Abstract

The region comprises parts of the southern zone of the Abitibi greenstone belt and of the Bellecombe gneiss belt, and the Belleterre–Angliers greenstone belt. The stratigraphic sequence of the Abitibi Belt consists of (1) a lower ultramafic division; (2) a middle tholeiitic division; and (3) an upper diverse division; these divisions lap onto an older volcanic sequence to the north and west. In the Bellecombe Belt, sediments overlie the lower ultramafic division; these sediments coarsen toward the Abitibi Belt and toward the stratigraphic top. The volcanic rocks of the Belleterre–Angliers Belt overlie the sediments of the Bellecombe Belt.Five paleogeographic phases have been recognized. During phase I, a deep marine ultramafic lava plain covered the south part of the Abitibi Belt and the Bellecombe Belt. Faulting took place at the Duparquet–Destor break. During phase II, tholeiitic basalts formed a deep marine lava plain in the west of the Abitibi Belt, whereas flows erupted mainly from central volcanic complexes in the east. Simultaneously, sediments derived from a volcanic–plutonic hinterland to the north began to accumulate in the Bellecombe Belt. In phase III, lavas of the upper diverse division erupted from well defined central volcanic complexes in the Abitibi Belt, and sedimentation continued in the Bellecombe Belt. In phase IV, volcanic centers built above sea level, and local fans of tuff and of volcanic-derived conglomerate and sandstone interfingered with the volcanic–plutonic-derived sediments at the southern limit of the Abitibi Belt. The volcanic sequence was uplifted at the Cadillac break during phase V, with consequent progradation of coarse conglomerates southward.The stratigraphic and paleogeographic evolution of the Abitibi Belt is comparable to the evolution of immature oceanic island arcs in the Cenozoic.

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