Development of the Australian-antarctic depth anomaly

Abstract

The oceanic Australian-Antarctic Discordance (AAD) contains two unusual features: (1) N-S trending anomalously deep bathymetries and (2) rough basement morphologies in young ( <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. Copyright 2010 by the American Geophysical Union.