New Developments in the Appalachian-Caledonian-Variscan Orogen
CONTAINS OPEN ACCESS

New analytical and field techniques, as well as increased international communication and collaboration, have resulted in significant new geological discoveries within the Appalachian-Caledonian-Variscan orogen. Cross-Atlantic correlations are more tightly constrained and the database that helps us understand the origins of Gondwanan terranes continues to grow. Special Paper 554 provides a comprehensive overview of our current understanding of the evolution of this orogen. It takes the reader along a clockwise path around the North Atlantic Ocean from the U.S. and Canadian Appalachians, to the Caledonides of Spitsbergen, Scandinavia, Scotland and Ireland, and thence south to the Variscides of Morocco.
A reevaluation of the tectonic history of the Dashwoods terrane using in situ and isotope-dilution U-Pb geochronology, western Newfoundland
*Corresponding author: ebenblake@berkeley.edu
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Published:May 19, 2022
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CiteCitation
Eben B. Hodgin*, Francis A. Macdonald, Paul Karabinos, James L. Crowley, Douglas N. Reusch, 2022. "A reevaluation of the tectonic history of the Dashwoods terrane using in situ and isotope-dilution U-Pb geochronology, western Newfoundland", New Developments in the Appalachian-Caledonian-Variscan Orogen, Yvette D. Kuiper, J. Brendan Murphy, R. Damian Nance, Robin A. Strachan, Margaret D. Thompson
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ABSTRACT
Synthesis of the Ordovician Taconic orogeny in the northern Appalachians has been hindered by along-strike variations in Laurentian, Gondwanan, and arc-generated tectonic elements. The Dashwoods terrane in Newfoundland has been interpreted as a peri-Laurentian arc terrane that collided with the Laurentian margin at the onset of the Taconic orogeny, whereas along strike in New England, the Moretown terrane marks the leading edge of peri-Gondwanan arcs. The peri-Laurentian affinity of the Dashwoods terrane hinges on the correlation of its oldest metasedimentary rocks with upper Ediacaran to Lower Ordovician rift-drift deposits of the Laurentian Humber margin in western Newfoundland. Here, we report U-Pb dates and trace-element geochemistry on detrital zircons from metasedimentary rocks in the southern Dashwoods terrane that challenge this correlation and provide new insights into the Taconic orogeny. Based on age and trace-element geochemistry of detrital zircons analyzed by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS), we identified ca. 462–445 Ma sedimentary packages with a mixed provenance consisting of Laurentian, Gondwanan, and arc-derived Cambrian–Ordovician sources. These deposits overlap in age with Upper Ordovician strata of the Badger Group of the Exploits subzone, which also contain Laurentian detritus. We infer dominantly east-directed transport of Laurentian detritus from the Taconic collision zone across a postcollisional arc–back-arc complex at ca. 462–455 Ma followed by dominantly west-directed transport of detritus from the Red Indian Lake arc at ca. 455–445 Ma. Our analysis of zircon inheritance from Dashwoods igneous rocks suggests that 1500–900 Ma Laurentian crystalline basement of the Humber margin is an unlikely source of Dashwoods inherited zircon. Instead, a more cosmopolitan Laurentian inheritance may be best explained as sourced from subducted Laurentian sediment. Our results demonstrate that the sampled metasedimentary units from the southern Dashwoods terrane do not correlate with rift-drift strata of the Humber margin as previously proposed, nor with the basement of the Moretown terrane; yet, these Middle to Upper Ordovician successions suggest the potential for an alternative plate-tectonic model in which the Taconic orogeny may have been initiated by collision of Gondwanan arc terranes that closed the main tract of the Iapetus Ocean along the Baie Verte–Brompton Line.
- absolute age
- Appalachians
- back-arc basins
- basins
- Cambrian
- Canada
- continental drift
- diorites
- Dunnage Zone
- Eastern Canada
- Ediacaran
- facies
- Gondwana
- greenschist facies
- Humber Zone
- Iapetus
- ICP mass spectra
- igneous rocks
- inclusions
- laser methods
- Laurentia
- lithofacies
- Lower Ordovician
- mafic composition
- mass spectra
- metamorphic rocks
- metamorphism
- metasedimentary rocks
- monazite
- Neoproterozoic
- nesosilicates
- Newfoundland
- Newfoundland and Labrador
- North America
- Ordovician
- orthosilicates
- Paleozoic
- phosphates
- plate collision
- plate tectonics
- plutonic rocks
- Precambrian
- Proterozoic
- reconstruction
- rifting
- sedimentary rocks
- silicates
- spectra
- subduction
- Taconic Orogeny
- tonalite
- trace elements
- U/Pb
- upper Precambrian
- volcanic rocks
- xenoliths
- zircon
- zircon group
- detrital zircon
- Cormacks Lake Complex
- Little Codroy Pond
- Baie Verte Line
- Badger Group
- Red Indian Lake Arc
- Dashwoods Terrane
- Moretown Terrane
- Dennis Pond Complex
- Bill Shears Pond