Paleoproterozoic basement-cover infolding and thick-skinned thrusting in Hearne domain, Nunavut, Canada: intracratonic response to Trans-Hudson orogen

Abstract

Enveloped by orogenic belts during the assembly of Laurentia (∼2.0–1.7 Ga), the Rae and Hearne domains of the western Churchill Province experienced a complex sequence of tectonic events historically referred to as the “Hudsonian orogeny”. In Hearne domain, diverse thick-skinned intraplate structures developed in response to accretionary processes in Trans-Hudson orogen. These structures include infolds of Archean basement and Paleoproterozoic cover, and broken foreland thrusts. In central Hearne domain, an intracratonic basin succession of continental to shallow-marine strata (Hurwitz Group; <2.45–<1.91 Ga) is exposed in outliers that constitute the keels of doubly plunging basement-cover synclinoria, defining a fold train with wavelengths of 35–45 km. With the exception of local out-of-syncline shear zones, basement and Hurwitz Group are welded. Formed under greenschist facies conditions, the basement-cover infolds are open, concentric, and commonly display complex structures in their interiors. In the Poorfish–Windy outlier, southwestern Hearne domain, continental rift deposits of the Kiyuk Group unconformably overlie the Hurwitz Group. In contrast to basement-cover infolding to the north and east, Archean basement, the Hurwitz Group and the Kiyuk Group are imbricated by thick-skinned northwest-vergent thrusts and folds. Thrusting in the Poorfish–Windy belt was completed by 1815±10 Ma, as indicated by new U–Pb data from hydrothermal–metamorphic titanite recovered from recrystallized cements at the top of the Kiyuk Group. We interpret that shortening from shallow-level basement-cover infolding is balanced at depth by intrabasement faulting and distributed ductile strain, and that the geometric link between central Hearne basement-cover infolding and Poorfish–Windy thrusting is via intrabasement faults that cut to the surface. The main controls on thick-skinned deformation were: the high competency of the lower Hurwitz Group; previous thermal weakening; basement heterogeneities; and possibly, shallow subduction preceding terminal collision in Trans-Hudson orogen.