Show simple item record  

dc.contributor.authorHopkins, Jenni L.en_NZ
dc.contributor.authorBidmead, Janine E.en_NZ
dc.contributor.authorLowe, David J.en_NZ
dc.contributor.authorWysoczanski, Richard J.en_NZ
dc.contributor.authorPillans, Bradley J.en_NZ
dc.contributor.authorAshworth, Luisaen_NZ
dc.contributor.authorRees, Andrew B. H.en_NZ
dc.contributor.authorTuckett, Fionaen_NZ
dc.date.accessioned2021-09-23T22:16:18Z
dc.date.available2021-09-23T22:16:18Z
dc.date.issued2021en_NZ
dc.identifier.citationHopkins, J. L., Bidmead, J. E., Lowe, D. J., Wysoczanski, R. J., Pillans, B. J., Ashworth, L., … Tuckett, F. (2021). TephraNZ: a major- and trace-element reference dataset for glass-shard analyses from prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation. Geochronology, 3, 465–504. https://doi.org/10.5194/gchron-3-465-2021en
dc.identifier.issn1871-1014en_NZ
dc.identifier.urihttps://hdl.handle.net/10289/14569
dc.description.abstractAlthough analyses of tephra-derived glass shards have been undertaken in New Zealand for nearly four decades (pioneered by Paul Froggatt), our study is the first to systematically develop a formal, comprehensive, openaccess reference dataset of glass-shard compositions for New Zealand tephras. These data will provide an important reference tool for future studies to identify and correlate tephra deposits and for associated petrological and magma-related studies within New Zealand and beyond. Here we present the foundation dataset for TephraNZ, an open-access reference dataset for selected tephra deposits in New Zealand. Prominent, rhyolitic, tephra deposits from the Quaternary were identified, with sample collection targeting original type sites or reference locations where the tephra’s identification is unequivocally known based on independent dating and/or mineralogical techniques. Glass shards were extracted from the tephra deposits, and major- and trace-element geochemical compositions were determined. We discuss in detail the data reduction process used to obtain the results and propose that future studies follow a similar protocol in order to gain comparable data. The dataset contains analyses of glass shards from 23 proximal and 27 distal tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 +- 12 cal yr BP) to the Hikuroa Pumice member (2.0 +- 0.6 Ma) from six or more caldera sources, most from the central Taupo Volcanic Zone. We report 1385 major element analyses obtained by electron microprobe (EMPA), and 590 trace-element analyses obtained by laser ablation (LA)-ICP-MS, on individual glass shards. Using principal component analysis (PCA), Euclidean similarity coefficients, and geochemical investigation, we show that chemical compositions of glass shards from individual eruptions are commonly distinguished by major elements, especially CaO, TiO2, K2O, and FeOtt (Na2+K2O and SiO2/K2O), but not always. For those tephras with similar glass major-element signatures, some can be distinguished using trace elements (e.g. HFSEs: Zr, Hf, Nb; LILE: Ba, Rb; REE: Eu, Tm, Dy, Y, Tb, Gd, Er, Ho, Yb, Sm) and trace-element ratios (e.g. LILE/HFSE: Ba/Th, Ba/Zr, Rb/Zr; HFSE/HREE: Zr/Y, Zr/Yb, Hf/Y; LREE/HREE: La/Yb, Ce/Yb). Geochemistry alone cannot be used to distinguish between glass shards from the following tephra groups: Taupo (Unit Y in the post-Oruanui eruption sequence of Taupo¯ volcano) and Waimihia (Unit S); Poronui (Unit C) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; and Kawakawa/Oruanui, and Okaia. Other characteristics, including stratigraphic relationships and age, can be used to separate and distinguish all of these otherwise-similar tephra deposits except Poronui and Karapiti. Bimodality caused by K2O variability is newly identified in Poihipi and Tahuna tephras. Using glass-shard compositions, tephra sourced from Taupo Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can be separated using bivariate plots of SiO2+K2O vs. Na2O/K2O. Glass shards from tephras derived from Kapenga Volcanic Centre, Rotorua Volcanic Centre, and Whakamaru Volcanic Centre have similar major- and trace-element chemical compositions to those from the MgVC, but they can overlap with glass analyses from tephras from Taupo and Okataina volcanic centres. Specific trace elements and trace-element ratios have lower variability than the heterogeneous majorelement and bimodal signatures, making them easier to fingerprint geochemically.en_NZ
dc.description.abstractAlthough analyses of tephra-derived glass shards have been undertaken in New Zealand for nearly four decades (pioneered by Paul Froggatt), our study is the first to systematically develop a formal, comprehensive, open-access reference dataset of glass-shard compositions for New Zealand tephras. These data will provide an important reference tool for future studies to identify and correlate tephra deposits and for associated petrological and magma-related studies within New Zealand and beyond. Here we present the foundation dataset for TephraNZ, an open-access reference dataset for selected tephra deposits in New Zealand. Prominent, rhyolitic, tephra deposits from the Quaternary were identified, with sample collection targeting original type sites or reference locations where the tephra's identification is unequivocally known based on independent dating and/or mineralogical techniques. Glass shards were extracted from the tephra deposits, and major- and trace-element geochemical compositions were determined. We discuss in detail the data reduction process used to obtain the results and propose that future studies follow a similar protocol in order to gain comparable data. The dataset contains analyses of glass shards from 23 proximal and 27 distal tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 ± 12 cal yr BP) to the Hikuroa Pumice member (2.0 ± 0.6 Ma) from six or more caldera sources, most from the central Taupō Volcanic Zone. We report 1385 major-element analyses obtained by electron microprobe (EMPA), and 590 trace-element analyses obtained by laser ablation (LA)-ICP-MS, on individual glass shards. Using principal component analysis (PCA), Euclidean similarity coefficients, and geochemical investigation, we show that chemical compositions of glass shards from individual eruptions are commonly distinguished by major elements, especially CaO, TiO2, K2O, and FeOtt (Na2O+K2O and SiO2/K2O), but not always. For those tephras with similar glass major-element signatures, some can be distinguished using trace elements (e.g. HFSEs: Zr, Hf, Nb; LILE: Ba, Rb; REE: Eu, Tm, Dy, Y, Tb, Gd, Er, Ho, Yb, Sm) and trace-element ratios (e.g. LILE/HFSE: Ba/Th, Ba/Zr, Rb/Zr; HFSE/HREE: Zr/Y, Zr/Yb, Hf/Y; LREE/HREE: La/Yb, Ce/Yb). Geochemistry alone cannot be used to distinguish between glass shards from the following tephra groups: Taupō (Unit Y in the post-Ōruanui eruption sequence of Taupō volcano) and Waimihia (Unit S); Poronui (Unit C) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; and Kawakawa/Ōruanui, and Okaia. Other characteristics, including stratigraphic relationships and age, can be used to separate and distinguish all of these otherwise-similar tephra deposits except Poronui and Karapiti. Bimodality caused by K2O variability is newly identified in Poihipi and Tahuna tephras. Using glass-shard compositions, tephra sourced from Taupō Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can be separated using bivariate plots of SiO2/K2O vs. Na2O+K2O. Glass shards from tephras derived from Kapenga Volcanic Centre, Rotorua Volcanic Centre, and Whakamaru Volcanic Centre have similar major- and trace-element chemical compositions to those from the MgVC, but they can overlap with glass analyses from tephras from Taupō and Okataina volcanic centres. Specific trace elements and trace-element ratios have lower variability than the heterogeneous major-element and bimodal signatures, making them easier to fingerprint geochemically.
dc.format.mimetypeapplication/pdf
dc.format.mimetypeapplication/octet-stream
dc.language.isoenen_NZ
dc.publisherCopernicus Publications on behalf of the European Geosciences Unionen_NZ
dc.relation.urihttps://doi.org/10.5194/gchron-3-465-2021en_NZ
dc.rights© Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License.
dc.subjecttephraen_NZ
dc.subjecttephra analysisen_NZ
dc.subjecttephrochronologyen_NZ
dc.subjecttephra correlationen_NZ
dc.subjectstatistical correlation of tephraen_NZ
dc.subjectelectron microprobeen_NZ
dc.subjectlaser abalationen_NZ
dc.subjectglass-shard analysesen_NZ
dc.subjectmajor elemental analysisen_NZ
dc.subjecttrace element analysisen_NZ
dc.subjectepmaen_NZ
dc.subjectLA-ICP-MSen_NZ
dc.subjectNew Zealanden_NZ
dc.subjecttephra databaseen_NZ
dc.subjectTephraNZen_NZ
dc.titleTephraNZ: a major- and trace-element reference dataset for glass-shard analyses from prominent Quaternary rhyolitic tephras in New Zealand and implications for correlationen_NZ
dc.typeJournal Article
dc.identifier.doi10.5194/gchron-3-465-2021en_NZ
dc.relation.isPartOfGeochronologyen_NZ
pubs.begin-page465
pubs.elements-id264929
pubs.end-page504
pubs.volume3en_NZ


Files in this item

This item appears in the following Collection(s)

Show simple item record