A critical appraisal of Archean basin–craton complexes

Abstract

Attempts have recently been made to define basins in the Superior Province. Criteria for outlining basin margins include the presence of oxide iron-formations, coarse clastic deposits, and felsic volcanics. However, oxide iron-formations commonly occur with turbidites in deep water, and do not define basin margins. Coarse clastics occur in two environmental settings in the Superior Province — subaerial alluvial fans and deep water submarine fans. They can only be used as basin margin indicators in the most general way. In many areas, submarine fan conglomerates stratigraphically overlie alluvial fan conglomerates, implying rapidly migrating 'basin margins' through time. An unjustified assumption has also been that the coarse clastics in any one 'basin' are time-equivalent. If they are diachronous, they do not necessarily define any one particular basin margin. There appears to be no a priori reason why felsic volcanics should mark basin margins unless the tectonic style of the basin has been assumed beforehand.Published maps of Archean basins purport to show the above facies associations at the 'margins'. Reexamination of the data shows that outlining the 'basins' is highly subjective, and that even in well mapped areas (Abitibi and Wabigoon basins), interpretation is ambiguous. Instead of an Archean craton in the Superior Province with many small basins, the data also suggest an Archean ocean with many small landmasses. Some of these are sialic and quiescent, some sialic with active volcanism, and some are entirely volcanic.