The Petrology of Abyssal Serpentinites: New Insights from Phase Petrology and Geochemical Reaction Path Modeling

海水与暴露的超镁铁质地幔和下部地壳岩石在缓慢和超慢扩张的大洋中脊的反应(称为蛇纹岩化作用)对海洋化学以及海底的机械和磁性具有重要影响。揭示这些反应的地球化学后果是加深我们对全球地球化学循环，特别是水和二氧化碳的了解的关键。蛇纹岩作用与强烈还原的条件有关，这些条件会导致产生游离氢气和低pH值的液体；蛇纹岩作用过程中释放的氢和甲烷支持微生物群落，这些微生物群落构成独特和复杂生态系统中食物网的基础。尽管蛇纹岩作用在改变大洋岩石圈的物理和化学性质方面很重要，但人们对蛇纹岩作用的反应途径知之甚少，而且比之前预期的要复杂得多。它们主要受蚀变温度、流体流量和初始岩石成分的控制，因此具有很大的变异性。本研究对大洋中脊、大陆裂谷边缘和俯冲带弧前地幔等不同深海环境中蛇纹岩橄榄岩的矿物学和地球化学进行了对比分析和模拟研究。大洋钻探计划钻探岩芯将结合使用传统的微探头和先进的同步加速器技术，以确定次生矿物的结构组合和化学成分。将结果与热力学模型进行了比较，以更深入地了解蛇纹化过程中的形成条件和反应途径。这项工作的更广泛影响包括支持一名之前没有NSF支持的早期职业研究人员，以及培训马萨诸塞州布里奇沃特州立学院的两名本科生。它还涉及使用加州劳伦斯伯克利实验室先进光源的国家实验室设施。

The reaction of seawater with exposed ultramafic mantle and lower crustal rocks at slow and ultra-slow spreading mid-ocean ridges (a process called serpentinization) has important implications for the chemistry of the oceans, as well as the mechanical and magnetic properties of the seafloor. Unraveling the geochemical consequences of these reactions is key to furthering our understanding of global geochemical cycles, particularly of water and carbon dioxide. Serpentinization is associated with strongly reducing conditions that lead to the generation of free hydrogen gas, and fluids with a low pH; and the Hydrogen and methane released during serpentinization support microbial communities that form the base of the food web in unique and complex ecosystems. Despite the importance of the serpentinization process in changing the physical and chemical nature of the oceanic lithosphere, the reaction pathways of serpentinization are poorly understood and much more complicated than previously anticipated. They are chiefly controlled by the temperature of alteration, fluid flux, and initial rock composition, and hence are highly variable. This research involves a comparative analytical and modeling study of the mineralogy and geochemistry of serpentinized peridotites from different deep-sea environments, including mid-ocean ridges, continental rifted margins, and the forearc mantle of subduction zones. A combination of traditional microprobe and cutting edge synchrotron techniques will be used on Ocean Drilling Program drill cores to determine the textural associations and chemical compositions of secondary minerals. Results with be compared with thermodynamic models to gain deeper insights into the formation conditions and reaction pathways during serpentinization. Broader impacts of the work include support of an early career researcher with no prior NSF support and train two undergraduate students from Bridgewater State College in Massachusetts. It also involves use of national lab facilities at the Advanced Light Source at Lawrence Berkeley Lab in California.