Evidence for recycled plate material in Pacific upper mantle unrelated to plumes
Evidence for recycled plate material in Pacific upper mantle unrelated to plumes
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DOI：
10.1016/j.gca.2009.01.026
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发表时间：
2009-05
影响因子：
5
通讯作者：
S. Machida;N. Hirano;J. Kimura
中科院分区：
文献类型：
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作者：
S. Machida;N. Hirano;J. Kimura
本文报道了太平洋板块西北部一个新类型火山（小斑火山）的年轻碱性玄武岩的Sr、Nd和Pb同位素数据。小斑点熔岩显示Dupal，或非常EM-1样，Sr-Nd-Pb同位素组成。尽管根据地质观察作出了预测，但这些数据不能用远洋沉积物的污染来解释。因此，我们认为，小斑点熔岩的地球化学表明，在北方半球的太平洋上地幔中存在的回收肥沃的板块材料，而不仅仅是杜帕尔同位素签名无关的一个或多个活动的羽。考虑到已发表的肥沃板块材料的实验结果，回收材料的选择性熔融是产生小点熔岩的关键过程。此外，小体积的火山和低程度的熔融所需的地幔源形成强碱性熔岩表明，小点火山作用起源于小规模的不均匀性的再循环材料。这一想法一致地解释了小点熔岩的地球化学和惰性气体同位素组成，并且还表明太平洋上地幔中广泛存在小规模的不均匀性。再加上上地幔异质性的修正观点，我们提出，总上地幔成分控制的丰度和规模的地区回收的材料，对应于不同的相对位置的泛古超大陆，这表明链接到构造起源的全球尺度的异质性。
We report Sr, Nd, and Pb isotopic data of young alkaline basalt lava from a new type of volcano (petit-spot) on the northwestern Pacific Plate. Petit-spot lavas show Dupal, or extremely EM-1-like, Sr–Nd–Pb isotopic compositions. The data cannot be explained by contamination of pelagic sediment, in spite of the prediction on the basis of geological observation. We thus consider that the geochemistry of petit-spot lava indicates the existence of recycled fertile plate materials, not only the Dupal isotopic signature, in the northern hemisphere Pacific upper mantle unrelated to one or more active plumes. In consideration of published experimental results for fertile plate materials, selective melting of recycled material is a process critical in generating petit-spot lava. Moreover, the small volume of the volcano and low degree of melting in the mantle source needed to form strongly alkalic lavas suggest that petit-spot volcanism is originated from small-scale heterogeneities of recycled material. This idea consistently explains the geochemistry and noble gas isotopic composition of petit-spot lava, and also suggests small-scale heterogeneity widespread in the upper mantle of the Pacific Ocean. Together with a revised view of upper mantle heterogeneity, we propose that gross upper mantle composition is controlled by abundances and scales of regions of recycled material that correspond to differences in the relative position to the Pangea supercontinent, suggesting the link to the tectonic origin of the global scale heterogeneity.