An inter-laboratory comparison of the electron probe microanalysis of glass geochemistry

Tephrochronology commonly relies upon grain-discrete analysis of glass shards to reveal the subtle geochemical differences between tephras from past explosive volcanic eruptions. The use of electron probe microanalysis for this purpose is widely accepted by tephrochronologists. It is widely recognised that both precision and accuracy must be maximised, and that rigorous standardisation procedures must be followed. In this paper the performances of seven northern European electron microprobe centres are compared, using a geochemically homogeneous obsidian secondary standard. The results reveal that a number of tephra-oriented probe centres could benefit from exercises similar to the programme outlined within. In particular, it is evident that a number of these centres undertaking tephrochronological investigations have generated geochemical data that may be inadequate in terms of distinguishing between tephras. Inaccuracy in the determination of sodium is seen to be the main difficulty. In recent years the application of distal tephrochronology to stratigraphical problems in the northern European Quaternary record has become increasingly common. Geochemical standardisation is essential at an early stage in the development of a regional tephrochronological framework and, we hope, exercises such as presented here will encourage the production of reliable tephra geochemical data. Copyright (C) 1996 INQUA/Elsevier Science Ltd