TRACES OF EARLY LIFE IN ARCHEAN VOLCANIC ROCKS FROM THE ABITIBI GREENSTONE BELT, CANADA

Over the past decade, the search for ancient life has shown that volcanic rocks are hospitable environments for microbial life. Pillow lava rims and glass shards within hyaloclastite deposits from the Abitibi Greenstone Belt (AGB) in Eastern Ontario contain microfossils indicative of ancient microbial activity. The ichnofossils are tubular mineralized structures formed during the etching of glass by microbes along fractures in ancient glassy rocks. The tubules have been mineralized by micro-meter scale titanite grains, which has allowed for them to be preserved through greenschist facies metamorphism.

The study area in the AGB is located on the Hurd Property, Harker Township, Eastern Ontario and has been dated to be 2701 Ma as part of the Blake River Group. The main outcrop is interpreted as an ancient hyaloclastite deposit, with massive to brecciated basalt flows as well as spherulitic dacite lobes, overlain by a thick sequence of hyaloclastite containing glass shards ranging from 1-2 mm in size. The hyaloclastite layer is overlain by a further massive basalt layer indicating subaqueous eruption in an ancient Archean Sea. Similar discoveries have been made in two other notable Archean greenstone sequences: the Barberton Greenstone Belt, South Africa and the Pilbara Craton, Australia.

Subaqueous volcanic rocks preserved in greenstone belts worldwide are a new geological setting in the search for early life on Earth. They are typically metamorphosed at a very low degree (greenschist facies) allowing the rocks to preserve delicate microbial microfossils. Recent missions to Mars have shown the presence of liquid water on the surface in the past. Basalts are common rocks on the surface of Mars making up a large percentage of the regolith and country rock. On a cratered surface like Mars, glassy impact breccias and possibly hyaloclastites could have easily come into contact with surface water. Since basalts are likely to be returned by any extra-terrestrial sample return mission, detailed studies of microbial alteration signatures preserved in aqueously altered basalts provide a useful Earth analogue for studies of possible extraterrestrial microbial habitats.