Back River volcanic complex
The Back River volcanic complex is an Archean stratovolcano spanning the Northwest Territories–Nunavut border in Northern Canada. It is located northwest of Yellowknife and to the northwest of the Back River from which it takes its name. The volcano constitutes the Back Group of the Yellowknife Supergroup and is somewhat anomalous in the Slave craton because it has undergone only a low degree of deformation and is subhorizontal. The southern half of the complex is exposed at the crest of a small dome. This is the eroded portion of the stratovolcano that has been preserved in an upright position. The complex comprises four volcanic sedimentary sequences that correspond to the phases of growth and destruction of this stratovolcano.
Innerring
The Innerring sequence, which constitutes the oldest rocks of the complex, represents the upper part of an eroded early phase of the volcano.Thlewyco
The Thlewyco sequence represents the main construction phase of the volcano and forms an outward dipping, annular succession around the Innerring sequence, with an aggregate thickness of -. Its stratigraphy changes dramatically around the crater, varying from five cycles of andesitic and rhylotic lava, followed by succession of volcanistic debris on the north side, to 30 subaerial andesitic flows and rare pyroclastic and epivolcaniclastic units on the eastern side, to interlayered dacitic and andesitic lava and tuff overlain by a thick succession of voluminous, nonwelded, ash-flow tuff and volcaniclastic rocks on the south side. Volcanism in this sequence ended with the eruption of large rhyolite and dacite dome-flow complexes.The Innerring and Thlewycho sequences represent a complex history of explosive eruptions from numerous eruptive centers.