Deformation features and critical field relationships of early Archaean rocks, Akilia, southwest Greenland

Lithologically varied early Archaean rocks on the island of Akilia, Godthåbsfjord, southwest Greenland include a quartz–pyroxene unit that has been proposed as a BIF. Carbon isotope data from graphite particles in apatites within this unit have further been proposed to represent evidence for Earth’s earliest life. We present field observations which demonstrate that all lithologies on SW Akilia have been intensely deformed during both early and late Archaean high-grade metamorphism. In our view, this deformation precludes unambiguous demonstration of purported sedimentary features in the quartz–pyroxene rock, a unit which we interpret as the result of metasomatic, metamorphic, and tectonic reworking of a mafic–ultramafic protolith. Such an origin is completely incompatible with the quartz–pyroxene rock hosting any signs of early biogenic activity. We also reappraise contact relationships between Amı̂tsoq gneisses and mafic–ultramafic rocks and can find no convincing evidence for the existence of intrusive relationships that have been central to geochronological interpretations on Akilia.