Experimental study of the effects of solute transport on reaction paths during incipient serpentinization
Experimental study of the effects of solute transport on reaction paths during incipient serpentinization
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初期蛇纹石化过程中溶质迁移对反应路径影响的实验研究
DOI：
10.1016/j.lithos.2018.09.020
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发表时间：
2018
期刊：
影响因子：
3.5
通讯作者：
Richard Leprovost
中科院分区：
文献类型：
--
作者：
S. Escario;M. Godard;P. Gouze;Richard Leprovost
本文介绍了4个反应渗流实验的结果，建立了调查的影响，流率的蛇纹石化反应路径的相关条件下的大洋橄榄岩海底在其热液蚀变的初始阶段。实验包括将人造海水注入多孔压缩橄榄石粉末岩心中，流速为Q：0.24、0.48、1.14和5.21 mL·h-1。实验在恒温（170 °C）和压力（25 MPa）下进行，持续11至28天。在实验结束时，出口流体组成显示出类似的组成，通过形成蛇纹石（aMg 2 +/a（H+）2= 9.7-10; aSiO 2 =-3.9至-5.2;原位pH = 6.1）来缓冲。这些值是在几个高达300小时的高流速实验表明，它们对应于一个稳态的质量传递制度，这取决于流速。流体的组成与时间的差异，并在反应样品的结构在四个反应渗流实验期间和之后也提出了各种初期蛇纹石化反应路径。低Q实验产生的SiO2（aq）丰富的出口流体和结节状聚集体被确定覆盖反应橄榄石表面。在高Q实验中，原蛇纹石的纤维丝形成的橄榄石表面和流体逐渐达到稳定状态的组合物类似于其他实验。这些结果与先前发表的反应渗流实验的结果一起，使我们提出了两个端员反应路径的初始蛇纹石化的橄榄石为主的渗透性岩石渗透海水热液流体：（1）在扩散主导区中发生的输运控制的反应路径的特征在于瞬时水镁石沉淀，其在溶液中产生Mg捕获和Si释放，随后是蛇纹石沉淀和（2）动力学控制的反应路径发生在平流主导区，其中输送条件有利于Mg浸出并且其中蛇纹石首先沉淀。这两个端元反应路径的出现由流体的成分局部地确定，该成分沿沿着流动路径变化。因此，这两种反应路径可以共存于样品中，这取决于局部孔几何形状。我们的研究表明，流体输运和反应动力学之间的相互作用控制矿物表面和本体溶液之间的化学通量，以及初期的蛇纹石化反应路径。在自然系统中，这些反应域的规模和分布将取决于超镁铁基底的复杂结构。我们的研究结果表明，沉淀的蛇纹石和富硅相将有利于流体聚焦区，如断层和裂缝，而水镁石的形成将优先发生的一部分，普遍的背景蛇纹石化。
This paper presents the results of 4 reactive percolation experiments set up for investigating the impact of flow rate on serpentinization reaction paths for conditions relevant of the oceanic peridotite sub-seafloor during the initial stages of its hydrothermal alteration. The experiments consisted in injecting artificial seawater into porous compressed olivine powder cores at constant flow ratesQ: 0.24, 0.48, 1.14 and 5.21 mL·h−1. The experiments were conducted at constant temperature (170 °C) and pressure (25 MPa) and lasted 11 to 28 days. At the end of the experiments, the outlet fluids composition displayed similar compositions, buffered by the formation of serpentine (aMg2+/a(H+)2= 9.7–10; aSiO2= −3.9 to −5.2; pHin situ= 6.1). These values were achieved in a few to up to 300 h for the high flow rate experiment suggesting that they corresponded to a steady-state regime of mass transfer which depended on flow rate. Differences in the composition of fluid versus time and in the structure of reacted samples during and after the four reactive percolation experiments suggested also various incipient serpentinization reaction paths. The lowQexperiments produced SiO2(aq) enriched outlet fluids and nodular aggregates were identified covering the reacted olivine surfaces. During highQexperiments, fibrous filaments of proto-serpentine were formed on the olivine surfaces and the fluids progressively achieved steady state compositions similar to the other experiments. These results together with those of previously published reactive percolation experiments lead us to propose two end-member reaction paths for incipient serpentinization of olivine-dominated permeable rocks infiltrated by seawater derived hydrothermal fluids: (1) a transport-controlled reaction path occurring in diffusion dominated zones is characterized by transient brucite precipitation, which produces Mg trapping and Si release in solution, followed by serpentine precipitation and (2) a kinetics-controlled reaction path occurring in advection dominated zones where transport conditions are favorable to Mg leaching and where serpentine precipitates first. The occurrence of these two end-member reaction paths is determined locally by the composition of the fluid, which varies along flow paths. Thus, both reaction paths can coexist in the sample depending on the local pore geometry. Our study shows that the interplay between fluid transport and reaction kinetics controls the chemical fluxes between the mineral surface and the bulk solution, and the incipient serpentinization reaction paths. In natural systems, the scale and distribution of these reaction domains will depend on the complex structure of the ultramafic basement. Our results suggest that the precipitation of serpentine and silica rich phases will be favored in fluid focusing zones such as faults and fractures, whilst formation of brucite will preferentially occur as part of pervasive background serpentinization.
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影响因子：
5.8
作者：
McCaig, Andrew M.;Cliff, Robert A.;MacLeod, Christopher J.
通讯作者：
MacLeod, Christopher J.
影响因子：
3.5
作者：
Klein, Frieder;Bach, Wolfgang;McCollom, Thomas M.
通讯作者：
McCollom, Thomas M.
影响因子：
5
作者：
A. Luhmann;B. Tutolo;B. Bagley;D. Mildner;Peter P. Scheuermann;J. Feinberg;K. Ignatyev;W. Seyfried
通讯作者：
A. Luhmann;B. Tutolo;B. Bagley;D. Mildner;Peter P. Scheuermann;J. Feinberg;K. Ignatyev;W. Seyfried
影响因子：
3.5
作者：
Bassett, Dan;Watts, Anthony B.
通讯作者：
Watts, Anthony B.
地壳中的流体 方辉橄榄石早期蛇纹石化过程中流体-岩石反应的实验限制
影响因子：
3.1
作者：
Klein F;Grozeva NG;Seewald JS;McCollom T;Humphris SE;Moskowitz B;Berquó TS;Kahl WA
通讯作者：
Kahl WA