Browsing by Author "Ojakangas, R.W."
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Item Geologic map of Minnesota, Hibbing sheet, bedrock geology(Minnesota Geological Survey, 1970) Sims, P.K.; Morey, G.B.; Ojakangas, R.W.; Viswanathan, S.Item Geologic map of Minnesota, International Falls sheet, bedrock geology.(Minnesota Geological Survey, 1979) Southwick, D.L.; Ojakangas, R.W.Item Geologic map of Minnesota, Roseau sheet, bedrock geology.(Minnesota Geological Survey, 1979) Ojakangas, R.W.; Mossler, J.H.; Morey, G.B.Item Guidebook 10. Field Trip Guidebook for the Western Vermilion District, Northeastern Minnesota(Minnesota Geological Survey, 1979) Southwick, D.L.; Ojakangas, R.W.The Vermilion Granitic Complex consists of granitic and migmatitic rocks of Archean age (2,700 m.y.) that are the westward extension into Minnesota of the Quetico gneiss belt of Ontario. The complex is chiefly light grayish-pink biotite granite (following the rock classification of Streckeisen, 1973) that grades into migmatite with increasing content of schistose inclusions. The major grayish-pink granite and its genetically related grani te rich migmati te were named the Vermilion Grani te by Grout (1923), who was the first to study the rocks in detail (Grout, 1923; 192~b,1926). Because migmatites are so abundant within the area Grout mapped as granite, and because other rock types such as quartz diorite and trondhjemite are important locally, the term Vermilion Granite has been replaced formally by the more inclusive term Vermilion Granitic Complex. Where the grayish-pink biotite granite that is the dominant component of Grout's Vermilion Granite is homogeneous, it has been renamed the Lac La Croix Granite, and it is understood to be a subunit within the Vermilion Granitic Complex.Item Guidebook 2. Field Trip Guide Book for Lower Precambrian Volcanic-Sedimentary Rocks of the Vermilion district, Northeastern Minnesota(Minnesota Geological Survey, 1972) Ojakangas, R.W.; Morey, G.B.The present investigation, carried out since 1962 as part of continuing studies of the Lower Precambrian rocks of northern Minnesota, has consisted of broad regional geologic mapping in the western half of the district and adjacent areas (Sims and others, 1968; Sims and others, 1970) and detailed mapping and study of critical areas (Gabbro Lake quadrangle, Green and others, 1966; and Green, 1970; Isaac Lake quadrangle, Griffin and Morey, 1969; Embarrass quadrangle, Griffin, 1969; Tower, Shagawa Lake, and Ely quadrangles, unpublished maps). Systematic geologic mapping has not been carried out in the eastern part of the district as a part of the present re-study; however, the excellent geologic map of Gruner (1941) in the type area of the Knife Lake Group remains a useful one, and S.S. Goldich, G.N. Hanson, and associates have examined critical areas in the Saganaga Lake Northern Light Lake area as part of regional geochronologic studies. This field trip starts a few miles south of Ely and ends a few miles west of Tower, and is designed as a two-day trip. Typical outcrops of all formations in the district are included, but most stops will examine the Lake Vermilion Formation. The rocks that will be seen on this trip are tightly folded and steeply plunging; therefore, we will be looking at a cross-section (but a structurally complicated one) of a volcanic-sedimentary pile. All the rocks in the area are metamorphosed, but for simplicity the prefix "meta" will generally be omitted.Item M-005 Preliminary geologic map of the Vermilion district and adjacent areas, northern Minnesota(Minnesota Geological Survey, 1968) Sims, P.K.; Morey, G.B.; Ojakangas, R.W.; Griffin, W.L.Item M-017 Geologic map of Lost Lake quadrangle, St. Louis County, Minnesota(Minnesota Geological Survey, 1977) Ojakangas, R.W.; Sims, P.K.Item M-020 Reconnaissance geologic map of Stingy Lake quadrangle, Itasca and St. Louis County, Minnesota(Minnesota Geological Survey, 1974) Viswanathan, S.; Ojakangas, R.W.Item M-022 Reconnaissance geologic map of Dewey Lake quadrangle, St. Louis County, Minnesota(Minnesota Geological Survey, 1974) Viswanathan, S.; Ojakangas, R.W.Item M-105 Bedrock geology of the Island View quadrangle, Koochiching County, north-central Minnesota(Minnesota Geological Survey, 2000) Hemstad, C.B.; Ojakangas, R.W.; Southwick, D.L.Item M-110 Bedrock geology of the Cranberry Bay quadrangle, Koochiching and St. Louis Counties, north-central Minnesota(Minnesota Geological Survey, 2001) Hemstad, C.B.; Ojakangas, R.W.; Southwick, D.L.; Nemitz, M.Item M-125 Bedrock geologic map of Voyageurs National Park and vicinity, Minnesota(Minnesota Geological Survey, 2002) Hemstad, C.B.; Southwick, D.L.; Ojakangas, R.W.Item RI-14 Stratigraphy of the Lower Precambrian Rocks in the Vermilion District, Northeastern Minnesota(Minnesota Geological Survey, 1970) Morey, G.B.; Green, J.C.; Ojakangas, R.W.; Sims, P.K.The system of stratigraphic nomenclature used previously for the Lower Precambrian rocks in the western part of the Vermilion district, northeastern Minnesota, is replaced by a formal nomenclature based on increased data gained from recent geologic mapping. The resulting changes in stratigraphic nomenclature are the following: 1. Previously recognized lithostratigraphic units -- the Ely Greenstone, Soudan Iron-formation, and Knife Lake Group -- are redefined and restricted in usage. 2. The Lake Vermilion Formation is formally established for rocks exposed in the vicinity of Lake Vermilion that were previously considered part of the Knife Lake Group. Four informal lithologic members are recognized in the Lake Vermilion Formation. These include a metagraywacke-slate member, a feldspathic quartzite member, a volcaniclastic member, and a mixed metagraywacke-felsic conglomerate member. Each is characterized by dominant and distinctive lithologies and may contain several mappable rock units, such as iron-formation and pillowed metabasalt, that can be recognized and delineated on the ground, but whose geographic extent and/or stratigraphic relationships are not known completely. 3. A second unit -- the Newton Lake Formation, a metavolcanic formation -- also is formally recognized. It is inferred to stratigraphically overlie rocks assigned to the Knife Lake Group and to consist of two informal lithologic members, a dominantly mafic volcanic member and a dominantly felsic-intermediate volcanic member. The two members interfinger in the Vicinity of the type locality at Newton Lake. 4. A variety of hypabyssal intrusive rocks are intimately associated with all the volcanic and sedimentary rocks in the Vermilion district. The hypabyssal rocks were emplaced over an interval of time as a consequence of the igneous cycle in the district. Accordingly the time term "Laurentian" should no longer be applied to these rocks in the Vermilion district. 5. The recognition that (1) mafic volcanism was not confined to a single period and (2) that a major unconformity separating an effusive volcanic episode ("Ely Greenstone" of the older literature) from a younger sedimentary series ("Knife Lake Group" of the older literature) is lacking raises serious doubts about the validity ofregionaJ correlations previously accepted in northern Minnesota. Accordingly, it seems necessary to abandon the terms "Keewatin" and "Coutchiching" as time-stratigraphic units for strata of Early Precambrian age in northern Minnesota.