Radiometric Age (Late Ordovician) of the Quincy, Cape Ann, and Peabody Granites from Eastern Massachusetts

Abstract

Research Article| April 01, 1971 Radiometric Age (Late Ordovician) of the Quincy, Cape Ann, and Peabody Granites from Eastern Massachusetts ROBERT E ZARTMAN; ROBERT E ZARTMAN U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar RICHARD F MARVIN RICHARD F MARVIN U.S. Geological Survey, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information ROBERT E ZARTMAN U.S. Geological Survey, Denver, Colorado 80225 RICHARD F MARVIN U.S. Geological Survey, Denver, Colorado 80225 Publisher: Geological Society of America Received: 13 Oct 1970 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (4): 937–958. https://doi.org/10.1130/0016-7606(1971)82[937:RALOOT]2.0.CO;2 Article history Received: 13 Oct 1970 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation ROBERT E ZARTMAN, RICHARD F MARVIN; Radiometric Age (Late Ordovician) of the Quincy, Cape Ann, and Peabody Granites from Eastern Massachusetts. GSA Bulletin 1971;; 82 (4): 937–958. doi: https://doi.org/10.1130/0016-7606(1971)82[937:RALOOT]2.0.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 A geochronologic study of several intrusive bodies of alkalic granite from eastern Massachusetts yields the following radiometric ages (in millions of years). The zircon ages show only mild internal discordancies and most diffusion models used to discuss U-Th-Pb isotopic systematics would give a true age about equal to that of the Pb207/Pb206 value. When plotted on a concordia diagram, the zircon data indicate a time of emplacement of 450 ± 25 m.y. for all three granite bodies. This Late Ordovician age for post-tectonic granites suggests that revisions in the commonly accepted geologic interpretation of eastern Massachusetts may be required. Previously, because of their massive, undeformed nature, the alkalic rocks were generally regarded as being Mississippian or Devonian in age and younger than the Early to Middle Devonian Acadian orogeny.The amphibole K-Ar and whole-rock Rb-Sr systems have responded in a complex way to postcrystallization disturbances. We interpret the pattern of ages for the Quincy Granite to reflect a late Paleozoic(?), low-temperature alteration that accompanied extensive faulting, and the patterns of ages for the Cape Ann and Peabody Granites to reflect a Devonian heating possibly related to contact metamorphism by a nearby mafic pluton. 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.