Strontium isotope ratios in volcanic rocks from the south-eastern part of the Hellenic arc

Isotopic ratios of strontium in 9 volcanic rocks from the south-eastern part of the Hellenic arc range from 0.7037 to 0.7075. Within individual series of differentiation, there seems to be a correlation between Sr⁸⁷/Sr⁸⁶ and K₂O/SiO₂.All strontium isotope data for the Hellenic arc are reviewed. Comparable (but slightly smaller) ranges of Sr isotope ratios are found in other island arcs with continental basement. To explain the high values of Sr⁸⁷/Sr⁸⁶ ratio for the Hellenic arc, a selective addition of Sr⁸⁷ from the wall rock, and a process of assimilation involving water, perhaps from subducted sediments, are suggested. Since closely-spaced individual volcanic centres of similar ages have very different Sr isotope ratios, and since the range of Sr isotopic composition in individual centres is quite large, the variation is unlikely to be due to primary variation in mantle composition.