Paleotectonic and structural setting of the western Notre Dame Bay area, Newfoundland Appalachians

Abstract

The Appalachian Orogen in Newfoundland records the birth and destruction of the Iapetus Ocean. The Dunnage Zone preserves remnants of the oceanic terranes, and is subdivided into the western (Laurentian) Notre Dame Subzone and the eastern (Gondwanan) Exploits Subzone. This focus of this thesis has been to determine the geologic history of the northernmost part of the Notre Dame Subzone, confined between the Green Bay and Lobster Cove Faults. -- The geological history of the western Notre Dame Bay area has been investigated using field, geochemical, geochronological and structural methods. Care was taken to integrate the results obtained from these diverse methods in order to obtain an internally consistent model. As a result of these studies a new stratigraphic order is proposed, a major nappe has been recognized, and the character and tectonic history of one of the oldest intraoceanic sequences in the Notre Dame Subzone of the Newfoundland Appalachians has been determined. -- In simple terms, the geological history of the western Notre Dame Bay area can be described as follows: (1) a pre-500 Ma intraoceanic arc/back-arc stage, which involves deposition of the Lushs Bight Group and the lower part of the Western Arm Group (Sugar Loaves Basalt, Skeleton Pond Formation, and Big Hill Basalt); (2) emplacement of the pre-500 Ma sequence on the Laurentian continental margin and intrusion by high-Mg dykes of sanukitoid/bajaite affinities at 495 Ma; (3) development of a calc-alkalic arc (Cutwell Group and the upper two formations, Welsh Cove and Western Head, of the Western Arm Group) from 485 to 465 Ma, which is dominantly submarine, but whose chemistry is variably influenced by inputs from continental lithospheric sources; (4) development of a major alpine style fold nappe and its southeasterly directed emplacement (Notre Dame Bay Nappe) in the post-lower Silurian; and (5) post-emplacement structural disruption of the nappe, probably in the post-lower Carboniferous.