Evolution of the south-central segment of the Archean Abitibi Belt, Quebec. Part III: Plutonic and metamorphic evolution and geotectonic model

Abstract

Textural criteria permit distinction between the pre-Kenoran and Kenoran phases of plutonism and metamorphism. The pre-Kenoran plutons and pre-Kenoran metamorphic phases are directly related to the volcanic evolution. Synvolcanic tonalite–trondhjemite plutons and swarms of mafic and felsic dykes core central volcanic complexes. The volcanic rocks underwent three types of pre-Kenoran metamorphism, namely, a pervasive alteration, a thermal contact metamorphism that affected narrow aureoles around synvolcanic plutons, and a high-intensity hydrothermal alteration that affected cross-cutting pipes in central volcanic complexes.Synkinematic Kenoran metamorphism resulted in the growth of minerals (chlorite, actinolite, etc.) parallel to schistosities. Synkinematic metamorphic grade ranges form the pumpellyite–prehnite facies to the amphibolite facies. Late- to post-kinematic metamorphic phases resulted in the growth of minerals across schistosities. Syn- to post-kinematic plutons are not voluminous in the part of the Abitibi Belt described here, but they underlie vast areas in the Bellecombe Belt. They range from gneissose early synkinematic plutons to late-kinematic plutons that have well preserved igneous textures.The paleogeographic, tectonic, plutonic, and metamorphic histories of the Abitibi and Bellecombe belts are reviewed and we conclude that the belts are analogous to an island arc – fore-arc basin system.