Description
European tephrochronology : fingerprinting footprintsMagmas that fuelled Plinian eruptions (0-80ka) across Europe and Iceland are preserved as lapilli and tephra in proximal and distal fall or flow deposits, as rims on proximal xenoliths, and as crypto-tephras. These juvenile glasses underpin a grain-specific geochemical approach to tephrochronology (>1000-2000km) because bulk clasts can be heterogeneous. We adopt a dual analytical strategy using LA-ICPMS for proximal/distal clasts (>50microns) and SIMS for thin, small distal shards (<50 microns). Tests on the same tephra clast show that both techniques produce identical data (r=0.99). Traditionally major-minor element data have been used to constrain silica saturation and mineral fractionation trends, but provenance solutions can be equivocal. The use of trace elements is more robust due to greater variability and the immobility of some elements (Nb, Zr, Ta). Correlations require consideration of a range of trace elements because chemically similar magmas can be erupted over variable timescales due to magma residency (e.g. Katla, Campi Flegrei). Examples of statistically valid continental-marine correlations include : Katla and Tindfjallajokull tephras and the North Atlantic Ash Zones I&II and the Vedde Ash of continental Europe; Campanian Ignimbrite & Biancavilla (Etna) tephras in distal sites in the Aegean, E. Europe, N. Africa. From a volcanological point of view our data indicates that widely dispersed ash (>1000-1500km) can originate from “fully convective” (First Plinian) and/or “collapse episodes” (Second Plinian). Overall the allocation of “time” to tephra-bearing lacustrine/marine cores (palaeoclimate proxy) and archaeological sites (human occupation) helps us investigate the causality between climatic change & human migration.
| Period | 27 Jun 2011 → 7 Jul 2011 |
|---|---|
| Event type | Other |
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