Acasta Gneiss

The Acasta Gneiss Complex, also called the Acasta Gneiss, is a body of felsic to ultramaficArcheanbasement rocks, gneisses, that form the northwestern edge of the Slave Craton in the Northwest Territories, Canada, about 300 km (190 mi) north of Yellowknife, Canada. This geologic complex consists largely of tonalitic and granodioritic gneisses and lesser amounts of mafic and ultramafic gneisses. It underlies and is largely concealed by thin, patchy cover of Quaternaryglacialsediments over an area of about 13,000 km (5,000 mi). The Acasta Gneiss Complex contains fragments of the oldest known crust and record of more than a billion years (>4.0–2.9 Ga) of magmatism and metamorphism. The Acasta Gneiss Complex is exposed in a set of anticlinoriums within the foreland fold and thrust belt of the PaleoproterozoicWopmay Orogen.