Ben Kuzmich HBSc thesis abstract
The Dog Lake Granite Chain is composed of six ovoid magnetite-bearing granitic intrusions within the Quetico Basin, Northwestern Ontario. From east- to west the intrusions are the Penasen Lake, White Lily, Barnum Lake, Trout Lake, Silver Falls, and Shabaqua intrusions. The Dog Lake Granite Chain is characterized by a linear trend, which parallels the tectonic boundary between the Wawa-Abitibi terrane to the south, and the Quetico Basin to the north.
Petrologic and geochemical data has been used to classify the granites as both I- and S-type. The I-type granites can be classified into three broad groups, a microcline-phyric monzonite/quartz-monzonite, syenite/quartz-syenite, and a monzodiorite. These granites are massive, silica poor, largely metaluminous, and characterized by a hornblende+ magnetite+ sphene +/-pyroxene assemblage. The microcline-phyric monzonite/quartz-monzonite and syenite/quartz-syenite groups are characterized by positive ɛNd (+1.44 to +2.11) values. The I-type granites have been recognized within the Trout Lake, Barnum Lake, White Lily, and Penasen Lake intrusions.
The S-type granites are typical of the Quetico Basin, and have a largely peraluminous affinity, variable ɛNd signatures (-1.44 to +1.09), and are characterized by a muscovite+ biotite+/- garnet assemblage. The S-type granites have been sampled within the Silver Falls, Trout Lake and White Lily intrusions.
The recognition of I-type granites within the Quetico Basin, which is predominantly composed of S-type granites, requires a different model for the formation of this relatively rare rock type. It is proposed that the formation of I-type granites within the Quetico Basin involves the partial melting of the mantle wedge beneath the Wawa-Abitibi island arc. The mafic melt would have underplated the Archean lithosphere, where they would have evolved into granitic melts through fractionation, thus giving rise to the I-type granites. Small volumes of these melts were then emplaced within the Quetico Basin, possibly along weaknesses associated with lithosphere scale structures at the boundary between the Wawa-Abitibi terrane and Quetico Basin. The majority of the underplated melts would likely have contributed to the production of large S-type granites, which are typical of the Quetico Basin. These S-type melts formed from the melting of sedimentary rocks, and may have interacted with the I-type granites, producing variations in isotopic and geochemical signatures as seen within the S-type granites of this study.
Although magnetite-bearing granitic intrusions within the Quetico Basin are not unique, the identification and classification of I-type granites has not been widely documented. The regional implication of I-type granites within the Quetico Basin is both profound and complex. It is suggested that other magnetite-bearing metaluminous granites within the Basin (e.g., the Vermillion complex, northern Minnesota) may have formed through a similar process as the Dog Lake Granite Chain.