Experimental study on mafic rock dissolution rates within CO2-seawater-rock systems
Experimental study on mafic rock dissolution rates within CO2-seawater-rock systems
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DOI：
10.1016/j.gca.2020.01.004
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发表时间：
2020-03
影响因子：
5
通讯作者：
C. Marieni;J. Matter;D. Teagle
中科院分区：
文献类型：
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作者：
C. Marieni;J. Matter;D. Teagle
远离平衡批次实验已进行研究的低温溶解潜力的结晶海底玄武岩（从胡安德富卡板块和大西洋中脊）和高度蚀变辉长岩从特罗多斯蛇绿岩（塞浦路斯）在海水和二氧化碳（CO2）的存在下。这些实验在40 °C下进行了长达20天，初始pH值为4.8，pCO 2低于0.1 bar，以确定渐进的水-岩相互作用。元素从岩石样品的稳态释放率已被确定为硅和钙，其中的溶液浓度被认为是最有效的监测岩石溶解。基于溶解的Si和Ca浓度的质量平衡计算表明，反应机制的操作集中在晶粒表面上，这是不一致溶解的特征。此外，基本的动力学模型强调了实验过程中质量传输限制的作用。在pH = 1.5的钙释放率表明斜长石溶解在所有岩石中的显着贡献，与角闪石溶解在蚀变辉长岩的额外贡献。硅释放速率的所有固体被发现是类似于以前研究的海水和玄武岩玻璃和结晶玄武岩之间的反应，从冰岛，但高于地下水结晶玄武岩相互作用系统测量的速率。这种与以前的实验结果的比较恢复的实验变量，如初始岩体和结晶度，二氧化碳分压，溶解过程和流体化学的作用的辩论。我们的新数据表明，富含CO2的盐溶液与镁铁质岩石反应的速率高于淡水，低pCO 2，在相同的pH值。最重要的是，蛇绿辉长岩和胡安德富卡玄武岩显示硅和钙的释放速率相似或高于未改变的结晶玄武岩从冰岛，突出潜在的实质性作用，蛇绿岩和海上镁铁质水库可以发挥地质封存CO2。
Far-from-equilibrium batch experiments have been performed to study the low temperature dissolution potential of crystalline submarine basalts (from Juan de Fuca Plate and Mid-Atlantic Ridges) and of a highly altered gabbro from the Troodos ophiolite (Cyprus) in presence of seawater and carbon dioxide (CO2). The experiments have been carried out at 40 °C for up to 20 days with initial pH of ∼4.8 and under ∼1 bar pCO2to identify the progressive water-rock interactions. Elemental steady-state release rates from the rock samples have been determined for silicon and calcium, the solution concentrations of which were found to be the most effective monitors of rock dissolution. Mass balance calculations based on dissolved Si and Ca concentrations suggest the operation of reaction mechanisms focussed on the grain surfaces that are characteristic of incongruent dissolution. Also, basic kinetic modelling highlights the role of mass-transport limitations during the experiments. Ca release rates at pH ∼ 5 indicate significant contributions of plagioclase dissolution in all the rocks, with an additional contribution of amphibole dissolution in the altered gabbro. Si release rates of all solids are found to be similar to previously studied reactions between seawater and basaltic glass and crystalline basalt from Iceland, but are higher than rates measured for groundwater-crystalline basalt interaction systems. This comparison with previous experimental results resumes the debate on the role of experimental variables, such initial rock mass and crystallinity, pCO2, and fluid chemistry on dissolution processes. Our new data suggest that CO2-rich saline solutions react with mafic rocks at higher rates than fresh water with low pCO2, at the same pH. Most significantly, both ophiolitic gabbro and Juan de Fuca basalts show Si and Ca release rates similar or higher than unaltered crystalline basalt from Iceland, highlighting the potential substantial role that ophiolitic rocks and offshore mafic reservoirs could play for the geological storage of CO2.