Recognition of Santorini (Minoan) Tephra in Lake Sediments from Gölhisar Gölü, Southwest Turkey by Laser Ablation ICP-MS

Abstract

Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has been applied to the analysis of fine-grained volcanic ash shards separated from a tephra layer deposited by the mid-second millenniumBC“Minoan” eruption of Santorini or Thera in Holocene lake sediments from Gölhisar Gölü, a small intramontane lake in southwest Turkey. In this study we have used minor isotopes of two major elements, routinely determined by EPMA in tephrochronological studies, as the internal standard in LA-ICP-MS analyses. These are30Si and57Fe for fully quantitative and single internal standard multi-element calibration (so-called semi-quantitative analysis) respectively. The results show that the determination of trace elements by LA-ICP-MS is a quick and accurate method. Typical accuracies are better than ±20% and precision measured as the mean RSD (relative standard deviation) is better than ±15% for most petrogenetically significant trace elements. These levels of precision actually reflect within sample heterogeneity, as repeat analyses on the homogenous NIST612 glass standard show that instrument precision is typically ±5% for most elements. The level of accuracy and precision obtained during this study is quite acceptable in tephrochronological studies and provides us with the confidence to proceed to the analysis of single glass shards by using a modified, small spot laser ablation system.