The Slave craton is an Archaean craton in the north-western Canadian Shield, in Northwest Territories and Nunavut. The Slave Craton includes the 4.03 Ga-old Acasta Gneiss which is one of the oldest dated rocks on Earth. Covering about 300,000 km2 (120,000 sq mi), it is a relatively small but well-exposed craton dominated by ~2.73–2.63 Ga (billion years-old) greenstones and turbidite sequences and ~2.72–2.58 Ga plutonic rocks, with large parts of the craton underlain by older gneiss and granitoid units. The Slave Craton is one of the blocks that compose the Precambrian core of North America, also known as the palaeocontinent Laurentia. The exposed portion of the craton, called the Slave Province, comprises 172,500 km2 (66,600 sq mi) and has an elliptical shape that stretches 680 km (420 mi) NNE from Gros Cap on the Great Slave Lake to Cape Barrow on the Coronation Gulf and 460 km (290 mi) EW along latitude 64°N. It covers about 700 km × 500 km (430 mi × 310 mi) and is bounded by Palaeoproterozoic belts to the south, east, and west, while younger rocks cover it to the north. The Slave Craton is divided into a west-central basement complex, the Central Slave Basement Complex, and an eastern province, named the Hackett River Terrane or the Eastern Slave Province. These two domains are separated by a 2.7 Ga-old suture defined by two isotopic boundaries running north to south over the craton.
Subdivisions
Central Slave basement complex
The Central Slave basement complex (CSBC) is the basement under the central and western part of the craton. The CSBC's eastern extent is unknown, as its disappearance is marked by Nd and Pb isotopic boundaries. The CSBC dips to the east and underlies at least the central part of the craton. Along the Acasta River the CSBC includes the Acasta Gneisses with a protolith age of about 4.03 Ga, one of the oldest dated rock units on Earth. These gneisses are polymetamorphic and have a tonalitic and gabbroic composition. The rest of the CSBC is younger with a central core <3.5 Ga and the remaining craton with detrial and protolith ages ranging from 3.4 to 2.8 Ga. The basement complex is overlain by Neoarchaean supracrustal sequences and intruded by plutonic suites. The Acasta gneisses are geochemically similar to other Archaean complexes but, four billion years old, they contain even older zircon cores. These cores indicate that the parental magmas of such complexes formed by interaction between the zircon-bearing crust and mantle-derived melts. No such older Acasta gneisses have been discovered yet, but the zircon cores indicate they could exist.
Back River volcanic complex The Back River volcanic complex is an Archaean stratovolcano preserved in an upright position surrounded by four sedimentary sequences reflecting the volcano's magmatic history. An exposed dome in the southern half of the complex is interpreted to be the eroded portion of the volcano. In contrast to the remaining craton, the complex has only undergone a low degree of deformation.
Yellowknife Supergroup The Yellowknife Supergroup, also known as the Yellowknife greenstone belt, was deposited over 300 million years from ca. 2.9-2.6 Ga, and directly overlies the CSBC including much of the Eastern Slave Province. The CSBC and the Yellowknife greenstone belt are separated by a distinct unconformity that is laterally continuous over hundreds of kilometres. The Yellowknife Supergroup has been exposed to major metamorphism around 2605 Ma resulting in a range of greenschist to lower amphibolite facies. The Supergroup contains at least four distinct sequences representing different tectonic environments, deposited in separate intervals. The four main sequences include from oldest to youngest, the Central Slaver Cover Group, Kam Group, Banting Group, and Jackson Lake Formation. The Yellowknife Supergroup has been used to represent the general stratigraphy of the greenstone belts in the Slave Craton, including belts in the Eastern Slave, in order to interpret the processes involved in the evolution of the Slave Craton.
Central Slave Cover Group The Neoarchean supracrustal sequence known as the Central Slave Cover Group (informally Dwyer Group) is a 2.9–2.8 Ga package of fuchsitic quartzites overlain by banded iron formations. This fuchisitic quartziite sequence seems to be characteristic of many other cratons between about 3.1 and 2.8 Ga and marks a global peak in quartzite production. The Central Slave Cover Group is typically 100 to 200 meters thick. A quartz pebble conglomerate found at the base of the Central Slave Cover Group marks a distinct unconformity that is laterally continuous over much of the CSBC. This quartz pebble conglomerate layer has been found as far northwest as the 4.03 Ga Acasta Gneiss Complex. The Central Slave Cover Group is autochthonous and represents a single continuous cover sequence, that links the basement complex in the northwest with the basement in the south-central Slave Province. Uniform, laterally continuous deposition implies that the CSBC was previously a part of a single ancient craton that existed as early as 2.85 Ga.
Kam Group The Kam Group is a 0.3–6 kilometre thick sequence that overlies banded iron formations of the Central Slave Cover Group. The contact between these two groups is not well preserved due to the intrusion of gabbro sills and moderate shearing. The Kam group is separated into a lower and upper group based on the existence of a thin felsic volcaniclastic layer (Ranney Chert) dated at 2722 Ma. The lower Kam group consists of the Chan Formation which contains flows of pillowed basalts intruded by a series of gabbroic sills and dikes that were produced in an extensional back-arc basin setting. Sedimentary rocks exposed in the northern part of the formation are between 2.84 and 2.80 Ga. The Upper Kam Group contains three formations deposited between 2772 and 2701 Ma. It is composed mainly of intermediate and basaltic volcanic rocks with thin intercalated rhyolite tuff layers and minor komatiite flows. Rocks in this formation were seemingly formed in an arc environment and may be a result of rifting of basement rocks due to increased mantle plume activity.
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