Hydrothermal contributions to global biogeochemical cycles: Insights from the Macquarie Island ophiolite
Hydrothermal contributions to global biogeochemical cycles: Insights from the Macquarie Island ophiolite
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热液对全球生物地球化学循环的贡献：来自麦格理岛蛇绿岩的见解
DOI：
10.1016/j.lithos.2016.08.024
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发表时间：
2016
期刊：
影响因子：
3.5
通讯作者：
Coggon R
中科院分区：
文献类型：
--
作者：
Coggon R
热液循环是海洋地壳形成和老化的一个基本过程，由此产生的地壳与海洋之间的化学交换是全球海洋地球化学循环的一个关键组成部分。热液蚀变洋壳的剖面提供了这种化学交换的时间综合记录。不幸的是，我们对热液交换的性质和范围的了解受到了限制，因为缺乏来自海底暴露或钻孔岩心的完整的海洋地壳剖面。亚南极麦夸里岛由约10 Ma的洋壳组成，形成于一个缓慢扩张的洋脊，是唯一一个在其形成的洋盆中有完整洋壳部分的近空中暴露。因此，麦夸里岛的热液蚀变岩石提供了一个独特的机会，以评估通过一个完整的海洋地壳部分的流体岩石交换的化学变化。在这里，我们利用热液蚀变过程中的一些元素的不动行为，以确定前体组合物改变麦格理全岩样品，并评估由于整个麦格理地壳的流体-岩石相互作用在散装岩石化学的变化。元素在每个样品中富集或贫化的程度取决于所形成的次生矿物组合，因此也取决于岩石中原生矿物的模式丰度和蚀变条件，如温度、流体成分和水岩比。因此，化学变化随深度而变化，最明显的是在熔岩岩脉过渡区，在K，S，Rb，Ba和Zn的富集观察。我们的研究结果表明，麦夸里地壳的热液蚀变导致了Si，Ti，Al和Ca向海洋的净通量，而地壳是H2O，Mg，Na，K和S的净汇。我们的研究结果还证明了包括静脉对某些元素的元素吸收贡献的重要性（例如，Si、Fe、Mg、S）。外推我们的结果，假设地壳生产率为3平方公里/年，产生估计的热液对全球地球化学循环的贡献。例如，镁向地壳的通量估计为3.3 ± 1.1 × 1012 mol/年，考虑到所涉及的不确定性，这足以平衡流入海洋的河流镁。然而，对扩展速率与热液化学交换通量之间的关系仍然知之甚少，这里所述的方法应适用于以各种扩展速率生成的地壳，以完善全球热液通量估计数。
Hydrothermal circulation is a fundamental process in the formation and aging of the ocean crust, with the resultant chemical exchange between the crust and oceans comprising a key component of global biogeochemical cycles. Sections of hydrothermally altered ocean crust provide time-integrated records of this chemical exchange. Unfortunately, our knowledge of the nature and extent of hydrothermal exchange is limited by the absence of complete oceanic crustal sections from either submarine exposures or drill core. Sub-Antarctic Macquarie Island comprises ~ 10 Ma ocean crust formed at a slow spreading ridge, and is the only sub-aerial exposure of a complete section of ocean crust in the ocean basin in which it formed. Hydrothermally altered rocks from Macquarie Island therefore provide a unique opportunity to evaluate the chemical changes due to fluid–rock exchange through a complete section of ocean crust. Here we exploit the immobile behavior of some elements during hydrothermal alteration to determine the precursor compositions to altered Macquarie whole rock samples, and evaluate the changes in bulk rock chemistry due to fluid–rock interaction throughout the Macquarie crust. The extent to which elements are enriched or depleted in each sample depends upon the secondary mineral assemblage developed, and hence the modal abundances of the primary minerals in the rocks and the alteration conditions, such as temperature, fluid composition, and water:rock ratios. Consequently the chemical changes vary with depth, most notably within the lava–dike transition zone where enrichments in K, S, Rb, Ba, and Zn are observed. Our results indicate that hydrothermal alteration of the Macquarie crust resulted in a net flux of Si, Ti, Al, and Ca to the oceans, whereas the crust was a net sink for H2O, Mg, Na, K, and S. Our results also demonstrate the importance of including the contribution of elemental uptake by veins for some elements (e.g., Si, Fe, Mg, S). Extrapolation of our results, assuming a crustal production rate of 3 km2/yr, yields estimates of the hydrothermal contribution to global geochemical cycles. For example, the Mg flux to the crust is estimated to be 3.3 ± 1.1 × 1012mol/year, sufficient to balance the riverine Mg input to the oceans given the uncertainties involved. However, the relationship between spreading rate and hydrothermal chemical exchange fluxes remains poorly understood, and the approach described here should be applied to crust produced at a range of spreading rates to refine the global hydrothermal flux estimates.
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影响因子：
3.9
作者：
Vadim Kamenetsky;R. Maas
通讯作者：
Vadim Kamenetsky;R. Maas
影响因子：
5.3
作者：
MacLeod, C. J.;Searle, R. C.;Harris, M.
通讯作者：
Harris, M.
影响因子：
64.8
作者：
D. Teagle;B. Ildefonse
通讯作者：
B. Ildefonse
6. 148 段（504B 孔）1 期间深层板岩岩脉中次生矿物的化学成分和来源
DOI：
--
发表时间：
1996
期刊：
影响因子：
--
作者：
D. Vanko;C. Laverne;P. Tartarotti;J. Alt
通讯作者：
J. Alt
麦夸里岛蛇绿岩杂岩：来自一个主要洋盆的中第三纪海洋岩石圈
DOI：
--
发表时间：
1980
期刊：
影响因子：
--
作者：
B. J. Griffin;R. Varne
通讯作者：
R. Varne