Abstract 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 pCO2 to 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.

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CO2-海水-岩石系统中基性岩溶解速率的实验研究

摘要 为了研究结晶海底玄武岩（来自胡安德富卡板块和中大西洋海脊）和来自特罗多斯蛇绿岩（塞浦路斯）的高度变化的辉长岩在海水和二氧化碳 (CO2)。实验在 40 °C 下进行了长达 20 天，初始 pH 值为~4.8，在~1 bar pCO2 下，以确定渐进的水-岩石相互作用。已经确定了岩石样品中硅和钙的元素稳态释放速率，发现它们的溶液浓度是岩石溶解的最有效监测器。基于溶解的 Si 和 Ca 浓度的质量平衡计算表明反应机制的运行集中在具有不一致溶解特征的晶粒表面。此外，基本动力学模型强调了实验过程中传质限制的作用。pH ~ 5 时的 Ca 释放速率表明斜长石溶解在所有岩石中的显着贡献，角闪石溶解在蚀变辉长岩中的额外贡献。发现所有固体的 Si 释放速率类似于先前研究的海水与玄武岩玻璃和冰岛结晶玄武岩之间的反应，但高于地下水-结晶玄武岩相互作用系统的测量速率。这种与以前的实验结果的比较重新开始了关于实验变量作用的争论，这些初始岩体和结晶度、pCO2 和溶解过程中的流体化学。我们的新数据表明，在相同的 pH 值下，富含 CO2 的盐水溶液与基性岩的反应速率高于低 pCO2 的淡水。最重要的是，蛇绿辉长岩和 Juan de Fuca 玄武岩的 Si 和 Ca 释放率与冰岛未改变的结晶玄武岩相似或更高，突出了蛇绿岩和近海基性岩储层在 CO2 地质储存方面可能发挥的潜在重要作用。