IMPLICATIONS FOR THE IGNEOUS, METAMORPHIC, AND STRUCTURAL EVOLUTION OF A DEEP-CRUSTAL MAFIC DIKE SWARM BASED ON THE INTEGRATION OF PETROLOGICAL, STRUCTURAL, AND GEOPHYSICAL DATA: ATHABASCA GRANULITE TERRANE, NORTHERN SASKATCHEWAN

Iron-titanium oxide and sulfide minerals such as magnetite, hematite, ilmenite, and pyrrhotite are common metamorphic and igneous phases that can directly influence the magnetic characteristics of rocks and can provide insight into the igneous and metamorphic history of crystalline terrains. The Chipman domain of the Athabasca granulite terrane is an excellent location to investigate variations in bulk magnetic properties due to a restricted array of lithologies, gradients in deformation magnitude, and the presence of large aeromagnetic anomalies ranging over 2000 nT in total field strength. In particular, the Chipman mafic dike swarm (emplaced at approx. 1.90 Ga into a tonalitic host) provides key metamorphic, structural, and geophysical constraints because they occur throughout the region, exhibit clear cross-cutting relationships, and display orders of magnitude variation in magnetic susceptibility and natural remanent magnetization. Although many dikes display internally uniform magnetic susceptibilities that range from values on the order of 0.0001 SI to 3.0 SI, wide variations in magnetic susceptibility (e.g. 0.001 SI to 1.0 SI) are occasionally observed within individual dikes. Natural remanent magnetization values also display orders of magnitude variation ranging from 0.001 A/m to over 1.0 A/m. Dikes with elevated magnetic properties typically occur in areas where host units also exhibit high magnetic susceptibilities, suggesting a possible metamorphic or igneous link between the dikes and the host. Petrophysical heterogeneity throughout the region is most likely related to aspects of the igneous and metamorphic history that may enable the use of geophysical data, such as aeromagnetic surveys, to investigate these properties at a broader scale. Information gained from investigations of the Chipman dikes may also help explain magnetic variations within the tonalitic host and associated lithologies. Beyond the implications for the regional history of the Athabasca granulite terrane, this study may add new insight into the magmatic and metamorphic traits of deep crustal mafic intrusions, as well as providing a framework for interpreting aeromagnetic anomalies in other regions and planets.