3.5-Ga hydrothermal fields and diamictites in the Barberton Greenstone Belt-Paleoarchean crust in cold environments

Maarten J de Wit; Harald Furnes

doi:10.1126/sciadv.1500368

3.5-Ga hydrothermal fields and diamictites in the Barberton Greenstone Belt-Paleoarchean crust in cold environments

Sci Adv. 2016 Feb 26;2(2):e1500368. doi: 10.1126/sciadv.1500368. eCollection 2016 Feb.

Authors

Maarten J de Wit¹, Harald Furnes²

Affiliations

¹ AEON and Earth Stewardship Science Research Institute, Nelson Mandela Metropolitan University 7701, Port Elizabeth 6031, South Africa.
² Department of Earth Science and Center for Geobiology, University of Bergen, Allegt. 41, Bergen 5007, Norway.

Abstract

Estimates of ocean temperatures on Earth 3.5 billion years ago (Ga) range between 26° and 85°C. We present new data from 3.47- to 3.43-Ga volcanic rocks and cherts in South Africa suggesting that these temperatures reflect mixing of hot hydrothermal fluids with cold marine and terrestrial waters. We describe fossil hydrothermal pipes that formed at ~200°C on the sea floor >2 km below sea level. This ocean floor was uplifted tectonically to sea level where a subaerial hydrothermal system was active at 30° to 270°C. We also describe shallow-water glacial diamictites and diagenetic sulfate mineral growth in abyssal muds. These new observations reveal that both hydrothermal systems operated in relatively cold environments and that Earth's surface temperatures in the early Archean were similar to those in more recent times.

Keywords: Barberton (South Africa); Paleoarchean; cold Archean climate; glacial diamictites; hydrothermal fields; oxygen isotopes; silicification; sulphate pseudomorphs.