Laser probe argon-40/argon-39 dating of pseudotachylyte from the Sudbury Structure: Evidence for postimpact thermal overprinting in the North Range

— Ten pseudotachylyte samples from the North Range of the 1850 Ma Sudbury impact structure have been analyzed by the 40Ar/39Ar laser spot fusion method. Field and petrological evidence indicate that the pseudotachylytes were formed at 1850 Ma by comminution and frictional melting due to impact-induced faulting. The cryptocrystalline to microcrystalline grain size (