Long‐Lived (180 Myr) Ductile Flow Within the Great Slave Lake Shear Zone

Abstract

The Great Slave Lake shear zone (GSLsz) is a type example for deeply eroded continental transform boundaries located in the Northwest Territories, Canada. Formed during the oblique convergence of the Archean Rae and Slave cratons, the GSLsz has accommodated up to 700 km of dextral shear. Here we present the results of in situ U‐Pb apatite and titanite geochronology from 11 samples that were collected across the strike of the shear zone. Both geochronometers record a near‐continuous history of ductile shear during crustal cooling and exhumation that spans ca. 1920–1740 Ma. By integrating the geochronological data with structural and metamorphic observations across the structure, we propose a tectonic model for the shear zone that consists of three stages. The first stage (ca. 1920–1880 Ma) is characterized by strain accommodation along two coeval fault strands. During the second stage (ca. 1880–1800 Ma), ductile shear ceases along the northernmost fault strand and the locus of strain migrates southwards towards the hinterland of the Rae cratonic margin. In the third stage (ca. 1800–1740 Ma), ductile strain localizes back along the southern of the two original fault strands, after which the present‐day surface level of the shear zone transitions to brittle shear. Our results highlight both the significance of the lateral migration of the zone of active deformation in major crustal shear zones as well as the localization of strain along existing crustal structures.This article is protected by copyright. All rights reserved.

A Contiguous Taltson‐Thelon Margin Revisited

“…Recent thermochronology data on the GSLsz (Šilerová et al., 2023) that are consistent with the north side of the LRf reflecting a cold, thick, and rigid crustal fragment, of which the Slave craton is a prime example (e.g., Snyder & Kjarsgaard, 2013).…”

“…Mapped occurrences of Slave crust immediately south of the Great Slave Lake, between the McDonald fault and the LRf (Hoffman, 1988; Janzen, 2015). The occurrence of carbonate metasedimentary rocks in the nearby Union Island group, which was deposited on the Slave margin, and on the north side of the LRf and their absence on the south side of the LRf and nearby Rae craton. Recent thermochronology data on the GSLsz (Šilerová et al., 2023) that are consistent with the north side of the LRf reflecting a cold, thick, and rigid crustal fragment, of which the Slave craton is a prime example (e.g., Snyder & Kjarsgaard, 2013). …”

“…Additionally, recent work has demonstrated that ductile shear along the LRf began at ca. 1920 Ma (Cutts & Dyck, 2022; Šilerová et al., 2023). As such, the Snowdrift granite may have originated south of the LRf and was likely juxtaposed against the mylonitic rocks along the late ENE‐striking Austin fault (Figure 1) following the cessation of ductile shear in the GSLsz.…”

“…Metamorphism in the Tmz has been ascribed to the collision of the Rae craton and BHT (Ross et al., 1991) and is constrained by U‐Pb zircon and monazite ages to 1.94–1.92 Ga (e.g., Bostock and van Breemen, 1994; M. R. McDonough et al., 2000). Ductile shear along the GSLsz occurred <1.90 Ga, concomitant with exhumation of the western Rae margin and cooling in the mid‐ to lower‐crust from 1.87 to 1.76 Ga (Camacho et al., 2020; Canam, 2023; Cutts & Dyck, 2022; Hoffman et al., 2023; Kellett et al., 2020; Regis & Kellett, 2018; Šilerová et al., 2023). The rocks along the GSLsz were variably altered at greenschist to amphibolite facies conditions during exhumation and ductile shear (Dyck et al., 2021).…”

“…In this study, we interrogate the age and geochemical affinity of plutonic rocks along the southwestern segment of the GSLsz, which includes the northernmost exposure of the Tmz (Figures 1a and 1b). This segment is of particular interest as there is an abrupt change in the structural, metamorphic, and lithological nature of the crust on either side of one of the main shear zone structures, the La Loche River fault (LRf) (Figures 1b and 1c) (Cutts & Dyck, 2022; Dyck et al., 2021; Hanmer, 1988; Hanmer et al., 1992; Šilerová et al., 2023). To focus on the primary magmatic geochronological and geochemical signatures of the rocks, we use a micro‐analytical approach to target the U‐Pb age, trace element, and Hf‐ and O‐isotope signature of magmatic core domains of zircon from plutonic rocks along the GSLsz.…”