Geometry of the allochthonous Daly Bay Complex, Northwest Territories: a model constrained by geology and a three-dimensional gravity interpretation

• Published in: Canadian Journal of Earth Sciences
• Main Authors: Gordon, Terence M., Lawton, Donald C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1995
• Subjects: General Earth and Planetary Sciences; Northwest Territories; Daly; Chesterfield Inlet; Daly Bay; Baker Lake; Keewatin
• Online Access: http://dx.doi.org/10.1139/e95-105; http://www.nrcresearchpress.com/doi/pdf/10.1139/e95-105

The Daly Bay Complex is one of several metamorphic complexes making up the Aqxarneq gneisses north of Chesterfield Inlet in central District of Keewatin. Granulite-facies metamorphism (0.55 GPa, 750 °C) and ductile deformation have affected all of the rocks in the complex. A 1–15 km wide, inward-dipping, ductile shear zone forms the outer part of the complex and contains strongly deformed equivalents of rocks in the core. Mesoscopic structures and metamorphic mineralogy suggest the Daly Bay Complex was emplaced into the surrounding lower grade rocks by northward-directed thrusting. A three-dimensional gravity model, constrained by structural observations and 1091 surface density measurements, shows that the relatively dense rocks of the complex form a spoon-shaped structure with a long axis trending northwest–southeast. It is approximately 50 km by 120 km in lateral extent and reaches a maximum depth of about 9 km. The thin-skinned geometry of the Daly Bay Complex supports the notion that the crust in central Keewatin between the Daly Bay Complex and Baker Lake comprises a series of undulating imbricated gneiss sheets of middle and lower crustal material, which were juxtaposed by a major tectonic event sometime between 2.5 and 1.9 Ga. The interpreted basal décollement is comparable to seismic features in many orogens, and a predictable consequence of increased ductility with depth in the crust.