Hauraki Rift
Geology
The Hauraki Rift, a half-graben is a still active NeS-to NWeSE-striking rift-valley system in the North Island of New Zealand that produced the Firth of Thames and the Hauraki Plains. It is approximately 25 kilometres (16 mi) wide by 250 kilometres (160 mi) long. The rift valley is limited to the west by the line of the Firth of Thames Fault and to the east by the Hauraki Fault and the mountains of the Coromandel and Kaimai Range. The active intra-rift Kerepehi Fault in the southern portion of the Hauraki Rift is complex and has the potential for large earthquakes.[1]
Structure
Initially between 10 to 5 million years ago the rift developed in a back arc region to the now extinct Coromandel volcanos. It has a basement of mesozoic greywacke and argillite. [2] To the north the rift is filled with 2.5-3 km thick Tertiary and Quaternary terrestrial sediments and beyond Waiheke Island it opens up into an oceanic basin.[3] Early work suggested the northern boundary might come ashore in Northland, near Whangarei. Work using geolocation on the Hauraki Rift reveals a widening rate of 0.9 mm (0.035 in)/year although some of the raw data suggests that at the Te Poi end it might be up to 1.5 mm (0.059 in)/year[4] However in this region it is now dominated by the much more recent rift (2 million years old at most) of the Taupō Volcanic Zone (TVZ) to which it is off-set by 60 degrees. TVZ eruptive output of 240,000 years ago, being Mamaku ignimbrite from the Rotorua caldera has filled in the far southern extremes.
Geothermal activity
Thermal springs along the rift edges and center are found throughout the region with a heat output of the order of 6.5MW in total.[5]
Other Context
At the far side of the Coromandel Peninsula there is a parallel structure of Late Miocene/Quaternary origin extending north, that has been called the East Coromandel Rift.
References
- ^ Persaud, Mira; Villamor, Pilar; Berryman, Kelvin; Ries, William; Cousins, J.; Litchfield, N.; Alloway, Brent (2 Jan 2016). "The Kerepehi Fault, Hauraki Rift, North Island, New Zealand: active fault characterisation and hazard" (PDF). New Zealand Journal of Geology and Geophysics. 59 (1). doi:10.1080/00288306.2015.1127826.
- ^ Hochstein, Manfred P.; Ballance, Peter F. (1993). "Hauraki Rift: A young, active, intra-continental rift in a back-arc setting". South Pacific Sedimentary Basins. 2: 295–305.
- ^ Fromont, Ashleigh (2017). "A seismic investigation of the evolution and structure of the Kerepehi Fault, in the context of the Hauraki Rift, New Zealand".
- ^ Eccles, Jennifer; Hreinsdottir, Sigrun; Rowland, Julie (2019). "Structure and Activity of the Hauraki Rift" (PDF).
- ^ Hochstein, Manfred P.; Nixon, I.M. (1979). "Geophysical study of the Hauraki Depression, North Island, New Zealand" (PDF). New Zealand Journal of Geology and Geophysics. 22 (1): 1–19. doi:10.1080/00288306.1979.10422550.