Precambrian Crustal Blocks in Minnesota
Precambrian Crustal Blocks in Minnesota

Author: S. R. Hemming

Publisher:

Published: 1995

Total Pages: 24

ISBN-13:

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Sm-Nd survey of Precambrian granitic and metasedimentary rocks collected from several geophysically defined blocks in central Minnesota confirms the presence of some fundamental geologic boundaries previously mapped on the basis of structure. The Malmo discontinuity an Early Proterozoic structure separates the Archean Minnesota River Valley ter- ranes from an Early Proterozoic (Penokean magmatic) terrane and the McGrath Gneiss dome of east-central Minnesota North of this boundary, the Penokean fold-and-thrust belt can be divided into fault-bounded terranes that were assembled during the Penokean orogeny. Each terrane within the study area has distinct crust formation ages.

Great Lakes Rocks
Great Lakes Rocks

Author: Stephen E Kesler

Publisher: University of MICHIGAN REGIONAL

Published: 2019-05-01

Total Pages: 369

ISBN-13: 0472053809

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The geologic story of the Great Lakes region is one of the most remarkable of any place on Earth. Great Lakes Rocks takes readers on this fascinating journey through geologic history, beginning with an investigation of the surface features—the hills and valleys, waterfalls and caves, and the Great Lakes themselves—that we encounter on a daily basis. From there the book digs deeper into the past, and readers learn about the amazing techniques geologists have used to reconstruct the events that shaped this region millions and even billions of years before humans set foot on Earth. Throughout, the book gives special attention to the link between the region’s geology and its modern history, including the impacts of geology on settlement patterns as well as the development of industries and the present-day economy. Other discussed topics include natural hazards that are geologic in nature, including earthquakes, floods, landslides, and coastal erosion, as well as information on rocks, minerals, and ancient life seen in fossils. Written for nonspecialist readers, this book provides a detailed but easy-to-follow introduction to the geology of the Great Lakes region, and it is an ideal fit for introductory geology courses, including those aimed at nonscience majors.

Nature and Style of Deformation in the Foreland of the Early Proterozoic Penokean Orogen, Northern Michigan
Nature and Style of Deformation in the Foreland of the Early Proterozoic Penokean Orogen, Northern Michigan

Author: J. S. Klasner

Publisher:

Published: 1991

Total Pages: 32

ISBN-13:

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Evidence for Early Proterozoic north-verging folding and thrusting in the continental foreland of the Penokean orogen is present in two widely separated areas in northern Michigan. In the eastern part of the exposed orogen, asymmetric to over-turned folds in the Early Proterozoic Michigamme Formation suggest an initial (D1) phase of possibly north verging thin-skinned deformation. A second phase (D2 ) is characterized by a more thick skinned deformation consisting of northward thrusting of Archean gneiss and overlying Early Proterozoic quartzite along ductile thrust faults. Crosscutting shear zones indicate a third phase (D3 ) of deformation involving east- northeast thrusting of Archean gneiss. Thick-skinned deformation D2 and D3 phases include spaced fracture cleavage, kink folds, and lineations in D1, foliation surfaces. Near the west end of the exposed orogen in Michigan, bedding-cleavage relationships in the Early Proterozoic Tyler Formation also indicate northward tectonic transport. These structures, which are interpreted as D1 lie along the north edge of the Archean Puritan batholith and associated Archean greenstone. The north-verging structures in the northern Michigan segment of the Penokean orogen were formed approximately 1,850 Ma during collision of the Wisconsin magmatic terranes with the continental foreland of Michigan, Wisconsin, and Minnesota.