Abstract

In the western pan of the Superior province, gneisses and plutonic rocks of the English River subprovince form a 100 km wide, east trending unit bound on both north and south by metavolcanic-granitic subprovinces. Recent investigations have resulted in a major twofold subdivision of the western portion of the English River subprovince. The northern part of the subprovince, termed the Ear Falls – Manigotagan gneiss belt, is characterized by a preponderance of sedimentary gneiss that records the development of a major Early Precambrian sedimentary basin. The southern part, termed the Winnipeg River batholithic belt, is a dominantly plutonic terrain with subordinate felsic gneissic rocks and minor metavolcanic and metasedimentary rocks. This latter belt records the almost complete obliteration of a greenstone terrain of unknown age and extent by felsic plutonism. Regional seismic, gravity, and magnetic data reflect the differing physical characteristics of the two bells. The Ear Falls-Manigotagan gneiss belt has a thicker granitic crust, thinner lower crust, thinner total crust, higher Bouguer gravity values, and lower intensity and shorter wavelength magnetic anomalies than the Winnipeg River batholithic bell.

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