QM5 Rotorua
The Rotorua 1:250 000 geological map covers 24 800 km2 of the Bay of Plenty, Waikato, Hawke's Bay, Gisborne and Manawatu-Wanganui regions in the North Island, New Zealand.The Hauraki Plains and Kaimai Range extend into the northwest quadrant of the map and the Hauhungaroa and Rangitoto ranges are close to the western margin. The Urewera ranges and Waikaremoana hill country in the east are separated from these by a NNE-trending belt of volcanoes, lakes, volcanic plateaus and grabens of the Taupo Volcanic Zone and Taupo Rift.
Offshore, the 23-30 km wide continental shelf slopes gently to water depths of 120-150 m; it is surrounded by a number of volcanic islands, the largest of which are Motiti, Moutohora (Whale) and White (Whakaari) islands. The heads of the submarine Tauranga and White Island canyons extend into the map area from beyond the continental shelf.
Complexly deformed Mesozoic sedimentary rocks underlie the entire area. Rocks of the Jurassic Manaia Hill Group of the Waipapa (composite) terrane form the western hill country and are probably juxtaposed against Torlesse (composite) terrane beneath volcanic deposits of the TVZ. Kaweka terrane is the westernmost of the Torlesse terranes exposed, and it is separated from the Early Cretaceous Pahau terrane (Waioeka petrofacies) to the east by either the Whakatane Melange or Whakatane Fault.
East of the Whakatane Fault, sub-vertical and deformed rocks of Pahau terrane are overlain by gently dipping, little-deformed, Early Cretaceous to Paleogene marine sandstone and mudstone, the oldest of which is only 5-14 million years younger than the underlying basement rocks.
A short but intense period of deformation, uplift and erosion was associated with the amalgamation of Kaweka and Pahua terranes and the formation of the Whakatane Melange. In the Late Cretaceous to Paleogene periods, the Tinui and Mangatu groups were deposited during a period of plate boundary quiescence.