RUI: Collaborative Research: Constraining peridotite alteration timescales with environmental tracers (3H, 39Ar, 14C and 81Kr)

该奖项全部或部分由《2021年美国救援计划法案》（公法117-2）资助。橄榄岩是地球上地幔的主要成分。水岩相互作用导致的橄榄岩蚀变在全球碳收支中起着重要作用，并产生能够支持以化学能为燃料的生命形式的氢气（H2）。该项目将利用阿曼的Samail蛇绿岩（地球表面最大的橄榄岩块）作为现场实验室，研究低温（25-60℃）橄榄岩蚀变过程。利用蛇绿岩地下水中的天然环境示踪剂，提供低温蚀变的最大时间尺度以及H2的来源和供应速率。这些结果最终将有助于计算低温橄榄岩蚀变速率和蛇绿岩系统中的流体流动，从而为利用蛇绿岩进行地质二氧化碳储存以应对气候变化提供信息。它们还将帮助我们了解在这种极端的高碱性环境中，在地球上其他低温橄榄岩蚀变的地方，以及可能在火星等其他地方，维持生命所需的化学能的数量。该项目将改变两所主要本科院校对地球科学家的教育和培训：萨克拉门托的加州州立大学（一所少数族裔院校）和纽约市的巴纳德学院（一所女子学院）。该项目将通过教师指导的学生项目和基于课程的本科生研究经验（CUREs）来支持学生的研究经验。CURE课堂模块将公开共享，供全国其他水文地质/地球化学讲师使用。该项目还将支助开发地下水示范箱，以说明环境示踪剂的使用和二次矿物的沉淀对地下水流动的影响。本项目旨在利用Samail蛇绿岩高碱性（pH 11-12）地下水中的一套环境示踪剂，确定低温橄榄岩蚀变的最大时间尺度以及H2气体的来源和供应速率。作为国际大陆科学钻探计划阿曼钻探项目的一部分，地下水样本将使用最近安装在Samail蛇绿岩地幔橄榄岩上的钻孔和采样设备收集。地下水年龄目前未知，估计跨越了几个数量级。对于这个项目，年龄分布将用环境示踪剂3H， 14C，稳定惰性气体，39Ar和/或81Kr来确定。这些年龄将确定低温橄榄岩蚀变的时间尺度的上限，并有助于确定引起这种蚀变的水-岩相互作用是否发生在水力传导的近地表，或者是否有更深或更早的贡献。其他示踪剂（溶解的He和H2, 3He/4He比率，H2中的δ2H）将用于区分先前提出的高碱性地下水中H2的几种来源：低温水岩相互作用的局部产生，深层来源的运输，或通过高温橄榄岩蚀变形成的流体包裹体风化释放。最后，结合地下水年龄和测量的H2浓度，将量化含水层中最小的H2积累速率。这个氢气积累速率可以用于在这个独特的生态系统中支持化学合成微生物生命的能力的生物能计算。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Peridotite is the main constituent of the Earth's upper mantle. Peridotite alteration through water-rock interaction plays an important role in the global carbon budget and produces hydrogen gas (H2) that can support lifeforms fueled by chemical energy. This project will use the Samail ophiolite in Oman, the largest chunk of peridotite rock at the Earth’s surface, as a field laboratory to investigate the process of low temperature (25-60oC) peridotite alteration. Natural environmental tracers in groundwater within the ophiolite will be used to provide a maximum timescale for low temperature alteration and the source and supply rate of H2. These results will eventually help to calculate the rate of low temperature peridotite alteration and fluid flow through the ophiolite system and thus inform the use of ophiolites for geological carbon dioxide storage to combat climate change. They will also provide insight into the amount of chemical energy available to support life in this extreme hyperalkaline environment and in other locations of low temperature peridotite alteration on Earth and potentially elsewhere, like Mars. This project will be transformative in the education and training of geoscientists at two primarily undergraduate institutions: California State University, Sacramento, a minority-serving institution, and Barnard College in New York City, a women's college. The project will support student research experiences through both faculty-mentored student projects and course-based undergraduate research experiences (CUREs). CURE classroom modules will be publicly shared for use by other hydrogeology/geochemistry instructors throughout the nation. The project will also support the development of groundwater demonstration tanks to illustrate the use of environmental tracers and the impact that precipitation of secondary minerals can have on groundwater flow. The aim of this project is to use a suite of environmental tracers in the hyperalkaline (pH 11-12) groundwater of the Samail ophiolite to determine the maximum timescale of low temperature peridotite alteration and the source and supply rate of H2 gas. Groundwater samples will be collected using boreholes and sampling equipment recently installed in the mantle peridotite of the Samail ophiolite as part of the International Continental Scientific Drilling Program's Oman Drilling Project. Groundwater ages are currently unknown and estimates span several orders of magnitude. For this project, age distributions will be determined with environmental tracers 3H, 14C, stable noble gases, 39Ar and/or 81Kr. These ages will place upper bounds on the timescale of low temperature peridotite alteration and help determine if the water-rock interaction causing this alteration is taking place in the hydraulically conductive near-surface or if there are deeper, and/or older contributions. Other tracers (dissolved He and H2, 3He/4He ratios, and δ2H in H2) will be used to distinguish between several previously proposed sources of H2 in hyperalkaline groundwater: local production by low temperature water-rock interaction, transport from deeper sources, or release through weathering of fluid inclusions formed by peridotite alteration at higher temperature. Finally, the combination of groundwater ages and measured H2 concentrations will be used to quantify a minimum H2 accumulation rate in the aquifer. This H2 accumulation rate can then be used in bioenergetic calculations of the capacity to support chemosynthetic microbial life in this unique ecosystem.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.