A resolved mantle anomaly as the cause of the Australian-antarctic Discordance
We present evidence for the existence of an Australian-Antarctic Mantle Anomaly 7 (AAMA), which trends northwest-southeast (NW-SE) through the Australian-Antarctic 8 Discordance (AAD) on the Southeast Indian Ridge (SEIR), is confined to the upper 9 120 km of the mantle beneath the AAD, and dips shal...
| Main Authors: | , , |
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| Other Authors: | |
| Format: | Text |
| Language: | English |
| Published: |
2003
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| Subjects: | |
| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.399.8916 http://ciei.colorado.edu/geophysics/pubs/mhrpubs/pubs/2003/aad.pdf |
| Summary: | We present evidence for the existence of an Australian-Antarctic Mantle Anomaly 7 (AAMA), which trends northwest-southeast (NW-SE) through the Australian-Antarctic 8 Discordance (AAD) on the Southeast Indian Ridge (SEIR), is confined to the upper 9 120 km of the mantle beneath the AAD, and dips shallowly to the west so that it extends to 10 a depth of about 150 km west of the AAD. Average temperatures within the AAMA are 11 depressed about 100°C relative to surrounding lithosphere and suggest very rapid cooling 12 of newly formed lithosphere at the AAD to an effective thermal age between 20 and 13 30 Ma. A convective down welling beneath the AAD is not consistent with the 14 confinement of the AAMA in the uppermost mantle. In substantial agreement with the 15 model of Gurnis et al. [1998], we argue that the AAMA is the suspended remnant of a slab 16 that subducted at the Gondwanaland-Pacific convergent margin more than 100 Myr ago, 17 foundered in the deeper mantle, and then ascended into the shallow mantle within the past 18 30 Myr, cutting any ties to deeper roots. The stability of the AAMA and its poor 19 correlation with residual topography and gravity imply that it is approximately neutrally 20 buoyant. The thermally induced density anomaly can be balanced by bulk iron depletion |
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