Lead isotope ratios of basalts from DSDP Leg 37 (Table 1)@en

Analyses of Pb from mid-ocean ridge basalts obtained from DSDP Leg 37 lie on a line of near-zero-age slope. The data seem consistent with an evolutionary model of three stages, the beginning of the second stage being at about 600 m.y. - the model age obtained for the least radiogenic Pb. The beginning of the third stage of evolution at the time of formation of the rocks apparently did not change the average Th/U ratio since measured values are consistent with the ratio deduced from Pb isotope ratios. Ratios of U/Pb are not consistent with Pb isotope ratios, however, thus ruling out a simple two-stage evolutionary model.对深海钻探计划（Deep Sea Drilling Project，DSDP）第37航次所获洋中脊玄武岩中的铅（Pb）开展的分析结果显示，其数据分布于一条近零年龄斜率的直线上。该数据与三阶段演化模型相契合：第二阶段的起始时间约为6亿年（600 m.y.），这一年龄也是通过最低放射成因铅所得到的模型年龄。在岩石形成之时开启的第三阶段演化，并未改变平均钍铀（Th/U）比值——这是因为实测值与通过铅同位素比值推导得到的钍铀比值相符。然而，铀铅（U/Pb）比值与铅同位素比值并不匹配，这一结果排除了简单两阶段演化模型的可能性。