Collaborative Research: Hf and Pb Isotope Ratios in Seawater: Indicators of Paleo-Hydrothermal Activity

合作研究：海水中的Hf和Pb同位素比值：古热液活动的指示本研究旨在研究Hf和Pb在海水和热液系统中的行为，目的是利用同位素比值将海洋沉积物中的这些元素作为过去火山活动速率的指标。海洋Hf和Ph的同位素组成表明，海洋中这些元素的大部分来自“地幔”来源：俯冲/造山带的年轻火山岩和大洋中脊。Hf和Pb2种元素由于在海洋中的停留时间不同而具有互补性。HF在海洋中的停留时间与海洋混合时间相似，使其在整个海洋中的同位素分布相对均匀。新的分析发展使现在有可能测量合理数量的天然水中的HF浓度和同位素组成。它的海洋化学现在可以更好地定义。铅在海水中的停留时间很短，来自大洋中脊的热液通量在当地占主导地位，因此可以确定这种通量的区域变化。地幔流量变化的模型将以同位素系统学为基础，从而能够明确地确定地幔中Hf和Pb在海洋中的比例。将铅、氢和锶通量模型结合起来，将有可能比单独使用锶更准确地确定过去流入海洋的地幔通量的变化。然后，通过与其他衡量扩张速度变化的指标相比，可以检验这样的假设，即更快的扩张速度、火山活动速度和增加的地幔流向海洋是同义词。这反过来将允许对碳等其他元素的全球地球化学循环模型进行改进。

Collaborative Research: Hf and Pb Isotope Ratios in Seawater: Indicators of Paleo-Hydrothermal Activity This study is to investigate the behavior of Hf and Pb in seawater and hydrothermal systems with the goal of using the isotope ratios of these elements in marine sediments as indicators of the past rates of volcanism. The isotopic compositions of marine Hf and Pb indicate that large proportions of the oceanic inventory of these elements are derived from 'mantle' sources: young volcanic rocks of subduction/.orogenic zones and mid-ocean ridges. Hf and Pb are complementary because of their different oceanic residence times. Hf has a residence time in the oceans similar to ocean mixing times, making it relatively isotopically homogeneous throughout the oceans. New analytical developments make it now possible to measure the concentration and isotopic composition of Hf in reasonable volumes of natural waters. Its marine chemistry can now be better defined. Pb has a short residence time in seawater, and the hydrothermal flux from mid-ocean ridges locally dominates its isotopic composition, thus allowing regional variations in this flux to be determined. Models of mantle flux variations will be based on isotope systematics that allow the proportion of mantle Hf and Pb to the oceans to be determined unequivocally. Combination of Pb and Hf with Sr flux models will make it possible to define past changes in mantle fluxes to the oceans more accurately than has been possible by using Sr alone. It will then be possible to test the hypothesis that faster spreading rates, volcanism rates, and increased mantle fluxes to the oceans are synonymous by comparison with other measures of spreading rate variations. This in turn will allow a refinement of models of global geochemical cycles of other elements, such as carbon.