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Research ArticleArticles

Tectonics and foreland basin development at the leading edge of the Humber Arm Allochthon, western Newfoundland, Canadian Appalachians

Ryan A. Lacombe, John W. F. Waldron and S. Henry Williams
American Journal of Science May 2020, 320 (5) 450-477; DOI: https://doi.org/10.2475/05.2020.02
Ryan A. Lacombe
* Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G2E3, Canada
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John W. F. Waldron
* Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, T6G2E3, Canada
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  • For correspondence: john.waldron@ualberta.ca
S. Henry Williams
** Suncor Energy, 150-6th Ave SW, Calgary AB, T2P 3E3, Canada
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Abstract

The thrust front of the Northern Appalachians involves Ediacaran rift-related structures of the Laurentian margin that were re-worked in Taconic (Ordovician), Salinic (mainly Silurian) and Acadian (mainly Devonian) deformation events. Much of the thrust front is concealed under the Gulf of St. Lawrence, but Port au Port Peninsula, in western Newfoundland provides a cross-section through the Laurentian passive margin, overlying foreland basins, and the Humber Arm Allochthon.

A large area of foreland basin strata is present in areas formerly mapped as Humber Arm Allochthon. Abrupt thickness changes and an abundance of fault-scarp-derived limestone conglomerate indicate that deposition was influenced by block faulting and differential subsidence in a basin undergoing active flexural extension. A coarsening upward trend in the Goose Tickle Group represents a transition from a distal to a proximal sediment source as the Humber Arm Allochthon was emplaced westwards.

Goose Tickle Group separates two packages of allochthonous rocks. The West Bay Thrust Sheet, the lower package, represents the leading edge of the Taconic allochthon. Its timing of emplacement is constrained by Darriwilian 3 graptolites both above and below the thrust sheet. Its present-day configuration results from a combination of processes including thrusting, extension by gravity spreading, gravity gliding, and subsequent erosion of material that was deposited in the Goose Tickle Group. The structurally higher Lourdes Thrust Sheet is an out-of-sequence structure associated with Acadian (Devonian) orogenesis. High-angle faults show a protracted history of movement that includes early Taconic flexural extension, Acadian inversion, and later Carboniferous or Mesozoic strike-slip motion. The leading edge of the Humber Arm Allochthon was influenced by both thin-skinned and thick-skinned tectonics throughout the development of the Appalachian orogen.

  • Newfoundland Appalachians
  • thrust front
  • faults
  • mélange
  • stratigraphy
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American Journal of Science: 320 (5)
American Journal of Science
Vol. 320, Issue 5
1 May 2020
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Tectonics and foreland basin development at the leading edge of the Humber Arm Allochthon, western Newfoundland, Canadian Appalachians
Ryan A. Lacombe, John W. F. Waldron, S. Henry Williams
American Journal of Science May 2020, 320 (5) 450-477; DOI: 10.2475/05.2020.02

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Tectonics and foreland basin development at the leading edge of the Humber Arm Allochthon, western Newfoundland, Canadian Appalachians
Ryan A. Lacombe, John W. F. Waldron, S. Henry Williams
American Journal of Science May 2020, 320 (5) 450-477; DOI: 10.2475/05.2020.02
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  • Article
    • Abstract
    • INTRODUCTION
    • GEOLOGICAL SETTING
    • STRATIGRAPHIC RELATIONSHIPS ON PORT AU PORT PENINSULA
    • STRUCTURE
    • DISCUSSION: HISTORY OF THE THRUST FRONT
    • CONCLUSIONS
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Keywords

  • Newfoundland Appalachians
  • thrust front
  • faults
  • mélange
  • stratigraphy

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