Between Dec 19, 2024 and Jan 2, 2025, datasets can be submitted to DRUM but will not be processed until after the break. Staff will not be available to answer email during this period, and will not be able to provide DOIs until after Jan 2. If you are in need of a DOI during this period, consider Dryad or OpenICPSR. Submission responses to the UDC may also be delayed during this time.

Browsing by Subject "GSA"

Now showing 1 - 3 of 3
  • Thumbnail Image
    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quadrangle, Griffin and Morey, 1969; Embarrass quadrangle, Griffin, 1969; Tower, Shagawa Lake, and Ely quadrangles, unpublished maps).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.
  • Thumbnail Image
    Item
    Guidebook 5. Field Trip Guide Book for Precambrian Migmatitic Terrane of the Minnesota River Valley
    (Minnesota Geological Survey, 1972) Grant, J.A.; Himmelberg, Glen R.; Goldich, S.S.
    The Minnesota River Valley provides a tantalizing window onto the Canadian Shield on the eastern margin of the Great Plains, tantalizing because of the high grade of the metamorphism, and especially because of the antiquity of the rocks there exposed. Essentially, this is a migmatitic terrane of granitic gneisses with lesser amphibolitic gneisses, commonly with pyroxene, and biotite-rich gneisses, which may contain garnet, cordierite, sillimanite, anthophyllite, or hypersthene. Some of the rocks are greater than 3.0 b.y. in age, and they have been involved in metamorphism and deformation at least 2.6 b.y. ago. These events left rocks with a metamorphic grade in the upper amphibolite or granulite facies, and with a major structure that is similar throughout most of the exposed area. Later minor intrusions, dominantly mafic, cut the older rocks, and conglomerate and quartzite of the Sioux Formation of Late Precambrian age locally overlie them. Deep weathering of the gneisses formed a regolith about 100 feet thick, a part of which was reworked in the formation of Cretaceous deposits of sand and clay. Over this came the glacial deposits of the Pleistocene. With the formation of Lake Agassiz, drainage via Glacial River Warren scoured out the precursor of the present valley leaving an underfit present-day Minnesota River and the glimpse of the Precambrian described in the following pages. The granitic gneisses in the vicinities of Morton, Granite Falls, and Montevideo are among the oldest known crustal rocks. Like very ancient rocks in other parts of the world the gneisses have had a complicated history, and metamorphic changes have masked their original characters and obscured their age. Conservatively the age may be given as 3200 or 3300 m. y. Goldich and others (1970) have attempted to probe the metamorphic history and concluded that the gneisses date back to 3550 m.y. ago. Similarly old, or older gneisses (3600 to 4000 m.y.) have been reported from the Godthaab district, West Greenland (Black and others, 1971). Field and more detailed geochronological and geochemical investigations are being continued, and the nature of this work is briefly indicated in following sections.
  • Thumbnail Image
    Item
    OFR13-02, Three-Dimensional Geological Mapping
    (2013) Thorleifson, Harvey; Berg, Dick; Russell, Hazen
    This workshop is designed for those constructing 3D geological maps and numerical models. Our objective is to bring together people dealing with large datasets, and who must integrate variable quality data with high quality data to construct 3D geological models for application such as hydrogeology, engineering, and energy resource assessment. Topics include (1) methods of model construction, (2) managing diverse data of variable quality, (3) ensuring data interoperability, (4) visualization tools, and (5) interaction between mappers, hydrogeologists, energy and mineral resource geologists, engineering geologists, and engineers. The emphasis is on deposits that host potable groundwater, as well as sedimentary basins as a whole.