Trace-element analysis of volcanic glass shards by laser ablation inductively coupled plasma mass spectrometry: application to tephrochronological studies

The trace-element composition of fine-grained (0.25-0.125 mm) volcanic glass shards in distal tephra beds has been determined using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Accuracy is within 15% for most elements and the precision, as defined by the mean relative standard deviation, is better than 20%. This is very acceptable for tephrochronological studies. The very small amount of glass ablated (∼80 μg) and the short time involved in a single analysis (∼2 min) means that contamination can be easily recognized in the presence of replicate analyses and a detailed definition of trace-element compositional variability of the glass can be obtained. The need to use another trace-element analytical method to obtain the internal standard, Ce in this study, is a disadvantage but preliminary work in progress suggests that ⁵⁷Fe can be used for this purpose. This would obviate the need to use another trace-element method because the major-element composition of glass shards, as determined by electron microprobe analysis, constitutes a routine part of tephra characterization studies.