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Northeastern Section - 59th Annual Meeting - 2024

Paper No. 1-8
Presentation Time: 10:40 AM

TIMING OF ORDOVICIAN VOLCANISM IN NORTHEASTERN MAINE: RETHINKING REGIONAL TECTONIC MODELS


LUDMAN, Allan, School of Earth and Environmental Sciences, Queens College, City University of New York, 65-30 Kissena Boulevard, Flushing, NY 11367, WANG, Chunzeng, College of Arts and Sciences, University of Maine at Presque Isle, 181 Main Street, Presque Isle, ME 04769, WHITTAKER, Amber, Maine Geological Survey, 17 Elkins Ln, 93 SHS, Augusta, ME 04333, O'SULLIVAN, Paul, GeoSep Services, 1521 Pine Cone Road, Moscow, ID 83843 and MCFARLANE, Chris, Earth Sciences, University of New Brunswick, 2 Bailey Drive, Fredericton, NB E3B 5A3, Canada

The first plate tectonic era bedrock mapping of three Cambro-Ordovician belts in northeastern Maine and recent geochronological and geochemical analyses offer new information about the closing of Iapetus and collision of Laurentia and Ganderia. The Munsungun-Winterville (MW) and Weeksboro-Lunksoos Lake (WL) belts are particularly valuable as they provide details about the Ganderia-Laurentia suture zone for which there is almost no information in New Brunswick.

  • The MW belt, long considered the leading edge of Ganderia, is, instead, peri-Laurentian. The suture, the Red Indian Line or Mckwe’jit Line, is buried beneath Silurian and Devonian cover rocks that separate MW and WL.
  • Coeval arc volcanism (485-460) in MW, WL, and the Miramichi (MI) belt is inconsistent with models of a northwestward-migrating single arc. We propose that there were two simultaneously active arcs above subduction zones of opposite polarity – NW- directed subduction beneath a MW arc and SE-directed subduction beneath an arc comprising the WL and MI belts.

The new data also reveal details of orogen-parallel asynchronous variations within the belts that are separated by major faults.

  • MI: Middle to Late Ordovician Tetagouche Group back-arc volcanic rocks (470-455Ma) in northern New Brunswick are separated by the Woodstock-Catamaran fault from Early Ordovician (~480 Ma) Meductic Group arc rocks to the southwest. These are in turn isolated by plutons from mostly younger (-474-465 Ma) MI arc rocks in Maine.
  • WL: The Cambro-Ordovician WL, containing 481-485 Ma back-arc and arc volcanic rocks, is separated by a NW-striking fault from the newly recognized Number Nine Mountain terrane. This belt includes 470 Ma arc volcanic rocks; 433 Ma (Salinic) volcanic rocks; and a hitherto unrecognized Silurian mélange.
  • MW: Two episodes of arc volcanism are recognized in the Munsungun segment of this belt. An older event (457-454 Ma) restricted to its southeastern area, and a younger event (450-455 Ma) confined to the northwest, possibly indicating advancing NW-directed subduction

Session No. 1

S2. Neoproterozoic and Paleozoic Geological Connections Among Northwest Africa, Europe, and Eastern North America I – A Session Honoring the Career of Sandra M. Barr
Sunday, 17 March 2024: 8:00 AM-12:00 PM
Pemigewasset Room (Doubletree by Hilton)

doi: 10.1130/abs/2024NE-397171
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