Late Cenozoic volcanics from the northern and southern Andes have restricted Pb isotope compositions which appear unrelated to rock type or basement age. Although regional differences in 2°6Pb/204Pb exist between the two areas, the uniform enrichment in 207Pb and 208Pb in the lavas is likely to be due to Pb leached from sediments and the altered igneous rocks of the subducted slab, which have with time been well mixed into the mantle wedge above the slab.
In the central Andes, igneous rocks of Mesozoic and Cenozoic age have Pb isotope compositions which indicate varying degrees of interaction with both U- and Th-rich upper crustal rocks and with Th-rich but U-poor high grade gneisses exposed in the Arequipa massif.
KeywordsIsotope Composition Volcanic Rock Mantle Wedge Lead Isotope Composition Granulite Gneiss
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