Age determination using tephra as indicator; Detailed identification by trace-element composition of volcanic glass shards

Kagami, Saya   

Tephrochronology, which uses tephra to determine the chronostratigraphy of strata is important to understand geotectonic events for the last few Myr. We used EPMA and LA-ICP-MS for major and trace element concentration of volcanic glass shards in Znp-Ohta tephra and Tng tephra, of which major elements are similar to that of Znp-Ohta. These two tephras could be distinguished by rare earth elements pattern, in addition to the conventional indices. Identification of tephras by more than one indicator could distinguish tephra with similar characteristics and prevent incorrect stratigraphic correlation. It is necessary to improve the chemical composition database of wide-spread tephras including trace element compositions, and we plan to measure various wide-spread tephras by the method in this study.