PALEOPROTEROZOIC TECTONIC ASSEMBLY OF NORTHEAST LAURENTIA THROUGH MULTIPLE INDENTATIONS

Recent detailed geological mapping and U-Pb geochronological studies i n the Torngat, Ungava and Baffin orogens of Northeast Laurentia have p rovided new information regarding the tectonic assembly of this region between similar to 1.92 and 1.74 Ga. In contrast with an earlier hypo thesis whereby the geometry of Archean continental fragments was thoug ht to have resulted entirely from northerly indentation of the Superio r Province and consequent extrusion tectonics, interpretation of recen tly acquired data shows that Superior Province indentation was the las t of multiple collisional events during the formation of Northeast Lau rentia. In the present model, we propose that Southeast Rae and North Rae provinces were separate prior to similar to 1.92 Ga, when regional tectonism changed from extension to contraction. Westerly subduction and westward translation of the Archean Disko terrane and Nain Provinc e between the North Rae and Southeast Rae provinces resulted in the de velopment of a continental magmatic are in the Cumberland batholithic complex and in the Torngat orogen, and deposition of the upper sequenc es of the Penrhyn-Piling-Karrat sequences in the Fore and Rinkian belt s of the Baffin orogen (1895-1880 Ma). Continental collision between t he Disko terrane and North Rae Province produced shortening across the Rinkian and Foxe belts at, or before, 1876 Ma. Meanwhile, early are m agmatism in the Ungava orogen (1898-1861 Ma) accompanied foredeep or t ranstensional basin formation in the New Quebec orogen (similar to 188 3-1870 Ma) and the onset of deformation in the southeastern Nagssugtoq idian orogen (similar to 1883 Ma). Nain-Southeast Rae provinces collis ion at similar to 1860 Ma across the Torngat orogen caused renewed gra nitic magmatism and metamorphism in the Cumberland batholithic complex between 1857 and 1853 Ma. Initiation of felsic volcanism in the Makko vik-Ketilidian orogen at this time indicates a shift in the locus of p late subduction from the Southeast Rae Province to the southern margin of the Nain Province. In the Ungava orogen, northerly subduction chan ged to southerly subduction resulting in the generation of a second ar e suite at between 1844 and 1826 Ma. Formation of the de Pas batholith in the hinterland of the New Quebec orogen at similar to 1840 Ma acco mpanied are-continent and Superior-Southeast Rae collision from 1845 t o 1829 Ma. At this time, accretion of are material in the Makkovik-Ket ilidian orogen was contemporaneous with high-grade sinistral shearing along the reactivated Torngat orogen and the northwestern Nagssugtoqid ian orogen. Southeast-directed thrusting along the southeastern margin of the Cumberland batholithic complex, and reactivation of the Rinkia n belt is predicted to have also occurred at this time. At less than o r equal to 1826 Ma, the onset of are-continent collision across the Un gava orogen initiated closure of the North Rae-Southeast Rae provinces juncture and generation of the Ford Lake plutonic suite. Subsequent S uperior-Southeast Rae continental collision (similar to 1810 Ma) resul ted in dextral ''escape tectonics'' in the Fore and Rinkian belts, and thick-skinned folding of basement and cover sequences in the Ungava o rogen. High-grade metamorphism and granitoid magmatism in the Makkovik -Ketilidian orogen also occurred. Reactivation of the Nain-Southeast R ae (east-directed thrusting) and Superior-Southeast Rae (west-directed thrusting) margins at similar to 1790 Ma resulted in ''pop-up'' of th e Southeast Rae Province between its more rigid neighbors. Final cooli ng and the emplacement of post-tectonic granitoid rocks took place at similar to 1790-1740 Ma.