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Te Riu-a-Māui Zealandia

A map of the ocean floor surrounding New Zealand shows a very large roughly triangular continent known as Zealandia. This sunken landmass (the pale coloured area on the map) is mainly made of continental silica-rich volcanic and sedimentary rocks that originated along the margin of ancient Gondwanaland. They are quite different from the surrounding (blue) ocean crust, made mostly of silica poor, iron rich volcanic basalt.

New Zealand Continent map.

Until about 100 million years ago (Ma), Zealandia consisted of two parts attached to the landmasses of Australia and Antarctica. After their separation from Gondwana the two parts of Zealandia drifted about 6,000 km to the north, whilst rotating towards each other.

At about 5 Ma, they joined and formed the present appearance of Zealandia. On land the suture (join) between the two parts is marked by the Southern Alps.

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The line where the Australian and Pacific plates meet runs from the far south (bottom left), through the South Island and then north east of the North Island, extending all the way to Tonga and beyond (top right).

Because the plate boundary is an active collision zone, there are frequent earthquakes, volcanic eruptions and massive rockslides near to it, resulting in an ever present tsunami hazard for New Zealand.