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UBC Theses and Dissertations

Complex P-T-t-d history of supracrustal rocks of the Metamorphic Internal zone of the southern Wopmay Orogen, NT Smar, Leanne Marie


An abundance of Paleoproterozoic orogenic belts are distributed globally, as peripheral terranes accreted against the margins of Archean cratons. The abundance of these terranes indicates a period of tectonic activity between 2.1 and 1.8 Ga. The study of such belts has offered insight into the nature and rate of tectonic activity in the Paleoproterozoic. Analysis of thermo-tectonic events, paired with the collection of geochronological data has led to the discovery of a supercontinent that existed before the formation of Rodinia, called Columbia. The 1.9 Ga Wopmay Orogen in northern Canada is a Paleoproterozoic belt, comprising a complex amalgamation of tectonic elements, which is thought to have formed during the assembly of Columbia. The advent of new geochronological data has demanded that the current P-T-t-d (Pressure-Temperature-time-deformation) model of the Wopmay Orogen be reconsidered. To reconstruct the evolution of an orogenic belt, structural analysis of overprinting kinetic fabrics, thermodynamic analysis of metamorphic mineral assemblages, and the determination of absolute timing of thermo-tectonic events are required. Two map areas were chosen to conduct an analysis of the kinetic and metamorphic evolution of the southern Wopmay Orogen, a region of the belt that has historically been under-studied. The Brown Water and the Little Crapeau Lake areas are situated south of 65˚N in the Metamorphic Internal zone of the orogen, and are bounded to the east and west by the Archean Slave craton and the ca. 1850 Ma Great Bear Magmatic zone, respectively. The areas comprise a sequence of pelitic to semi-pelitic schists and gneisses that overlie parautochthonous Archean basement. Rocks in both areas show evidence for five generations of overprinting fabrics, S₁C-S₅C at Little Crapeau Lake, and S₁B-S₅B at Brown Water Lake. Conditions of peak metamorphism were attained synchronous with the intrusion of the ca. 1877 Ma Little Crapeau Sill, and the regionally expansive ca. 1850 Ma Rodrigues granite. At Brown Water Lake peak metamorphic conditions were reached syn-S₅B at 3.1-4.2 kbars and 570-670˚C, and syn-S₂C at 3.1-3.9 kbars and 570-630˚C at Little Crapeau Lake. Chemical and isotopic geochronological dating of monazite provided metamorphic age constraints that concurred with ages of local intrusions.

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