Australian Antarctic Discordance as a simple mantle boundary

• Published in: Geophysical research letters Vol. 37; no. 9
• Main Authors: Holmes, R. Chadwick, Tolstoy, Maya, Harding, Alistair J., Orcutt, John A., Morgan, Jason Phipps
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.05.2010; American Geophysical Union; John Wiley & Sons, Inc
• Subjects: Antarctica; Australian Antarctic Discordance; Boundaries; Earth sciences; Earth, ocean, space; Exact sciences and technology; Geophysics; Indian; Mantle; Marine; Marine geology; Melts; mid-ocean ridge; Plate tectonics; Ridges; Seismic engineering; Seismic phenomena; Seismology; Southeast Indian Ridge; Mid-Indian Ridge; Indian Ocean; polar regions; Pacific Ocean; Antarctica; Southeast Indian Ridge; East Pacific; Central Indian Ridge; Australia; IE, East Pacific; ISW, Indian Ocean, Southeast Indian Ridge; wavelength; models; seismic refraction; morphology; geologic sections; thickness; melting; global; mantle; Polar region; relief; melts; reduction
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2010GL042621

Several complex models require unique mantle conditions to explain the Australian Antarctic Discordance (AAD), an unusually deep and rugged section of the Southeast Indian Ridge (SEIR) between ∼120°–128°E. Seismic evidence suggests the AAD is instead the manifestation of two contrasting mantle domains converging along its eastern edge. Variations in axial morphology and flanking topographic relief along the SEIR arise as ridge segments to the west (Indian mantle) grade into a cooler melting regime while those to the east (Pacific mantle) are more magmatically robust. Seismic refraction data show crustal thickness decreases from the west into the AAD at a rate of 0.1 km/100 km, then rapidly increases from 4.8 ± 0.4 km to 7.3 ± 0.2 km across the eastern border. The AAD thus appears to be the terminal end of a long‐wavelength reduction in melt supply at what may be the simplest global example of a mantle boundary.