Potassium?argon ages from some of the Papua New Guinea highlands volcanoes, and their relevance to Pleistocene geomorphic history

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Abstract
Isotopic dating of 32 whole rock samples from seven of the Papua New Guinea highlands volcanoes shows a wide spread of ages ranging from 1.6 m.y., or possibly 1.9 m.y., to around 200 000 years B.P. These dates, with evidence of recent activity on two volcanoes, suggest that the highlands volcanic province has been active for at least the last 1.6 million years and that early volcanism was contemporaneous with intrusive igneous activity in the Star Mountains. Major eruptions of lavas, however, ceased at about 200 000 years B.P. and there is evidence from some of the volcanoes of apparent long breaks in activity. Glacial activity on Mt Giluwe may date back to 700 000 years, and certainly to about 300 000 years, indicating that altitudes of present magnitudes existed early in the Pleistocene, and that most of the volcanism probably postdates the uplift of the central ranges. Volcanism is also responsible for major changes in the highlands drainage system, but dating of these events is difficult. The isotopic ages are not always consistent with the erosional state of the volcanoes; this also suggests a long and complex history of volcanism in the highlands.
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