Download or read book 35th Annual Institute on Lake Superior Geology written by and published by . This book was released on 1989 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book 35th Annual Meeting Institute on Lake Superior Geology written by and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book 35th Annual Institute on Lake Superior Geology written by John C. Green and published by Houghton, Mich. : The Institute. This book was released on 1989 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book 36th Annual Institute on Lake Superior Geology written by Institute on Lake Superior Geology. Meeting and published by . This book was released on 1990 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Proceedings and Abstracts for the Annual Institute on Lake Superior Geology written by and published by . This book was released on 1990 with total page 114 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book U S Geological Survey Bulletin written by and published by . This book was released on 1983 with total page 372 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Publications of the Geological Survey written by Geological Survey (U.S.) and published by . This book was released on 1989 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book U S Geological Survey Bulletin written by Paul Kibler Sims and published by . This book was released on 1983 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Early Proterozoic Michigamme Formation of northern Michigan was deposited in the southeastern part of the Animikie basin. The formation conformably overlies the Goodrich Quartzite and comprises three widespread members a lower member of thin-bedded shale, siltstone, and sandstone; the Bijiki Iron-formation Member; and an upper member of tur- biditic graywacke, siltstone, and mudstone and a few local members. The Goodrich Quartzite is interpreted as having been deposited in a tidally influenced shallow marine environ- ment. The lower member of the Michigamme is interpreted as having been deposited in a tidally influenced environment, the iron-formation member as having been deposited below wave base in somewhat deeper water, and the upper member as having been deposited in still deeper water with turbidity currents being a major depositional mechanism. Several lines of evidence including paleocurrents, paleo- geographic setting, and neodymium isotopes suggest that the graywacke of the southern part of the outcrop area was derived from the south (Early Proterozoic Wisconsin magmatic terranes, Archean miniplates, and older Early Proterozoic sedimentary units formed on the continental margin), and that the graywacke in the northern area was derived from an Archean terrane to the north. The tectonic model that best fits the available data is a northward-migrating foreland basin.
Download or read book U S Geological Survey Bulletin written by Gene L. LaBerge and published by . This book was released on 1991 with total page 346 pages. Available in PDF, EPUB and Kindle. Book excerpt: A reconnaissance study carried out in conjunction with regional geologic mapping.
Download or read book Structural Geology of Parautochthonous and Allochthonous Terranes of the Penokean Orogeny in Upper Michigan written by William J. Gregg and published by . This book was released on 1993 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Publications of the U S Geological Survey written by and published by . This book was released on 1989 with total page 386 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book New Observations on the Age and Structure of Proterozoic Quartzites in Wisconsin written by Gene L. LaBerge and published by . This book was released on 1991 with total page 28 pages. Available in PDF, EPUB and Kindle. Book excerpt: Proterozoic quartzite is exposed at several isolated localities within an area of nearly 13,000 square kilometers in Wisconsin. Although early workers proposed that the quartzite is of two different ages, more recent workers have suggested that the various quartzite bodies are correlative, and that their protoliths were deposited between 1,760 and 1,630 Ma. Structural and stratigraphic studies of the quartzite deposits together with new age data indicate that the quartzite is at least of two distinct ages. Quartzite at McCaslin and Thunder Mountains, in northeastern Wisconsin, is older than 1,812 Ma, as indicated indirectly by a dated intrusion, and quartzite boulders in conglomerates in central Wisconsin are at least as old as the rhyolite country rock (=1,840 Ma). Deformed quartzite at Hamilton Mounds, in south-central Wisconsin, is intruded by undeformed granite that is 1,764 Ma. The ages of many other quartzite bodies, however, cannot be tightly constrained at present. Quartzite exposed in central and southern Wisconsin, south of the Eau Pleine shear zone, is interpreted as remnants of a passive margin sequence that was deposited on an Archean microcontinent (Marshfield terrane) and subsequently deformed in a major south-verging fold-thrust system during collision between the microcontinent and oceanic-arc rocks of the Pembine-Wausau terrane. The occurrence of quartzite-bearing conglomerates in the 1,860 Ma volcanic rocks of the Marshfield terrane suggests that the allochthonous quartzite bodies are 1,860 Ma or older. Collision occurred at about 1,840 Ma, and marked the end of the Penokean orogeny.
Download or read book Nature and Style of Deformation in the Foreland of the Early Proterozoic Penokean Orogen Northern Michigan written by J. S. Klasner and published by . This book was released on 1991 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Precambrian Crustal Blocks in Minnesota written by S. R. Hemming and published by . This book was released on 1995 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Paleomagnetism of the Early Proterozoic Sioux Quartzite Southwestern Minnesota implications for Correlating Quartzites of the Baraboo Interval written by Val W. Chandler and published by . This book was released on 1993 with total page 24 pages. Available in PDF, EPUB and Kindle. Book excerpt: Paleomagnetic studies were conducted on the Early Proterozoic Sioux Quartzite, one of the so-called "Baraboo interval" red-bed sequences of the Lake Superior region. A total of 158 samples were collected from 17 sites scattered across four basins (Cottonwood County, New Ulm, northern Pipestone, and southern Pipestone) in southwestern Minnesota. Alternating-field and thermal demagnetization studies indicate that the magnetization is dominantly single component, and that the magnetic carrier is hematite. Hematite occurs both as a diagenetic mineral whose long paragenetic history began shortly after deposition and as veinlets that formed during a strain event possibly related to regional tilting. The magnetization is tentatively interpreted to have occurred before regional tilting, although a definitive fold test is difficult because dips are low. Measured paleomagnetic directions at both site and basin levels show good clustering, and the average directions obtained from each of the four basins are not significantly different at the 95 percent confidence level. The good clustering at all levels of sampling indicates that the Sioux Quartzite was magnetized either within a short time interval or during a period of subdued apparent polar wander. The structurally corrected paleomagnetic directions from the four basins yield a combined paleopole location at 1 01 ° W. and 16° N. (k=65, alpha 95=11 °). Dated paleopoles for Early Proterozoic rocks in North America and age dates of rocks interpreted to underlie the Sioux Quartzite imply that its age is 1,700-1,650 Ma. This interval corresponds in part with the age of 1,800-1,630 Ma of the Central Plains orogen, which lies some 200-300 kilometers south of the Sioux Quartzite out- crop. Quartzite may reflect a tectonic pulse related to the Central Plains orogen. Preliminary paleomagnetic data on Baraboo-interval quartzites from Wisconsin indicate that the Sioux paleopole cannot be distinguished at the 95 percent confidence level from that of the Barren Quartzite, but that it differs from that of the Baraboo Quartzite, which on the basis of existing apparent polar wander data could be as much as 100 million years older. The paleomagnetic data support previously raised cautions that some Baraboo interval quartz arenites may have been deposited in separate basins at significantly different times.
Download or read book Precambrian Geology of the Southern Canadian Shield and the Eastern Baltic Shield written by Richard W. Ojakangas and published by . This book was released on 1991 with total page 196 pages. Available in PDF, EPUB and Kindle. Book excerpt:
