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Browsing Guidebook Series by Author "Ojakangas, R.W."
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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quadrangle, Griffin and Morey, 1969; Embarrass quadrangle, Griffin, 1969; Tower, Shagawa Lake, and Ely quadrangles, unpublished maps).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.