Basalts being erupted in the Pacific Ocean Basin vary in Sr isotopic composition in a simple geographic pattern. 87Sr/86Sr increases away from the East Pacific Rise to very high values for islands in the south-central Pacific. The 87Sr/86Sr variations are almost certainly related to past segregation of Rb, K, and other large cations. The segregation process was probably incipient partial melting which resulted in various mantle zones being enriched or depleted. ?? 1978.
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Strontium isotopes in basalts from the Pacific Ocean basin