Crustal shortening and thickening in Neoarchean granite-greenstone belts: A case study from the link between the ∼2.7 Ga Elu and Hope Bay belts, northeast Slave craton, Canada

Abstract

The Elu Link between the ∼2.7 Ga Hope Bay and Elu belts in the northeast Bathurst Block of the Slave craton comprises supracrustal and intrusive rocks variably deformed by three tectono-metamorphic events (D1–D3). The geometry of D1 structures formed during prograde metamorphism is uncertain, because of subsequent overprint. D2 occurred in two stages predating (D2a) and postdating (D2b) peak metamorphism. D1 and D2a were thrusting events inferred from peak metamorphic pressures of ∼6.7 kbar (670 MPa) retained by a garnet orthogneiss. The latter is diagnostic of thrust tectonism in Archean granite-greenstone belts with no characteristic thrust faults. Unlike D2a, D2b was a vertical general flattening event prevailing during the formation of magmatic domes and interdomal folds that form the main strain patterns of the belts. This was followed by the formation of buckled F3 folds associated with D3 vertical constriction. The switch from thrust to vertical tectonics during peak metamorphism and subsequent deformation resulted in intense recrystallization that explains the poor preservation and scarcity of early-formed shears, including thrust zones. A tectonic process, combining D1+D2a thrust stacking, sagduction, and vertical stretching during D2b and D3, is suggested to explain crustal thickening in the Elu Link and terrains of similar ages.