ASTROBIOLOGICAL SIGNIFICANCE OF EARLY ARCHEAN ROCKS, OUTER GODTHåBSFJORD, SW GREENLAND: STILL SEARCHING, AND WHAT ARE WE FINDING?

More than a decade after the first claims about the discovery of paleobiological remnants in Early Archean (> 3.7 Ga) rocks on Akilia in the Outer Godthåbsfjord area of SW Greenland, considerable debate about virtually every aspect of the rocks (qtz-amph-px rock; QAP) in question continues, including, their age, their protolith, their petrogenesis, and their likelihood for containing relics of an Early Archean biosphere. Mere preservation of carbonaceous inclusions in any mineral phase in these rocks does not a priori constitute evidence for geologically and geochemically reworked relicts of a biosphere predating the more generally accepted evidence in the nearby ~3.71 Ga Isua Greenstone Belt (IGB). U-Pb geochronology of apatite, the host mineral for the carbonaceous inclusions, is Paleoproterozoic in age, indicating that the carbonaceous material is only older than that. Other minerals have radiometric ages coeval with known metamorphic events, all younger than the age of the IGB. The only age in excess of the IGB comes from cores of zircons in TTG-suite gneisses, which is nowhere in contact with the rocks containing carbonaceous inclusions, and does not necessarily date emplacement anyway. Claims for an igneous cross-cutting relationship with adjacent mafic and ultramafic rocks cannot be demonstrated in the field and requires a stratigraphic relationship between them and QAP that also cannot be demonstrated. Neither S- nor Fe-isotopes measured in QAP and adjacent rocks clearly point to a specific protolith; bulk rock and mineral geochemistry indicates that QAP was metasomatized, most likely by siliceous and carbonate-rich fluids. A discovery of rocks similar in field characteristics and lithology to QAP on the nearby island of Innersuartuut contains additional minerals, including what appears to be bands of disseminated feldspar. Continued work is required to demonstrate a correlation with QAP on Akilia, but the possible presence of feldspar would render a BIF protolith unlikely.