Characterising volcanic glass sources in the Banks Islands, Vanuatu.(Research Report)

Abstract

In 2006 volcanic glass deposits on Vanua Lava and Gaua Islands were re-visited and systematically sampled. Twenty-nine source samples were analysed using EDXA-SEM and LA-ICP-MS with a focus on detecting possible intrasource variation. The results show both Banks Islands deposits are readily distinguishable from each other and from other sources in the region and their chemical compositions are highly homogenous. Surface survey of other prospective areas established that these two are the only volcanic glass sources in the Banks Islands.

Keywords: Western Remote Oceania, Obsidian, Provenance studies, Laser ablation ICP-MS, EDXA-SEM

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Due to its strategic location in the Western Pacific, Northern Vanuatu has acted as a crossroad between other archipelagos from the time of initial human colonisation. Although this island group is very important for the understanding of human colonisation of the Pacific, few archaeologists have visited it. Compared to the long successful history of volcanic glass provenance studies in the North-Western Pacific (Leach 1996; Ambrose 1978; Summerhayes 2003; Torrence et al. 1996), which identified and unambiguously distinguished major sources and their exchange systems (Bird et al. 1997; Duerden et al. 1987; Torrence 2004; Specht 2002; White 1996), little is known about the distribution of northern Vanuatu volcanic glasses (Ambrose 1976).

Initial research in the Northern islands of Vanuatu in the early 1970s indicated there were additional sources to the previously-located sources in Papua New Guinea and Western Polynesia (Ambrose 1976; Bird et al. 1981; Ward 1979). A small number of samples of Banks Islands material were analysed using XRF and PIXE-PIGME with characteristically high Al, Mn and Fe concentrations detected (Duerden et al. 1987).

Artefacts from the southern Solomon Islands and Fiji, which had similar elemental composition to these Vanuatu sources, were the basis for assuming there had been a regional exchange system (Kirch & Yen 1982; Hedrick 1980; Best 1984). This interpretation was complicated by the proposition that more than two sources of volcanic glass might be found in the Banks Islands (Smith et al. 1977). After analysis of geological maps (Ash et al. 1980; Mallick & Ash 1975) and field exploration with the help of local guides on six most likely islands of the Banks Islands group, two volcanic glass exposures were identified and sampled.