87Sr/86Sr ratios in seven seamount basalts from the northeastern Pacific Ocean range from 0.7022 to 0.7034 and correlate significantly with chemical composition as expressed by the ratio K2O/(K2O + Na2O). These basalts seem to be similar to oceanic island basalts in alkali element concentrations, 87Sr/86Sr and K2O/(K2O + Na2O) ratios suggesting similar mantle source materials, possibly least depleted in dispersed elements. However, in places, seamount basalts also appear to resemble ridge tholeiites. Large differences in 87Sr/86Sr and Rb/Sr ratios for the samples from the Cobb seamount appear to indicate isotopic variations in the source materials, perhaps resulting in the formation of different lava flows within the seamount.

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