Overview of regional geophysical studies in Manitoba and northwestern Ontario

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.

Midlithospheric discontinuities and complex anisotropic layering in the mantle lithosphere beneath the Wyoming and Superior Provinces

“…The Superior Province is composed of a number of Neoarchean to Mesoarchean (2.5–3.4 Ga) subprovinces, ranging from high‐grade gneiss in the northern and southern portions of the province to interlacing plutonic, volcano‐plutonic, and metasedimentary regions in its center [e.g., Card , ]. The subprovinces are generally east‐west trending and are divided by faults that extend across the width of the province and are frequently correlated with Moho offsets at depth and north dipping structure [ Hall and Brisbin , ; Musacchio et al ., ; Percival et al ., ], supporting a model of progressive accretion.…”

Lithospheric structure and composition of the Archean western Superior Province from seismic refraction/wide‐angle reflection and gravity modeling

“…Prior to commencement of the LITHOPROBE Western Superior Transect, knowledge of the lithospheric structure within this region was modest, as it was largely based on seismic refraction data acquired prior to 1980 [e.g., Hall and Hajnal , 1969, 1973; Hall and Brisbin , 1982; Mereu and Hunter , 1969; Young et al , 1986]. These early surveys identified a two‐layer crust comprising a 13–21 km thick upper crust with velocities of 6.0–6.3 km s −1 and a lower crust extending to depths of 30–44 km having velocities of ∼6.9–7.0 km s −1 , underlain by upper mantle velocities of 7.9–8.1 km s −1 .…”