Mineralogical controls on the nature and composition of fluids in serpentinites

超镁铁质岩石构成了地球上可接触到水的很大一部分，通常在低压和低温下发生水化变质作用。在适当的物理化学条件下，这可以导致在各种构造环境中形成蛇纹岩（主要由蛇纹岩矿物组成的岩石，如温石棉）。在蛇纹石化过程中，发生了许多重要的反应。特别感兴趣的是；1)产生大量氢气；2)随着流体温度的降低，pH值升高，溶解二氧化硅含量降低，这可能导致富二氧化硅岩石与其超镁铁质寄主界面的钙硅酸盐蚀变；3)形成镍等金属矿床。在蛇纹石化过程中，条件可以变得足够还原，以稳定铁镍合金和天然铁，并将固体或溶解形式的碳转化为碳氢化合物。然而，很少有研究试图将蛇纹岩中的矿物组合与蛇纹岩成矿流体的性质联系起来。在什么条件下流体是气态的还是液态的？在地壳内的压力和温度条件范围内建立后者是进一步评价碳氢化合物气体的产生、碳氢化合物的水解和矿石金属的流动性的重要的第一步。对矿物学和在蛇纹石化时期被困在矿物中的化石流体的详细研究可以为解决这些突出问题提供线索，并形成本研究计划的主体。对上述过程的理解将为评估全球海洋的非生物烃收支，形成经济沉积物的金属质量传递效率以及极端环境下细菌生物的主要食物来源输入提供工具。

Ultramafic rocks form a large part of the Earth accessible to water and are subject to hydration metamorphism, commonly at low pressure and temperature. Under appropriate physico-chemical conditions, this can lead to formation of serpentinites (rocks essentially composed of serpentine minerals such as chrysotile asbestos) in various tectonic settings. During serpentinization, a number of important reactions take place. Of particular interest are; 1) the generation of large amounts of hydrogen; 2) the increase in pH and lowering in dissolved silica with decreasing temperature of the fluids, which may induce calc-silicate alteration at the interface between silica-rich rocks and their ultramafic host; and 3) the formation of metallic ore deposits such as nickel. During serpentinization, conditions can become sufficiently reducing to stabilize iron-nickel alloys and native iron, and transform solid or dissolved forms of carbon into hydrocarbons. However, very few studies have attempted to correlate the mineral assemblages in serpentinites with the nature of the serpentinizing fluids. Under what conditions are fluids gas-like or liquid-like? Establishing the latter within the range of pressure and temperature conditions found within the Earth's crust is an essential first step to further evaluation of the generation of hydrocarbon gases, the hydrolysis of hydrocarbons and the mobility of ore metals. Detailed studies of the mineralogy and of fossil fluids that were trapped into minerals that grew during serpentinization episodes can provide clues to solving these outstanding issues and forms the body of this proposed research program. An understanding of the processes outlined above will provide the tools for evaluating the global abiogenic hydrocarbon budget to oceans, the efficiency of metal mass transfer for the formation of economic deposits, and the input of primary food source for bacterial organism in extreme environments.