Timing constraints of orogeny to cratonization: Thermochronology of the Paleoproterozoic Trans-Hudson orogen, Manitoba and Saskatchewan, Canada

A comprehensive thermochronometric investigation across a 600 km transect of the Paleoproterozoic Trans-Hudson orogen (THO) in Canada has resolved two first-order thermal events: (1) widespread peak metamorphism at 1.82–1.79 Ga associated with terrane amalgamation and (2) a late-collisional metamorphic episode at ca. 1.77 Ga that is characterized by significant strike-slip deformation and rapid cooling. Geophysical observations of the lithosphere beneath the THO reveal crust that is markedly different on either side of the crustal-scale Tabbernor/Sturgeon-Weir (TSW) strike-slip fault system, which offsets lower crustal reflectors. The THO east of the fault system records U–Pb titanite and total-Pb monazite domain ages that are relatively indistinguishable from 40Ar/39Ar hornblende and mica cooling ages, indicating rapid cooling, and perhaps exhumation, following 1.77 Ga metamorphism. Seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks, and our thermochronometric data demonstrate it behaved as a single coherent element shortly (20–30 m.y.) following cessation of convergence. In contrast, rocks located west of the TSW fault system cooled distinctly later, preserving 40Ar/39Ar muscovite and biotite ages between 1.74 and 1.72 Ga; this crustal architecture delineated from seismic surveys illustrates a more homogeneous, slightly (5 km) thinner crust. In the case of this orogen, apparent stabilization and cratonization occurred ca. 100 m.y. after peak terrane amalgamation, and notably the orogen was likely cratonized as two blocks, east and west of the TSW fault system.