40Ar/39Ar dating of Silurian and Late Devonian cleavages in lower greenschist-facies rocks in the Westminster terrane, Maryland, USA

Abstract

Research Article| May 01, 2010 40Ar/39Ar dating of Silurian and Late Devonian cleavages in lower greenschist-facies rocks in the Westminster terrane, Maryland, USA R.P. Wintsch; R.P. Wintsch † 1Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA2U.S Geological Survey, M.S. 926, National Center, Reston, Virginia 20192, USA †E-mail: [e-mail] Search for other works by this author on: GSW Google Scholar M.J. Kunk; M.J. Kunk 2U.S Geological Survey, M.S. 926, National Center, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar B.K. Mulvey; B.K. Mulvey 1Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA Search for other works by this author on: GSW Google Scholar C.S. Southworth C.S. Southworth 2U.S Geological Survey, M.S. 926, National Center, Reston, Virginia 20192, USA Search for other works by this author on: GSW Google Scholar Author and Article Information R.P. Wintsch † 1Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA2U.S Geological Survey, M.S. 926, National Center, Reston, Virginia 20192, USA M.J. Kunk 2U.S Geological Survey, M.S. 926, National Center, Reston, Virginia 20192, USA B.K. Mulvey 1Department of Geological Sciences, Indiana University, Bloomington, Indiana 47405, USA C.S. Southworth 2U.S Geological Survey, M.S. 926, National Center, Reston, Virginia 20192, USA †E-mail: [e-mail] Publisher: Geological Society of America Received: 10 Feb 2009 Revision Received: 02 May 2009 Accepted: 04 May 2009 First Online: 08 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 © 2010 Geological Society of America GSA Bulletin (2010) 122 (5-6): 658–677. https://doi.org/10.1130/B30030.1 Article history Received: 10 Feb 2009 Revision Received: 02 May 2009 Accepted: 04 May 2009 First Online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation R.P. Wintsch, M.J. Kunk, B.K. Mulvey, C.S. Southworth; 40Ar/39Ar dating of Silurian and Late Devonian cleavages in lower greenschist-facies rocks in the Westminster terrane, Maryland, USA. GSA Bulletin 2010;; 122 (5-6): 658–677. doi: https://doi.org/10.1130/B30030.1 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 40Ar/39Ar dating of muscovite, biotite, and K-feldspar combined with microstructural analysis of lower greenschist-facies, polymetamorphic, phyllitic rocks, and marbles were successfully used to decipher the thermal and tectonic histories of the Westminster and adjacent terranes in western Maryland. The presence of unreset detrital muscovite in some samples demonstrates that temperatures in these rocks never exceeded the closure temperature for argon diffusion in muscovite, ∼350 ± 50 °C. Minor biotite in some arkoses constrains the minimum metamorphic temperatures to ≥∼320 °C. These data show an Early Silurian (ca. 430 Ma) cleavage in the western part of the Westminster terrane and a Late Devonian event (ca. 370 Ma) in the eastern Westminster and adjacent Potomac terranes. These two cleavage domains are separated by the NE-trending, newly identified Parrs Ridge fault zone. We propose that the sinistral transpressive collision of the Carolina terrane with Laurentia emplaced the western portion of the Westminster terrane in the Pennsylvania embayment along the Martic fault where it was folded and cleaved at ca. 430 Ma but otherwise largely sheltered from later deformation. The later Late Devonian dextral transpressive accretion of the outboard Potomac terrane thrust rocks of the eastern Westminster and Potomac terranes to the west, causing Late Devonian (360–370 Ma) S2 cleavage in these rocks, but only minimal discrete overprinting S3 cleavages in rocks farther west. Final juxtaposition and thermal convergence of these terranes occurred along reactivated dextral strike-slip faults in the Alleghanian at ca. 300 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.