Research Article| June 01, 1989 Quimby, Iowa, scientific drill hole: Definition of Precambrian crustal features in northwestern Iowa W. R. Van Schmus; W. R. Van Schmus 1Department of Geology, University of Kansas, Lawrence, Kansas 66045 Search for other works by this author on: GSW Google Scholar M. E. Bickford; M. E. Bickford 1Department of Geology, University of Kansas, Lawrence, Kansas 66045 Search for other works by this author on: GSW Google Scholar R. R. Anderson; R. R. Anderson 2Geological Survey Bureau, Iowa Department of Natural Resources, 123 Capitol Street, Iowa City, Iowa 52242 Search for other works by this author on: GSW Google Scholar C. K. Shearer; C. K. Shearer 3Institute for the Study of Mineral Deposits, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701 Search for other works by this author on: GSW Google Scholar J. J. Papike; J. J. Papike 3Institute for the Study of Mineral Deposits, South Dakota School of Mines and Technology, Rapid City, South Dakota 57701 Search for other works by this author on: GSW Google Scholar B. K. Nelson B. K. Nelson 4Department of Geological Sciences, University of Washington, Seattle, Washington 98195 Search for other works by this author on: GSW Google Scholar Geology (1989) 17 (6): 536–539. https://doi.org/10.1130/0091-7613(1989)017<0536:QISDHD>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation W. R. Van Schmus, M. E. Bickford, R. R. Anderson, C. K. Shearer, J. J. Papike, B. K. Nelson; Quimby, Iowa, scientific drill hole: Definition of Precambrian crustal features in northwestern Iowa. Geology 1989;; 17 (6): 536–539. doi: https://doi.org/10.1130/0091-7613(1989)017<0536:QISDHD>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Geophysical data and sparse subsurface samples suggest that the Spirit Lake trend (SLT) in the aeromagnetic fabric of northwest Iowa is the southern boundary of the Archean Superior craton. Several small-diameter, positive aeromagnetic anomalies south of the SLT have been interpreted as Middle Proterozoic anorogenic, magnetite-bearing granites that intruded juvenile Early Proterozoic crust. A scientific drill hole 609 m deep was drilled into a 1200 gamma aeromagnetic anomaly near Quimby, Iowa, to test these interpretations. Precambrian basement was reached at a depth of 510 m, and 99 m of undeformed, megacrystic, magnetite-bearing granite core was collected. Petrographic and chemical data are consistent with derivation of the granite magma by melting of preexisting tonalitic continental crust. A U-Pb zircon age of 1433 ±4 Ma shows that this granite is part of the older anorogenic granite-rhyolite suite of the United States. Sm-Nd data yield a depleted-mantle separation age of 1860 Ma, which confirms that the source for the pluton magma was Early Proterozoic crust. All data are consistent with the hypothesis that the aeromagnetic anomalies are caused by Middle Proterozoic anorogenic plutons and with interpretation of the SLT as an Archean/Early Proterozoic crustal boundary. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.