ISOTOPIC COMPOSITION OF LEAD IN SOME BASIC AND ULTRABASIC ROCKS FROM ALPS

Lead from several basic and ultrabasic rocks (peridotites, gabbros, amphibolites, eclogites) from the Alps has been extracted for determination of the isotopic composition. The leads from peridotites, gabbro and eclogite-although differing significantly in isotopic composition-lie quite close to a common growth curve with μ ≈ 8.9 for the Houtermans model (∼=8.3 for modern constants). This very low value- ordinary galena leads from adjacent regions have values of ≥ 9.4 (∼= 9.0 for modern constants)-seems to indicate that the source region of these rocks lies in the upper mantle. Trace lead from a small lense of peridotite and eclogite in the Pennide gneiss area (Alpe Arami), showing strong differences in concentration and isotopic composition for the two rock samples, fits the same growth curve also. © 1969.