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.