(Table 3) Isotope ratios of Sr, Nd and Ce and LREE concentrations in Pacific and Atlantic MORB samples from DSDP holes

Isotope ratios of Ce, Nd and Sr, and light rare-earth elements (La, Ce, Nd and Sm) concentrations were measured for sixteen N-type MORB samples from DSDP Sites 420, 421, 429, 597B and 597C (East Pacific Rise), 504B (Costa Rica Rift), and 395, 519A, 522B, 562 and 564 (Mid Atlantic Ridge). All the samples were confirmed as N-type MORB based on Nd and Sr isotope ratios, and LREE patterns. The Ce isotope ratios ranged from 0.0225616 (e-Ce = -1.6) to 0.0225633 (e-Ce = -1.0). Averages of e-Ce and e-Nd of N-type MORB were -1.4 and 9.5, respectively. The average of e-Ce is quite different from previous estimates. We propose that e-Ce = -1.4 should be used as the typical MORB Ce isotope ratio in future studies.对取自深海钻探计划（Deep Sea Drilling Project, DSDP）420、421、429、597B及597C站位（东太平洋海隆）、504B站位（哥斯达黎加裂谷），以及395、519A、522B、562、564站位（大西洋中脊）的16件N型洋中脊玄武岩（Mid-Ocean Ridge Basalt, MORB）样品，测定了其铈（Ce）、钕（Nd）、锶（Sr）同位素比值，以及轻稀土元素（light rare-earth elements, LREE，La、Ce、Nd、Sm）的含量。所有样品均依据钕、锶同位素比值及轻稀土元素配分模式被确认为N型洋中脊玄武岩。铈同位素比值范围为0.0225616（ε-Ce = -1.6）至0.0225633（ε-Ce = -1.0）。N型洋中脊玄武岩的ε-Ce与ε-Nd平均值分别为-1.4与9.5。本次测得的ε-Ce平均值与既往研究估算结果存在显著差异，我们建议未来相关研究中应采用ε-Ce = -1.4作为典型洋中脊玄武岩的铈同位素比值。