Australian Plate
My Blogs (olelog) are mainly based on my daily reading of earth science news. Here on whatonearth.olehnielsen.dk I try to weave some of the pieces together to a greater whole with added background info.

The onset of seafloor spreading west of Australia at ~130 Ma marks the breakup between India and Australia. Roughly at the same time, subduction east of Australia ceased. The break between Australia and Antarctica was the last event in the Gondwana breakup. It began about 80 million years ago when a deep rift valley formed along the southern edge of Australia; this widened to form the present Southern Ocean. Since then Australia has been moving steadily north at the rate of about 5 cm per year. Prior to 43 million yhears ago a triple junction formed north of the Ross Sea, accommodating motion between East and West Antarctica. At the same time spreading between India and Australia ceased and the northward motion of Australia accelerated as it separated from Antarctica. The Southeast Indian Ridge now completely separated the Australian and Antarctic Plates. At the same time spreading between India and Australia ceased and subduction north of Papua New Guinea was initiated.

Major plate tectonic events since the early Miocene (~20 Ma) include the breakup of the Indo-Australian plate, and various collisional processes and plate boundary reorganizations north and east of Australia. The sector of oceanic crust containing Macquarie Island, between Tasman Sea oceanic crust and continental crust of the Campbell Plateau, was generated from 39 to 10.5 million years ago at the Proto-Macquarie Spreading Ridge, that propagated from the Pacific/Antarctic spreading ridge. The Proto-Macquarie Spreading Ridge evolved with time from long ridge segments of NNE-trend to short ridge segments of E-trend in the vicinity of Macquarie Island and generated during the latest episodes of seafloor spreading. The overall trend of the Proto-Macquarie Spreading Ridge was NNE-SSW throughout and roughly coincided with the present day Macquarie Ridge. Plate reconstructions suggest coincident seafloor spreading and strike-slip movements at the Proto-Macquarie Spreading Ridge between 14 and 10.5 Ma. The present day Australian/Pacific plate margin is coincident with the Macquarie Ridge, an arcuate 2100 km long crustal fracture system connecting the Pacific/Antarctic and Indo-Australian/Antarctic spreading ridges with the Alpine Fault system in New Zealand.

Volcanoes in New Zealand result from the subduction of the Pacific Plate under the Australian Plate. South of the North Island the tectonic boundary between the Indian-Australian and Pacific plates changes to a transform fault. New Zealand straddles the boundary of the Australian and Pacific plates. Along New Zealand, the Australian plate moves to the northeast at a rate of 35 to 45 mm/yr relative to the Pacific plate. In the central South Island, this plate motion results in predominantly strike-slip movement along the Alpine Fault. In southwestern South Island, relative plate motion is accommodated by oblique subduction of the Australian plate along the Puysegur trench and deformation of the overriding Pacific plate inland of the trench. The Southern Alps of New Zealand result from this oblique plate convergence.

New Zealand tectonics map, USGS, USGS Earthquake Seismicity webpage

Australian plate treated in Olelog

p.m.

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