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.