Important geochemical and tectonic events in the Paleoproterozoic Era lay the foundation for the status and operation of the modern Earth, including the initial rise of atmospheric oxygen paving the path for animal evolution, and the emergence of modern plate tectonic processes leading to the amalgamation of the Canadian Shield (Laurentia). Rudimentary geological and geochronological documentation of Paleoproterozoic sedimentary basins is the foundation from which we can ask larger questions about geochemical changes or plate tectonic events on the evolving Earth, since those questions are largely answered by analyzing the sedimentary record. This thesis outlines the stratigraphy, detrital zircon U-Pb geochronology, elemental and isotopic geochemistry, and basin evolution of the Paleoproterozoic Penrhyn and Piling basins on the Rae craton in Arctic Canada, which record important tectonic and geochemical events on both a regional and global scale.
The concentration of the redox-sensitive trace element, U, in seawater has not been constant throughout geologic time and is linked to changes in oceanic and atmospheric oxygen content. Secular variations in the record of U contents of shales and iron formations indicate that the redox state of the atmosphere-ocean system after the Great Oxidation Event (GOE) was more dynamic than previously thought. Trends towards lower oxygen content recorded after ~2.05 Ga in the middle Proterozoic suggest that oxygen level decreased. This is contrary to traditional models assuming unidirectional atmospheric oxygen rise throughout the Proterozoic. The data demonstrate the earliest signal of oxidative U cycling, manifested in 2.47 - 2.43 Ga iron formations, and show that oxygenation was a protracted process initiated shortly after the end of the Archean.
It has been proposed that a global and long-lived magmatic and tectonic shutdown event from ~2.45 to 2.22 Ga played a causal role in the GOE, since it overlaps the time interval in which atmospheric oxygen initially rose on Earth. Coupled U-Pb, Hf, and O isotope data on magmatic and detrital zircon determine that plate tectonic processes continued to operate during this interval. It is argued instead that plate tectonic processes are necessary to promote conditions favorable for atmospheric oxygen to rise.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:MWU.1993/22727 |
| Date | January 2013 |
| Creators | Partin, Camille Ann |
| Contributors | Bekker, Andrey (Geological Sciences), Camacho, Alfredo (Geological Sciences) Wang, Feiyue (Chemistry) Galven Halverson (Earth and Planetary Sciences, McGill University) |
| Publisher | Elsevier |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Detected Language | English |
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