Experimental evidence for the origin of lead enrichment in convergent-margin magmas
Experimental evidence for the origin of lead enrichment in convergent-margin magmas
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DOI：
10.1038/378054a0
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发表时间：
1995-11
期刊：
影响因子：
64.8
通讯作者：
J. Brenan;H. Shaw;F. Ryerson
中科院分区：
文献类型：
--
作者：
J. Brenan;H. Shaw;F. Ryerson
有人提出1 - 5，相对于大洋玄武岩，俯冲相关玄武岩的低Ce/Pb比是由于铅通过非岩浆过程优先转移到地幔楔（覆盖俯冲板片）所致。俯冲洋壳脱水产生的低Ce/Pb流体对地幔楔的作用是这一过程的有利机制之一（例如，见参考文献5）。在这里，我们报告了一系列的高压实验的结果，这证实了低Ce/Pb流体共存的蚀变玄武岩高压脱水过程中产生的主要矿物相（石榴石和单斜辉石）。我们的研究结果表明，由玄武岩衍生流体流动的地幔源产生俯冲带岩浆是将相对富含铅、贫铈的地幔衍生物质添加到大陆的一种机制。因此，地球陆壳的铅富集是一个发生在会聚边缘的持续过程。
IT has been proposed1–5that the low Ce/Pb ratio of subduction-related basalts, relative to their oceanic counterparts, arises by the preferential transfer of lead to the mantle wedge (overlying the subducting slab) by non-magmatic processes. Fluxing of the mantle wedge by low-Ce/Pb fluids, generated by the dehydration of sub-ducted oceanic crust, is one mechanism favoured for this process (see, for example, ref. 5). Here we report the results of a series of high-pressure experiments, which confirm that low-Ce/Pb fluids coexist with the dominant mineral phases (garnet and clinopyroxene) produced during high-pressure dehydration of altered basalt. Our results show that the production of subduction-zone magmas from mantle sources fluxed by basalt-derived fluid is a mechanism by which relatively lead-rich, cerium-poor, mantle-derived material is added to the continents. The lead enrichment of the Earth's continental crust is thus a continuing process occurring at conver-gent margins.