5:15 PM - 5:30 PM
[BAO01-15] Were Archean volcanic glasses habitats for microbial organisms?
Keywords:Archean, pillow lava, microbes, Abitibi
Here I examined pillow lavas from 2.7 Ga Abitibi Greenstone Belt in Canada. Pillow lavas have clear reaction rims, which were quenched and altered glasses before metamorphism. Typical mineral assemblages in reaction rims are paragonite, chlorite, actinolite, titanite, quartz, calcite, pyrite and epidote. Low metamorphic grade (lower greenschist facies) is suggested by those mineral assemblage. Mineral chemistries suggest that alkaline solutions was responsible for formation of primary minerals, implying alkaline 2.7 Ga ocean.
Titanite occurs in aggregates of fine crystals in chlorite matrix, and often accompanied by unclear tubes. Occurrence of titanite aggregates is identical to bio-alteration features found in other Archean pillow lavas. However, the length and density of tubes are much less compared to others. The examined samples in the present study were less metamorphosed compared to others (upper greenschist facies). Absence of clear tubes in less metamorphosed rocks suggest that tubes in Archean pillow lavas were not products of bio-alteration, but products of metamorphism.