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.

The 3‐dimensional construction of the Rae craton, central Canada

“…Gold surface was constrained by one subset of these “worms” and surface outcrops (red spheres) related to the Central Structural Domain (CSD) of Sanborn‐Barrie et al . []. Green cubes and red‐white triangles indicate magnetotelluric and teleseismic sites at the surface, respectively.…”

“…Some satellite blocks (Chesterfield and Cumberland) historically have been associated with the Rae craton in various ways [ Hoffman , ; St‐Onge et al ., ; Berman et al ., ; Eglington et al ., ]. A northeast‐trending axis of relatively juvenile Meso‐ to Neoarchean crust distinguished by komatiite‐quartzite sequences (2.74–2.69 Ga Committee Bay, Woodburn Lake, Eqe Bay greenstones) may define the central nucleus of the Rae craton [ Sanborn‐Barrie et al ., ] much as a similar distinctive cover sequence (2.73–2.58 Ga Yellowknife Supergroup) defines the oldest part of the Slave craton [ Bleeker , ]. Major adjacent non‐Rae crustal terranes include Slave, Superior, Hearne, Meta Incognita, and Sugluk (Figures and ).…”

“…The central Rae craton, which is the focus of this paper, comprises the Committee Bay, Repulse Bay, and Chesterfield blocks. The Committee Bay block has Neoarchean, amphibolite to granulite‐grade, tonalitic to granitic orthogneisses as well as northeast‐striking 2.730–2.687 Ga komatiite‐bearing greenstone belts [ Frisch , ; Skulski et al ., ; Sanborn‐Barrie et al ., ]. These rocks are intruded by 2.72–2.68 Ga tonalite and voluminous 2.63–2.58 Ga monzogranitic plutons [ Hinchey et al ., and references therein]; Nd model ages of 2.87–2.52 Ga suggest predominantly juvenile isotopic source regions for these rocks [ Peterson et al ., ].…”

“…Amphibolite‐grade remnants of 2.1–1.9 Ga Paleoproterozoic sedimentary cover occur both in the southwest (Amer, Chantrey, Penrhyn Groups) and northeast (Piling, Hoare Bay Groups) parts of the central Rae craton [ Rainbird et al ., and references therein]. The Repulse Bay block is separated from the Committee Bay block by a set of cryptic structures that include ancient northeast‐southwest trending, steeply dipping structures [ Sanborn‐Barrie et al ., ] that are apparently offset by neotectonic faults such as the Wager Bay shear zone (Figure , A1) [ Spratt et al ., ].…”

“…Apparent Rae under Hearne crustal geometry imaged along a magnetotelluric profile [ Jones et al ., ] represents late‐collisional shortening on the Chesterfield fault related to 1.87 Ga accretion of the composite MISH microcontinent to the southeastern flank of the Rae [ Snyder et al ., ]. Development of a regionally extensive northeast (050°)‐striking, northwest‐vergent fold and thrust belt through the central Rae craton also occurred during this time [ Carson et al ., ; MacLachlan et al ., ; Sanborn‐Barrie et al ., ], consistent with the 1.88–1.865 Ga timing constraints derived from geological relationships on central Baffin Island [ St‐Onge et al ., ; Wodicka et al ., ].…”