Using geochemistry as a tool for correlating proximal andesitic tephra: case studies from Mt Rainier (USA) and Mt Ruapehu (New Zealand)

Abstract

Volcanic hazards assessments at andesite stratovolcanoes rely on the assessment of frequency and magnitude of past events. The identification and correlation of proximal and distal andesitic tephra, which record the explosive eruptive history, are integral to such assessments. These tephra are potentially valuable stratigraphic marker beds useful to the temporal correlation and age dating of Quaternary volcanic, volcaniclastic and epiclastic sedimentary deposits with which they are interbedded. At Mt Ruapehu (New Zealand) and Mt Rainier (USA), much of the detail of the recent volcanic record remains unresolved because of the difficulty in identifying proximal tephra. This study investigates the value of geochemical methods in discriminating andesitic tephra. Our dataset comprises petrological and geochemical analyses of tephra that span the late Quaternary eruptive record of each volcano. Our data illustrate that andesitic tephra are remarkably heterogeneous in composition. Tephra compositions fluctuate widely over short time intervals, and there are no simple or systematic temporal trends in geochemistry within either eruptive record. This complexity in tephra geochemistry limits the application of geochemical approaches to tephrostratigraphic studies, beyond a general characterisation useful to provenance assignation. Petrological and geochemical data suggest that the products of andesite systems are inherently variable and therefore intractable to discrimination by simple geochemical methods alone. Copyright © 2006 John Wiley & Sons, Ltd.

The Middle Stone Age of the northern Kenyan Rift: age and context of new archaeological sites from the Kapedo Tuffs

“…This is in part due to the wide recognition of the many potential sources of withinsample compositional variation, which include instrumental error, postdepositional weathering and selective element leaching, heterogeneous batches of parent magma, the inclusion of older deposits during eruption and magma ascent, and reworking by fluvial or other processes (e.g., Hunt and Hill, 1993;Orton, 1996;Feibel, 1999a;Riehle et al, 2000;Donoghue et al, 2007). In general, the strongest correlations are those that show concordance between multiple independent datasets, including stratigraphic, fossil, chronological, and geochemical evidence.…”

Tephrochronology and its application: A review

“…Also, andesitic glass is more susceptible to weathering than rhyolitic glass, meaning it can become unsuitable for analysis for correlation purposes. Consequently, wide compositional ranges may occur (Nakagawa et al, 1999;Shane et al, , 2008bDonoghue et al, 2007;Turner et al, 2009). …”

Tephra without Borders: Far-Reaching Clues into Past Explosive Eruptions

“…Geochemical time-series studies on timescales of months to thousands of years typically address eruptive histories and magmatic evolution of individual volcanoes and mostly focus on proximal terrestrial tephra sequences (e.g., Smith et al, 2005Smith et al, , 2011aDonoghue et al, 2007;Óladóttir et al, 2008Hasegawa et al, 2011;Turner et al, 2011;Firth et al, 2014;Iverson et al, 2014;Schindlbeck et al, 2014;Fontijn et al, 2015;Ponomareva et al, 2015). On a longer time scale (thousands to millions of years), tephras are more readily preserved in nonerosive marine environments that are relatively close to active volcanoes.…”