Retro-arc extension and continental rifting: A model for the paleoproterozoic Baker Lake basin, Nunavut

摘要

Within Baker Lake sub-basin, the ca. 1.84-1.78 Ga Baker Sequence formed in two stages. At the start of the first stage, during rift initiation, half-graben were host to siliciclastic alluvial, eolian, and lacustrine deposits and to localized felsic minette volcanics. Back-stepping of facies indicate high accommodation rates and areal expansion, which, combined with extrusion of voluminous minette volcanic rocks, are interpreted to record increased extension and rift climax. Low accommodation post-rift deposits from the second stage of basin development are relatively thin and coeval felsite domes spatially restricted. Volcanic rocks and some siliciclastic units correlate between sub-basins, and hence the interpreted history of Baker Lake sub-basin is extended across greater Baker Lake Basin. This implies that the basin formed in response to regional extension and crustal thinning. The Baker Lake Basin marks the northern extent of a series of basins that trend northeastward along the Snowbird Tectonic Zone, including an inlier of the correlative Martin Group in northern Saskatchewan. The high accommodation first stage of basin development is proposed to have been the result of intra-continental retro-arc extension during ca. 1.85-1.84 Ga formation of the Kisseynew back-arc basin of the Trans-Hudson Orogen. Upon closure of the Kisseynew back-arc basin and collision of the Superior Province with the western Churchill Province, Baker Lake Basin was subject to strike-slip faulting. The second, low accommodation stage of basin development and strike-slip faulting is proposed to record lateral tectonic escape between the Saskatchewan-Manitoba and Baffin Island - Committee Bay foci of the western Churchill - Superior Province collision.