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<p>The 1.8&#xa0;ka Taupō tephra is a key chronostratigraphic marker bed in terrestrial and marine environments in New Zealand. In proximal deposits, juvenile clasts from fall and ignimbrite units of the Taupō eruption display a distinctive narrow chemical range, with groundmass glasses having lower-silica (~ 74&#xa0;–&#xa0;76 wt.% SiO<sub>2</sub>, volatile free) than older eruptive units. In contrast, distal Taupō tephra deposits variably contain glasses that span a wider range of compositions (~ 74&#xa0;–&#xa0;79 wt.% SiO<sub>2</sub>), with a distinct cluster at ~ 78 wt.% SiO<sub>2</sub>. Higher silica glass shards are typically found in the fine ash component and become more common in deposits from the later, most explosive phases of the eruption. Through a systematic assessment of different depositional settings and dispersal axes, we demonstrate that the Taupō tephra contains significant proportions of glass shards recycled from earlier deposits, particularly the 25.5&#xa0;ka Ōruanui supereruption. Recycling of glass was facilitated by overlapping vent sites, the outstandingly explosive nature of the 1.8&#xa0;ka Taupō eruption and the fine-grained texture and kilometre-scale intracaldera thicknesses of the Ōruanui deposits. The mixed modal glass compositions found in multiple locations and depositional settings (including Antarctica) represent a unique duplicate chemical fingerprint for the Taupō tephra. Our study highlights that mixed tephra compositions can occur even when the eruption involves only a single unzoned magma body. These results emphasise the need for caution when interpreting tephra compositional fields from single tephra sites, or when inferring magmatic processes from glasses in distal ash deposits, without sound volcanological context.</p>

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Recycling of ash particles during highly explosive eruptions: multiple glass populations in the 1.8 ka Taupō tephra

  • 期刊论文

  • 发表日期：

    2025年12月4日

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  • Simon J. Barker,
  • Stephen B. Piva,
  • Colin J. N. Wilson,
  • David J. Lowe,
  • Bruce L. A. Charlier,
  • Alan R. Orpin

摘要

The 1.8 ka Taupō tephra is a key chronostratigraphic marker bed in terrestrial and marine environments in New Zealand. In proximal deposits, juvenile clasts from fall and ignimbrite units of the Taupō eruption display a distinctive narrow chemical range, with groundmass glasses having lower-silica (~ 74 – 76 wt.% SiO2, volatile free) than older eruptive units. In contrast, distal Taupō tephra deposits variably contain glasses that span a wider range of compositions (~ 74 – 79 wt.% SiO2), with a distinct cluster at ~ 78 wt.% SiO2. Higher silica glass shards are typically found in the fine ash component and become more common in deposits from the later, most explosive phases of the eruption. Through a systematic assessment of different depositional settings and dispersal axes, we demonstrate that the Taupō tephra contains significant proportions of glass shards recycled from earlier deposits, particularly the 25.5 ka Ōruanui supereruption. Recycling of glass was facilitated by overlapping vent sites, the outstandingly explosive nature of the 1.8 ka Taupō eruption and the fine-grained texture and kilometre-scale intracaldera thicknesses of the Ōruanui deposits. The mixed modal glass compositions found in multiple locations and depositional settings (including Antarctica) represent a unique duplicate chemical fingerprint for the Taupō tephra. Our study highlights that mixed tephra compositions can occur even when the eruption involves only a single unzoned magma body. These results emphasise the need for caution when interpreting tephra compositional fields from single tephra sites, or when inferring magmatic processes from glasses in distal ash deposits, without sound volcanological context.