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Geological Setting

The New Zealand region lies in the southwest of the Pacific Ocean. It is a zone of active plate collision that is part of the Pacific Ring of Fire.

The oldest rocks were laid down up to about 125 million years ago when the ancient continent of Gondwanaland existed. These rocks, which today have become the underlying bedrock of most of New Zealand’s mountain ranges, were deposited as sediments and some volcanic rocks, in the ocean to the east of Gondwanaland.

A new phase began when the Tasman Sea opened up about 85 million years ago, and these ancient rocks were pushed away from their original source area (which itself became Australia and Antarctica). This breakaway mass of continental crust is called Zealandia by geologists. Although it was initially mostly land, it slowly sank underwater and by 23 million years ago was almost totally submerged.

The next phase involved the gradual appearance of the modern plate boundary, with the Pacific and Australian Plates pushing into each other in a north to south line through Zealandia. Subduction of the Pacific Plate in the north, uplift along the Alpine Fault and subduction of the Australian Plate to the South, has uplifted modern New Zealand out of the sea, with a much larger surrounding area of Zealandia still remaining below sea level.

Watch this short video of the tectonic evolution of New Zealand.