Water in garnet as a record of fluid flow during metamorphism

水是生命的重要组成部分，但它在地球深处的存在也有重大影响。地球中的水影响岩石的变形和融化，它在对社会至关重要的现象中发挥作用，包括地震，火山和具有经济价值的金属的集中。在地球深处10公里处形成的变质岩提供了这些过程的快照，对这些岩石和其中的矿物的研究可以更好地了解水如何影响这些重要现象。矿物石榴石通常在变质岩中发现，并且它在同心生长带中生长一段时间。这些生长带就像树木的年轮，记录着矿物所经历的历史信息，而不仅仅是时间的最终快照。测量石榴石不同区域的水含量可以作为地壳深处水释放和流动的记录器。这项工作将使用测量的水含量石榴石从五个不同的领域的地方寻找证据，有多少流动事件发生在石榴石的生长过程中，他们可能已经持续了多久。这项工作的结果将使人们能够在岩石中记录的水流与产生地震活动和富集具有经济价值的金属的过程之间建立联系。拟议的工作还将包括在马里兰州日期间向当地社区宣传水在地球上的重要性，届时马里兰州大学将向公众开放。该提案旨在结合其他流体流动示踪剂，对石榴石中的H2O进行现场测量（O同位素、Li同位素、石榴石中的微量元素浓度）来研究石榴石生长过程中的流体释放和流体流动事件的过程，并约束单个流体流动事件的周期性和持续时间。该项目将调查来自五个不同地区的石榴石，每个地区都有记录的流体释放或流体流动事件的证据。对各种地质背景下的变质岩的研究表明，流体流动事件的持续时间范围很广，其中一些非常迅速，从几周到几百年不等。这些估计是基于同位素和岩石示踪剂的大块岩石测量，因此代表了时间综合测量。变质岩中的许多特征表明，流体流动是循环的，可能会重新访问路径，在这种情况下，估计的持续时间可能会高估流体流动的持续时间，低估流体流动事件的数量。建议的工作解决了变质作用过程中流体释放和流体流动的基本问题。利用石榴石中的氢作为流体流动和流体释放事件的示踪剂的适用性将充分探讨耦合测量石榴石中的氢与其他示踪剂的流体流动。拟议中的工作将限制性质，周期性和持续时间的流体输送，帮助在变质设置的流体流动过程的理解。了解流体流动的周期性和时间尺度是很重要的，原因有很多-流体传输热量和质量，驱动变质反应，影响流变学，并有助于地震活动。这项工作也将提供一个更好的理解的行为和纳入石榴石中的H。这个奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

Water is an essential ingredient for life, but its presence in the deep Earth also has significant impacts. Water in the Earth affects how rocks deform and melt and it plays a role in phenomena critical to society including earthquakes, volcanoes, and the concentration of metals of economic value. Metamorphic rocks that form 10s of km deep in the Earth provide a snapshot of these processes, and study of these rocks and the minerals in them provides a better understanding of how water affects these important phenomena. The mineral garnet is commonly found in metamorphic rocks, and it grows over a period of time in concentric growth zones. These growth zones are like tree rings, recording information about the history experienced by the mineral rather than just a final snapshot in time. Measurements of water contents in different zones of a garnet can act as a recorder of the release and flow of water deep in the crust. This work will use measurements of the water content of garnets from five different field localities to look for evidence for how many flow events occurred during garnet growth and how long they may have lasted. The results of this work will allow for connections to be made between the flow of water recorded in the rocks with processes generating seismicity and concentrating metals of economic value. The proposed work will also include a component of outreach to the local community showing the importance of water in the Earth during Maryland Day, when the University of Maryland opens its doors to the general public.This proposal seeks to use in situ measurements of H2O in garnet in conjunction with other tracers of fluid flow (O isotopes, Li isotopes, trace element concentrations in garnet) to investigate processes of fluid release and fluid flow events during the growth of garnet and to constrain the cyclicity and duration of individual fluid flow events. This project will investigate garnets from five different localities, each of which has documented evidence for either fluid release or fluid flow events. Studies of metamorphic rocks from a variety of geologic settings show a range of durations of fluid flow events, some of which are quite rapid, on the scale of weeks to hundreds of years. These estimates are based on bulk-rock measurements of isotopic and petrologic tracers, and therefore represent a time-integrated measurement. Many features in metamorphic rocks suggest that fluid flow is cyclic and may revisit pathways, in which case the estimated durations may overrepresent the duration of fluid flow and underestimate the number of fluid flow events. The proposed work addresses fundamental questions about fluid release and fluid flow during metamorphism. The applicability of using H in garnet as a tracer of fluid flow and fluid release events will be fully explored by coupling measurements of H in garnet with other tracers of fluid flow. The proposed work will constrain the nature, cyclicity, and duration of fluid transport, aiding in the understanding of fluid flow processes in metamorphic settings. Understanding the cyclicity and timescales of fluid flow is important for a variety of reasons – fluids transport heat and mass, drive metamorphic reactions, impact rheology, and contribute to seismicity. This work will also provide a better understanding of the behavior and incorporation of H in garnet.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.