What is potassium argon dating
The zone extends approximately 300 km north-northeast across the North Island from Ohakune to White Island (fig.1) and is up to 50 km wide in the central part, narrowing northward and southward. Ngauruhoe in the Taupo Volcanic Zone (TVZ), New Zealand, showing the main structural features.The vent lineation lies above this axis, which is considered to mark a major basement fracture that allows the intrusion of andesite dikes.1214 The Tongariro volcanics unconformably overlie late Miocene marine siltstones beneath Hauhungatahi, and a minimum age for the onset of volcanism is measured by the influx of andesite pebbles in early Pleistocene conglomerates of the Wanganui Basin to the south.1617 The oldest dated lavas from the Tongariro massif are hornblende andesites exposed at Tama Lakes between Ngauruhoe and Ruapehu, at 0.26±0.003 Ma; from Ruapehu, 0.23±0.006 Ma; and from Kakoramea, 0.22±0.001 Ma (potassium-argon dates).18 Tongariro itself is a large volcanic massif that consists of at least twelve composite cones, the youngest and most active of which is Ngauruhoe.A broad division has been made into older (20 There is a north-northeast alignment of the younger vents of Tongariro, particularly evident between Te Mari and Ngauruhoe.Eruptions from a central 400 m diameter crater have constructed the steep (33°) outer slopes of the cone.34 The Taupo Volcanic Zone, a volcanic arc and marginal basin of the Taupo-Hikurangi arc-trench (subduction) system,5 is a southward extension on the Tonga-Kermadec arc into the continental crustal environment of New Zealand’s North Island.
The Ngauruhoe area was accessed from State Highway 47 via Mangateopopo Road. Care was taken to ensure correct identification of each lava flow and that the samples collected were representative of each flow and any variations in textures and phenocrysts in the lavas.
As this interval is long in comparison with the secular variation of the direction of the geomagnetic field, in a given volcanic province the direction of natural thermoremanent magnetization is a unique characteristic of each cooling unit.
Ash-flow sheets investigated include the Stone Cabin Formation, the tuff of Pancake Summit, the Windous Butte Formation, the Needles Range Formation, the Bates Mountain Tuff, and the tuff of Clipper Gap, of Oliogcene to early Miocene age.
Directions of natural remanent magnetization are used to identify and correlate individual cooling units in the middle Tertiary ash-flow province in central and eastern Nevada and western Utah.
Potassium-argon dating indicates that the minimum time between eruptions of individual but genetically related ash-flow cooling units is on the order of 0.8 m.y.
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1).12 Though not as well publicized as its neighbor, Mt.