Mineralogical controls on the nature and composition of fluids in serpentinites

对蛇纹岩中流体的性质和成分的矿物学控制

• 批准号: 327166-2007
• 负责人: Normand, Charles
• 金额: $ 1.13万
• 依托单位: Université du Québec à Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2008
• 资助国家: 加拿大
• 起止时间: 2008-01-01 至 2009-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=397612
• 关键词: Mineralogical; controls; nature; composition; fluids

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.

超镁铁岩构成了地球的一大部分，可以接触到水，并且通常在低压和低温下进行水化变质。在适当的物理化学条件下，这可能导致在各种构造环境中形成蛇纹岩（主要由温石棉等蛇纹矿物组成的岩石）。在蛇纹石化过程中，发生了许多重要的反应。特别令人感兴趣的是; 1）产生大量的氢; 2）随着流体温度的降低，pH值升高，溶解的二氧化硅降低，这可能会在富二氧化硅岩石与其超镁铁质寄主之间的界面处引起钙硅酸盐蚀变; 3）形成金属矿床，如镍。在蛇纹岩化过程中，条件可以变得足够还原，以稳定铁镍合金和自然铁，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化流体的性质联系起来。流体在什么条件下是类气体还是类液体？在地壳内发现的压力和温度条件范围内确定后者是进一步评价碳氢化合物气体的生成、碳氢化合物的水解和矿石金属的流动性的重要的第一步。详细研究矿物学和被困在蛇纹石化事件中生长的矿物中的化石流体，可以为解决这些悬而未决的问题提供线索，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非生物成因的碳氢化合物向海洋的收支、金属物质转移对形成经济矿床的效率以及极端环境中细菌生物体的主要食物来源的输入提供工具。