Deposition and generation of multiple widespread fall units from the c. AD 1314 Kaharoa rhyolitic eruption, Tarawera, New Zealand

Sahetapy-Engel, Steve T.; Self, Stephen; Carey, Rebecca J.; Nairn, I. A.

doi:10.1007/s00445-014-0836-4

Cited by 16 publications

(13 citation statements)

References 42 publications

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“…Kaharoa deposits erupted from the Tarawera vent zone, comprise sub-plinian fall deposits, lava domes and associated pyroclastic flows with magma volume of 9.1 km 3 (Sahetapy-Engel et al, 2014). The rhyolite lavas and pumice contain an average of 11% crystals, comprising plagioclase (40-45%), quartz (40-45%), biotite (<5%), cummingtonite (<2 %), Fe-Ti oxides (<2%), and trace hornblende, in an vitric groundmass.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra-caldera rhyolite system, Okataina volcano

Shane

2015

Journal of Volcanology and Geothermal Research

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Section: Accepted Manuscriptmentioning

confidence: 99%

Contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra-caldera rhyolite system, Okataina volcano

Shane

2015

Journal of Volcanology and Geothermal Research

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“…Walker, 1980) but differences can be expected to occur 580 according to the azimuths of wind direction during an eruption and the number and degree of interconnectedness of magma bodies involved in the eruption (e.g. Walker, 1981;Kilgour and Smith, 2008;Sahetapy-Engel et al, 2014;Storm et al 2014;Rubin et al, 2016). The tephrochronological principle is much more likely to utilise distal unknown deposits, and therefore we suggest that using the distal signature (or signatures) maybe more appropriate for 585 correlation.…”

Section: Homogeneous Heterogeneous and Bimodal Samplesmentioning

confidence: 94%

“…Schneider et al, 2001) For example, the heterogeneous signature identified for the Kaharoa tephra agrees with previous findings for this eruption. Nairn et al (2004) and Sahetapy-Engel et al (2014) reported that tephra compositional variability within the Kaharoa deposits shows sequential tapping of a stratified magma 575 body coupled with syn-eruptive changes in dispersal patterns. In general, this is likely one of the reasons why some of the proximal tephra deposits analysed in this study have a more variable geochemical signature in comparison to those of their distal counterparts (Fig.…”

Section: Homogeneous Heterogeneous and Bimodal Samplesmentioning

confidence: 99%

TephraNZ: a major and trace element reference dataset for prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation

Hopkins

Bidmead

Lowe

et al. 2020

Preprint

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Abstract. Although 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 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 twenty-three proximal and twenty-seven distal tephra samples characterising 45 eruptive episodes ranging from Kaharoa (636 &pm; 12 cal. yrs BP) to the Hikuroa Pumice member (2.0 &pm; 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 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, FeOt (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, Okaia, and Unit L (of the Mangaone subgroup eruption sequence). Other characteristics can be used to separate and distinguish all of these otherwise-similar eruptives 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 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 geochemically fingerprint.

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“…Their mineralogy (plagioclase+quartz >> Fe-Ti oxides > 112 orthopyroxene+hornblende) is also typical of recently erupted magmas, although Kaharoa contains biotite and 113 minor cummingtonite, whereas in Rotoma cummingtonite is a major ferromagnesian mineral and biotite is 114 absent (any biotite in Rotoma is relict; Leonard et al, 2002;Nairn et al, 2004;Smith et al, 2005). 115 Kaharoa is the youngest rhyolitic eruption and the largest (~9 km 3 ) TVZ eruption in the last 1,000 116 years, with eruptive materials including both lavas and pyroclastics with SiO 2 = 75 -77 wt% (Leonard et al, 117 2002;Nairn et al, 2004;Sahetapy-Engel et al, 2014). The Kaharoa magmatic system has been modelled as a 118 stratified, sill-like (8 km x 1 km, >1 km in thickness) reservoir with three compositionally diverse and 119 individually homogeneous rhyolitic magmas: (1) T1, the first to erupt, (2) T2, the last to erupt and with higher 120 Zr and Sr relative to T1, and (3) T3, un-erupted rhyolite that mixed with basalt-derived residual melt (dacite) 121 to produce erupted rhyodacites (Nairn et al, 2004).…”

Section: Okataina Volcanic Centre and Sample Selection 89mentioning

confidence: 99%

The ion microprobe as a tool for obtaining strontium isotopes in magmatic plagioclase: A case study at Okataina Volcanic Centre, New Zealand

et al. 2019

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We investigated the potential of multi-collector secondary ion mass spectrometry (MC-SIMS) as a 15 tool for obtaining Sr isotopic compositions in plagioclase, a ubiquitous mineral in igneous rocks that serves as 16 a recorder of crystallisation history. MC-SIMS allows for high spatial resolution analysis (~12 μm in this 17 study) of isotopes, and therefore improves the temporal scale at which fluctuations in crystallization 18 conditions can be recognized, ultimately improving our understanding of rates of magmatic processes. 19Plagioclase crystals from two young rhyolitic deposits from two major eruptive complexes, Tarawera and 20Haroharo, of the Okataina Volcanic Centre in New Zealand were analysed. Results were corrected for matrix 21 effects using linear modelling of MC-SIMS data versus An contents, as well as 87 Sr/ 86 Sr ratios acquired via 22 laser ablation inductively-coupled plasma mass spectrometry (LA-MC-ICP-MS). Corrected MC-SIMS Sr 23 isotopic ratios had an average 2σ uncertainty of ± 0.0008 per spot, and were homogeneous in Okataina 24 plagioclase at high spatial resolutions. Average LA-MC-ICP-MS 87 Sr/ 86 Sr ratios of plagioclase from both 25 intra-caldera volcanic complexes (Tarawera 87 Sr/ 86 Sr = 0.7056 and Haroharo 87 Sr/ 86 Sr = 0.7054) suggest 26 similar magma sources and similar assimilation and fractional crystallization processes for the two complexes. 27Overall homogeneity of plagioclase (excluding relict cores) indicates no significant changes in contributions 28 (i.e., crustal assimilation, mafic influx) to the system during the majority of plagioclase crystal growth. 29 Furthermore, lack of 87 Sr/ 86 Sr ratio fluctuations in plagioclase rims suggest interaction between the resident 30 silicic magma and the intruding mafic magma that triggered the eruptions was largely limited to volatile and 31 heat transfer. Using appropriate standards and analysis, this MC-SIMS method can be used to detect short-32 lived, open-system events in magma reservoirs where differences in 87 Sr/ 86 Sr isotopic ratios are significant.

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Deposition and generation of multiple widespread fall units from the c. AD 1314 Kaharoa rhyolitic eruption, Tarawera, New Zealand

Cited by 16 publications

References 42 publications

Contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra-caldera rhyolite system, Okataina volcano

Contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra-caldera rhyolite system, Okataina volcano

TephraNZ: a major and trace element reference dataset for prominent Quaternary rhyolitic tephras in New Zealand and implications for correlation

The ion microprobe as a tool for obtaining strontium isotopes in magmatic plagioclase: A case study at Okataina Volcanic Centre, New Zealand

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