Rock groups, structural slices and deformation in the Humber Arm allochthon at Serpentine Lake, western Newfoundland

Godfrey, Stephen C. (1982) Rock groups, structural slices and deformation in the Humber Arm allochthon at Serpentine Lake, western Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The Humber Arm Allochthon is a well exposed composite allochthon on the west coast of the island of Newfoundland. It extends from the Port au Port Peninsula in the south to Daniels Harbour in the north, and its rocks record the evolution and destruction of the ancient continental margin of eastern North America in early Paleozoic time. -- At Serpentine Lake, the allochthon comprises eight major structural slices and numerous smaller blocks, each enveloped in shaley melange. Transported clastic and carbonate rocks form the structurally lower slices. These are interpreted as rise-prism sediments deposited east of the morphological edge of the ancient continental shelf. The sedimentary rocks are laterally traceable into a regionally extensive melange terrane preserved along the east sides of Blow Me Down Mountain and the Lewis Hills. The melange records tectonic disruption of the alloehthonous sediments and localized olistostromal deposition. A north-dipping sliver of platformal carbonate rocks that lies south of Serpentine Lake records detachment of an upfaulted portion of the collapsing autochthonous terrane during Middle Ordovician (Taconic) emplacement of the allochthon. -- Structurally higher slices contain ophiolitic lithologies and metamorphic rocks related to the evolution and early transport of oceanic crust and mantle. Volcanic rocks structurally beneath the ophiolitic slices are of tholeiitic composition, and formed in the same general tectonic setting. -- Contrasting structural styles within and between slices of the allochthon are attributable to deformational events pre-dating, coeval with, and post-dating allochthon assembly and emplacement. Geological relationships at Serpentine Lake suggest assembly and emplacement of the allochthon through attempted subduction of the North American craton beneath a westward migrating oceanic plate.

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