Dating Neovolcanic Ocean Ridge Basalts

洋中脊新火山带玄武岩年龄的确定一直是一个棘手的问题。首席研究员将开发一种辐射测量技术，利用观察到的Ra226与其母体Th230之间的不平衡来确定年轻的洋中脊玄武岩的年龄，这些玄武岩的年龄不到8000年。地质年代学中通常的方法是将子同位素的浓度改为同一元素的稳定或寿命很长的同位素，因为通常可能比浓度更准确地估计初始比率。由于Ra226是寿命最长的镭同位素，而Ra没有稳定的同位素，因此将以Ba作为参考。Ra和Ba是碱土元素，具有较大的离子半径和+2氧化态，预计在岩浆成因的化学分馏过程中具有相似的作用。因此，烃源岩中Ba/Th的比值对于测定年代的一组岩石来说必须是基本恒定的。

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.