Aleutian Lead Isotopic Data: Additional Evidence for the Evolution of Lithospheric Plumbing Systems

Lead isotopic ratios and concentrations have been measured in lavas from the Aleutian volcanic centers of Adak (12) and Atka (12). Whereas lavas from Atka have very small Pb-isotopic ranges (206Pb204Pb = 18.78−18.86; 207Pb204Pb = 15.55−15.62; 208Pb204Pb = 38.31−38.52) those from Adak have ranges nearly twice as large (206Pb204Pb = 18.34−18.86; 207Pb204Pb = 15.47−15.63; 208Pb204Pb = 37.81−38.56). On lead-lead isotopic diagrams, Atka data form tight clusters whereas those from Adaak define a well-developed linear trend extending from the Atka field toward less radiogenic values. At a given 206Pb204Pb, the lavas from both islands plot in the MORB trend for 208Pb204Pb but Atka lavas plot above the MORB 207Pb204Pb-206Pb/204Pb trend and those from Adak fall both within and above the trend.