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A source for Icelandic magmas in remelted Iapetus crust

机译：重熔伊阿佩图斯地壳中冰岛岩浆的来源

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摘要

The geochemistry and large melt volume in the Iceland region, along with the paucity of evidence for high, plume-like temperatures in the mantle source, are consistent with a source in the extensive remelting of subducted lapetus crust. This may have been trapped in the Laurasian continental mantle lithosphere during continental collision in the Caledonian orogeny at ～420-410 Ma, and recycled locally back into the asthenosphere beneath the mid-Atlantic ridge by lithospheric delamination when the north Atlantic opened. Fractional remelting of abyssal gabbro can explain the major-, trace- and rare-earth-element compositions, and the isotopic characteristics of primitive Icelandic tholeiite. An enriched component already present in the recycled crustal section in the form of enriched mid-ocean-ridge basalt, alkalic olivine basalt and/or related differentiates could contribute to the diversity of Icelandic basalts. Compositions ranging from ferrobasalt to olivine tholeiite are produced by various degrees of partial melting in eclogite, and the crystallization of ferrobasalt as oxide gabbro, i.e., containing the magmatic Fe-Ti oxide minerals, ilmenite and magnetite, may explain the anomalously high density of the Icelandic lower crust. The very high ~3He/~4He ratios observed in some Icelandic basalts may derive from old helium preserved in U+Th-poor residual Caledonian oceanic mantle lithosphere or olivine-rich cumulates in the crustal section. The persistence of anomalous volcanism at the mid-Atlantic ridge in the neighborhood of Iceland suggests that in the presence of lateral ridge migration, the shallow fertility anomaly must be oriented transverse to the mid-Atlantic ridge. The Greenland-Iceland-Faeroe ridge is co-linear with the western frontal thrust of the Caledonian collision zone, which may thus be associated with the fertility source. The fertile material beneath the Iceland region must lie at a steep angle or be thickened by deformation or imbrication to supply the large volumes of basalt required to build the thick crust there. "Hot spot" volcanism and large-igneous-province emplacement often occurs within or near to old suture zones and similar processes may thus explain anomalous magmatism elsewhere that is traditionally attributed to plumes.
机译：冰岛地区的地球化学和大量熔体，以及缺乏地幔源类似于羽状温度的证据，与俯冲的羽扇豆皮大范围重熔的源一致。这可能是在〜420-410 Ma的加里东造山带发生大陆碰撞时被困在Laurasian大陆幔岩石圈中，并在北大西洋开放时通过岩石圈分层而局部再循环回到大西洋中脊下方的软流圈。深渊辉长岩的部分重熔可以解释主要，痕量和稀土元素的组成，以及原始冰岛黄铁矿的同位素特征。以中洋脊玄武岩，碱化橄榄石玄武岩和/或相关特征为富集形式的已存在于再循环地壳部分中的富集成分可能有助于冰岛玄武岩的多样性。通过在榴辉岩中进行不同程度的部分熔融，生成了从铁玄武岩到橄榄石黄铁矿的组成，而铁玄武岩以氧化物辉长岩的形式结晶，即含有岩浆中的Fe-Ti氧化物矿物，钛铁矿和磁铁矿，可以解释其异常高密度。冰岛下地壳。在某些冰岛玄武岩中观察到的非常高的〜3He /〜4He比可能来自保存在U + Th贫余的加里东洋地幔岩石圈中的旧氦或地壳剖面中富含橄榄石的堆积物。冰岛附近大西洋中脊的异常火山活动持续存在，这表明在存在侧向脊移动的情况下，浅生育力异常必须垂直于大西洋中脊。格陵兰-冰岛-法罗脊与加里多尼亚冲撞带的西部锋面推力共线，因此可能与肥力源有关。冰岛地区下方的肥沃材料必须成一个陡峭的角度，或者通过变形或成岩作用使其增稠，以提供在该地区建造浓厚地壳所需的大量玄武岩。 “热点”火山作用和大火成岩侵位通常发生在旧缝合线区内或附近，并且类似的过程可能因此解释了传统上归因于羽状流的其他地方的岩浆异常。

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