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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Ancient refractory asthenosphere revealed by mantle re-melting at the Arctic Mid Atlantic Ridge
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Ancient refractory asthenosphere revealed by mantle re-melting at the Arctic Mid Atlantic Ridge

机译：古代难治性哮喘圈透露在北极中大西洋山脊上的地幔重新融化

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The upper mantle is a heterogeneous mixture of refractory and recycled crustal domains. The recycled portions, more fertile and thus preferentially melted, dominate the composition of the basalts erupted on the surface, whereas the imprint of melting of the refractory counterparts is more difficult to discern from the basalt chemistry. Contrasting radiogenic isotopic signatures of mid-ocean ridge basalts and oceanic mantle, however, show that Hf isotope ratios may provide hints for melting of refractory source materials despite ubiquitous magma mixing during ascent and stalling in the crust. This property may allow identifying contributions from depleted mantle materials unseen in other isotope systematics in basalts. Here, we show that basalts from Mohns and Knipovich ridges, two >500-km long oblique super-segments in the Arctic Atlantic, have distinctly high Hf isotope ratios, not mirrored by comparatively high Nd and low Sr and Pb isotope ratios. These compositions can be explained if a highly depleted asthenospheric mantle melts beneath this section of the Arctic Mid Atlantic Ridge. We argue that this depleted source consists of high proportions of ancient (>1 Ga), ultra-depleted mantle, previously drained of enriched components before being re-melted in its current location following a recent ridge-jump, allowing the identification of ultra-depleted mantle components in the arctic subridge mantle. (C) 2021 Elsevier B.V. All rights reserved.
机译：上地幔是难熔和再循环地壳域的不均匀混合物。再生部分更肥沃，因此优先熔融，主导了表面喷发玄武岩的成分，而耐火材料对应物的熔融印记更难从玄武岩化学中辨别。然而，洋中脊玄武岩和大洋地幔的对比放射成因同位素特征表明，尽管地壳上升和停滞期间岩浆混合普遍，但Hf同位素比值可能为难熔源材料的熔融提供了线索。这一性质可能有助于确定玄武岩中其他同位素系统学中未发现的亏损地幔物质的贡献。在这里，我们表明，来自莫恩斯和克尼波维奇海脊的玄武岩（北极大西洋中两个长度>500 km的斜向超段）具有明显的高Hf同位素比值，而不是相对较高的Nd和较低的Sr和Pb同位素比值。如果一个高度亏损的软流圈地幔在北极中大西洋海脊的这一部分下融化，则可以解释这些成分。我们认为，这种亏损源由高比例的古代（>1 Ga）超亏损地幔组成，这些地幔在最近的山脊跃变后在其当前位置重新熔融之前已被富集成分排出，从而可以识别北极次山脊地幔中的超亏损地幔组分。（c）2021爱思唯尔B.V.保留所有权利。

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