A resolved mantle anomaly as the cause of the Australian-antarctic Discordance

• Main Authors: M. H. Ritzwoller, N. M. Shapiro, G. M. Leahy
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2003
• Subjects: Antarctic; Australian-Antarctic Discordance; Indian; Pacific; Southeast Indian Ridge; Antarc*
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.399.6532; http://ciei.colorado.edu/geophysics/pubs/mhrpubs/pubs/2003/3_old.pdf

We present evidence for the existence of an Australian-Antarctic Mantle Anomaly (AAMA) that trends northwest-southeast (NW-SE) through the Australian-Antarctic Discordance (AAD) on the Southeast Indian Ridge (SEIR), is confined to the upper 120 km of the mantle beneath the AAD, and dips shallowly to the west so that it extends to a depth of about 150 km west of the AAD. Average temperatures within the AAMA are depressed about 100 C relative to surrounding lithosphere and suggest very rapid cooling of newly formed lithosphere at the AAD to an effective thermal age between 20- 30 Ma. A convective down-welling beneath the AAD is not consistent with the confinement of the AAMA in the uppermost mantle. In substantial agreement with the model of Gurnis et al. (1998), we argue that the AAMA is the suspended remnant of a slab that subducted at the Gondwanaland-Pacific convergent margin more than 100 Ma ago, foundered in the deeper mantle, and then ascended into the shallow mantle within the past 30 Ma cutting any ties to deeper roots. The stability oft he AAMA and its poor correlation with residual topography and gravity imply that it is approximately neutrally buoyant. The thermally induced density