Petrology and Sedimentation of the Archean Seine Group Conglomerate and Sandstone, Western Wabigoon Belt, Northern Minnesota and Western Ontario
1987-02
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Petrology and Sedimentation of the Archean Seine Group Conglomerate and Sandstone, Western Wabigoon Belt, Northern Minnesota and Western Ontario
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1987-02
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Thesis or Dissertation
Abstract
The Seine Group conglomerate and sandstone are part of the Wabigoon Volcanic Superbelt (Subprovince), located in northern Koochiching County in Minnesota and the Fort Frances-Mine Centre area in western Ontario. This fault-bound wedge of complexly interbedded rocks, that comprises a belt of Archean metasedimentary and metavolcanic rocks, is located north of the Rainy Lake-Seine River Fault and south of the Quetico Fault. The Seine Group occupies a narrow belt both in Minnesota (approximately 16 km by 0.9 km), and in Ontario (approximately 36 km by 2 km). The sedimentary rocks of the Seine Group include orthoconglomerate, feldspathic sandstone, and minor mudstone and banded iron-formation. A. C. Lawson was the first to record geological investigations in the area. Poulsen and others suggested the Keewatin metavolcanic unit is the oldest unit in the area. The Seine Group nonconformably overlies the metamorphosed plutonic rocks (Lawson's Laurentian) in the eastern part of the study area near Mine Centre. All rocks in the area have undergone at least greenschist facies metamorphism. Bedding consistently strikes east-northeast and dips nearly vertical. Foliation has a similar trend throughout the study area. Criteria such as cross-bedding, graded bedding, load casts, and vesicular texture in the tops of lava flows usually indicate top to the south. Lineations are usually found in the foliation plane and vary in plunge from 30-70 degrees to the east-northeast. In the eastern part of the study area, clasts within the conglomerate are more deformed than the conglomerate clasts in the western part of the study area. Megascopic modal analyses, carried out on field exposures, showed that volcanic cobbles and pebbles are the most abundant clasts, usually of felsic to intermediate compositions. Felsic plutonic clasts within the conglomerate are identical to the nearby plutons. Volcanic sandstone interbeds have nearly the same composition, as indicated by microscopic modal analyses, as the conglomerate itself. In the eastern part of the study area, schistose feldspathic sandstone part of the study area, consisting of muscovite biotite schist, overlies the conglomerate. Modal analyses of the f eldspathic sandstone yield an average of 50 percent quartz, 18 percent rock fragments, and 15 percent plagioclase. Cobaltinitrite staining of thin section heels shows an average of less than 2 percent alkali feldspar while Amarand yields approximately 17 percent plagioclase. The feldspathic sandstone is characterized by abundant cross-bedding, poor to moderate sorting, subrounded grains, immature compositions and a fairly high percentage of matrix material. Cross-stratification is mostly of low to high angle trough type. Paleocurrent measurements are unimodal and suggest paleocurrents were flowing to the present-day south. Using modern sedimentological criteria it is proposed that the Seine Group was deposited as a middle to distal alluvial fan and related braided fluvial environment.
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A Thesis submitted to the faculty of the Graduate School of the University of Minnesota by James R. Frantes in partial fulfillment of the requirements for the degree of Master of Science, February 1987. Plates 1-2 referenced in the thesis are also attached to this record.
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