Pb- and Sr-isotopic data for subduction-related Late Cretaceous and Cenozoic granitoids of the coastal region and lowermost Pacific slope of the Western Cordillera of central Peru suggest that these granitoids are derived from an undepleted mantle source (OIB–type or enriched sub-continental). A depleted MORB–type mantle did not have a major role in the genesis of the magmas.

The mantle source appears to have changed slightly with time. The data suggest that the asthenospheric wedge was isotopically heterogeneous during the early stages of Coastal batholith emplacement. During this time, the subduction slab geometry changed from steeply to moderately dipping, and the...