控制北太平洋深水中Pb、Nd同位素演化的不同因素

Different Controls over Pb and Nd Isotope Evolution of the Central North Pacific Ocean

近年研究表明，大洋中溶解的Pb和Nd以陆源来源占主导。但对Pb和Nd进入大洋的途径存在很大争议。笔者研究了3块中北太平洋铁锰结壳（CJ01，CLD01，CB12）的元素含量和Pb、Nd同位素组成。根据Co含量经验公式法定年，结合几块结壳的剖面Pb同位素演化曲线与Os同位素演化曲线，确定所研究的中北太平洋铁锰结壳的底部年龄约为75Ma。3块结壳不论磷酸盐化与否，其Pb、Nd同位素随时间的演变曲线均十分相似，且Pb同位素演化趋势与北太平洋岩心（LL44-GPC3）中的风沙的Pb同位素演化趋势相似。这些结壳的Nd同位素演化趋势也相似，但与岩心LL44-GPC3中风沙的Nd同位素的演化曲线完全不同。由此得到以下结论：

Nd and Pb isotopic dating results are presented for three ferromanganese crusts, whose ages are inferred to be -75 Ma. These data provide for the first time an opportunity to trace the Nd and Pb isotope evolution of central North Pacific seawater hack to the latest Cretaceous. The three crusts, no matter they have been phosphatized or not, display very similar Pb and Nd isotope trends with age, suggesting no modification of the Pb and Nd isotope distribution by post-depositional phosphatization. The authors＇ data suggest that the isotope evolution of dissolved Pb in central North Pacific seawater has been mainly controlled by Pb released from eolian dust from North America prior to 50 Ma and from Asia after 40 Ma. In contrast, eolian dusts have had negligible contributions to the dissolved Nd in the central North Pacific deep water. The rise of Nd isotope ratios of Pacific seawater in Cenozoic was most likely caused by the increasing volcanic activity and erosion of the volcanic arcs around the Pacific Ocean.