Part 3. Present plate boundary and its evolution in the New Zealand region: Evolution of the India-Pacific plate boundary in North Island, New Zealand

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Abstract
The plate boundary is first clearly identifiable on land in New Zealand from tectonic activity and arc magmatism, at about 20 m.y.b.p. (this date is poorly controlled, and lies in the interval 24 to 19 m.y.). Subsequent evolution of the plate boundary is inferred from the history of the New Zealand magmatic arc, which migrated eastwards to yield a succession of five geographically separated volcanic arcs (Fig. 1). Volcanism began with an initial 'oceanic' phase of basic/intermediate activity erupting through a substantial graben (20?15 m.y.). It then evolved to 'continental' phases erupting through basement horst; these eruptions were initially andesiticdacitic (18 to 6 m.y.) and later rhyolitic/ ignimbritic/dacitic/andesitic/basaltic (6 m.y. to 0). The last phase has been accompanied by abundant mineralization. Sporadic, behind-arc volcanic activity, from 16 m.y.b.p., has been of two types: high-K andesites in the south, and basalts in the north.

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