Structure of the Spruce Brook thrust stack at the base of the Humber Arm Allochthon, Western Newfoundland Appalachians

Meade, Steven R. (Steven Roy) (2008) Structure of the Spruce Brook thrust stack at the base of the Humber Arm Allochthon, Western Newfoundland Appalachians. Masters thesis, Memorial University of Newfoundland.

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Abstract

Spruce Brook drains a low-lying area east of the Lewis Hills and south of Blow-Me-Down Mountain in Western Newfoundland. The area is underlain by a dismembered succession of Cambrian-Ordovician platform carbonate and a succession of siliciclastic rocks assigned to the Taconic syn-tectonic flysch deposits of the Goose Tickle Group. Structurally juxtaposed against these strata are rocks of the Humber Arm Allochthon including altered ultramafic rocks and metamorphic rocks of the Bay of Islands Complex, as well as continental shelf and slope sedimentary rocks of the Humber Arm Supergroup. -- The occurrences of platform carbonate constitute thin, planar, structural slices that are bounded by thrust faults. The thrust slices are overall moderately east-dipping and imbricated from west to east. Their internal structural architecture is characterized by west-verging asymmetrical fold forms that are attributed to a combination of buckle folding and ramp-related bending. Contact relationships at the leading edge of the carbonate thrust stack indicate that strata of the Goose Tickle Group are structurally interleaved with the carbonate thrust sheets. Furthermore, the eastern trailing edge of the carbonate thrust stack is structurally overlain by the basal strata of the Humber Arm Supergroup, suggesting that the carbonate thrust stack lies as a duplex within the deformed Taconic foreland flysch succession and carries on its roof thrust the Humber Arm Allochthon. -- The thrust stack is cut by a major out-of-sequence thrust array that truncates and re-imbricates pre-existing structures related to the initial emplacement in the thrust stack. The out-of-sequence array includes a steep fault zone that carries a duplex of serpentinite and amphibolite of the Bay of Islands Complex suggesting that the emplacement and subsequent deformation of the Spruce Brook Thrust Stack is indicative of the structural interaction between the basal portion of the allochthon and the upper portion of the par-autochthonous succession during the Taconic Orogeny.

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