HR: 16:35h
AN: U44A-02    [Abstracts]
TI: Plume Magmatism, Continental Tectonics, Increased Subaerial Volcanism and the Rise of Atmospheric Oxygen
AU: * Barley, M E
EM: mbarley@cyllene.uwa.edu.au
AF: The University of Western Australia, School of Earth and Geographical Sciences, 35 Stirling Highway, Crawley, WA 6009, Australia
AU: Kump, L R
AF: Pennsylvania State University, NASA Astrobiology Institute, Department of Geosciences, 535 Deike Building, University Park, PA 16802, United States
AB: The remarkable coincidence of the rise of atmospheric oxygen with the transition from the Archean to the Proterozoic Eons suggests that a likely cause-and-effect relationship with the defining tectonic change (the stabilization of continental cratons). A shift in the locus of volcanism from largely submarine to a mix of submarine and subaerial is argued to be the primary cause. This shift would have been accompanied by a significant reduction in the sink for oxygen provided by reduced volcanic gases: Archean submarine volcanoes emitted molecular hydrogen in excess, allowing hydrogen to accumulate in the atmosphere and prevent the build up of oxygen, whereas Proterozoic subaerial/submarine volcanoes did not, so oxygen came to dominate atmospheric composition. Evidence for a possible early rise to low oxygen levels between 2.94 and 2.74 Ga coincides with stabilization of the Pilbara and Kaapvaal Cratons and subsequent continental subaerial flood basalt volcanism. In contrast, the most intense episode of dominantly submarine mantle plume activity and growth and stabilisation of continental crust recorded in Earth history between 2.74 and 2.66 Ga resulted in a return to anoxic conditions. An abrupt switch close to the Archean-Proterozoic transition from dominantly submarine volcanic eruptions to a mixture of submarine and subaerial eruptions similar to that of the Phanerozoic during the 2.45 Ga plume break out and the final stages of amalgamation of Archean cratons into Earth's first large stable continents or supercontinent was coincident with strong evidence for the permanent establishment of atmospheric oxygen. Either cyanobacterial evolution was somehow tied to the 2.45 Ga event, or more likely, cyanobacterial oxygen photosynthesis evolved earlier, but its expression in the atmosphere was delayed by an overwhelming volcanic sink.
DE: 0325 Evolution of the atmosphere (1610, 8125)
DE: 8110 Continental tectonics: general (0905)
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8430 Volcanic gases
DE: 9622 Proterozoic
SC: Union [U]
MN: 2007 Joint Assembly