Lead isotope systematics in batholithic rocks of the Western and Coastal Cordilleras, Peru.

The Pb isotope results are presented on carefully selected and prepared feldspars from the Central batholith in the areas of the Arequipa Department and the Huaura River just north of Lima, the northern sector of the San Nicholas batholith between San Juan and Pisco, and from the Cordillera Blanca batholith and the stocks that share its trend. The data were evaluated in the Pb correlation diagram framework established by previous workers. Conclusions reached are: 1) there is a spatial association between the occurrence of a Precambrian basement component of Pb in the Phanerozoic intrusives and extrusives of Precambrian granulites and gneisses, 2) the dominant Pb component in all super-units appears to have come from a (time-adjusted) isotopically homogeneous reservoir very similar to that identified for Quaternary ores and volcanic and plutonic rocks in Central Chile, which might be enriched sub-continental mantle, and 3) assuming the same degree of fractional crystallization of Pb-rich phases in all pre- contaminated magmas, mixing models suggest that there is a greater Precambrian crustal component in the Plio-Pleistocene volcanics of southern Peru than in the Arequipa segment plutons of the same area.-J.M.H.