Testing for an enhanced metamorphic carbon flux on the Proterozoic Earth, Central Metasedimentary Belt, Ontario, Canada

当大陆碰撞和山脉形成时，深埋岩石中的化学反应会将二氧化碳释放到地球的海洋和大气中。虽然与人类活动（如燃烧化石燃料）相比，这些“构造通量”中释放的碳量微不足道，但这些碳在漫长的地质时间尺度（超过100万年）上可能非常重要。事实上，这些地质碳循环过程对于维持一个生命可以进化和繁荣的宜居星球至关重要。然而，关于地质碳循环的大部分工作都集中在显生宙，即复杂生命进化以来的最后5.41亿年；然而，我们有理由怀疑，在地球早期，构造碰撞可能释放了更多的碳。因此，本文的工作是对加拿大安大略省中央元沉积带古岩石的构造碳释放和造山过程进行实地研究。这些岩石在10亿多年前以沉积物的形式沉积下来，埋在山脉中，远远早于植物、动物或任何多细胞生命的进化。野外工作、数值模拟和地球化学技术的结合将被用来了解这些构造驱动的反应是如何释放碳的。这将成为我们理解地质、气候和生物过程之间相互作用的基本约束。此外，对古代地球的研究可以作为考虑太阳系内外行星可居住性的类比。本研究将结合详细的岩石学、矿物化学、整体岩石质量平衡计算、热力学模型和稳定的碳氧同位素测量，探索中晚元古代造山带变质脱碳作用。为了验证地球早期变质脱碳作用增强的假说，我们将重建中央变质沉积带的CO2释放幅度和机制。结合现有的地质年代学，这项工作将产生：(1)严格的基于现场的元古代造山带二氧化碳释放速率、时间和规模的估计；(2)对变质脱碳过程中控制压力、温度、原岩组成和流体流动的机制理解。这种现场测试对于解释由空间可变的开放系统流体流动、交代作用和动力学效应引入的复杂性是必要的。这项工作将支持至少一名博士生、多名本科生和高中生发展科学技能。此外，该项目将为K-8学生和更广泛的当地社区开发一个关于板块构造的推广计划。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。

When continents collide and mountain ranges are formed, chemical reactions in deeply-buried rocks can release carbon dioxide into Earth’s oceans and atmosphere. While the amount of carbon released in these ‘tectonic fluxes’ is miniscule in comparison to human activities (like the burning of fossil fuels), this carbon can be very important on long geologic timescales (more than one million years). In fact, these geologic carbon cycling processes have been essential to maintaining a habitable planet on which life could evolve and flourish. However, much of the work on geologic carbon cycling has focused on the Phanerozoic Eon, i.e., the last 541 million years since the evolution of complex life; yet, there is reason to suspect that tectonic collisions may have released significantly more carbon on the early Earth. The proposed work is, therefore, a field-based study of tectonic carbon release and mountain building in the ancient rocks from the Central Metasedimentary Belt in Ontario, Canada. These rocks were deposited as sediments and buried in a mountain range more than one billion years ago, long before the evolution of plants, animals, or any kind of multicellular life. A combination of field work, numerical modeling, and geochemical techniques will be used to understand how these tectonically-driven reactions released carbon. This will serve as an essential constraint on our understanding of the interplay between geological, climatic, and biological processes. Furthermore, study of the ancient Earth may serve as an analogue for consideration of planetary habitability both in our solar system and beyond.The proposed work will explore metamorphic decarbonation in an orogenic belt of the middle to late Proterozoic using a combination of detailed petrography, mineral chemistry, bulk rock mass-balance calculations, thermodynamic modeling, and stable carbon and oxygen isotope measurements. The magnitude and mechanisms of CO2 release in the Central Metasedimentary Belt will be reconstructed to test the hypothesis that metamorphic decarbonation was enhanced on the early Earth. Combined with existing geochronology, this work will generate (1) rigorous field-based estimates of the rate, timing, and magnitude of CO2 release in a Proterozoic orogen and (2) a mechanistic understanding of the controls pressure, temperature, protolith composition, and fluid flow exerted in metamorphic decarbonation. This field test will be necessary to account for the complexities introduced by spatially variable open-system fluid flow, metasomatism, and kinetic effects. The work will support at least one PhD student, multiple undergraduates, and high school students in developing scientific skills. In addition, the project will develop an outreach program on plate tectonics for K-8 students and the broader local community.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.