Structural and metamorphic evolution of the North Star Lake area, Manitoba

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Norquay, Lawrence I.
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The North Star Lake area of northwestern Manitoba lies within the Flin Flon domain which, along with the Kisseynew domain, forms the internal zone of the Reindeer zone of the Early Proterozoic Trans-Hudson Orogen. The North Star Lake area consists predominantly of an Early Proterozoic assemblage of metavolcanic, metasedimentary and intrusive rocks. The North Star Lake area has undergone polyphase deformation and metamorphism. The initial deformation in the North Star Lake area was the result of the accretion of the Flin Flon domain volcanic terrane that juxtaposed the juvenile arc assemblages of the Flin Flon domain by intraoceanic tectonics into an accretionary complex during the period of 1.88-1.87 Ga. Subsequently, the North Star Lake area underwent a progressive deformational cycle (D$\sb1$-D$\sb3)$ and a contemporaneous prograde-retrograde metamorphic cycle (M$\sb1$-M$\sb3)$ during the period of 1.83-1.80 Ga. The progressive deformation cycle was a result of south-southwest-directed thrusting during the closure of the Kisseynew basin. This resulted in overthrusting of the Amisk collage of the Fin Flon domain by the Snow Lake arc segment of the Flin Flon domain and by the Kisseynew domain. Progressive deformation produced a succession of folds (F$\sb1$-F$\sb3)$ which initially formed perpendicular to the south-southwest-directed movement vector. Early folds (F$\sb1$ and F$\sb2)$ were reoriented towards parallelism with the direction of transport. Metamorphism in the North Star Lake area followed a clockwise medium-pressure (Barrovian) P-T-t evolution with maximum pressure predating maximum temperature. Peak metamorphism is associated with the second phase of deformation and culminated at upper-amphibolite facies grade during the period of 1820-1805 Ma. The final deformation in the North Star Lake area produced brittle-ductile and brittle structures under greenschist facies conditions. This phase of deformation occurred in a northwest-southeast stress regime and was probably the result of the terminal collision between the Reindeer zone and the Superior craton. (Abstract shortened by UMI.)