Southeast Indian Ridge

There is an active submarine volcano, the 1,100 m (3,600 ft)-high Boomerang Seamount, 18 km (11 mi) north of Amsterdam Island near the SEIR.

Analyses of the isotope composition of basalts recovered from its caldera support that the ASP hotspot contributed to the formation of the southern Ninety East Ridge.

[17] Trending east-west between Australia and Antarctica, the SEIR traverses the Australian-Antarctic Discordance (AAD), a morphologically complex region overlying an area of mantle down-welling.

[18] Located midway between the ASP-Kerguelen and the Balleny-Tasmantid hotspots, the AAD overlies a region where cooler mantle temperatures have produced a thin oceanic crust and a rough topography with deep valleys.

[19] The AAD is found between 120° and 128° E and covers about 500 km (310 mi) of the SEIR which at this point is deep mid-ocean ridge at between 4,000–4,500 m (13,100–14,800 ft) in the centre of the Australian–Antarctic depression.

Located at 126°E, the AAD would thus mark the 40 km (25 mi)-long transition between Indian Ocean and Pacific MORBs (mid-ocean ridge basalts), a boundary that has been migrating westward during the past tens of million years.

The flanks of the SEIR are dominated by fracture zones perpendicular to the ridge and gravitational lineations oblique to the spreading direction and sometimes zigzag-shaped.

[23] In south-western Australia the Albany-Fraser Orogen formed during the Mesoproterozoic collision between the Australian Yilgarn and Antarctic Mawson cratons.

[24] Archaean and Paleoproterzoic rocks in the Kalinjala Mylonite Zone of the Eyre Peninsula, Australia, match those found in Terre Adelie in Eastern Wilkes Land, Antarctica.

[25] Faults in Tasmania–Victoria and Northern Victoria Land have been identified as Cambrian remains of the west-dipping subduction zone along the eastern margin of Gondwana.