The Nuvvuagittuq Greenstone Belt (NGB;
Inuktitut: ) is a sequence of
metamorphosed
Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...
mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks incl ...
to
ultramafic
Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates a ...
and associated
sedimentary rock
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
s (a
greenstone belt) located on the eastern shore of
Hudson Bay, 40 km southeast of
Inukjuak,
Quebec
Quebec ( ; )According to the Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is one of the thirtee ...
. These rocks have undergone extensive metamorphism, and represent some of the oldest 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
microorganism
A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s in these rocks, which would be the
oldest trace of life yet discovered on Earth.
History and geography
![Nuvvuagittuq Map White](https://upload.wikimedia.org/wikipedia/commons/8/84/Nuvvuagittuq_Map_White.png)
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.
[O'Neil, J., Carlson, R. W., Paquette, J.-L. & Francis, D. Formation age and metamorphic history of the Nuvvuagittuq Greenstone Belt. Precambrian Res. 220-221, 23–44 (2012).][Cates, N. L., Ziegler, K., Schmitt, A. K. & Mojzsis, S. J. Reduced, reused and recycled: Detrital zircons define a maximum age for the Eoarchean (ca. 3750–3780 Ma) Nuvvuagittuq Supracrustal Belt, Québec (Canada). Earth Planet. Sci. Lett. 362, 283–293 (2013).] The Nuvvuagittuq Greenstone Belt is part of a
mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks incl ...
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, using
uranium–lead dating
Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...
on
zircon
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
s, the Nuvvuagittuq was dated to be a minimum of 3.7 billion years old.
[Cates, N. L. & Mojzsis, S. J. Pre-3,750 Ma supracrustal rocks from the Nuvvuagittuq supracrustal belt, northern Québec. Earth Planet. Sci. Lett. 255, 9–21 (2007).] This measurement was made using
uranium–lead dating
Uranium–lead dating, abbreviated U–Pb dating, is one of the oldest and most refined of the radiometric dating schemes. It can be used to date rocks that formed and crystallised from about 1 million years to over 4.5 billion years ago with routi ...
on
zircon
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...
s found within
granitic
A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...
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
Samarium–neodymium dating is a radiometric dating method useful for determining the ages of rocks and meteorites, based on the alpha decay of the long-lived samarium isotope () to the stable radiogenic neodymium isotope (). Neodymium isotope ra ...
and
neodymium
Neodymium is a chemical element with the symbol Nd and atomic number 60. It is the fourth member of the lanthanide series and is considered to be one of the rare-earth metals. It is a hard, slightly malleable, silvery metal that quickly tarnishe ...
isotope fractionation
Isotope fractionation describes fractionation processes that affect the relative abundance of isotopes, phenomena which are taken advantage of in isotope geochemistry and other fields. Normally, the focus is on stable isotopes of the same element. ...
was used to establish an age of 4321 Ma for the Nuvvuagittuq Greenstone Belt.
This was accomplished by dating intruding
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...
s and measuring neodymium isotope fractionation in less-deformed members of the
Ujaraaluk unit. The age of 4321 Ma would make the Nuvvuagittuq Greenstone Belt the oldest known rocks on Earth.
In 2012, further studies of detrital zircons taken from
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
–
biotite schist
Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
s in the NGB reported a maximum age of 3780 Ma.
The latter study states that the 4321 Ma age is not reflective of the NGB, but rather, reflects isotope ratios inherited from
Hadean crust that was melted to form the parent rocks of the NGB.
As of March 2017, this disagreement in dating remained unresolved.
Geology
![Nuvvuagittuq belt rocks](https://upload.wikimedia.org/wikipedia/commons/c/cf/Nuvvuagittuq_belt_rocks.jpg)
The Nuvvuagittuq Greenstone Belt contains 3 major components:
[O’Neil, J. et al. in ''Earth's Oldest Rocks'', Chapter 3.4, Vol. 15, (Elsevier, 2007).]
*
Cummingtonite
Cummingtonite ( ) is a metamorphic amphibole with the chemical composition , magnesium iron silicate hydroxide.
Monoclinic cummingtonite is compositionally similar and polymorphic with orthorhombic anthophyllite, which is a much more common ...
s, metamorphic
amphiboles
Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol ...
, which form most of the belt
*
Mafic
A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks incl ...
and
ultramafic
Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...
sills that intrude the amphibolites
*
Banded iron formation
Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert. They can be up to several hundred meters in thickness ...
s, sedimentary rock that formed in sea water
![Garnet paragneiss Nuvvuagittuq Greenstone Belt, 4](https://upload.wikimedia.org/wikipedia/commons/c/c9/Garnet_paragneiss_Nuvvuagittuq_Greenstone_Belt%2C_4.28_Ga.jpg)
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
gneiss
Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...
ic
foliation
In mathematics (differential geometry), a foliation is an equivalence relation on an ''n''-manifold, the equivalence classes being connected, injectively immersed submanifolds, all of the same dimension ''p'', modeled on the decomposition of ...
, with cummingtonite,
quartz
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
,
biotite and
plagioclase feldspar
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prop ...
being the primary components. The cummingtonite amphibolites range from
garnet
Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...
-rich to garnet-poor and are interpreted to be highly metamorphosed volcano-sedimentary rocks.
Ultramafic
Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous and meta-igneous rocks with a very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium, and are composed ...
and
gabbro
Gabbro () is a phaneritic (coarse-grained), mafic intrusive igneous rock formed from the slow cooling of magnesium-rich and iron-rich magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...
ic sills appear commonly on the northern portion of the belt. These sills range from in width, and have
serpentine and
talc
Talc, or talcum, is a clay mineral, composed of hydrated magnesium silicate with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent a ...
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
Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...
,
magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With th ...
, and
grunerite
Grunerite is a mineral of the amphibole group of minerals with formula Fe7 Si8 O22( OH)2. It is the iron endmember of the grunerite-cummingtonite series. It forms as fibrous, columnar or massive aggregates of crystals. The crystals are monoclini ...
.
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,
and geochronometric
high-pressure deformation is evident throughout the belt as one of the earliest periods of deformation.
This period caused significant
foliation
In mathematics (differential geometry), a foliation is an equivalence relation on an ''n''-manifold, the equivalence classes being connected, injectively immersed submanifolds, all of the same dimension ''p'', modeled on the decomposition of ...
and meter-scale
folding
Fold, folding or foldable may refer to:
Arts, entertainment, and media
* ''Fold'' (album), the debut release by Australian rock band Epicure
* Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot
*Abov ...
in the faux-amphibolite and banded iron formations. The work of Nadeau and O'Neil both agree on a thermal event after the first phase of deformation,
and it is dated by O'Neil to be 2.7
Ga.
This event is recorded by igneous intrusions in the NGB, and the formation of the nearby
Boizard Suite, an intrusive igneous formation.
This event is followed by a period of meter-scale folding that affects all parts of the belt.
It has also been proposed that the NGB represents a zone of paleo
subduction.
[Turner, S., Rushmer, T., Reagan, M. & Moyen, J.-F. Heading down early on? Start of subduction on Earth. Geology 42, 139–142 (2014).] Similarities between the NGB and the
Izu-Bonin-Mariana forearc
Forearc is a plate tectonic term referring to a region between an oceanic trench, also known as a subduction zone, and the associated volcanic arc. Forearc regions are present along a convergent margins and eponymously form 'in front of' the vo ...
, 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.
It has been suggested that Algoma-type iron deposits can precipitate due to bacterial activity in an anoxic environment, as would be found in the very early Earth.
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
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
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.
The authors vigorously defended their conclusions, and are confident that their conclusions will stand the test of time.
It was reported in a 2019 paper that hematite tubes and filaments with the same shape and chemical makeup can be produced abiotically by
chemical garden
Comparison of chemical gardens grown by NASA scientists on the International Space Station (left) and on the ground (right)
A chemical garden while growing
up Cobalt(II) chloride
upA chemical garden
A chemical garden is a set of complex biol ...
s, which may form naturally in some hydrothermal settings. 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
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of ch ...
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
*
Earliest known life forms
The earliest known life forms on Earth are believed to be fossilized microorganisms found in hydrothermal vent precipitates, considered to be about 3.42 billion years old. The earliest time for the origin of life on Earth is at least 3.77 bill ...
*
List of greenstone belts
This is a list of greenstone belts
Africa Burkina Faso
*Hounde greenstone belt
*Boromo greenstone belt
Democratic Republic of the Congo
*Kilo-Moto
Angola
*Lufico - Cabinda
*Cassinga
South Africa
*Barberton Greenstone Belt, Barberton greenston ...
References
{{Greenstone belts
Volcanism of Quebec
Greenstone belts
Hadean volcanism
Eoarchean volcanism
First 100 IUGS Geological Heritage Sites