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Central volcanic sedimentary basement rocks

Cnetral Volcanic Sedimentary Basement Map

The ancient plate boundary that existed through New Zealand between 300 and 100 million years ago is known from belts of distinctive rocks that occur in Southland and west Otago and that reappear in the hills behind Nelson and are again visible in western Waikato. The zone extends more than 1200 km.

One of the belts is the remains of a 275 million year old volcanic arc that eroded into another distinctive sedimentary belt. A third belt is a strip of ocean floor made of low (mafic) and very low silica (ultramafic) volcanic rocks. The ultramafic rocks are distinctive; they are conspicuous as the bare red-brown Dun Mountain-Red Hills near Nelson and Red Mountain-West Dome of west Otago. The ocean floor was scraped off and incorporated into a major collision zone at the plate boundary around 270 million years ago.

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