Fluvial, lacustrine and volcanic sedimentation in the Angikuni sub-basin, and initiation of ∼1.84–1.79 Ga Baker Lake Basin, western Churchill Province, Nunavut, Canada

Abstract

Abstract Continental siliciclastic and volcanogenic deposits of the Baker Lake Group accumulated in numerous sub-basins in the interior of the western Churchill Province between 1.84 and 1.79 Ga. In the Angikuni sub-basin, on the southeast flank of greater Baker Lake Basin, Baker Lake Group rocks outcrop in two segments that extend northeast from Angikuni Lake. They are also exposed in scattered outliers throughout the region. At northern Angikuni Lake in the northern segment, conglomerates, pebbly sandstones and mudrocks of the Angikuni Formation unconformably overlie Archean basement, and are unconformably overlain by ultrapotassic volcanic and siliciclastic rocks of the Christopher Island Formation. These rocks record alluvial fan-fluvial and sand flat-playa deposition in a fault-bounded trough formed adjacent to a wedge-shaped basement uplift. Although the Angikuni Formation was tilted before principal Christopher Island Formation volcanism at northern Angikuni Lake, geochemical and Nd isotopic data from mudrocks indicate derivation from earlier or coeval Christopher Island volcanic-like sources. The outliers demonstrate that faulting produced significant changes in the structural level of Archean basement before Christopher Island Formation volcanism. Near “Rack” lake in the southern segment, Angikuni Formation conglomerates, sandstones and mudrocks define 100-m scale upward-fining and upward-coarsening to upward-fining sequences. Relative to the northern segment, these rocks were deposited in a more distal, fine-grained sand flat to semi-perennial fresh-water (±evaporitic) lake setting. The Angikuni Formation at “Rack” lake records deposition between (and likely during) periods of volcanism as indicated by: a conformable Angikuni–Christopher Island contact; abundant volcanic detritus; and local lacustrine chemical sediments that contain magnesite, strontianite, barite and apatite, which reflect the chemistry of the volcanic rocks. Baker Lake Basin may have originated during regional uplift and extension within the western Churchill Province due to terminal collision and post-collision processes in Trans-Hudson orogen to the south, while the western margin of ancestral North America was a free face.