THE SLAVE CRATON OF NORTH AMERICA: AN OVERVIEW

The Slave craton of the northwestern Canadian Shield is one of the oldest and most distinct building blocks of North American cratonic lithosphere. It hosts Earth’s oldest intact rocks, the Acasta gneisses. These ancient gneisses are embedded in a large Mesoarchean to Hadean basement complex that underlies the west-central parts of the craton. Poorly mineralized, the basement complex is overlain by Neoarchean supracrustal sequences, and heavily intruded and cannibalized by plutonic suites ranging in age from 2720-2670 Ma synvolcanic plutons to 2590-2565 Ma late-orogenic batholithic granites. Supracrustal sequences, collectively known as the Yellowknife Supergroup, are represented by an early cover sequence comprising quartzite and banded iron formation (ca. 2800 Ma), a thick dominantly tholeiitic greenstone sequence (ca. 2700 Ma), younger arc-like sequences (ca. 2690-2610 Ma), extensive turbidite blankets (ca. 2680-2620 Ma), and finally syn-orogenic conglomerates deposited at ca. 2600 Ma, or shortly thereafter. The early cover sequence and the overlying tholeiites represent subaerial exposure and then volcanic-dominated rifting of the basement. Arc-like sequences formed in part on top of the attenuated basement and in progressively widening, juvenile, back-arc-like basins and contain some of Canada’s largest undeveloped volcanogenic massive sulphide deposits. After 2680 Ma, much of the Slave craton became overlain by the Burwash Basin, one of the largest and best-preserved Archean turbidite basins in the world, comparable in size and setting to the Japan Sea. During orogenesis, supracrustal sequences were telescoped, thickened, and multiply folded between ca. 2650 Ma and 2580 Ma, with a peak in crustal anatexis between 2590-2580 Ma (the “granite bloom”). Numerous orogenic gold deposits formed throughout the Slave craton, either as shear- or vein-hosted deposits in deformed greenstones or within the chemical traps provided by banded iron formations in the turbidites. Proterozoic rift-related magmatic suites and arcs around the margins of the craton host a variety of mineral deposits. Finally, the craton was punctured by several hundred Phanerozoic kimberlite pipes, some of which support Canada’s first diamond mines.