Metamorphic petrology of the Bird Lake area, southeastern Manitoba

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Butrenchuk, S. B.
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A total of 114 samples was collected from the Bird Lake and Cat Lake greenstone belts. Thin sections were made from 100 samples in order to determine mineral assemblages and textures. Chemical analyses were done on 25 samples to determine their bulk composition and its relationship to the mineralogy. Five facies of metamorphism have been interpreted to be present in this area: 1. Albite-epidote hornfels facies 2. Hornblende-hornfels facies 3. Greenschist facies 4. Almandine-amphibolite facies (a. with epidote) 5. Almandine-amphibolite facies (b. without epidote) Facies one and two are products of a first period of thermal metamorphism. A second period of metamorphism, dyamo-thermal type,produced facies three, four and five as well as a regional foliation that is parallel to the original bedding. A third period of metamorphism, dynamic type, produced a poorly developed secondary foliation and shears along which chlorite formed. A gradient of intensity of deformation exists in this area. Recrystallization was greatest in the east and quartz-mica schists were developed. In the west the foliation is not well developed and the rocks have retained many of their original sedimentary features.