A multiple-system study of the geochemical evolution of the mantle with force-balanced plates and thermochemical effects
A multiple-system study of the geochemical evolution of the mantle with force-balanced plates and thermochemical effects
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DOI：
10.1016/j.epsl.2008.08.027
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发表时间：
2008-11-30
影响因子：
5.3
通讯作者：
Ballentine, Chris J.
中科院分区：
文献类型：
--
作者：
Brandenburg, J. P.;Hauri, Erik H.;Ballentine, Chris J.
在这里，多个同位素系统同时跟踪地幔对流的模型，它表明，这可以提供强大的约束作用的海洋地壳循环同位素端元成分的发展。动力学模型是基于高分辨率的圆柱计算力平衡板和可变的化学密度。动态结果跨越可变的现实过剩地壳密度的参数空间相比，实验估计和对流活力测量板块速度和表面热流。同位素地球化学模拟的U-Th-Pb，Sm-Nd，Rb-Sr和Re-Os同位素系统。一个致密的地壳层的作用，在发展中的HIMU同位素签名得到证实。大陆地壳的提取被认为是必不可少的所有同位素组成的端员，包括HIMU的形成。这一提取是作为一个临时过程进行的，其次是洋中脊的部分熔融，并受到现今地壳中估计同位素丰度的限制。而以前的研究产生的地幔同位素阵列，跨越DMM-HIMU，在这个分析中的额外的同位素系统表明，富集纯粹从古洋壳也可能产生EM-I组件，而不调用俯冲的沉积物。在这种情况下，EM-I特征可能表明2.25 Byr之前产生的洋壳富集了地幔，而HIM特征表明最近提取的洋壳富集了地幔。然而，它被发现是很难保持一个真正的DMM同位素端员在Sr-Nd同位素空间时，显着富集的端员存在。这可能突出了Rb-Sr系统对上下地幔物质交换的敏感性。(C)2008 Elsevier B. V.保留所有权利。
Here, multiple isotope systems are tracked simultaneously in models of mantle convection and it is show that this can provide powerful constraints on the role of oceanic crust recycling in the development of isotopic end-member compositions. The dynamical models are based on high-resolution cylindrical calculations with force-balanced plates and variable chemical density. The dynamic results span a parameter space of variable realistic excess crustal density compared to experimental estimates and convective vigor measured by plate velocities and surface heat flow. Isotope geochemistry is then modeled for the U-Th-Pb, Sm-Nd, Rb-Sr, and Re-Os isotope systems. The role of a dense crustal layer in development of a HIMU-isotope signature is confirmed. The extraction of continental crust is found to be essential for the formation of all isotope compositional end-members, including HIMU. This extraction is implemented as an ad-hoc process secondary to partial melting at mid-ocean ridges and constrained by estimated isotopic abundances in the present-day crust. Whereas previous studies generated mantle isotopic arrays that spanned DMM-HIMU, the additional isotope systems in this analysis indicate that enrichment purely from ancient oceanic crust may also generate an EM-I component without invoking the subduction of sediment. In this case, the EM-I signature may be indicative of mantle enriched by oceanic crust produced before 2.25 Byr, while the HIM signature indicates enrichment by oceanic crust extracted more recently. However, it is found to be difficult to maintain a true DMM isotopic end member in Sr-Nd isotope space when significantly enriched end-members are present. This may highlight the sensitivity of the Rb-Sr system to mass exchange between the upper and lower mantle. (C) 2008 Elsevier B.V. All rights reserved.