Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia–Maryland—discrimination by 40Ar/39Ar and fission-track thermochronology

Abstract

Research Article| September 01, 2005 Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia–Maryland—discrimination by 40Ar/39Ar and fission-track thermochronology Michael J. Kunk; Michael J. Kunk 1U.S. Geological Survey, Denver Federal Center, Box 25046, MS 963, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Robert P. Wintsch; Robert P. Wintsch 2Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA Search for other works by this author on: GSW Google Scholar Charles W. Naeser; Charles W. Naeser 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar Nancy D. Naeser; Nancy D. Naeser 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar C. Scott Southworth; C. Scott Southworth 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar Avery A. Drake, Jr.; Avery A. Drake, Jr. 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar Jennifer L. Becker Jennifer L. Becker 4Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Michael J. Kunk 1U.S. Geological Survey, Denver Federal Center, Box 25046, MS 963, Denver, Colorado 80225, USA Robert P. Wintsch 2Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA Charles W. Naeser 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Nancy D. Naeser 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA C. Scott Southworth 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Avery A. Drake, Jr. 3U.S. Geological Survey, National Center, MS 926A, Reston, Virginia 20192, USA Jennifer L. Becker 4Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA Publisher: Geological Society of America Received: 25 Feb 2004 Revision Received: 28 Oct 2004 Accepted: 16 Feb 2005 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2005) 117 (9-10): 1347–1366. https://doi.org/10.1130/B25599.1 Article history Received: 25 Feb 2004 Revision Received: 28 Oct 2004 Accepted: 16 Feb 2005 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Michael J. Kunk, Robert P. Wintsch, Charles W. Naeser, Nancy D. Naeser, C. Scott Southworth, Avery A. Drake, Jennifer L. Becker; Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia–Maryland—discrimination by 40Ar/39Ar and fission-track thermochronology. GSA Bulletin 2005;; 117 (9-10): 1347–1366. doi: https://doi.org/10.1130/B25599.1 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 SocietyGSA Bulletin Search Advanced Search Abstract New 40Ar/39Ar data reveal ages and thermal discontinuities that identify mapped and unmapped fault boundaries in the Potomac terrane in northern Virginia, thus confirming previous interpretations that it is a composite terrane. The rocks of the Potomac terrane were examined along the Potomac River, where it has been previously subdivided into three units: the Mather Gorge, Sykesville, and Laurel Formations. In the Mather Gorge Formation, at least two metamorphic thermal domains were identified, the Blockhouse Point and Bear Island domains, separated by a fault active in the late Devonian. Early Ordovician (ca. 475 Ma) cooling ages of amphibole in the Bear Island domain reflect cooling from Taconic metamorphism, whereas the Blockhouse Point domain was first metamorphosed in the Devonian. The 40Ar/39Ar data from muscovites in a third (eastern) domain within the Mather Gorge Formation, the Stubblefield Falls domain, record thrusting of the Sykesville Formation over the Mather Gorge Formation on the Plummers Island fault in the Devonian. The existence of two distinctly different thermal domains separated by a tectonic boundary within the Mather Gorge argues against its status as a formation. Hornblende cooling ages in the Sykesville Formation are Early Devonian (ca. 400 Ma), reflecting cooling from Taconic and Acadian metamorphism. The ages of retrograde and overprinting muscovite in phyllonites from domain-bounding faults are late Devonian (Acadian) and late Pennsylvanian (Alleghanian), marking the time of assembly of these domains and subsequent movement on the Plummers Island fault. Our data indicate that net vertical motion between the Bear Island domain of the Mather Gorge complex and the Sykesville Formation across the Plummers Island fault is east-side-up. Zircon fission-track cooling ages demonstrate thermal equilibrium across the Potomac terrane in the early Permian, and apatite fission-track cooling ages record tilting of the Potomac terrane in the Cretaceous or later with the west side up at least 1 km. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.