Regional variation of ⁸⁷Sr/⁸⁶Sr ratio in late Cenozoic volcanic rocks from southern Peru

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We determined the ⁸⁷Sr/⁸⁶Sr ratios of 53 late Cenozoic volcanic rocks collected in an area of 700km × 300km in southern Peru along the Central Andes volcanic arc. The measured ⁸⁷Sr/⁸⁶Sr ratios scatter largely, ranging from 0.7049 to 0.7082. The ratios roughly correlate with SiO₂ contents, suggesting that the source magma is contaminated by crustal materials during fractional crystallization process. The lowest value is obtained in a basaltic rock. Regional variation in ⁸⁷Sr/⁸⁶Sr ratios is observed. In the along-arc direction from northwest to southeast, the ratios increase, reach the maximum value near Arequipa City and then decrease in accordance with the change of descending mode of the Nazca plate. The maximum ⁸⁷Sr/⁸⁶Sr ratio is observed in the region where the simple subduction of the Nazca plate is being distorted.