eastern boundary of the AAD at least 7 million years ago, but it was not until 3–4 million years ago that lavas derived from Pacific mantle were first erupted within the AAD. This long hiatus, combined with the ridge–transform geometry across the AAD boundary, constrains the locus of mantle migration to a narrow, relatively shallow region, directly beneath the spreading axis of the Southeast Indian ridge.

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Figure 1: Regional setting of the Australian–Antarctic Discordance (AAD).
Figure 2: Bathymetry of the eastern boundary region of the AAD to a maximum sea-floor age of ∼7 Myr.
Figure 3: Average sea-floor densities and depths calculated from gravity data along profiles on either side of the eastern AAD boundary.
Figure 4: Results of multibeam bathymetry, illuminated from direction 065°, for part of the AAD and the region to the northeast, extending to sea floor as old as 30 Myr.
Figure 5: Variation diagram showing the distinct Indian and Pacific fields defined by 208Pb/204Pb and 206Pb/204Pb isotopic ratios of lavas from the vicinity of the AAD.
Figure 6: Schematic diagrams illustrating the potentially complex relationships between a migrating mantle boundary and its expression at the sea floor, in the vicinity of a transform fault.

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Acknowledgements

This work was supported by the US NSF.

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Authors and Affiliations

  1. College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, 97331-5502, Oregon, USA

    David M. Christie & Brian P. West

  2. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, 02543, Massachusetts, USA

    Brian P. West

  3. Department of Geological Sciences, San Diego State University, San Diego, 92182-1020, California, USA

    Douglas G. Pyle & Barry B. Hanan

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Correspondence to David M. Christie.

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Christie, D., West, B., Pyle, D. et al. Chaotic topography, mantle flow and mantle migration in the Australian–Antarctic discordance. Nature 394, 637–644 (1998). https://doi.org/10.1038/29226

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