QM2 Whangarei
The Whangarei 1:250 000 geological map covers about 8700 km2 of Northland, in the north of the North Island, New Zealand : a further 12 300 km2 of the adjacent offshore area is also included. The area is dominated by rolling dissected hill country up to about 400 m in elevation with a few isolated ranges reaching heights of up to 770 m. Areas of flat land are uncommon and usually restricted to narrow river valleys and coastal areas. Offshore, the sea floor slopes gently to the shelf edge, between 16 and 60 km from the coast and at a water depth of about 150 m. The map area is underlain by Permian to Early Cretaceous basement rocks belonging to four tectonostratigraphic terranes, though only two are exposed. In the east, greywacke and argillite of the Waipapa (composite) terrane crop out between Whangaroa Harbour and Te Arai Point, south of Mangawai Heads. In the northwest, metagreywacke and argillite with associated basalt, chert and volcanic sediments forming the Waipapa horst, are correlated with the Caples terrane. Concealed rocks of the Murihiku and Dun Mountain-Maitai terranes underlie southwestern parts of the map area.A predominantly transgressive sequence of Late Eocene to Oligocene coal measures, glauconitic sandstone, calcareous mudstone and limestone of the Te Kuiti Group unconformably overlies basement rocks. The Cretaceous and Paleogene units present onshore are mainly displaced sedimentary rocks and ocean floor volcanics, occurring in thrust-bounded units and melange of the Northland Allochthon, and were emplaced from the northeast in the Early Miocene. Mainly autochthonous Early Miocene, shelf to bathyal sedimentary rocks of the Waitemata Group underlie, overlie and are incorporated within the Northland Allochthon. Early Miocene Otaua Group sedimentary rocks unconformably overlie the allochthon in the northwest. Early Miocene subduction-related volcanism post-dating the Northland Allochthon produced several stratovolcano complexes, the eroded remnants of which are included in the Waitakere and Coromandel Groups.
Resources currently mined within the map area include rock aggregate, sand, high quality ceramic clay, and limestone. A high temperature geothermal field near Ngawha is utilised for geothermal power.