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Rubidium and strontium concentrations and strontium isotopic compositions have been determined for 70 samples of basalt from 22 volcanoes in the Hawaiian Islands-Emperor Seamount volcanic chain. The mean Sr/Sr ratios for basalts of the tholeiitic suite range from 0.70316 to 0.70411 and have a mean value and standard deviation of 0.70369 ± 0.00028. Basalts of the alkalic suite show a range from 0.70290 to 0.70394 and have a mean value and standard deviation of 0.70344 ± 0.00026. In addition to the difference between these two suites, the variations in Sr isotopic composition within each suite indicate real differences in the Rb/Sr and Sr/Sr ratios of the source regions from which individual flows were derived. The isotopic composition of Sr in tholeiitic basalts erupted during the past 43 m.y., from Kilauea Volcano on Hawaii to the Hawaiian-Emperor bend, is relatively uniform; but Sr/Sr ratios decrease systematically from the Hawaiian-Emperor bend to 65-m.y.-old Suiko Seamount. This pattern may be related to the difference in age between the underlying crust and the volcano. There is essentially no correlation between Sr/Sr and Rb/Sr for basalts of the Hawaiian-Emperor chain. These data do not support the concept of a mantle isochron indicating a time when the source region for the basalts was established. The source regions for basalts of the Hawaiian-Emperor chain probably lie within the lithospheric plate; the Hawaiian hot spot or melting anomaly is probably an energy source that produced melting in the overlying plate. Variations in Sr isotopic composition within individual volcanoes and between volcanoes indicate that the source regions for basalt are quite heterogeneous in detail.

Rb-Sr Systematics of Basalts from the Hawaiian-Emperor Volcanic Chain