Geochronological constraints on metamorphism, magmatism and exhumation of deep-crustal rocks of the Kramanituar Complex, with implications for the Paleoproterozoic evolution of the Archean western Churchill Province, Canada

U-Pb and Sm-Nd geochronology establishes an important Paleoproterozoic (~1.9 Ga) history for the Kramanituar Complex, located in the interior of the Archean western Churchill Province, and provides further insight into the Snowbird tectonic zone, a crustal-scale (>2000 km) feature whose role during Precambrian time remains controversial. The Kramanituar Complex is a window of deep-crustal rocks, dominated by a granulite-facies metagabbroic suite of ~1902 Ma age, with minor supracrustal rocks and charnockite. These yield peak equilibrium conditions of 12-15 kbar and 850-900 °C, which are bracketed between ~1910 Ma, the age of prograde metamorphic monazite in sillimanite- and kyanite-bearing paragneiss, and 1901 Ma, the cooling ages of titanite and rutile in gabbroic and paragneissic rocks. Although mineral assemblages reflecting peak metamorphic conditions are widespread, some rocks record near-isothermal decompression to ~8 kbar and 800 °C. The timing of uplift and exhumation is tightly bracketed between magmatic crystallization of gabbroic anorthosite under granulite-facies conditions at 1902 Ma and widespread rutile cooling ages of 1901 Ma. Time-averaged cooling rates of >100 °C/Ma are estimated for gabbroic anorthosite and leucogranite. Rocks surrounding the Kramanituar Complex are mainly amphibolite-facies Archean plutonic and supracrustal rocks. Those to the north were at deep-crustal conditions coeval with the complex, whereas those to the south appear to preserve a record of older, mainly Neoarchean tectonometamorphic assemblages and fabrics. The southern boundary of the complex is inferred to be a normal fault that accommodated tectonic unroofing of the Kramanituar Complex at ~1.9 Ga. This geochronological data set highlights the protracted history of a segment of the geophysically defined Snowbird tectonic zone, a structure along which latest significant magmatism and tectonometamorphism has been interpreted as either ~2600 or ~1800 Ma. Penetrative ~1900 Ma activity in the east-trending Chesterfield segment, as documented at the Kramanituar Complex, suggests that the complex may have represented a favorably oriented segment of a crustal-scale Archean fault that was reactivated during Paleoproterozoic time, possibly in response to collision between the Slave and Churchill cratons (Thelon Orogen) at ~1.97-1.9 Ga.