as Pacaud, Stoughton-Roquemaure, Kidd-Munro and Tisdale. The Swayze greenstone belt further south is interpreted to be a southwestern extension of the Abitibi greenstone belt. The Archean Red Lake greenstone belt in western Ontario consists of basaltic and komatiitic volcanics ranging in age from 2,925 to 2,940 million years old and younger rhyolite-andesite volcanics ranging in age from 2,730 to 2,750 million years old. It is situated in the western portion of the Uchi Subprovince, a volcanic sequence comprising a number of greenstone belts. The 1884- to 1870‑million-year-old Circum-Superior Belt constitutes a large igneous province extending for more than from the Labrador Trough in Labrador and northeastern Quebec though the Cape Smith Belt in northern Quebec, the Belcher Islands in southern Nunavut, the Fox River and Thompson belts in northern Manitoba, the Winnipegosis komatiite belt in central Manitoba, and on the southern side of the Superior craton in the Animikie Basin of northwestern Ontario. Two volcano-sedimentary sequences exist in the Labrador Trough with ages of 2,170–2,140 million years and 1,883–1,870 million years. In the Cape Smith Belt, two volcanic groups range in age from 2,040 to 1,870 million years old called the Povungnituk volcano-sedimentary Group and the Chukotat Group. The Belcher Islands in eastern Hudson Bay contain two volcanic sequences known as the Flaherty and Eskimo volcanics. The Fox River Belt consists of volcanics, sills and sediments some 1,883 million years old while magmatism of the Thompson Belt is dated to 1,880 million years old. To the south lies the 1,864‑million-year-old Winnipegosis komatiites. In the Animikie Basin near Lake Superior, volcanism is dated 1,880 million years old. During the Mesoproterozoic era of the Precambrian eon 1,109 million years ago, northwestern Ontario began to split apart to form the Midcontinent Rift System, also called the Keweenawan Rift. Lava flows created by the rift in the Lake Superior area were formed from basaltic magma. The upwelling of this magma was the result of a hotspot which produced a triple junction in the vicinity of Lake Superior. The hotspot made a dome that covered the Lake Superior area. Voluminous basaltic lava flows erupted from the central axis of the rift, similar to the rifting that formed the Atlantic Ocean. A failed arm extends north into mainland Ontario where it forms a geological formation known as the Nipigon Embayment. This failed arm includes Lake Nipigon, the largest lake entirely within the boundaries of Ontario. Periods