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U-Pb dating of zircon in hydrothermally altered rocks as a correlation tool: application to the Mangakino geothermal field, New Zealand

Wilson, C. J. N.; Charlier, B. L. A.; Fagan, C. J.; Spinks, K. D.; Gravley, D. M.; Simmons, S. F. and Browne, P. R. L. (2010). U-Pb dating of zircon in hydrothermally altered rocks as a correlation tool: application to the Mangakino geothermal field, New Zealand. Journal of Volcanology and Geothermal Research, 176(2) pp. 191–198.

DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1016/j.jvolgeores.2008.04.010
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Abstract

Recognition and correlation of rock units within geothermal fields is often hampered by high degrees of alteration that obscure primary mineralogies and lithological boundaries and preclude direct dating by radiometric techniques. Magmatic zircons are commonly present in silicic volcanic rocks, where zircon saturation was achieved and zircons crystallized up to the point of eruption. Young zircons are highly resistant to hydrothermal alteration and can yield a record of their crystallization ages in otherwise heavily altered rocks. Zircon crystallization age spectra have been obtained from three samples of cuttings and a core sample from ignimbrite penetrated in 3 drillholes up to ~3.2 km deep at the Mangakino geothermal field in New Zealand. The crystallization ages are similar between the drillcore and cuttings samples, indicating that downhole mixing of cuttings has not been important, and showing collectively that volcanic units of closely similar ages are represented between ~1.4 and ~3.2 km depth. This is despite apparent changes in the inferred primary volcanic lithology that had led to earlier inferences that multiple ignimbrites of contrasting age were present in this depth interval. Comparisons of zircon crystallization age spectra and inferred primary mineralogical characteristics from the drillhole samples with surficial ignimbrites that crop out west of Mangakino suggest that the boreholes have entered a >1.8-km-thick intracaldera fill of ignimbrite generated in the closely-spaced Kidnappers and Rocky Hill eruptions at ~1 Ma.

Item Type: Journal Article
Copyright Holders: 2008 Elsevier
ISSN: 0377-0273
Project Funding Details:
Funded Project NameProject IDFunding Body
Not SetNot SetMighty River Power
Not SetNot SetNew Zealand Tertiary Education Commission
Keywords: Zircon; U–Pb dating; Mangakino geothermal field; Taupo Volcanic Zone
Academic Unit/Department: Science > Physical Sciences
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID: 16189
Depositing User: Bruce Charlier
Date Deposited: 03 Feb 2012 09:47
Last Modified: 14 Nov 2012 12:12
URI: http://oro.open.ac.uk/id/eprint/16189
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