Trace-element contents in ash samples from DSDP Leg 19 sediments

The age of each ash sample had been established previously by faunal criteria and had been confirmed by fission-track dating. Variations in the trace-element concentrations through the past 8 m.y. are clearly seen.

Seven of the ashes are older than 4 m.y., have low TiO2 contents, and have Sr concentrations of less than 200 ppm; they are thus similar to tholeiitic basalts of island arcs. Nine ashes are younger than 4 m.y. and are similar in trace-element content to andesite. Magmatic evolution of the Aleutian arc over the past 8 m.y. is clearly shown.