Early proterozoic evolution of the saskatchewan craton and its allochthonous coyer, trans-hudson Orogen

Abstract

The composition, chronology, and structural relations of the Saskatchewan Craton and enveloping mylonitic rocks exposed in basement windows of the Glennie Domain, Trans‐Hudson Orogen, have been determined by geochemical, geochronologic, and structural studies accompanying detailed field mapping. Basement windows lie along the hinge zone of a regional crustal culmination and consist mostly of 2.4–2.5 Ga felsic plutonic rocks enveloped by the Nistowiak Thrust. The Nistowiak Thrust is a folded, 1–2 km thick, upper amphibolite facies mylonite zone formed during emplacement of the Flin Flon–Glennie Complex across the Saskatchewan Craton. It is likely correlative to the Pelican Thrust, which envelops basement windows in the Hanson Lake Block ∼100 km to the east. An internal high strain zone within the overlying nappe pile, the Guncoat Thrust, is composed primarily of mylonitized porphyroclastic pelitic and psammitic migmatites. U‐Pb geochronological results suggest calc‐alkaline plutonism from 1889–1837 Ma, thrust stacking, peak metamorphism and associated anatexis between 1837 and 1809 Ma, isotopic closure of titanite at 1790–1772 Ma, and intrusion of late granitic rocks at 1770–1762 Ma. This is in agreement with ages from the Hanson Lake Block, and La Ronge, Kisseynew, and Flin‐Flon domains in Saskatchewan and Manitoba, and from the Ungava‐Baffin portion of Trans‐Hudson Orogen, suggesting broadly synchronous thermotectonic processes along a strike length of 2000 km. We speculate that the Saskatchewan Craton, rather than representing an exotic continental fragment, rifted from the Superior and/or Hearne Provinces at ca. 2.1 Ga and that the Trans‐Hudson Orogen is an internal orogen. In this scenario the Maniwekan Ocean, developed between the Rae‐Hearne and Superior cratons, opened and closed about similar pole(s) of plate motion.