Reaction-induced porosity and onset of low-temperature carbonation in abyssal peridotites: Insights from 3D high-resolution microtomography
Reaction-induced porosity and onset of low-temperature carbonation in abyssal peridotites: Insights from 3D high-resolution microtomography
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DOI：
10.1016/j.lithos.2016.11.014
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发表时间：
2017-01-01
期刊：
影响因子：
3.5
通讯作者：
Bach, Wolfgang
中科院分区：
文献类型：
--
作者：
Joens, Niels;Kahl, Wolf-Achim;Bach, Wolfgang
在从最上层的大洋地壳（大西洋中脊，ODP腿209，站点1270）的蛇纹石化hazburstenes的岩心样品中，我们证明使用高分辨率的三维显微断层扫描，微米大小的开口腔存在。孔隙度的发展被解释为水镁石和/或橄榄石溶解的结果。岩相学观察表明，孔隙被整合在碳酸盐脉的网络中，其形成与溶解反应结合的碱度变化有关。部分碳酸盐填充孔隙空间表明，在静态条件下，低温碳酸盐化导致流体通道堵塞，从而降低渗透率。电子探针分析表明，开口空洞的内壁衬有富铁沉淀物。我们建议，在这些阶段的铁被释放水镁石或橄榄石溶解，随后被氧化和沉淀的氢氧化铁。热力学计算表明，这一过程可能是蛇纹岩中微生物分解代谢能量的潜在来源。建议的碳酸化机制意味着，碳酸盐沉淀可能会开始后不久，深海橄榄岩暴露，水镁石溶解和风化的橄榄石开始，并继续，直到阶段变得无法进入海水。因此，预测深海橄榄岩的碳酸化速率需要了解渗透性反应。(C)© 2016 Elsevier B. V.版权所有。
In a drillcore sample of serpentinized harzburgite from the uppermost oceanic crust (Mid-Atlantic Ridge, ODP Leg 209, Site 1270), we demonstrate using high-resolution 3D-microtomography that micron-sized open cavities are present. The development of porosity is interpreted to result from dissolution of brucite and/or olivine. Petrographic observations indicate that voids are integrated in a network of carbonate veins, the formation of which is linked to changing alkalinity in conjunction with dissolution reactions. Partial carbonate filling of pore spaces indicates that under static conditions low-temperature carbonation leads to clogging of fluid pathways and thus to a reduction in permeability. Electron microprobe analyses show that the inner walls of open voids are lined with Fe-rich precipitates. We propose that the iron in those phases was released by brucite or olivine dissolution and was subsequently oxidized and precipitated as ferric hydroxide. Thermodynamic computations show that this process may be a potential source of catabolic energy for microorganisms inhabiting serpentinites. The proposed carbonation mechanism implies that carbonate precipitation may start soon after exposure of the abyssal peridotites, when dissolution of brucite and weathering of olivine begin, and continue until the phases become inaccessible to seawater. Predicting carbonation rates of abyssal peridotites will hence require understanding of permeability reactions. (C) 2016 Elsevier B.V. All rights reserved.