Geographical Extent
The Indian subcontinent, Meganesia (Australia, New Guinea, and Tasmania), New Zealand, and New Caledonia are all fragments of the ancient supercontinent of Gondwana. Seafloor spreading separated these land masses from one another, but as the spreading centers became inactive the land masses fused into a single plate.
Recent GPS measurement in Australia confirms the plate's velocity of 67 mm/yr at 35 degrees east of north . Note also the same directions and velocities for points at Auckland, Christmas Island and southern India. A slight difference in local direction at Auckland is presumed due to a slight buckling of the plate there, where it is being compressed by the Pacific Plate.
The southeasterly side is a complex but generally convergent boundary with the Pacific Plate. The Pacific Plate is subducting under the Australian Plate, which forms the Tonga and Kermadec Trenches, and the parallel Tonga and Kermadec island arcs. It has also uplifted the eastern parts of New Zealand's North Island.
The continent of Zealandia, which separated from Australia 85 million years ago and stretches from New Caledonia in the north to New Zealand's subantarctic islands in the south, is now being torn apart along the transform boundary marked by the Alpine Fault.
South of New Zealand the boundary becomes a transitional transform-convergent boundary, the Macquarie Fault Zone, where the Australian Plate is beginning to subduct under the Pacific Plate along the Puysegur Trench. Extending southwest of this trench is the Macquarie Ridge.
The southerly side is a divergent boundary with the Antarctic Plate called the Southeast Indian Ridge (SEIR). The westerly side is a transform boundary with the Arabian Plate called the Owen Fracture Zone, and a divergent boundary with the African Plate called the Central Indian Ridge (CIR). The northerly side of the Indo-Australian Plate is a convergent boundary with the Eurasian Plate forming the Himalaya and Hindu Kush mountains.
The northeast side of the Indo-Australian plate forms a subducting boundary with the Eurasian plate on the borders of the Indian Ocean from Bangladesh, to Myanmar (formerly Burma) to the south-west of Indonesian islands of Sumatra and Borneo.
The subducting boundary through Indonesia is not parallel to the biogeographical Wallace line that separates the indigenous fauna of Asia from that of Australasia: the Eastern islands of Indonesia lie mainly on the Eurasian Plate, but have Australasian-related fauna and flora.
Read more about this topic: Indo-Australian Plate
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