Abstract

In the south-central part of the Abitibi greenstone belt, a succession of Archean epiclastic sediments at least 2 km thick was deposited in the Duparquet Basin. The Destor–Porcupine fault and a secondary fault that splays off the major fault define the margins of this basin, which is at least 15 km long and up to 2.5 km wide. Sedimentary evidence of tectonic influence includes (i) rapid vertical and lateral facies changes over tens of metres; (ii) cyclic repetition of facies associations; (iii) mixed fining-upward – coarsening-upward – fining-upward sequences in conglomerate units; (iv) local derivation of most clasts; and (v) asymmetric distribution of fan deltas and braid deltas along the strike of the fault-bounded basin. Three basic facies associations are recognized: (i) conglomerate–sandstone facies association (CSFA); (ii) sandstone–argillite facies association (SAFA); and (iii) argillite–sandstone facies association (ASFA). The CSFA, which predominates at the faulted basin margins, constitutes 60–70% of the basin sediments. It exhibits salient features of streamflow-dominated fans or fan deltas, proximal braid deltas, and (or) coarse clastic braidplains. Large angular clasts of local derivation near the basin margins reflect limited distances of transport, supporting the alluvial fan – fan delta interpretation. The SAFA is assigned to a subaerial to subaqueous fan delta – braid delta setting, in part deposited during episodic storms and floods. The ASFA for the most part records sedimentation in a calm aqueous environment in which suspension deposition prevailed; a lacustrine setting is inferred, but incised conglomerates and channel-fill sandstones attest to sporadic floods and (or) storms. The CSFA in places occupies channels in the ASFA, suggesting progradation of alluvial fans into shallow water in response to source-area uplift. Modern analogues of the Duparquet Basin occur at convergent plate margins. Because it developed during a late orogenic stage, the Duparquet Basin may be classified as a successor basin. Sedimentary facies organization and basin configuration are similar to successor basins of the Cordillera of western Canada, as well as pull-apart basins adjacent to the San Andreas fault in California and the East Anatolian fault in Turkey.

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