Development of the North Island subduction system

Zealand began near the beginning of the Neogene, when the Tonga-Kermadec Subduc-tion System propagated southwards into the New Zealand continental crustal block, together with the southwards migration of the relative pole of rotation between the Pacific and Australian plates. Many geological and geophysical spects of the North Island, both on land and offshore, are in agreement with models of subduction systems from elsewhere. Several NE-trending zones can be distinguished: Taupo Volcanic Zone (volcanic arc), Axial Ranges (exposed part of arc massif), East Coast Depression (forearc basin), Coastal Ranges (structural high of subduction complex), continental shelf and slope (trough-inner-slope of subduction complex). A west-dipping Benioff zone underlies the volcanic arc and arc massif. A negative gravity anomaly coincides with the surface extension of the Benioff zone. However, no subduction trench exists below the negative gravity anomaly. Sensu stricto, Fhe Hikurangi Trough, to the east of the subduction complex, is not a subduction trench. The forearc basin and subduction complex are riding passively on top of the Pacific plate to the east of the Benioff zone. The forearc basin initially was shallow marine, bu