Lead Isotope Systematics in Batholithic Rocks of the Western and Coastal Cordilleras, Peru
Lead isotope ratios have been determined on plutonic rocks of various compositions and ages from the San Nicolás, Coastal and Cordillera Blanca Batholiths in the Western and Coastal Cordilleras, Peru. The data have been evaluated in the Pb correlation diagram framework established by previous workers from Pb isotope determinations on the Precambrian Mollendo and Charcani granulitic gneisses, volcanic and plutonic rocks, and ores of southern Peru and central Chile.
Results indicate that the dominant Pb component in the plutonic rocks came from an isotopically homogeneous reservoir very similar to that identified by Tilton (1979) and Tilton and Barreiro (1980) for Quaternary ores, and volcanic and plutonic rocks in central Chile. The homogeneous reservoir might be enriched subcontinental mantle.
Additionally, the data also show that there is spatial association between the occurrence of a Precambrian basement Pb component in the Phanerozoic batholithic rocks and exposures of the Precambrian granulitic gneisses. Precambrian basement Pb is detected in all samples from the San Nicolás Batholith and in those from the Arequipa segment of the Coastal Batholith. In contrast, samples from the Cordillera Blanca Batholith and associated stocks, and those from the Lima segment of the Coastal Batholith, which occur where Precambrian exposures are totally lacking, exhibit no detectable old crustal Pb component. However, the more felsic rocks in this group seem to have undergone high-level mixing with crustal materials such as those found in the Jurassic to Upper Cretaceous marginal basin of Peru.
KeywordsPlutonic Rock Precambrian Basement Lead Isotope Ratio Mantle Reservoir Western Cordillera
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