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

当大陆相撞并形成山脉时，深埋岩石中的化学反应可以向地球的海洋和大气中释放二氧化碳。虽然与人类活动(如化石燃料的燃烧)相比，这些“构造流”中释放的碳量微不足道，但这种碳在长地质时间尺度(超过100万年)上可能非常重要。事实上，这些地质上的碳循环过程对于维持一个生命可以进化和繁衍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界，即自复杂生命进化以来的最后5.41亿年；然而，有理由怀疑构造碰撞可能在早期地球上释放了显著更多的碳。因此，这项拟议的工作是对加拿大安大略省中央变质沉积带古岩石中的构造碳释放和造山进行的现场研究。这些岩石在10亿多年前以沉积物的形式沉积并埋藏在山脉中，远远早于植物、动物或任何类型的多细胞生命的进化。将结合实地工作、数值模拟和地球化学技术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重要制约因素。此外，对古代地球的研究可以作为考虑太阳系内外行星宜居性的类比。拟议的工作将结合详细的岩石学、矿物化学、块状岩石质量平衡计算、热力学模拟和稳定的碳和氧同位素测量来探索中晚元古代造山带的变质脱碳作用。将重建中央变质沉积带CO2释放的大小和机制，以验证早期地球上变质脱碳作用得到加强的假说。结合现有的地质年代学，这项工作将产生(1)对元古代造山带中二氧化碳释放速度、时间和大小的严格现场估计，以及(2)对变质脱碳作用中施加的压力、温度、原岩成分和流体流动的控制机制的理解。这项现场测试将是必要的，以解决空间可变的开放系统流体流动、交代作用和动力学效应带来的复杂性。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外展项目。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.