Volcanology of New Zealand - Older Volcanism

Older Volcanism

Older remnants of volcanism are also found in several places around New Zealand. These were generally formed either when New Zealand still formed part of the Gondwana supercontinent, or while Zealandia was rifting away from the rest of Gondwana, although some have been emplaced in their current setting more recently. (New Zealand is the main part of the submerged microcontinent of Zealandia that currently emerges above the sea.)

A band of granitic intrusions covering over 10,000 km², the Median Batholith, stretches from Stewart Island through Fiordland, and again through the West Coast and Nelson after interruption by the Alpine Fault. This was produced between 375 and 105 million years ago in the course of subduction-related volcanism in a long mountain range along the Gondwanan coast somewhat like today's Andes. Two more batholiths, the Karamea-Paparoa and Hohonu Batholiths, are also found on the West Coast.

Basaltic lava flows, dikes, and tuff from fissure eruptions between 100 million and 65 million years ago, during Zealandia's separation from Gondwana, are found in Marlborough, the West Coast and offshore further west. Ultramafic intrusions are found in Marlborough and north Canterbury, including at the summit of Tapuae-o-Uenuku, the country's highest mountain outside the Southern Alps.

Rhyolitic ignimbrite from 85 million years ago is found in Otago at Shag Point and in the Kakanui Mountains.

The Hikurangi Plateau is an oceanic plateau on the Pacific Plate that attached to the Chatham Ridge after partially subducted under it, and is now subducting under the North Island. It likely formed in one of the world's largest volcanic outpourings, the greater Ontong Java event.

Ophiolites, volcanic deposits from the ocean floor, have been incorporated into the continental basement of New Zealand in the Dun Mountain Ophiolite Belt, found at both ends of the South Island, and in Northland.