U-Pb detrital zircon geochronology and provenance of the late Paleoproterozoic Dubawnt Supergroup: Linking sedimentation with tectonic reworking of the western Churchill Province, Canada

Abstract

U-Pb sensitive high-resolution ion micro-probe (SHRIMP) analysis of detrital zircon in 11 sandstone samples from the late Paleo-proterozoic Dubawnt Supergroup of the Baker Lake and Thelon Basins are presented here. Alluvial fan and braided stream facies of the ca. 1.84–1.78 Ga Baker Sequence yield age spectra with significant groupings at 2.70 and 2.60 Ga, reflecting provenance chiefly from local sources in the northwestern Hearne domain of the western Churchill Province. Age spectra are consistent with sed-imentological and stratigraphic information, which indicate provenance from the proximal uplifted shoulders of an intracontinental rift that developed in response to inboard effects of the Hudsonian orogeny (collision of Superior craton into western Churchill Province). The unconformably overlying 1.76–1.74 Ga Whart Sequence exhibits a more varied provenance and has an abundance of 2.0–1.9 Ga detrital zircon. These ages match those of synorogenic plutons in the Taltson-Thelon orogen (collision of Slave craton into the western Churchill Province). Provenance from the Taltson-Thelon orogen is supported by easterly paleocurrents and Rb-Sr cooling ages from mafic dikes that indicate reactivated collision of the Slave craton and related uplift and denudation coeval with deposition of the Whart Sequence. The depositional age of the Whart Sequence is constrained by intercalated rhyolite flows with conventional 207 Pb/ 206 Pb crystallization ages of 1757.6 ± 3.4 Ma and 1753.0 ± 1.7 Ma (2σ). The thermal effects of this collision also are recorded in isotopic data from basement rocks throughout the western Churchill Province and in syndepositional to postdepositional faults that parallel the main boundary faults of the Slave indentor. Late reactivation and associated metamorphism, faulting, and basin development could be the result of the inboard effects of subduction and related collision along the southern margin of Laurentia. The detrital zircon geochronology of the Barrens Sequence supports recycling of local supracrustal sequences and weathering of underlying granitic gneisses. Zircons of Hudsonian affinity (ca. 1.9–1.8 Ga) are nearly absent, which argues against a distant eastern source region for the Barrens Sequence. The Dubawnt Supergroup detrital zircon age data set shows concentrations ca. 2.75–2.6 Ga, 2.1–1.9 Ga, and 1.85–1.75 Ga, which are concordant with the known ages of major juvenile crust–forming events leading up to final amalgamation of Late Archean and Paleoproterozoic supercontinents. Detritus of this age was shed cratonward and captured by interior basins, such as the Baker Lake and Thelon Basins, during major collisional events that reworked the margins of the western Churchill Province (e.g., Hudsonian and Thelon-Taltson orogenies).