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Approximately three hundred Keewatin volcanic rocks have been analyzed from nine greenstone areas in the southern part of the Superior province. Basalt-andesite-dacite-rhyolite series are typical of each area and indicate a continental orogenic origin. The non-spilitic composition of the lavas confirms the continental orogenic origin rather than volcanism during accumulation of geosynclinal material.
A regional study of the volcanic areas shows that each area is merely a part of a great volcanic province instead of a series of subparallel volcanic belts. The present state of the volcanic formations is related to the depth of the granitic crust, to the intrusion of granite diapirs, and to major slip folding involving the volcanic series.
The continent was present before the Keewatin volcanism. The earliest known rocks of the Shield consist of a series of sedimentary rocks, possibly 20 km. thick, from which the Kenoran granites were derived by crustal melting.
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