Low-potash dacite drift pumice from the Coral Sea

Abstract

SUMMARY: Drift pumice collected in December, 1964, from the Herald Cays in the western Coral Sea is chemically and petrographically a dacite, unusually low in K₂O and with very calcic plagioclase. It is apparently identical to pumice washed ashore in Fiji in March, 1965; both collections are divisible into light and dark varieties on megascopic, optical and chemical criteria. This pumice is distinguishable from the widely distributed pumice of the 1962 South Sandwich eruption; it is considered to have originated along the Tonga-Kermadec ridge on the basis of available seismic and compositional data.