School of GeoSciences

Tephra Analysis Unit

The Tephra Analysis Unit (TAU) is an internationally recognised centre for the electron probe microanalysis of volcanic glasses and melt inclusions. It is located at the School of Geosciences, University of Edinburgh The TAU has numerous clients from the UK and the rest of Europe, and South America.

Introduction

EPMA

The TAU provides a service to researchers and students from earth and environmental sciences and archaeology. It facilitates components of many research programmes each year, spanning applications in Holocene climate change, palaeoenvironmental reconstruction, physical volcanology and dating of cultural remains.

Other than the reliable identification of source volcanoes, the TAU can routinely measure concentrations of volatile elements F, Cl and S for studies of degassing and environmental impacts of eruptions.

The TAU has actively engaged in the development of improved methods for the microanalysis and preparation of tephras since the 1990s. More recent developments include analytical protocols for analysis of crypto-tephras with beam diameters as low as 3 microns without sodium loss (Hayward 2012), and preparation of crypto-tephras with grain sizes below 50 microns (Hall and Hayward, 2015).

Please do not hesitate to contact Chris Hayward to discuss working at the TAU.

EPMA COVID-19 UPDATE: The facility will be available as soon as safely possible. For any clients who are unable to travel in person to Edinburgh, the Facility Manager can analyse samples, provided with suitable detailed instructions from the client. Please contact Chris Hayward to discuss specific work.

Instrumentation

The TAU uses the world-class Cameca SX100 instrument of the electron probe microanalysis facility. This features five wavelength dispersive spectrometers, energy dispersive spectrometer, transmitted and reflected light, secondary and backscatter imagery. It is operated via Cameca’s Windows-based Peak Sight software. Off-line data processing using Peak Sight is available.

The SX100 is configured in a way that is ideal for tephra analysis. Most importantly, it has large analysing crystals for analysis of volatlle elements Na and K, preventing their mobilisation during analysis. Other large crystals enable rapid and sensitive analysis of trace elements including P and Ti to detection limits of the order of 70 - 80 ppm.

The SX100’s exceptional imaging capabilities include backscattered electron imagery, for identification and avoidance of crystals within glasses, and transmitted and reflected light microscope at magnifications between x100 and x900. The energy dispersive detector allows rapid discrimination between glass and mineral fragments.

 

 

Tephra

Secondary electron image of an approximately 10 x 15 micron crypto-tephra grain, after analysis. Beam diameter was 5 microns.

Plag and Mag

Backscattered electron image of plagioclase and magnetite crystals within a melt inclusion within a clinopyroxene of the Fimmvörduhals fissure eruption, Iceland, 2010.