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.

The Thakkhola graben is a large-scale N-S striking, E-W structure located in west-central Nepal that was actively extending ca. 17 Myr ago. New multi-system geochronological data from the immediate footwall of the Dangardzong fault, the main graben-forming structure in the Thakkhola, outline decelerating cooling paths. The average cooling rate in the immediate footwall of the Dangardzong fault progressively decreases from 55 ± 10 ˚C/Ma in the early Miocene (~ 22-13 Ma, monazite U-Th/Pb, mica Ar/Ar and zircon U-Th/He), to 23 ± 8 ˚C/Ma in the middle to late Miocene (~13-8 Ma, zircon and apatite U-Th/He), and finally to 10 ± 2 ˚C/Ma from 8 Ma to present day (cooling post apatite U-Th/He closure). The deceleration in cooling rate is interpreted to reflect the widespread development of N-S striking graben structures in the Tibetan plateau in the middle Miocene and the progressive partitioning of strain away from the Thakkhola into other, younger, extensional features.