Research Article| December 01, 1993 Moho in the Archean Minnesota gneiss terrane: Fossil, alteration, or layered intrusion? Nicholas K. Boyd; Nicholas K. Boyd 1Program for Crustal Studies, Department of Geology and Geophysics, University of Wyoming, P.O. Box 3006,Laramie, Wyoming 82071 Search for other works by this author on: GSW Google Scholar Scott B. Smithson Scott B. Smithson 1Program for Crustal Studies, Department of Geology and Geophysics, University of Wyoming, P.O. Box 3006,Laramie, Wyoming 82071 Search for other works by this author on: GSW Google Scholar Author and Article Information Nicholas K. Boyd 1Program for Crustal Studies, Department of Geology and Geophysics, University of Wyoming, P.O. Box 3006,Laramie, Wyoming 82071 Scott B. Smithson 1Program for Crustal Studies, Department of Geology and Geophysics, University of Wyoming, P.O. Box 3006,Laramie, Wyoming 82071 Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1993) 21 (12): 1131–1134. https://doi.org/10.1130/0091-7613(1993)021<1131:MITAMG>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 Nicholas K. Boyd, Scott B. Smithson; Moho in the Archean Minnesota gneiss terrane: Fossil, alteration, or layered intrusion?. Geology 1993;; 21 (12): 1131–1134. doi: https://doi.org/10.1130/0091-7613(1993)021<1131:MITAMG>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 A seismic survey in the Archean Minnesota gneiss terrane (3.6-3.8 Ga) imaged a seismically variable, discontinuous Moho at both vertical incidence and wide angles. The wide-angle data show the gneiss terrane crust to be thick (49 km) with a high average velocity (6.8 km/s). The vertical-incidence data show a sharp, 10-km-long Moho-depth (Fresnel zone radius = 2.8 km) reflection that disappears laterally, and data analysis suggests a 1 km Moho zone with 100-m-thick internal layering. Changes in the signal/noise ratio across the survey or energy losses from reflectors within the crust do not affect the variability in the reflection Moho; therefore, the reflection discontinuity is a geologic feature, and lateral structural variation of the Moho occurs over short (tens of kilometres) distances. Possible interpretations of the layered structure are (1) a layered intrusion, (2) localized alteration to eclogite by intrusion of fluids along shear zones or zones of weakness, or (3) fossil granulite-facies structures preserved within an eclogitized lower crust. A thin gradient, or thin layered zone with small impedance contrasts, or an abrupt velocity change are possible models for the regional Moho. The Moho shows considerable lateral structural variation within an early Archean high-grade terrane. 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.