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Variation in rhyolitic magma composition linked with fractionation from a common source: insights from the Rotoiti eruption, Taupo Volcanic Zone, New Zealand
Stockholm University, Faculty of Science, Department of Geological Sciences.
Number of Authors: 1
2016 (English)In: International Geology Review, ISSN 0020-6814, E-ISSN 1938-2839, Vol. 58, no 16, 1967-1982 p.Article in journal (Refereed) Published
Abstract [en]

The Taupo Volcanic Zone (TVZ), New Zealand, is a well-documented volcanic arc characterized by explosive rhyolitic magmas within a series of caldera complexes that include the Okataina Volcanic Centre (OVC). New quartz melt inclusion and volcanic glass data from the 45ka caldera-forming Rotoiti eruption within the OVC are compared to published studies. The new data are characterized by low K2O (similar to 1.5-3.5wt.%), Rb (similar to 30-70 ppm), Sr (similar to 40-90 ppm), U (similar to 0.5-2.5 ppm), and Ba (similar to 300-1000 ppm) ranges that differ significantly from other OVC systems (similar to 3.0-4.5wt.% K2O, similar to 80-150 ppm Rb, and similar to 2.5-5.0 ppm U). Most interestingly, the Rotoiti melt inclusion data measured in this study show a decrease in Rb, Sr, and U, although the fractionation trends originate from the same source point as published OVC data. This progressive decreasing trend is interpreted as an interaction with a less enriched rhyolitic melt (represented by the low Rb, Sr, and U of glasses) during fractionation processes from a common TVZ source. The established model for TVZ rhyolites is that they are extracted from a middle or upper crustal source (mush' zone) prior to eruption. Adding to this model, new melt inclusion data suggest that all TVZ rhyolites are fractionated from this common TVZ source and, prior to eruption, the Rotoiti system was rejuvenated by this source (evidenced by the low REE glasses). Exactly what triggers the common TVZ source to fractionate remains unclear, but a proposed mechanism to account for this involves the successive melting of the upper crust by upwelling mantle induced by incremental subduction.

Place, publisher, year, edition, pages
2016. Vol. 58, no 16, 1967-1982 p.
Keyword [en]
Rotoiti eruption, melt inclusion, rhyolite, Okataina Volcanic Centre, Taupo Volcanic Zone
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:su:diva-134159DOI: 10.1080/00206814.2016.1196400ISI: 000381048300001OAI: diva2:1014899
Available from: 2016-10-03 Created: 2016-10-03 Last updated: 2016-10-03Bibliographically approved

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