Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia

Abstract

Research Article| November 01, 1996 Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia John N. Aleinikoff; John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar J. Wright Horton, Jr.; J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Search for other works by this author on: GSW Google Scholar Marianne Walter Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information John N. Aleinikoff 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 J. Wright Horton, Jr. 2U.S. Geological Survey, 926 National Center, Reston, Virginia 20192 Marianne Walter 1U.S. Geological Survey, Box 25096, M.S. 963, Denver, Colorado 80225 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1996) 108 (11): 1481–1491. https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>2.3.CO;2 Article history First Online: 01 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 John N. Aleinikoff, J. Wright Horton, Marianne Walter; Middle Proterozoic age for the Montpelier Anorthosite, Goochland terrane, eastern Piedmont, Virginia. GSA Bulletin 1996;; 108 (11): 1481–1491. doi: https://doi.org/10.1130/0016-7606(1996)108<1481:MPAFTM>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 SocietyGSA Bulletin Search Advanced Search Abstract Uranium-lead dating of zircons from the Montpelier Anorthosite confirms previous interpretations, based on equivocal evidence, that the Goochland terrane in the eastern Piedmont of Virginia contains Grenvillian basement rocks of Middle Proterozoic age. A very few prismatic, elongate, euhedral zircons, which contain 12–29 ppm uranium, are interpreted to be igneous in origin. The vast majority of zircons are more equant, subangular to anhedral, contain 38–52 ppm uranium, and are interpreted to be metamorphic in origin. One fraction of elongate zircon, and four fragments of a very large zircon (occurring in a nelsonite segregation) yield an upper intercept age of 1045 ± 10 Ma, interpreted as the time of anorthosite crystallization. Irregularly shaped metamorphic zircons are dated at 1011 ± 2 Ma (weighted average of the 207Pb/206Pb ages). The U-Pb isotopic systematics of metamorphic titanite were reset during the Alleghanian orogeny at 297 ± 5 Ma. These data provide a minimum age for gneisses of the Goochland terrane that are intruded by the anorthosite. Middle Proterozoic basement rocks of the Goochland terrane may be correlative with those in the Shenandoah massif of the Blue Ridge tectonic province, as suggested by similarities between the Montpelier Anorthosite and the Roseland anorthosite. Although the areal extent of Middle Proterozoic basement and basement-cover relations in the eastern Piedmont remain unresolved, results of this investigation indicate that the Goochland terrane is an internal massif of Laurentian crust rather than an exotic accreted 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.