Tectonometamorphic history across the Chesterfield Fault Zone: Implications for tectonic evolution of the Rae Craton, Nunavut, Canada

Abstract

Extensive debate has focussed on the nature and location of the Snowbird Tectonic Zone (STZ), the suture between the Rae and Hearne cratons. Geological mapping in the Baker Lake area revealed a ∼7 km wide deformation zone associated with the Chesterfield Fault Zone (CFZ), a south-dipping, dextral strike-slip structure previously interpreted to represent the northern segment of the STZ. New geochronology across the CFZ indicates both the footwall and hangingwall are dominated by ca. 2.72 Ga tonalite gneisses and ca. 2.6 Ga porphyritic monzogranite, effectively ruling out the CFZ as the northern segment of the STZ. Geochronology, thermobarometry, and thermodynamic modelling from the hangingwall indicate three Paleoproterozoic metamorphic events (M1-M3) that outline a clockwise P-T-t path. Prograde metamorphism (M1) reaching peak conditions of 0.75 GPa and 700 °C is dated by early titanite growth at ca. 1.92 Ga, consistent with burial during southeast-verging folding and thrusting associated with collision of the Rae-Chesterfield and Hearne cratons. Peak conditions of ∼1.0 GPa and 740 °C at ca. 1.87 Ga (M2; garnet Lu-Hf) are coeval with northwest-vergent folding and thrusting during early, intra-oceanic accretionary episodes associated with the Trans-Hudson Orogeny. Dextral strike-slip kinematics argue against the CFZ as the structure responsible for exhumation of ca. 1.9 Ga high-pressure rocks to the south. Instead, exhumation may have been accommodated along discrete, reverse-sense shear zones associated with the CFZ, or an alternate structure to the south. Together, these data highlight that crustal-scale shear zones can preserve tectonometamorphic information, critical for tectonic reconstructions and understanding orogenic processes, that is not recorded in the surrounding lithotectonic blocks.