| Summary: | Includes bibliographical references. Includes illustrations and maps. The Avakutakh iron formation, the basal unit of the Aphebian-aged Falls Brook Group, is exposed in the Snyder Bay - Avakutakh River area of Labrador. Together with the metasedimentary Snyder Group, it forms part of the contact aureole of the Kiglapait intrusion. Thin section study, oxygen isotope analysis, and microprobe analysis were used to determine the petrography, mineral chemistry, and metamorphic history of the Avakutakh iron formation. The Avakutakh iron formation is comprised of three metamorphic zones: grunerite-zone, hypersthene zone, and pigeonite zone. During the metamorphic event, temperatures ranged from 625 - 860°C over a distance of 565 m and pressure was essentially constant at 2.2 kbar. Anomalously low temperatures were obtained from oxygen isotope 18 analysis and appear to be the result of diffusion of ¹⁸O between quartz and magnetite with cooling. Chemical diffusion between the Avakutakh iron formation and adjacent mafic orthogranulites is limited to a band several centimeters wide. Thus, it can be assumed that the Avakutakh iron formation behaved as a closed system with respect to major non-volatile components. M.S. (Master of Science)
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