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. Although analyses of tephra-derived glass shards have been undertaken in NewZealand for nearly four decades (pioneered by Paul Froggatt), our study isthe first to systematically develop a formal, comprehensive, open-accessreference dataset of glass-shard compositions for New Zealand tephras. Thesedata will provide an important reference tool for future studies to identifyand correlate tephra deposits and for associated petrological andmagma-related studies within New Zealand and beyond. Here we present thefoundation dataset for TephraNZ, an open-access reference dataset forselected tephra deposits in New Zealand. Prominent, rhyolitic, tephra deposits from the Quaternary were identified,with sample collection targeting original type sites or reference locationswhere the tephra's identification is unequivocally known based onindependent dating and/or mineralogical techniques. Glass shards wereextracted from the tephra deposits, and major- and trace-element geochemicalcompositions were determined. We discuss in detail the data reductionprocess used to obtain the results and propose that future studies follow asimilar protocol in order to gain comparable data. The dataset containsanalyses of glass shards from 23 proximal and 27 distaltephra 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 VolcanicZone. 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 eruptionsare commonly distinguished by major elements, especially CaO, TiO2,K2O, and FeOtt (Na2O+K2O and SiO2/K2O), but notalways. For those tephras with similar glass major-element signatures, somecan 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 fromthe following tephra groups: Taupō (Unit Y in the post-Ōruanuieruption sequence of Taupō volcano) and Waimihia (Unit S); Poronui (UnitC) and Karapiti (Unit B); Rotorua and Rerewhakaaitu; andKawakawa/Ōruanui, and Okaia. Other characteristics, includingstratigraphic relationships and age, can be used to separate and distinguishall of these otherwise-similar tephra deposits except Poronui and Karapiti.Bimodality caused by K2O variability is newly identified in Poihipi andTahuna tephras. Using glass-shard compositions, tephra sourced fromTaupō Volcanic Centre (TVC) and Mangakino Volcanic Centre (MgVC) can beseparated using bivariate plots of SiO2/K2O vs.Na2O+K2O. Glass shards from tephras derived from KapengaVolcanic Centre, Rotorua Volcanic Centre, and Whakamaru Volcanic Centre havesimilar major- and trace-element chemical compositions to those from theMgVC, but they can overlap with glass analyses from tephras from Taupō andOkataina volcanic centres. Specific trace elements and trace-element ratioshave lower variability than the heterogeneous major-element and bimodalsignatures, making them easier to fingerprint geochemically.

geochronology

TephraNZ: a major- and trace-element reference dataset for glass-shard analyses from prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation