In this paper, we describe the relations between the paleogeographic and tectonic evolution of the southwestern part of the Archean Abitibi and Bellecombe belts. Volcanism in the Abitibi Belt created a very thick, anisotropic plate composed of competent volcanic rocks and broken by the Duparquet–Destor break. The depocenters of the upper division of diverse volcanic rocks subsided about 10 km relative to their surroundings, and some central volcanic complexes within this division were consolidated by synvolcanic plutons and their thermal metamorphic aureole. The Cadillac break, a normal fault, separated the Abitibi and Bellecombe belts. The latter consisted of comparatively incompetent sedimentary rocks on top of a basement composed of ultramafic–mafic flows.North–south compression of the volcanic terrain during the Kenoran Orogeny produced a set of flexure folds, F1, that curve around the consolidated cores of central volcanic complexes generally in an easterly direction. Synclinoria nucleated at the deeply subsident depocenters of the upper diverse division. Further north–south flattening and subvertical stretching produced the east-trending F2 folds, their axial-plane schistosity S2, and local superposed schistosities S3 and S4. Southward verging recumbent folds suggest that the Bellecombe Belt simultaneously was pulled northward below the Abitibi Belt. During the orogeny, the Duparquet–Destor and Cadillac breaks were transformed to thrust faults; the Duparquet–Destor break also shows minor (< 3 km) right-lateral strike slip. Diapiric rise of late- to post-kinematic plutons locally distorted earlier schistosities.
The pre-Kenoran Archean stratigraphy has always been of prime interest to geologists working in the Superior Province. However, one must realize that the problems raised have remained, for the most part, without satisfactory solution. Thus, the respective age relation of the thick lithostratigraphic metavolcanic and metasedimentary units (Pontiac), forming respectively the Baby Rift and its northern flank to the northeast of Ville-Marie in Temiscaming, has not been defined with certainty to date.During a geological mapping project on a scale of 1:12 000, covering the township of Baby and adjacent parts of the townships of Guérin and Guigues, it has become possible for us to remove the uncertainty and to define the age relation of the two units mentioned. We can now state that the metasedimentary unit (Pontiac) forms the stratigraphic base of the metavolcanic unit.To arrive at this conclusion it was first necessary to determine the size of the main folded structures in the region of Rapide des Quinze, then to uncover and let weather the outcrops over several kilometers, in order to define the actual contact of the two units. [Translated by the Journal]
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