Fission-track age and trace element geochemistry of some Minden Rhyolite obsidians

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Abstract
Fission⋅track age determinations on obsidians from Mt. Young on Great Barrier Island, Hahei near Whitianga, Bowentown, and Mt. Maunganui give ages of 8⋅32, 7⋅80, 2⋅29, and 4⋅34 million years respectively. An approximate age of 7–8 million years has been estimated for Paku Island at Tairua. X-ray fluorescence analyses of trace elements of obsidian from the above localities and from the Alderman Islands show some distinct differences from rhyolites of the Taupo Volcanic Zone, namely a relative enrichment in the light rare earths, especially La, Ce, and Nd. Ce is strongly enriched; Rb is more, and Sr less abundant. The differences may be indicative of a different genesis.