PRECAMBRIAN METAMORPHIC AND TECTONIC EVOLUTION OF NORTHERN BAFFIN ISLAND, NUNAVUT, CANADA

Abstract

The northern part of Baffin Island, in Nunavut, lies within the ca. 3.0–2.5 Ga Committee belt, characterized by episodic granitic plutonism and greenschist- to upper-amphibolite-facies belts of supracrustal rocks. Whereas the entire belt on Baffin Island was likely affected by ca. 2.7 Ga plutonism and associated metamorphism, there is also evidence of a high-grade event at ca. 2.55–2.5 Ga. Evolution of the Baffin orogen in south-central Baffin Island led to generation of the ca. 1.86 Ga Cumberland Batholith, ca. 1.85–1.83 Ga northwest-directed thrusting of the Foxe fold-and-thrust belt over the Dexterity granulite belt (DGB), and variable structural and metamorphic reworking of the Committee belt on northern Baffin Island. Thermobarometric data for granulite-facies rocks in the western DGB indicate ~8.7 kbar paleopressure, interpreted to have been achieved in continental crust thickened by thrust imbrication. Paleopressure decreases gradually northward from the western DGB to <4 kbar, but decreases sharply south of the Isortoq fault zone (IF), which approximates the southern boundary of the DGB. Combined thermobarometric and structural constraints suggest that the IF represents an important crustal-scale structure involved in both NW-directed thrusting and tectonic loading of the DGB, as well as subsequent extensional unroofing of the DGB. Southwest-directed thrusting in the ca. 1.825–1.81 Ga Northeast Baffin thrust belt (NBTB) is interpreted to have produced similar tectonic thickening and ~10.5 kbar pressures along most of the length of this belt on northern Baffin Island, including the eastern part of the DGB. The ~6–8 kbar Archean Bylot Batholith represents a higher structural level that may have contributed to tectonic loading of adjacent high-pressure rocks in the NBTB.