Geologic Setting of the Hydrothermal Systems of the North Island
1992. "Geologic Setting of the Hydrothermal Systems of the North Island", Active and Extinct Hydrothermal Systems of the North Island, New Zealand, Stuart F. Simmons, Patrick R.L. Browne, Robert L. Brathwaite
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A simplified geologic map of the North Island is shown in Figure 1. The oldest rocks which form the basement are of late Paleozoic to Mesozoic age. The New Zealand lithosphere only began to develop as a separate crustal entity in the late Cretaceous-early Tertiary when it broke away from the Gondwana supercontinent as the Tasman Sea opened (Sporli, 1987). Much of the geology of this continental fragment, which extends from New Caledonia to the Campbell Plateau, is obscured by the fact that about 70% of it is submerged (Fig. 2).
New Zealand's Cenozoic history relates to its proximity to a major active boundary between the Indian and Pacific plates (Figs. 3 and 4). Accurate reconstruction of the plate boundaries for most of this era is difficult, although several versions are published (e.g. Cole and Lewis, 1981; Ballance et al., 1982; Brothers, 1984; Walcott, 1987). In the following summary, we focus on the products of arc magmatism and closely related hydrothermal activity (Fig. 5). We start with the present situation.