What is Acasta Gneiss?
[[File:Acasta gneiss.jpg|thumb|Fragment of Acasta gneiss at the Natural History Museum in [[Vienna]]]] [[File:Acasta Gneiss fragment.JPG|thumb|Another fragment of Acasta gneiss (Collection: H. Martin, [[Blaise Pascal University]])]] The '''Acasta [[Gneiss]]''' is the oldest rock in the world. It is in the [[Slave craton]] in [[Northwest Territories]], Canada. The rock body is exposed on an island about 300 kilometres north of [[Yellowknife]]. The rock of the [[outcrop]] was [[Metamorphism|metamorphosed]] 3.58 to 4.031 billion (10<sup>9</sup>) years ago. It is the oldest known intact crustal fragment on Earth.<ref>[http://www2.ess.ucla.edu/~schauble/Isotope_geochemistry/Acasta_Concordia_Bowring.pdf 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]</ref> 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 [[granit|granitoid]] that formed 4.03 billion years ago. This age is based on radiometric dating of [[zircon]] crystals at 4.031x10<sup>9</sup> years.<ref>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. [https://www.sciencedirect.com/science/article/abs/pii/S0301926806002737?via%3Dihub]</ref> The Acasta Gneiss is important in establishing the early history of the [[continental crust]]. == References == {{reflist}} [[Category:Igneous rocks]] [[Category:Hadean]] [[Category:Northwest Territories]] [[Category:Geology of Canada]]