Several samples from the rhyolitic lavas encountered in Hole 841 B in the Tonga Forearc were made available by A. Ewart for potassiumargon (K-Ar) dating in an attempt to constrain the age of the eruptions.The material was supplied in crushed form and consisted primarily of volcanic glass together with some microphenocrysts made up mainly of plagioclase and quartz. Plagioclase could not be separated in sufficient amount for dating, especially as the potassium content of the plagioclase was quite low (~0.055% K). Petrographic examination of the volcanic glass indicated that it was remarkably fresh: it was clear, unaltered, and essentially isotopic. Thus, it was decided to attempt to date the volcanic glass.

lambda e + lambda e' = 0.581 * 10-10/a; lamda beta = 4.962 * 10-10/a; 10K/K = 1.167 * 10**-4 mol/mol

Supplement to: McDougall, Ian (1994): Data report: Dating of rhyolitic glass in the Tonga forearc (Hole 841B). In: Hawkins, J; Parson, L; Allan, J; et al. (eds.), Proceedings of the Ocean Drilling Program, Scientific Results, College Station, TX (Ocean Drilling Program), 135, 923