Nuvvuagittuq Greenstone Belt

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 3,750 Ma. 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). Age controversy In 2007, 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. Based on field relationships, this would establish a minimum age for the mafic units of Nuvvuagittuq Greenstone Belt supporting the fact that they are indeed Hadean. == Geology ==

The Nuvvuagittuq Greenstone Belt contains 3 major components: • Cummingtonites, metamorphic amphiboles, which form most of the belt • Mafic and ultramafic sills that intrude the amphibolites • Banded iron formations, sedimentary rock that formed in sea water The cummingtonite amphibolite that dominates the belt is unusual that sections of the rock have a grayish-beige color, compared to the dark green of common amphibolites, giving it the nickname "faux-amphibolite". The cummingtonite amphibolite displays gneissic foliation, with cummingtonite, quartz, biotite and plagioclase feldspar being the primary components. The cummingtonite amphibolites range from garnet-rich to garnet-poor and are interpreted to be highly metamorphosed volcano-sedimentary rocks. Ultramafic and gabbroic sills appear commonly on the northern portion of the belt. These sills range from in width, and have serpentine and talc rich interiors with amphibole rich margins. They represent a significant intrusion event in the history of the NGB. The banded iron formation can be traced continuously across the northern portion of the belt. The formation is composed mainly of quartz, magnetite, and grunerite. == Alteration history ==

The history of alteration and metamorphism in the Nuvvuagittuq Greenstone Belt remains poorly understood in many regards. However, attempts have been made to constrain the history using structural techniques, Similarities between the NGB and the Izu-Bonin-Mariana forearc, a modern subduction zone, suggest that the NGB may have experienced episodic subduction in its lifetime. This theory does not depend on the timing of the formation of the belt, and either ages would represent subduction occurring at a remarkable age. == Evidence of early life ==

Banded iron formation The banded iron formation bears many similarities to similar formations found in Algoma-type iron deposits. These iron formations may be one of the oldest fingerprints of life, indicating that there may have been biological activity at the time that the NGB was being formed. Chert A controversial paper published in March 2017 reported evidence for early life in these rocks. The paper describes putative fossilized microorganisms. The structures seen are interpreted as hematite tubes, and filaments, similar in morphology and size to those produced today by bacteria living in subsea hydrothermal vents. Several detailed microstructures, both shape and chemical makeup match modern structures. Collectively these multiple observations led the authors to conclude that they were produced by "biological activity" more than 3.77 billion years ago. This conclusion was greeted with both approval and skepticism. A 2022 paper added that large (up to 1 cm), complex structures were present, with a central stem and parallel side branches, and ellipsoids alongside the tubules and filaments. The filaments were said to resemble filaments of Mariprofundus ferrooxydans, a deep sea siderophilic bacterium. Critics pointed out that metamorphism and the effects of a crystal lattice could account for some of the effects seen, particularly the parallel filaments. ==IUGS geological heritage site==

In respect of having 'some of the oldest, if not the oldest, rocks on Earth, with potentially earliest traces of life', the International Union of Geological Sciences (IUGS) included the 'Hadean to Eoarchean Nuvvuagittuq greenstone belt' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an IUGS Geological Heritage Site as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.' == See also ==