The Sr isotopic ratios of 39 glass and microcrystalline basalt samples along the Juan de Fuca Ridge and one glass sample from Brown Bear Seamount are at the lower end of the range for normal MORB; the average 87Sr/86Sr ratio is 0.70249 + or - 0.00014 (2sigma ). Although subtle variations exist along the strike of the ridge, the Sr isotopic data do not show systematic variation relative to the proposed Cobb hotspot. The isotopic data are inconsistent with an enriched mantle-plume origin for the Cobb-Eikelberg Seamount chain.-W.H.B.
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Sr isotopic variations along the Juan de Fuca Ridge.