Geology of New Zealand - Northland and East Cape Allochthons

Northland and East Cape Allochthons

An allochthon is land that formed elsewhere, and slid on top of other land (in other words, the material of an enormous landslide). Much of the land of Northland and East Cape were created in this manner. Around 25-22 Ma, Northland and East Cape were adjacent, with East Cape near Whangarei. Northland-East Cape was an undersea basin. Much of the land that now forms Northland-East Cape was higher land to the Northeast (composed of rocks formed 90-25 Ma). The Pacific-Australian plate boundary was further to the Northeast, with the Pacific Plate subducting under the Australian Plate. Layers of rocks were peeled off the higher land, from the top down, and slid Southwest under the influence of gravity, to be stacked the right way up, but in reverse order. The last rocks to be slid across were slabs of oceanic crust, mainly basalt. Widespread volcanic activity also occurred (23-15 Ma), and is intermixed with the foreign rocks. East Cape was later separated from Northland and moved further south and east to its present position.