Water in Nominally Anhydrous Minerals of the Lower Crust

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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.