Incipient collision of the Rae and Slave cratons at ca. 1.95 Ga

Abstract

Abstract Incipient collision between the Rae and Slave cratons represents a critical initial stage in the final assembly of the composite Laurentian craton. However, the timing and kinematics of this event remain poorly constrained. Here, we integrate phase equilibria modeling and Lu-Hf garnet and U-Pb monazite and zircon petrochronology to precisely date the timing of peak metamorphism along the Great Slave Lake shear zone, the central segment of the western Rae cratonic margin that was the locus of terminal Rae-Slave collision. Zircon and monazite U-Pb ages broadly constrain prograde-to-peak metamorphism to 1933–1913 Ma, whereas the timing of upperamphibolite facies peak metamorphism (0.8–1.0 GPa and 750–800 °C) is best constrained by two garnet Lu-Hf ages of 1931 ± 12 and 1917 ± 6 Ma. Our results highlight the inherent strengths and limitations of garnet, monazite, and zircon petrochronology in the context of dating Paleoproterozoic-aged metamorphism. Based on the timing of crustal thickening constrained by Lu-Hf garnet geochronology, we posit that the Slave craton first collided with the western Rae margin at ca. 1950 Ma. Taken together with prior constraints on the timing of metamorphism elsewhere along the western Rae margin, we propose incipient collision was followed by the northwards zippering of the margins and the eventual ~500 km of dextral translation of the Slave craton along the Great Slave Lake shear zone.