Rhenium-osmium isotopic investigation of Java subduction zone lavas

Arc lavas from Java have low concentrations of osmium (from 0.10 to 17.18 p pt) and variable isotopic compositions (Os-187/Os-188 ratios between 0.241 and 3.704). Inverse relationships between isotopic compositions and concent rations are observed for two groups of samples with distinct ages and Pb co mpositions. These results reveal mixing processes between unradiogenic Os f rom the peridotitic upper mantle and two different radiogenic Os components , reflecting two different crustal contaminants or different proportions of subducted oceanic crust and sediments. Mixing relationships seen in single lavas indicate that radiogenic and unradiogenic Os-bearing phases can coex ist at the sample scale without isotopic equilibration. (C) 1999 Elsevier S cience B.V. All rights reserved.