Parallel evolution of Archaean low- and high-grade terrane: A view based on relationships between the Abitibi, Wawa and Kapuskasing belts

Abstract

Abstract The Kapuskasing structural zone (KSZ) is a region of high-grade Archaean gneiss transverse to the regional east—west structural trends of the adjacent lower-grade Abitibi, Wawa and Quetico belts. The structural zone is made up of granulite and amphibolite facies paragneiss, tonalitic gneiss and anorthosite-suite gneiss, whereas adjacent regions are metavolcanic—metasedimentary belts, with gneissic and plutonic components. Foliations in the KSZ strike northeast and dip moderately northwest. To account for the development of contrasting lithological, structural and metamorphic characteristics in adjacent areas, a unique Archaean history is postulated for the KSZ. Psammitic sedimentary rocks, possibly deposited in a fault-bounded basin, were intruded by anorthosite which may have had its erruptive equivalents in the tholeiitic volcanic rocks in the adjacent Abitibi belt. During the Kenoran orogeny the KSZ was metamorphosed and intruded at infrastructural levels while low-grade regions outside underwent sub-greenschist to amphibolite metamorphism at higher levels. Late ductile shear in the KSZ reoriented gneissic structural elements into northeast directions. Proterozoic fault movements juxtaposed low and high-grade regions.