Geophysical expression of the Canadian Shield of northeastern Alberta

The Canadian Shield of northeastern Alberta has a geophysical expression controlled by lithology and complex structural- metamorphic features. The magnetic field of the Alberta Shield (the exposed part of the Canadian Shield in Alberta) shows a variety of patterns that result from combinations of several geological factors: principally regional metamorphism local shear and plutonic intrusion. Magnetic susceptibility determinations of the study area indicate hat the Archean granite gneisses typically have higher susceptibilities than do the younger granitoid masses. The gravity ield of the Alberta Shield is influenced not only by the volume shape and distribution of exposed and near-surface masses but also by variations in metamorphic facies structural fabric and lithology of the deep subsurface. Measurements of residual gravity fields and specific gravities of outcrop are generally consistent with the hypothesis that diapirism is responsible for placement of the granitoid domes in the Alberta Shield. Airborne radiometric data on the study area suggest that uranium is concentrated in six areas. The sources of radioactivity include pegmatitic phases of both granitoid and highgrade metasedimentary rock associations rock contacts metasedimentary inclusions in granitoids and fault zones.