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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 >Generation of Hawaiian post-erosional lavas by melting of a mixed lherzolite/pyroxenite source
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Generation of Hawaiian post-erosional lavas by melting of a mixed lherzolite/pyroxenite source

机译：通过混合锂铁矿/辉石岩源生成夏威夷侵蚀后的熔岩

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Melting of mafic veins in a marble-cake mantle may play an important role in generating isotopic and chemical heterogeneities in mid-ocean ridge and ocean island basalts. Mafic veins have lower solidi than mantle peridotite and will be preferentially sampled during partial melting, particularly at low melt fractions. However, the abundance of mafic components in the mantle or their role during melt generation has been difficult to quantify because most isotopic systems (e.g. Rb-Sr, Sm-Nd, U-Th-Pb) are not diagnostic of the presence or absence of mafic components. The compatible behavior of Os during mantle melting combined with the incompatible behavior of Re makes the Re-Os isotopic system uniquely well suited for distinguishing mafic and ultramafic contributions to melt generation. Almost all peridotites have low ~(187)Os/~(188)Os (e.g. chondritic to subchondritic). In contrast, mafic rocks have much higher Re/Os than peridotites, which results in the rapid ingrowth of ~(187)Os and the development of large isotopic contrasts between mafic and ultramafic components within the mantle. In this paper, we show that Os-isotopes in Hawaiian post-erosional lavas extend to more radiogenic values than are found in Hawaiian lherzolites, abyssal peridotites or most other ultramafic samples. Os-isotopes are not correlated with other isotopic tracers, in contrast with plume-derived Hawaiian shield-stage lavas. The lack of correlation between Os-isotopes and Sr-, Nd- or Pb-isotopes and the more 'depleted' or MORB-like Sr-Nd isotopic signature of the post-erosional lavas relative to other Hawaiian lavas precludes significant melt input from the Hawaiian plume. However, Os-isotopes are correlated with major and trace elements. Lavas with more radiogenic Os-isotope compositions have higher silica and alumina and lower calcium and incompatible trace element abundances than lavas with less radiogenic Os-isotopes. These correlations result from mixing of pyroxenite- and peridotite-derived melts, both likely derived from the ～100 Ma Pacific lithospheric mantle.
机译：大理石饼状地幔中镁铁矿脉的融化可能在洋中脊和海洋岛玄武岩中产生同位素和化学异质性方面发挥重要作用。基性岩脉的固结度低于地幔橄榄岩，将优先在部分熔融过程中进行采样，尤其是在熔融率低的情况下。但是，由于大多数同位素系统（例如，Rb-Sr，Sm-Nd，U-Th-Pb）无法诊断出存在或不存在氢氧根，因此很难量化地幔中镁铁质组分的数量或其在熔体生成过程中的作用。铁基体成分。地幔融化过程中Os的相容行为与Re的不相容行为相结合，使得Re-Os同位素系统特别适合区分镁铁质和超镁铁质对熔体生成的贡献。几乎所有橄榄岩都具有较低的〜（187）Os /〜（188）Os（例如软骨状至亚软骨状）。相反，镁铁质岩石的Re / Os比橄榄岩高得多，这导致〜（187）Os迅速向内生长，并且在地幔中镁铁质和超镁铁质组分之间形成了较大的同位素对比。在本文中，我们证明了夏威夷侵蚀后熔岩中的Os同位素比夏威夷锂橄榄石，深渊橄榄岩或大多数其他超镁铁质样品中的Os同位素具有更高的放射价值。与羽状派生的夏威夷盾构阶段的熔岩相反，Os同位素与其他同位素示踪剂无关。 Os同位素与Sr，Nd或Pb同位素之间缺乏相关性，且侵蚀后的熔岩相对于其他夏威夷熔岩更“耗竭”或MORB状的Sr-Nd同位素特征使得从该熔岩输入的大量熔体无法进入夏威夷羽。但是，Os同位素与主要和微量元素相关。与具有较低放射性同位素的熔岩相比，具有较高放射性同位素的熔岩具有更高的二氧化硅和氧化铝，较低的钙含量和不相容的痕量元素丰度。这些相关性是由辉石岩和橄榄岩衍生的熔体混合而成的，它们都可能来自〜100 Ma太平洋岩石圈地幔。

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