Geochemical fingerprinting of Australia’s youngest volcanoes: The Newer Volcanic Province, South Australia and Victoria

Abstract

Traces of volcanic tephra, known as cryptotephra can provide an important isochronous marker that allows sedimentary archives to be aligned in space and time. However, this use of cryptotephra requires an understanding of the unique chemical fingerprint of the glass shards that originate from a particular volcano. Subsequently, this study investigates how the geochemical composition of volcanic centres varies between volcanic centres using collected samples from 9 volcanoes within the NVP, SA and Victoria. Analysis of geochemical data was obtained through laser ablation ICP-MS, to augment previously analysed electron microprobe data for 7 of the 9 sites. This study also investigates the viability of trace element analysis of cryptotephra grains through laser ablation as a useful addition to the major oxide analysis that can be carried out by electron microprobe. Statistical models of linear regression analysis, regression trees and KS-tests, were employed to identify the degree to which the volcanoes studied can be discriminated according to their elemental composition, on the basis of their major oxides and trace elements. The experimental results indicate that a quantifiable difference in major and trace elemental composition can be determined for all volcanic centres analysed except samples obtained from Warrnambool. Subsequently, this study has successfully identified 8 volcanoes with tephra and crypyotephra that possess specific geochemical fingerprints.