ABSTRACT

High-pressure experiments were performed to investigate the effectiveness, rate and mechanism of carbonation of serpentinites by a carbon saturated COH-fluid between 1.5-2.5 GPa and 375-700 °C. This allows a better understanding of the fate and redistribution of slab-derived carbonic fluids when they react with the partially hydrated mantle within and above the subducting slab under pressure and temperature conditions corresponding to the forearc mantle.Interactions between carbon saturated CO₂-H₂O-CH₄-fluids and serpentinite were investigated using natural serpentinite cylinders with natural grain sizes and shapes in piston-cylinder experiments. The volatile composition of post-run fluids was quantified by gas-chromatography. Solid phases were examined by Raman-spectroscopy, electron microscopy and Laser-Ablation-ICP-MS. Textures, porosity and phase abundances of recovered rock-cores were visualized and quantified by three-dimensional, high-resolution computed tomography.We find that carbonation of serpentinites is efficient at sequestering CO₂ from the interacting fluid into newly formed magnesite. Time-series experiments demonstrate that carbonation is completed within ∼96 h at 2 GPa and 600 °C. With decreasing CO_2,aq antigorite is replaced first by magnesite + quartz followed by magnesite + talc + chlorite in distinct, metasomatic fronts. Above antigorite stability magnesite + enstatite + talc+chlorite occur additionally. The formation of fluid permeable reaction zones enhances the reaction rate and efficiency of carbonation. Carbonation likely occurs via an interface-coupled replacement process, whereby interconnected porosity is present within reaction zones after the experiment. Consequently, carbonation of serpentinites is self-promoting and efficient even if fluid flow is channelized into veins. We conclude that significant amounts of carbonates may accumulate, over time, in the hydrated forearc mantle.

中文翻译：

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利用蛇纹岩岩心在高压实验中研究水合前臂地幔楔的流体驱动碳酸化作用

摘要

进行了高压实验，以研究在1.5-2.5 GPa和375-700°C之间的碳饱和COH流体对蛇纹岩碳化的有效性，速率和机理。这允许更好的板坯衍生碳酸流体的命运和再分配的理解时，他们和内压力和温度的条件下对应于碳之间的弧前mantle.Interactions饱和CO俯冲板坯以上与部分水合反应地幔₂ -H ₂ O-CH ₄在活塞缸实验中，使用具有天然晶粒尺寸和形状的天然蛇纹石圆柱体研究了流体和蛇纹岩。运行后流体的挥发性成分通过气相色谱法定量。通过拉曼光谱，电子显微镜和激光烧蚀-ICP-MS检查固相。通过三维高分辨率的计算机断层扫描，可视化和量化了回收的岩心的质地，孔隙度和相丰度。我们发现蛇纹石的碳化能有效地将CO ₂从相互作用的流体中螯合成新形成的菱镁矿。时间序列实验表明，碳化在2 GPa和600°C的约96小时内完成。随着CO _2的减少_，aq菱铁矿先由菱镁矿+石英代替，然后由菱镁矿+滑石+亚氯酸盐取代，形成明显的交代前沿。超过抗蛇麻石的稳定性还会另外发生菱镁矿+顽辉石+滑石+亚氯酸盐。流体可渗透的反应区的形成提高了反应速率和碳酸化效率。碳化可能是通过界面耦合的置换过程发生的，因此实验后反应区内存在互连的孔隙。因此，蛇纹石的碳酸化是自我促进的，并且即使流体流被引导到静脉中也能有效地进行碳化。我们得出的结论是，随着时间的流逝，大量的碳酸盐可能会积聚在水合前臂地幔中。