Acasta Gneiss

rock that is among the oldest known crustal fragments on Earth

The Acasta Gneiss is the oldest rock in the world. It is in the Slave craton in Northwest Territories, Canada.

Fragment of Acasta gneiss at the Natural History Museum in Vienna
Another fragment of Acasta gneiss (Collection: H. Martin, Blaise Pascal University)

The rock body is exposed on an island about 300 kilometres north of Yellowknife. The rock of the outcrop was metamorphosed 3.58 to 4.031 billion (109) years ago. It is the oldest known intact crustal fragment on Earth.[1]

The nearby Acasta River east of Great Bear Lake gave the rock its name. It is the oldest known exposed rock in the world.

The rock, before it was metamorphized, was a granitoid that formed 4.03 billion years ago. This age is based on radiometric dating of zircon crystals at 4.031x109 years.[2] The Acasta Gneiss is important in establishing the early history of the continental crust.

ReferencesEdit

  1. Bowring, S.A., and Williams, I.S., 1999. Priscoan (4.00–4.03 Ga) orthogneisses from northwestern Canada. Contributions to Mineralogy and Petrology, v. 134, 3–16
  2. Iizuka, Tsuyoshi; Komiya, Tsuyoshi; Ueno, Yuichiro; Katayama, Ikuo; Uehara, Yosuke; Maruyama, Shigenori; Hirata, Takafumi; Johnson, Simon P.; Dunkley, Daniel J. 2007. Geology and zircon geochronology of the Acasta Gneiss Complex, northwestern Canada: New constraints on its tectonothermal history. Precambrian Research. 153 (3–4): 179–208. [1]