Archean unconformity in the Qalluviartuuq greenstone belt, Goudalie domain, northern Quebec

An unconformity in the northern Qalluviartuuq greenstone belt separates basement of metasedimentary and tonalitic rocks from conglomerate and sandstone. The basal conglomerate has tonalitic clasts, grading upward into a polymict assemblage of tonalite, basalt, andesite, granodiorite, metasedimentary and ultramafic clasts. The basalt, gabbro, and ultramafic clasts suggest that a metavolcanic terrane was being eroded in the (local) source area for the conglomerate, and yet the conglomerate passes with apparent stratigraphic continuity upwards into mafic volcanics. Either an older greenstone sequence within the basement complex contributed detritus to the conglomerate, or a tectonic break may be hidden in the complex structure of a fragmental mafic unit marking the contact between the conglomerate and metavolcanic units. In this second hypothesis, an overriding greenstone sheet would have shed clasts as it was thrust over synorogenic conglomerate deposited on basement.