Overview of regional geophysical studies in Manitoba and northwestern Ontario

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Abstract
This paper presents an overview of six geophysical projects (seismic reflection and refraction, gravity and magnetic anomaly interpretation, specific gravity and magnetic property measurements) carried out in an area in Manitoba and northwestern Ontario bounded by 93 and 96°W longitude, and 49 and 51°N latitude.The purpose of the surveys was to define crustal structure in the Kenora–Wabigoon greenstone belt, the Winnipeg River batholithic belt, the Ear Falls – Manigotagan gneiss belt, and the Uchi greenstone belt. The following conclusions emerge.In all of the belts, a major discontinuity divides the crust into the commonly found upper and lower crustal sections. At the top of the lower crust, a seismically distinct layer (the mid-crustal layer) occurs. Seismic velocities in this layer suggest either intermediate to basic igneous rocks or metamorphic rocks of the amphibolite facies.Crustal geophysical characteristics vary sufficiently among the four belts to justify the classification of all four as distinct subprovinces of the Superior Province.Cet article présente une vue générale sur six projets de géophysique (réflexion et réfraction sismique, interprétation d'anomalies de gravité et magnétiques, déterminations de densité et de propriétés magnétiques) réalisés dans une région du Manitoba et du nord-ouest de l'Ontario encadrée par les longitudes 93 et 96°O et les latitudes 49 et 51°N.

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