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

Florida State University, Tallahassee FL

Investigators

Abstract

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.