Water in Nominally Anhydrous Minerals of the Lower Crust

下地壳名义无水矿物中的水

• 批准号: 1119472
• 负责人: Sheila Seaman
• 金额: $ 17.5万
• 依托单位: University of Massachusetts Amherst
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2015-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119472&HistoricalAwards=false
• 关键词: Water; Nominally; Anhydrous; Minerals; Lower

Intellectual Merit. In contrast to long-held opinion that the lower crust and mantle are nearly anhydrous domains, it is increasingly recognized that nominally anhydrous minerals (NAMs; i.e., those for which water is not a stoichiometric part of the mineral formula) potentially constitute a significant inventory of water in the Earth?s interior. Water plays a critical role in many fundamental interior Earth processes. For example, despite low estimated abundance, water in the mantle it is thought to influence convection and recycling of chemical components, planetary rheology and deformation, and seismic velocity characteristics. The Earth?s crust is dominated by feldspar and quartz that may host significant amounts (up to hundreds of ppm) of water, thus comprising a major planetary water reservoir. In an attempt to quantify the content and distribution of water in the lower crust, this project focuses on a study of the Athabasca Granulite Terrane, northern Saskatchewan, that exposes some ~20,000 km2 of representative lower crustal lithologies. Concentrations of water will be measured and mapped using Fourier transform infrared (FTIR) spectroscopy. Cathodoluminescence imaging also will be used to identify preserved primary zoning in quartz that might correlate with localization of primary fluid inclusions. The abundance and distribution of water in these rocks will be quantified and this knowledge used to assess the following aspects of the influence of water on crustal processes: [1] to what extent does water in NAMs act as a flux to promote partial melting in the lower crust?, [2] to what extent are metamorphic reactions that seemingly involve only ?anhydrous? minerals actually dependent on progressive dehydration of NAM reactants?, and [3] to what does water liberated from NAMs influence crustal deformation? Broader Impacts. In addition to the typical societal benefits of training and financially supporting graduate and undergraduate students, this project offers the opportunity of continuing a rich exchange of ideas in a field setting with members of the Geologic Survey of Canada and the Saskatchewan Geologic Survey, and to conduct evening geologic forums for the residents of the remote town of Stony Rapids, Canada. The study area will be the site of a field forum for geophysicists and geologists in the future. Research results will also be shared in various outreach activities. For example, a series of articles is to be published in Canadian newspapers, focusing on the geology of the Athabasca Granulite Terrane; these are based on interviews with PI Williams.

智力优势。 与长期以来认为下地壳和地幔几乎是无水区域的观点相反，人们越来越认识到，名义上的无水矿物（NAMs;即，那些水不是矿物化学式的化学计量部分的物质）可能构成地球上水的重要库存？的内部。水在地球内部的许多基本过程中起着关键作用。 例如，尽管地幔中的水的丰度估计较低，但据认为它会影响化学成分的对流和再循环、行星的流变和变形以及地震速度特征。 地球？地球的地壳主要由长石和石英组成，可能含有大量的水（高达数百ppm），因此构成了一个主要的行星水库。 为了量化下地壳中水的含量和分布，本项目重点研究萨斯喀彻温省北方的阿萨巴斯卡麻粒岩地体，该地体暴露了约20，000平方公里的代表性下地壳岩性。 将使用傅里叶变换红外光谱法测量和绘制水的浓度。阴极发光成像也将被用来确定保存在石英原生环带，可能与本地化的原生流体包裹体。 这些岩石中水的丰度和分布将被量化，这一知识将用于评估水对地壳过程的影响的以下方面：[1] NAMs中的水在多大程度上充当促进下地壳部分熔融的通量？[2]变质反应在多大程度上似乎只涉及？无水？矿物实际上依赖于NAM反应物的逐步脱水？[3] NAMs释放的水对地壳形变的影响是什么？ 更广泛的影响。除了培训和资助研究生和本科生的典型社会效益外，该项目还提供了与加拿大地质调查局和萨斯喀彻温省地质调查局成员在实地继续进行丰富的思想交流的机会，并为加拿大偏远城镇斯托尼拉皮兹的居民举办晚间地质论坛。该研究区将成为未来地球化学家和地质学家的现场论坛。研究成果也将在各种外联活动中分享。 例如，将在加拿大报纸上发表一系列文章，重点介绍阿萨巴斯卡麻粒岩地体的地质情况;这些文章是根据对PI威廉姆斯的采访撰写的。