Dating Neovolcanic Ocean Ridge Basalts

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Obtaining the ages of the basalts in mid-ocean ridge neovolcanic zones has been a vexing problem. The principal investigator will develop a radiometric technique that uses observed disequilibrium between Ra226 and its parent Th230 to determine the ages of yound mid-ocean ridge basalts less than about 8000 years old. The usual approach in geochronology is ton moralize concentrations of the daughter isotope to a stable or very long-lived isotope of the same element since it is of ten possible to estimate initial ratios more accurately than concentrations. Since Ra226 is the longest-lived radium isotope and Ra has no stable isotope, Ba will be used as the reference. Ra and Ba are alkaline earth elements with large ionic radii and +2 oxidation state and are expected to act similarly during chemical fractionation associated with magma genesis. Thus, the ratio Ba/Th in the source must be essentially constant for the suite of rocks being dated.