Thermotectonic evolution of the Proterozoic-Archaean boundary in the Saglek area, northern Labrador

• Main Author: Mengel, Flemming Cai
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1987
• Subjects: Nain; Saglek Fiord
• Online Access: https://research.library.mun.ca/6763/; https://research.library.mun.ca/6763/1/FlemmingCaiMengel.pdf; https://research.library.mun.ca/6763/3/FlemmingCaiMengel.pdf

In the Saglek Fiord area, northern Labrador, sediments of the Lower Proterozoic Ramah Group occur as a north-trending fold belt which overlies the boundary between the Nain Province to the east and the Churchill Province to the west. The Nain Province is a polycyclic Archaean gneiss complex, consisting of tonalitic to granodioritic gueisses with remnants of supracrustal sequences. The metamorphic grade varies from amphibolite to granulite facies. In the Saglek area, rocks in the Churchill Province are mainly Archaean gneisses thoroughly reworked in a major north-south oriented transcurrent sinistral shear zone. Three tectonically juxtaposed north-trending lithotectonic terranes can be distinguished in the Churchill Province (from east to west): the Amphibolite Facies Terrane (AFT), the Granulite Facies Terrane (GFT), and the Tasiuyak Terrane (TT). -- The sediments of the Ramah Group were deposited unconformably on the peneplained Archaean basement, as evidenced by a well preserved regolith and basal conglomerate. Subsequently, the Hudsonian Orogeny caused deformation and metamorphism of the Ramah Group. -- Two thermotectonic events of Proterozoic age can be distinguished in the Saglek area. Using Proterozoic dykes (2300-2400 Ma) as time markers, the structural evolution can be subdivided into "Early Proterozoic" and "Hudsonian" orogenic events. The Early Proterozoic orogeny is characterized by transcurrent shearing and counterclockwise rotation of structures into parallelism with the north-south oriented sinistral shear zone. Proterozoic dykes clearly demonstrate the rotation; these are east-west oriented in the Nain Province, and rotate towards a north-south orientation in the AFT and GFT. The GFT, TT and most of the AFT are located within the shear zone, and are characterized by well developed subhorizontal mineral lineations and steeply west-dipping planar (mylonitic) foliations. Rocks In the GFT and TT are in granulite facies, and are interpreted to correspond to the deeper levels of a major shear zone, ...