The Fraser fault in central Westland, New Zealand, and its associated Rocks

In central Westland a major fault, extending for 30 miles from Waitaha Valley in the south to Lake Kaniere in the north, and separating the “Gneissic and Dark Schist” and some Tuhua Granite, from Precambrian or Lower Paleozoic greywacke and Tertiary sediments, occurs several miles west of the Alpine Fault. Its possible extension southward is masked by Pleistocene and Recent gravels, and northwards it may extend another 30 miles along the west flanks of Mt Tuhua, Island Hill, and Hohonu Range to Mt Elliot. For the rocks between the Alpine and Fraser faults, which consist mostly of various mylonitic types and gneissic granite with smaller amounts of cataclasite, the new comprehensive Fraser Formation is proposed. It is suggested that most of the lateral movement that caused the mylonitisation occurred before the late Mesozoic, probably during the Rangitata Orogeny. The date of uplift is uncertain but the nature of lamprophyre intrusions suggests that, although up to 40,000 ft of uplift occurred in the Kaikoura Orogeny, an appreciable amount may also have occurred during the earlier orogeny.