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The 'Indo-Australian Plate' is an overarching name for two tectonic plates that include the continent of Australia and surrounding ocean extending northwest to include the Indian subcontinent and adjacent waters. It is subdivided into the Australian Plate and the smaller India Plate along a low-activity boundary. The two plates fused together between 50 to 55 million years age; prior to that time, they moved independently.
Depositional age of the Mount Barren Group on the southern margin of the Yilgarn Craton and zircon provenance analysis support the hypothesis that collisions between the Pilbara–Yilgarn and Yilgarn–Gawler Cratons assembled a proto-Australian continent approximately 1696±7 Ma (Dawson et al. 2002). [1]
India, 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 they were thought to have fused into a single plate. Recent research indicates that the plates are separating, however it will take some time to properly publicise this fact. [2], [3]
Recent GPS measurement in Australia confirms the plate's movement as being 35 degrees east of north with a velocity of 67 mm/yr. Note also the same directions and velocities for points at Auckland, Christmas Island and southern India. The slight change in direction at Auckland is presumably 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 subducting under the Australian Plate 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 convergent again, albeit in the opposite direction, with the Australian Plate subducting under the Pacific Plate to form the Puysegur Trench and Macquarie Ridge. [4]
The southerly side is a divergent boundary with the Antarctic Plate. The westerly side is subdivided with the India Plate that forms a boundary with the Arabian Plate to the north and the African Plate to the south. The northerly side of the Indian Plate is a convergent boundary with the Eurasian Plate forming the Himalaya and Hindu Kush mountains.
The north-east side of the 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.

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References

★ Dawson, Galvin C., Ian R. Fletcher, Bryan Krape, Neal J. McNaughton and Birger Rasmussen. (2002) "Did late Palaeoproterozoic assembly of proto-Australia involve collision between the Pilbara, Yilgarn and Gawler Cratons? Geochronological evidence from the Mount Barren Group in the Albany–Fraser Orogen of Western Australia." Precambrian Research, Vol. 118, Issues 3-4, 25 November, pp. 195-220.