Late Archean to Early Paleoproterozoic global tectonics, environmental change and the rise of atmospheric oxygen Mark E. Barley a, * , Andrey Bekker b,1 , Bryan Krapez ˇ a,2 a School of Earth and Geographical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009, Australia b Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, Washington DC 20015, USA Received 23 August 2004; received in revised form 14 June 2005; accepted 24 June 2005 Available online 24 August 2005 Editor: E. Boyle Abstract Analysis of the tectonostratigraphic records of Late Archean to Early Paleoproterozoic terranes indicates linkage between global tectonics, changing sea levels and environmental conditions. A Late Archean tectonic cycle started at ~2.78 Ga involving the breakup of a pre-existing continent (Vaalbara) and the most prodigious period of generation and preservation of juvenile continental crust recorded in Earth history during a period of plume breakout (~2.72 to 2.65 Ga) accompanied by high sea levels. During this period, cratons formed by accretion of granitoid–greenstone terranes at convergent margins started to aggregate into larger continents (e.g. Kenorland). Lower sea levels between ~2.65 and 2.55 Ga were followed by a second (~2.51 to 2.45 Ga) period of plume breakout resulting in a global peak in magmatism, high sea levels and deposition of banded iron formations (BIF) on the trailing margins of the Pilbara and Kaapvaal cratons. Cratons in South Australia, Antarctica, India, and China record convergent margin magmatism, orogeny and high-grade metamorphism between 2.56 and 2.42 Ga. Continued aggregation of continental fragments (e.g. amalgamation of Indian cratons) may have formed the Earth’s first supercontinent by ~2.4 Ga with a return to low sea levels and relative tectonic quiescence before the supercontinent started to breakup from ~2.32 Ga. Although oxygenic photosynthesis had evolved by 2.71 Ga, the irreversible rise of atmospheric O 2 to N 10 À 5 PAL appears to have occurred between 2.47 and 2.40 Ga following the second plume breakout and coinciding with a decline in BIF deposition and the maximum extent of the supercontinent suggesting dynamic linkage between tectonics and both the sources and sinks of oxygen. Periods of plume breakout (2.72 to 2.65 Ga and 2.51 to 2.45 Ga) would have limited ocean productivity and the rate of photosynthesis and also enhanced the reduced conditions typical of the Archean biosphere, as well as the greenhouse gas contents of the atmosphere necessary to maintain temperate conditions. This suggests that either an increase in the oxidation state of volcanic gasses during the second plume breakout, or a decreased flux of reduced gasses following plume breakout, coupled with the filling of crustal oxygen sinks and possibly also an increase in ocean productivity and the rate of photosynthesis resulted in the global flux of reduced gasses falling below oxygen production leading to a rise of atmospheric 0012-821X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2005.06.062 * Corresponding author. Tel.: +61 8 64887322; fax: +61 8 64881037. E-mail addresses: mbarley@segs.uwa.edu.au (M.E. Barley), a.bekker@gl.ciw.edu (A. Bekker), bryank@segs.uwa.edu.au (B. Krapez ˇ). 1 Tel.: +1 202 4787974; fax: +1 202 4788901. 2 Tel.: +61 8 64882771; fax: +61 8 64881037. Earth and Planetary Science Letters 238 (2005) 156 – 171 www.elsevier.com/locate/epsl