Timing of volcanic, plutonic and geothermal activity at Ngatamariki, New Zealand

• Published in: Journal of volcanology and geothermal research Vol. 116; no. 3; pp. 201 - 214
• Main Authors: Arehart, G.B, Christenson, B.W, Wood, C.P, Foland, K.A, Browne, P.R.L
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.08.2002; Amsterdam Elsevier; New York, NY
• Subjects: Crystalline rocks; Earth sciences; Earth, ocean, space; Exact sciences and technology; geochronology; geothermal; Igneous and metamorphic rocks petrology, volcanic processes, magmas; New Zealand; Ngatamariki; New Zealand; Taupo volcanic zone; North Island; New Zealand; geothermal; geochronology; Ngatamariki; emplacement; andesites; activity; diorites; ignimbrite; Australasia; volcanic rocks; mica; chronology; igneous rocks; pyroclastics; secondary minerals; hydrothermal alteration; crystallization; plutonic rocks; sheet silicates; silicates; geothermal systems; Ar-40/Ar-39; dating; sericite; age
• ISSN: 0377-0273; 1872-6097
• DOI: 10.1016/S0377-0273(01)00315-8

Four 40Ar/ 39Ar dates on mineral separates from fresh and hydrothermally altered volcanic and plutonic rocks from the Ngatamariki geothermal field indicate that andesitic volcanism took place in the eastern portion of the Taupo Volcanic Zone (TVZ) prior to 1.2 Ma and probably considerably earlier. These data significantly extend the onset and duration of andesitic volcanism in the east-central TVZ over previous estimates. Intrusive activity is represented at Ngatamariki by a dioritic pluton, the only such pluton yet recognized in the entire TVZ. Hornblende from the pluton yields a crystallization age of near 550 ka. Hydrothermal alteration spatially associated with the pluton produced sericite of a similar age. Overlying and postdating the most intense hydrothermal alteration zone is the Whakamaru Ignimbrite (or its equivalent) which was emplaced at 330 ka. Two distinct geothermal systems may have been active at nearly the same site from 550 ka to present. The most intense activity occurred before 330 ka and was associated with emplacement of the Ngatamariki diorite. This was followed by the less intense system that is currently active. The geothermal regime at Ngatamariki has, therefore, probably been active intermittently for at least 550 ka.