MAGNETIC PROPERTIES OF DEEP CRUSTAL ROCKS FROM THE ATHABASCA GRANULITE TERRANE: WESTERN CANADIAN SHIELD

Collecting magnetic data on deep crustal rocks is required for modeling and understanding the nature of long wavelength anomalies and aiding the interpretation of recently discovered large-scale Martian magnetic anomalies, in addition to preparing for upcoming international satellite missions. We present results from an Earth analog focused on the magnetic properties of deep crustal rocks from the Athabasca granulite terrane. The exposure represents >20,000 k m2 of exhumed continental lower crust in the western Canadian Shield. A detailed aeromagnetic map (200 m resolution) publicly available from the Geological Survey of Canada guided the study of the relationship between aeromagnetic anomalies and the magnetic properties of 13 rock samples. Samples include granulite facies orthogneiss and schist, as well as granite and mafic dikes. Each sample had 1-3 cores drilled and oriented in a sandbox to within 10 degrees. Data were collected on the cores for susceptibility, density, and natural remanent magnetization (NRM), and Koenigsberger ratios (Q) were calculated for each sample. The Koenigsberger ratio (Q) is a measure of remanent magnetization versus induced magnetization and it provides information on the source of the observed anomalies. Susceptibilities ranged between 1.33x10-4 and 1.04 SI units, and NRM ranged between 1.11x10-2 and 38.8 A/m, while Q values were between 1.85x10-2 and 3.21 with 5 samples having Q values greater than one. A range of magnetic properties over several orders of magnitude is surprising for an area with large magnetic anomalies. Based on the Q values, some of the sampled units are dominated by induced anomalies (magnetic highs on the anomaly map) while others have a remanent component influencing the observed anomalies, particularly in the case of negative anomalies. Hysteresis properties along with microscope work indicate a range of oxide phases are present; on-going work is investigating which are the primary carriers of the induced and remanent magnetizations.