Structural style and timing of deformation on the Bathurst fault in the eastern Slave craton, western Nunavut, Canada
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Crustal-scale basement faults persist as long-lived structures that localize deformation and can enhance permeability in the Earth’s crust. The NNW-striking left-lateral Bathurst fault in the eastern Slave craton displaces the 1.9 Ga Kilohigok basin and the ca. 2.07-1.96 Ga Thelon tectonic zone by up to ~ 115 km. The Bathurst fault intersects the 1.7 Ga Thelon basin, where unconformity uranium occurrences are spatially associated with basement faults. This thesis investigates the deformation-temperature-time history of the Bathurst fault rocks using field structural and microstructural observations paired with U-(Th-)Pb and 40Ar/39Ar geochronology. Highly-strained hornblende-bearing granitoid rocks with minor phyllosilicate-rich layers are predominant along the Bathurst fault and show ambiguous sense of shear suggesting flattening by coaxial deformation. Quartz and feldspar microstructures show ductile deformation conditions ≥ 500°C. Along the main fault trace, the pervasive ductile flattening fabric is overprinted by brittle fractures, cataclasis, and hydrothermal alteration. In situ U-Th-Pb dating of syn-kinematic monazite suggests ductile fabric formation at ca. 1933 ± 4 Ma and 1895 ± 11 Ma, whereas zircon from a cross-cutting dyke constrains the brittle deformation to ≤ 1839 ± 14 Ma. 40Ar/39Ar analyses of fabric-defining minerals yield cooling ages of ca. 1920-1900 Ma and ca. 1900-1850 Ma for hornblende and muscovite, respectively, and a maximum cooling age of ca. 1840 Ma for biotite. The ductile flattening fabric developed between ca. 1933-1895 Ma, and is associated with the orthogonal collision and indentation of the Slave craton into the Thelon tectonic zone and Rae craton. Brittle deformation on the Bathurst fault was localized parallel to the ductile flattening fabric after ca. 1840 Ma and preceded Thelon basin deposition. Brittle deformation features in Bathurst fault rocks demonstrate fluid-rock interaction and enhanced basement permeability. Thus, the Bathurst fault is a possible conduit basement structure for unconformity-associated uranium mineralization.