A proposed methodology for analyses of wide-ranged elements in volcanic glass shards in widespread Quaternary tephras

Abstract

The abundances of 58 elements from lithium to uranium of volcanic glass shards in 11 Quaternary widespread tephras of Japan and those of 4 tephras of North America have been analyzed using the laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) technique. The analytical values of the major components (SiO2, TiO2, Al2O3, FeO, MnO, MgO, CaO, and K2O) were systematically lower (<10%) than those of analyzed using electron microanalysis techniques in previous researches, whereas that Na2O tend to be ∼20% higher than those of previous researches using the electron-beam microanalysis technique. The higher values of Na2O obtained by LA-ICP-MS may result from the absence of the Na-loss phenomenon associated with the electron-beam analytical techniques. Most elements were analyzed with less than 20% of the relative standard deviations (RSDs), whereas some trace elements such as beryllium and some transition metals exhibit higher RSDs (up to ∼120%) in 5-repeated analyses on the single glass shard. The LA-ICP-MS technique can be reasonably available for quantitative analyses of the major elements in volcanic glass shards, in addition to the trace elements. The volcanic glass can be clearly distinguished from each other by the patterns of the element abundances. The element abundances and the patterns of the elements of the volcanic glass shards are helpful to more precise identification and correlation of tephra samples.