Fission Track Ages of Deep Sea Glasses

Abstract

THE results of K : Ar measurements on several deep sea basalts^1,2 have been interpreted as indicating that the basaltic outflows on the crest of the East Pacific Rise are fairly young (<1 m.y.), that there is no systematic increase in age with distance from the Rise of three sea mounts studied, and that excess Ar is a frequent component of deep sea rocks. This excess of argon means that K : Ar ages on deep sea materials must be regarded as maxima until the extent of the excess is determined for each sample. The excess is probably produced by K-decay before eruption and is frozen into the rock as it cools. It is therefore associated with the hydrostatic pressure and with the rapidity of cooling of each sample (that is, with the glass content). The presence of glass in terrestrial (non-pelagic) rocks is usually thought to indicate the possibility of Ar loss (so that K : Ar ages of glassy materials may indicate only minimum ages) and so it was clear that an independent means of dating these rocks would help substantiate our interpretations.