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Degassing of the H2O-rich rhyolites of the Okataina Volcanic Center, Taupo Volcanic Zone, NZ


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Johnson, ER, Kamenetsky, VS, McPhie, J and Wallace, PJ 2011 , 'Degassing of the H2O-rich rhyolites of the Okataina Volcanic Center, Taupo Volcanic Zone, NZ' , Geology, vol. 39, no. 4 , pp. 311-314 , doi: 10.1130/G31543.1.

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The Taupo Volcanic Zone (TVZ), New Zealand, is the most active region of rhyolitic volcanism on Earth, with >50 rhyolitic eruptions and ∼780 km3 of magma erupted in the past 60 k.y. Here we use analyses of quartz-hosted melt inclusions from eight eruptions in the Okataina Volcanic Center (OVC) of the TVZ to constrain magmatic volatile contents, pressures, and temperatures of quartz crystallization, and degassing of H2O, Cl, and minor CO2 from the rhyolitic magmas. The OVC melt inclusions trapped volatile-rich melts with ≤6 wt% H2O and ≤0.27 wt% Cl. Our data indicate that vapor-saturated crystallization of quartz occurred at low temperatures (760–805 °C) over a wide range of pressures (50–200 MPa). For some eruptions, variations in volatiles and major and trace elements provide evidence for simultaneous crystallization and partial loss of H2O, Cl, and CO2 into a vapor phase. Using the combination of melt inclusion and pumice glass volatile contents, we calculate minimum volatile emissions of ∼3 × 1011 to 8 × 1012 kg H2O and ∼7 × 109 to 4 × 1010 kg Cl during the OVC eruptions. We estimate that emissions from the smaller volume (<13 km3 magma) OVC rhyolitic eruptions would have been equivalent to ∼15%–40% of the yearly global arc flux of H2O and ∼10%–50% of the global arc flux of Cl, whereas the large-volume (≥100 km3) Rotoiti eruption ca. 60 ka would have been equivalent to >100% of the global arc H2O flux and as much as 90% of the global arc Cl flux. These results underscore the importance of individual magmatic provinces in creating large temporal variations in global arc volatile fluxes to Earth's hydrosphere

Item Type: Article
Authors/Creators:Johnson, ER and Kamenetsky, VS and McPhie, J and Wallace, PJ
Journal or Publication Title: Geology
ISSN: 0091-7613
DOI / ID Number: 10.1130/G31543.1
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First published online March 8, 2011 Copyright © 2011 Geological Society of America

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