| Summary: | Degree: Master of Science Abstract: The Slave craton underwent widespread extension during the Paleoproterozoic. In the southern Slave craton, this extension is manifest in multiple periods of continental mafic magmatism emplaced between 2.3–2.2 Ga and prior to 2.0–1.9 Ga calc-alkaline magmatism of the Taltson and Thelon zones along the Slave-Rae boundary. During this time the East Arm basin of Great Slave Lake was formed and now preserves a protracted sedimentary and volcanic record along the southeastern margin of the Slave craton. Within the East Arm basin package, the Union Island Group represents voluminous mafic volcanism with subordinate interbedded carbonate/shale sedimentary strata. Previous stratigraphic interpretations posit that the ca. 1928 Ma Wilson Island Group is the base of the East Arm basin stratigraphy, and that the Union Island Group is younger. This relationship is however equivocal; the Wilson Island Group is structurally isolated, and new field observations indicate that the Union Island Group was deposited unconformably on Archean granitic basement, the latter considered to be derived from the nearby Slave craton. We report the first U–Pb baddeleyite crystallization age, 2042.7±3.0 Ma, for a diabase body which intrudes volcaniclastic horizons belonging to the Union Island Group lower basalt unit; the diabase intrusion is geochemically identical to flows of the lower basalt unit and is therefore interpreted as a feeder to these flows. The diabase crystallization age demonstrates that the Union Island Group is the oldest identified supracrustal package in the East Arm basin and that the East Arm basin is ~115 Myr older than previously thought. Our new stratigraphic interpretation is supported by detrital zircon provenance age distribution in two Union Island Group sedimentary samples. These detrital zircons are dominated by 2.76–2.56 Ga ages reflecting prominent input from the Archean basement. The youngest detrital zircons have ages indistinguishable from the emplacement age of the ...
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