Dating Neovolcanic Ocean Ridge Basalts

约会新火山洋脊玄武岩

• 批准号: 9012188
• 负责人: J. Douglas Macdougall
• 金额: $ 16万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1990
• 资助国家: 美国
• 起止时间: 1990-09-01 至 1993-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9012188&HistoricalAwards=false
• 关键词: Dating; Neovolcanic; Ocean; Ridge; Basalts

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.

大洋中部玄武岩年龄的确定 山脊新火山带一直是个棘手的问题。的 首席研究员将开发一种辐射测量技术， 使用观察到的Ra 226和其亲本Th 230之间的不平衡 来确定洋中脊玄武岩的年龄 大约有8000年的历史。地质年代学中通常的方法是 将子体同位素的浓度稳定在 或者说是同一种元素的长寿命同位素， 10可能更准确地估计初始比率 比浓度。因为Ra 226是最长寿命的镭 同位素，Ra没有稳定同位素，Ba将被用作 参考Ra和Ba是碱土金属元素， 半径和+2氧化态，并预计将发挥类似的作用 在与岩浆成因有关的化学分馏过程中。 因此，源中的Ba/Th比必须基本恒定 这套岩石的年代