LATE-OROGENIC BASINS IN THE ARCHEAN SUPERIOR PROVINCE, CANADA - CHARACTERISTICS AND INFERENCES

The late-orogenic Archaean Duparquet, Kirkland and Stormy basins of th e Canadian Superior Province are characterized by bounding crustal-sca le faults and abundant porphyry stock emplacement. Lava flows and pyro clastic deposits are restricted to the Kirkland and Stormy basins, and coarse elastic detritus characterizes the Duparquet basin. Seven dist inct lithofacies are identified: (1) mafic volcanic, (2) felsic volcan ic, (3) pyroclastic, (4) volcaniclastic, (5) conglomerate-sandstone, ( 6) sandstone-argillite (+/-conglomerate), and (7) argillite-sandstone (+/-tuffaceous sandstone). The mafic and felsic volcanic lithofacies r epresent effusive lava flows, the pyroclastic lithofacies is formed of subaerial surge and airfall deposits and the volcaniclastic lithofaci es is composed of reworked volcanic debris. The conglomerate-sandstone lithofacies is interpreted as alluvial fan, fan delta or proximal bra ided stream deposits, whereas the sandstone-argillite lithofacies is c onsistent with sandy-dominated flood- or braidplain deposits. A domina ntly shallow-water lacustrine setting is inferred for the argillite-sa ndstone lithofacies. These different lithofacies record the basin hist ory and can be used to identify basin-forming processes. Lithofacies s tacking and rapid lateral changes of lithological units in conjunction with interformational unconformities and basin margin faults suggest tectonically induced sedimentation. Volcanism can also influence basin evolution and the delicate balance between erosion, sedimentation, an d prevalent transport processes is affected by volcanic input. Catastr ophic influx of pyroclastic material facilitated mass-wasting processe s and formation of non-confined hyperconcentrated flood flow deposits account for local congestion of alluvial or fluvial dispersal patterns . Confined stream flow processes govern sedimentation during intravolc anic phases or prominent tectonic uplift. In addition, climate which c ontrols the weathering processes, and vegetation which stabilizes unco nsolidated material, affects the transport and depositional process. A CO2-rich aggressive weathering, humid Archaean atmosphere favours tra ction current deposits and an absence of vegetation promotes rapid den udation. Although tectonism is the prevalent long-term controlling fac tor in restricted basins, the effects of volcanism, climate and lack o f vegetation can also be detected. (C) 1998 Elsevier Science B.V. All rights reserved.