The Acasta Gneiss is a rock outcrop of Archaean tonalite gneiss in the Slave craton in Northwest Territories, Canada. It was found in 1989 and was named for the nearby Acasta River east of Great Slave Lake, some 350 km north of Yellowknife.[1][2] The Acasta outcrop is found in a remote area of the Tlicho people land settlement. It is the second oldest exposed rock in the world.
Contents |
The rock exposed in the outcrop formed just over four billion (4 x 109) years ago; an age based on radiometric dating of zircon crystals at 4.03 Ga, [3] which were the oldest rocks in the world at that time. It was the oldest known rock outcrop in the world until a McGill University team reported a 4.28 billion year old outcrop on the eastern shores of Hudson Bay, 40 kilometres south of Inukjuak, Quebec, Canada.[1]
The Acasata gneiss is important in establishing the early history of the continental crust. It was formed in the Basin Groups unofficial period of the Hadean eon, which came before the Archean: see Timetable of the Precambrian.
In 2003 a team from the Smithsonian Institution collected a four-tonne boulder of Acasta Gneiss for display outside the National Museum of the American Indian in Washington, D.C.
 |
This Canadian Northwest Territories location article is a stub. You can help Wikipedia by expanding it. |
