TEXTURAL AND MINERALOGICAL VARIATION OF THE NORTHBROOK PLUTON, ONTARIO, CANADA

The Northbrook pluton is an elongate L-shape pluton located in the Mazinaw Terrane of the Grenville Province, Ontario Canada. Results are presented from a freshman research project undertaken as part of NSF-AIMS (NSF S-STEM). Optical techniques were utilized to identify mineral compositions and textures within the Northbrook pluton. Particular focus was on samples from the western, central and northeastern sections of the pluton. Rock type was determined through hand sample analysis and verified by thin section examination. Thin section analysis was used for final identification of major and accessory mineral phases, modal abundances, and textural relationships among minerals. The pluton contains rock types granite and granodiorite. Granite contains biotite, muscovite and calcite. Granodiorite contains green biotite and trace amounts of apatite, zircon and epidote. Apatite occurs as inclusions in plagioclase, and zircon as inclusions in biotite. Plagioclase compositions, determined using the Michel-Levy method, are albite/oligoclase. Texture of grain boundaries indicate varying degrees of recrystallization throughout the pluton. Furthermore, the presence of muscovite and calcite in some samples may have been produced during recrystallization. The Northbrook pluton is compositionally variable, ranging from 64-70 wt% SiO₂. The analysis provides initial steps toward understanding mineralogical variation within the Northbrook pluton, and its relationship to the compositional variation.