Late Proterozoic and Devonian plutonic terrane within the Avalon zone of Rhode Island

Abstract

Research Article| February 01, 1985 Late Proterozoic and Devonian plutonic terrane within the Avalon zone of Rhode Island O. DON HERMES; O. DON HERMES 1Department of Geology, University of Rhode Island, Kingston, Rhode Island 02881 Search for other works by this author on: GSW Google Scholar ROBERT E. ZARTMAN ROBERT E. ZARTMAN 2U.S. Geological Survey, Denver Federal Center, MS 963, Denver, Colorado 80225 Search for other works by this author on: GSW Google Scholar Author and Article Information O. DON HERMES 1Department of Geology, University of Rhode Island, Kingston, Rhode Island 02881 ROBERT E. ZARTMAN 2U.S. Geological Survey, Denver Federal Center, MS 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 (1985) 96 (2): 272–282. https://doi.org/10.1130/0016-7606(1985)96<272:LPADPT>2.0.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 O. DON HERMES, ROBERT E. ZARTMAN; Late Proterozoic and Devonian plutonic terrane within the Avalon zone of Rhode Island. GSA Bulletin 1985;; 96 (2): 272–282. doi: https://doi.org/10.1130/0016-7606(1985)96<272:LPADPT>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 The U-Th-Pb radiometric age of zircons demonstrates that much of Rhode Island consists of a late Proterozoic plutonic complex that subsequently was intruded by a large Devonian alkalic to subalkalic igneous complex.Two groups of late Proterozoic rocks can be recognized: (1) the Esmond Granite and related plutonic rocks in northern Rhode Island, ranging in composition from gabbro to granite and yielding an upper concordia intercept of 621 ± 8 m.y., and (2) quartz-rich, recrystallized gneissic rocks (Ten Rod Granite Gneiss and Hope Valley Alaskite Gneiss) in southern Rhode Island, giving an upper concordia intercept age of 601 ± 5 m.y. The lower intercept of the zircon discordia for the gneissic rocks indicates the isotopic systems were disturbed during the late Paleozoic Alleghanian Orogeny, whereas zircons from the Esmond Granite and related plutonic rocks have been subjected mainly to loss of lead attributable to recent dilatancy.Rocks determined to be of Devonian age include the Scituate Granite and plutonic rocks of the East Greenwich Plutonic Suite. The Quincy Granite of Quinn (1971) in northeastern Rhode Island may be of a similar Devonian age, or it may be slightly younger. Zircon data from these rocks fall upon a chord that gives an upper concordia intercept of 370 ± 7 m.y. and a lower intercept close to the origin. Collectively, these rocks form a composite pluton with an area >700 km2. The Devonian rocks exhibit petrologic characteristics distinct from slightly older Acadian orogenic rocks that occur in lithostratigraphic zones to the west and are more comparable to anorogenic Ordovician to Devonian alkalic granitoids that trend north-northeast across Massachusetts and the Gulf of Maine.The new age determinations confirm that much of Rhode Island contains plutonic rocks intruded during the Avalonian Orogeny but that a hertofore unrecognized major Devonian plutonic episode also occurred. The distinctly different ages probably had gone unrecognized because of generally similar lithologic and textural features exhibited by the late Proterozoic and Devonian rocks. We present new petrologic and geochemical criteria that should assist in distinguishing the rocks of different ages as additional mapping and geologic study proceeds. 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.