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Development of the Australian-Antarctic depth anomaly

Whittaker, Joanne M. and Müller, R. Dietmar and Gurnis, Michael (2010) Development of the Australian-Antarctic depth anomaly. Geochemistry Geophysics Geosystems, 11 . Art. No. Q11006. ISSN 1525-2027. doi:10.1029/2010GC003276.

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The oceanic Australian-Antarctic Discordance (AAD) contains two unusual features: (1) N–S trending anomalously deep bathymetries and (2) rough basement morphologies in young (<~20 Ma) crust between 120°E and 128°E. Models generally attribute AAD formation to underlying cold and/or depleted upper mantle, but no model adequately accounts for all the anomalous attributes. We quantify anomalous basement roughness and basement depths utilizing new seismic reflection data, in combination with all available geophysical and geological observations. We find that the interaction of negative dynamic topography and crustal thickness variations results in the observed complex patterns of residual basement depths. Downwelling, caused by a sinking Mesozoic slab, is the most likely cause of the broad N–S trending residual depth anomalies, while overprinting by westward flowing, buoyant Pacific mantle resulted in the distinctive V-shaped eastern boundary of the AAD. The particularly large residual depths proximal to the Australian and Antarctic margins may be due to negative dynamic topography combined with thinned oceanic crust caused by ultraslow (<10 mm/yr) half-spreading rates and sampling of depleted subduction wedge contaminated mantle. Only oceanic basement aged <20 Ma is anomalously rough, a result of sampling of cool/depleted upper mantle material. Although oceanic crust older than 43 Ma may have sampled depleted mantle, the resulting oceanic basement is not anomalously rough likely because a melt volume controlled threshold of accretion-related roughness had already been reached due to ultraslow spreading rates. Our analysis reveals that the enigmatic roughness of the Diamantina Zone is mainly related to >45° spreading obliquities.

Item Type:Article
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URLURL TypeDescription DOIArticle
Müller, R. Dietmar0000-0002-3334-5764
Gurnis, Michael0000-0003-1704-597X
Additional Information:© 2010 American Geophysical Union. Received 12 July 2010; accepted 14 September 2010; published 10 November 2010. Figures 1–5 and 8–10 were created using GMT [Wessel and Smith, 1991], and Figures 6 and 7 were provided by Geoscience Australia from material provided by H. Stagg. M.G. was partially supported by NSF grant EAR‐0810303. We thank two anonymous reviewers for their helpful comments that greatly improved this paper, as well as the numerous people with whom we had helpful discussions, in particular H. Stagg (Geoscience Australia) and Simon Williams (University of Sydney).
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:oceanic accretion; mantle dynamics
Record Number:CaltechAUTHORS:20101213-141948692
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Official Citation:Whittaker, J. M., R. D. Müller, and M. Gurnis (2010), Development of the Australian-Antarctic depth anomaly, Geochem. Geophys. Geosyst., 11, Q11006, doi:10.1029/2010GC003276
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:21332
Deposited By: Tony Diaz
Deposited On:14 Dec 2010 23:54
Last Modified:29 Sep 2022 22:24

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