Extreme intensity of fluid-rock interaction during extensive intraplate volcanism
Extreme intensity of fluid-rock interaction during extensive intraplate volcanism
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DOI：
10.1016/j.gca.2019.04.017
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发表时间：
2019-07
影响因子：
5
通讯作者：
C. Beier;W. Bach;A. Busch;F. Genske;Christian Hübscher;S. Krumm
中科院分区：
文献类型：
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作者：
C. Beier;W. Bach;A. Busch;F. Genske;Christian Hübscher;S. Krumm
大型火成岩高原的初始形成和时间演化以及这些大型火成岩特征对其直接和遥远生态环境的影响程度仍然是一个积极研究的问题。在大火成岩省的成分变化主要是由于熔融制度和浅地壳过程的变化，通常范围从亏损拉斑玄武岩富集碱性熔岩。然而，在海底环境中爆发的大型火成岩省也可能在其形成期间经历强烈的热液蚀变，这是由于在其爆发历史期间海水与喷发熔岩之间的交换增加。中北方大西洋的亚速尔群岛海底高原通常被认为是自1000年以来由广泛的火山活动和独特的构造体制形成的大型火成岩省，这种体制导致大型断层系统暴露出喷发的熔岩。在这里，我们提出了新的地震，岩石学和主要元素，微量元素和同位素地球化学数据，从一个1000米的海底熔岩暴露在西埃内萨爱丽丝银行的地层部分。从近乎垂直的裂谷壁上回收的22个样品提供了迄今为止在海洋地壳取样中没有观察到的强烈水岩交换的证据。流体不流动的不相容微量元素表明，样品形成于地幔源的较高程度的部分熔融，该地幔源的富集程度低于今天形成岛屿的源。融化的程度今天是非常小的，这意味着在融化制度的变化，因为最初形成的Alessa爱丽丝高原玄武岩，对应于在亚速尔群岛的熔融异常。我们的观察结果表明，极端水平的蚀变可能是由于在亚速尔群岛高原的初始形成过程中的岩浆活动和构造制度提供的流体通道的组合。我们的研究结果的解释浅层次的地壳岩浆过程中，地壳源上升熔体的贡献可能是不同的，以前曾建议。我们认为，海底火成岩高原形成事件中的热液蚀变可以彻底改变火成岩地壳的成分。大洋高原侵位过程中，伴随的大洋地壳与水圈之间的元素和同位素交换，可显著改变大洋与地壳之间的化学通量。
The initial formation and temporal evolution of large igneous plateaus and the extent to which these large enigmatic igneous features impact on their immediate and distant ecological surrounding remains a matter of active research. The compositional variability in large igneous provinces has mainly been attributed to changes in the melting regime and shallow crustal processes and commonly ranges from depleted tholeiitic basaltic to enriched alkaline lavas. Large igneous provinces erupted in the submarine environment however, may also experience intense hydrothermal alteration during their formation resulting from an increased exchange between seawater and the erupting lavas during their eruptive history. The submarine Azores Plateau in the Central Northern Atlantic has generally been treated to represent such large igneous province formed since ∼10 Ma by widespread volcanism and the unique tectonic regime which results in large fault systems exposing the erupted lavas. Here, we present new seismic, petrological and major element, trace element and isotope geochemical data from a ∼1000 m stratigraphic section of submarine lavas exposed at the western Princessa Alice bank. The 22 samples recovered from the near-vertical rift wall provide evidence for intense water-rock exchange not observed anywhere in oceanic crust sampled to date. Fluid-immobile incompatible trace elements show that the samples formed from higher degrees of partial melting of a mantle source that is less enriched than the source that gives rise to the islands today. The extents of melting today are very small, implying a change in melting regime since initial formation of the Princessa Alice Plateau basalts that correspond to a melting anomaly in the Azores. Our observations indicate that the extreme levels of alteration may result from a combination of intensified magmatic activity during initial formation of the Azores Plateau and the tectonic regime providing pathways for the fluids. Our results impact on the interpretation of shallow level crustal magmatic processes, in which the contribution of crustal sources to the ascending melt may be different to what had previously been suggested. We propose that hydrothermal alteration during submarine igneous plateau forming events can drastically change the compositions of the igneous crust. The associated elemental and isotopic exchange between the oceanic crust and hydrosphere may substantially change the chemical fluxes between oceans and crust during the emplacement of oceanic plateaus.