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首页> 外文期刊>Contributions to Mineralogy and Petrology >Isotopic evidence for interaction between Oraefajokull mantle and the Eastern Rift Zone, Iceland
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Isotopic evidence for interaction between Oraefajokull mantle and the Eastern Rift Zone, Iceland

机译：Oraefajokull地幔与冰岛东部纵谷带相互作用的同位素证据

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The off-rift central volcano of Orasfajokull has very distinctive EMl-like isotopic compositions compared with other Icelandic lavas. New Pb-Nd-Sr isotopic data from Orarfajokull show strong correlations interpreted as a result of mixing. End-members are a depleted mantle source incorporating 0.5 % subduction-processed sediment and a mantle source with an isotopic signature similar to lavas of the Reykjanes Peninsula. Sr-Nd-Pb isotopic correlations of Icelandic Eastern Rift Zone (ERZ) lavas are almost completely distinct from those of the Reykjanes Peninsula and the Western Rift Zone (WRZ) and require a high-~(207)Pb/~(204)Pb, low-~(143)Nd/~(144)Nd end-member that resembles Orarfajokull compositions, which is very distinct from the enriched end-members suggested for the Reykjanes Peninsula and the WRZ. Given the similar depth and degree of melting at rift zones, variation in the observed enriched end-members between rift zones must indicate spatial variations in enriched mantle sources within the shallow mantle under Iceland rather than purely mixing of melts from a bi-lithological mantle. This is consistent with observations that the ERZ lavas erupted closest to Orarfa-jokull exhibit the most Orarfajokull-like isotopic compositions, implying that a homogenised Orarfajokull source with positive Δ~(207)Pb is focused under the drafajokull centre and its associated flank zone. This then mixes laterally with the dominant negative-A Pb ERZ mantle source. Like Reykjanes Peninsula and WRZ lavas, the ERZ mantle source has strongly negative A Pb and low K/Nb (<170), and these provide evidence for a recycled oceanic crust contribution. The range in ~(206)Pb/~(204)Pb in mantle sources with negative A Pb was probably generated by heterogeneity in ~(206)Pb/~(204)Pb and μ in the recycled oceanic crust, which is the dominant source of incompatible elements in Icelandic lavas.
机译：与其他冰岛熔岩相比，Orasfajokull的裂谷中央火山具有非常独特的类似于EM1的同位素组成。来自Orarfajokull的新的Pb-Nd-Sr同位素数据显示，强烈的相关性被解释为混合的结果。末端成员是贫化的地幔源，其中包含0.5％的俯冲作用沉积物，地幔源的同位素特征类似于雷克雅尼斯半岛的熔岩。冰岛东部裂谷带（ERZ）熔岩的Sr-Nd-Pb同位素相关性与雷克雅尼斯半岛和西部裂谷带（WRZ）的熔岩几乎完全不同，需要较高的〜（207）Pb /〜（204）Pb ，类似于Orarfajokull组成的低（143）Nd /〜（144）Nd末端成员，这与为雷克雅尼斯半岛和WRZ建议的富集末端成员非常不同。考虑到裂谷带融化的深度和程度相似，在裂谷带之间观察到的富集末端成员的变化必须表明冰岛下浅地幔内富集幔源的空间变化，而不是纯粹地将双岩性地幔融化。这与观察结果一致，即最接近Orarfa-jokull喷发的ERZ熔岩表现出最类似于Orarfajokull的同位素组成，这表明均质化的具有正Δ〜（207）Pb的Orarfajokull源集中在drafajokull中心及其相关的侧面区域下方。然后将其与占主导地位的负A Pb ERZ地幔源横向混合。像雷克雅尼斯半岛和WRZ熔岩一样，ERZ地幔源具有强烈的负Pb和低K / Nb（<170），这些为循环利用的海洋地壳贡献提供了证据。 A Pb为负的地幔源〜（206）Pb /〜（204）Pb的范围可能是由于再生海洋地壳中〜（206）Pb /〜（204）Pb和μ的异质性产生的冰岛熔岩中不相容元素的来源。

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