DEVELOPMENT OF SEDIMENTARY BASINS IN THE ARCHEAN ABITIBI BELT, CANADA - AN OVERVIEW

Sedimentation in the Archean Abitibi greenstone belt occurred during four depositional episodes: (i) sedimentary cycle 1, 2730 - 2720 Ma; (ii) sedimentary cycle 2, 2715 - 2705 Ma; (iii) sedimentary cycle 3, 2700 - 2687 Ma; and (iv) sedimentary cycle 4, 2685 - 2675 Ma. Records of the first two sedimentary cycles are preserved in basins within the northern volcanic zone, whereas basins formed during the latter two sedimentary cycles are located within the southern volcanic zone of the Abitibi belt. Sedimentary cycles 1 and 3 represent deep-water facies, as indicated by turbidites, resedimented conglomerates, pelagic sediments, and ubiquitous iron-formations; subaerial deposits have not been identified. In contrast, sedimentary cycles 2 and 4 show a prevalence of fluvial to shallow-water marine and (or) lacustrine deposits. Tectono-magmatic influence on sedimentation during cycles 2 and 4 is documented by (i) the presence of numerous unconformities underlain by plutonic and volcanic rocks; (ii) locally voluminous shoshonitic and calc-alkaline volcanic rocks; (iii) abundance of plutonic detritus; (iv) rapid vertical and lateral facies changes; and (v) repetition of successions of large-scale (50-250 m thick) alluvial and shallow-water deposits. Sedimentary cycle 1 represents incipient arc basins dominated by volcaniclastic debris, whereas cycle 2 reflects unroofing of arc volcanoes down to the plutonic roots. The sedimentary basins of cycle 3 have been tentatively interpreted as basins connecting arc terranes, within which small extensional cycle 4 basins of the successor or pull-apart type developed. The sedimentary facies associations, the tectono-magmatic influence on sedimentation, the chronological basin evolution, and overall southward younging of the basins invite comparison with modem island arcs formed by plate-tectonic processes.