Obsidian floater washed up on a beach in the Chatham Islands: geochemical composition and comparison with other volcanic glasses: Tuhinga 27

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Obsidian floater washed up on a beach in the Chatham Islands: geochemical composition and comparison with other volcanic glasses: Tuhinga 27 (for print)

Obsidian floater washed up on a beach in the Chatham Islands: geochemical composition and comparison with other volcanic glasses: Tuhinga 27 (for download)

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NameObsidian floater washed up on a beach in the Chatham Islands: geochemical composition and comparison with other volcanic glasses: Tuhinga 27

AuthorsDr Foss Leach, Dr Hamish Campbell, Nelson Eby, Marcel Regelous, Rhys Richards, Steve Weaver

Publication date2016

Publication typeArticle

Overview

Tuhinga 25: 20-49

ABSTRACT: A large block of pumice with a thick layer of volcanic glass attached to one side was found on a beach in the Chatham Islands. The geochemical signature of the specimen was most unusual: it proved to be a peralkaline phonolite with a negative europium anomaly. Since there was no obvious eruptive event that might have been the source of the floating object, identification of its geographic source involved a series of steps that progressively narrowed in on fewer and fewer potential sources. This process eventually pointed most strongly to McDonald Island in the Antarctic region southwest of Australia. This was confirmed only after unpublished geochemical data for the island were found. The process of identification described could have wider application when trying to find the volcanic source of obsidian artefacts with greater certainty.

KEYWORDS: obsidian, pumice, Chatham Islands, McDonald Island, geochemistry, Pacific archaeology, sourcing model.