Sequence stratigraphy and evolution of the Paleoproterozoic intracontinental Baker Lake and Thelon basins, western Churchill Province, Nunavut, Canada

Abstract

Abstract The Baker Lake and Thelon basins lie along the border between the Rae and Hearne domains of the western Churchill Province. Basin fill comprises the Dubawnt Supergroup, a ca. 1.85–1.70 Ga succession of predominantly continental clastic and intercalated volcanic rocks that nonconformably and unconformably overlies granitic and supracrustal rocks, most of late Archean age. The Dubawnt Supergroup comprises three second-order sedimentary sequences that record deposition within a rift basin, a modified rift basin and a thermal sag basin, respectively. The Baker sequence is inferred to represent the principal phase in the development of Baker Lake Basin, a series of generally elongate, northeast-striking, half-graben and fault-bounded troughs filled with continental redbeds and coeval voluminous ultrapotassic volcanic rocks. Faults parallel to the basin margin exhibit evidence for strike-slip ca. 1.83–1.81 Ga. The nature and timing of basin development and associated magmatism allows that it may be a transtensional basin that formed by lateral escape in response to crustal thickening during the Trans-Hudson orogeny, similar to the formation of Mesozoic and Cenozoic strike-slip and associated rift basins on the margins of the Tibetan Plateau. The overlying Whart sequence was deposited in small basins formed by block-faulting and tilting of the Baker sequence. Basin fill comprises eolian and alluvial redbeds with intercalated rhyolite flows and epiclastic rocks. Distribution of facies and stratigraphy suggest that faulting occurred throughout deposition of the Whart sequence, but ceased before deposition of the overlying Barrens sequence (ca. 1.72 Ga). Deformation and basin formation can be linked to a regional episode of granite emplacement and associated thermal metamorphism (ca 1.76–1.75 Ga). The Barrens sequence represents deposition over a broader area, primarily in Thelon Basin. Strata generally are thinner and flatter than underlying sequences, and display lateral continuity, indicating minimal influence from syndepositional faulting. The depositional record reflects progressive upward fining and eventually the first record of marine transgression within the Dubawnt Supergroup. These features suggest that the Barrens sequence was deposited over a broad region of thermal subsidence, likely related to cooling of previously attenuated continental lithosphere. The Barrens sequence may be a remnant of a huge cratonic sand sheet that included the Thelon, Athabasca, Amundsen and Elu basins. A regional subsidence mechanism to account for these basins may be mantle downwelling linked to the late-stage amalgamation of Laurentia. The tripartite sequence evolution of the Baker Lake and Thelon basins represents a framework for future sequence correlation among late Paleoproterozoic basins in Laurentia, and shares characteristics with the evolution of contemporaneous intracontinental basins from north-central Australia and southeastern Brazil.