In situ monitoring of reaction progress during serpentinization of oceanic lithosphere using synthetic fluid inclusions

目前很少有技术可以对天然宿主矿物内部的矿物反应进行实时的视觉观察和成分测量。弗吉尼亚理工大学（Virginia Tech）的两名研究人员进行的这项研究探索了一种令人兴奋的、具有潜在变革意义的新实验方法，通过这种方法，在实验室中培养充满类似海水成分的流体的合成流体包裹体，然后将其保持在发生重要地质矿物反应的温度和压力下。在这些反应中，由于流体和宿主矿物之间的反应，次生矿物在包裹体中沉淀。这项研究的目标是海洋地壳的蛇纹石化，它涉及蛇纹石，一种含水矿物，以及其他由无水富镁硅酸盐矿物（橄榄石，辉石和石榴石）形成的次生相，这些矿物是海底熔岩的主要成分。海洋地壳的蛇纹石化作用将水释放到地幔中，从而引发熔融和弧火山作用。它还与矿物反应过程中由于氢的释放而产生的非生物有机化合物有关。这些有机分子可以构成生活在海洋地壳中的微生物食物链的基础。更广泛的影响包括：(1)开发新的实验方法并证明其实用性，(2)开发与蛇纹石化反应相关的含水矿物的拉曼光谱鉴定，(3)支持早期职业女性科学家和少数民族研究生；(4)用西班牙语创建科学播客，让西班牙观众了解科学和拟议的研究。该实验程序将在~280℃下对矿物中的流体进行数周的反应，并使用各种最先进的分析技术监测流体包裹体中发生的溶解和沉淀反应，这些反应是时间、温度、流体成分和宿主矿物成分的函数，包括：显微测温、拉曼光谱、激光烧蚀电感耦合等离子体质谱、微傅立叶变换红外光谱和聚焦离子束扫描电子显微镜。另一个研究目标是发展拉曼光谱作为鉴定与蛇纹石化有关的相的工具，包括鉴定温石棉、蜥蜴石、反长花岗岩和磁铁矿，以及正在进行反应的原岩相。实验结果将与热力学模型的预测结果进行比较。这项实验技术的成功发展及其适用性的证明有可能影响其他科学领域，如药理学和材料科学，在这些领域，实时观察化学反应及其在宿主晶体中的反应速率的能力可能会导致理解上的突破。

Few techniques exist where visual observations and compositional measurements can be made of mineral reactions inside natural host minerals in real-time. This research by two investigators at Virginia Tech, one of whom is early career, explores an exciting and potentially transformative new experimental method by which synthetic fluid inclusions, filled with fluids of seawater-like composition, are grown in the laboratory and then held at temperatures and pressures at which important geological mineral reactions occur. In these reactions, secondary minerals precipitate inside the inclusion due to the reaction between the fluid and host mineral. This research targets serpentinization of the ocean crust, which involves the formation of serpentine, a hydrous mineral, and other secondary phases from anhydrous magnesium-rich silicate minerals (olivine, pyroxene,and garnet) that are the primary constituents of seafloor lavas. Serpentinization of ocean crust releases H2O into the mantle which can trigger melting and arc volcanism. It is also linked to the generation of abiotic organic compounds due to the release of hydrogen during mineral reaction. These organic molecules can form the base of the food chain for microbes living in in the ocean crust. Broader impacts of the work include (1) developing new experimental methods and demonstrating their utility, (2) developing the Raman spectroscopic identification of hydrous minerals associated with serpentinization reactions, (3) support of an early career female scientist and a minority graduate student; and (4) creation of podcasts on science in Spanish to inform and excite Hispanic audiences about science and the proposed research. This experimental program will react fluids in minerals at ~280 degrees C for a number of weeks and monitor the dissolution and precipitation reactions that take place in the fluid inclusions as a function of time, temperature, fluid composition, and host mineral composition using a variety of state-ot-the-art analytical techniques that include: microthermometry, Raman spectroscopy, laser ablation inductively coupled plasma mass spectrometry, micro-FTIR (Fourier Transform Infrared) spectroscopy, and FIB-SEM (focused ion beam scanning electron microscopy). An additional research goal is to develop Raman spectroscopy as a tool for the identification of phases associated with serpentinization, including the identification of chrysotile, lizardite, antigorite, and magnetite, as well as the protolith phases undergoing reaction. Results of the experiments will be compared with predictions from thermodynamic models. Successful development of this experimental technique and demonstation of its applicabilty has the potential to impact other fields of science such as pharmachology and materials science where the ability to observe chemical reactions and their rates of reaction in host crystals in real-time may lead to breakthroughs in understanding.