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

Abstract

We determined the 87Sr/86Sr ratios of 53 late Cenozoic volcanic rocks collected in an area of 700km X 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 SiO2contents, 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 south-east, 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. © 1984, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.