Structural characterisation and geochronological constraints on the Wager shear zone, northwestern Hudson Bay, Nunavut

• Main Author: Therriault, Isabelle
• Format: Thesis
• Language: English
• Published: University of British Columbia 2019
• Subjects: Hudson; Hudson Bay; Nunavut; Kivalliq
• Online Access: http://hdl.handle.net/2429/70015

The Proterozoic Wager shear zone (WSZ) is a major zone of high strain located on the northwestern coast of Hudson Bay, Nunavut. New geological mapping was conducted during the summer of 2017 to characterise the timing, duration and kinematics of the deformation recorded by the WSZ and to interpret this new information in the regional tectonic context. At the outcrop scale, the shear zone is marked by a steep, east-west striking mylonitic foliation and a sub-horizontal mineral-stretching lineation and displays abundant dextral shear-sense indicators. Fieldwork outlined boundaries of an apparent strain gradient within the shear zone that generally correlates with microstructural observations. Paleopiezometry investigations of feldspar suggest that deformation occurred in the dislocation creep regime for that phase, near the transition into the diffusion creep field. It also revealed that strain rates recorded by the WSZ are consistent with those from other ductile high-strain zones. Zr-in-titanite thermometry of a suite of granodioritic rocks establish that temperatures of deformation exceeded 750°C, in good agreement with microstructural observations and results from the quartz c-axis fabric opening-angle deformation thermometer. Quartz fabrics from mylonitic specimens also indicate a local component of constrictional strain to the deformation. The timing of deformation within the shear zone is informed by titanite petrochronology results from specimens in which cores, as well as recrystallised domains within the crystals form two age populations, a younger, ca. 1755–1740 Ma age population and an older, ca. 1815 Ma population. The younger population is only recorded in specimens from within and at the margin of the WSZ and the interval is interpreted to represent the timing of high deformation along the structure, earlier than what was previously thought. Deformation along the WSZ is coeval with dextral strike-slip movement along the Amer mylonite zone post-1750 Ma, widespread heating across the western Churchill Province, emplacement of the Kivalliq igneous suite (1.77–1.73 Ga) and the final phase of exhumation along shear zones that make up the Snowbird tectonic zone. Irving K. Barber School of Arts and Sciences (Okanagan) Earth and Environmental Sciences, Department of (Okanagan) Graduate