Neoarchean continental crust formation and Paleoproterozoic deformation of the central Rae craton, Committee Bay belt, Nunavut

Abstract

Integrated mapping, structural analysis, and U–Pb geochronology of the Committee Bay area, Nunavut, establish a record of Neoarchean crustal growth followed by penetrative Paleoproterozoic deformation. Supracrustal rocks include a lower ca. 2.73 Ga mafic–ultramafic volcanic-dominated sequence, a middle, economically significant 2.71 Ga intermediate volcanic-bearing sequence with intercalated sulphidized, gold-bearing iron formation, and an upper <2.69 Ga clastic ± komatiite–quartzite sequence. Following an 80 million year hiatus, this succession was intruded by voluminous ca. 2.61–2.57 Ga granodiorite–tonalite–granite ± diorite, which do not appear to have thermally or tectonically affected the supracrustal belt. Instead, three generations of structures record polyphase Paleoproterozoic deformation of the region. D1 structures are consistent with a doubly vergent structural fan developed at ca. 2.35 Ga in response to the Arrowsmith orogeny that affected the western Rae margin. Penetrative D2 structures dominate the map pattern and include northeast-trending, southeast-dipping folds and fabrics within which gold is localized. The general southeast dips of S2 and inclined, northwest-vergent attitude of F2 reflect northwest-directed shortening at 1.84–1.82 Ga. The absence of syn-D2 plutonic rocks in the west and central Committee Bay belt support amphibolite-facies metamorphism as a response to crustal thickening, which, in turn, led to syn-D2 crustal melting in the east. Regionally extensive upright to northwest-vergent D2 structures and associated ca. 1.85–1.82 Ga tectonometamorphism across the Rae craton are attributed to an early stage of the Hudsonian orogeny involving microcontinent collision(s) with its southeastern margin. D3 folds and dextral shearing at ca. 1780 Ma accommodated localized, late-stage compressional strain during final amalgamation of Laurentia.