Structural and metamorphic history of the Gneisses of the Port aux Basques region, Newfoundland

Brown, Peter A. (1972) Structural and metamorphic history of the Gneisses of the Port aux Basques region, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

Three geological subdivisions are recognized in the Port aux Basques area, the Cape Ray Complex, the Port aux Basques Complex and the Windsor Point Group. The first two are separated by, and the third overlies, the Cape Ray Fault. The Cape Ray Complex is thought to be the oldest division and comprises a gneissic basement intruded by two ages of granite. The gneissic basement, the Long Range Gneiss, is a somewhat homogeneous leucogneiss with basic pods, and has been intensely retrogressed. The early Cape Ray Granite is megacrystic and contains two tectonite fabrics. The later Red Rocks Granite is undeformed. -- The Port aux Basques Complex comprises a series of banded gneisses intruded by the Port aux Basques Granite. These gneisses are complexly deformed and metamorphosed. The second recognised phase is the most intense and is responsible for the dominant composite fabric and gneissic banding observed in the rocks. In general the metamorphism and deformation increase in intensity from west to east as shown by the progressive development of garnet, garnet-staurolite-kyanite, kyanite-garnet, and sillimanite-garnet zones and the development of the migmatite terrain in the Margaree-Foxroost area. The second phase of deformation produced recumbent isoclinal folds with axial planes trending northwest-southeast. The third phase produced upright asymmetric folds trending northeast-southwest. The fourth phase resulted in the crenulation of pre-existing fabrics and open monoclinal folds. The Port aux Basques Granite was intruded after the first and before the second phase of deformation. -- The Windsor Point Group comprises a series of metasedimentary and metavolcanic rocks which overlie the Cape Ray Fault and have suffered three phases of deformation which are related to movements on the fault. These deformations also overprint the fabrics in the Port aux Basques and Cape Ray Complexes. -- The Cape Ray Fault extends for 80 km inland and is of fundamental importance in the structure of the area in that it separates two gneissic complexes of differing age, the older of which was relatively unaffected during the deformation and metamorphism of the younger.

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