Modern New Zealand is world renown for being geological active with high mountains, frequent earthquakes, geothermally active areas and volcanoes. This is due to New Zealand's modern position on the boundary of the Australian and the Pacific Plates. The collision of these plates caused the Pacific plate to subduct underneath the Australian plate which carries the North Island. To the south of the South Island, the situation is reversed. The subduction zones in New Zealand are defined by trenches in the north and in the south and by the Alpine Fault which connects the two. This plate boundary has shaped the size of New Zealand and also defines its geology.

The islands forming New Zealand developed as part of a broader continental shield made up of Antarctica and Australia, forming part of Gondwana. Radiometric dating places the oldest rocks in New Zealand being at least 500 million years old.

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New Zealand's geological history can be divided into three main periods of sedimentation and three periods of mountain building (orogeny):

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1. The early sedimentation depositional phase, Cambrian to Devonian period (about 545 to 370 million years)

This was the period when the earliest major recorded rock formation was taking place, with the oldest rocks being found on the west coast of the South Island. It was the beginning of the area that is now known as New Zealand and was just off the coast of Gondwana.

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2. The Tuhua Orogeny, late Devonian to Carboniferous period (about 370 to 330 million years ago)

The long period of sedimentation ended with a period of pressure and uplift. Sea floor sediments were pushed up, folded and melted together to form mountains.

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3. The New Zealand Geosyncline, Carboniferous to Jurassic period (about 330 to 142 million years ago)

During this time enormous thicknesses of sediment accumulated, extending northwest from New Zealand to New Caledonia and south far below the South Island. The rocks of this second cycle of deposition have formed much of the foundations of New Zealand.

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4. The Rangitata Orogeny, Early Cretaceous period (about 142 to 99 million years ago)

During this orogeny, the previously deposited geosyncline (3) sediments were compressed and folded. Some seafloor was caught in the folding and later exposed when the orogeny had finished and erosional forces had levelled the mountains.

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5. The break-up, Cretacous to Oligocene period (99 to 24 million years ago)

This period is characterised by a long period of weathering and erosion of the mountains that were formed during the preceding orogeny, so much so that some places were reduced to so called peneplains, that is areas of low relief. About 85 million years ago a rift valley formed to separate the New Zealand region from the rest of Gondwana, resulting in the formation of a new ocean floor by means of sea floor spreading. This spreading resulted in the gradual formation of the Tasman Sea.

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6. The Kaikoura Orogeny, Miocene to Quaternary period (24 million years ago to modern)

Due to the new spreading ridge between Antarctica and Australia there was a build up of strain in the southwest Pacific crust that led to vertical and transcurrent fault movements. .