PROVENANCE OF A POLYDEFORMED METASEDIMENTARY SUCCESSION ON THE CANADIAN SHIELD: INSIGHTS FROM NEW U-PB, HF, AND O ISOTOPE ANALYSIS OF DETRITAL ZIRCON FROM THE PALEOPROTEROZOIC MURMAC BAY GROUP

Abstract

The proximity and positions of the cratons that make up the Canadian Shield prior to and during the Rhyacian Period (2.30-2.05 Ga) are poorly known. The position of the Rae craton relative to the now proximal Slave, Hearne, and other microcontinents, such as the Buffalo Head-Chichaga domains, during this time period is not well defined. This is due in part to their boundaries having been overprinted by younger orogenic events. Sedimentary successions deposited near craton margins provide an opportunity to test hypotheses regarding nearest cratonic neighbors during deposition by reconstructing their sedimentary provenance using detrital zircon isotopic data. The polydeformed nature of the Murmac Bay Group, a metasedimentary succession deposited near the southwestern margin of the Rae craton in northern Saskatchewan, Canada, presents challenges in determining detailed stratigraphic relationships in the upper succession, which lacks distinct marker beds. Presented here is the first integrated detrital zircon U-Pb geochronology, Lu-Hf, and O isotope analysis of detrital zircon from these rocks in order to elucidate provenance, basin tectonic setting, and characterize crustal growth in the source regions. Previous U-Pb geochronology suggests the lower succession was deposited <2.32 Ga and the upper succession between <2.17 Ga and >1.93 Ga. New U-Pb detrital zircon ages for the upper succession define a new maximum depositional age constraint at <2.00 Ga. Analysis of published U-Pb detrital zircon age spectra suggest the tectonic setting for the upper Murmac Bay Group paleobasin was in the foreland of the Taltson orogeny. Integrating the U-Pb data with new Lu-Hf and O isotope data shows that the most probable source rocks, in addition to Rae crustal rocks, were granites that are currently buried under Phanerozoic cover in the Buffalo Head-Chinchaga domains of northern Alberta. Unique U-Pb age peaks that would point to the Hearne craton as a sediment source were not identified. Hafnium model ages calculated from the upper Murmac Bay Group identify two periods of regional crustal growth at 2.83 Ga and 2.70 Ga, agreeing with Sm-Nd model ages from the western Churchill province.