Alexander Hughes HBSc thesis abstract

Thesis Title: 
Petrology and Geochemistry of the McKenzie Granite, Northwestern Ontario

The McKenzie granite is an approximately 18 km igneous intrusion within the Quetico Subprovince, located 20 km northeast of Thunder Bay, Ontario. Petrologic and geochemical data has been used to classify the McKenzie granite as dominantly S-type. The intrusion is classified as a quartz monzonite with assemblages characterized by muscovite+biotite┬▒sphene┬▒hornblende. The McKenzie granite contains a peraluminous geochemistry with SiO2 contents ranging from 63.8-68.2% along with enrichment in light rare earth elements, fractionated heavy rare earth elements, decreasing trends of major oxides, transition metals and high field strength elements and scattered large ion lithophile elements due to remobilization during chlorite, sericite, and carbonate alteration. Formation of the McKenzie granite was likely similar to the model proposed for the later stages of the genesis of the Dog Lake Granite Chain, which involved partial melting of the mantle wedge beneath the Wawa-Abitibi island arc. The mafic melt produced from the subducting oceanic lithosphere would underplate the Quetico Subprovince leading to formation of granitic I-type melts via fractionation. These melts would then rise through structural conduits at the Quetico-Abitibi border. The majority of the underplated melt would contribute to the production of the S-type granites that are normally seen in Quetico Subprovince. These S-type melts formed from the partial melting of the overlying metamorphosed sedimentary rock and may have been allowed to interact with I-type melts. This would allow for variations in geochemical and petrological data that is not common for standard S-type granites.