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The Altiplano of southern Peru displays a large spectrum of Cenozoic potassic (K) and ultrapotassic (UK) mafic rocks that delineate two deep lithospheric mantle blocks that have undergone different depletion and enrichment events. Phlogopite lamproites indicate that the eastern Altiplano block is underlain by a metasomatized harzburgitic mantle of Paleoproterozoic to Archean age (depleted mantle age, [T.sub.DM] = 1130-2485 Ma; [[epsilon].sub.Nd] = -5.0 to -11.4; [sup.87]Sr/[sup.86][Sr.sub.i] = 0.7100-0.7159). Beneath the western Altiplano block, the presence of a younger ([T.sub.DM] = 837-1259 Ma; [[epsilon].sub.Nd] = +0.6 to -6.3; [sup.87]Sr/[sup.86][Sr.sub.i] = 0.7048-0.7069) metasomatized lherzolitic mantle is deduced from multiple occurrences of diopside-rich K-UK lavas (leucitites, leucite-bearing tephrites, olivine, and diopside trachybasalts). A third suite of young ( Keywords: Altiplano, Peru, potassic-ultrapotassic rocks, lithospheric mantle.

The high precision analyses of platinum-group elements (PGE) from upper-mantle lherzolites indicates that the Pd/Ir ratio, at 1.76, is considerably more than that of chonidritic meteorites. The mantle is heterogeneous in its PGE content, and the Pd and Rh content of the terrestrial mantle vary on the spatial scale up to nearly 100 km. The Pd/Rh ratio of undifferentiated meteorite is less than the Pyrenean lherzolites.