Astride A Plate Boundary
New Zealand is currently astride the convergent boundary between the Pacific and Australian Plates. The Pacific Plate is subducted beneath the Australian Plate from around Samoa and Tonga in the north, through the Tonga Trench, Kermadec Trench, and Hikurangi Trough to the east of the North Island of New Zealand, down to Cook Strait, and the Marlborough Sounds and Kaikoura region. Through most of the South Island, the plates slide past each other, with slight obduction of the Pacific Plate over the Australian Plate, forming the Alpine Fault and Southern Alps. From Fiordland south, the Australian Plate subducts under the Pacific Plate forming the Puysegur Trench.
Over time, the position of the plate boundary has altered. Around 23 Ma, the convergent plate boundary formed Northland. Around 10 Ma, the Coromandel Ranges were formed. Activity has now moved further East, generating the Kermadec Ridge and Trench, and the Taupo Volcanic Zone. The Southern Alps are quite recent, only forming in the last 10 million years.
Read more about this topic: Geology Of New Zealand
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