Canada Travel – Acasta Gneiss261 – Old

Canada Travel – Acasta Gneiss

Acasta Gneiss – N.W terrotories Canada



The Acasta Gneiss is a metamorphic rock over 4 billion years old. (metamorphic rocks form when other rocks are modified by heat and pressure.) The Acasta Gneiss is composed in part of quartz and feldspar, minerals that are derived from metamorphosed granite. Granite itself forms when igneous rocks such as basalt are melted in the presence of water. The composition of the Acasta Gneiss thus implies that granitic continents and surface water existed during the Hadean more than 4 billion years ago. The Acasta Gneiss is a rock outcrop of Hadean tonalite gneiss in the slave craton in Northwest Territories, Canada. Located about 300 kilometers north of Yellowknife, the Acasta River rock deposit is the oldest known intact crustal deposit on Earth. Found in 1989, it was named for the nearby Acasta River east of Great Slave Lake. The Acasta outcrop is found in a remote area of the Tlicho people land settlement. It is the oldest known exposed rok in the world. The rock exposed in the outcrop formed just over four billion (4.2×10ˆ9) years ago; an age based on radiometric dating of zircon crystals at 4.03 Ga, the Acasta 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.

 

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Acasta Gneiss P1 Acasta Gneiss P2
   

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