Abstract

Investigation of the stratigraphy and structure of the 1.9 Ga Wilson Island Group has led to sedimentological and tectonic interpretations that are consistent with models for an Early Proterozoic collision between the Slave and Rae provinces. The lower part of the 8 km thick Wilson Island Group consists of alluvial clastic rocks and a bimodal volcanic suite. These are overlain by mixed siliciclastic and carbonate rocks that are inferred as representing a combination of alluvial and shallow-marine sedimentation. Finally, an upward-fining succession of feldspathic sandstone, ironstone, and mudstone records progradation of an alluvial system followed by a major transgression. Soft-sediment deformation structures, intrabasinal coarse detritus, and abrupt vertical facies changes collectively indicate that the early stages of deposition were tectonically controlled.Regional penetrative foliations and a steeply plunging stretching lineation reflect deformation concomitant with greenschist-facies to lower amphibolite-facies metamorphism. Open to tight, plunging, northwesterly overturned folds formed synchronously with axial-plane cleavage in quartzites and deformed an older cleavage in pelites. These synmetamorphic structures were refolded by postmetamorphic kinks and dissected by transcurrent and normal faults.The Wilson Island Group evolved during postcollisional convergence, when thrusting and dextral transcurrent shearing characterized the regional tectonic style. However, the bimodal volcanic suite indicates a component of crustal extension that, in the regional context, favours a pull-apart-basin origin for the Wilson Island Group.

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