Investigating Influences on the Pb Pseudo-Isochron Using Three-Dimensional Mantle Convection Models With a Continental Reservoir
Investigating Influences on the Pb Pseudo-Isochron Using Three-Dimensional Mantle Convection Models With a Continental Reservoir
复制标题
利用三维地幔对流模型和大陆储层研究对 Pb 伪等时线的影响
DOI：
10.1029/2021gc010309
复制
发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Panton J
中科院分区：
文献类型：
--
作者：
Panton J
对于洋中脊玄武岩和洋岛玄武岩，Pb同位素比值的测量结果显示出广泛的线性相关性和一定程度的散射。在207pb /204Pb - 206pb /204Pb空间中，最佳拟合线定义的伪等时年龄（τPb）为~ 1.9 Gyr。先前的模型表明，在2.25和2.5 Ga之间，U和Pb的行为发生了相对变化，导致HIMU（高U/Pb）物质在地球历史后期的净再循环，以解释观测到的τPb。然而，在整个模型运行过程中，分馏由一组分配系数控制的模拟无法再现τ p波段观测到的Pb同位素比率的散射。我们在这些模型的基础上进行了三维地幔对流模拟，包括熔融、大陆U循环和俯冲洋壳Pb优先去除的参数化。我们发现，为了拟合观测到的207pb /204Pb - 206pb /204Pb和208pb /204Pb - 206pb /204Pb阵列的梯度和散射，需要在大氧合事件后进行U循环和在板块构造开始后进行Pb提取。与以前的许多工作不同，我们的模型不需要俯冲海洋地壳的积累在地核-地幔边界长时间持续，以匹配地球化学观测。
For mid‐ocean ridge basalts and ocean island basalts, measurements of Pb isotope ratios show broad linear correlations with a certain degree of scatter. In207Pb/204Pb—206Pb/204Pb space, the best fit line defines a pseudo‐isochron age (τPb) of ∼1.9 Gyr. Previous modeling suggests a relative change in the behaviors of U and Pb between 2.25 and 2.5 Ga, resulting in net recycling of HIMU (high U/Pb) material in the latter part of Earth's history, to explain the observedτPb. However, simulations in which fractionation is controlled by a single set of partition coefficients throughout the model runs fail to reproduceτPband the observed scatter in Pb isotope ratios. We build on these models with 3D mantle convection simulations including parameterizations for melting, U recycling from the continents and preferential removal of Pb from subducted oceanic crust. We find that both U recycling after the great oxygenation event and Pb extraction after the onset of plate tectonics, are required in order to fit the observed gradient and scatter of both the207Pb/204Pb—206Pb/204Pb and208Pb/204Pb—206Pb/204Pb arrays. Unlike much previous work, our model does not require accumulations of subducted oceanic crust to persist at the core‐mantle boundary for long periods of time in order to match geochemical observations.