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Concept
Ceinture de roches vertes de Nuvvuagittuq
Résumé
The Nuvvuagittuq Greenstone Belt (NGB; Inuktitut: nuv.vu.a.git.tuq) is a sequence of metamorphosed mafic to ultramafic volcanic and associated sedimentary rocks (a greenstone belt) located on the eastern shore of Hudson Bay, 40 km southeast of Inukjuak, Quebec. These rocks have undergone extensive metamorphism, and represent some of the oldest surface rocks on Earth.
Two papers dating the age of the Nuvvuagittuq Greenstone Belt have been published. One paper gave an age of million years (Ma), while the other gave an age of Ma. In March 2017, the age of the Nuvvuagittuq Greenstone Belt was still unresolved.
In March 2017, a published report gave evidence for fossils of microorganisms in these rocks, which would be the oldest trace of life yet discovered on Earth.
Formerly called the Porpoise Cove Greenstone Belt, the Nuvvuagittuq Greenstone Belt was first mapped in 1965 by the Quebec Ministry of Natural Resources. The area remained more or less unexamined until the 2000s when preliminary reports of U-Pb zircon dating in the area of the belt found zircons with ages up to 3750 Ma. Since then, the Nuvvuagittuq Greenstone Belt has become the focus of intense study. There is still considerable disagreement between scientists regarding the history and age of this structure. The Nuvvuagittuq Greenstone Belt is part of a mafic unit called the Ujaraaluk unit, both of which are in the Inukjuak subprovince of the Minto Block in North Eastern Superior Province(NESP).
In 2007, using uranium–lead dating on zircons, the Nuvvuagittuq was dated to be a minimum of 3.75 billion years old (3,750 Ma). This measurement was made using uranium–lead dating on zircons found within granitic intrusions that cut portions of the belt, and therefore, are younger than the features it cuts. This measurement is widely accepted. However, it alone does not provide a maximum age.
In 2012 samarium–neodymium dating and neodymium isotope fractionation was used to establish an age of 4321 Ma for the Nuvvuagittuq Greenstone Belt.
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